This may be pedantic on my part, but I don't like this framing. It has the implication that our models dictate what happens in the universe and not the other way around. The universe is expanding faster than our models predict or there's something up with our observations or both. Maybe this is what people have in mind, but I think it's a subtle communication difference and can miscommunicate that science is truth, whereas science is the collection and evolution of models and observations describing the reality we experience.
It is pedantry. This is just idiomatic human communication and not specific to any single domain. People say thing like this all the time. Saying ‘than it should be’ instead of ‘than we expect’ is everyday English language usage that confuses nobody and complaining about it is entirely performative. You’re technically correct, here have a round of applause, but it contributes nothing. Dealing with smug nitpicking like this that’s completely beside the point is one of the tedious chores or reading HN.
It's a problem because it miscommunicates to non-scientists about what science actually is and it causes scientists themselves to be misinformed about what they're really doing. I greatly enjoy science, but you have to admit that there's a problem of scientists being viewed as "elites who think they know everything" that is fueled by journalism and the miscommunication of science.
It's alright to critique something to try and improve it, you know?
Lastly, it's not really besides the point, as our models and possibly our observations being wrong is entirely the crux of this "problem".
I admitted it was possibly pedantic, and then I got "smug nitpicking". And this happens all the time, so there's some pre-existing bias on my part in terms of being bothered by these communication mishaps. I struggle to watch many science documentaries these days due to communication issues such as these.
Absolutely. If one person does their best work and is still frustrated after trying dozens of options, it is fair for them to be scratching their head and saying, "This shouldn't be happening."
The article itself provides exceptionally precise reporting (though IANAA) of mutual work toward a grand challenge in astronomy --- which is still leaving people scratching their heads at discrepancies after trying dozens of model or analysis variations. The word 'should' in the title (I believe it only appears there) to me conveys well-enough (it is only a title) that there are human elements/expectations and legitimate after-the-best-of-care puzzles remaining.
I don't know if it is a good comparison, but if the time for the g-2 result reveal came, and the result was a 20-sigma discrepency, I would expect every experimentalist and every theorist involved to immediately scowl and say, "F***, this should never have happened."
Also perfectly ordinary and ideomatic: To say, This should be compiling without errors.
Great science reporting in the article, hence my rant to defend it.
Right, when you say, deep in a debugging session, "hmm, this variable shouldn't have this value", this is shorthand for "according to my assumptions about the way this code operates and the initial conditions, it shouldn't be possible to observe the variable with this value". As far as I can see, it's similar here.
To be fair, in the programming case you change the code or data to make the variable correct, while in science unless there's a mistake somewhere you follow the data, you don't change things to 'fix' it. However we all know this, we know scientists aren't going to try and 'correct' reality or the data to fit our assumptions. Well, excepting the tin foil hat brigade, but we shouldn't pander to them or let them dictate our use of language.
Right, but when you say "this variable shouldn't have this value", it doesn't imply that you doubt your observation of the variable - it is well understood that you are doubting your understanding of the code / initial conditions.
It’s just wording. When you talk to a scientist they would tell you “ The Universe Is Expanding Faster Than It Should Be according to our models”. That’s how fundamental research is done. You collect data, develop a model that fits the data, collect more data and check if the model still works. If not, go back to the drawing board and develop a model that fits the new data. And most scientists will be excited if they find such a gap because now the interesting work starts.
Agree. Models are only our attempts of describing how something behaves.
That's why I'm also not a fan of using the word "law" for names of the models, because it implies as if the universe is obligated to follow this "law", but a law of physics is still essentially only our description (even if it uses math equations instead of words to describe).
The amazing thing about the universe's home address is that it is always right here, no matter where here is. The Big Bang happened exactly at the tip of your nose. And mine.
So our gravitation models weren’t working very well, so we thought maybe dark matter. Then that wasn’t working very well either, so we thought maybe dark energy? And now this is showing a lot of shortcomings too? I know nothing of astro physics, but I find it odd that a majority of astro physicians think of dark energy as a near certainty when all mainstream articles are about contradicting its implications.
Expansion of the universe (dark energy) has nothing to do with the dark mater. At least not according to any models known today. We know galaxies are racing away faster because we can see it (from red shift) so that part is certain. Why they are moving away is not certain hence “dark” energy
Yes; the "dark" in these terms reflects our lack of understanding about both topics, not that they share some "dark" aspect in common. They're names for holes in our models, not for entities predicted by them.
That's true but even more than that, we're not really sure dark matter is actual particles at all. Modified gravity for example is one alternative explanation that don't require a new particle or field.
Neither "dark matter" nor "dark energy" can be made from atoms (i.e. from the periodic table), because atoms interact with photons. I think to say "it is something" is a strong claim, requiring strong evidence.
Dark energy, in particular, can't be a kind of "stuff".
We could "understand" something that doesn't interact with EM; but we'd have trouble observing it.
I don’t know about dark energy, but dark matter isn’t called such because it’s a “hole in our models”. The theory is it doesn’t react electromagnetically with other matter. So it’s quite literally, “dark” matter.
Is that theory or observation? My understanding is that we know it doesn't react electromagnetically with other matter because we (failed to) observe that behavior, not because we expected it to behave that way a priori.
If modified Newtonian (MOND) theories won out, the theory would explain this observation by saying that there was no matter there to begin with. If neutrino theories won out, the theory would explain this observation by saying that dark matter is electromagnetically neutral. But those are two entirely different theories, trying to explain the same observations, and trying to fill the hole in our currently accepted models in different ways.
EDIT: Per a child comment, you might mean "theory" as "idea", as in "the [idea] is that it doesn’t react electromagnetically with other matter." In which case, yes!
There seems to be a lot of evidence for dark matter, that's how I understand it as an outsider. What it means is that there is a lot of consistency in observations, things add up, to the dark matter theory.
I usually agree with your understanding of dark matter/dark energy as placeholders for missing knowledge.
Ah; I think we might only be disagreeing on terminology at this point, then. A physical "theory" is a coherent model that makes testable predictions in its own right, as in the "theory of gravitation". A hypothesis is an explanatory idea, like dark matter.
There's definitely lots of evidence for dark matter, yes~!
a priori is the wrong term because our physical theories are not a priori.
Dark matter has lots of reasons to be assumed but a common one is that when we try to explain the gravitational effects of galaxies based on a quantification of observable matter, there is a huge shortfall. That creates a space for something with a gravitational effect that is unobservable otherwise.
That many of the objects of our physics are theory laden is true, but that they are therefore “unreal” or merely an artefact of theory does not necessarily follow.
Just to be pedantic, I’ll point out that’s literally “transparent” matter and we use the term “dark” which is really more appropriate for something that absorbs EM radiation because it also implies the mystery of the holes in our knowledge. English is great.
Light exiting from stars deep in a galaxy (which is in turn deep in a galaxy cluster) is subject to gravitational redshift. The greater the mass of the galaxy and cluster, the greater the redshift.
If we add transparent, non-radiating mass to a galaxy and its cluster, the mean redshift of starlight from the galaxy will redshift, and we'll see the result on various absorption and emission lines in the spectrum.
Note, we do not need dark matter for this; increasing the central mass of a galaxy cluster will do the trick too. We can do this by adding more stars, or by adding black holes, or by making a central black hole more massive. All of this will cause an increase in gravitational redshift.
However, adding more central mass to galaxies will be reflected in the trajectories of clouds of gas and collections of stars within the galaxies; likewise, adding more concentrated mass to a galaxy cluster will alter the trajectory of galaxies within it. In general, these objects will have faster orbits -- fast enough that a non-gravitational redshift will be apparent in the arrangement of spectral lines. (We would also need to figure out how to keep any central masses from being extremely bright anywhere in the electromagnetic spectrum, and how to keep them from eclipsing parts of their home galaxies and clusters that are behind them from our perspective.)
If we instead redistribute our increase in galactic mass into a gaseous halo-like structure that extends well beyond the outer stars, we get the increased gravitational redshift without requiring stars and gas to travel faster to avoid falling inwards. The halo still has to be electromagnetically quiet, and non-eclipsing, or we would see it. (This all applies to clusters, too).
Stepping away from the "dark matter puzzle" of the spectral lines of molecular and atomic gas clouds in galaxies and clusters of them, we can then look at another aspect of your question.
Galaxy clusters, from their point of view, are just floating passively in space.
The expansion of the universe follows a model wherein if we treat the astrophysical content of galaxies and clusters as sensitive accelerometers that in aggregate show off the peculiar accelerations experienced by these large scale objects, there is no evidence that these accelerometers should report a non-zero magnitude or point in any particular direction. That is, galaxies and galaxy clusters are themselves in free fall, and we can see this because of lines of evidence including expansion-direction-and-magnitude squashings of https://en.wikipedia.org/wiki/Light_echo lines turn out to be null, likewise there are no radio-loud edge shocks for galaxies that appear to be accelerating away from us, there are no shape distortions of the most highly "accelerated" distant galaxies, and so forth. There is simply a spectral redshift.
So, for an isolated galaxy the spectrum it emits depends on a combination of its starshine, any noise from close to its central black hole(s), the noise from any thick gas clouds undergoing gravitational collapse, and the absorption and reemission of diffuse gas clouds heated by these types of emission and absorption-and-reemission sources and the distribution of dark matter within and around the galaxy. The more dark matter, the more redshifted the galaxy's spectral lines will be.
Preserving the Copernican Principle, immersing a set of such isolated galaxies into an expanding cosmos leads to the inhabitants of each galaxy observing a cosmological redshift on the gravitatonally-redshifted spectrum emitted by other sufficiently distant galaxies. The gravitational-redshift depends on the mass of the galaxies including their dark matter. The cosmological redshift only depends on a light-travel distance from the galaxy, no matter how light or how massive that galaxy (or its parent cluster) is.
One important caveat to all this is that the gravitational redshift for a galaxy or galaxy cluster is an incredibly tiny effect. For example, the mean gravitational redshift for massive galaxy clusters has been measured (e.g., link below), and has a value of ~ 10 or 15 km/s. This can be compared with the typical motions of galaxies within a cluster (dispersions of ~ 1000 km/s) and the cosmological redshift of the clusters (for the sample in the paper I linked to, it's equivalent to an average Doppler shift of ~ 50,000 km/s).
In order to make that measurement, the authors had to combine redshift measurements for ~ 20,000 galaxies from ~ 2,500 different clusters; as they note, it's impossible to detect the effect for just a single cluster: "... even assuming that every galaxy in a cluster could be spectroscopically measured, there are simply too few galaxies to allow the statistical detection of a non-zero gravitational redshift."
So while it's technically true that adding dark matter to a galaxy would increase its gravitational redshift and thus its total observed redshift, this effect is immeasurably small.
I can only reply to your "impossible to detect" with respect to clusters with the "technically challenging but apparently real and prospects for better measurements and extension to larger scales is promising" at the end of Kaiser's 2018 slide deck https://chalonge-devega.fr/Kaiser_29mars2018.pdf which I do not think is contradicted by the (interesting, thank you!) Mpetha et al (2021) paper, which cites at least three of Kaiser's earlier publications.
Broadhurst & Scannapieco (2000) https://iopscience.iop.org/article/10.1086/312630 is also relevant here, as it distinguishes between X-Ray studies and optical ones (SPIDERS being an example of the latter) pointedly at §4.2.
I do not disagree that ~ 10-20 km/s is small, but it's the little things that cause "tension" headaches, isn't it?
Kaiser's presentation doesn't suggest you can do the measurement for individual clusters; the example analysis is from Wojtak et al. (2011), which is similar to Mpetha et al. in using thousands of galaxies and thousands of clusters.
The Broadhurst & Scannapieco discussion about X-ray studies is interesting and potentially promising, but no one seems to have tried doing for real.
The reddening is because of the additional mass of the dark-matter-containing structures, and also because the distribution of the dark matter into halos allows for slower orbits of stars and gas clouds, thus suppressing their non-gravitational non-cosmological redshifts. (In an edge-on spiral galaxy without dark matter we would see a greater difference in the blueshift of one extreme tip of the thin disk and the redshift of the opposite extreme tip of the thin disk, compared to the same spiral galaxy with dark matter; the light-and-radio from the central bulge would be less redshifted in the absence of dark matter).
This is the exact opposite of the truth. An edge-on spiral galaxy without dark matter would have less extreme observed rotation velocities (comparing the blueshifted and redshifted sides of the disk), because only the visible mass (stars and gas) is relevant. But in practice we see higher rotation velocities (greater difference between blueshifted and redshifted sides) than can be explained by just the visible mass, and so we have to postulate extra mass in the form of "dark matter" in the galaxy.
(Dark matter halos are not just dark matter outside the visible galaxy, they extend all the way to the centers of galaxies, and in fact become denser the closer to the galaxy center you get. Of course, the visible matter also becomes denser the closer to the center you get, and usually faster than the dark matter does, so the central regions of massive galaxies are dominated by the visible matter. But there's still dark matter there, and in some dwarf galaxies, the dark matter even in the central regions.)
You're quite right about the non-parenthetical, I failed to re-read what I wrote in an editing pass. It should of course be "with" instead of "without", or alternatively change the "greater" to "lesser". I am grateful for the correction.
As to your parenthetical, cuspiness is not really relevant to the scale of the points raised in the bulk of my comment, and it is not clear to me why you raise the DM density profile here.
It wasn't clear to my why you said what you did. (Good to know it was just an editing failure.) Sometimes people get confused and think "dark matter halo" means all the dark matter is outside the main body of the galaxy, so I was pointing out that this isn't the case.
It depends on what exactly you mean with "... non-zero energy", but the best answer is probably "no".
On the one hand, in vacuum, an accelerating expanding universe's geometry breaks time-translation invariance. Let's look at the vacuum geometry with a pair of test photons in the otherwise empty test universe. In the early universe we have the photons widely spacelike-separated but on trajectories where they will ultimately collide in the far future. The photons in the future will be redshifted compared to their wavelengths in the past, with the redshift proportional to the expansion history of the test universe. (In our universe, the cosmic microwave background photons have behaved this way when two CMB photons meet at a detector).
Since photon energy can be calculated E = (hc)/\lambda, where \lambda is the photon wavelength, a redshift corresponds to a decrease in the photon energy.
Where did this energy go? One can simply say that constancy of photon energy is premised on time-translation invariance, which is not a large-scale feature of an accelerating expanding universe.
This position is just that thermodynamics was developed to describe engineering phenomena in the 19th century, and not to describe the motion of clusters of galaxies over the course of billions of years. Since Noether, thermodynamics's first law has its foundations in time-translation invariance, which we only have in some spacetimes (e.g., Minkowski's flat space, the spacetime of special relativity) or in local pieces of general curved spacetime. In the absence of strict time-translation invariance globally, the first law of thermodynamics is just a weak-gravitational-field approximation.
Sean Carroll expands upon some of this here : https://www.preposterousuniverse.com/blog/2010/02/22/energy-... wherein he also discusses an effectively pseudogravitational-field view of our test spacetime's geometry, in order to think of our pair of converging photons donating energy to that (pseudo-)gravitational field. As he says, such a view, which leans on a notion of gravitational potential energy which is simply absent in General Relativity, is often unhelpful.
On the other hand, one can take a different approach and treat \Lambda, the cosmological constant, as a matter field rather than as a geometrical feature of the accelerating expanding spacetime. When we do this, then we are left with either an inertially-expanding spacetime, or with a flat spacetime, and in the stress-energy tensor we have what makes that acceleration or acceleration + expansion field cause everything in the stress-energy tensor (including those fields themselves) to fly apart.
It can be reasonable enough to do this. Einstein and Schrödinger discussed this in correspondence during the first world war : https://arxiv.org/abs/1211.6338 wherein they seem to agree that it is a matter of taste. We know from work in the more modern Hamiltonian formulation of General Relativity that we can't do this generally, but there are large families of spacetimes and matter content that are amenable to this approach of encoding aspects of the dynamical geometry as a form matter we can describe with canonical position & momentum.
We can also note here that the distribution of matter in a spacetime can pick out preferred foliations or even preferred frames of reference.
In our standard cosmology, which you are asking about, we treat the distribution of matter isotropic and homogeneous, where each form of matter is a perfect fluid with a density and a pressure. As the universe expands (with or without acceleration of expansion) the matter and radiation fluids dilute away, their density dropping over time. ...
Note that the red shift data has been coming into question lately, as it relies on some assumptions of the uniformity of the universe beyond the scale of galaxy super clusters, which doesn't seem like a safe assumption anymore as far as I understand.
dark matter is pretty solid of an idea. it's been around for over a hundred years at this point. it isn't a band-aide fix for wonky math in an inaccurate theory. the foundations of the concept of dark matter are fairly reasonable.
Not really. It is a hypothesized form of matter. There are competing hypotheses. Dark matter came to popularity in order to explain observations of galaxy rotation curves in the late 1930s. But these galaxies were observed in isolation, giving the illusion of gravitational isolation, which doesn't exist. Once accounting for the tidal effects of nearby galaxies, [1] dark matter becomes unnecessary to explain galaxy rotation curves, all that is needed is Newtonian physics. But in the period since dark matter was hypothesized, other observations that could not be readily explained were lumped into dark matter. Dark matter is nothing if not an amalgamation of unexplainable observations. So while dark matter is unnecessary to explain galaxy rotation curves, it is still somehow useful to explain unrelated observations.
> it isn't a band-aide fix
It really sort of seems like that: can't explain an observation, so invent something out of thin air to explain it. Honestly, an hypothesis that elves are causing the observations has just as much validity (or lack thereof). Now, elves have not been proven to be the cause of these unexplained observations, but neither has dark matter.
> the foundations of the concept of dark matter are fairly reasonable.
See above concerning galaxy rotation curves and endnote. Please understand it is quite possible that dark matter does not exist. The reason why it seems like accepted science has to do with scientific paradigms. Once a notion becomes an accepted part of the science paradigm, it takes years if not decades after disproving it beyond all doubt to dislodge it from the paradigm. If science has a problem, it is paradigms.
The observations in the 1930s you allude to were of the motions of galaxies in galaxy clusters. The rotation-curve measurements for individual galaxies started in the 1970s and really took off in the 1980s.
"Tidal effects" are a non-starter, and do nothing to explain galaxy rotation curves. Nor do they explain the excess motions of individual galaxies in galaxy groups and clusters, or the excess pressure of hot, X-ray emitting gas in groups and clusters -- all of which requires either some kind of dark matter, or some kind of alternate theory of gravity, or both.
> The observations in the 1930s you allude to were of the motions of galaxies in galaxy clusters. The rotation-curve measurements for individual galaxies started in the 1970s and really took off in the 1980s.
Nice catch.
> "Tidal effects" are a non-starter, and do nothing to explain galaxy rotation curves. Nor do they explain the excess motions of individual galaxies in galaxy groups and clusters, or the excess pressure of hot, X-ray emitting gas in groups and clusters -- all of which requires either some kind of dark matter, or some kind of alternate theory of gravity, or both.
What a well formed and well supported argument, and not just a matter of fact statement that you've left entirely unsupported. I'm totally convinced!
We observe with telescopes that the universe is expanding. We don't know why, so we call the mysterious force dark energy. It's just a name for something that we are objectively observing.
(Also this has nothing to do with dark matter, that unrelated to this discussion and you're just getting the names conflated.)
Failure is so common in this area that using “should” is a bit odd. The problem today is not like the Mercury minor difference (which in one stage some tried to invent a planet inside Mercury orbit called Vulcan).
But we are not of that scale. 90+% things we do not know, we just label them as dark … matters or energy. It looks like we know. The key is the dark part.
If you do not know 90+% things out there, there is no way you can think of should.
Just say the universe once again serve us a curve ball …
> If you do not know 90+% things out there, there is no way you can think of should.
They're just leaving off the implied "according to our models" at the end of the sentence. This is mostly fine, because it's obvious we don't know the true model of the universe, so our expectations are based on our current understanding.
The key is just not observation. Theory has a lot of issues. For that problem mentioned in the article see this https://en.wikipedia.org/wiki/Cosmological_constant_problem . As a joke, whilst I agreed hard to deal with matters and energy, but even nothing you can model that is tough.
I love cosmology and reading about it. Always exciting. But not because of the human part. More positively as said in the article … a lot to be learnt, just do not use the word should you are ok I am ok.
I have a tiny theory but since I'm not anywhere near this domain it could just look dumb.
It implies the existence of a multiverse system, billions of universes like ours, like soap bubbles, all floating around each other.
Well, if the gravity (and other forces, matter, energy, etc) works as intended then "objects/forces" closer to the universe edge gets pulled away by "objects/forces" from the other universe.
Same I feel like that is the only way. I can’t wrap my head around the concept of infinity. There has to be a beginning and end. What the heck caused the Big Bang? Why?
You think that there has to be a beginning, yet are looking for something that has caused the big bang. Isn't that inconsistent? Why cant the Big bang be the beginning? Otherwise you might next be looking for what caused whatever caused the big bang
Well we can use this to execute a reductio ad absurdam on scientific materialism. Let us assume that the logic of cause and effect is all there is to the universe. Then the big bang must have had a cause, and that cause a cause in turn, and so on. That's obviously absurd, even if we point at time beginning with the big bang. Within any human reasoning, things do not appear ex nihilo.
The alternative is that the thing on which our universe depends (being careful not to say 'caused' here) is beyond our ideas of cause and effect, and certainly passes human understanding.
What's far more reasonable is that the universe is a loop. The big bang is simply equivalent to the death of the universe: see conformal cyclic cosmology. Cause and effect cease to have priority over eachother. We are equally coupled to both faces of the boundary, the past and the future, which are actually two sides to the same coin, our origin and our destination.
Is it? That's still wedded to cause and effect, it just moves the frame of reference outside the looped universe to ask what sustains it or why it exists.
It is no longer unidirectional wedding, it's bidirectional as QM would predict, which is commonly known as coupling. Once a circle is drawn, the starting point is no longer visible. All you have is the symmetries of the circle itself :-)
(caveat: IANA astrophysicist/cosmologist/whatever, I just like to wrap my head around things with some bits of logic)
> Let me ask you; How long was the time before you were alive, and how long will the time be after you are dead?
This is misleading as it posits that since there's a "before you" and an "after you", "you" are standing within some time continuum.
> There has to be a beginning and end.
Wrap your head around this: if there is a "beginning" and an "end" to our universe, both would define discrete stop points, thus there would be some way to say "before" or "after" these discrete points, and thus the universe sits inside something that has time.
But then either this something of a container either has infinite time (which goes back to square one of things not having beginning and end) or has a beginning and end itself.
But again, if this container has a discrete beginning and end then you can apply the same logic that you applied to our universe in the first place. So there's another container of the container, to which you can recursively apply the same logic (assuming logic itself somehow applies to this container). So if you want all these container things to have beginnings and ends, it implies there's an infinite set of nested containers.
The alternative is that time exists within our universe, but our universe doesn't sit within time. Thus "beginning" and "end" are not discrete points but concepts that only exist as limits (in the mathematical sense of "limit"): by travelling the arrow of time forward or backward you can only move closer and closer to either but never actually reach these because these points don't actually exist.
Such a universe could be freestanding (as in: it's all there is), or it could have a container of sorts, and maybe even neighbour universes. But since time only exists within our universe, there could very well be no concept of time in the container (or other universes), or similar concepts but behaving entirely differently. In any case these (the container, the other universes) would be unbelievably incomprehensible to us.
These concepts of unreachable zero, unreachable infinite, or unreachable value do exist in other areas: absolute zero is basically unreachable, reaching c velocity requires infinite energy†...
† which creates other interesting conundrums such as a pair of photons travel at the same delta speed whether they go away or towards each other, or there's no "velocity = 0" either, or tachyonic vs baryonic realms.
Not an uncommon lay theory, actually. Unfortunately, I recall reading somewhere [0] that, experimentally, the effects of gravity are consistent with it propagating in only three spatial dimensions. If it could leak out of (or into) "our" universe along an auxiliary dimension, gravity's effects would be weaker than we observe.
Not to say it couldn't work some other way -- I'm not a physicist either! But (as these things always seem to end up) it would have to be a little more complicated. (Part of the "rolled-up dimensions" side of string theory is that the extra dimensions can't meaningfully attenuate the effects of gravity.)
I'm not thinking of other dimensions, a multiverse could be something like our body with millions and millions of cells that are interacting. Somehow I just cannot stand with this "universe is infinite" when for sure it has a border but we will never be able to go past that border to know what's beyond.
Sorry, when I say "dimension" I mean another continuous spatial direction that you could move along, not the "another place" understanding of the word. Flatland [0] is a classic for trying to get in the right headspace.
Also, not having a border is not the same as being infinite. Zogg from Betelgeuse started a great series on the topic [1], but disappeared after two episodes. I highly recommend it! But, long story short, it's entirely possible to have a finite universe that, nonetheless, has no edge. Go far enough in one direction and you might end up back where you started.
Assuming there's a physical edge to our universe, there's still the problem of the "observable universe" -- there's a lot more of the universe that we will simply never be able to see or reach, because it's moving away from us too quickly. That defines another kind of edge, one that's much "closer". Entities beyond our observable universe can't affect us gravitationally; it takes time for the effects of gravity to propagate from one point to another, as "gravitational waves", and the universe is inflating too quickly for those to reach us.
You might say that things further away from us, but within the observable universe, might be affected by things beyond, because they're "closer" to it than we are. I think that's correct, but by the same token, I think the information about those effects would never reach us in finite time.
That's why I was thinking in terms of extra spatial dimensions. You might have a bunch of matter "nearby" but totally inaccessible to you, because we're incapable of moving along the extra axis. But that gets back to the research I linked.
Further to @Twisol's answer, consider the surface of a sphere - it is two-dimensional (if you're confined to the surface, you can only move in two directions) and bounded in size, but it has no boundary as such; if you started walking around on a sphere, you could keep walking forever without hitting a wall.
Now imagine there are two such spheres near to each other. Two beings whose physical laws and interactions were entirely confined to their respective surfaces would be unaware of each other and unable to influence each other in any way - gravity for example is only able to travel around the surface of the sphere, not into whatever 'space' lies in between. The surface of each sphere is its own universe.
While we are airing our pet dumb theories, is there any way that a universe with a cyclic geometry, like the geometry of a sphere, could explain the accelerating universe with just gravitation? Could the attraction of the matter in our universe from “the other side of the world” be made to explain the observed acceleration?
Waho impressive. This theory you invented sounds so much like all the popsci articles you see in ads like "Scientists dont want you to know it, but this guy think we live in a multiverse" kind of things.
Are you the one who started this whole movement ? Or in fact you just rehash the same bullcrap ? Closer to the universe edge he says, not defining the universe or an edge...
Possible, but we would to be more or less in the center of the host universe since we see the same expansion rate in every direction. Statistically, that is unlikely.
Also, we see far away clusters or galaxies receding faster than light away from us. This is impossible in a non expanding universe since faster than light travel _through_ spacetime is impossible but spacetime between two objects expanding faster than light is.
Could we say that we simply don't know what is going on in the universe?
We (well, Einstein & Co. I was not involved.) made models about how the universe works. Then when looking at the broader scope, we noticed that the models differ from reality. So instead of saying the models are wrong, we invented "dark matter". Some unmeasurable type of matter that is responsible for the difference of how reality behaves in contrast to our models. And then we invented dark energy.
Now to make our models "work" we have to assume 85% of the matter in the universe is made of dark matter. And 68% of energy in the universe is made from dark energy.
How about just saying that our models do not work on large scales?
I have a lot more arguments that prove dark matter is a hoax. Let me write them down in dark text (an unmeasurable form of text). Here we go:
She should stick to physics, not philosophy. Proving free will with physics is ignorant and arrogant. The hard problem of consciousness is much deeper than "in our models, we see that there is no randomness anywhere, ergo no free will."
Dark matter and dark energy are models, "made up" to try and model reality's differences from general relativity. General relativity was "made up" when the Newtonian model was found to differ from reality. The Newtonian model was "made up" to explain the Copernican model, which was "made up" when the Ptolemaic model was found to differ from reality.
All models are wrong. Some models are useful. Everyone knows that the models aren't perfectly accurate; that's what models do: model. We literally say "this model is wrong" all the time.
There is a difference between models like Newton and Einstein, and models like dark energy and dark matter. Do dark matter and dark energy make any falsifiable predictions ?
no, they can't. the dark matter debacle is the tip of the iceberg. they feel compelled to produce theories that do not involve supernatural or divine concepts.
We are having an impostor syndrome as humanity, which is a good thing.
There was an obvious security hole sitting for years in the most common library in the most common programming language, and no one noticed... We fly to space and begin to do some mega projects, yet some of the most intelligent people in the world are facepalming themselves on a daily basis... We are not smart enough yet.
Cosmology is not a done science. There are a great number of advances that have answered specific problems regarding the behavior of light and energy, mass and gravity and so forth, but our knowledge is not complete (and will likely never be).
Articles like this get traction because the lay person may have believed that the science was more mature than it is. (Some) scientists are also notoriously famous for exaggerating how much science "knows" - Stephen Hawkings claim to the mind of God comes to mind.
We need to relieve such scientists of the burden of needing to know it all, and be grateful for all the things still left to discover.
Strictly that's a question about philosophy, not cosmology. Cosmology just says the universe is unbounded and leaves it at that. In fact "The Universe", meaning all the matter or energy which we will ever even theoretically be able to obvserve, is definitely finite. The distance to the point of infinite redshift (where we're looking at the big bang, essentially) is finite. It doesn't make sense to talk about anything "farther" out.
Is that true? (Honest question) Whatever the “thing” was that exploded at the big bang (which I read once was the size of a grapefruit for what it’s worth) - could there not have been other similar “things”? And what about where that “thing” came from? I’ve read theories of the universe expanding, but then eventually falling back onto itself to recreate another “thing” that will explode again. Anyway, it feels like there might indeed be more.
A way that I heard this described, is that what we recognize as the observable universe right now was the size of a grapefruit at the beginning of the big bang. The stuff that expanded due to whatever the big bang actually did, that stuff could have been just the size of a grapefruit and nothing more, or itself infinite. But the part we can access given speed of light restrictions was the part that was the size of a grapefruit. There might actually be a lot more stuff out there ... we can just never get to it.
due to the isotropic principle we assume that the universe is infinite (because our vantage point is random, and since we don't see any orientation at the edge of the observable universe)
I picture the big bang as a bunch of heavy "black holes" approaching eachother discharging something that looks like lightening between them that grows more intense as they all pulled closer together. Eventually fusing into a persistent electromagnetic "explosion." Like a really bad welding accident.
Let me be stricter: models consistent with general relativity don't discuss the idea of a universe being "infinite", and just in general theories in science don't predict the unobservable. Open universe topologies are unbounded. They aren't "infinite".
There are plenty of unknown numbers :) For example, the number that is 1 if the Goldbach Conjecture is true, and 0 if it is false.
(BTW, if you want to know the difference between constructive and nonconstructive mathematics, it's that constructive mathematics doesn't let you say "well, it's definitely 0 or 1" because it leaves open the possibility that there's no proof of either termination or nontermination in the current theory... which is basically the philosophical distinction under discussion).
In the book "When Einstein Walked with Gödel" by Jim Holt,
It seems like that assumption is not as clear as it seems.
I am not able to articulate it well enough and I don't have the
book at hand.
If my recall is accurate then there is a bit of a question if
there exists a "final number".
Yet we can describe most of what we observe with a tiny set of equations. What's more meaningful to science is that the universe is not bound to our models and assumptions. Even the assumption that the universe is ordered and so will remain ordered is not guaranteed. It's just a convenient and historically effective assumption that appears to be justified as far back as we can look. No science, therefore, is a done science.
> ...the human mind is finite.
A whiteboard is finite. It is bound in spacetime and no matter how small the writing, there is an upper limit to the amount of information that can be displayed on it at any one time. No matter how quick the erasing, there is an upper limit amount of information that can be displayed within the lifetime of the board.
Despite this, it can have an uncountably infinite variety of information impressed upon it.
Something not being a done science is one of the core assumptions of science to begin with. Any statement where further progress is excluded is not scientific in a strict sense.
In my opinion scientists (and everyone else) should be allowed, maybe even encouraged to fantasize. Fantasizing, play, shifting around assumptions can help progress. But the problem arises if we accept anything a scientists says as scientific truth.
Understanding that science is always evolving and that scientists often need play and fantasize, increases trust and accelerates progress. We need both to face the challenges of nature.
You can do whatever you want, but most of us don't try to operate in a system where the only knowledge that can exist is that which is verified by the scientific method. In fact, inherent to the scientific method is an underlying philosophy of science which does not come from science, nor could it without being at best circular reasoning.
Science and the scientific method is basically the best means by which we can understand the physical world, but it doesn't help us determine the nature of truth, ethics, or the nature of science. It works on various assumptions (e.g. physical matter actually exists, it is possible to gain knowledge about physical matter, there is such a thing as time, logic is a valid aapproach to determining truth) that it cannot validate.
Stephen Baxter is one of my absolute favorites when it comes to SciFi literature. He incorporates hard physics with great storytelling in amazing settings few other authors dare to touch. No one manages to imagine the end of the universe better than he...
This is probably really dumb but I'm interested to hear people's reactions to yet another amateur dark energy theory.
Could the observation that the universe is expanding actually be the result of a sort of gravitational lensing and not the result of space expanding or bodies moving through space?
My rough line of thinking is:
- We believe that gravity has a warping effect on spacetime.
- We believe that this warping can distort light.
- When we observe light from distant galaxies, it must first exit the gravity well of the source, traverse the universe and then make its way down into our gravity well.
- Therefore, the light must have been subject to some distortion. It traversed two regions of 'stretched' space time and so became 'stretched' itself.
- This 'stretching' is interpreted as redshift and is indistinguishable from if the light source had just been moving away quickly.
Naively, I would have thought this interpretation explains a couple of things quite well:
- Light would be redshifted in every direction as every bright and distant source (i.e. galaxies) resides in a large gravity well.
- It would explain a lack of redshift in nearby objects as we sit in a broadly similar part of the Milky Way's gravity well. As such the relative lensing effect would not be apparent.
Anyway, I obviously have no idea what I'm talking about and someone will have thought of this before - however I'm interested to know why the theory doesn't work.
Most likely I don't really understand gravitational lensing and it wouldn't distort the wavelength of light as I suggested. Alternatively, perhaps someone has done the maths and the impact of any such effect does not align with observations.
Light is indeed redshifted as it climbs through a gravitational well, but it is also blueshifted again when it travels down the gravitational well of our own galaxy. For distant galaxies, the total effect is negligible compared to the doppler redshift due to their velocity. Also, when you look in any direction in the sky, the redshift increases with distance, irrespective of galaxy or cluster masses. So the further they are away, the faster they are receding from us. This is also exactly what the Hubble constant measures.
> the further [galaxies] are away, the faster they are receding from us
I've heard this repeated many times as a surprising discovery. Why is this surprising? Let's say you have some number of objects moving at different speeds (relative to Earth). After enough time, the objects that move fastest should be farthest away, by the simple definition of speed!
Substitute "speed" (really, "velocity") with "acceleration" and your statement is true. So, you're pretty close in your reasoning - if everything is accelerating at the same rate, then things further away from us should be moving away from us faster.
So here's the problem: maintaining a constant velocity requires no outside force, but acceleration does. So, we're seeing everything accelerate away from us.... but why? Where does that force come from?
One more question: How do we know that each galaxy is actually accelerating and not moving at a constant speed?
I'm seeing some circular logic. As I understand it, we think they are accelerating _because_ we see that galaxies that are farther away are moving faster away from us.
But we just agreed that we expect to see this same observation even if each individual galaxy maintains constant velocity. Apologies. It's a bit late. I'm sorry if I'm missing something incredibly obvious.
Possibly dumb answer: If everything else was moving at a constant velocity and we were slowing down, wouldn't the things on the other side of us appear to be accelerating towards us?
My understanding is that basically everything is moving away from us (presumably our reputation precedes us).
Amateur so I’m sure this is a stupid idea. What if they’re not accelerating away from us but space time itself is growing (because of the original Big Bang) and taking everything else along for the ride on top of the original exploding outward, resulting in acceleration of acceleration? Probably it’s growth rate would be decreasing which might be observable in the derivative of the derivative of acceleration? If that were happening, I wonder if virtual particles have some link to that process.
My reasoning here is that everything is accelerating from everything else since our position in the galaxy isn’t particularly special right? Then the only way for that really to be true would be for space time itself to be growing.
That's sort of what's happening. If you imagine space as a rubber sheet with the galaxies pinned to certain places, something is pulling the sheet apart, making it seem like the galaxies are accelerating away from each other. We know the math behind this mechanism thanks to general relativity (it only needs a certain energy density for empty space), but we don't know what causes it. So we just call it "dark energy." Without it, the original expansion of the universe caused by the big bang should be slowing down due to gravity. Dark energy causes it to accelerate instead.
Another amateur, but I think it's more likely the reverse. As we travel through time, us, and the atoms we are made of, shrink(or another way to look at it is 'being consumed', or using up its energy). And we shrink according to how fast we travel through time, and we move through time based on mass. The relative shrinking causes gravity. This would result in that same change in 'acceleration' that we observe, but really it's not that anything is moving, everything is simply changing sizes.
This must be wrong because it feels obvious and testable, simply make 2 satellites, send one to space, then confirm they are the same size when it gets back. And yet I can't find evidence either way.
That seems like it would itself need an explanation. Why would the initial conditions be objects starting at the ~same place but moving with random velocity?
The CMB would also need explanation and I'm thinking the curves of galaxy speeds wouldn't match unless you tweak the initial speeds way too much, but I'm not sure how to formulate that right.
I’ve always wondered whether there might be some other large scale effect happening that causes light frequencies to shift. What if photons travelling through a vacuum just slowly lose energy and their frequency drops? Would that be distinguishable from expansion by any of the measurements we can do here?
so earth is moving with the expanding universe? why I'm not feeling any motion? while earth is spinnging wobbling, tilting, going around the sun at 66600mph.following the sun at 450000mph, following the milkyway at 1.3million mph, following the expanding universe at millions of mph.
One of the early patch sets had a much higher speed of light; but it was eventually fixed.
There's debate about further revising it in a future release; but no consensus on if it needs to be faster or slower. People kept hard coding it as a constant so the legacy issues would make the tachyon situation look simple.
More seriously: when the Universe was smaller and denser could the speed of light been higher, analogous to speed of sound in higher pressure and density materials?
Density doesn't figure into it. It's about space itself, rather than the rate at which light travels. Light in a vacuum moves at that rate, which is a straightforward constant that figures into several other things.
The space itself does change and you could try to redefine the formulas in terms of a changing speed of light, but it just makes it harder. The space metric fits very neatly into the Einstein field equations, and the expanding universe pops out of that directly. The acceleration doesn't, but it's a very simple tweak to make it do so. (Einstein had originally added that tweak to make the universe not expand, but then expansion was discovered.)
If you change the speed of light you throw off chemistry, and all of the observations of distant galaxies show that chemistry still works. So a changing speed of light is unlikely.
> The space metric fits very neatly into the Einstein field equations, and the expanding universe pops out of that directly.
Is there a simple way to understand why? I don't have an understanding of the relevant math. It's a bit hard for me to imagine how we get from the axiom of "speed of light is constant in every reference frame" to an expanding universe. Unless there are other axioms used for this.
The equivalence is between uniform acceleration and a uniform gravitational field. Breaking the uniformity, which the universe does for us whether we like it or not, has consequences.
Real gravitational sources aren't uniform (they tend towards spherical) and come equipped with a tidal field with a potential and gradient. This is intrinsically gravitational, not accelerational.
The non-uniform distribution of matter (including radiation) in the universe also matters.
You can rest an accelerometer on the surface of the Earth and it will report ~ 1 g (upwards) for many -- even billions of -- years, with no ill effect.
How long can you accelerate a rocket containing an identical accelerometer? Consider fuel, and crashing into matter (up to distant starlight and the cosmic microwave radiation) after a few months (of ship time) of the accelerometer indicating ~ 1 g (forwards).
You don't get strong twin-paradox effects involving the Moon-walking astronauts, or long-mission robot probes on the Moon or Mars, even though the local equivalent of "g" is considerably lower than that here on Earth. By comparison, if you and and two roughly identical astronauts were to undergo hundreds of days (or Martian sols, or a few lunar days) ship's time in spacecraft doing a round-trip under constant accelerations of ~ 1g, 0.6g, and 0.17g respectively, the lesser-accelerated "twins" would be visibly older than you at the end of your respective round-trip journeys.
It comes out of extending that to an accelerating reference frame, which gives you a curved spacetime. That doesn't stay stable by itself. It has to either expand or contract, depending on how much energy is in it. (Mass is a form of energy, and so you get gravity.)
It's a bit like noticing that objects can't float. They can either fly away or fall but they can't just sit there. It's not exactly the same thing, since we're talking about the spacetime itself rather than gravity as separate from the objects, but the analogy mostly works.
The speed of light is just a constant for converting units of time into distances, even if the speed of light were to change we'd probably choose to just change the units of distance to forcibly keep it constant.
The speed of light differs depending on the medium it's transiting already though. I've wondered in the past if in the primordial universe time or space were different than what we've observed "now." It seems like they could both compress or expand like other physical characteristics of reality.
There's two different meanings for the phrase 'the speed of light'. One is the conversion constant I mentioned (which is currently used to define the metre in terms of time and is therefore constant by definition).
The other is the speed at which light travels (through a medium).
It's still an exotic model, but if there's an extra dimension that light can fit into - even a tiny loop that it just spirals around as it propagates - then it's possible that at higher energy densities, it spirals at a shallower angle. That would make it appear to propagate through the three normal spatial dimensions faster even if it has the same speed across all four dimensions.
João Magueijo wrote an approachable book on this called "Faster than the Speed of Light: The Story of a Scientific Speculation".
I've always maintained that we are slowly falling toward the center of a black hole that is larger than our current known universe. The rate of expansion is just the speed the universe is "falling, yet due to the absolutely fantastic size of the black hole it will take billions of years to collapse in on ourselves.
Is it not a bit odd to consider things that will happen long after the sun is a cinder "scary." There are enough genuinely scary things that could flash-sterilize the planet, or smash a big enough hole in it to end all complex life forms. Nearer-term scary things are likely to come from how poorly humans can adapt to long term life in space or on planets with different gravity.
Time stretches beyond the ability of life to survive in both directions. Nobody will be around to be scared.
At the speed of light we’d all be gone. Even if the Mars colony was snuffed out first, we wouldn’t even know, since the information about the change wouldn’t be able to reach us before the decay did!
Fun idea. However, acceleration would be different in different directions, were this the case. In our universe, the acceleration is the same in every direction.
That would add a directionality component as some objects closer to said black hole would accelerate faster.
A more plausible but unprovable option is that we are close to the center of a big void (the density of the matter in our neighborhood is much lower than outside the observable universe). So the higher mass concentration attracts objects in our neighborhood giving the impression of an accelerating expansion.
The problem with this theory are that we would have to be almost at the center of this bubble of almost nothing (so the notion that earth is not in a special position is lost) and that if spacetime is not expanding we cannot explain why very distant galaxies recede from us faster than light. FTL travel though spacetime should be impossible but spacetime expanding faster than light is.
If we are within the event horizon, then the direction towards the center of the black hole is not a spatial direction, but a temporal one. The cental singularity is in the future.
As it turns out, the temporal direction is the only direction of spacetime which is not symetric. Objects in the future are accelerating faster, which is presisly the prediction you made.
If I understand correctly, if you add up the mass in the universe, the Schwarzchild radius of that mass is 13 billion light years, which is a really interesting number.
If we were inside a universe-sized black hole, would we be able to tell? Can we experimentally distinguish a black hole universe from a not-black-hole universe?
Good point! However, inside an event horizon we should have a preferred direction in which all the light cones that can catch up to us actually catch up to us (if Penrose diagrams hold true within an event horizon). That would mean that looking in that direction the universe would appear brighter and given how smooth is the CMB that doesn't seem to happen. It could still work if we assume that when this black hole was created either everything or nothing was causally connected to us.
Do you ever marvel at the fact that we have learned and continue to learn so much and yet still really understand basically nothing about why this universe exists, what its limits are, what’s driving its changes, and what its ultimate fate will be?
We don’t know what we don’t know, and we’re trying to figure out how a black box works from inside an infinitesimally small corner of it. Frankly, I find it amazing we’ve worked as much as we have.
Do you ever marvel at the fact that we have learned and continue to learn so much and yet still really understand basically nothing about why this universe exists, what its limits are, what’s driving its changes, and what its ultimate fate will be?
Not really. Modern science has been looking at the origin of the universe for less than a single human lifespan. It's not surprising how little we know. It's pretty amazing that we know anything really. If you'd been studying physics 70 years ago you'd be wondering if the Big Bang or the Steady State theory is right.
Honestly our rate of increased knowledge is unreal, basically humanity had very little tech/science improvements for most of our history and then just world changing improvements in the last 2 generations/lifetimes.
Crazy.
Who knows what things will look like in 1 more lifetime. I'm still blown away by the memory of getting constantly lost growing up, my dad hand drawing maps for people, comedians stopped telling jokes about men not asking for directions and it still feels like nobody stopped to notice.
It's partly that impulse to never stop and appreciate what we have, that dissatisfaction, that keeps people pushing into the unknown.
>Who knows what things will look like in 1 more lifetime.
The usual prediction I see is that the rate of discovery will continue and in another 2 lifetimes everything we think we know now will seem just as silly and naive as what people believed 2 lifetimes before us.
I don't think that's the case. It's a question of whether we're on a (near) infinite exponential curve of discovery, or on the rapid upward stretch of an S curve. I'm in the S curve camp, and I suspect we're at least half way up it on most topics.
Just look at relativity, quantum mechanics and cosmology. Most of the great discoveries in these fields were actually quite a while ago. Relativity and Quantum mechanics are over 100 years old and most of the advances were made in the early decades. Progress has not stopped but massively slowed down.
In cosmology it's been slower progress, but we've charted time back to milliseconds after T=0 of the big bang, detected thousands of exoplanets, analysed the gravitational waves from black hole collisions and mapped the cosmic microwave background. There's more to learn about dark matter and dark energy for sure, some serious mysteries there, but how much difference will those answers actually make? The Higgs boson discovery was cool, but really just a cherry on top of the standard model rather than a revolutionary discovery that upended science. I'm not sure there are any of those still to come.
The closing chapter on the big questions in science still has to be written, but I think the chances it will force us to completely rewrite, rather than simply revise and update the previous chapters, seems slight IMHO. I'm expecting the GUT to simply update or reframe relativity and quantum mechanics to make them compatible, not throw them out completely.
It truly is astonishing to be alive at this nexus in human development, whatever our individual take on it might be.
Progress has slowed down because we solved all the easier problems that we could with the human mind.
Now technology is catching up to give us the computing power, massive collective memory, digital records, and AI to start gaining again. We basically have to build a better mind to get to the next level.
Agree. I think people really underestimate how many intractable "needle in a haystack" problems are now tractable due to RNNs, CNNs and other ML/ai stuff.
We are still in the early days of applying that tech to the fields it's going to effect most.
We're in the "get a home page for your local business" phase not yet the "faang has changed the face of civilization" (for the better or worse) phase.
This is going to continue to ramp knowledge in bioinformatics and other areas, the technology is still in the infancy of being harnessed for biology and medicine.
That combined with cheaper robotic arms and cheaper sequencing machines which is just now coming dropping below certain cost thresholds.
(I know a group/lab that's automating discovery of drug/compound targets doing purely NDA'd work for merck and other pharmaceuticals, the tech is wild and still in it's infancy.)
Cutting edge voice and image style transfer, realistic computer speech, computer vision.. the list goes on, that's just the highly visible stuff and there is still only a small pool of people versed in those areas of tech.
I think it is likely that some things will be revised and tweaked, but other things will have to be majorly rewritten. We may not know what those are yet, but from looking at history, it is wise to believe that in some things we are hammering away at a faulty path. When we rewrite that, there will probably be major rapid improvements very quickly, then slow over time. Perhaps a lot is slowing recently because we've had less major breakthroughs which usually open up fertile fields. Maybe that's because we have the low hanging fruit of major breakthroughs or our society isnt as good at getting them, either way, it will be interesting to see what the future holds.
Everything is not amazing. We’re still social creatures and there is arguably a lot of stress and angst in the social world we find ourselves in. If “everything” is so amazing why are people working over 40/50/60+ hours a week to make ends meet? Why are people made destitute over hospital bills in America? This is something the more privileged among us seem to forget over and over again. Humanity has a ways to go yet before everything is amazing. We can’t just look at our incredible advances in science and technology and call that enough. Yes I’m fun at parties.
It's just the title of a clip of a comedian on a late night show more than a decade ago; not a thesis on current society. And yes, I'm fully aware and very grateful that I live a life better than billions, however it's also indisputable that the world is better today than it's ever been before.
> "incredible advances in science and technology"
That's what this thread is about. Please note the context.
My apologies. Obviously I don’t agree with what’s implied by “we have all this cool tech, how could people be unhappy?”, but I admittedly read some context into it and regardless I could have dialed it down a notch.
> Honestly our rate of increased knowledge is unreal, basically humanity had very little tech/science improvements for most of our history and then just world changing improvements in the last 2 generations/lifetimes.
I feel like this is more a modern misconception than reality. Play a game of Civilization and you'll start to appreciate just how deep human technology really is. In Roman times, they probably said similar things thinking about how advanced they were compared to the Macedonians a couple hundred years back.
Yea we lost some progress or at least the rate of change greatly slowed from 400 - 1600, but other than that blip I think the progress has actually been fairly linear from 4000 BC to 2021 CE. It just seems like it's not because of the cognitive bias to take for granted all the things that seem so basic compared to computers or nuclear reactors, but in reality, those things actually were very difficult to develop with the knowledge and production techniques available at the time.
We'll have to disagree on the shape of the curve I guess, it's just my personal take.
For what it's worth...
I've been to Ephesus (which is amazing, I'd like to check out Pompeii as well) the armory in Venice is one of my favorite repos of old cutting edge tech and having spent time in Rome, truly their achievements are amazing and the Pantheon absolutely blows my mind, it's no wonder the village dwellers believed the God's lived in Rome, I would have.
But harnessing the power of the atom, understanding fundamental physics, biology and sound/light speed global communication... and the technology that these things have enabled (including my own living past 3 years of age due to modern medicine) is truly a leap, in my opinion the Roman's and those brilliant technologists and logistics civilizations of the past were still closer to living in caves by modern comparison.
I would not have wanted to live back then and I literally couldn't have. Our recent exponential explosion certainly depends on their hard fought knowledge, but in my reckoning even their best tech and logistics are deep in the early part of the curve.
> In Roman times, they probably said similar things thinking about how advanced they were compared to the Macedonians a couple hundred years back.
The fall of the Roman Empire, and actually really even the decline from when the city stood at more than a million people during the time of Augustus and Tiberius until the far, saw massive declines in technological knowledge and even scientific knowledge. Much of that information was not rediscovered until the Renaissance when the last remaining archives of the Roman Empire were evacuated from Constantinople to nobles and merchants across Europe during the Turkish invasion. Even today we're still rediscovering material science knowledge that the Romans and ancient Chinese had. In fact, much of our rapid advancement in technology was not even due to knew ideas, it was due to ideas that had be theorized by Greek and Roman philosophers and alchemists, and which were recorded and stored in the archives.
There was real stagnation in most knowledge and technology throughout the world. In the West because of the decline of the Roman Empire (most likely caused in part due to lead poisoning and decreasing fertility of North Africa and Judea) and in the East due to constant infighting and political strife preventing unification of India or China under stable rulers for long enough to see real advancement.
It's not, but I can see how it seems that way - I found this with a two second search:
The world population increased from 1 billion in 1800 to 7.7 billion today.
I'm not going to do the math but there's something to be said about how many we are today vs. even 200 years ago. But, no, the majority of humans ever born are not, in fact, still alive today...
I think OP is saying that if you add up all the humans that have died in the past 10,000 years or so (modern humans), then that number is smaller than today’s global population.
This. It's amazing when you also take into account that the beings evaluating it originated from the very arbitrary matter that we strive to understand.
I always express that the greatest science "fiction" story is actually the reality above us, and the multitude of unanswered questions.
I actually find that the process of formation of everything around us is pretty straight forward. After all, none of it is explained by magic.
Now, how all this shocking amount of matter came to exist from energy, which also had to come from somewhere... That's a head scratcher alright. The path to God is hidden behind rock solid plausible deniability.
say an advanced civilization learns how to time travel and walk the multiverse. trying to find us would be hard. the time scale is very small, yes, we occupy a small area, true, but also the scale of life itself may not be discussed much.
there's dozens upon dozens of orders of magnitude of space that a being could occupy. scanning for life through the multiverse and time, it would also be easy to miss us. too small and you see cells and organelles, larger we see organs mixed with bacterial cultures, etc, and at just the right scale we are visible.
there are arguments that earth is a living entity, and there may be larger forms of life going many orders of magnitude larger than planet-sized.
with such a large range of time, location and scale to scan for life, it could be argued we basically don't even exist.
A couple of years ago, Netflix added a science series about the Universe, and I could not understand why they referred to the process behind planet and star formation as a mystery. We know that dust, left to just float in space, will create clumps, rocks, boulders, and so on - due to microgravity.
The series was from the mid 2000s.
No one suggested this very obvious process until an astronaut on the ISS had a fine-grain substance in a small plastic bag (no, not THAT one), and they noticed the grains stuck together.
Interesting as I thought that the theory was quite old. Certainly sure I believed that well before the mid 2000s. And a quick search on DDG says that theory was first proposed in 1941 referring to plant formation?
> The formation of planetesimals is the biggest unsolved problem in the nebular disk model. How 1 cm sized particles coalesce into 1 km planetesimals is a mystery. This mechanism appears to be the key to the question as to why some stars have planets, while others have nothing around them, not even dust belts.
It is not the scale of the universe that would determine if Earth matters or not, but whether or not there is significance to the universe and to Earth. Significance conferred by observers or parties interested in these things.
Example: $100 isn’t less or more just because of increasing or decreasing the physical footprint of the bill. We still confer a purchasing power of $100 to a $100 bill regardless of the bill’s physical dimensions.
So the takeaway here is that it’s a non-sequitur to say that because of Earth’s small scale relative to the rest of space, nothing on Earth matters.
You're right, we still matter as people, but only for our own feelings and circumstances.
It's humbling because it puts all that hubris away, which most people tend to have an excessive amount of - and begin to focus on living and achieving simple happiness instead of some illusion of grandeur.
It does sometimes feel like we wake up, stretch, and open our eyes every morning to realise we're at the edge of a cliff, the ground plummeting away into fog beneath us. But then we roll over and there's green grass on the other side, so off we go to work.
That said, whatever breakthroughs we make from one generation to the next, what a stroke of luck it is that some things remain constant: we can fall in love, enjoy a good story, drink, eat, be merry, and argue about the meaning of life in whatever fora present themselves.
Modern physics indeed isn't any closer answering the big questions as it was when physics got established as part of science.
We don't know what space, time or matter are. We don't know where it's coming form or where it's going. And we don't know most things in between.
It's a marvel we figured out so much about how some details seem to work given we still don't know mostly anything about the more fundamental phenomena.
I made my peace with the fact that some set of sets of abstract rules makes absurd but precise predictions about what I perceive, and I will never know why. I try to direct my marvel on how can I be but a collection of interconnected automata perceiving these rules on scale.
By what scale, exactly? This corner is just as large as it is small. There are an equivalent number of grains of sand on Earth than there are stars in the observable universe.
We are not small. Size doesn't work like that. Space is everywhere, including here.
As far as I understand current physics, the solution seems simple: Just through some more "dark" matter in there, and the standard model is save again.
The target audience of National Geographic are people with some science background but not researchers/experts. It a publication for the masses and so they have to tone down the technical lingo. For physics I read Nature, but for every other topic that might interest me but is above my knowledge level National Geographic works.
Honestly, I find that unacceptable. It's National Geographic. Could at least have some higher standards considering the above average audience.
It's not technical lingo using the actually correct wording for the effects of the expanding universe. Galaxies do not fly apart, the space in between grows. The difference is significant, even though the observer wouldn't notice any.
I know it seems like a non-issue, but in the end it's misleading all the people who would blindly believe NG to be accurate.
I thought that if more stuff collapses into singularity there might be something pushing outwards... Maybe like turning a balloon inside-out - which leads to the space-time expansion...
Like how accurate are these models? Could these be software or hardware errors? I mean, are these running on 1970 terminals in Fortran or is there real development going on? I imagine it's super hard to measure such tiny disrepancies in the cosmos when we are failing constantly in common modern software.
I mean, if it’s Fortran that’s been around since the 70s, it’s probably been around long enough that it is both better vetted for accuracy, and not burdened by “real development” affecting some static mathematical principals that the code is computing….
Valid argument, my main point though is how do we know whether these are not errors in the model generation and not in the universe acting in weird ways? It's not that you can make tests against the universe, you have to always rely on some algorithms giving you the results, which could be wrong and every institute could be using the same ones from the same vendor. Where are the data and what is the software is my worry.
235 comments
[ 4.7 ms ] story [ 268 ms ] threadThis may be pedantic on my part, but I don't like this framing. It has the implication that our models dictate what happens in the universe and not the other way around. The universe is expanding faster than our models predict or there's something up with our observations or both. Maybe this is what people have in mind, but I think it's a subtle communication difference and can miscommunicate that science is truth, whereas science is the collection and evolution of models and observations describing the reality we experience.
A friend once told me, “stop shoulding yourself.” Turns out, I should’ve listened.
It's alright to critique something to try and improve it, you know?
Lastly, it's not really besides the point, as our models and possibly our observations being wrong is entirely the crux of this "problem".
Have you even glanced at the article?
I admitted it was possibly pedantic, and then I got "smug nitpicking". And this happens all the time, so there's some pre-existing bias on my part in terms of being bothered by these communication mishaps. I struggle to watch many science documentaries these days due to communication issues such as these.
Absolutely. If one person does their best work and is still frustrated after trying dozens of options, it is fair for them to be scratching their head and saying, "This shouldn't be happening."
The article itself provides exceptionally precise reporting (though IANAA) of mutual work toward a grand challenge in astronomy --- which is still leaving people scratching their heads at discrepancies after trying dozens of model or analysis variations. The word 'should' in the title (I believe it only appears there) to me conveys well-enough (it is only a title) that there are human elements/expectations and legitimate after-the-best-of-care puzzles remaining.
I don't know if it is a good comparison, but if the time for the g-2 result reveal came, and the result was a 20-sigma discrepency, I would expect every experimentalist and every theorist involved to immediately scowl and say, "F***, this should never have happened."
Also perfectly ordinary and ideomatic: To say, This should be compiling without errors.
Great science reporting in the article, hence my rant to defend it.
That's why I'm also not a fan of using the word "law" for names of the models, because it implies as if the universe is obligated to follow this "law", but a law of physics is still essentially only our description (even if it uses math equations instead of words to describe).
This is probably just youthful exuberance. If it's still at it after another 13 billion years, take away its license.
I share the opinion that they're names for holes, not entities; but I'm not qualified to defend that opinion.
And, in order to understand a something, do we always need that something to interact with EM radiation?
Dark energy, in particular, can't be a kind of "stuff".
We could "understand" something that doesn't interact with EM; but we'd have trouble observing it.
If modified Newtonian (MOND) theories won out, the theory would explain this observation by saying that there was no matter there to begin with. If neutrino theories won out, the theory would explain this observation by saying that dark matter is electromagnetically neutral. But those are two entirely different theories, trying to explain the same observations, and trying to fill the hole in our currently accepted models in different ways.
EDIT: Per a child comment, you might mean "theory" as "idea", as in "the [idea] is that it doesn’t react electromagnetically with other matter." In which case, yes!
I usually agree with your understanding of dark matter/dark energy as placeholders for missing knowledge.
There's definitely lots of evidence for dark matter, yes~!
Dark matter has lots of reasons to be assumed but a common one is that when we try to explain the gravitational effects of galaxies based on a quantification of observable matter, there is a huge shortfall. That creates a space for something with a gravitational effect that is unobservable otherwise.
That many of the objects of our physics are theory laden is true, but that they are therefore “unreal” or merely an artefact of theory does not necessarily follow.
Light exiting from stars deep in a galaxy (which is in turn deep in a galaxy cluster) is subject to gravitational redshift. The greater the mass of the galaxy and cluster, the greater the redshift.
If we add transparent, non-radiating mass to a galaxy and its cluster, the mean redshift of starlight from the galaxy will redshift, and we'll see the result on various absorption and emission lines in the spectrum.
Note, we do not need dark matter for this; increasing the central mass of a galaxy cluster will do the trick too. We can do this by adding more stars, or by adding black holes, or by making a central black hole more massive. All of this will cause an increase in gravitational redshift.
However, adding more central mass to galaxies will be reflected in the trajectories of clouds of gas and collections of stars within the galaxies; likewise, adding more concentrated mass to a galaxy cluster will alter the trajectory of galaxies within it. In general, these objects will have faster orbits -- fast enough that a non-gravitational redshift will be apparent in the arrangement of spectral lines. (We would also need to figure out how to keep any central masses from being extremely bright anywhere in the electromagnetic spectrum, and how to keep them from eclipsing parts of their home galaxies and clusters that are behind them from our perspective.)
If we instead redistribute our increase in galactic mass into a gaseous halo-like structure that extends well beyond the outer stars, we get the increased gravitational redshift without requiring stars and gas to travel faster to avoid falling inwards. The halo still has to be electromagnetically quiet, and non-eclipsing, or we would see it. (This all applies to clusters, too).
Stepping away from the "dark matter puzzle" of the spectral lines of molecular and atomic gas clouds in galaxies and clusters of them, we can then look at another aspect of your question.
Galaxy clusters, from their point of view, are just floating passively in space.
The expansion of the universe follows a model wherein if we treat the astrophysical content of galaxies and clusters as sensitive accelerometers that in aggregate show off the peculiar accelerations experienced by these large scale objects, there is no evidence that these accelerometers should report a non-zero magnitude or point in any particular direction. That is, galaxies and galaxy clusters are themselves in free fall, and we can see this because of lines of evidence including expansion-direction-and-magnitude squashings of https://en.wikipedia.org/wiki/Light_echo lines turn out to be null, likewise there are no radio-loud edge shocks for galaxies that appear to be accelerating away from us, there are no shape distortions of the most highly "accelerated" distant galaxies, and so forth. There is simply a spectral redshift.
So, for an isolated galaxy the spectrum it emits depends on a combination of its starshine, any noise from close to its central black hole(s), the noise from any thick gas clouds undergoing gravitational collapse, and the absorption and reemission of diffuse gas clouds heated by these types of emission and absorption-and-reemission sources and the distribution of dark matter within and around the galaxy. The more dark matter, the more redshifted the galaxy's spectral lines will be.
Preserving the Copernican Principle, immersing a set of such isolated galaxies into an expanding cosmos leads to the inhabitants of each galaxy observing a cosmological redshift on the gravitatonally-redshifted spectrum emitted by other sufficiently distant galaxies. The gravitational-redshift depends on the mass of the galaxies including their dark matter. The cosmological redshift only depends on a light-travel distance from the galaxy, no matter how light or how massive that galaxy (or its parent cluster) is.
In order to make that measurement, the authors had to combine redshift measurements for ~ 20,000 galaxies from ~ 2,500 different clusters; as they note, it's impossible to detect the effect for just a single cluster: "... even assuming that every galaxy in a cluster could be spectroscopically measured, there are simply too few galaxies to allow the statistical detection of a non-zero gravitational redshift."
So while it's technically true that adding dark matter to a galaxy would increase its gravitational redshift and thus its total observed redshift, this effect is immeasurably small.
Mpetha et al. (2021), "Gravitational redshifting of galaxies in the SPIDERS cluster catalogue" https://arxiv.org/abs/2102.11156
Broadhurst & Scannapieco (2000) https://iopscience.iop.org/article/10.1086/312630 is also relevant here, as it distinguishes between X-Ray studies and optical ones (SPIDERS being an example of the latter) pointedly at §4.2.
I do not disagree that ~ 10-20 km/s is small, but it's the little things that cause "tension" headaches, isn't it?
The Broadhurst & Scannapieco discussion about X-ray studies is interesting and potentially promising, but no one seems to have tried doing for real.
This is the exact opposite of the truth. An edge-on spiral galaxy without dark matter would have less extreme observed rotation velocities (comparing the blueshifted and redshifted sides of the disk), because only the visible mass (stars and gas) is relevant. But in practice we see higher rotation velocities (greater difference between blueshifted and redshifted sides) than can be explained by just the visible mass, and so we have to postulate extra mass in the form of "dark matter" in the galaxy.
(Dark matter halos are not just dark matter outside the visible galaxy, they extend all the way to the centers of galaxies, and in fact become denser the closer to the galaxy center you get. Of course, the visible matter also becomes denser the closer to the center you get, and usually faster than the dark matter does, so the central regions of massive galaxies are dominated by the visible matter. But there's still dark matter there, and in some dwarf galaxies, the dark matter even in the central regions.)
As to your parenthetical, cuspiness is not really relevant to the scale of the points raised in the bulk of my comment, and it is not clear to me why you raise the DM density profile here.
On the one hand, in vacuum, an accelerating expanding universe's geometry breaks time-translation invariance. Let's look at the vacuum geometry with a pair of test photons in the otherwise empty test universe. In the early universe we have the photons widely spacelike-separated but on trajectories where they will ultimately collide in the far future. The photons in the future will be redshifted compared to their wavelengths in the past, with the redshift proportional to the expansion history of the test universe. (In our universe, the cosmic microwave background photons have behaved this way when two CMB photons meet at a detector).
Since photon energy can be calculated E = (hc)/\lambda, where \lambda is the photon wavelength, a redshift corresponds to a decrease in the photon energy.
Where did this energy go? One can simply say that constancy of photon energy is premised on time-translation invariance, which is not a large-scale feature of an accelerating expanding universe.
This position is just that thermodynamics was developed to describe engineering phenomena in the 19th century, and not to describe the motion of clusters of galaxies over the course of billions of years. Since Noether, thermodynamics's first law has its foundations in time-translation invariance, which we only have in some spacetimes (e.g., Minkowski's flat space, the spacetime of special relativity) or in local pieces of general curved spacetime. In the absence of strict time-translation invariance globally, the first law of thermodynamics is just a weak-gravitational-field approximation.
Sean Carroll expands upon some of this here : https://www.preposterousuniverse.com/blog/2010/02/22/energy-... wherein he also discusses an effectively pseudogravitational-field view of our test spacetime's geometry, in order to think of our pair of converging photons donating energy to that (pseudo-)gravitational field. As he says, such a view, which leans on a notion of gravitational potential energy which is simply absent in General Relativity, is often unhelpful.
On the other hand, one can take a different approach and treat \Lambda, the cosmological constant, as a matter field rather than as a geometrical feature of the accelerating expanding spacetime. When we do this, then we are left with either an inertially-expanding spacetime, or with a flat spacetime, and in the stress-energy tensor we have what makes that acceleration or acceleration + expansion field cause everything in the stress-energy tensor (including those fields themselves) to fly apart.
It can be reasonable enough to do this. Einstein and Schrödinger discussed this in correspondence during the first world war : https://arxiv.org/abs/1211.6338 wherein they seem to agree that it is a matter of taste. We know from work in the more modern Hamiltonian formulation of General Relativity that we can't do this generally, but there are large families of spacetimes and matter content that are amenable to this approach of encoding aspects of the dynamical geometry as a form matter we can describe with canonical position & momentum.
We can also note here that the distribution of matter in a spacetime can pick out preferred foliations or even preferred frames of reference.
In our standard cosmology, which you are asking about, we treat the distribution of matter isotropic and homogeneous, where each form of matter is a perfect fluid with a density and a pressure. As the universe expands (with or without acceleration of expansion) the matter and radiation fluids dilute away, their density dropping over time. ...
Before criticizing physicists you should keep this in mind.
Not really. It is a hypothesized form of matter. There are competing hypotheses. Dark matter came to popularity in order to explain observations of galaxy rotation curves in the late 1930s. But these galaxies were observed in isolation, giving the illusion of gravitational isolation, which doesn't exist. Once accounting for the tidal effects of nearby galaxies, [1] dark matter becomes unnecessary to explain galaxy rotation curves, all that is needed is Newtonian physics. But in the period since dark matter was hypothesized, other observations that could not be readily explained were lumped into dark matter. Dark matter is nothing if not an amalgamation of unexplainable observations. So while dark matter is unnecessary to explain galaxy rotation curves, it is still somehow useful to explain unrelated observations.
> it isn't a band-aide fix
It really sort of seems like that: can't explain an observation, so invent something out of thin air to explain it. Honestly, an hypothesis that elves are causing the observations has just as much validity (or lack thereof). Now, elves have not been proven to be the cause of these unexplained observations, but neither has dark matter.
> the foundations of the concept of dark matter are fairly reasonable.
See above concerning galaxy rotation curves and endnote. Please understand it is quite possible that dark matter does not exist. The reason why it seems like accepted science has to do with scientific paradigms. Once a notion becomes an accepted part of the science paradigm, it takes years if not decades after disproving it beyond all doubt to dislodge it from the paradigm. If science has a problem, it is paradigms.
[1] https://www.youtube.com/watch?v=PL0ewiwqoTw&t=6m11s
"Tidal effects" are a non-starter, and do nothing to explain galaxy rotation curves. Nor do they explain the excess motions of individual galaxies in galaxy groups and clusters, or the excess pressure of hot, X-ray emitting gas in groups and clusters -- all of which requires either some kind of dark matter, or some kind of alternate theory of gravity, or both.
(I notice that I pointed out the ignorant nonsense of that video when you posted a link to it 7 months ago -- https://news.ycombinator.com/item?id=27085979#27090683)
Nice catch.
> "Tidal effects" are a non-starter, and do nothing to explain galaxy rotation curves. Nor do they explain the excess motions of individual galaxies in galaxy groups and clusters, or the excess pressure of hot, X-ray emitting gas in groups and clusters -- all of which requires either some kind of dark matter, or some kind of alternate theory of gravity, or both.
What a well formed and well supported argument, and not just a matter of fact statement that you've left entirely unsupported. I'm totally convinced!
We observe with telescopes that the universe is expanding. We don't know why, so we call the mysterious force dark energy. It's just a name for something that we are objectively observing.
(Also this has nothing to do with dark matter, that unrelated to this discussion and you're just getting the names conflated.)
But we are not of that scale. 90+% things we do not know, we just label them as dark … matters or energy. It looks like we know. The key is the dark part.
If you do not know 90+% things out there, there is no way you can think of should.
Just say the universe once again serve us a curve ball …
They're just leaving off the implied "according to our models" at the end of the sentence. This is mostly fine, because it's obvious we don't know the true model of the universe, so our expectations are based on our current understanding.
I love cosmology and reading about it. Always exciting. But not because of the human part. More positively as said in the article … a lot to be learnt, just do not use the word should you are ok I am ok.
The alternative is that the thing on which our universe depends (being careful not to say 'caused' here) is beyond our ideas of cause and effect, and certainly passes human understanding.
Ha! No, there does not. Humans use create a hallucinated duality as a means of navigating a non-dual reality.
Let me ask you; How long was the time before you were alive, and how long will the time be after you are dead?
As Julian Barbour puts it: "We see from this that time has no role to play as an independent element of reality."
http://www.platonia.com/nature_of_time_essay.pdf
You should read his whole book, it's time to wake up!
> Let me ask you; How long was the time before you were alive, and how long will the time be after you are dead?
This is misleading as it posits that since there's a "before you" and an "after you", "you" are standing within some time continuum.
> There has to be a beginning and end.
Wrap your head around this: if there is a "beginning" and an "end" to our universe, both would define discrete stop points, thus there would be some way to say "before" or "after" these discrete points, and thus the universe sits inside something that has time.
But then either this something of a container either has infinite time (which goes back to square one of things not having beginning and end) or has a beginning and end itself.
But again, if this container has a discrete beginning and end then you can apply the same logic that you applied to our universe in the first place. So there's another container of the container, to which you can recursively apply the same logic (assuming logic itself somehow applies to this container). So if you want all these container things to have beginnings and ends, it implies there's an infinite set of nested containers.
The alternative is that time exists within our universe, but our universe doesn't sit within time. Thus "beginning" and "end" are not discrete points but concepts that only exist as limits (in the mathematical sense of "limit"): by travelling the arrow of time forward or backward you can only move closer and closer to either but never actually reach these because these points don't actually exist.
Such a universe could be freestanding (as in: it's all there is), or it could have a container of sorts, and maybe even neighbour universes. But since time only exists within our universe, there could very well be no concept of time in the container (or other universes), or similar concepts but behaving entirely differently. In any case these (the container, the other universes) would be unbelievably incomprehensible to us.
These concepts of unreachable zero, unreachable infinite, or unreachable value do exist in other areas: absolute zero is basically unreachable, reaching c velocity requires infinite energy†...
† which creates other interesting conundrums such as a pair of photons travel at the same delta speed whether they go away or towards each other, or there's no "velocity = 0" either, or tachyonic vs baryonic realms.
It was not misleading, it was a question. What person does not think they were born or that someone died?
In my experience, time does not exist. It is an illusion. Have you read Barbour's book?
Not to say it couldn't work some other way -- I'm not a physicist either! But (as these things always seem to end up) it would have to be a little more complicated. (Part of the "rolled-up dimensions" side of string theory is that the extra dimensions can't meaningfully attenuate the effects of gravity.)
[0] I don't think this is the one I read, but it rings the right bells: https://www.sciencealert.com/gravitational-waves-have-ruled-...
[0] http://www.geom.uiuc.edu/~banchoff/Flatland/
Also, not having a border is not the same as being infinite. Zogg from Betelgeuse started a great series on the topic [1], but disappeared after two episodes. I highly recommend it! But, long story short, it's entirely possible to have a finite universe that, nonetheless, has no edge. Go far enough in one direction and you might end up back where you started.
[1] https://www.youtube.com/watch?v=_k3_B9Eq7eM
Assuming there's a physical edge to our universe, there's still the problem of the "observable universe" -- there's a lot more of the universe that we will simply never be able to see or reach, because it's moving away from us too quickly. That defines another kind of edge, one that's much "closer". Entities beyond our observable universe can't affect us gravitationally; it takes time for the effects of gravity to propagate from one point to another, as "gravitational waves", and the universe is inflating too quickly for those to reach us.
You might say that things further away from us, but within the observable universe, might be affected by things beyond, because they're "closer" to it than we are. I think that's correct, but by the same token, I think the information about those effects would never reach us in finite time.
That's why I was thinking in terms of extra spatial dimensions. You might have a bunch of matter "nearby" but totally inaccessible to you, because we're incapable of moving along the extra axis. But that gets back to the research I linked.
Now imagine there are two such spheres near to each other. Two beings whose physical laws and interactions were entirely confined to their respective surfaces would be unaware of each other and unable to influence each other in any way - gravity for example is only able to travel around the surface of the sphere, not into whatever 'space' lies in between. The surface of each sphere is its own universe.
There's no reason to believe our "common sense" or "intuitive understanding" has any relevance to how the universe is or isn't.
According to an ant's common sense humans for sure have antennas somewhere on their bodies, even if not visible to an ant.
Are you the one who started this whole movement ? Or in fact you just rehash the same bullcrap ? Closer to the universe edge he says, not defining the universe or an edge...
entia non sunt multiplicanda praeter necessitatem.
Thou shalt not multiply entities beyond necessity.
Also, we see far away clusters or galaxies receding faster than light away from us. This is impossible in a non expanding universe since faster than light travel _through_ spacetime is impossible but spacetime between two objects expanding faster than light is.
We (well, Einstein & Co. I was not involved.) made models about how the universe works. Then when looking at the broader scope, we noticed that the models differ from reality. So instead of saying the models are wrong, we invented "dark matter". Some unmeasurable type of matter that is responsible for the difference of how reality behaves in contrast to our models. And then we invented dark energy.
Now to make our models "work" we have to assume 85% of the matter in the universe is made of dark matter. And 68% of energy in the universe is made from dark energy.
How about just saying that our models do not work on large scales?
I have a lot more arguments that prove dark matter is a hoax. Let me write them down in dark text (an unmeasurable form of text). Here we go:
She should stick to physics, not philosophy. Proving free will with physics is ignorant and arrogant. The hard problem of consciousness is much deeper than "in our models, we see that there is no randomness anywhere, ergo no free will."
All models are wrong. Some models are useful. Everyone knows that the models aren't perfectly accurate; that's what models do: model. We literally say "this model is wrong" all the time.
There was an obvious security hole sitting for years in the most common library in the most common programming language, and no one noticed... We fly to space and begin to do some mega projects, yet some of the most intelligent people in the world are facepalming themselves on a daily basis... We are not smart enough yet.
Articles like this get traction because the lay person may have believed that the science was more mature than it is. (Some) scientists are also notoriously famous for exaggerating how much science "knows" - Stephen Hawkings claim to the mind of God comes to mind.
We need to relieve such scientists of the burden of needing to know it all, and be grateful for all the things still left to discover.
Cosmology will never be a done science. The universe is infinite but the human mind is finite.
Well, an open question in cosmology is whether the universe is actually infinite or not...
I don't think that's right. The shape and topology of the universe is an open question in cosmology, and cosmologists haven't just "left it at that".
(BTW, if you want to know the difference between constructive and nonconstructive mathematics, it's that constructive mathematics doesn't let you say "well, it's definitely 0 or 1" because it leaves open the possibility that there's no proof of either termination or nontermination in the current theory... which is basically the philosophical distinction under discussion).
If my recall is accurate then there is a bit of a question if there exists a "final number".
Yet we can describe most of what we observe with a tiny set of equations. What's more meaningful to science is that the universe is not bound to our models and assumptions. Even the assumption that the universe is ordered and so will remain ordered is not guaranteed. It's just a convenient and historically effective assumption that appears to be justified as far back as we can look. No science, therefore, is a done science.
> ...the human mind is finite.
A whiteboard is finite. It is bound in spacetime and no matter how small the writing, there is an upper limit to the amount of information that can be displayed on it at any one time. No matter how quick the erasing, there is an upper limit amount of information that can be displayed within the lifetime of the board.
Despite this, it can have an uncountably infinite variety of information impressed upon it.
In my opinion scientists (and everyone else) should be allowed, maybe even encouraged to fantasize. Fantasizing, play, shifting around assumptions can help progress. But the problem arises if we accept anything a scientists says as scientific truth.
Understanding that science is always evolving and that scientists often need play and fantasize, increases trust and accelerates progress. We need both to face the challenges of nature.
Then that is not a scientific statement.
Science and the scientific method is basically the best means by which we can understand the physical world, but it doesn't help us determine the nature of truth, ethics, or the nature of science. It works on various assumptions (e.g. physical matter actually exists, it is possible to gain knowledge about physical matter, there is such a thing as time, logic is a valid aapproach to determining truth) that it cannot validate.
[1] https://web.archive.org/web/20080725045740/http://www.solari...
Thank you for sharing it.
Could the observation that the universe is expanding actually be the result of a sort of gravitational lensing and not the result of space expanding or bodies moving through space?
My rough line of thinking is:
Naively, I would have thought this interpretation explains a couple of things quite well: Anyway, I obviously have no idea what I'm talking about and someone will have thought of this before - however I'm interested to know why the theory doesn't work.Most likely I don't really understand gravitational lensing and it wouldn't distort the wavelength of light as I suggested. Alternatively, perhaps someone has done the maths and the impact of any such effect does not align with observations.
edit: formatting
I also hadn't heard of Hubble's constant, which I am now learning about :). Very mysterious indeed.
I've heard this repeated many times as a surprising discovery. Why is this surprising? Let's say you have some number of objects moving at different speeds (relative to Earth). After enough time, the objects that move fastest should be farthest away, by the simple definition of speed!
What am I missing?
So here's the problem: maintaining a constant velocity requires no outside force, but acceleration does. So, we're seeing everything accelerate away from us.... but why? Where does that force come from?
One more question: How do we know that each galaxy is actually accelerating and not moving at a constant speed?
I'm seeing some circular logic. As I understand it, we think they are accelerating _because_ we see that galaxies that are farther away are moving faster away from us.
But we just agreed that we expect to see this same observation even if each individual galaxy maintains constant velocity. Apologies. It's a bit late. I'm sorry if I'm missing something incredibly obvious.
My understanding is that basically everything is moving away from us (presumably our reputation precedes us).
My reasoning here is that everything is accelerating from everything else since our position in the galaxy isn’t particularly special right? Then the only way for that really to be true would be for space time itself to be growing.
This must be wrong because it feels obvious and testable, simply make 2 satellites, send one to space, then confirm they are the same size when it gets back. And yet I can't find evidence either way.
maybe this is where the c² in the famous equation comes from
>everything is accelerating from everything else
but what about galactic collisions? we are told the big bang did not happen from one single point but instead everywhere at once
The CMB would also need explanation and I'm thinking the curves of galaxy speeds wouldn't match unless you tweak the initial speeds way too much, but I'm not sure how to formulate that right.
The universe is not expanding faster than it "should" be! Your math is wrong!
Let me fix it:
"Scientists models of the expanding universe fail again."
There's debate about further revising it in a future release; but no consensus on if it needs to be faster or slower. People kept hard coding it as a constant so the legacy issues would make the tachyon situation look simple.
More seriously: when the Universe was smaller and denser could the speed of light been higher, analogous to speed of sound in higher pressure and density materials?
The space itself does change and you could try to redefine the formulas in terms of a changing speed of light, but it just makes it harder. The space metric fits very neatly into the Einstein field equations, and the expanding universe pops out of that directly. The acceleration doesn't, but it's a very simple tweak to make it do so. (Einstein had originally added that tweak to make the universe not expand, but then expansion was discovered.)
If you change the speed of light you throw off chemistry, and all of the observations of distant galaxies show that chemistry still works. So a changing speed of light is unlikely.
Is there a simple way to understand why? I don't have an understanding of the relevant math. It's a bit hard for me to imagine how we get from the axiom of "speed of light is constant in every reference frame" to an expanding universe. Unless there are other axioms used for this.
Real gravitational sources aren't uniform (they tend towards spherical) and come equipped with a tidal field with a potential and gradient. This is intrinsically gravitational, not accelerational.
The non-uniform distribution of matter (including radiation) in the universe also matters.
You can rest an accelerometer on the surface of the Earth and it will report ~ 1 g (upwards) for many -- even billions of -- years, with no ill effect.
How long can you accelerate a rocket containing an identical accelerometer? Consider fuel, and crashing into matter (up to distant starlight and the cosmic microwave radiation) after a few months (of ship time) of the accelerometer indicating ~ 1 g (forwards).
You don't get strong twin-paradox effects involving the Moon-walking astronauts, or long-mission robot probes on the Moon or Mars, even though the local equivalent of "g" is considerably lower than that here on Earth. By comparison, if you and and two roughly identical astronauts were to undergo hundreds of days (or Martian sols, or a few lunar days) ship's time in spacecraft doing a round-trip under constant accelerations of ~ 1g, 0.6g, and 0.17g respectively, the lesser-accelerated "twins" would be visibly older than you at the end of your respective round-trip journeys.
It's a bit like noticing that objects can't float. They can either fly away or fall but they can't just sit there. It's not exactly the same thing, since we're talking about the spacetime itself rather than gravity as separate from the objects, but the analogy mostly works.
The other is the speed at which light travels (through a medium).
João Magueijo wrote an approachable book on this called "Faster than the Speed of Light: The Story of a Scientific Speculation".
Time stretches beyond the ability of life to survive in both directions. Nobody will be around to be scared.
A more plausible but unprovable option is that we are close to the center of a big void (the density of the matter in our neighborhood is much lower than outside the observable universe). So the higher mass concentration attracts objects in our neighborhood giving the impression of an accelerating expansion. The problem with this theory are that we would have to be almost at the center of this bubble of almost nothing (so the notion that earth is not in a special position is lost) and that if spacetime is not expanding we cannot explain why very distant galaxies recede from us faster than light. FTL travel though spacetime should be impossible but spacetime expanding faster than light is.
If we were inside a universe-sized black hole, would we be able to tell? Can we experimentally distinguish a black hole universe from a not-black-hole universe?
Fascinating point!
We don’t know what we don’t know, and we’re trying to figure out how a black box works from inside an infinitesimally small corner of it. Frankly, I find it amazing we’ve worked as much as we have.
Not really. Modern science has been looking at the origin of the universe for less than a single human lifespan. It's not surprising how little we know. It's pretty amazing that we know anything really. If you'd been studying physics 70 years ago you'd be wondering if the Big Bang or the Steady State theory is right.
Crazy.
Who knows what things will look like in 1 more lifetime. I'm still blown away by the memory of getting constantly lost growing up, my dad hand drawing maps for people, comedians stopped telling jokes about men not asking for directions and it still feels like nobody stopped to notice.
It's partly that impulse to never stop and appreciate what we have, that dissatisfaction, that keeps people pushing into the unknown.
The usual prediction I see is that the rate of discovery will continue and in another 2 lifetimes everything we think we know now will seem just as silly and naive as what people believed 2 lifetimes before us.
I don't think that's the case. It's a question of whether we're on a (near) infinite exponential curve of discovery, or on the rapid upward stretch of an S curve. I'm in the S curve camp, and I suspect we're at least half way up it on most topics.
Just look at relativity, quantum mechanics and cosmology. Most of the great discoveries in these fields were actually quite a while ago. Relativity and Quantum mechanics are over 100 years old and most of the advances were made in the early decades. Progress has not stopped but massively slowed down.
In cosmology it's been slower progress, but we've charted time back to milliseconds after T=0 of the big bang, detected thousands of exoplanets, analysed the gravitational waves from black hole collisions and mapped the cosmic microwave background. There's more to learn about dark matter and dark energy for sure, some serious mysteries there, but how much difference will those answers actually make? The Higgs boson discovery was cool, but really just a cherry on top of the standard model rather than a revolutionary discovery that upended science. I'm not sure there are any of those still to come.
The closing chapter on the big questions in science still has to be written, but I think the chances it will force us to completely rewrite, rather than simply revise and update the previous chapters, seems slight IMHO. I'm expecting the GUT to simply update or reframe relativity and quantum mechanics to make them compatible, not throw them out completely.
It truly is astonishing to be alive at this nexus in human development, whatever our individual take on it might be.
Now technology is catching up to give us the computing power, massive collective memory, digital records, and AI to start gaining again. We basically have to build a better mind to get to the next level.
We are still in the early days of applying that tech to the fields it's going to effect most.
We're in the "get a home page for your local business" phase not yet the "faang has changed the face of civilization" (for the better or worse) phase.
This is going to continue to ramp knowledge in bioinformatics and other areas, the technology is still in the infancy of being harnessed for biology and medicine.
That combined with cheaper robotic arms and cheaper sequencing machines which is just now coming dropping below certain cost thresholds.
(I know a group/lab that's automating discovery of drug/compound targets doing purely NDA'd work for merck and other pharmaceuticals, the tech is wild and still in it's infancy.)
Cutting edge voice and image style transfer, realistic computer speech, computer vision.. the list goes on, that's just the highly visible stuff and there is still only a small pool of people versed in those areas of tech.
> "incredible advances in science and technology"
That's what this thread is about. Please note the context.
I feel like this is more a modern misconception than reality. Play a game of Civilization and you'll start to appreciate just how deep human technology really is. In Roman times, they probably said similar things thinking about how advanced they were compared to the Macedonians a couple hundred years back.
Yea we lost some progress or at least the rate of change greatly slowed from 400 - 1600, but other than that blip I think the progress has actually been fairly linear from 4000 BC to 2021 CE. It just seems like it's not because of the cognitive bias to take for granted all the things that seem so basic compared to computers or nuclear reactors, but in reality, those things actually were very difficult to develop with the knowledge and production techniques available at the time.
For what it's worth...
I've been to Ephesus (which is amazing, I'd like to check out Pompeii as well) the armory in Venice is one of my favorite repos of old cutting edge tech and having spent time in Rome, truly their achievements are amazing and the Pantheon absolutely blows my mind, it's no wonder the village dwellers believed the God's lived in Rome, I would have.
But harnessing the power of the atom, understanding fundamental physics, biology and sound/light speed global communication... and the technology that these things have enabled (including my own living past 3 years of age due to modern medicine) is truly a leap, in my opinion the Roman's and those brilliant technologists and logistics civilizations of the past were still closer to living in caves by modern comparison.
I would not have wanted to live back then and I literally couldn't have. Our recent exponential explosion certainly depends on their hard fought knowledge, but in my reckoning even their best tech and logistics are deep in the early part of the curve.
The fall of the Roman Empire, and actually really even the decline from when the city stood at more than a million people during the time of Augustus and Tiberius until the far, saw massive declines in technological knowledge and even scientific knowledge. Much of that information was not rediscovered until the Renaissance when the last remaining archives of the Roman Empire were evacuated from Constantinople to nobles and merchants across Europe during the Turkish invasion. Even today we're still rediscovering material science knowledge that the Romans and ancient Chinese had. In fact, much of our rapid advancement in technology was not even due to knew ideas, it was due to ideas that had be theorized by Greek and Roman philosophers and alchemists, and which were recorded and stored in the archives.
There was real stagnation in most knowledge and technology throughout the world. In the West because of the decline of the Roman Empire (most likely caused in part due to lead poisoning and decreasing fertility of North Africa and Judea) and in the East due to constant infighting and political strife preventing unification of India or China under stable rulers for long enough to see real advancement.
That means, more people than ever working on more problems, with more tools, background knowledge, resources, distinct goals, and collaboration.
This is not even close to being true
The world population increased from 1 billion in 1800 to 7.7 billion today.
I'm not going to do the math but there's something to be said about how many we are today vs. even 200 years ago. But, no, the majority of humans ever born are not, in fact, still alive today...
https://ourworldindata.org/world-population-growth
I always express that the greatest science "fiction" story is actually the reality above us, and the multitude of unanswered questions.
Now, how all this shocking amount of matter came to exist from energy, which also had to come from somewhere... That's a head scratcher alright. The path to God is hidden behind rock solid plausible deniability.
Our entire civilization past and future may be just a momentary bubble in a cosmic ocean frothing with countless happenings for aeons.
there's dozens upon dozens of orders of magnitude of space that a being could occupy. scanning for life through the multiverse and time, it would also be easy to miss us. too small and you see cells and organelles, larger we see organs mixed with bacterial cultures, etc, and at just the right scale we are visible.
there are arguments that earth is a living entity, and there may be larger forms of life going many orders of magnitude larger than planet-sized.
with such a large range of time, location and scale to scan for life, it could be argued we basically don't even exist.
Or maybe they found us but they just don't care because on cosmic scales we aren't as special as we appear to be from our own limited perspective.
The series was from the mid 2000s.
No one suggested this very obvious process until an astronaut on the ISS had a fine-grain substance in a small plastic bag (no, not THAT one), and they noticed the grains stuck together.
Take a look at the wikipedia page for this topic: https://en.wikipedia.org/wiki/Nebular_hypothesis
Just as an example:
> The formation of planetesimals is the biggest unsolved problem in the nebular disk model. How 1 cm sized particles coalesce into 1 km planetesimals is a mystery. This mechanism appears to be the key to the question as to why some stars have planets, while others have nothing around them, not even dust belts.
Very blessed to be an observer though.
Example: $100 isn’t less or more just because of increasing or decreasing the physical footprint of the bill. We still confer a purchasing power of $100 to a $100 bill regardless of the bill’s physical dimensions.
So the takeaway here is that it’s a non-sequitur to say that because of Earth’s small scale relative to the rest of space, nothing on Earth matters.
It's humbling because it puts all that hubris away, which most people tend to have an excessive amount of - and begin to focus on living and achieving simple happiness instead of some illusion of grandeur.
That said, whatever breakthroughs we make from one generation to the next, what a stroke of luck it is that some things remain constant: we can fall in love, enjoy a good story, drink, eat, be merry, and argue about the meaning of life in whatever fora present themselves.
We don't know what space, time or matter are. We don't know where it's coming form or where it's going. And we don't know most things in between.
It's a marvel we figured out so much about how some details seem to work given we still don't know mostly anything about the more fundamental phenomena.
https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_p...
By what scale, exactly? This corner is just as large as it is small. There are an equivalent number of grains of sand on Earth than there are stars in the observable universe.
We are not small. Size doesn't work like that. Space is everywhere, including here.
Am I the only one who thinks that the wording roots in Hubris?
And then, at the same time, I read "are flying apart" as if that's how it actually works. It doesn't. Wording it that way is misleading.
I never read National Geographic, but I thought it's better than this.
“faster than our best models of the cosmos predict it should.”
It’s more an implied statement about the current models than the limits of human of human knowledge.
It's not technical lingo using the actually correct wording for the effects of the expanding universe. Galaxies do not fly apart, the space in between grows. The difference is significant, even though the observer wouldn't notice any.
I know it seems like a non-issue, but in the end it's misleading all the people who would blindly believe NG to be accurate.
What do they know??