There needs to be a real Kuhnian paradigm shift IMO; it's embarrassing to have modern-day epicycles used as a fudge whenever a model breaks down vs. questioning the core assumptions of the model.
There are more interesting and less implausible hypotheses out there than the "just so" dark matter one.
There are more interesting and less implausible TESTABLE hypotheses out there?
Dark matter and dark energy are the simplest (literally single parameter) fits to the cosmological data we see. Why we see data consistent with these parameters (e.g. what is the non-interacting massive particle) is up in the air, but adding multi-parameter new forces without more justification seems a little too interesting.
I think the goal is a paradigm shift via ADS-CFT correspondences:
Eg, if we’re looking at pseudo-tangles in shadow projections, that would solve why QM looks statistical while relativity looks continuous.
But that would raise deep questions about “warp” in the macro and whether galactic scale tangles would generate additional binding energy — ie, dark matter. Large scale tangles hiding mass would explain why we can’t interact with it, for instance.
This isn't an argument so much for science as it is for funding of scientific experiments. I don't know about you but I feel like this public, cultural, collective investment of time and energy toward dark-matter-seeking projects is not bearing out. It's worth testing other theories more completely.
For instance, I've seen a convincing argument[1] that dark matter researchers consistently underestimate galactic inclination, which in turn results in poor fits between model and data, leading to the epicycle-like fudge inclusion of dark matter as "everywhere we would expect mass to be, given xyz".
No, there are not. Pretty much all the popular contenders are less plausible, and most still need dark matter to explain all observations, so they only add more complexity.
Dark matter is a simple theory that explain a wide variety of unrelated observations.
I mean, until we actually prove that dark matter is "something", we need to stop calling it that. All it is, is some constant that we apply to make sense of the motion of galactic-scale objects. And we use "dark energy" as a constant to explain why the universe keeps apparently accelerating its expanse beyond what we would have predicted given what we know about the universe. There is no reason to believe that these phenomena are caused by some singular thing. These latest development only strengthens that conclusion.
In any case, until we actually are able to test that this is one "thing" rather than a bunch of things we still have no idea about, we should stop calling it "dark <foo>". Because I think that a lot of people are under the impression that there is some discrete substance out there causing this discrepancy, and there really is no reason to believe that's the case.
I think it helps to give a name to the concept, and then do a better job of educating people that this is basically a placeholder name until it's better understood. (and yes, I realize that is not an easy task, might be easier to find the solutions and figure out the best name)
Right, I'm not sure there's one unifying theory that you could bundle it under, not sure what the right term is for a general concept rather than a hard testable theory. But that just further proves the need to stop calling it one thing in particular, because it leads the vast majority of people (including scientists!) to think that "dark matter" is some big unifying theory, when there is no such thing as some singular substance called "dark matter".
You've described the search for dark matter as it is performed. There's already a percentage that's been filled in and most theories try to fill in additional chunks rather than as you say "some singular thing".
I'm really not sure why so many people have such a strong reaction to dark matter theories.
Yes, dark matter is the best way we currently have for fitting the data within most of our existing frameworks for understanding the universe. I really don't see the relation to epicycles.
There are people out there working very hard on modified gravity theories. I'm not aware of any that are able to explain the current data. If anything, trying to modify gravity to fit the dark matter data would be most similar to epicycles, it's devilishly difficult to come up with increasingly complex theories that fit more and more data that's coming in.
> Yes, dark matter is the best way we currently have for fitting the data
This is the key problem. Since there is no theory of what dark matter is made of or how it is created and destroyed, you can always have as much or as little of it as you need to fit the data.
As for gravity, we don't have anything close to a working theory of quantum gravity. We can't even measure the classical gravitational constant to more than about 4 digits. The reproducibility by different experiments has not demonstrably improved since the 1940's! Clearly there is a lot more we have to learn about gravity.
There's actually an embarrassingly large number of theories for what makes up dark matter. I doubt most people have ever even heard of the form that was ruled out in this article. There's not just a ton of theories, a great number of them are falsibiable with experiments we can plausibly perform.
And yes, quantum gravity is also something we don't understand. But the domain where we are missing that understanding doesn't overlap with the dark matter "problem".
Having a large number of theories is embarrassing! That means you have no idea. Gravity and QM are so great because they are clear winners – they are not easy to modify a little bit and nothing approaches them in terms of practical power.
Falsifiability comes from having specific predictions, which means one theory that's an island, not a bunch of approximations.
The fact that there's any "amount" - a single scalar quantity of a thing we already have all the equations for - that neatly explains multidimensional data, is highly suggestive by itself, no?
It's not just a fudge factor, it's a fudge factor that behaves exactly like mass.
Any fudge factor with a continuous effect on the output that covers the range of interest can be used to adjust a given output to an output of choice.
For dark matter, one of the problems is that any given instance is allowed to have whatever amount of dark matter gives the output we want. This makes the math work out great, but weakens its predictive power.
but the odds that somebody with a personality profile who'd think creatively enough to do this, then make it out through a modern scientific programme, and also sticks to academia are from low to zero.
most people creative enough are driven to the arts, which in modern society are only good for entertainment.
Correct me if I'm wrong, but we call it dark because we can't directly observe it. Us not being able to observe something seems quite plausible. We spent most of our existence as a species with no way to observe viruses.
Pedantic: dark matter does affect electromagnetic radiation via gravity.
“The most successful technique with which to investigate [dark matter] has so far been the effect of gravitational lensing. The curvature of space-time near any gravitating mass (including dark matter) deflects passing rays of light - observably shifting, distorting and magnifying the images of background galaxies”.
“Dark matter appears not to interact via the electromagnetic force, and therefore neither emits nor reflects light.”
I am sure you know that, but perhaps not everyone does?
I did know that, but it's not amiss to point it out.
I must confess, when you said "pedantic", I expected something more annoying and less worthwhile. That's the best "pedantic" I've seen in quite a while.
People are trying to shift the paradigm all the time, but so far nothing has worked. Replacing General Relativity and the Standard Model is the mother of all hard problems.
One interesting approach I've heard of is abandoning reductionism and looking at how the macroscopic might actually determin the microscopic. We'll know how it pans out in half a century or so.
Yep, I'm with you. I'm afraid this is another misunderstanding and a new quest for ether. But this is a good thing.
I bet one coffee that there is no dark matter in the form it's been looked for in the last decades. I bet two coffees that when somebody will discover the cause of the measured effects we'll be able to build some great new stuff, much like general relativity eventually gave us GPS and then navigation, etc.
"Epicycles" worked fine for a very long time. They are predictive. And accurate! And can be translated to a physical compuation mechanism (see: Antikythera mechanism).
In addition, "epicycles" are a manifestation of Fourier decomposition, which is a perfectly fine mathematical tool. The errors are due to the fact that reality isn't purely mathematical.
"Epicycles" were quite fine until we got both 1) much better clocks and 2) much better astronomical observations.
People forget that physics was in pretty close to this same state about 150 years ago (roughly) right before quantum mechanics. Physics was pretty much buttoned down except for that really strange Black Body Radiation problem (Ultraviolet Catastrophe), but they'd have that sorted in a couple of years. Certainly no later than 1900--the end of the century. No big deal.
Everything we know about neutrinos says they move too fast to account for what we see. Doesn't mean that there couldn't be some discovery they completely changes our understanding of neutrinos though.
Pretty sure. The problem is, that neutrinos are too light, and when they are produced in the early universe they are too fast. That means galaxies do not form like we observe them. Basically, neutrino dark matter would "orbit the outskirts" of the galaxy instead of building a defined center.
Yes. We have a pretty good understanding of how neutrinos are created and destroyed and there should not be enough of them to explain the anomalous gravitation.
As other replies have said, neutrinos move too fast. They seem to move almost exclusively at the speed of light. (So close that we can only infer indirectly that they don't ... and it's possible that one kind still might.)
Unless the galaxy were a black hole, they'd escape. Since it's not, it can't be them.
It would be great if there were something producing slow-moving neutrinos, which would not only solve this but give us a huge leg up in understanding what's going on with neutrinos. But it doesn't look like that's the case.
As others have said, they are too fast. But that just raises the question of why do we expect that if dark matter is particles they must be slow?
The episode "Is Dark Matter Made of Particles?" [1] of PBS Space Time covers that.
They have several other dark matter episodes looking into other possibilities, such as black holes, axions, gravity not working the way we think it does, and more. If you are interested in this topic doing a search for "dark matter" in the video list on the YouTube channel would be a great place to start.
Complete armchair novice here, but I always found "dark matter" as I have seen it to be pretty implausible.
It just kind of feels like there's a scale with weight on it that, by everything we now observe, should only weigh 200lbs and instead is reading 300 -- it just seems that "broken scale" is a better explanation than "invisible stuff on the scale."
It'd be a much different problem if everything it was like this. This is more of a "most things we measure" give a heavier reading, but not by any consistent amount. But not all. And very often the scale shows a number when there's absolutely nothing to see.
Yeah this comment is posted whenever dark matter comes up. I'm a similar novice and I feel the same way. However, I also know that the experts out there don't say this for no reason and that, even if "dark matter" just a construct/illusion that turns out to be something else (not a new kind of matter), it can still be a useful placeholder to work with (like how we still model gravity as a force).
Dismissing it as an incorrect measurement ignores the depth people have long gone into to verify this discrepancy between predictions and reality is not a sensor problem.
I kind of had the same intuition as the op, but you are most likely correct. A lot of ridiculously smart people all seem to think it's out there somewhere. Are there any popular theories that posit that gravity behaves differently at these large scales? Or are all the smart people in the same camp of the being dark matter somewhere?
Another novice here, but every time the matter of dark matter comes up I remember this story.
Almost 2 centuries ago astronomers found that the orbit of Mercury didn't make sense according to Newton's laws, laws which were at the time considered infallible. The astronomers only explanation was that there was a planet closer to the sun that we couldn't see, they believed this so much that they even named the planet Vulcan and spent many years searching for it.
Turns out that there was no Vulcan and general relativity explains the discrepancy in the orbit of Mercury.
Another important part of the story is that a central figure in this was Urbain Le Verrier, who just a couple of years earlier had predicted the orbit of a planet based on the orbit of Uranus being a bit weird. That planet was found and named Neptune.
That discovery made both Le Verrier and the world at large very excited, and the race to repeat that feat lead to everyone jumping to conclusions about Vulcan.
Sometimes you look for a missing planet (Vulcan) and turns out the theory is wrong. Sometimes you look for a missing particle to carry away momentum and indeed it is there (the Neutrino).
The thing is, your proposed change to the scale has to work exactly like "invisible stuff on the scale." So, we can observe dark matter in the early universe with the CMB, we can observe it in the large scale structure, and we can observe it in rotation curves. And the results of these observations is, that dark matter has to behave like matter, just dark. So your proposed new theory would need to deviate from standard theory in precisely the way an additional matter component would.
Dark matter works well because it's designed to fill in the gaps in our current understanding of astrophysics data. Given it's origin it of course can perfectly explain the data, because that's what it was designed to do.
However, that doesn't necessarily make dark matter particularly useful for understanding how nature actually works.
This is not a tautology because it's not being used as a final explanation. It's called "matter" because the observational gaps appear to fit what would be some mass that we're missing and we think of matter as "stuff with mass". It's called "dark" because we can only observe it's gravitational impact and by all other observables, it doesn't show up.
> Dark matter works well because it's designed to fill in the gaps in our current understanding of astrophysics data.
"Works well" seems like you are looking at it the wrong way. Nobody is touting "dark matter" as a solution. It's the problem itself.
This could be true, but it could also be true that there is something else at play that we are unaware of. In science there have been cases of things that did not fit the model, but the model was not wrong. One example is the precession of Mercury[1]. Newtonian models were right that this anomaly does not agree with our understanding and calculations of gravity. But later on it was shown by Einstein that this anomaly was caused by relativistic effects. It wasn't that there was a large miscalculation, or our understanding of gravity was completely wrong, it was that the model did not count on a previously undiscovered phenomenon.
I am a novice as well, but as far as I understand, "Dark Matter" ultimately is really just a term for "there's a phenomena we don't understand yet, and we call it Dark Matter".
I heard a podcast with top scientists about this (in French, still available online) about this: it's indeed a nickname for the phenomenon - but the scientists using it know that, of course.
However, this nickname is not absurd, in the sense that the gravity equations for the movement of stars in galaxies don't match the observation.
In order for the stars to move inside their galaxies at their observed speed, these galaxies should have much larger mass.
Hence the "dark matter".
Scientists do not all agree that there is an "invisible" matter to be found. Many think that Einstein's relativity has a more limited domain of validity than we thought.
But then the issue is as dark (in the sense of mysterious), since many of Einstein's predictions - based on his equations - have been observed in experimentations. The gravitational waves (LIGO experiment and other replications) appear to prove that the relativity equations are right. The precision of this instruments are extraordinary.
It's a terrible situation for Physics as a discipline: the equations are confirmed in all know situations, except this case (well, as far as I understood).
There are plenty of theories for explaining the phenomenon, but they lack an feasible experiment to see if their predictions match the observation.
Today, all the theories with feasible experiments have proven to be false. Physicists are stuck.
Many think that we need a new Einstein or a new Newton, meaning a genius among the geniuses, capable of think a whole new paradigm for gravity.
Gravity is a "law" and not a "force". It's as well the nickname for a phenomenon ; that phenomenon is sensible in the domain of validity of Newton, e.g. in our daily life.
The planets in the solar system move all accordingly with Newton's equations, except Mercury. Einstein had to totally put upside down the way we represent the world we live in, from a 3D world with a totally independent time to a 4D world, where everything and everyone live in its own spacetime.
Let's imagine two atomic clock set next to each other and synchronized. If we elevate one by 1 cm, then the clocks have a super slight desynchronizarion. And the tiny tiny difference match Einstein's equations.
Newton and Einstein are a few centuries apart. When will such genius reveal itself? Some physicists point that both were outsiders in their times. Nowadays, the knowledge is so vast that it takes ten years to master a fraction of it: by that time, a brain is so entrenched in the current representations that it's difficult to break the paradigm.
Others think likely that one of the theories already published is right but we'll need to wait a very long time, if ever, before being able to make the experiment that will prove it.
Maybe we will have to accept not being able to explain our universe. After all, since Gödel, mathematicians have kept going despite his proof that the mathematics are based on a quite fragile foundation.
I never quite understood that Gödel thing. Anyone to try and explain us that "dark" theorem?
The Gödel thing isn't quite as a big a problem as it seems. One way of looking at it is that there will always exist true theorems that you cannot prove.
That may seem surprising, but I don't think it is. There are infinite sets and infinite things you can say about them. It's not really a shock that there might be some properties about that set you can only prove by inspecting all of the elements, but you can't actually do that in finite time -- even though it's true. The sets are infinite, the theorems and their proofs are (by definition) not.
That doesn't mean that the foundations of math are fragile. It just means that there are facts you don't know. But you already knew that, too.
The specific theorems that can't be proven are just a subject of your axiom set. You can prove, or disprove, any specific thing you want, by taking it as axiomatic. It's just a question of whether anything interesting follows. That's a judgment for mathematicians, not a fact of mathematics.
I am, of course, handwaving like crazy, and probably driving the mathematicians nuts. Even though I said that the theorem is less surprising than it might seem, the fact that you can prove the theorem itself strikes me as very surprising.
> Many think that Einstein's relativity has a more limited domain of validity than we thought.
I'm not aware of any significant number of scientists who think this. Even proponents of MOND acknowledge that they need to come up with a viable relativistic formulation of their theory.
> The planets in the solar system move all accordingly with Newton's equations, except Mercury.
This is not correct. Our measurements are accurate enough now that we have detected relativistic corrections in the motion of, IIRC, at least all the planets out to Jupiter or Saturn.
You’re missing an important part: “and extra matter that doesn’t interact with the electromagnetic field would explain it.”
It’s called dark because it doesn’t interact with the electromagnetic field (i.e. we cannot see it) and matter because it’s otherwise assumed to behave just like the matter we can see.
It is a bit of a “We don’t like it, but it’s the best we can do for now”, but it is not like physicists invented something completely out of thin air to make the theory explain observations.
I basically came into the comments here just to see all the complete armchair novices come out of the woodwork to explain how they think they're smarter than the actual physicists.
I think dark matter (and dark energy, for the same reason) invite lots of armchair discussion by curious non-experts precisely because they are basically fudge factors. There's no ontological baggage and the theories are fairly "decoupled" from other aspects of physics. It's basically data, a fitted curve, and some X factor (or Lambda for dark energy) added on to make the data fit the curve. That X does not interact with any other models outside of cosmology in any currently observable way, and not for lack of searching.
That makes it really tempting to think "well maybe it's the model/equation that's wrong", which has been exactly the case throughout scientific history: planet Vulkan vs Relativity, phlogiston vs oxygen, luminiferous ether vs QED.
Yea, I'm with you and have been really interested the MOND (Modified Newtonian Dynamics) research, as their charts seem to fit the data better.
For those who haven't heard of this, the idea is that the gravitational constant actually changes at very high rotational speeds / centripetal accelerations (such as those at the galactic scale), and this is why our Earth-based gravity experiments don't detect this because we're in roughly the same reference frame and don't see the effect.
But there are also galaxies that do agree with what our gravity laws say, and therefore don't seem to have much dark matter. That's a big problem for theories that want to change the laws of physics, I believe?
> the idea is that the gravitational constant actually changes at very high rotational speeds / centripetal accelerations
First, the MOND regime is not very high (large) accelerations, but very low (small) accelerations.
Second, the MOND hypothesis is not quite that the gravitational constant changes; it's that the form of the gravitational force changes--it's no longer the Newtonian inverse square force.
The key issue with this is that Newtonian gravity isn't our best current theory of gravity: General Relativity is. MOND as it was originally proposed is not a relativistic theory; there have been attempts to formulate a relativistic version, but none of them have resolved all of the open issues.
> this is why our Earth-based gravity experiments don't detect this because we're in roughly the same reference frame and don't see the effect.
No, that's not why MOND proponents say we don't detect the effect in Earth-based experiments. It's simply that we can't reproduce the required conditions on Earth (the net gravitational acceleration from all sources being small enough to get into the MOND regime).
I'm unsure the differences between "same reference frame" vs. "can't reproduce the required conditions" - ie Isn't it that in order to reproduce the very low accelerations we can't be in our current location with its high accelerations? I'm guessing there's some nuance between location / ref frame here that I'm missing.
> I'm unsure the differences between "same reference frame" vs. "can't reproduce the required conditions"
"Same reference frame" is just an abstraction (and quite often a meaningless one--according to the proper concept of "reference frame" in physics, there is no such thing as being "in" one reference frame but not another).
"Can't reproduce the required conditions" is a straightforward statement about the limitations of what we can do with our current technology.
> Isn't it that in order to reproduce the very low accelerations we can't be in our current location with its high accelerations?
According to MOND, yes, in order to test it we would have to set up a lab out in deep space (i.e., not near any planet or star) far enough away from the center of our galaxy that the sum of all the "accelerations due to gravity" from all sources was less than the MOND threshold. Which of course is well beyond our current technical capability. But none of that has anything to do with "reference frames".
A good recent look at MOND and how it compares to dark matter theories is the recent episode "What If Our Understanding of Gravity is Wrong?" [1] on PBS Space Time.
The difference is the existence and proportion of dark matter has been confirmed across multiple different scales and context, from galaxy rotation curves to the cosmic microwave background to gravitational lensing. We've also found galaxies where dark matter doesn't exist in any measurable quantities.
So it'd be more like a couch that's supposed to weight 200 lbs reads 300 lbs on a scale. But we've tested it on a half dozen different scales from different makers and keep getting 300 lbs. In addition we've tested this other couch that's suppose to read 100 lbs on some of these scales, and it correctly reads 100 lbs.
Part of the problem is bad PR. Its induced by 1: a terrible name, dark matter implies a lot. and 2: Pop science doing an utterly awful job of explaining the topic.
Many people walk away with the assumption that dark matter is literally massive lumps of stuff out there that is just really hard to see. Kind of analogous to stealth aircraft or something. This sounds absurd and it is. And its why a common reaction is to consider it absurd and that we probably just have gravity wrong.
The reality is that dark matter is just the name given to a set of observations. It wasn't intended to be descriptive. We are talking about scientists here, not public relations. So they are liable to fumble in the PR bit. Its not what they are good at. I consider the Neil DeGrasse Tysons and Michio Kakus of the world more to blame than the community at large. They have chosen to become the popular face of science and with that have a responsibility to properly communicate it. Their failure contributes to why people distrust academia to some degree.
Most people do not understand "dark matter" because they do not understand astronomy. Astronomy would be better defined as the study of celestial objects by the collection of photons, and inferential calculations made upon those collections. Astronomers collect photons from stars, which is to say "matter that gives off light." In a practical sense, the Earth is made of dark matter, because it does not shine by its own light (okay, if you are near enough, shielded from the Sun, and looking in infrared, if you like splitting hairs). Dark matter need not be particularly exotic, just ... almost hard to find by definition.
Dark matter has already had some success. Just as an example, the discovery of Neptune -- made entirely through dark matter. We couldn't see it obviously, too much space to search over, but some kind of gravitational disturbance gave suggestions as to where to look. Boom, a whole planet. That is quite literally search via dark matter: it doesn't shine, so we must look for its knock-on effects.
Easy enough in the local neighborhood, but at a galactic scale, it is much much harder. And I wouldn't expect anything quick, either. If you want a fascinating journey through astronomy, look up the history of the various estimations of the "standard candle," used as a way to gauge distance. This took quite a lot of time to bounce back and forth between numbers.
This is incorrect. Yes, Dark Matter is matter that does not emit light but it does not absorb nor reflect light as well. In other words, it does not interact with the electromagnetic force. That makes it extremely exotic.
That's a rather newer definition. The concept has been around longer than the name, which is why I mentioned Neptune. The original definition was literally anything where the presence is puzzled out from its gravitational attraction instead of than its luminosity. Hence why MACHOs (MAssive Compact Halo Objects) were under consideration for being dark matter. They would consist of brown dwarfs, planets, and the like. They are currently out of vogue for not supplying enough gravitation, but that matter had no special properties to it. Not exotic at all. You can look this up.
I sort of feel the frustration here of people on Wikipedia trying to correct something they actually know about.
It's interesting the way language works, and specifically naming. It's almost magic.
There's various places where gravitational effects don't seem to line up with the distribution of mass that we see or expect. Something is generating gravity, that we can't see, in places we didn't expect. Call it 'dark' matter, because it's not shiny.
But now that it has a name, it's treated a bit like a proper noun. Dark Matter. We do some observations that probably rule out simple nonluminous planetoids or dark stars. Whatever is causing the galactic rotation discrepancies doesn't seem to be normal matter. That translates into: 'Dark Matter' isn't normal matter. As if it is a certain thing, and not a reference to an unknown set.
By naming it, and talking about it, even though we don't understand it, we run the risk of attaching all sorts of presumptions to its identity. We're prematurely normalizing a certain way of thinking about it. We may have done a similar thing to quantum mechanics. (I may not be making much sense here, it's just a thought that struck me and I'm working through it.)
We have known about Neptune far longer than Dark Matter - no idea what you are talking about here. I mean we have great photographs of the planet itself - obviously it reflects light !
"Light matter" is basically stars. Now, sometimes bodies reflect light (which is why we can see the Moon or Neptune).
Bu before the name "dark matter" existed, the practice of it was evident. How did they discover Neptune? Gravitationally, not by seeing it first via a telescope. Its existence was inferred by the orbits of other planets, namely a gravitational disturbance suggesting a big glob of matter we had not collected photons from.
But we did not discover Neptune by collecting its photons. We had to infer that some glob of matter was present by gravitation. Then we pointed telescopes in the vicinity of prediction until this was confirmed.
Going further, we use these collected to infer all kinds of things -- a consistent dimming of a star in a certain period might suggest a planet occluding the star in an orbit coplanar to ours, which is our current method of locating exoplanets, but that wouldn't count.
You might recall how the neutrino was originally simply a placeholder, and actual detection came later. Similarly, the coining of the phase dark matter was simply as a contrast and a placeholder: we know something is there, but it ain't stars (light matter). Historically, many suggestions were made, and quite a few of them weren't exotic: MACHOs (Massive Compact Halo Objects), intergalactic gas, and so on. WIMPs would classify as a candidate for dark matter that would be somewhat exotic, so would axions.
Frustratingly, as the article suggests, we can do a lot of things to rule out (or more typically, set a maximum contribution as a fraction from each candidate), but we have little ruled in. We don't even have detection of axions yet, and those have been in the running for decades.
This is the sort of stuff that lured me into getting a physics degree.
As a grad student in High-Energy Physics I worked at the XENON1T dark matter detector in Italy. I left feeling disenchanted about the search for dark matter, and I felt like a lot of us were just doing the best we could at the time, which was build a bigger and bigger detector to get more and more sensitivity.
One talk started with a lecture on the lamppost problem. It asked: why exactly are we looking for WIMPs? Because we know how to build a WIMP detector.
I'm not equipped to answer questions about dark matter anymore, but I will say that a lot of the knee-jerk comments in this thread underestimate how smart physicists are. Some of the most brilliant minds in science have contributed to dark matter cosmology. They are particle physicists, cosmologists, fluid dynamicists, and simulationists (reaching a little bit with the terminology here) all working together.
Science is progressing in the natural way of excluding theories from easiest to hardest. The fact that there are so many people working to exclude the "obvious" (or even "obviously wrong") theories should be evidence of how difficult this problem really is.
It may turn out that dark matter is explained by a non-particle phenomenon, or that it is matter that simply acts purely via the gravitational force and nothing else. I don't know what the implications of this would be. But none of that is obvious or easy to prove at the moment.
Nor is it easy to come up with a dark matter model which satisfies all the necessary constraints. You cannot just say, "there's some stuff out there" without collateral effects on (say) the distribution of matter in the universe.
The reasons given for Dark Matter always begin with galaxy rotation curves (the galaxy rotation problem and the galaxy winding problem). But the problem with this "evidence" is that the observations were made of galaxies in isolation, but even galaxies are not gravitationally isolated.[1] I can not speak to the veracity of the rest of the evidence for Dark Matter, but galaxy rotation curves can no longer be counted as evidence of Dark Matter because they are more simply explained by a gravitational phenomenon caused by the out of frame mass of other nearby galaxies.
There are many theories of dark matter given at conferences like this. Around that time (2013-2014) I remember hearing about axion theories too. I don't know anything about this person's presentation so I can't say how it displaces the problem of galaxy rotation curves. If the math checks out, I think it would have, but you never know. I would like to see a reaction from cosmologists.
I would hesitate leaning too much on the always part. Fritz Zwicky was the first to notice the anomalous galaxy rotation curves and propose dark matter (is the story that I remember, anyway.) This is probably why it's presented first. It does not mean that it's the most important piece of evidence.
I'm intentionally writing with a light touch here because I don't consider myself an expert in the field.
> a gravitational phenomenon caused by the out of frame mass of other nearby galaxies
There have been papers published on this, but it is still speculative, so it's premature to say that this kind of alternative theory rules out dark matter.
Explanations always begin with Galaxy rotation curves because that's how it was first notified that something about our understanding of the universe was off.
It's been a long time since then and there's been a ton more data collected about wide ranging phenomenon since.
But we are only talking about it because we can observe it. Or rather observe how it interacts with other things, but that's just semantics: all observation happens via interactions.
Dark matter could be a neighboring universe interacting with ours or something like that where the actual particle causing it is fundamentally out of reach (if it even is a particle), but just the fact that it interacts with our universe means we should in principle be able to interact with it and characterize it with experiments.
Thats more along the lines of what I was thinking - we can observe this specific interaction but without also observing other interactions it seems very difficult to define exactly what it is. Or maybe it is just that our current frame of reference (both physically and in terms of time) is just a bad vantage point to do so.
An important property of dark matter need to fit what we are seeing is that it also doesn't interact with itself. It would seem weird if it can't interact with itself because of some innate property, but we can't interact with it because we are somehow out of phase with it.
A naive question from a hobbyist with over-average interest in particle physics: quantum theory is based on complex numbers. Has anyone considered that mass/gravity may also have an imaginary component that manifests itself as "dark matter"? (I.e., it's not "matter" at all, just an incomplete understanding of gravity.)
The term tachyon was coined by Gerald Feinberg in a 1967 paper titled "Possibility of faster-than-light particles". He had been inspired by the science-fiction story "Beep" by James Blish.“
Good question. Imaginary mass -> negative 4-momentum -> momentum exceeds energy -> object is moving faster than light (backwards in time in some reference frames).
There are some reasons to suspect/hope such things might not exist, such as protecting causality.
In general, asking "what if <simple field type> was <more complex field type>" can actually produce super fruitful lines of inquiry. You can use "complex numbers", "quaternions", "finite fields", whatever you like. There's plenty of unexplored ground here.
Given the quantum eraser experiment and general lack of time directionality in particle physics it seems causality as an "axiomatic" physical truth is already broken. At least at a quantum level. My suspicion is that event-based causality falls into the 'its only resolved for >= hbar/2' realm. Then even if you had a bunch "tachyons" it'd be impossible to send a signal back in time more than a few planck constants of time much like its hard to entangle more than a few qbits.
Superluminality isn't required by all interpretations of QM. MW doesn't need it, for example.
I'm not aware of a mechanism by which causality would arise from known QM, so I wouldn't expect a priori planck scale to play into it. There would also need to be an energy term for h to make sense as the relevant constant.
The most compelling source of temporal direction I'm familiar with is that it's a regional cosmological entropy gradient rather than a fundamental aspect of physics, although it strikes me as suspicious that the time direction lies inside the 4-cone generated by the odd-dimension-out in our spacetime
metric. That certainly lends some credence to theories which would predict the direction of time as fundamental to physics.
As someone who is similarly and over-interested hobbyist, I wonder what happens when you throw in even more, for lack of the proper term, deviant math systems. The cousins of imaginary numbers using either epsilon (where epsilon^2 = 0, epsilon not a member of R) or j (where j^2 = 1, j not a member of R). Or quaternions. Or the family of quaternions similar to the family of complex numbers. And so on.
My guess is that it falls back to Occam's Razor and there has yet to be any physics to use it thus it isn't a serious contender for current problems until much more work has been done on all the threads already being followed.
Dark matter is possibly the best evidence in support of Dr. Mills' Hydrino theory https://brilliantlightpower.com/theory/ which deserves a fair reading. There are about 20 experimental results supporting this theory that models electron orbits as spherical shells instead of probability clouds. He has machines that produce 100s of kW from small quantities of hydrogen - 200 times the energy produced by burning hydrogen. https://brilliantlightpower.com/tpv-suncell-rectanguloid-cav...
In 1999, the Nobel prize winning physicist Philip Warren Anderson said he is "sure that it's a fraud",[12] and in the same year another Nobel prize winning physicist, Steven Chu, called it "extremely unlikely".[23] The following year, a 2000 patent based on its hydrino-related technology[24][25] was later withdrawn by the United States Patent and Trademark Office (USPTO) due to contradictions with known physics laws and other concerns about the viability of the described processes, citing Park and others.[26]
So how do these Nobel prize winners explain dark matter?
Do "known physics laws" not evolve as new discoveries are made?
Wikipedia is policed by skeptics that only support the status quo. IMO that article is not a fair description of Brilliant Light Power.
As for my submissions, if as I believe hydrinos turn out to be real, it will be the greatest scientific discovery since the genome, so worth harping on about.
In scientific study you want and need failure. Knowing what doesn't work is as important as knowing what does. This way we can make lists of dangerous or useless things to be avoided. As long as things are documented and reproducible to the best of your abilities, you've won.
I do not consider the search for dark matter a waste of time. But when you are working with a team of WIMP-detector-building specialists, it is (unsurprisingly) hard to have a conversation about whether we should continue building WIMP detectors. People’s egos and emotions are all wrapped up in the science, and that is the part I came away disenchanted about. Definitely don’t misinterpret my feelings to be about science in general, or about getting a negative result (the Michelson-Morley experiment comes to mind.)
Might dispersed matter have a higher mass than more condensed matter as an alternative hypothesis? Where the more distant and small a unit of matter is, the more curved the spacetime around it. Lonely particles longing to coalesce? These particles would reflect and scatter too little to be visible and hence be "dark matter". If this was the case, stronger attraction at either extreme of distance might be an effecient accelerator of formation of celestial bodies. This kind of wonky gravitation could also explain the accelerating expansion of the universe.
I don't think dark matter exists? Some part of me wants to really sit down and formulate the possibility of 'banding' in spacetime: where there may be discrete "steps" in its density -- similar to the interference patterns when particles travel through a medium. The interactions between these waves can, at times, cancel out, or even repel, as waves do when propagating through matter...?
I've also always wondered about how we account for the physical presence of the astronomical objects now versus the observed position of those objects as they were, since light has taken however long to reach us...
In my opinion, there is a reason it has dug up nothing. Please take a look at this modified gravity proposal. It explains galactic rotation rates and also cosmological expansion without the need for dark matter or dark energy. It also adapts general relativity:
119 comments
[ 0.18 ms ] story [ 277 ms ] threadThere are more interesting and less implausible hypotheses out there than the "just so" dark matter one.
Dark matter and dark energy are the simplest (literally single parameter) fits to the cosmological data we see. Why we see data consistent with these parameters (e.g. what is the non-interacting massive particle) is up in the air, but adding multi-parameter new forces without more justification seems a little too interesting.
Eg, if we’re looking at pseudo-tangles in shadow projections, that would solve why QM looks statistical while relativity looks continuous.
But that would raise deep questions about “warp” in the macro and whether galactic scale tangles would generate additional binding energy — ie, dark matter. Large scale tangles hiding mass would explain why we can’t interact with it, for instance.
For instance, I've seen a convincing argument[1] that dark matter researchers consistently underestimate galactic inclination, which in turn results in poor fits between model and data, leading to the epicycle-like fudge inclusion of dark matter as "everywhere we would expect mass to be, given xyz".
[1] https://tritonstation.com/2022/01/10/the-curious-case-of-agc...
Einstein would be happy!
Dark matter is a simple theory that explain a wide variety of unrelated observations.
In any case, until we actually are able to test that this is one "thing" rather than a bunch of things we still have no idea about, we should stop calling it "dark <foo>". Because I think that a lot of people are under the impression that there is some discrete substance out there causing this discrepancy, and there really is no reason to believe that's the case.
Yes, dark matter is the best way we currently have for fitting the data within most of our existing frameworks for understanding the universe. I really don't see the relation to epicycles.
There are people out there working very hard on modified gravity theories. I'm not aware of any that are able to explain the current data. If anything, trying to modify gravity to fit the dark matter data would be most similar to epicycles, it's devilishly difficult to come up with increasingly complex theories that fit more and more data that's coming in.
This is the key problem. Since there is no theory of what dark matter is made of or how it is created and destroyed, you can always have as much or as little of it as you need to fit the data.
As for gravity, we don't have anything close to a working theory of quantum gravity. We can't even measure the classical gravitational constant to more than about 4 digits. The reproducibility by different experiments has not demonstrably improved since the 1940's! Clearly there is a lot more we have to learn about gravity.
And yes, quantum gravity is also something we don't understand. But the domain where we are missing that understanding doesn't overlap with the dark matter "problem".
Falsifiability comes from having specific predictions, which means one theory that's an island, not a bunch of approximations.
It's not just a fudge factor, it's a fudge factor that behaves exactly like mass.
For dark matter, one of the problems is that any given instance is allowed to have whatever amount of dark matter gives the output we want. This makes the math work out great, but weakens its predictive power.
I'd love to hear about all of the less implausible hypotheses you're referring to.
most people creative enough are driven to the arts, which in modern society are only good for entertainment.
In the case of dark matter, we only observe their downstream effects but have no other direct evidence of its existence.
“The most successful technique with which to investigate [dark matter] has so far been the effect of gravitational lensing. The curvature of space-time near any gravitating mass (including dark matter) deflects passing rays of light - observably shifting, distorting and magnifying the images of background galaxies”.
“Dark matter appears not to interact via the electromagnetic force, and therefore neither emits nor reflects light.”
I am sure you know that, but perhaps not everyone does?
I must confess, when you said "pedantic", I expected something more annoying and less worthwhile. That's the best "pedantic" I've seen in quite a while.
One interesting approach I've heard of is abandoning reductionism and looking at how the macroscopic might actually determin the microscopic. We'll know how it pans out in half a century or so.
I bet one coffee that there is no dark matter in the form it's been looked for in the last decades. I bet two coffees that when somebody will discover the cause of the measured effects we'll be able to build some great new stuff, much like general relativity eventually gave us GPS and then navigation, etc.
Why are "epicycles" embarrassing?
"Epicycles" worked fine for a very long time. They are predictive. And accurate! And can be translated to a physical compuation mechanism (see: Antikythera mechanism).
In addition, "epicycles" are a manifestation of Fourier decomposition, which is a perfectly fine mathematical tool. The errors are due to the fact that reality isn't purely mathematical.
"Epicycles" were quite fine until we got both 1) much better clocks and 2) much better astronomical observations.
People forget that physics was in pretty close to this same state about 150 years ago (roughly) right before quantum mechanics. Physics was pretty much buttoned down except for that really strange Black Body Radiation problem (Ultraviolet Catastrophe), but they'd have that sorted in a couple of years. Certainly no later than 1900--the end of the century. No big deal.
HAH! We know how that turned out.
Unless the galaxy were a black hole, they'd escape. Since it's not, it can't be them.
It would be great if there were something producing slow-moving neutrinos, which would not only solve this but give us a huge leg up in understanding what's going on with neutrinos. But it doesn't look like that's the case.
The episode "Is Dark Matter Made of Particles?" [1] of PBS Space Time covers that.
They have several other dark matter episodes looking into other possibilities, such as black holes, axions, gravity not working the way we think it does, and more. If you are interested in this topic doing a search for "dark matter" in the video list on the YouTube channel would be a great place to start.
[1] https://www.youtube.com/watch?v=fidzLZQyaJE
It just kind of feels like there's a scale with weight on it that, by everything we now observe, should only weigh 200lbs and instead is reading 300 -- it just seems that "broken scale" is a better explanation than "invisible stuff on the scale."
Dismissing it as an incorrect measurement ignores the depth people have long gone into to verify this discrepancy between predictions and reality is not a sensor problem.
Almost 2 centuries ago astronomers found that the orbit of Mercury didn't make sense according to Newton's laws, laws which were at the time considered infallible. The astronomers only explanation was that there was a planet closer to the sun that we couldn't see, they believed this so much that they even named the planet Vulcan and spent many years searching for it.
Turns out that there was no Vulcan and general relativity explains the discrepancy in the orbit of Mercury.
https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet)
That discovery made both Le Verrier and the world at large very excited, and the race to repeat that feat lead to everyone jumping to conclusions about Vulcan.
https://en.wikipedia.org/wiki/Discovery_of_Neptune
Dark matter works well because it's designed to fill in the gaps in our current understanding of astrophysics data. Given it's origin it of course can perfectly explain the data, because that's what it was designed to do.
However, that doesn't necessarily make dark matter particularly useful for understanding how nature actually works.
> Dark matter works well because it's designed to fill in the gaps in our current understanding of astrophysics data.
"Works well" seems like you are looking at it the wrong way. Nobody is touting "dark matter" as a solution. It's the problem itself.
https://aether.lbl.gov/www/classes/p10/gr/Precessionperiheli...
However, this nickname is not absurd, in the sense that the gravity equations for the movement of stars in galaxies don't match the observation.
In order for the stars to move inside their galaxies at their observed speed, these galaxies should have much larger mass.
Hence the "dark matter".
Scientists do not all agree that there is an "invisible" matter to be found. Many think that Einstein's relativity has a more limited domain of validity than we thought.
But then the issue is as dark (in the sense of mysterious), since many of Einstein's predictions - based on his equations - have been observed in experimentations. The gravitational waves (LIGO experiment and other replications) appear to prove that the relativity equations are right. The precision of this instruments are extraordinary.
It's a terrible situation for Physics as a discipline: the equations are confirmed in all know situations, except this case (well, as far as I understood).
There are plenty of theories for explaining the phenomenon, but they lack an feasible experiment to see if their predictions match the observation.
Today, all the theories with feasible experiments have proven to be false. Physicists are stuck.
Many think that we need a new Einstein or a new Newton, meaning a genius among the geniuses, capable of think a whole new paradigm for gravity.
Gravity is a "law" and not a "force". It's as well the nickname for a phenomenon ; that phenomenon is sensible in the domain of validity of Newton, e.g. in our daily life.
The planets in the solar system move all accordingly with Newton's equations, except Mercury. Einstein had to totally put upside down the way we represent the world we live in, from a 3D world with a totally independent time to a 4D world, where everything and everyone live in its own spacetime.
Let's imagine two atomic clock set next to each other and synchronized. If we elevate one by 1 cm, then the clocks have a super slight desynchronizarion. And the tiny tiny difference match Einstein's equations.
Newton and Einstein are a few centuries apart. When will such genius reveal itself? Some physicists point that both were outsiders in their times. Nowadays, the knowledge is so vast that it takes ten years to master a fraction of it: by that time, a brain is so entrenched in the current representations that it's difficult to break the paradigm.
Others think likely that one of the theories already published is right but we'll need to wait a very long time, if ever, before being able to make the experiment that will prove it.
Maybe we will have to accept not being able to explain our universe. After all, since Gödel, mathematicians have kept going despite his proof that the mathematics are based on a quite fragile foundation.
I never quite understood that Gödel thing. Anyone to try and explain us that "dark" theorem?
That may seem surprising, but I don't think it is. There are infinite sets and infinite things you can say about them. It's not really a shock that there might be some properties about that set you can only prove by inspecting all of the elements, but you can't actually do that in finite time -- even though it's true. The sets are infinite, the theorems and their proofs are (by definition) not.
That doesn't mean that the foundations of math are fragile. It just means that there are facts you don't know. But you already knew that, too.
The specific theorems that can't be proven are just a subject of your axiom set. You can prove, or disprove, any specific thing you want, by taking it as axiomatic. It's just a question of whether anything interesting follows. That's a judgment for mathematicians, not a fact of mathematics.
I am, of course, handwaving like crazy, and probably driving the mathematicians nuts. Even though I said that the theorem is less surprising than it might seem, the fact that you can prove the theorem itself strikes me as very surprising.
I'm not aware of any significant number of scientists who think this. Even proponents of MOND acknowledge that they need to come up with a viable relativistic formulation of their theory.
This is not correct. Our measurements are accurate enough now that we have detected relativistic corrections in the motion of, IIRC, at least all the planets out to Jupiter or Saturn.
It’s called dark because it doesn’t interact with the electromagnetic field (i.e. we cannot see it) and matter because it’s otherwise assumed to behave just like the matter we can see.
It is a bit of a “We don’t like it, but it’s the best we can do for now”, but it is not like physicists invented something completely out of thin air to make the theory explain observations.
I basically came into the comments here just to see all the complete armchair novices come out of the woodwork to explain how they think they're smarter than the actual physicists.
Speaking of which, shall we start a discussion on climate science? ;-)
Here's a Monty Hall explainer. Will a plane on a treadmill take off? When you shower, do you explicitly wash your legs? Did you know that 0.999...=1?
That makes it really tempting to think "well maybe it's the model/equation that's wrong", which has been exactly the case throughout scientific history: planet Vulkan vs Relativity, phlogiston vs oxygen, luminiferous ether vs QED.
For those who haven't heard of this, the idea is that the gravitational constant actually changes at very high rotational speeds / centripetal accelerations (such as those at the galactic scale), and this is why our Earth-based gravity experiments don't detect this because we're in roughly the same reference frame and don't see the effect.
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
(Also, I am really not a physicists, so I'll let them chime in)
First, the MOND regime is not very high (large) accelerations, but very low (small) accelerations.
Second, the MOND hypothesis is not quite that the gravitational constant changes; it's that the form of the gravitational force changes--it's no longer the Newtonian inverse square force.
The key issue with this is that Newtonian gravity isn't our best current theory of gravity: General Relativity is. MOND as it was originally proposed is not a relativistic theory; there have been attempts to formulate a relativistic version, but none of them have resolved all of the open issues.
> this is why our Earth-based gravity experiments don't detect this because we're in roughly the same reference frame and don't see the effect.
No, that's not why MOND proponents say we don't detect the effect in Earth-based experiments. It's simply that we can't reproduce the required conditions on Earth (the net gravitational acceleration from all sources being small enough to get into the MOND regime).
I'm unsure the differences between "same reference frame" vs. "can't reproduce the required conditions" - ie Isn't it that in order to reproduce the very low accelerations we can't be in our current location with its high accelerations? I'm guessing there's some nuance between location / ref frame here that I'm missing.
"Same reference frame" is just an abstraction (and quite often a meaningless one--according to the proper concept of "reference frame" in physics, there is no such thing as being "in" one reference frame but not another).
"Can't reproduce the required conditions" is a straightforward statement about the limitations of what we can do with our current technology.
> Isn't it that in order to reproduce the very low accelerations we can't be in our current location with its high accelerations?
According to MOND, yes, in order to test it we would have to set up a lab out in deep space (i.e., not near any planet or star) far enough away from the center of our galaxy that the sum of all the "accelerations due to gravity" from all sources was less than the MOND threshold. Which of course is well beyond our current technical capability. But none of that has anything to do with "reference frames".
[1] https://www.youtube.com/watch?v=0sTBZ2G4vow
So it'd be more like a couch that's supposed to weight 200 lbs reads 300 lbs on a scale. But we've tested it on a half dozen different scales from different makers and keep getting 300 lbs. In addition we've tested this other couch that's suppose to read 100 lbs on some of these scales, and it correctly reads 100 lbs.
Many people walk away with the assumption that dark matter is literally massive lumps of stuff out there that is just really hard to see. Kind of analogous to stealth aircraft or something. This sounds absurd and it is. And its why a common reaction is to consider it absurd and that we probably just have gravity wrong.
The reality is that dark matter is just the name given to a set of observations. It wasn't intended to be descriptive. We are talking about scientists here, not public relations. So they are liable to fumble in the PR bit. Its not what they are good at. I consider the Neil DeGrasse Tysons and Michio Kakus of the world more to blame than the community at large. They have chosen to become the popular face of science and with that have a responsibility to properly communicate it. Their failure contributes to why people distrust academia to some degree.
Dark matter has already had some success. Just as an example, the discovery of Neptune -- made entirely through dark matter. We couldn't see it obviously, too much space to search over, but some kind of gravitational disturbance gave suggestions as to where to look. Boom, a whole planet. That is quite literally search via dark matter: it doesn't shine, so we must look for its knock-on effects.
Easy enough in the local neighborhood, but at a galactic scale, it is much much harder. And I wouldn't expect anything quick, either. If you want a fascinating journey through astronomy, look up the history of the various estimations of the "standard candle," used as a way to gauge distance. This took quite a lot of time to bounce back and forth between numbers.
And, no, the Earth is not made of dark matter.
I sort of feel the frustration here of people on Wikipedia trying to correct something they actually know about.
There's various places where gravitational effects don't seem to line up with the distribution of mass that we see or expect. Something is generating gravity, that we can't see, in places we didn't expect. Call it 'dark' matter, because it's not shiny.
But now that it has a name, it's treated a bit like a proper noun. Dark Matter. We do some observations that probably rule out simple nonluminous planetoids or dark stars. Whatever is causing the galactic rotation discrepancies doesn't seem to be normal matter. That translates into: 'Dark Matter' isn't normal matter. As if it is a certain thing, and not a reference to an unknown set.
By naming it, and talking about it, even though we don't understand it, we run the risk of attaching all sorts of presumptions to its identity. We're prematurely normalizing a certain way of thinking about it. We may have done a similar thing to quantum mechanics. (I may not be making much sense here, it's just a thought that struck me and I'm working through it.)
And we are imaging the Earth in infrared. Well, infrared from non-geologic sources, but oh man are we sure imaging in infrared.
https://en.wikipedia.org/wiki/Suomi_NPP
Bu before the name "dark matter" existed, the practice of it was evident. How did they discover Neptune? Gravitationally, not by seeing it first via a telescope. Its existence was inferred by the orbits of other planets, namely a gravitational disturbance suggesting a big glob of matter we had not collected photons from.
But we did not discover Neptune by collecting its photons. We had to infer that some glob of matter was present by gravitation. Then we pointed telescopes in the vicinity of prediction until this was confirmed.
Going further, we use these collected to infer all kinds of things -- a consistent dimming of a star in a certain period might suggest a planet occluding the star in an orbit coplanar to ours, which is our current method of locating exoplanets, but that wouldn't count.
You might recall how the neutrino was originally simply a placeholder, and actual detection came later. Similarly, the coining of the phase dark matter was simply as a contrast and a placeholder: we know something is there, but it ain't stars (light matter). Historically, many suggestions were made, and quite a few of them weren't exotic: MACHOs (Massive Compact Halo Objects), intergalactic gas, and so on. WIMPs would classify as a candidate for dark matter that would be somewhat exotic, so would axions.
Frustratingly, as the article suggests, we can do a lot of things to rule out (or more typically, set a maximum contribution as a fraction from each candidate), but we have little ruled in. We don't even have detection of axions yet, and those have been in the running for decades.
This is the sort of stuff that lured me into getting a physics degree.
One talk started with a lecture on the lamppost problem. It asked: why exactly are we looking for WIMPs? Because we know how to build a WIMP detector.
I'm not equipped to answer questions about dark matter anymore, but I will say that a lot of the knee-jerk comments in this thread underestimate how smart physicists are. Some of the most brilliant minds in science have contributed to dark matter cosmology. They are particle physicists, cosmologists, fluid dynamicists, and simulationists (reaching a little bit with the terminology here) all working together.
Science is progressing in the natural way of excluding theories from easiest to hardest. The fact that there are so many people working to exclude the "obvious" (or even "obviously wrong") theories should be evidence of how difficult this problem really is.
It may turn out that dark matter is explained by a non-particle phenomenon, or that it is matter that simply acts purely via the gravitational force and nothing else. I don't know what the implications of this would be. But none of that is obvious or easy to prove at the moment.
Nor is it easy to come up with a dark matter model which satisfies all the necessary constraints. You cannot just say, "there's some stuff out there" without collateral effects on (say) the distribution of matter in the universe.
For why we believe dark matter exists, see here: https://kids.frontiersin.org/articles/10.3389/frym.2021.5760...
[1] https://www.youtube.com/watch?v=PL0ewiwqoTw&t=4m5s
I would hesitate leaning too much on the always part. Fritz Zwicky was the first to notice the anomalous galaxy rotation curves and propose dark matter (is the story that I remember, anyway.) This is probably why it's presented first. It does not mean that it's the most important piece of evidence.
I'm intentionally writing with a light touch here because I don't consider myself an expert in the field.
There have been papers published on this, but it is still speculative, so it's premature to say that this kind of alternative theory rules out dark matter.
No, it only eliminates the need for Dark Matter to explain galaxy rotation curves.
It's been a long time since then and there's been a ton more data collected about wide ranging phenomenon since.
Dark matter could be a neighboring universe interacting with ours or something like that where the actual particle causing it is fundamentally out of reach (if it even is a particle), but just the fact that it interacts with our universe means we should in principle be able to interact with it and characterize it with experiments.
> In physics, a tachyonic field, or simply tachyon, is a quantum field with an imaginary mass.
The term tachyon was coined by Gerald Feinberg in a 1967 paper titled "Possibility of faster-than-light particles". He had been inspired by the science-fiction story "Beep" by James Blish.“
I don’t think “Beep” introduced the word, though (https://archive.org/details/galaxymagazine-1954-02)
There are some reasons to suspect/hope such things might not exist, such as protecting causality.
In general, asking "what if <simple field type> was <more complex field type>" can actually produce super fruitful lines of inquiry. You can use "complex numbers", "quaternions", "finite fields", whatever you like. There's plenty of unexplored ground here.
I'm not aware of a mechanism by which causality would arise from known QM, so I wouldn't expect a priori planck scale to play into it. There would also need to be an energy term for h to make sense as the relevant constant.
The most compelling source of temporal direction I'm familiar with is that it's a regional cosmological entropy gradient rather than a fundamental aspect of physics, although it strikes me as suspicious that the time direction lies inside the 4-cone generated by the odd-dimension-out in our spacetime metric. That certainly lends some credence to theories which would predict the direction of time as fundamental to physics.
My guess is that it falls back to Occam's Razor and there has yet to be any physics to use it thus it isn't a serious contender for current problems until much more work has been done on all the threads already being followed.
Every submission you've made seems to be about this company (https://news.ycombinator.com/submitted?id=dave333).
In scientific study you want and need failure. Knowing what doesn't work is as important as knowing what does. This way we can make lists of dangerous or useless things to be avoided. As long as things are documented and reproducible to the best of your abilities, you've won.
"Dark" matter refers to something that does not interact at all with photons - not that it scatters too little light.
:D
https://www.cosmology.info/media/open-letter-on-cosmology.ht...
https://web.archive.org/web/20170624042109/http://www.nytime...
I've also always wondered about how we account for the physical presence of the astronomical objects now versus the observed position of those objects as they were, since light has taken however long to reach us...
https://vixra.org/pdf/2203.0032v2.pdf