This is not incidental. Space between atoms is also huge. And the space between electrons and core relative to core density. The world as a whole is largely empty at microscopic and macroscopic level. And in fact when it's in balance, it looks like that at every level.
So when some wise guy tells you "well so what if we're 8 billion, Earth has plenty of land for more people" think about that. We're not in balance, and reality has a way of getting back to balance one way or another. If not through wisdom and intelligence, then through brute force.
Emptiness is an abundance of environment. It's all it is. Then you have the freedom to play. If your environment is scarce, your resources are scarce, then existence becomes an increasingly desperate play in which no one wins.
BTW when looking for "aether"... consider the stupidity of a water wave... looking for and not finding the water it's a wave of. It's all I'll say, if you need more, ask me.
I'm sitting in the middle of one of the densest metropolises in the hemisphere and yet there are probably only three other people within 10m of me. This space is also mostly "empty" of people even when dense with them in relative terms.
This framing of "balance" and "reality" has some unsettling undertones imo, in a world where resources are plentiful enough in raw terms but there are other barriers to people accessing them. What's your suggested path back to "balance?"
We are getting so far off the path here, but to give you an idea of how much of the earth human activity is taking up, wild mammals account for a mere 4% of mammal biomass.
What I was trying to say is that a human habitat is a vastly more complex network of relationships than merely the land we occupy, in which we feel relatively by ourselves within 10m of each other.
For example how much forest should there be between two cities, to produce the oxygen you're breathing right now? Many magnitudes higher than those 10m. I'm still barely scratching the surface.
As for suggestions... I don't even feel like going there today, I'm merely acknowledging my observations about realities that I believe are not up to our opinions. Reality is hugely empty, and when it's not, it's turbulent, vicious, and violent, like the center of our Sun. A neutron star. A black hole.
These are concepts of "density" and properties of the resulting system, which we can apply not only in physical context, but also biological, and social. All systems are alike in some basic fundamental ways.
70% of the oxygen on Earth comes from algae in the sea, not forests - which notably, also aren't really "carbon sinks" either since trees breath O2 and emit CO2 as well sometimes.
But it's also weird to say that you'd need more forest then that, as though it's mutually exclusive. Our suburbs can be extremely green filled, as can our cities, but probably more notably is the simply wrong element of it: the Earth is at no risk of running out of oxygen due to "too many human beings".
PS:
Of note [1] it's not a super reliable source, but this eyeballs that you'd probably need about 10,000 leaves or 700 house plants[2] (keeping in mind a houseplant is very small, so a large tree probably does substantially better).
The point is not about literal forests, it's about the fact that just because there is 10m between people doesn't mean that you can therefore tile the world with humans 10m apart (or even closer). You need empty space, huge amounts of it, to make life not horrific. Whether that space is forests or ocean isn't the important aspect. What's important is that just because there is 'empty' space doesn't mean that filling it with more people won't have an impact on how people live.
Looking through history i am forced to draw the opposite conclusion. Life was pretty uniformly horrific except for a very few people at a time that happened to draw some density around themselves. Nobility with servants lived ok, everyone else had a very bad go of it.
"But I stress that the universe is mainly made of nothing, that something is the exception. Nothing is the rule. That darkness is a commonplace; it is light that is the rarity." - Carl Sagan
> It appears as a repulsive gravitational force, and we’ve named it dark energy.
That's actually not true. Space is actually expanding, meaning new space is coming into existence and no one really knows what that looks like at a quantum level. Then again, we don't know how gravity works at a quantum level either.
The quoted figure is 72km/s/MPsc (+/-5). That means if two objects are 1 megaparsec apart (3.26 million light years) then space itself is expanding between them at the rate of ~72km/s.
Dark energy is really the fudge for all this. The idea is that creating new space takes energy. That has to come from somewhere and dark energy is our fudge factor for that. No one really knows what dark energy is or looks like just like we don't know what creating new space looks like. It just solves a conservation problem.
This isn't gravitational repulsion. It's why the universe is ~13.8 billion years old but we can see the light of objects that we now estimate to be >40 billion light years away. Space itself has expanded. It's not gravitational repulsion.
> In our most advanced quantum theories, we can calculate the energy contained in the vacuum, and it’s infinite. As in, suffusing every cubic centimeter of space and time is an infinite amount of energy, the combined efforts of all those countless but effervescent particles.
That's not true either. The calculation of vacuum energy by QFT isn't infinite. It's just really, really large. This is one of the largest errors between theory and observation in all of physics because the measured energy of a vacuum is ~120 orders of magnitude less. This is a well-known (and open) problem known as the vacuum catastrophe [1].
Lastly, on empty space, it's well-known that atmos are mostly empty space (as the article notes). I mean this is why neutron stars can be so dense. But it's worse than that. The nucleus itself (already a tiny portion of an atom's volume) is mostly empty space. Nucleons are made up three quarks and those quarks are tiny compared to the nucleon's size.
Particles have measurable sizes. Now you can argue this is a collapsing wavefunction, which I guess it is, but what size does a wavefunction have? I think the general interpretation is that the wavefunction is probability distribution and in that case the electron "cloud" is really the uncertainty about where the electron is not a larger object.
My layman’s understanding matches up with what you said, and my curiosity about this is what brought me to the comments. What I don’t get is that the author appears to be an astrophysicist who must surely understand the difference. Can someone shed more light on this? E.g. is there a version of the theory where these formulations are equivalent?
Yeah, I found this strange too. I too am a layman and that prompted me to comment: why is an astrophysics professor making statements that dark energy is gravity repulsion?
The most charitable interpretation is that the author has dumbed down the theory to make it digestible by the layman and in doing so has used a bad analogy. But I think you can correctly describe the core concepts in simpler terms that are a lot closer to taht theory.
Because it's true. When I got my PhD in cosmology, this is what everyone kept saying, including my thesis advisor, who is an accomplished professor in the field. So it's not just the author of this article.
Gravity works a bit different at the scales we are talking about, but generally we would expect an expanding universe filled with only matter and radiation to slow down and eventually collapse back into itself. Or at least it would slow down and approach some constant velocity. Not unlike a ball that you kick into the air with below or above the escape velocity. But what we actually observed in the late 90ies is that is indeed not slowing down, but accelerating, as if some force was pushing it apart. The cause of this - whatever it may be - has been dubbed "dark energy". At these scales we don't think of gravity as a "force" like we did in Newtonian physics, so I don't think it's wrong at all to say that dark energy has the opposite effect of matter and is pushing the universe apart, i.e. has an repelling effect.
> This isn't gravitational repulsion. It's why the universe is ~13.8 billion years old but we can see the light of objects that we now estimate to be >40 billion light years away. Space itself has expanded. It's not gravitational repulsion.
To add:
Masses repelling and space expanding would have the same effect on the observable universe boundary: linear models break down.
However, light redshifting, where more distant objects are more redshifted, fits with expansion. That cannot be explained by gravity. (Whether it's expansion or some other mechanism is still unknown, AFAIU.)
Nucleons are made up three quarks and those quarks are tiny compared to the nucleon's size.
Does it really make sense to even refer to the "size" of a point particle? In physics there's really no such thing as a "solid" object that has a "volume". It's just fields of a certain radius and the centers of those fields we refer to as the "location" of a zero-volume entity.
Depends. For instance in the case of the Lennard-Jones potential, which is basically the easiest but still good enough approximation of intermolecular interactions that we have, you have two fields between ~two molecules : one short-range repulsive, another long-range attractive. This results in a minimum potential at a distance r_min (see graph) that you can arguably think of as the "size" of the (spherical) molecule (at low temperatures, molecules will form "clumps" with that distance between them) :
This is news to me. The story I was taught was that Einstein's equations predicted a universe that wasn't static, i.e. an expanding universe. Einstein didn't like that and introduced the cosmological constant to leave the possibility of a static universe. Then, it was found that it was indeed expanding. Einstein promptly regretted his decision ("biggest blunder") to introduce the cosmological constant. Then, it was found that the universe was not only expanding, but expanding in an accelerated fashion. That is at odds with Einstein's equations without the cosmological constant, so it was re-introduced, but with the opposite sign. If you interpret the cosmological constant as part of the already present energy-stress tensor, it could represent the energy density of vacuum itself. That is only one interpretation of "dark energy" though, as the term is an umbrella term for whatever is responsible for the acceleration.
Energy conservation never entered the discussion. In fact, energy conservation generally isn't even expected to hold in cosmology. Energy is not even well defined, as it is directly associated with time translation invariance as per Noether's theorem, which doesn't exist in an expanding universe. See: https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
> The calculation of vacuum energy by QFT isn't infinite. It's just really, really large. This is one of the largest errors between theory and observation in all of physics because the measured energy of a vacuum is ~120 orders of magnitude less.
They are infinite if we sum up all frequencies naively. But just like with renormalization, we kinda say handwaveingly that we can probably cut off frequencies at the Planck scale, and then we arrive at this number 120.
There were two problems with Einstein's original (1917) cosmological model. The first was what you mention: Einstein assumed the universe was static, but later observations showed this wasn't true. The second was that his static model turned out to be unstable to either expansion or contraction, something he had forgotten to check.
> Dark energy is really the fudge for all this. The idea is that creating new space takes energy. That has to come from somewhere and dark energy is our fudge factor for that. No one really knows what dark energy is or looks like just like we don't know what creating new space looks like. It just solves a conservation problem.
That's simply not true. You don't need energy to create new space (and you wouldn't magically get energy from nowhere if the universe were contracting). General relativity gives you expanding (or contracting) space just fine if dark energy doesn't exist -- in fact, that was the most common cosmological model before the late 1990s discovery that the expansion was accelerating.
The fact that the simplest version of dark energy is the cosmological constant tells us your basic idea is wrong: if that energy was going into creating new space, then it would decrease over time, not remain constant.
In fact, it's worse than that, because the cosmological constant is a constant energy density. So if expansion doubles some volume of intergalactic space, then the total amount of dark energy also doubles (while the total energy in the form of ordinary or dark matter stays the same, and the energy in the form of photons decreases due to redshifting).
Could energy decay (by fusion or chemical reaction) of glowing matter towards iron create space as byproduct? I find the idea quite funny, of dark matter being a sort of invisible smoke bubbling from light reactions and this "byproducts" bubbling along gravity wells towards "flat" space were they surface creating new space.
But that idea could be tested, the more flat the space becomes, the more "positional" push-back by the bubbling space a space faring object would experience.
1. There is variance in matter distribution. If fusion created or expanded space I would assume there'd be a measurable variance in the wavelength of the cosmic microwave background;
2. The initial phase of the Universe was a massive period of inflation. This was before atoms could exist (and thus fuse) so to be consistent this would have to be a different mechanism;
3. The energy released by fusing light nuclei comes the nuclear binding energy (ie the strong interaction). So the nuclear binding energy of a helium atom is less than twice the nuclear binding energy of two hydrogen atoms. As you note, this goes as far as iron because this pattern is no longer true (ie the heavier fused element has more binding energy than the two lighter elements combined). I believe this particular conservation is "solved" or at least consistent with established theory, specifically QCD.
4. Fusion in stars is highly localized. Think of the volume of the Sun compared to the volume of every point in space to which the Sun was the closest star (ie approximately 2 light years in radius). It is astronomically small. To may layman's intuition it seems like this would be measurable in some way.
We know spacetime curves (based on the energy and mass present). We have detected the compression of space (ie gravity waves). We also know there is a minimum distance between objects (ie the Planck length) but (AFAIK) space isn't discrete as that might suggest.
There are huge gaps in our understanding of any of this.
Maybe the annhilation of anti-hydrogen and hydrogen produces massive amounts of space. Which would then pearl away from the mass, towards "flat" foamable space, aka the center, driving the sphere of annhilation apart, moving at almost lightspeed (relative to the created space), leaving behind only structures, who created lagrange points relative to the sphere, at which space could bubble up.
I have no idea what im doing, i just like to take a idea and run with it.
Articles reflect reality, too, I suppose. This kind of article is one of the reasons I recently cancelled my subscription. I don't know whether their quality actually did degrade over time or if it was always fluffy and I only just started noticing it last year.
The casual use of the word "infinity" is a tell tale sign of a lack of rigor. People think of infinity as just an incredibly large value, but Cantor and others have shown is more. Just take aleph-naught infinity -- the "smallest" infinity. I could count every particle in the universe and square it a million times and you are nowhere near any bound to aleph-naught infinity. Then jump up the aleph-one and now you are dealing with uncountable sets -- far "denser" that the simple countably infinite sets. Of course you can keep going to aleph-n for you favorite n. There are no actual infinities in terms of something measurable in the universe -- only potential infinities -- things that you can add on to indefinitely -- but you never reach any actual infinite quantity of anything. You can't even truly divide space an infinite numbers of times -- you will eventually reach the Planck length were anything smaller does not make any real sense in terms of actual existence.
Ok, the HN pedants are out in force. The guy is an astrophysicist and knows what he's talking talking. He's not saying dark energy is a repulsive gravitational force, he's saying it appears to us as such because we just see the macro effect of objects moving apart.
Nothing contains all things. It is more precious than gold, without beginning and end, more joyous than the perception of bountiful light, more noble than the blood of kings, comparable to the heavens, higher than the stars, more powerful than a stroke of lightening, perfect and blessed in every way. - Otto von Guericke
in my opinion this is a little disingenious (the quoted line) - we know that our physics is incomplete; the discrepancy between observed and calculated vacuum energy is vast - it's sort of like our ancesters wondering if we'd be able to mine the cheese in the moon (but with a slightly stronger reason for believing that the moon could be made of cheese).
From the article:
> In December 2022, an international team of astronomers released the results of their latest survey of galaxies, and their work has confirmed that the vacuum of spacetime is wreaking havoc across the cosmos. They found that matter makes up only a minority contribution to the energy budget of the universe.
The linked paper -- https://arxiv.org/pdf/2212.11319.pdf -- isn't about measuring dark energy at all. (It's using data from a study meant to do that, but it's looking at something else.)
Also,
> This phenomenon has various names: the quantum foam, the spacetime foam, vacuum fluctuations.
This confuses two different phenomena. The vacuum fluctuation of known quantum fields (electromagnetic, electron, Higgs, etc.) is what is thought to give rise to the cosmological constant/dark energy, and is what this article is about. (A limited version of it involving the electromagnetic field produces the Casimir effect, which has been measured.) "Spacetime/quantum foam" is the hypothetical fluctuation of spacetime itself, assuming a quantum theory of gravity. It has nothing to do with dark energy.
51 comments
[ 2.5 ms ] story [ 105 ms ] threadSo when some wise guy tells you "well so what if we're 8 billion, Earth has plenty of land for more people" think about that. We're not in balance, and reality has a way of getting back to balance one way or another. If not through wisdom and intelligence, then through brute force.
Emptiness is an abundance of environment. It's all it is. Then you have the freedom to play. If your environment is scarce, your resources are scarce, then existence becomes an increasingly desperate play in which no one wins.
BTW when looking for "aether"... consider the stupidity of a water wave... looking for and not finding the water it's a wave of. It's all I'll say, if you need more, ask me.
This framing of "balance" and "reality" has some unsettling undertones imo, in a world where resources are plentiful enough in raw terms but there are other barriers to people accessing them. What's your suggested path back to "balance?"
https://upload.wikimedia.org/wikipedia/commons/thumb/1/17/Di...
The Earth is big, really big, but 8 billion humans and their livestock are also a really big number.
For example how much forest should there be between two cities, to produce the oxygen you're breathing right now? Many magnitudes higher than those 10m. I'm still barely scratching the surface.
As for suggestions... I don't even feel like going there today, I'm merely acknowledging my observations about realities that I believe are not up to our opinions. Reality is hugely empty, and when it's not, it's turbulent, vicious, and violent, like the center of our Sun. A neutron star. A black hole.
These are concepts of "density" and properties of the resulting system, which we can apply not only in physical context, but also biological, and social. All systems are alike in some basic fundamental ways.
But it's also weird to say that you'd need more forest then that, as though it's mutually exclusive. Our suburbs can be extremely green filled, as can our cities, but probably more notably is the simply wrong element of it: the Earth is at no risk of running out of oxygen due to "too many human beings".
PS:
Of note [1] it's not a super reliable source, but this eyeballs that you'd probably need about 10,000 leaves or 700 house plants[2] (keeping in mind a houseplant is very small, so a large tree probably does substantially better).
[1] https://gizmodo.com/how-many-plants-would-you-need-to-genera...
[2] https://medium.com/@candidegardening/how-many-plants-would-i...
I do enjoy some of the popular science articles from this source, but this headline begs a silly question.
That's actually not true. Space is actually expanding, meaning new space is coming into existence and no one really knows what that looks like at a quantum level. Then again, we don't know how gravity works at a quantum level either.
The quoted figure is 72km/s/MPsc (+/-5). That means if two objects are 1 megaparsec apart (3.26 million light years) then space itself is expanding between them at the rate of ~72km/s.
Dark energy is really the fudge for all this. The idea is that creating new space takes energy. That has to come from somewhere and dark energy is our fudge factor for that. No one really knows what dark energy is or looks like just like we don't know what creating new space looks like. It just solves a conservation problem.
This isn't gravitational repulsion. It's why the universe is ~13.8 billion years old but we can see the light of objects that we now estimate to be >40 billion light years away. Space itself has expanded. It's not gravitational repulsion.
> In our most advanced quantum theories, we can calculate the energy contained in the vacuum, and it’s infinite. As in, suffusing every cubic centimeter of space and time is an infinite amount of energy, the combined efforts of all those countless but effervescent particles.
That's not true either. The calculation of vacuum energy by QFT isn't infinite. It's just really, really large. This is one of the largest errors between theory and observation in all of physics because the measured energy of a vacuum is ~120 orders of magnitude less. This is a well-known (and open) problem known as the vacuum catastrophe [1].
Lastly, on empty space, it's well-known that atmos are mostly empty space (as the article notes). I mean this is why neutron stars can be so dense. But it's worse than that. The nucleus itself (already a tiny portion of an atom's volume) is mostly empty space. Nucleons are made up three quarks and those quarks are tiny compared to the nucleon's size.
[1]: https://en.wikipedia.org/wiki/Cosmological_constant_problem
That formulation strikes me as being a Rutherford model tier of wrong.
My layman’s understanding matches up with what you said, and my curiosity about this is what brought me to the comments. What I don’t get is that the author appears to be an astrophysicist who must surely understand the difference. Can someone shed more light on this? E.g. is there a version of the theory where these formulations are equivalent?
The most charitable interpretation is that the author has dumbed down the theory to make it digestible by the layman and in doing so has used a bad analogy. But I think you can correctly describe the core concepts in simpler terms that are a lot closer to taht theory.
Gravity works a bit different at the scales we are talking about, but generally we would expect an expanding universe filled with only matter and radiation to slow down and eventually collapse back into itself. Or at least it would slow down and approach some constant velocity. Not unlike a ball that you kick into the air with below or above the escape velocity. But what we actually observed in the late 90ies is that is indeed not slowing down, but accelerating, as if some force was pushing it apart. The cause of this - whatever it may be - has been dubbed "dark energy". At these scales we don't think of gravity as a "force" like we did in Newtonian physics, so I don't think it's wrong at all to say that dark energy has the opposite effect of matter and is pushing the universe apart, i.e. has an repelling effect.
To add:
Masses repelling and space expanding would have the same effect on the observable universe boundary: linear models break down.
However, light redshifting, where more distant objects are more redshifted, fits with expansion. That cannot be explained by gravity. (Whether it's expansion or some other mechanism is still unknown, AFAIU.)
Does it really make sense to even refer to the "size" of a point particle? In physics there's really no such thing as a "solid" object that has a "volume". It's just fields of a certain radius and the centers of those fields we refer to as the "location" of a zero-volume entity.
https://en.wikipedia.org/wiki/Lennard-Jones_potential
This is news to me. The story I was taught was that Einstein's equations predicted a universe that wasn't static, i.e. an expanding universe. Einstein didn't like that and introduced the cosmological constant to leave the possibility of a static universe. Then, it was found that it was indeed expanding. Einstein promptly regretted his decision ("biggest blunder") to introduce the cosmological constant. Then, it was found that the universe was not only expanding, but expanding in an accelerated fashion. That is at odds with Einstein's equations without the cosmological constant, so it was re-introduced, but with the opposite sign. If you interpret the cosmological constant as part of the already present energy-stress tensor, it could represent the energy density of vacuum itself. That is only one interpretation of "dark energy" though, as the term is an umbrella term for whatever is responsible for the acceleration.
Energy conservation never entered the discussion. In fact, energy conservation generally isn't even expected to hold in cosmology. Energy is not even well defined, as it is directly associated with time translation invariance as per Noether's theorem, which doesn't exist in an expanding universe. See: https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
> The calculation of vacuum energy by QFT isn't infinite. It's just really, really large. This is one of the largest errors between theory and observation in all of physics because the measured energy of a vacuum is ~120 orders of magnitude less.
They are infinite if we sum up all frequencies naively. But just like with renormalization, we kinda say handwaveingly that we can probably cut off frequencies at the Planck scale, and then we arrive at this number 120.
That's simply not true. You don't need energy to create new space (and you wouldn't magically get energy from nowhere if the universe were contracting). General relativity gives you expanding (or contracting) space just fine if dark energy doesn't exist -- in fact, that was the most common cosmological model before the late 1990s discovery that the expansion was accelerating.
The fact that the simplest version of dark energy is the cosmological constant tells us your basic idea is wrong: if that energy was going into creating new space, then it would decrease over time, not remain constant.
In fact, it's worse than that, because the cosmological constant is a constant energy density. So if expansion doubles some volume of intergalactic space, then the total amount of dark energy also doubles (while the total energy in the form of ordinary or dark matter stays the same, and the energy in the form of photons decreases due to redshifting).
Conservation of energy in general relativity is messy and sometimes counter-intuitive; e.g. https://math.ucr.edu/home/baez/physics/Relativity/GR/energy_...
But that idea could be tested, the more flat the space becomes, the more "positional" push-back by the bubbling space a space faring object would experience.
1. There is variance in matter distribution. If fusion created or expanded space I would assume there'd be a measurable variance in the wavelength of the cosmic microwave background;
2. The initial phase of the Universe was a massive period of inflation. This was before atoms could exist (and thus fuse) so to be consistent this would have to be a different mechanism;
3. The energy released by fusing light nuclei comes the nuclear binding energy (ie the strong interaction). So the nuclear binding energy of a helium atom is less than twice the nuclear binding energy of two hydrogen atoms. As you note, this goes as far as iron because this pattern is no longer true (ie the heavier fused element has more binding energy than the two lighter elements combined). I believe this particular conservation is "solved" or at least consistent with established theory, specifically QCD.
4. Fusion in stars is highly localized. Think of the volume of the Sun compared to the volume of every point in space to which the Sun was the closest star (ie approximately 2 light years in radius). It is astronomically small. To may layman's intuition it seems like this would be measurable in some way.
We know spacetime curves (based on the energy and mass present). We have detected the compression of space (ie gravity waves). We also know there is a minimum distance between objects (ie the Planck length) but (AFAIK) space isn't discrete as that might suggest.
There are huge gaps in our understanding of any of this.
I have no idea what im doing, i just like to take a idea and run with it.
Nothing contains all things. It is more precious than gold, without beginning and end, more joyous than the perception of bountiful light, more noble than the blood of kings, comparable to the heavens, higher than the stars, more powerful than a stroke of lightening, perfect and blessed in every way. - Otto von Guericke
That might in handy, if only we could tap into it.
The linked paper -- https://arxiv.org/pdf/2212.11319.pdf -- isn't about measuring dark energy at all. (It's using data from a study meant to do that, but it's looking at something else.)
Also, > This phenomenon has various names: the quantum foam, the spacetime foam, vacuum fluctuations.
This confuses two different phenomena. The vacuum fluctuation of known quantum fields (electromagnetic, electron, Higgs, etc.) is what is thought to give rise to the cosmological constant/dark energy, and is what this article is about. (A limited version of it involving the electromagnetic field produces the Casimir effect, which has been measured.) "Spacetime/quantum foam" is the hypothetical fluctuation of spacetime itself, assuming a quantum theory of gravity. It has nothing to do with dark energy.