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I am aware I have almost no knowledge about dark matter in physics, but whenever it's mentioned, I can't help but think that our modern 'dark matter', is the 'e

I am aware I have almost no knowledge about dark matter in physics, but whenever it's mentioned, I can't help but think that our modern 'dark matter', is the 'ether of the 21st century'. That is, an interrim scientific theory that will eventually be completely replaced by revisions of our physics.

caymanjim 5y ago
I think most academics studying dark matter are pretty upfront about not knowing what it is. The theories with the most fans tend to not be very specific about the source, but agree that it's most likely an "unknown something" with mass that causes gravity. There are some theories like MOND that instead postulate that there's no missing mass, but that our understanding of gravity needs to be altered at galactic scales. In any case, it's a placeholder, not a specific theory. There are many candidate theories, but so far they're either untestable or the tests have had negative outcomes.
- UnpossibleJim 5y ago
  Just to put it in context, I'll share one of my favorite (even though I think it's one of the more outlandish and less accepted): In the Multiverse/Multidimensional universe theory, all of these dimensions aren't necessarily in different universes. Some are of different dimensions, laid over top of ours, but we can't see them because we can't perceive the dimensions they exist in. The only dimension that bleeds into ours, that we can track so far, is gravity. This is what we call "Dark matter". It is actually gravity leaking over from an "Nth" dimension laid over our own that we can't perceive. Again, as to the veracity I can't say. And I wish I remembered to author, but I don't =/ maybe I'll look it up later and make an annotation.
  - 867-5309 5y ago
    sounds like Brane Cosmology https://en.wikipedia.org/wiki/Brane_cosmology https://en.wikipedia.org/wiki/Brane_cosmology
Hemospectrum 5y ago
You've got plenty of scientists as company. There are cute names like WIMP and MOND for different types of hypotheses about what the heck dark matter actually is, or how to explain what's going on if it doesn't exist at all. Each of these is a huge headache for astrophysicists in one respect or another.
- deleted 5y ago
  [deleted]
passivate 5y ago
But in modern science we differentiate between facts/hypotheses/laws/theories. What you're referring to is a hypothesis - and those should be replaced with a more concrete explanation - once we have it. I don't quite understand your point about connecting it to ether though. I can't think of any established theory in modern science that was completely replaced - but I'm not a physicist either.
interestica 5y ago
> 'ether of the 21st century' Or 'caloric' or 'phlogiston' https://en.wikipedia.org/wiki/Superseded_theories_in_science https://en.wikipedia.org/wiki/Superseded_theories_in_science
- kiba 5y ago
  Dark matter is not a theory, it's a name for an unexplained phenomena.
- tigerlily 5y ago
  Phlogiston, now there's a word I haven't seen in a while. A lot of big names on that list of superseded theories by the way :)
generalizations 5y ago
I mean, the name is literally 'the stuff we can't see'. Dark matter is very much just a question mark looking for an explanation.
- iainmerrick 5y ago
  The word “stuff” there is exactly the point. It’s a lot more specific than “just a question mark” -- the hypothesis is that it’s some exotic form of matter. If something like MOND gains popularity and there’s no longer a need to postulate invisible matter, it would be fair to say that dark matter is incorrect and outdated, just like ether or phlogiston.
  - generalizations 5y ago
    That would be fair. However, from what I've read MOND is relatively unlikely. If its proponents can address the biggest difficulties (e.g. not every galaxy appears to have "dark matter") and make it somewhat more feasible, then I'd agree the name is insufficiently broad.
  - dnautics 5y ago
    Not really, MOND and the like falls into the category of "dark matter theory", and that's the problem with the name.
    - pdonis 5y ago
      > MOND and the like falls into the category of "dark matter theory" No, it doesn't. See my response to your other post upthread about the two hypotheses. "Dark matter" is one hypothesis; "MOND" and friends are the other.
    - raattgift 5y ago
      No, it is unfair to call MOND (and at least much of "the like") as a dark matter theory, because it manifestly generates a solution (or solutions) in the absence of any matter at all. MOND is characterized by an interpolating function between its fundamental constant a_0 and acceleration, such that in the "deep-MOND" regime, F = m \frac{a^2}{a_0} rather than Newton's F = ma. Both MOND and Newton work in everywhere-vacuum, and in everywhere-vacuum perturbed by a point mass. Neither the vacuum case nor the point mass case qualifies as a "dark matter theory" any more than the vacuum Schwarzschild solution of General Relativity does. These are model universes where one can calculate a Gauss law for gravity. MOND would behave differently for deep deep extragalactic space with small icy body moving around a large gassy body than Newton would, or than we would get from e.g. a roughly Einstein-de Sitter solution. Milgrom has pursued several relativistic corrections to the simple MOND formula, and they generally allow for solutions where the stress-energy tensor is everywhere 0, and everywhere 0 except for one point. Milgrom originated MOND. He has collected numerous thoughts and many links at http://www.scholarpedia.org/article/The_MOND_paradigm_of_modified_dynamics http://www.scholarpedia.org/article/The_MOND_paradigm_of_mod... When applied to large systems like galaxies and especially galaxy clusters, Milgrom's corrections may be insufficient, and other corrections (catalogued well in https://arxiv.org/abs/1112.3960 https://arxiv.org/abs/1112.3960 section 7). Several of these are very hard to make work with the stress-energy tensor everywhere zero, and those (certainly not all of them) one might ungraciously call "just another dark matter theory". On the other hand, several of these theories admit plausible gravitational radiation in the total absence of matter, just as does General Relativity. (Gravitational radiation is not a feature of Newton or the simple original Milgrom formula.) McGaugh runs tritonstation and is a well known sceptic of particle dark matter. Relativistic dark matter theories deliberately introduce nonzeros into the stress-energy tensor. You need a distribution of dark matter and trace out how that generates curvature, or you don't have a (relativistic) dark matter theory. You can also of course set out a distribution of cold dark matter and see how it behaves under F = ma or F = m \frac{a^2}{a_0}. Neither MOND nor Newton requires dark matter; likewise neither MOND nor Newton is incompatible with dark matter. Likewise, General Relativity doesn't require dark matter. But one gets more physically realistic solutions at a wide range of scales when one adds dark matter to a defined large-scale distribution of matter and radiation. MOND or the various attempts at generally covariant Milgrom gravitation would also behave differently when one adds dark matter to a large-scale distribution of matter and radiation. That is unlikely to produce more physically realistic solutions to a wide range of scales, however. Indeed, Milgrom et al's most concrete argument is that their formula for gravitation is worse if one adds in a distribution of dark matter, and that their formula is better than e.g. a Lemaître-Tolman-Bondi solution equipped with a distribution of cold dark matter. That's as much a non-dark-matter theory as I think it is possible to have!
da_chicken 5y ago
I mean, we need to have a convenient term for a phenomenon even if we don't understand it. What's the alternative? "The unnamed phenomenon were some astronomic bodies behave as though a vast quantity of matter were affecting them but that matter can't be otherwise detected or identified"? In medicine, they often call it a "syndrome". A collection of symptoms that together form a known pattern that is often closely associated with a disease or disorder but has no understood cause or origin (although some syndromes continue to be called that after they are better understood). How do you think we arrived at terms like "planets"? We noticed that some stars in the sky moved around while the rest didn't, and we called them "wandering stars". We still call them "atoms" even though that word means "indivisible". Weather is full of such names: rain, thunder, lightning, wind, morning glory, dew, tornado, rainbow, etc. All these words for material phenomenon existed long before we knew how they worked. So what's wrong with "dark matter" as a name?
- colordrops 5y ago
  I didn't read a negative judgment of the term in the grandparent comment, just an observation.
  - da_chicken 5y ago
    Yes, and I'm challenging that observation. "Making an observation" doesn't mean you're not subject to criticism or questioning.
    - burnished 5y ago
      You haven't meaningfully challenged anything they said, though. Your thing was an odd rant about the need to name things (not a hot take), and theirs seemed more focused, well >>That is, an interrim scientific theory that will eventually be completely replaced by revisions of our physics.
      - deleted 5y ago
        [deleted]
hitpointdrew 5y ago
I also have almost no knowledge about dark matter in physics, and maybe I am a complete moron. But what do you think is more likely, there is this matter out there that no one has been able to find in decades of searching, or the mainstream assumptions/math on gravity are wrong/incomplete? I am going with the later.
- mr_mitm 5y ago
  It's interesting that this sentiment almost exclusively comes from people with almost no knowledge about dark matter. What do you think is more likely, there is a theory that makes all observations look exactly like there is invisible matter without actually being invisible matter, or that there is invisible matter? I am going with the latter. I also do not understand why laypeople are of the opinion that all massive particles must interact electromagnetically. If you are open to the idea that there is a massive particle that doesn't, you got dark matter.
- jug 5y ago
  MOND theories etc. like this has fallen kind of out of favor because it’s just so hard to adapt our theory of gravity to resolve this. It’s surprising how often this topic pops up. I think it’s based on a misjudgment that simply missing something in gravity follows Occams Razor better but it actually seems to be the opposite. I think the killer is that dark matter seems to not just hold galaxies together (given their “too high” rotational speeds), but also clump together, and also sometimes be missing in galaxies and other times overwhelm galaxies. It’s super hard to adapt the well proven theory of gravity to especially localized phenomena.
- pdonis 5y ago
  > what do you think is more likely, there is this matter out there that no one has been able to find in decades of searching, or the mainstream assumptions/math on gravity are wrong/incomplete? You are mis-stating the real issue here. The distribution of matter is already a free parameter in our current theory of gravity, General Relativity. GR in no way requires that all matter be visible to humans. The "no one has been able to find" thing is not a problem for GR, it's a problem for the Standard Model of particle physics, which does not contain any particles that dark matter could be made out of. But most physicists already believe that there are more kinds of particles than the SM describes, we just haven't figured out how to make them in accelerators so we can study them in a controlled experimental fashion, and we haven't figured out any "smoking gun" signature that will tell us if such particles exist out there in the universe. "Dark matter" is really just a name for those kinds of particles that are already believed to exist anyway, we just can't detect them with the technology we currently have. But the technology we currently have is very limited. So the real question you should be asking is, what do you think is more likely, that there are particles that aren't included in the Standard Model of particle physics--which is already believed to be the case anyway--or that General Relativity is wrong in its description of the dynamics of galaxies, even though this is a domain in which GR has already passed stringent experimental tests with predictions accurate to many decimal places? I'm going with the former.
salty_biscuits 5y ago
As a counterpoint, Neptune and Pluto were "dark matter" prior to confirmation with observations. They were theorized to exist due to their perturbations to observed motion of known planets.
- dnautics 5y ago
  Well by that token so was the discrepancy in the precession of mercury (which was not, as it turns out,matter).
  - pdonis 5y ago
    > so was the discrepancy in the precession of mercury No, it wasn't, because, as you note, that observation was accounted for by adopting new laws of gravity, not by adding more matter to the distribution of matter we used in our model. Those are two different things.
    - nimish 5y ago
      It was thought for decades the anomalous precession of Mercury could be due to matter, including an entirely new planet, Vulcan.
      - pdonis 5y ago
        Yes, that was one hypothesis, but it didn't turn out to be the correct one. The correct hypothesis was that Newtonian gravity was wrong and had to be replaced by General Relativity. That hypothesis is not a "dark matter" hypothesis. But the poster I was responding to, dnautics, is claiming (not just here but elsewhere in this thread) that it is.
        dnautics 5y ago
        That's exactly the point. It was a dark matter hypothesis until they found out it wasn't actually matter. Physicists couldn't go back in time and tell themselves, hey, this isn't actually matter. By analogy suppose we find out in 35 years that some non-lambda-cdm, non-particle theory is correct? It would be revisionist to say we didn't believe in dark matter today.
claytongulick 5y ago
Even "Ether" has come back around a bit in certain circles. It's not called that anymore, I think it's called the "Grid" or something similar. Milo Wolff discusses some of this in his WSM theories, IIRC.
mr_mitm 5y ago
Except the very first experiment that was supposed to confirm the ether showed that there is no ether, while every astrophysical observation we made on any scale [1] confirmed that there is dark matter. [1] https://www.twitter.com/seanmcarroll/status/1371141258236764160?lang=de https://www.twitter.com/seanmcarroll/status/1371141258236764...
- dnautics 5y ago
  We don't have any confirmation that it exists, we have more observations that Newton's law is wrong. Moreover, these observations collectively are unimodal; to date we only have observations of more gravitational discrepancies, not corroborating phenomena which correlate to the existing discrepancies.
  - pdonis 5y ago
    > we have more observations that Newton's law is wrong No, we don't. We have observations that show that the motion of stars in galaxies is not what we would predict if we used our current laws of gravity with a distribution of matter that matches just what is visible to us. There are two possible hypotheses to explain these observations: (1) There is matter present that is not visible to us; (2) Our current laws of gravity are wrong and need to be modified. "Dark matter" is basically a name for #1; "MOND" and similar models are in category #2.
- bopbeepboop 5y ago
  What do you mean? Aether theories are the dominant model (“quantum fields” are renamed aethers), and we’ve directly detected aether waves with a scaled up version of the original experiment — which turned out not to be sensitive enough, because the aether is squishy rather than firm. LIGO is literally Michelson-Morley, but larger. Most of modern science is based on the techniques of Michelson-Morley. It’s a nearly prescient experiment — and it says more about us psychologically than the world at large we remember it as “wrong” rather than “not accurate enough”. LIGO proved them right. https://physics.mit.edu/wp-content/uploads/2021/01/physicsatmit_09_whatisspace_wilczek.pdf https://physics.mit.edu/wp-content/uploads/2021/01/physicsat...
keithnz 5y ago
Sabine is a great science (physics) communicator to the "masses", she recently did an update on dark matter. https://www.youtube.com/watch?v=4_qJptwikRc https://www.youtube.com/watch?v=4_qJptwikRc
- Hypx_ 5y ago
  Summary: Both dark matter and modified gravity are true. Could be caused by wave-particle duality.
RedComet 5y ago
Ether very much exists. Its just now referred to as emptiness or "the vacuum of space".
- Ono-Sendai 5y ago
  Also known as fields (as in fields from quantum field theory)
- 1_player 5y ago
  It doesn't. Aether was supposed to be an element, substance that filled the emptiness of space, not the emptiness itself.
  - RedComet 5y ago
    You seem to be mistakenly conflating the modern conception of chemical elements with classical philosophical notions of elements.
megablast 5y ago
>I am aware I have almost no knowledge about dark matter in physics Thank you for introducing your comment like this so I can give it the true weight it deserves.

caymanjim 5y ago

I think most academics studying dark matter are pretty upfront about not knowing what it is. The theories with the most fans tend to not be very specific about the source, but agree that it's most likely an "unknown something" with mass that causes gravity. There are some theories like MOND that instead postulate that there's no missing mass, but that our understanding of gravity needs to be altered at galactic scales. In any case, it's a placeholder, not a specific theory. There are many candidate theories, but so far they're either untestable or the tests have had negative outcomes.

UnpossibleJim 5y ago
Just to put it in context, I'll share one of my favorite (even though I think it's one of the more outlandish and less accepted): In the Multiverse/Multidimensional universe theory, all of these dimensions aren't necessarily in different universes. Some are of different dimensions, laid over top of ours, but we can't see them because we can't perceive the dimensions they exist in. The only dimension that bleeds into ours, that we can track so far, is gravity. This is what we call "Dark matter". It is actually gravity leaking over from an "Nth" dimension laid over our own that we can't perceive. Again, as to the veracity I can't say. And I wish I remembered to author, but I don't =/ maybe I'll look it up later and make an annotation.
- 867-5309 5y ago
  sounds like Brane Cosmology https://en.wikipedia.org/wiki/Brane_cosmology https://en.wikipedia.org/wiki/Brane_cosmology

Hemospectrum 5y ago

You've got plenty of scientists as company. There are cute names like WIMP and MOND for different types of hypotheses about what the heck dark matter actually is, or how to explain what's going on if it doesn't exist at all. Each of these is a huge headache for astrophysicists in one respect or another.

deleted 5y ago
[deleted]

passivate 5y ago

But in modern science we differentiate between facts/hypotheses/laws/theories. What you're referring to is a hypothesis - and those should be replaced with a more concrete explanation - once we have it. I don't quite understand your point about connecting it to ether though. I can't think of any established theory in modern science that was completely replaced - but I'm not a physicist either.

interestica 5y ago

> 'ether of the 21st century' Or 'caloric' or 'phlogiston' https://en.wikipedia.org/wiki/Superseded_theories_in_science https://en.wikipedia.org/wiki/Superseded_theories_in_science

kiba 5y ago
Dark matter is not a theory, it's a name for an unexplained phenomena.
tigerlily 5y ago
Phlogiston, now there's a word I haven't seen in a while. A lot of big names on that list of superseded theories by the way :)

generalizations 5y ago

I mean, the name is literally 'the stuff we can't see'. Dark matter is very much just a question mark looking for an explanation.

iainmerrick 5y ago
The word “stuff” there is exactly the point. It’s a lot more specific than “just a question mark” -- the hypothesis is that it’s some exotic form of matter. If something like MOND gains popularity and there’s no longer a need to postulate invisible matter, it would be fair to say that dark matter is incorrect and outdated, just like ether or phlogiston.
- generalizations 5y ago
  That would be fair. However, from what I've read MOND is relatively unlikely. If its proponents can address the biggest difficulties (e.g. not every galaxy appears to have "dark matter") and make it somewhat more feasible, then I'd agree the name is insufficiently broad.
- dnautics 5y ago
  Not really, MOND and the like falls into the category of "dark matter theory", and that's the problem with the name.
  - pdonis 5y ago
    > MOND and the like falls into the category of "dark matter theory" No, it doesn't. See my response to your other post upthread about the two hypotheses. "Dark matter" is one hypothesis; "MOND" and friends are the other.
  - raattgift 5y ago
    No, it is unfair to call MOND (and at least much of "the like") as a dark matter theory, because it manifestly generates a solution (or solutions) in the absence of any matter at all. MOND is characterized by an interpolating function between its fundamental constant a_0 and acceleration, such that in the "deep-MOND" regime, F = m \frac{a^2}{a_0} rather than Newton's F = ma. Both MOND and Newton work in everywhere-vacuum, and in everywhere-vacuum perturbed by a point mass. Neither the vacuum case nor the point mass case qualifies as a "dark matter theory" any more than the vacuum Schwarzschild solution of General Relativity does. These are model universes where one can calculate a Gauss law for gravity. MOND would behave differently for deep deep extragalactic space with small icy body moving around a large gassy body than Newton would, or than we would get from e.g. a roughly Einstein-de Sitter solution. Milgrom has pursued several relativistic corrections to the simple MOND formula, and they generally allow for solutions where the stress-energy tensor is everywhere 0, and everywhere 0 except for one point. Milgrom originated MOND. He has collected numerous thoughts and many links at http://www.scholarpedia.org/article/The_MOND_paradigm_of_modified_dynamics http://www.scholarpedia.org/article/The_MOND_paradigm_of_mod... When applied to large systems like galaxies and especially galaxy clusters, Milgrom's corrections may be insufficient, and other corrections (catalogued well in https://arxiv.org/abs/1112.3960 https://arxiv.org/abs/1112.3960 section 7). Several of these are very hard to make work with the stress-energy tensor everywhere zero, and those (certainly not all of them) one might ungraciously call "just another dark matter theory". On the other hand, several of these theories admit plausible gravitational radiation in the total absence of matter, just as does General Relativity. (Gravitational radiation is not a feature of Newton or the simple original Milgrom formula.) McGaugh runs tritonstation and is a well known sceptic of particle dark matter. Relativistic dark matter theories deliberately introduce nonzeros into the stress-energy tensor. You need a distribution of dark matter and trace out how that generates curvature, or you don't have a (relativistic) dark matter theory. You can also of course set out a distribution of cold dark matter and see how it behaves under F = ma or F = m \frac{a^2}{a_0}. Neither MOND nor Newton requires dark matter; likewise neither MOND nor Newton is incompatible with dark matter. Likewise, General Relativity doesn't require dark matter. But one gets more physically realistic solutions at a wide range of scales when one adds dark matter to a defined large-scale distribution of matter and radiation. MOND or the various attempts at generally covariant Milgrom gravitation would also behave differently when one adds dark matter to a large-scale distribution of matter and radiation. That is unlikely to produce more physically realistic solutions to a wide range of scales, however. Indeed, Milgrom et al's most concrete argument is that their formula for gravitation is worse if one adds in a distribution of dark matter, and that their formula is better than e.g. a Lemaître-Tolman-Bondi solution equipped with a distribution of cold dark matter. That's as much a non-dark-matter theory as I think it is possible to have!

da_chicken 5y ago

I mean, we need to have a convenient term for a phenomenon even if we don't understand it. What's the alternative? "The unnamed phenomenon were some astronomic bodies behave as though a vast quantity of matter were affecting them but that matter can't be otherwise detected or identified"? In medicine, they often call it a "syndrome". A collection of symptoms that together form a known pattern that is often closely associated with a disease or disorder but has no understood cause or origin (although some syndromes continue to be called that after they are better understood). How do you think we arrived at terms like "planets"? We noticed that some stars in the sky moved around while the rest didn't, and we called them "wandering stars". We still call them "atoms" even though that word means "indivisible". Weather is full of such names: rain, thunder, lightning, wind, morning glory, dew, tornado, rainbow, etc. All these words for material phenomenon existed long before we knew how they worked. So what's wrong with "dark matter" as a name?

colordrops 5y ago
I didn't read a negative judgment of the term in the grandparent comment, just an observation.
- da_chicken 5y ago
  Yes, and I'm challenging that observation. "Making an observation" doesn't mean you're not subject to criticism or questioning.
  - burnished 5y ago
    You haven't meaningfully challenged anything they said, though. Your thing was an odd rant about the need to name things (not a hot take), and theirs seemed more focused, well >>That is, an interrim scientific theory that will eventually be completely replaced by revisions of our physics.
    - deleted 5y ago
      [deleted]

hitpointdrew 5y ago

I also have almost no knowledge about dark matter in physics, and maybe I am a complete moron. But what do you think is more likely, there is this matter out there that no one has been able to find in decades of searching, or the mainstream assumptions/math on gravity are wrong/incomplete? I am going with the later.

mr_mitm 5y ago
It's interesting that this sentiment almost exclusively comes from people with almost no knowledge about dark matter. What do you think is more likely, there is a theory that makes all observations look exactly like there is invisible matter without actually being invisible matter, or that there is invisible matter? I am going with the latter. I also do not understand why laypeople are of the opinion that all massive particles must interact electromagnetically. If you are open to the idea that there is a massive particle that doesn't, you got dark matter.
jug 5y ago
MOND theories etc. like this has fallen kind of out of favor because it’s just so hard to adapt our theory of gravity to resolve this. It’s surprising how often this topic pops up. I think it’s based on a misjudgment that simply missing something in gravity follows Occams Razor better but it actually seems to be the opposite. I think the killer is that dark matter seems to not just hold galaxies together (given their “too high” rotational speeds), but also clump together, and also sometimes be missing in galaxies and other times overwhelm galaxies. It’s super hard to adapt the well proven theory of gravity to especially localized phenomena.
pdonis 5y ago
> what do you think is more likely, there is this matter out there that no one has been able to find in decades of searching, or the mainstream assumptions/math on gravity are wrong/incomplete? You are mis-stating the real issue here. The distribution of matter is already a free parameter in our current theory of gravity, General Relativity. GR in no way requires that all matter be visible to humans. The "no one has been able to find" thing is not a problem for GR, it's a problem for the Standard Model of particle physics, which does not contain any particles that dark matter could be made out of. But most physicists already believe that there are more kinds of particles than the SM describes, we just haven't figured out how to make them in accelerators so we can study them in a controlled experimental fashion, and we haven't figured out any "smoking gun" signature that will tell us if such particles exist out there in the universe. "Dark matter" is really just a name for those kinds of particles that are already believed to exist anyway, we just can't detect them with the technology we currently have. But the technology we currently have is very limited. So the real question you should be asking is, what do you think is more likely, that there are particles that aren't included in the Standard Model of particle physics--which is already believed to be the case anyway--or that General Relativity is wrong in its description of the dynamics of galaxies, even though this is a domain in which GR has already passed stringent experimental tests with predictions accurate to many decimal places? I'm going with the former.

salty_biscuits 5y ago

As a counterpoint, Neptune and Pluto were "dark matter" prior to confirmation with observations. They were theorized to exist due to their perturbations to observed motion of known planets.

dnautics 5y ago
Well by that token so was the discrepancy in the precession of mercury (which was not, as it turns out,matter).
- pdonis 5y ago
  > so was the discrepancy in the precession of mercury No, it wasn't, because, as you note, that observation was accounted for by adopting new laws of gravity, not by adding more matter to the distribution of matter we used in our model. Those are two different things.
  - nimish 5y ago
    It was thought for decades the anomalous precession of Mercury could be due to matter, including an entirely new planet, Vulcan.
    - pdonis 5y ago
      Yes, that was one hypothesis, but it didn't turn out to be the correct one. The correct hypothesis was that Newtonian gravity was wrong and had to be replaced by General Relativity. That hypothesis is not a "dark matter" hypothesis. But the poster I was responding to, dnautics, is claiming (not just here but elsewhere in this thread) that it is.
      - dnautics 5y ago
        That's exactly the point. It was a dark matter hypothesis until they found out it wasn't actually matter. Physicists couldn't go back in time and tell themselves, hey, this isn't actually matter. By analogy suppose we find out in 35 years that some non-lambda-cdm, non-particle theory is correct? It would be revisionist to say we didn't believe in dark matter today.

claytongulick 5y ago

Even "Ether" has come back around a bit in certain circles. It's not called that anymore, I think it's called the "Grid" or something similar. Milo Wolff discusses some of this in his WSM theories, IIRC.

mr_mitm 5y ago

Except the very first experiment that was supposed to confirm the ether showed that there is no ether, while every astrophysical observation we made on any scale [1] confirmed that there is dark matter. [1] https://www.twitter.com/seanmcarroll/status/1371141258236764160?lang=de https://www.twitter.com/seanmcarroll/status/1371141258236764...

dnautics 5y ago
We don't have any confirmation that it exists, we have more observations that Newton's law is wrong. Moreover, these observations collectively are unimodal; to date we only have observations of more gravitational discrepancies, not corroborating phenomena which correlate to the existing discrepancies.
- pdonis 5y ago
  > we have more observations that Newton's law is wrong No, we don't. We have observations that show that the motion of stars in galaxies is not what we would predict if we used our current laws of gravity with a distribution of matter that matches just what is visible to us. There are two possible hypotheses to explain these observations: (1) There is matter present that is not visible to us; (2) Our current laws of gravity are wrong and need to be modified. "Dark matter" is basically a name for #1; "MOND" and similar models are in category #2.
bopbeepboop 5y ago
What do you mean? Aether theories are the dominant model (“quantum fields” are renamed aethers), and we’ve directly detected aether waves with a scaled up version of the original experiment — which turned out not to be sensitive enough, because the aether is squishy rather than firm. LIGO is literally Michelson-Morley, but larger. Most of modern science is based on the techniques of Michelson-Morley. It’s a nearly prescient experiment — and it says more about us psychologically than the world at large we remember it as “wrong” rather than “not accurate enough”. LIGO proved them right. https://physics.mit.edu/wp-content/uploads/2021/01/physicsatmit_09_whatisspace_wilczek.pdf https://physics.mit.edu/wp-content/uploads/2021/01/physicsat...

keithnz 5y ago

Sabine is a great science (physics) communicator to the "masses", she recently did an update on dark matter. https://www.youtube.com/watch?v=4_qJptwikRc https://www.youtube.com/watch?v=4_qJptwikRc

Hypx_ 5y ago
Summary: Both dark matter and modified gravity are true. Could be caused by wave-particle duality.

RedComet 5y ago

Ether very much exists. Its just now referred to as emptiness or "the vacuum of space".

Ono-Sendai 5y ago
Also known as fields (as in fields from quantum field theory)
1_player 5y ago
It doesn't. Aether was supposed to be an element, substance that filled the emptiness of space, not the emptiness itself.
- RedComet 5y ago
  You seem to be mistakenly conflating the modern conception of chemical elements with classical philosophical notions of elements.

megablast 5y ago

>I am aware I have almost no knowledge about dark matter in physics Thank you for introducing your comment like this so I can give it the true weight it deserves.