4 ms·

So this rules out many kinds of WIMPs, but not axions, or the more exotic white holes of loop quantum gravity. There's also the JWST observations which oddly se

So this rules out many kinds of WIMPs, but not axions, or the more exotic white holes of loop quantum gravity. There's also the JWST observations which oddly seem to fit certain MOND scenarios better. Or Claudia DeRahm's massive gravity.

marcosdumay 2y ago
Shouldn't axions interact with atom nucleus? This rules out any interaction except for gravitational, right?
- throwawaymaths 2y ago
  To a certain floor. Of course a particle which only interacts gravitationally is still possible but that's the cosmologist's nightmare. It'd be basically impossible to prove it's existence and anything could happen (like a small but fast fairly massive ~asteroid mass clump of dark matter explaining poltergeists)
  - ajross 2y ago
    > like a small but fast fairly massive ~asteroid mass clump of dark matter explaining poltergeists This is clever, but I have to believe the back of an envelope would show that a dark-matter scale distribution of "dark blobs" big enough to throw things around the room and frequent enough to be given names in human experience would be many, many orders of magnitude higher than the observed gravitational effects.
    - throwawaymaths 2y ago
      > have to believe A lot of weird shit gets floated around, like planet X is dark matter, or at one point someone suggested sag x-1 was a dark matter blob. At that point Why not poltergeists?
- physicsdude 2y ago
  Axions can seem a bit goofy. One thing to know is that when talking about particle physics, we like to talk about particles, but "particles" are really a concept from classical physics. When doing quantum physics, one is fundamentally concerned with waves. If you've read any about quantum mechanics, you've heard of "wave/particle duality," which is something of a connection between the two pictures. Another thing to know is that axions should interact electromagnetically. The bottom line is that because axions would necessarily be very "light" (that is, very much not-massive), it is misleading to picture them as "particles" and better to picture them as "waves." So while it's true that axions would feel the electromagnetic field of an atom's nucleus, that's really just because it's an electromagnetic field. So to make an experiment which is sensitive by modern standards, you say "forget individual atoms, I'm just going to make a cavity and crank it up to large electromagnetic field." And that's exactly what is done in practice.
Enginerrrd 2y ago
I think white holes actually pop up from calculations outside of LQG as well. Specifically I seem to recall there's something using Einstein-Cartan as a basis, written by someone of note which predicts white holes as a permanent endpoint of evaporation. Then again, maybe it was rovelli? Alas, I can't seem to find the paper now. Google sucks and keeps dumbing down my query.

marcosdumay 2y ago

Shouldn't axions interact with atom nucleus? This rules out any interaction except for gravitational, right?

throwawaymaths 2y ago
To a certain floor. Of course a particle which only interacts gravitationally is still possible but that's the cosmologist's nightmare. It'd be basically impossible to prove it's existence and anything could happen (like a small but fast fairly massive ~asteroid mass clump of dark matter explaining poltergeists)
- ajross 2y ago
  > like a small but fast fairly massive ~asteroid mass clump of dark matter explaining poltergeists This is clever, but I have to believe the back of an envelope would show that a dark-matter scale distribution of "dark blobs" big enough to throw things around the room and frequent enough to be given names in human experience would be many, many orders of magnitude higher than the observed gravitational effects.
  - throwawaymaths 2y ago
    > have to believe A lot of weird shit gets floated around, like planet X is dark matter, or at one point someone suggested sag x-1 was a dark matter blob. At that point Why not poltergeists?
physicsdude 2y ago
Axions can seem a bit goofy. One thing to know is that when talking about particle physics, we like to talk about particles, but "particles" are really a concept from classical physics. When doing quantum physics, one is fundamentally concerned with waves. If you've read any about quantum mechanics, you've heard of "wave/particle duality," which is something of a connection between the two pictures. Another thing to know is that axions should interact electromagnetically. The bottom line is that because axions would necessarily be very "light" (that is, very much not-massive), it is misleading to picture them as "particles" and better to picture them as "waves." So while it's true that axions would feel the electromagnetic field of an atom's nucleus, that's really just because it's an electromagnetic field. So to make an experiment which is sensitive by modern standards, you say "forget individual atoms, I'm just going to make a cavity and crank it up to large electromagnetic field." And that's exactly what is done in practice.

Enginerrrd 2y ago

I think white holes actually pop up from calculations outside of LQG as well. Specifically I seem to recall there's something using Einstein-Cartan as a basis, written by someone of note which predicts white holes as a permanent endpoint of evaporation. Then again, maybe it was rovelli? Alas, I can't seem to find the paper now. Google sucks and keeps dumbing down my query.