5 ms·

Neutrons bonk into stuff. If you're at a rave in a 100ft by 100ft warehouse, you look around and see four other people, but you keep bonking into ... something

Neutrons bonk into stuff. If you're at a rave in a 100ft by 100ft warehouse, you look around and see four other people, but you keep bonking into ... something ... that you can't see every inch you move, you would surmise something is up. If dark matter were a cloud of slow neutrons, we would know quite a bit about it. Actually we wouldn't because we'd all be dead, but that's a different story.

frongpik 6y ago
How would they bonk onto anything? A neutron is a tiny particle 50000 smaller than a hydrogen atom. Without an electric charge, it would float straight thru anything and we wouldn't know.
- magicalhippo 6y ago
  Neutrons have a nucleus, just like a proton, and that would bonk into things. Yes the chance[1] of doing so is much less due to it having an effectively smaller radius, but on the other hand there would have to be a _lot_ of them to explain dark matter. There's also a lot of stuff for them to bump into. The interstellar medium is filled with diffuse gas, and there's there's highly energetic events like jets from black holes which when slamming into the neutrons surely would lead to some observable effect. [1]: https://en.wikipedia.org/wiki/Neutron_cross_section#Typical_cross_sections https://en.wikipedia.org/wiki/Neutron_cross_section#Typical_...
  - frongpik 6y ago
    Iirc, we'd only need 10 neutrons per each hydrogen atom to explain the dark matter gravity. OK, if neutrons would be observable, are there any weird visual effects in galaxy cores that could be attributed to such neutron clouds?
    - magicalhippo 6y ago
      You say "only" but that's a _lot_ of neutrons, and space is vast. For one, I'd be very surprised if they didn't bump into each other, cooled down and clumped up like normal matter, which is precisely the opposite of what we expect from dark matter based on observations. Secondly we know[1] from nuclear experiments[2] what happens when neutrons interact with matter. I'm certain a nuclear scientist could list a bunch of effects we'd see if a whole lot of neutrons were hanging around black holes and similar. The whole point of dark matter is that observations show it interact extremely little, if any at all, with regular matter. [1]: https://en.wikipedia.org/wiki/Neutron_scattering https://en.wikipedia.org/wiki/Neutron_scattering [2]: https://en.wikipedia.org/wiki/Neutron_diffraction https://en.wikipedia.org/wiki/Neutron_diffraction
      - frongpik 6y ago
        Neutrons visibly interact with matter, but only when there's a lot of that matter, e.g. reactors use neutrons to heat water. I'm yet to read the two links you provided, though. The story is different in the interstellar space. The only matter there is sparse gas and neutrons, even lots of them, would have little opportunity to bounce into each other or those gas atoms. Those neutron clouds could eventually form asteroid-like rings around galaxies: invisible, but massive. For the same reason, every massive object, including our planet, would have such a ring. That's a falsifiable hypothesis. As for the black hole argument, there could be two explanations: first is that neutrons that are nearby don't get to stay too long and either transform into protons and become visible gas, or fall into the black hole; second is that neutrons that are really far, light years away, could happily orbit around the black hole unnoticed and if there's enough of them, we would see subtle gravitational lensing effects. There's another valid point against neutrons: their lifetime is only 10 minutes. However neutrons and protons are two particular compositions of quarks. Are there reasons why quarks can't form a stable neutral particle in the interstellar space? That particle would be much like a neutron, but stable. The reason I'm pushing for this idea is that there's an odd flyby effect: it causes spacecrafts to accelerate and decelerate slightly. We could use those observations to calculate the precise shape, mass and velocity of that "neutron ring", make a satellite fly in the opposite direction and observe if there's strange heating of water or other reactions that could be caused by neutrons. Since it can visibly accelerate a spacecraft, there should be a good deal of those neutral particles and thus they should visibly heat up water. I'm not a physicist, but this seems a way simpler explanation of dark matter than "axion fields" or whatever is currently trending.

frongpik 6y ago

How would they bonk onto anything? A neutron is a tiny particle 50000 smaller than a hydrogen atom. Without an electric charge, it would float straight thru anything and we wouldn't know.

magicalhippo 6y ago
Neutrons have a nucleus, just like a proton, and that would bonk into things. Yes the chance[1] of doing so is much less due to it having an effectively smaller radius, but on the other hand there would have to be a _lot_ of them to explain dark matter. There's also a lot of stuff for them to bump into. The interstellar medium is filled with diffuse gas, and there's there's highly energetic events like jets from black holes which when slamming into the neutrons surely would lead to some observable effect. [1]: https://en.wikipedia.org/wiki/Neutron_cross_section#Typical_cross_sections https://en.wikipedia.org/wiki/Neutron_cross_section#Typical_...
- frongpik 6y ago
  Iirc, we'd only need 10 neutrons per each hydrogen atom to explain the dark matter gravity. OK, if neutrons would be observable, are there any weird visual effects in galaxy cores that could be attributed to such neutron clouds?
  - magicalhippo 6y ago
    You say "only" but that's a _lot_ of neutrons, and space is vast. For one, I'd be very surprised if they didn't bump into each other, cooled down and clumped up like normal matter, which is precisely the opposite of what we expect from dark matter based on observations. Secondly we know[1] from nuclear experiments[2] what happens when neutrons interact with matter. I'm certain a nuclear scientist could list a bunch of effects we'd see if a whole lot of neutrons were hanging around black holes and similar. The whole point of dark matter is that observations show it interact extremely little, if any at all, with regular matter. [1]: https://en.wikipedia.org/wiki/Neutron_scattering https://en.wikipedia.org/wiki/Neutron_scattering [2]: https://en.wikipedia.org/wiki/Neutron_diffraction https://en.wikipedia.org/wiki/Neutron_diffraction
    - frongpik 6y ago
      Neutrons visibly interact with matter, but only when there's a lot of that matter, e.g. reactors use neutrons to heat water. I'm yet to read the two links you provided, though. The story is different in the interstellar space. The only matter there is sparse gas and neutrons, even lots of them, would have little opportunity to bounce into each other or those gas atoms. Those neutron clouds could eventually form asteroid-like rings around galaxies: invisible, but massive. For the same reason, every massive object, including our planet, would have such a ring. That's a falsifiable hypothesis. As for the black hole argument, there could be two explanations: first is that neutrons that are nearby don't get to stay too long and either transform into protons and become visible gas, or fall into the black hole; second is that neutrons that are really far, light years away, could happily orbit around the black hole unnoticed and if there's enough of them, we would see subtle gravitational lensing effects. There's another valid point against neutrons: their lifetime is only 10 minutes. However neutrons and protons are two particular compositions of quarks. Are there reasons why quarks can't form a stable neutral particle in the interstellar space? That particle would be much like a neutron, but stable. The reason I'm pushing for this idea is that there's an odd flyby effect: it causes spacecrafts to accelerate and decelerate slightly. We could use those observations to calculate the precise shape, mass and velocity of that "neutron ring", make a satellite fly in the opposite direction and observe if there's strange heating of water or other reactions that could be caused by neutrons. Since it can visibly accelerate a spacecraft, there should be a good deal of those neutral particles and thus they should visibly heat up water. I'm not a physicist, but this seems a way simpler explanation of dark matter than "axion fields" or whatever is currently trending.