The possibilities for dark matter have shrunk

Post by pfdietz » Wed, Aug 28, 2024, 12:46 PM UTC

physicsdude wrote: post #51

pfdietz wrote: post #49

Earlier quoted context omitted.

It's actually due to both (for different DM particle masses). https://physics.aps.org/assets/0ce5ba95-0367-46ce-890b-de3a4... (which is from https://physics.aps.org/articles/v14/96 )

This is absolutely correct, as there are no solar neutrinos with energy above ~20 MeV (but below that, the solars dominate). Thanks for the clarification.

The interesting thing is the physical process creating the floor is a fairly novel one, coherent scattering of neutrinos off nuclei. This is where the neutrino scatters off all the nucleons together, with the contributions adding coherently, rather than incoherent scattering off individual nucleons.

This process was first observed only fairly recently, at the Spallation Neutron Source using neutrinos from stopped pions. IIRC, they realized a service corridor under the target room would be unintentionally suitable for the experiment.

https://coherent.ornl.gov/

Post by rbanffy » Wed, Aug 28, 2024, 1:38 PM UTC

pfdietz wrote: post #80

rbanffy wrote: post #75

Earlier quoted context omitted.

I wasn’t thinking of the speed of the neutrinos, but the increase in encounter frequency. From a passenger’s perspective, the number of interactions per second will be much higher, not just because the ship is covering large distances and hitting more particles (although I’m not sure about that - it might cancel out) but hitting them more frequently from the crew’s perspective because of time dilation.

No large amount of time dilation is likely to be practical, even with laser propelled light sails or antimatter. And the heat load on the vehicle from running into interstellar matter would be very high. The more massive DM particle issue I discussed might be problematic even with very little time dilation.

Whatever tech is used, it'll need to be something really fancy (as in new, fancy laws of physics being bent in fancy ways) to make near light-speed travel feasible.

Even Alcubierre-White warp drives would create interesting problems because compressing spacetime in front of the ship would heat up whatever matter is there.

Unless something miraculous happens, I don't think we'll live to see these problems in real life, but, if we do, it'll be fun to work in solving them.

Re: The possibilities for dark matter have shrunk

Re: The possibilities for dark matter have shrunk