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Subluminal
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During the trip from their supernova, they passed through expanding space together. The photon says to the neutrino, "I think I've been redshifted."
What happened to the neutrino?
What happened to the neutrino?
DaveC426913 said:Two neutrinos pass through a bar...
bcrowell said:Wait, I was assuming this was a joke, and we were supposed to guess the punchline...?
marcus said:Roughly equivalent loss of momentum. That is also why dark matter has been able to cool and gradually collect in clouds. Dark matter particles would have started out with relativistic momenta. Expansion drained them of so much of their kinetic energy (as seen by an observer at rest relative to CMB) that we now call them *Cold* Dark Matter.
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marcus said:There is a paper on the arxiv about this which refers to a math derivation of it in Steven Weinberg's book Cosmology
Subluminal said:During the trip from their supernova, they passed through expanding space together. The photon says to the neutrino, "I think I've been redshifted."
What happened to the neutrino?
BillSaltLake said:Redshifted also, by the same ratio. (Some of the redshift is due to climbing away from the SN).
marcus said:Roughly equivalent loss of momentum. That is also why dark matter has been able to cool and gradually collect in clouds. Dark matter particles would have started out with relativistic momenta. Expansion drained them of so much of their kinetic energy (as seen by an observer at rest relative to CMB) that we now call them *Cold* Dark Matter.
EDIT: didn't see Bill SL answer. I didn't need to post, he said what needed saying.
Jack21222 said:Have the first neutrinos really slowed down to the point they're considered CDM? I thought those neutrinos were still considered "hot" even after the expansion.
DaveC426913 said:Two neutrinos pass through a bar...
Flatland said:...of solid iron.
Jack21222 said:Have the first neutrinos really slowed down to the point they're considered CDM?...
marcus said:My guess is that the temperature of the primordial neutrinos is about 2 Kelvin. Somebody here probably knows the more precise estimate. It would be similar to the CMB temperature but a little cooler.
A photon is a fundamental particle of light, while a neutrino is a subatomic particle that has no electric charge and very little mass.
No, this phrase is simply a joke or a play on words and does not refer to actual particles going into a physical bar.
This phrase is often used as a humorous way to talk about two seemingly unrelated things coming together.
Photons and neutrinos are both fundamental particles in the Standard Model of particle physics, but they have different properties and interactions.
The use of a bar in this phrase is simply for comedic effect and has no scientific significance.