Gas pressure at rest is also proportional to the number of molecules. (PV=nRT) Which at constant volume and known composition basically means mass, i.e. how much gas you’re hitting, which does matter.
That said, I still don’t get the exact calculation, so I’m not sure that it’s correct reasoning.
My argument is typical physicist fare—note that the answer has a spurious dependence, therefore it’s wrong. That it also has one of the right dependences wouldn’t matter.
I was off on what the implied steps in the derivation were, so it didn’t have the problem I described.
At the interstellar temperatures (2.7K or so) the ideal gas pressure has negligible contribution to the kinetic friction at near-light speeds. The situation is somewhat different for photon gas, where pressure is always large, of the order of density speed of light^2, not density RT. But in the end it does not matter, since the CMB density is much much less than the dust density even in the intergalactic space.
Gas pressure at rest is also proportional to the number of molecules. (PV=nRT) Which at constant volume and known composition basically means mass, i.e. how much gas you’re hitting, which does matter.
That said, I still don’t get the exact calculation, so I’m not sure that it’s correct reasoning.
My argument is typical physicist fare—note that the answer has a spurious dependence, therefore it’s wrong. That it also has one of the right dependences wouldn’t matter.
I was off on what the implied steps in the derivation were, so it didn’t have the problem I described.
At the interstellar temperatures (2.7K or so) the ideal gas pressure has negligible contribution to the kinetic friction at near-light speeds. The situation is somewhat different for photon gas, where pressure is always large, of the order of density speed of light^2, not density RT. But in the end it does not matter, since the CMB density is much much less than the dust density even in the intergalactic space.
OK, I got it, I think. I was confused both about the question and the answer :-)