Raymond Tallis: Time Travel and Other Myths about Time

Agreed - space is filled with blackbody radiation! The ZPE is there too according to QFT (which I only know vaguely) but there doesn't seem to be any way to do anything with it.

Anyway, my point is that this radiation is to be expected anyway - it doesn't need a BB to 'explain' it.

David

I will refrain myself from going into QFT as I can't claim I understand it. However, I severely doubt that the characteristic blackbody spectrum observed in the CMB can be explained by vacuum energy, or that vacuum energy has sufficient intensity or energy to match that of the observed CMB photons.

I will refrain myself from going into QFT as I can't claim I understand it. However, I severely doubt that the characteristic blackbody spectrum observed in the CMB can be explained by vacuum energy, or that vacuum energy has sufficient intensity or energy to match that of the observed CMB photons.

Please forget the question of vacuum energy - as I understand it, it is more or less inaccessible. I am suggesting that space has a temperature and that if you allowed a hot object to sit in interstellar space, it would cool down by radiating until it reached the temperature of that volume of space - just as happened for the JWST. After that there is an equilibrium - photons of heat radiation are still emitted by the body, but an equal number of such photons arrive at the body and are absorbed.

David

Please forget the question of vacuum energy - as I understand it, it is more or less inaccessible. I am suggesting that space has a temperature and that if you allowed a hot object to sit in interstellar space, it would cool down by radiating until it reached the temperature of that volume of space - just as happened for the JWST. After that there is an equilibrium - photons of heat radiation are still emitted by the body, but an equal number of such photons arrive at the body and are absorbed.

David

In a complete vacuum, there is no matter, and therefore, there is no temperature. Temperature is a property of matter and depends on the kinetic energy of particles within a substance. In a vacuum, there are no particles to have kinetic energy, so the concept of temperature as we understand it does not apply. The absence of matter and particles means there is no temperature in a true vacuum.

So you must be referring to some matter being present uniformly and isotropic distributed in the entire universe for it to have a temperature (and immune to gravity to stay perfectly uniformly distributed forever) to provide an alternative explanation for the CMB.

There might of course be other explanations than Big Bang, but they are unlikely to be as mundane as you try to make them.

In a complete vacuum, there is no matter, and therefore, there is no temperature. Temperature is a property of matter and depends on the kinetic energy of particles within a substance. In a vacuum, there are no particles to have kinetic energy, so the concept of temperature as we understand it does not apply. The absence of matter and particles means there is no temperature in a true vacuum.

There may be no matter in a certain volume of space, but there will always be radiation. Measuring that and using Plank's law, you get a temperature. The JWST cooled to 25 K, so assuming that was the limit of its cooling, 25 K can be considered to be the temperature of the surrounding space! I know the concept sounds a bit weird, but my point is that space is never devoid of radiation - so looking out into space and finding some thermal radiation doesn't need an extra explanation, and therefore cannot be used as evidence of something else.

If there really is a difference between gas and the emptiness of outer space, how is this described in terms of an equation?

Using that equation (which I don't think exists), it would be possible to determine exactly how rarefied the gas can become before it lo-longer can be said to have a temperature. If we were only talking about the kinetic energy of the molecules, that distinction would not matter, but the energy in the form of far infra-red electromagnetic waves would seemingly have to be distributed differently in a pure vacuum as opposed to a partial vacuum!

Again, what I suspect, but unfortunately can't prove, is that the matter and radiation inside a box (real or imaginary) will store energy in accordance to Plank's law for some temperature T, assuming it is at equilibrium.

David