Glynis said:
If everywhere in the universe is at above 0 degrees Kelvin, then there must be some degree of heat everywhere, so this could be considered a universal medium or not, and if what I heard about the sound of the big bang still reverberating throughout the universe is correct (see my contribution to
https://www.physicsforums.com/showthread.php?t=149924")
and sound can only propogatge in a medium then perhaps heat could be the medium
Heat isn't a physical entity in and of itself. It is a description of the energy of a material. It would be that material which provides the medium you're seeking.
The "sound of the big bang" is a bit of poetry that you're taking too literally. The big bang was an energetic event involving so much energy that it produced a complex soup of particles and photons. In principle, that soup should have been perfectly homogeneous, since as far as we know there was nothing to imprint any shadows or concentrations in any particular places. But quantum uncertainty and random fluctuations prevented absolute uniformity at small scales, and as the universe expanded, including inflation, those submicroscopic fluctuations resulted in density waves, and I think that's what you're referring to as sound.
Sound as normally understood means longitudinal vibrations in a fairly dense material, by the elements of that medium bumping into each other. Air is such a dense material for the sounds we hear. For the word sound to apply with all the physical connotation normally ascribed to it, the mean free path of the particles which make up the material medium would have to be very much less than the wavelength of the sound. Clearly in the vacuum of space that does not apply.
Also, light cannot be the medium to convey sound in this sense (though you can encode sound information in laser beams, it's secondary effects in the encoding and decoding equipment that produces the sounds you eventually hear). Photons don't bounce off each other like air molecules do -- they're not that kind of particle. Photons can pass right through other photons and so cannot be a medium to sustain longitudinal waves.
I suspect you're just starting to get into reading about physics, and you're looking at some popular books that are more intended to inspire awe in the reader than they are to teach physics. While public awareness of the beauty of physics is wonderful, it can also be superficial and misleading. It seems that without a good grounding in the fundamentals of physical processes, your interest in more advanced topics has caused you some confusion.
I'd recommend you start with conventional mechanics, kinematics and all the simple Newtonian stuff. The common example of billiards will give you an appreciation for working with force, momentum and energy. An appreciation of the conservation of energy and momentum is absolutely critical to understanding phycis, and this is a good way to get it. Afterwards you can move on to heat and thermodynamics, and electricity and magnitism, and eventually to relativity and quantum mechanics. The old science books of Isaac Asimov are excellent for this purpose, and would serve you very well if you can find them. They are fun to read and will teach you a lot without making it seem like work. They may not teach you the equations, but you can suppliment that kind of reading with textbooks if you like.
Then and only then will you be able to get out of the popular books both the awe and the science they contain. It's not quick and easy, but it is well worth it.
