According to my measly understanding of the universe, when particles hit one another, some of their kinetic energy is transformed into heat. But when we heat particles (for instance, putting a bucket of water on a stove) we can see they gain kinetic energy (the water-particles start fidgeting about until they turn to gas, which moves freely).

So, heat transforms to movement, movement transforms to heat. Cool. Which came first and started the chain?

I tried to solve it by imagining a dude standing inside a bubble, watching the big-bang (he has a very special bubble, called Mr. Bubble). When the universe went all BOOOOM, at that first time-unit, I tried thinking about what would happen to the bubble. Having only a bit of world experience and a bit of logic, my first thought was "it'd heat up". But I hardly think that qualifies as an actual answer.

Am I getting it completely wrong? Will Mr. Bubble be blown back but remain at present temperature? Is movement a form of heat? Or are all kinds of energy essentially the same thing, with different manifestations? Or maybe Mr. Bubble was the culprit all along?

  • $\begingroup$ there is a sweet conceptual misunderstanding that Bailerlein talks about in his Thermo book, I'll paraphrase, since I think it helps remove some of the internal conflict: "heat is a verb, not a noun." There is no "thing" called heat... $\endgroup$
    – kηives
    Nov 8, 2012 at 0:18

1 Answer 1


The universe is much more complex than you think :-)

Assuming you believe in inflation, when inflation ended it had diluted the universe so much that hardly any matter was present. So to a good approximation there was no matter in the universe at this time. The inflaton field then decayed into matter in a way that we can't be sure of (because we don't have a proven model for the process). However we can be sure it produced lots of particles with high energies i.e. a high temperature. The decay products of these particles are what we see around us today.

Your idea of watching the Big Bang from inside a protective bubble isn't possible, not even in principle. The Big Bang didn't happen at a point that you could watch. It happened everywhere in the universe at the same time. Also it wasn't an explosion. It was the process by which the universe expanded from infinite density and zero spatial separation to something like the universe we see today.

We don't really believe the density was infinite and spatial separation zero at the moment of the Big Bang, but we'll have to wait for a working theory of quantum gravity to find out what actually happened.

  • $\begingroup$ Of course, the bubble idea was more than impossible, was a mere thought experiment. So, if I understand your explanation correctly, neither came "first" - there were only energized particles, and these energies transformed into "lesser" forms (heat & movement)? $\endgroup$
    – Zirak
    Nov 7, 2012 at 19:14
  • $\begingroup$ I'm not sure what you mean by "lesser forms (heat & movement)". Heat is an emergent property from random particle kinetic energies but it is in no sense "lesser". When inflation ended particles were created with high kinetic energies, i.e. high temperature, and all that has happened since is that the expansion of space has red shifted everything so the universe is now on average a lot cooler. $\endgroup$ Nov 8, 2012 at 6:48

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