A multiquestion on the Universe’s stuff getting created/destroyed

Factual Questions
1

The idea that the Laws of Thermodynamics do not apply to the entire Universe has set me thinking. Is the amount of stuff in our Universe a constant one? Maybe not. Or maybe it is. Or maybe nobody knows and will never know. It’s all speculation then. And since the Laws of Thermodynamics do not apply to speculation, it can be limitless. Or can it?

I’ll try to get a little more specific:

  1. Does the Big Bang break the Laws of Thermodynamics since so much stuff got created apparently out of nowhere/nowhen?
  2. Is matter/energy still being created at the moment?
  3. Is matter/energy being destroyed at the moment (by irreversibly being turned into heat, for instance)?
  4. Since we know so little about dark matter, is it possible that observable matter and dark matter should form a system of communicating vessels so that matter never gets really created/destroyed?
  5. Since dark energy is accelerating, does that count as an increase in the amount of energy in our universe?
  6. Will the accelerating dark energy cause (at least some) observable matter/energy to vanish?
  7. Since additional space has been created since the Big Bang, can we say that space is a result of energy exertion? Is space a property or something in itself? Once created, can it be destroyed?
  8. Since physics deals with spacetime these days (rather than just space), I wonder whether time gets created as well? Does this question even make sense?
2

1: The Big Bang model actually describes the expansion of the Universe after the initial point. That does all follow the laws of thermodynamics. The initial moment itself, we have no idea what laws it might or might not follow, or even how to describe laws that it might follow.

2: It depends on precisely what you mean (more on this in a bit). But whatever happened right at the initial moment (if “happened” is even the right word), it’s not an ongoing process.

3: Energy that’s turned into heat is not destroyed. Heat is a form of energy. It’s not a very useful form of energy, but it is energy. I suppose you could talk about usefulness being destroyed when other forms of energy are converted to heat, and yes, that goes on all the time everywhere.

4: You mean, can “normal” matter be converted to dark matter, and vice-versa? Probably. In fact, I can think of at least one way to do so that would be certain to work. But it can’t be very easy, or we would see evidence of it happening.

5: In a sense, yes. Again, more on that in a bit.

6: We can’t completely rule out anything involving dark energy, since we know so little about it, but if anything, the reverse seems more likely (dark energy turning into “ordinary” matter), and it’s speculated that something much like that already happened long ago.

7: I’m not sure that I would speak of space being “created”, but we can certainly say that it’s expanded, and it could in principle contract. So far as we can tell, it (well, spacetime) is a thing in and of itself.

8: Again, it’s easier to say “expanded” or “contracted”, rather than “created” or “destroyed”. But yes, time can and does expand and/or contract, just as space does.

Now, onto the more detail I promised for a couple of questions. One of the laws of physics, and the First Law of Thermodynamics, is the law of conservation of energy. This law is, so far as we can tell, absolute, but it does not mean what most people think it means. It does not state that energy cannot be created or destroyed. What it actually states in a nutshell is that, if you have a box, and the energy content of the box changes, it’s because of energy flowing through the walls of the box (though of course, the actual Law is stated mathematically). Compare, for instance, to people: You can have a box containing some number of people, with no people going into or out of the box through the walls, and yet have the number of people in the box change, if they die or reproduce, so people are not conserved in this way.

Now, what does this state about the Universe as a whole? Not much, because the Universe is not a box. The Universe doesn’t have any walls, and it’s possible for something that might be defined (if you’re very careful about how you write your definitions) as “the energy content of the Universe” to change. For instance: You would expect that as the Universe expands, the density of energy in it would decrease. Specifically, if it expanded by a factor of 2 in all directions, you’d expect the density to go down by a factor of 8. And this does seem to happen, with matter. But the density of radiant energy (like light), while it does go down, goes down by a different factor. And dark energy (which seems to be most of the energy in the Universe) doesn’t change its density at all, no matter how space expands or contracts. So if space gets twice as big, and any given volume still contains the same amount of dark energy, one could say that dark energy is created.

Now, what I mentioned about dark energy maybe turning into other forms: When the Universe was very young, there was a lot more dark energy (or something that behaved very much like dark energy). How much more? Let’s just say that, however much more you’re thinking of, it was a lot more than that. This was an era that’s referred to as “inflation”, and it was characterized by extremely rapid acceleration of expansion. But then it stopped. And the speculation is that the way that it stopped is that (almost) all of the dark energy converted into other forms, and that those other forms of energy eventually coalesced into, well, us (and everything else). Now, we don’t know why we still have any dark energy at all. Maybe what’s left is some different sort of stuff that won’t convert into other forms of energy (and we don’t know why there was so little of that kind of stuff, relative to the other kinds). Maybe what’s left is the same kind of stuff (and we don’t know why it didn’t convert at the same time that the rest of it did). Maybe it will eventually convert to other kinds of energy, for one reason or another. This is just one of the many things we don’t know about dark energy.

3

Could you expand on this please? What’s the method you envision? I love your contributions here!

4

The method I envision is to throw the matter you don’t want into a black hole, wait for the hole to evaporate, and then sift through all of the stuff produced in the evaporation for whatever fraction is the kind of matter you do want. Which, yes, is horribly slow and inefficient, but it’d work.

There may or may not be some other method that works better, depending on precisely what the properties of the dark matter are. All we can say definitively about dark matter is that it does interact gravitationally, and it doesn’t interact electromagnetically. It might or might not interact via the weak interaction. The black hole idea will work for anything that interacts gravitationally, so we’re OK there. If it also interacts via the weak interaction, then we could convert it in that way, but that’s, well, weak, and so it’d be tough to convert it (though still far, far easier than the black hole method). If it doesn’t even interact via the weak, though, there aren’t many options left. I suppose it’s possible that there are multiple kinds of dark matter, which interact via some new, hitherto-unknown fundamental interaction, and some of which interact via weak: In that case, you could maybe convert the nonweak kind to the weak kind using that new interaction… but since we don’t even know if that new interaction exists, we have no clue how to carry out that conversion.

5

If there were dark particles and anti-dark particles, could they annihilate each other and form regular matter in pairs?

6

Only if there is some fundamental interaction which applies both to the dark particles and the “regular” particles.

For example: You can take a muon and an anti-muon, and react them to get an electron and a positron at very high energies. This happens because the muons interact with photons, and so do electrons. Roughly speaking, the muons turn into photons, and then the photons turn into electrons. But you can’t do that with muons and neutrinos, because neutrinos don’t interact with photons. You can turn a muon-antimuon pair into a neutrino-antineutrino pair, using the weak force (with Ws or Zs as the intermediary, instead of photons), because neutrinos do interact via weak, but it’s much harder to do that, because the weak is so much weaker than electromagnetism.

Or going the other way: If you react a proton and an antiproton, you can get photons as the result, since quarks do have a charge (i.e., they interact electromagnetically). But you’re far more likely to get a bunch of pions (which will eventually result in a mix of photons and neutrinos, mostly the latter), because quarks also interact via strong, and that’s (as you might guess) stronger than electromagnetism, and hence reactions that can proceed using strong are much easier than ones that proceed using electromagnetism.

7

Well, there is one — namely gravity. But gravity-mediated pair production is probably even more inefficient for creating dark matter than your “throw everything into a black hole” method is, since gravity is much much much weaker than the other three fundamental forces.

8

Does that mean if there are dark particles and antiparticles they could only annihilate by forming graviton pairs, unless the interact weakly? But then if they do form graviton pairs, couldn’t those form electron positron pairs (in principle)?

Or are we stuck with all the lightest dark matter particles there are?

I assume no one knows.

9

Personally, I suspect that there are other fundamental interactions which affect none of the known particles, only dark matter particles. If that’s the case, then heavier dark matter particles might annihilate or decay into lighter ones, or even into dark massless particles of some sort (“dark photons”). But that’s all just pure speculation; there’s no actual evidence of such “dark forces”.