**Ask a monkey a physics question thread**

[MadMojoMonkey]

But if we're to assume the universe had a start, and that start was a singularity containing all the energy that exists, then we have the same problem. There is a transition from no space and time, to space and time.

To say this transition cannot happen is the same as saying the universe had no beginning.

You said it correctly that we assume the universe had a start. We assume this start was a singularity. We don't know that.

The most popular model rising in support among cosmologists now is not of a singular point going all Big Bang. The exponential expansion of the universe doesn't have to start after the Big Bang. It could be the entire Big Bang. That is to say, the Universe may extend into the infinite past to where it was a singularity, and it has been undergoing exponential expansion forever.

Either way, the symmetry of having a beginning and an end is nice from a human storytelling perspective, but I don't see any reason the Universe should follow rules of plot.

No idea, but this does remind me of a long forgotten recurring dream I had as a young child, it's hard to explain but there was basically a line moving through space and on the one side everything was normal and on the other side it was black, this line was basically consuming the universe. I don't think that happens but it's interesting that this caused me to remember a childhood dream.

I mean, I would imagine a sudden collapse. If there's nothing but photons, it becomes meaningless to even talk of the speed of light. Speed through what? At the instant of the last interaction, spacetime suddenly collapses into a singularity. All of it, instantly. Nothing else can make any sense to me.

I have real difficulties with the simultaneity, here. You're invoking GR to support this hypothesis, but you're ignoring GR in the conclusion.

If there's 1 thing the Universe loves to do to us as physicists, it's remind us that all equivalent descriptions are equivalent. I.e. if you can describe something with a function, and there are mathematically equivalent ways to construct that function, then the Universe "sees" all those descriptions as valid, and will do anything any of those descriptions allows.

Like the fact that linearly polarized photons have their electric fields disturbed only parallel or anti-parallel to some vector (which is itself perpendicular to the direction of propagation and the disturbances in the magnetic field). However, mathematically, a sine wave in a plane is equivalent to the sum of 2 counter-rotating helices. We observe interactions which can only be described as those 2 helices interacting with 1 molecule in different ways, rotating the plane in which the linearly polarize photon's electric field disturbances occur.

So if there is a mathematical equivalence to a photon being described as a disturbance in the EM fields that propagates through spacetime, then I have a very strong suspicion that description will always be a way the Universe "sees" what photons are.

What acceleration is this frame undergoing?

I only know for certain that Einstein said so. What follows is some guesswork on my part that seems to make some sense of why.

The frame undergoes no accelerations, not because the sum of forces = 0 N, but because all the laws of forces and motion break down when you have infinite relativistic gamma factor.

You could say that with infinite relativistic mass, no matter how big a force you apply, F = ma will mean that a is always 0, because m is infinite. So no matter what force is applied, it cannot be enough to accelerate any mass moving at c.

Or you could say that with infinite time dilation, there is no passage of time that allows a force to apply a change in momentum via F = dp/dt. Anything described mathematically with a d/dt in it becomes undefinable when dt can only equal 0 s.

We also have to understand that we know that we don't understand physics completely yet. We can't actually expect to successfully predict what happens in the very late universe based on a current understanding of physics that is yet to unify QM and GR. There's always got to be a certain amount of philosophy to physics. The goal is to convert philosophy into fact over time. Science starts with banging rocks together. It's all philosophy and no fact. If we ever achieve complete knowledge, then it's all fact and no philosophy. The relationship between physics and philosophy is kinda like converting potential energy into kinetic energy.

So I don't think it's unreasonable to answer the question of "what else could happen" with "something", and to then speculate. I assume the universe had a beginning, and it certainly appears that it did, so I assume it has an end. And since it can be argued that the beginning and end are indistinguishable from one another, ie all the energy compressed into a singularity, then my best guess on what happens next is a new big bang.

A complete decay into radiation takes me down this path. I can imagine a heat death that is basically like counting to infinity, where it approaches heat death while never actually getting there, but the problem I have here is that it implies there was a start but not an end. It also implies an infinite universe with infinite time, because otherwise we're not counting to infinity, just a very large number.

So for me, heat death means a total decay, followed by a collapse of space and time since there is nothing left to observe it, there is no more mass to cause gravity, there is nothing left that experiences time. At this point all of the photons, which is all of the energy in the universe, are in the same place at the same time... a singularity, and, based on observations from the very distant past, I assume that a singularity that contains all of the energy that exists is not stable and will explode.

Or we're counting to infinity. It's one or the other.

This is all pretty great thinking, IMO. It's fine to be lead by your suspicions, or your intuition, or whatever you want to call it. I'd even argue that this purely subjective drive is the backbone of excellent science. Just follow it up with research and experiment and try to prove yourself wrong. If you can't... you might be on to something.


The Universe doesn't seem to have any issues at all with things moving ever-toward infinite values.