No, it doesn’t follow; if it does, please explain. It’s quite possible that “that which is” is finite. (Personally, I suspect that even if our Universe is finite, there is an infinite number of them – not necessarily the “multiverse”. But that’s just a guess, not a fact, and not a consequence of the definition of “everything”.
According to “The Fabric of the Cosmos”, If the universe is infinite now, it was then, in which case the above statement is not correct.
Oh my – something I never gave any thought to. It’s obviously true if the universe is finite that it happened “everywhere” (one point) at once. But if it’s infinite … then, what does it even mean to say that it happened everywhere at once?
BTW, is the jury in regarding whether the Universe could have existed (in some unknowable state) before the BB? I understand that theory predicts we can’t say much about it if it did. And yet, if black holes preserve information, might a BB do so as well?
The Big Bang is popularly portrayed as an explosion radiating outward from a point. This is very misleading.
Think of it this way instead. When the universe popped into existence it was infinite in extent. Everywhere it was very dense. Instantly the density started dropping. From inside the universe, this drop in density manifests itself as a physical expansion of space. But the universe is not getting bigger (it’s already infinite) and its not expanding into anything (because the universe is all there is).
It depends what you mean, if you mean is it possible for an object that is currently in our observable Universe to not be in our observable Universe at some future point: then you are correct it is not possible to leave the observable universe in any model where the concept exists.
I believe anyway as I can’t think of any possible loopholes that don’t involve FTL travel of some sort. I noticed on the big rip article on Wikipedia it’s claimed (or at least implied) that the size of the observable Universe shrinks to zero in a finite time where expansion is governed by phantom energy. However I am pretty certain this is a mistake, the observable Universe actually expands to an infinite size in a finite time in the big rip scenario and it’s the event horizon which shrinks to zero.
Yeah, that’s what I meant, I was thinking if a future Columbus tried this, we’d always be able to see him. And where he went. Quite boring. But I guess he’d be able to see beyond our observable universe.
Of course the observable Universe is getting larger both in terms of the proper and co-moving distances. The current edge of the observable Universe is about 46 billion light years away, but in the future we could in theory see galaxies that are currently just over 60 billion light years away (though we would see them as they were in the very early Universe). If we set off on a rocket ship now at a speed arbitrarily close to the speed of light I believe we would eventually (again in theory) be able to see galaxies that are currently about 80 billion light years away.
It doesn’t make snese to talk about how fast the Universe expands in terms of an actual speed. But what it does tell us is that the edge of the observable Universe has been moving away from us on average over the history of the Universe at just over 3c (the age of the Universe is ~13.8 billion years).
That is confusing. If it is moving away from us at 3c, faster than light, how could it be observable? By definition, I would think that observability would have to be constrained by the light cone. What are the dynamics of super-c travel, with respect to the light (information) emitted by such bodies, does special relativity have anything to suggest about that?
After light that would eventually reach us left that spot, the spot continued to recede away from us, so it’s further away now than it was at the time the light was emitted.
The OP did not really mention the speed, so let’s assume he got into a ship powered by an Alcubierre drive. He travels arbitrarily faster than c, but his local velocity is always less than c, or he may even be stationary w.r.t. the bubble that propogates his ship.
Given this, the ship would eventually overcome the expansion of the universe, and reach galaxies that would be otherwise permanently beyond the light horizon.
Question then is, what does he see? Does he see the Big Bang? Assuming the BB expanded as a bubble, ordinary intuition suggests there would be a “wall” that marks the boundary of the Universe - a wall of radiation that we could observe if only we could move fast enough beyond c.
Maybe a basic question first: my ship, powered by the Alcubierre drive, is moving at 40c. Would I still see photons moving away from me at c? Or would I eventually overtake them? I guess this is critical to understand.
It is definitely confusing. Firstly I think I would largely ignore this particular ‘3c’ figure I gave as it’s largely irrelevant to your concern for a whole host of reasons as it really is just the radius of the observable Universe divided by the age of the Universe.
However it does happen that if we look into your concern a bit more, it doesn’t diminish at all because it just so happens that co-incidentally galaxies on the furthest reaches of the observable Universe are receding from us at bit over 3c. That is how fast they are receding now though, and in fact the furthest light that is reaching us now was emitted from those galaxies* when they were receding from us at about 60c(!!!)
If anything you may now be even more confused,however the recession velocity of the space that the light travel through drops off for several reasons, so the question as to whether the light reaches us becomes does the recession velocity of the space it is travelling through drop off quick enough to allow it to get to zero?
These receeding stars and galaxies-at the vlocities they are travelling at, their light should be shifted way into the RF frequency regions. Is that the “background noise” we interpret at the primal radiation from the “Big bang”?
As I said above, the popular depiction of the Big Bang as a bubble expanding from a point is very misleading. The universe began with every point in space in a hot, dense state. The universe then began expanding and it became cooler and less dense. But there was no “wall” marking its edge.
The background noise (the CMB) doesn’t come from stars and galaxies. It comes from the cloud of superheated plasma that filled the universe for the first several hundred thousand years of its existence.
When we look far away (and farther back in time) we see:
Stars and galaxies.
A big void where the universe was cool enough to be transparent, but stars hadn’t formed yet.
A wall of opaque superheated plasma.
The red-shifted light from that plasma is the Cosmic Microwave Background.
The universe is not speeding up in its expansion as Einstein posited it would. Instead it is decelerating. Could this be a precursor to an accelerating contraction? If so, all we’ll have to do is wait a while and perhaps the edge of the universe will come to us.
