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skulblaka@sh.itjust.works 2 days agoThis does, however, lead to the existence of “local groups”.
Meaning that, there is a local group of celestial bodies that we may theoretically be able to visit at some time in the future, which are held somewhat together by gravitational forces which help to counteract the expansion of space. But anything outside of that local group will be expanding away from the group at greater than the speed of light.
Meaning, effectively, that the universe is going to be / is already separated out into small pockets of local neighbors, who will never be able to reach other local groups unless they invent some sort of much faster than light travel. The universe is very, very large, but the percentage of the universe that is physically reachable by us is quite small.
Personally I find that to be one of the more disappointing true facts about the universe.
SpacetimeMachine@lemmy.world 2 days ago
Exactly, there will be causally disconnected pocket universes in the future. I’m thankful we still live in a time when we can see the rest of the universe. Creatures alive in 100 billion years might have no way to figure out how the universe started, or that there is anything outside of their local cluster at all.
wonderingwanderer@sopuli.xyz 2 days ago
Do we though? How do you know our entire known universe isn’t just a local cluster?
If we could see the entire universe, then somewhere in the center we’d be able to point to the origin of the Big Bang. Since we can’t, that implies we’re only looking at a section of the universe analogous to a portion of the surface of a globe.
SpacetimeMachine@lemmy.world 2 days ago
Someone else already replied probably better than I can, but this is one of my favorite subjects to study.
The big bang didn’t really start in a place, it happened at a point in time. As we look at all of the galaxies around us (minus the close ones we are gravitationally interacting with) they are all moving away from us, so either 1) we are exactly where the big bang took place (vanishingly unlikely) or 2) the big bang happened everywhere and all of space is expanding from that event.
We can actually see the first light ever released in the universe (not from the big bang, as the universe was a dense plasma for the first ~400,000 years until the recombination era) as the cosmic microwave background radiation. And it is (relatively) even in all directions, minus some minor temperature variations.
I highly suggest looking at a channel on YouTube called PBS Spacetime. They have videos going back years and years that dive into great depth on all of these topics!
wonderingwanderer@sopuli.xyz 2 days ago
Yes, I already responded to the other comment. Summarily, I don’t find their argument convincing.
To add, it’s not surprising that everything is moving away from us. To use the other commenter’s balloon analogy, as the balloon expands, so do the circumference and surface area. So any two points on that surface will be moving away from each other as it does so.
It’s also not surprising that the cosmic microwave background radiation appears relatively uniform. 14 billion years of expansion, and we can only observe or “neighborhood” of the universe, mind-bogglingly large as even that is. 14 billion years of moving on a more or less stable trajectory. We can’t see far enough backwards to view the origin point.
Also, if the background radiation came from the big bang, then it would have outpaced us as our galaxy slowed down and the radiation continued moving at the speed of light. This suggests that the background radiation we witness was emitted after the energy that coalesced into our galaxy, and is just now catching up/surpassing us. Unless it’s reflecting off of something further outward, and on it’s way back.
Is there any known pattern to the actual direction of cosmic background radiation? Is it aligned in any way or more or less random?
thebestaquaman@lemmy.world 2 days ago
By the nature of the Big Bang and the expansion of the universe, everywhere is at the origin. That is, if we believe that the universe started out as a singularity, and that the expansion of space itself is what causes that singularity to grow, then every point in the universe originated from the exact same point, and that nothing has “moved”, in the sense that the point itself is expanding. Thus, every place is at the “origin”.
To use the balloon analogy: Draw a small dot on the balloon, that dot is the entire universe as a singularity. Now, inflate the balloon so the dot grows, and try to determine the “origin” of the dot. Of course, you could point to the centre of the dot, but I would argue that if the initial dot is infinitely small (a singularity) then every point on the expanded dot in fact originates from the exact same point.
This does cause a bit of a headache because we’re arguing that a zero-dimensional thing suddenly became 3-dimensional. I’m honestly not sure how astrophysicists reconcile that, but I seem to remember reading that they boil down to saying “we know what happened <some extremely short time> after the Big Bang, but we don’t really know anything about what happened at t=0” per my understanding, even the concept of time breaks down when you go to t=0, so it becomes impossible to get to t = 0 + h.
wonderingwanderer@sopuli.xyz 2 days ago
That doesn’t make any sense, down to the geometric level.
By the nature of expansion itself, there is an origin point somewhere in the center. That holds especially true in the case of uniform expansion.
If “every point in the universe originated from the exact same point” then that origin point is somewhere in the center of the universe, and tracing the trajectories of every point backwards should intersect somewhere very close to that point.
Your balloon analogy supports this thesis. No matter how much the dot expands, the center of the dot is where it originated. Yes, every point on the expanded dot originates from the same point. That point is in the center.
Saying “sometimes physics is mindboggling” in order to rationalize invalid leaps is not a strong argument. Yes, sometimes physics is mindboggling. But that’s no reason to handwave away inconvenient facts whenever we’re trying to argue for something illogical. You need rigorous evidential support to justify a mindboggling conclusion, as is the case with quantum mechanics. Speculative or theoretical physics however cannot simply fill in the gaps with this sort of handwaving.
Honestly, if the concept of time breaks down when you look at t=0, then that only tells me that the idea of t=0 itself is invalid and needs to be abandoned. Especially since there’s no evidential support for that theory, it’s entirely speculative, and has only been justified with the explanation that “We don’t have any better ideas.”
Time didn’t just magically start at some random point before which time didn’t exist. And space didn’t just magically expand into 3 dimensions before which there was only 0. Energy and matter didn’t just suddenly appear without any prior cause initiating some action. All of those things would require violations of the laws of thermodynamics. And in the absence of far more evidence than ever has or even can be found, this “best guess” is full of more holes than many people seem ready to admit…