Comment on wat
thebestaquaman@lemmy.world 2 days agoBy 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…
thebestaquaman@lemmy.world 1 day ago
This is where I’m disagreeing. Since space itself is expanding, every point “originated” where it currently sits, and has “expanded in place” so to speak. You can’t really imagine this as an expanding bubble (the balloon analogy was bad here), since a bubble necessarily expands into existing space. In our case, the bubble itself is the space.
That’s where you get a problem. Space is expanding, so if you pick an arbitrary point in space, you’ll observe that the universe appears to be expanding out from that point. No matter where you are, and what direction you look, you will see that everything is moving away from you. Thus, if you reverse that process to “trace it backwards”, then no matter where you stand, you’ll see everything contracting towards you, and conclude that you are at the centre. For reference, Hubble agrees with this interpretation.
I’m not trying to make any bombastic claims and hand-wave them away with “physics is hard”. I’m trying to give an accurate recollection of the current consensus based on my own understanding of it (which is rudimentary at best).
It breaks down within our current models. You can of course always ask the question of “what happened before X”, and the answer today is that our current models can take us more or less arbitrarily close to a singularity (t=0), but not all the way there. There are several theories out there regarding what the “initial state” was.
I’m not really saying it did. I’m saying that, as far as I know, we have no better model or understanding than that if we extrapolate to t=0, we get a singularity (0 D), that for some unknown reason “magically” started expanding into the 4 D space-time we inhabit today. The fact that this process violates pretty much every known law of nature really just means there’s something here we don’t understand yet. I believe it’s pretty well established that our current models more or less completely break down at around the Planck time (see the “in cosmology” section).
wonderingwanderer@sopuli.xyz 1 day ago
Right, so in other words we have some major epistemic gaps that not even the some of every expert in the field can explain.
That’s why it shouldn’t be viewed as ignorant to ask questions that put a different spin on the problem, that potentially no one has asked yet. And why “this is the best explanation that we have at this time” is no reason to shut down conversation/speculation about it.
Returning to my original point:
How does anybody presume that the universe isn’t vastly bigger than what we’ve observed of it to date?
thebestaquaman@lemmy.world 1 day ago
I don’t view you as ignorant, and it hasn’t been my intention to shut down the conversation. If that was your impression, I apologise. I was very honestly just trying to give my own best interpretation of what the common consensus is, and why it is the way it is. Asking questions is an unequivocally good thing, and I enjoy trying to answer them to the best of my (meagre) ability: It helps me gain new perspective.
I’m honestly not quite sure, but I think it’s broadly accepted that the entire universe is far larger than the observable universe. From a more philosophical stance one could ask if anything outside the observable universe should really be considered part of “our universe” since, as far as we know, it is unreachable even for light (hence, unobservable).
As for estimating the size of the (entire) universe, I think they do that indirectly by estimating the age based on observing the cosmic microwave background, and then estimating the size based on the age and rate of inflation.
Of course, as with anything in natural science, everything is based on imperfect models that (I personally believe) will never more than asymptotically approach the true underlying reality. Thus, there’s always a possibility that anything we haven’t explicitly verified empirically will turn out to be completely wrong.
Someone once asked me how I would react if the second law of thermodynamics was proven to be wrong (I’m a theoretical chemist), and I responded that I see the second law as an extremely good model that’s been shown capable of representing a truckload (put mildly) of things accurately. A single counter-example doesn’t mean it suddenly becomes inapplicable to all the things we use it for today. The same things apply to Newton’s laws, and a bunch of other models that already have been proven wrong. The point is: I see no reason at all to believe our current astronomical models are the “actual truth”, but I do think they’re good models for the things that we’ve actually verified that they work for.
SpacetimeMachine@lemmy.world 1 day ago
I think the balloon analogy does not work well here. As far as we know the big bang was the start of our universes spacetime. There are plenty of theories on what might have happened “before.”.
Here is a good playlist to get you started on learning some more info.
youtube.com/playlist?list=PLsPUh22kYmNAV2T4af0Di7…
And this video from that playlist is directly related to this discussion.
youtu.be/K8gV05nS7mc