Obviously inspired by EnolaStraight’s question, but different.
If the Universe began with an initial explosive expansion from one state into a different one. Is there a large amount of energy and maybe something else, that we can never see or detect that is on some sort of outer side? Initially I suppose that the density did not allow light or anything else to escape beyond the leading edge of the expansion. But as it expanded the density and speed would lessen. More “stuff” could escape outward. But there would remain a sort of demarcation line for us who are still inside that radius point where things could not get out. I am having a difficult time describing my idea of it. We only see the stuff that was trapped and forced to radiate inward only. There may now be a lot of stuff on the other side of that line that we cannot see.
I imagine that some observer outside our Universe that eventually did see our Universe, because it finally reached them. Could never see the Big Bang, because all of it was trapped inward. They would only see what happened after a certain period of time. The outside of what we see inside.
But maybe they could actually see things we cannot. Due to being on the outside.
Sorry, it is hard to word. But I suspect what we can see from the inside is less in diameter and effect than could be detected from outside?
What is your definition of the “universe”?
Under the common definition the “universe” includes everything. There can be no other side. There can be no outside observer looking in because nothing is “outside”. The term is meaningless.
Some confusion arises from the expansion of space, which means that although the universe was formed 13.8 billion years ago, the farthest parts are now 46 billion light years away, yet we can see objects from the cosmic beginning. However, the beginning is still part of our “universe”. The expansion of space did not send “light” (at all wavelights) outward but contained its energy within an expanding volume. So nothing can “escape” the universe. Everything is part of the same spacetime.
Spacetime is counterintuitive because it is unique. If you think of the universe as an everyday explosion in space, every conclusion will be wrong.
Yes. The Big Bang/begining of the universe was not an expansion of something into something else, it was the creation of all space and time, which is still expanding. Even thinking of the universe as expanding into nothing is wrong. Nothing is Something and there was no nothing. Words are inadequate.
If you think of the universe as a small bubble of something new growing inside something else, a larger void, that is wrong. Under our current understanding there can be no outside of the universe.
All we can usefully talk about are theories of the early universe that are consistent with both our understanding of physics and observations. Which are of course intertwined.
That gets us consistent and generally accepted view back to a very short time after a notional time zero.
Ideas of size have become more nuanced. Now we talk about the observable universe as one bounded by the distance at which the apparent speed of recession exceeds the speed of light. But also with an understanding that this is a special boundary that has any meaning beyond where we the observer sits.
The question about how much more universe is beyond the observable is an open one. It is difficult to come up with an argument that says there is none. But it is generally accepted that it is just more of the same. How much more is a different question.
The total universe could be infinite. That may suggest that the Big Bang didn’t arise from a single location but itself was just a state change from some other infinite universe. A change that brought into existence the current fabric of space time.
Then you get the multi-universe guys, positing an infinite array of universes each with different physics. We are the product of the anthropic principle and there is nothing else special.
Here be dragons. Lots of dragons. Eventually it is just dragons all the way down.
To misquote Arthur C Clarke. There are two possibilities. Either the universe is finite in size, or it is infinite. Both are equally terrifying.
In a sense the answer to this is yes, but not as you have posed the question. Both @Exapno_Mapcase and @Dallas_Jones have pointed out that there is no “outside” into which the universe is expanding. But there is a boundary beyond which any observer located anywhere in the universe cannot see. This is because there is maximum speed at which information of any sort can propagate, the well known speed of light. Calculating this distance is complicated by the fact that the universe is expanding, so the galaxies that we now see were actually closer to us when the light we now detect was emitted. This distance is known as the particle horizon, here’s a PDF link to a 2016 paper which discusses this and provides a calculation: https://www.researchgate.net/profile/Nick-Tomasello/publication/311954421_Size_of_the_Observable_Universe/links/59f26eda0f7e9beabfcc63a8/Size-of-the-Observable-Universe.pdf
I disagree with that characterization. It’s really the word “everything” that is so ambiguous as to be meaningless. The concept of “universe” is amenable to several quite specific definitions. One is that it’s the extent of the entire detectable physical environment. A much better one is that it’s the entirety of everything that was created at the Big Bang, where the nature of matter, spacetime, and physical laws are presumed to be exactly the same everywhere even beyond the bounds of detectability.
But that doesn’t preclude concepts like the multiverse, parallel universes, or “many worlds”. Max Tegmark’s four-level multiverse hierarchy is rather elegant. Level 1 consists of universes created from different initial conditions, Level 2 of universes with different physical constants, Level 3 of “many worlds” quantum branches, and Level 4 of universes with entirely different mathematical descriptions.
Maybe a bit of a semantic nitpick, but any or all of these can come under the rubric of “everything” while retaining quite a precise definition of what a “universe” is.
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I hope the intent was clear anyway.
Of course not. But none of those are outside our “universe” looking in. In fact, while they would include our “universe” as one among many, just in the names alone one sees that these are other “universes” completely separate from ours, as far as we know. Some conceptual math may include notional bridges or pathways to these other “universes”, but they remain separate items.
The OP clearly thought of our common, everything is part of it, “universe”. Throwing additional concepts on top of that merely obfuscates understanding.
To paraphrase Clarke: either we are using terms in common with one another or we are not. The latter is terrifying.
Indeed. I was going to rail against how “infinity” gets thrown around carelessly, but it is a different battle. The entire conversation rests on a lot of hidden assumptions of common terminology. And arguments about them. Every word carries a lot.
I just Googled the age of the universe. It popped up 13.77 billion years. Maybe.
So an observer more than 13.77 billion light years away should be unaware of our Universe. And us of their Universe. If a thing has no detectable effect in any way, we consider it to not exist. But it may not have got to us yet. Or us to them. I did say Our Universe in the post. I think it is quite possible for other Universes to exist distant from ours. Maybe one or more are currently interacting with ours, but we cannot yet detect it or understand what we see.
The diameter of our current universe is ~93 billion light years. So, it is 46.5 billion light years from you on earth to the “edge” of our universe. It may well extend beyond that (probably does) but from your perspective the edge is 46.5 billion light years away.
But I am curious about the initial situation. The Big Bang happens. The total mass of our Universe is there. So light should not be able to move outward from it. It expands. At some point the density lessens so light can begin exiting from the mass. When? A micro second? A year? At what point in it’s evolution would an observer begin to see it?
Is the 13.77 billion year old number wrong?
Edited.
I see that the age has been increased to over 26 billion.
The whole universe came into existence in all places at the same time. Space itself did not exist before the Big Bang. The Big Bang is not exploding into space…it is creating space. There is no “center” such that someone is further away from the explosion (not the right word) than anyone else.
No. That number is correct (13.77 billion years old). But space is expanding and has been since the beginning. Indeed…in the first micro seconds most of it poofed into existence. See Inflation:
The inflationary epoch is believed to have lasted from 10^-36 seconds to between 10^-33 and 10^-32 seconds after the Big Bang. - SOURCE
I think you’re thinking of the “observable universe”, which due to the expansion of space, actually goes out 46 billion years.
That actually leads to a question I’ve had, if you will…
If space continues to expand, a future civilization may emerge on a planet of a star that has no other objects in its observable universe. Would they ever be able to figure out that at some point in the past, there were many other of galaxies, stars, etc. that existed (and still do exist, but just can’t be observed)?
That will happen to our galaxy. Eventually the rest of the universe will expand beyond our horizon. We will only be left with our galaxy and the local group of galaxies kind of near us which are gravitationally bound together. Kinda scary and lonely.
To be fair, that will happen long after our sun dies and earth and this solar system are done. Not something for us to worry about.
ETA: You have almost certainly never seen a star that is not in our galaxy. It is possible to see the Andromeda galaxy unaided (and that galaxy will collide with us in the future). But, even if all other galaxies leave our horizon your night sky will look pretty much the same. Astronomers will be bummed though.
This image may help and be more intuitive:
I was not really wanting to delve into what constitutes the Universe. But I always like to get into that.
What precludes another Universe from being in existence?
If we are far enough away from it so there is no interaction. We would not know of it. Even if it is close enough that it does interact, but we do not understand the interaction for what it is, we think it is not there.
We seem to define our universe by the extent of it existing to us in some detectable or theoretical way. But a force of some sort takes time to propagate. If it is yet too far away to have acted upon us, that does not mean it does not exist.
I assume that the Quantum Fluctuations are not actually a glowing light. Not radiating, but happening in an area of…space? Hmmm. When does the space thing come into play.
So is the Afterglow Light Pattern the point when light might begin escaping outward?
I say light, but I mean any energy.