Edge of the Universe
LiptonCambell: IF the universe is finite then what happens once you reach the edge of space? And once you have reached space's end, what does it look like? If you were at spaces end but were looking beyond space's end, what would you see? It should be nothing right? What does nothing look like? I realise that what we "see" is just a subjective interpretation of light by our minds, but I pose the question regardless. What would happen if you took a step past the edge?
Bourbaki: The universe (in the sense of 'everything that exists', not the observable universe) is not believed to have a boundary (edge).
Momentarily digressing, it is currently believed that bodies which are at least ~13.8 billion light years apart "move away" from each other faster than light. This of course does not mean that their relative velocity is greater than that of light; rather, the cause for this is the expansion of space itself. What this does mean, is that you could not reach the edge of the universe even had there been one. This is because the radius of the observable universe alone is ~46 billion light years (at this time), so already there are points in it which move away from you so fast that even light will not reach them.
Going back to the edge bit - the best I can do is give the standard (and excellent) balloon analogy. Imagine an ant living on the surface of an enormous expanding balloon. For the ant, the universe is the surface of the balloon, which due to its vastness appears to be locally flat (like the Earth's surface). A smart ant will raise questions analogical to yours, but your reply will be terse - the balloon has no edge, and the ant can not discover this because the balloon is expanding too fast. Furthermore, you cannot explain to the ant what is happening in a way it will understand, because you can see the balloon in 3D, and it is limited to 2D - how will you explain 'where the balloon is expanding from', or that 'the universe is curved'?
If you insist on asking 'what will you see beyond the edge' (assuming it exists), I think the question is devoid of meaning, since the universe is defined to 'everything'. Anywhere light goes - anywhere anything exists really - is a part of the universe. Higher level theoretical physics often constructs models in which our universe is not defined as 'everything', but is a rather local natural phenomenon. Personally, I can't make out of this anything more than consistent math (not to underestimate) so I can't imagine what it means intuitively.
In summary I guess the punchline is double:
1. We don't believe the universe has a boundary
2, Even if it did, you wouldn't be able to reach it, so "don't worry about it"
Corwin: I imagine that there is a loop-hole in physics that would make that [reaching the "edge"] impossible.... like say, if the outer "boundry" (although I think "horizon" is a better word) is receding at the speed of light... that would make it unreachable, and unseeable.
Think of a black-hole, but in reverse.... which could very well be what our universe actually is.
(Edited by Corwin)
I think of it as a giant sphere no matter where you go to try to reach the end it would be like trying to go around the earth we would never reach an edge, but just keep going around the earth. But except imagine walking inside a circle.
Corwin: That's thinking too 3-dimensionally... comparing the Universe to a sphere is like comparing a sphere to a 2-dimensional circle.
PokerMan: Ok and we live in a 3 dimensional world, so you know how to think in a 4 5 6 7 8 9 10 or even in a 11th dimension way? One such theory is the 11-dimensional M-theory, which requires spacetime to have eleven dimensions, as opposed to the usual three spatial dimensions and the fourth dimension of time.
PokerMan: But we are not yet 100% certain that the expansion of the universe is real; it is simply our best working hypothesis at present. For example, the distance between hydrogen clouds and the distance between galaxies in the early universe seem to be the same as the distance we see now. If the universe has been expanding for the last 14 billion years or so, we would expect to see them closer together in the past than they are today.
This study is called the Lyman alpha forest.
Check this diagram out. http://photontheory.com/clouds.png
Yan26: If you are at the edge of space and look back you will see millions of stars ( going by the assumption that the universe is the same as we see it) If you looked forward beyond the edge you wouldnt see anything as to see something light would have to be reflected by an object. As you are standing at the edge of the universe you would be the last object and without any object in front of you you wouldnt be able to see anything.
Concepts like multiverse etc are still concepts they havent even been theoretically proven or agreed upon hence I assumed there is only 1 universe.
Corwin: Well... from our standpoint, we see ourselves at the center of our "visible" universe... with a 14 billion year old "horizon" observed in all directions. Now, if there is a tangible "center" to this vast expanding fabric of space-time, it would be far too much of a coincidence that we would happen to occupy that center.
Which suggests that the universe is far larger than our visible bubble of 28 billion light-years in diameter. Maybe due to the theoretical "inflationary" epoch shortly after the Big Bang, the universe could be many times larger than what we see, which is limited by the 14 billion year calculated age which is based on that visible horizon.
So......... what if we in fact ARE near the "edge" of the universe in it's actual entirety... and THIS is what it looks like?
Or does every galaxy see a 14 billion light-year horizon, no matter where you happen to be situated in the grand scheme of it all?
Or is the universe in a manner of speaking infinite, from our perspective... but seemingly finite from the perspective of an even larger picture where there could be multiples of infinity along further dimensions than our limited minds can fathom?
And I'm giving myself a headache...... somebody pass the Vodka......
Despite the age of the universe being estimated at ~13.8, the diameter of the observable universe is actually far greater than 28 billion light years; In particular it is estimated to be ~93 billion light years. This is because space expands.
As far as a center of expansion, it's unlikely that such a point exists within our universe. This can be seen from the balloon analogy (see my previous post) - if a spherical balloon expands radially, then the ant's universe (the balloon's surface) expands isotropically yet does not contain the center of expansion.
Geoff: I was under the impression (from something I read several years ago) that the universe was expanding at the speed of light.
Since it is impossible to exceed the speed of light, it would be impossible to reach the edge of it.
However, since that was several years ago, and in a book that was already at least a decade old when I read it; it's probably been proven wrong. And since I quite possibly either misunderstood it or took it out of context (not being a physicist), it may have never been suggested anyway.
Bourbaki: "The universe expands" means space itself expands. Space is not subject to Einstein's Theory of relativity; It can expand faster than light. Indeed it is believed that beyond a certain distance from us, objects move away faster than light - again, not because their velocity is superluminal - it doesn't seem like anyone reads previous posts.
(Edited by Bourbaki)
CoIin: I don't know much about edges of universes but I can vouch that Bourbaki is an EXTREMELY clever young fellah
Geoff: I wasn't suggesting that space could not move faster than light. I was referring to the fact that the observer could not match the speed of the edge of the universe.
And, yes - sorry I did only skim through the previous posts. I did not spot that you had already made the exact same point in a more learned way, Bourbaki.
Corwin: Yeah... that was the gist of my first point too... that if there really is something that could be described as an "edge", that it is probably unreachable from a relativistic standpoint.
I don't think the Universe would allow us the possibility of escaping it's "boundaries"... if that term even applies.
Although to dive into a black-hole is a form of "exiting" the Universe, as space/time curves around it... but I imagine that getting crushed into a dimensionless point of infinite density would be somewhat lethal. I doubt very much that a singularity is a happening place to be, and I don't subscribe to the notions that they are "gateways" to anywhere else but oblivion.
(Edited by Corwin)
PokerMan: Try to imagine the entire universe being back at the single point it was at 13.8 billion years ago. Imagine the universe being in this tiny area of space before it expanded. Now blow a bubble from some soap and watch the colors swirl around that bubble as it floats in the air. Eventually the bubble will pop! Because evaporation of its water content, air turbulence, and, most commonly, dryness or contact with a dry surface or dry air. When there is a strong wind, or even a gentle breeze, bubbles are much more difficult to create and are popped by the wind's force. If the air is very dry, as it is in the desert, or if a bubble touches a dry finger or a piece of clothing or the ground, it pops instantly.
Imagine this bubble being the universe 13.8 billion years ago. Then something caused it to explode/pop and everything inside it went everywhere.
Sometimes there is either too much soap or too much water or both and the bubble becomes unstable. The soap and water begin to collect at the most dense point, because of gravity the bubble pops!
PokerMan: Gravity is the culprit of the big bang. Which explains why some parts of the universe are more dense than others.
PokerMan: For a universe so old and so illustrious, the end may be boring and lightning quick: According to one Fermi National Accelerator Laboratory theoretician, if what we know about the Higgs boson subatomic particle is true, the universe may come to an end when another universe slurps us up at light speed.
"If you use all the physics that we know now and you do what you think is a straightforward calculation, it's bad news," Joseph Lykken said at a meeting of the American Association for the Advancement of Science in Boston on Monday. "It may be that the universe we live in is inherently unstable and at some point billions of years from now it's all going to get wiped out. This has to do with the Higgs energy field itself."
Here's how he explained his theory to NBC News' Cosmic Log:
"He said the parameters for our universe, including the Higgs mass value as well as the mass of another subatomic particle known as the top quark, suggest that we're just at the edge of stability, in a 'metastable' state. Physicists have been contemplating such a possibility for more than 30 years. Back in 1982, physicists Michael Turner and Frank Wilczek wrote in Nature that "without warning, a bubble of true vacuum could nucleate somewhere in the universe and move outwards at the speed of light, and before we realized what swept by us our protons would decay away."
"Lykken put it slightly differently: 'The universe wants to be in a different state, so eventually to realize that, a little bubble of what you might think of as an alternate universe will appear somewhere, and it will spread out and destroy us.'"
I found this after writing my previous post.
(Edited by PokerMan)
"Gravity is the culprit of the big bang. Which explains why some parts of the universe are more dense than others."
The second part is plainly untrue. The fact the universe is not completely homogeneous is believed to be due to quantum effects at its very beginnings.
"The second part is plainly untrue. The fact the universe is not completely homogeneous is believed to be due to quantum effects at its very beginnings"
In reference gravity plays a huge roll depending which theory the universe will end and how it began. The universe if you look here-----> en.wikipedia.org/wiki/File:Ilc_9yr_moll4096.png
"The image reveals 13.77 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies."
Which is why you said do to quantum effects, which there are many depending which theory you believe in, therefore you cannot say this is, "plainly untrue."
Well have you taken a look at the density parameter? The average matter density of the universe divided by a critical value of that density. Even so average is used to calculate one of three possible geometries; these are called, respectively, the flat, open and closed universes. And in order to calculate this there must be an average, which means some areas of the universe have more density than others proven by the model when you click on the link I gave, and proven by several different theories of how the universe may end.
So you were saying?