# Does the universe have an edge?

I've heard the universe is just an empty cavity. Does the universe have any edge or stop or is it just an infinite empty cavity?

As far as theories I've heard of, we can't see the edge of the universe (if truly exists) because the farther you look out into space through a telescope, the farther back in time you are actually looking. For example, if you are looking at a star 20 light-years away... you're actually currently observing what was happening on that star 20 years ago... the theory is that there is only so far you can look out into the universe because there is only so much history post Big Bang.

Image above: What is the furthest we can see? In 2003, NASA's WMAP satellite took images of the most distant part of the universe observable from Earth. The image shows the furthest we can see using any form of light. The patterns show clumps of matter that eventually formed into galaxies of stars. Credit: NASA/WMAP Science Team

• Don't understand why the down vote. [link]nasa.gov/audience/foreducators/5-8/features/… – MegaMark Jul 24 '14 at 10:11
• Ya I think a down vote fairy flew by, Good answer by the way, upvoted – Baked Potato Jul 24 '14 at 14:36
• That means that as time succeeds our field of view permanently extends doesn't it? – MinecraftShamrock Jul 31 '14 at 12:51

Galaxies extend as far as we can detect... with no sign of diminishing.There is no evidence that the universe has an edge. The part of the universe we can observe from Earth is filled more or less uniformly with galaxies extending in every direction as far as we can see - more than 10 billion light-years, or about 6 billion trillion miles. We know that the galaxies must extend much further than we can see, but we do not know whether the universe is infinite or not. When astronomers sometimes refer (carelessly!) to galaxies "near the edge of the universe," they are referring only to the edge of the OBSERVABLE universe - i.e., the part we can see

If we know the universe is expanding, we are saying the universal boundary is expanding. Before the big bang(s), there was "nothing". Which seems an impossibility, because something happened. So we have the big bang(s) and the boundary begins to move outward, at least at the speed of light (knowing there is debate about variable speeds of light, I am keeping this open). That means that according to our understanding thus far, there is an edge to the universe.

I try to keep in mind that as a creature with everyday experience in three dimensions, it is next to impossible to really understand all the multidimensional possibilities which may make up "the edge". Just like I cannot imagine a time from my viewpoint where there was a "nothing". I believe that the answer lies in a better understanding of multi-dimensions than we have now.

We are so very, very early in our use of a scientific method of exploration, and it seems that every year we are bowled over by the implications of a new discovery - especially in quantum physics.

• I believe the question is about a possible edge of the "whole" Universe, not the observable Universe which is what you're referring to (and which increases its distance to us not only at $c$, but at $4.3c$). – pela Feb 12 at 19:20
• Great comment. I guess I'm extrapolating that as we see the observable universe expand, the entire universe is also expanding. Presumptuous perhaps, but isn't anything we can measure "observable" (directly or indirectly)? In either case, a bang from "nothing" (which I have a hard time with) would seem to create a boundary between that nothing and something...observable or not. And if we are questioning the speed of light, and if it may be variable, how can we convincingly state that the universe expands at 4.3c? – Smorss2011 Feb 14 at 1:25
• I don't think assuming that the rest of the Universe is expanding is presumptuous. Anyway, a bang from nothing doesn't necessarily create a boundary. The Universe is either finite of infinite, but certainly neither implies that is has an edge. If it's finite, then it "curves back on itself", like the surface of a balloon. In "mainstream physics" we don't question the speed of light, and by Hubble's law galaxies the edge of the observable Universe (which is not a physical edge) recede at $v = H_0 d \simeq 3.3c$. – pela Feb 14 at 22:16
• Because light from increasingly far away will reach us, the distance to the edge increases by another factor of $c$, so the obs. Uni. increases its radius at $v\simeq 4.3c$. – pela Feb 14 at 22:16
• But, if you're floating in the inside of a balloon, and travel to the balloon itself, that is an edge to whatever is beyond it. I totally get the "edge" idea. But I don't think we can answer it any more than we can answer "what was there before the big bang?", and if the speed of light is indeed variable (or slowing down), that has major implications in our understanding of all kinds of things...age of universe, how relativity would work, where the edge of the universe is, and how long that light would indeed take to reach us. – Smorss2011 Feb 16 at 0:18

Dark energy is driving the accelerated expansion of our universe.

Is it accelerating into itself?

Or is it accelerating into nothing, An outer void?

If we could see the furthest away accelerating object that would be the edge of the Universe. Thus there is an edge to the Universe.

Remember, just because we can't look and see today doesn't mean it doesn't exist.

• Your last two statements appear contradictory. Your first states that the observable universe is the entire universe, while your last statement seems to indicate the exact opposite. – HDE 226868 Aug 12 '14 at 18:44