Douglas Scott
Professor
University of British Columbia
By definition the Universe has no edge. It is either infinite or wrapped around on itself (closed).

Dr. Michael M. Davis
Astronomer
SETI Institute
This is a truly profound question. The standard answer is that it wraps back upon itself if there is enough matter to 'close' the universe, but not if the matter density is less than critical. But I think you are asking if more than one universe can exist, which goes well beyond the usual answers. The answer is 'yes', in the brilliant book "Just Six Numbers" by Martin Rees. Take a look at his description of how six 'numbers' (actually, ratios of well-known physical constants) have to be exactly 'just so' for human life to have evolved in our universe. He suggests that one way for this remarkable 'accident' to have happened is that many zillions of "universes" have tried and failed, and that we exist in 'our' universe because it is the only one that got the numbers just right. It's a fascinating concept, and certainly blows away any estimates I used to make about how many trillions of stars and planets may have existed up until now.

Yervant Terzian
Professor
Cornell University
The universe creates its own space and time as it expands.

Mordecai-Mark Mac Low
Curator/Professor of Astrophysics
American Museum Natural History
Probably not; however we can only see as far as light can travel in the age of the Universe: some 13 billion light-years. So, the *observable* universe has an edge, but the evidence is that the Universe continues beyond that artificial edge indefinitely.

Astronomer*
Space without time has no meaning.

Andrew Liddle
Astronomer
University of Sussex, UK
As far as we are aware the Universe is likely to go on forever, though there is no way of being sure since light can only have come from a finite distance away. Even if it is finite it doesn't necessarily have to have an edge -- think of the surface of the earth which has a finite area but no edge.

Karen Vanlandingham
Assistant Professor
Columbia University's Biosphere 2 Center
No. The Universe has no center and no edge.

Astronomer*
There is no spatial end, just as there is no spatial center to the universe. Einstein taught us that we cannot separate space and time when we consider the entire universe.

Eilat Glikman
Graduate Student
Columbia University
This question, like #2, is ill posed. Space is defined by the universe pervading it. The simple answer is no, space does not have an end. There is nothing 'beyond' it - by definition. This may seem like a cop-out answer, but really space expands into time *creating* space as it does so.

Professor*
The answer to the question as posed is believed to be"no". But it is possible (and a subject of current research) that there are many Universes, each different from the others, and not connected with each other. Not surprisingly, this idea is very difficult to test.

Ed Churchwell
Professor/Astronomer
University of Wisconsin
These are questions that science cannot answer at this time and the last question not all because we cannot experience anything beyond the outer edge.

Prof. Wayne G. Roberge
Theoretical Astrophysicist
Rensselaer Polytechnic Inst.
Einstein's theory of general relativity says that gravity curves space (and time). It is possible for the curvature to "fold the Universe" back on itself in such a way that there is a finite amount of space but no edges. This is called the Closed Universe.

The other possibility is that the space in our Universe is infinite (which also means no edge to space). During the past year, astronomers have found very strong evidence that our Universe is this kind (called the Flat Universe).

Steven Novotny
Air Force Officer/Graduate Student
University of Florida Astronomy Department
By definition the universe cannot have an end as it encompasses all of space-time.

Bob Mathieu
Professor of Astronomy
Department of Astronomy, University of Wisconsin - Madison
This is a question that many of my students ask. If the Universe is "open", which means that its mass density is less than a certain value, then it is infinite and has no end in space. If the Universe is more dense then the "critical density" and is thus "closed", then it is finite ... but it still doesn't have an edge.

How can this be? It results from space curvature. As an analogy, imagine that you are an ant on the surface of a ball. The universe of the ants is only the surface - they can't jump off the ball or burrow into the ball. Now a friend asks you, does our universe have an edge, so you decide to find out. You walk and you walk, until you come back to where you started ... and so your universe has no edge. But is it infinite, your friend asks? No, for you could lay down a finite number of tiles and cover your entire universe.

So, if space can be curved (and it can by the presence of mass - Einstein showed us this), a universe can be finite without an edge!

At the moment we think that our universe is infinite, but the final word is not yet in. Note that like the ant's universe which was two dimensional (the ant could only move in two independent directions - front/back and left-right) but existed in a three-dimensional space that the ant knew nothing about, our universe may exist within a grander universe that has more than three dimensions!

Professor Rex A. Saffer
Physicist, Astronomer, Educator
Dept. of Astronomy & Astrophysics, Villanova University
We don't think the universe has an edge. It is kind of like the surface of a big beach ball - imagine an ant crawling around on it. The ant could crawl around forever on the surface of the beach ball and never reach the "edge". The universe could be like that, only in more dimensions than the three we are able to understand here on Earth.

Steven Balbus
Astronomy Professor
University of Virginia
What lies north of the north pole? The issue is the same. The geometry of the universe has no "outer edge" for anything to lie beyond.

James Pantaleone
Professor of Physics
University of Alaska Anchorage
We have no idea what led up to the Big Bang. Some people make guesses, but there is currently no way to test these guesses.

David Batuski
Astronomer
University of Maine
No edge!

Eric McKenzie
Graduate student
University of Florida
The universe has no end in space because of its curvature. This sounds hard to imagine, but the same basic idea is true on the Earth's surface. The Earth has no 'end' either: if you keep going in the same direction, you'll end up where you started from. But the Eath is finite, too--there are only so many countries--and the universe is finite in the same way, even though neither has a boundary. For getting a handle on the 4th dimension, I'd recommend Edwin Abbott's book, Flatland. It tells the story of a 2-dimensional creature trying to understand the 3rd-dimension, and the analogies work for us 3-dimensional creatures trying to understand the 4th dimension :-).

Astronomy Professor*
There is no edge... current evidence suggests the Universe is infinite in all directions. Carl Sagan's Cosmos has a very good discussion of this issue.

John Huchra
Astronomer/Professor
Harvard-Smithsonian
Probably not. More Universe. We think the Universe is infinite in extent, but there is a "horizon" defined by the speed of light times the age of the Universe. We can't see the stuff beyond that.

*Respondents opted for anonymity and we respect their wishes.