Photo: Ben Walsham

What's beyond the universe?

The trite answer is that both space and time were created at the big bang about 14 billion years ago, so there is nothing beyond the universe. However, much of the universe exists beyond the observable universe, which is maybe about 90 billion light years across.

newscientist.com - The universe is expanding, but what exactly is it expanding into?

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Andrew Taubman

Queens Park, New South Wales, Australia

By definition, the universe is everything, so there is nothing external to it for it to expand into. It is not expanding into anything as such – everything is expanding.

Richard Swifte

Darmstadt, Germany

It is all too easy to think of the big bang and the resulting expanding universe as being like an ordinary explosion, with everything expanding out from a central point. A better analogy is to consider the surface of an inflating balloon where the surface is a two-dimensional equivalent of our three-dimensional universe. The balloon fabric is space; dots marked on this surface (equivalent to galaxies) will move apart as the balloon expands, but only because the fabric (space itself) is expanding, and without any central point for the expansion.

The balloon is expanding into the third dimension, but here the analogy is more problematic. Is our universe also expanding into a higher dimension?

If the universe is all there is, and isn’t part of a larger multiverse, then there is nothing outside it (not even a vacuum, which is still space), so it probably makes no sense to ask what it is expanding into.

Nick Canning

Coleraine, County Londonderry, UK

A two-dimensional being on the surface of an expanding balloon can observe all distances in its surface world getting larger. It can’t see the third dimension into which the balloon is expanding. We three-dimensional creatures see all the distances between galaxies expanding, indicating an inflation of space, but we can’t perceive extra space dimensions beyond our three, into which the expansion is taking place.

Roger Leitch

Bath, UK

There are two parts to the answer to this question.

First, when mathematicians and physicists want to describe space – any space – the mathematical tools and techniques they use don’t depend in any way on the space being part of a higher dimensional space. So they can, for example, do geometry on the surface of a sphere without considering that the sphere is embedded in our everyday three-dimensional space. Four-dimensional space-time is more complicated than the surface of a sphere, but the idea is the same. It is possible to calculate the shortest distance between two points, for example. Second, if space is expanding into some higher dimensional space, we can’t, with our current knowledge of physics, know anything about it. And it may even be beyond our comprehension.

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Mike Follows

Sutton Coldfield, West Midlands, UK

This isn’t a question that physics can answer with our present knowledge or without some form of qualification. The trite answer is that both space and time were created at the big bang about 14 billion years ago, so there is nothing beyond the universe. However, much of the universe exists beyond the observable universe, which is maybe about 90 billion light years across. Because the universe is homogenous on this scale, we imagine that what is beyond our observation looks much the same as what we can see. If the universe is infinite, there is nothing beyond it, by definition. A finite expanding universe conjures up the idea that it would have a boundary or edge, separating it from something beyond. Of course, the universe has at least four dimensions (three for space and one for time) which is nigh on impossible for us to visualise. However, space could be represented as two dimensions, confined to the gossamer-thin surface of a sphere. You could travel in any direction on the surface without encountering an edge. If the radius were to increase, the “universe” would expand as ours does, but it wouldn’t be expanding into anything. Finally, we could speculate that our universe is part of a multiverse with many other universes beyond our own, but it is unlikely that we are expanding into them. To answer this question – or ask a new one – email lastword@newscientist.com. Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address. New Scientist Ltd retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format.

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newscientist.com - The universe is expanding, but what exactly is it expanding into?

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