The universe is often defined simply as “everything that exists” – the word universe originating from the latin word universus, which can be translated literally as “combined into one whole”. However, this posses certain questions of physics and metaphysics, such as: Is the universe infinite in size? Does the Universe have a boundary of some sort? If the Universe does have a boundary, is there anything outside of it? Has the Universe always existed? Did anything exist before the Universe? Will the Universe ever come to an end? …and so on.
It is certainly very difficult – perhaps impossible – for the human mind to fully comprehend an infinite Universe. It is perhaps equally difficult for us to comprehend how the Universe could be finite but without boundaries or, alternatively, if the Universe does have boundaries, how anything could possibly exist outside of our familiar four dimensions of space and time. Although, if anything can exist outside of space and time, then perhaps, whatever that is should be included within the definition of “the Universe”, anyway, if this simply means “everything that exists”.
However, if the definition of the Universe is simply limited to our concept of all of space and time, then it could be considered meaningful to talk about something outside of our Universe. For example, “parallel” universes to our own might exist, or the Universe might simply be a “bubble” of space-time within a higher dimensional space, perhaps containing other Universes – maybe even an infinite number.
Has the Universe always existed?
Many fundamental questions about the Universe do lie within the realms of metaphysics, and, with our current scientific understanding, we cannot possibly answer them.
All is not hopeless, however, and physics can at least say something about the nature of space and time. For example, in confronting the question “Has the Universe always existed?”, modern cosmology offers the big bang theory. This theory is based primarily on the observation that distant galaxies are receding away from us in every direction (see Hubble’s law). Extrapolating this expansion backwards in time leads us to our current estimate for the age of the universe – around 13.8 billion years. Time, itself is usually considered to have started at this moment.
Unfortunately, General relativity, which currently provides our best description of the evolution of the early Universe, entirely breaks down when the expansion is extrapolated back to a point of infinite density and temperature, known in physics as a singularity. It is possible that some future quantum theory of gravity might be able to describe the universe during the Planck epoch – the first 10−43 seconds of time.
*This page is still under construction. Please call back soon to read about the following questions:
Did anything exist before the Universe?
Will the Universe ever come to an end?
Is the Universe infinite in size?
Does the Universe have a boundary?
Does anything exist outside of the Universe?