“Mathematicians deal with possible worlds, with an infinite number of logically consistent systems. Observers explore the one particular world we inhabit. Between the two stands the theorist. He studies possible worlds but only those which are compatible with the information furnished by observers. In other words, theory attempts to segregate the minimum number of possible worlds which must include the actual world we inhabit.” -Edwin Hubble
The combined work of many 20th century astronomers and physicists — including Einstein, Slipher, Leavitt and Hubble — led to the conclusion that the fabric of space itself is expanding. One of the most commonly asked questions that people have upon learning this is then, “what’s it expanding into?”
Yet that question itself makes an unnecessary assumption: that there is something more to the Universe than the three dimensional physical space that makes up the Universe we perceive. There could be an extra spatial dimension, a boundary to the Universe as we know it or other additional physics, but there doesn’t need to be. The Universe may be expanding into a space greater than what we know, but it may simply be stretching of its own volition, and we presently have no way to know.
Go get the answer to one of the most frequently asked questions about the Universe over on Forbes today!