Physics Question #71

George Murphy, a 52 year old male from the Internet asks on September 27, 1999,

An article in the National Geographic magazine describes the Big Bang event as linear in form. Does that mean that when the big bang occured, that the dimension of time was also condensed into a singularity? Could time have affected the way the universe unfolded? Would the way galaxies form and behave be a clue to the origins of how our universe behaves and what its eventual fate will be? Would time have existed only in relevance to the universe or as part of the infinity beyond as well?

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The answer

Doug Hube answered on September 27, 1999

One cannot speak of an "infinity [in time] beyond [the Universe]." The Universe is by definition everything that is, ever was, and ever will be. Although there has been speculation about our 4-dimensional Universe existing in a still higher order Universe, we have no -- and cannot have -- any direct, observational evidence of higher dimensions. The Big Bang event marked the beginning of space and time. There was no "before" nor was there an "elsewhere." The Universe, in the classical view, did not begin as a small thing exploding, and expanding outward into a still larger something. It was an unfolding of space and time. (There's no point in trying to create a mental or physical model: that can't be done.) The expansion is linear in that within the spacetime coordinates of our Universe there is a linear relationship between expansion rate and separation between two points. There has been discussion, and claimed detection, of a rotation of the Universe as a whole. That, too, is difficult to picture because classically we would need an external frame of reference -- which. as noted, is lacking -- in order to detect it. There are claims of a detection of shear motion between distant and nearby regions of the Universe, and one could interpret that as a cosmic rotation, although other interpretations exist. Time can, in principle, be measured in terms of any sequential set of events, although there are physical and philosophical difficulties there, for example, as a result of special relativistic effects and what we mean by simultaneity. On a cosmic scale one could measure time in terms of the variation in the progressive changes in the abundances of the elements.

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