Just what the title says.

The clock in question I am assuming to be infinitesimal in size (no spacetime curvature inside the clock). What would the proper time of a single point be at this epoch of the universe, according to the current cosmological models?

Is that number 13.7 billion years? Or something else. Does cosmological inflation affect the answer?

  • $\begingroup$ This could be rephrased as "What is the length of a geodesic connecting the big bang and us now?" $\endgroup$
    – Trebor
    Commented Aug 19, 2022 at 5:05
  • $\begingroup$ This may help - What happened before the Big Bang? $\endgroup$
    – mmesser314
    Commented Aug 19, 2022 at 5:27
  • $\begingroup$ I think that the OP is not allowing for the possibility that the universe might be local (causally separated from others that, like our own, would be in a multiverse). Some physicists (for instance, Nikodem Poplawski) put this situation into an English language context by capitalizing "Universe", as the names of localities are capitalized in English: However, NASA's Style Manual recommends against this, and, consequently, appears to favor the "single universe" view favored by Penrose, who, nevertheless, considers it to have already had infinite temporal iterations. $\endgroup$
    – Edouard
    Commented Aug 22, 2022 at 16:40
  • $\begingroup$ @Edouard, interesting, would that change the answer to the clock question? $\endgroup$
    – RC_23
    Commented Aug 22, 2022 at 16:45
  • $\begingroup$ I don't think so: Since NASA is a governmental organization in an English-speaking country, I think its preference is only intended to emphasize the fact that mathematical descriptions of cosmology are more apt to be accurate (or falsifiable) and complete, compared to purely linguistic descriptions. $\endgroup$
    – Edouard
    Commented Aug 22, 2022 at 16:57

1 Answer 1


We have a pretty good understanding of the evolution of the current state of the universe from a very hot, dense, uniform expanding plasma.

If there was (somehow) a stopwatch in that plasma that read 0 at that time, and it moved with the Hubble flow until the present day (which is to say that it moved in such a way that the universe around it appeared isotropic), then it would read about 13.7 billion years today.

Where the plasma came from is unclear. It might have come from an inflationary epoch. The inflationary epoch can last for an arbitrarily long time, and the beginning of the inflationary epoch is not (necessarily) the beginning of time, but just another state of the universe. That state might not be isotropic enough for there to be a well-defined elapsed time since the beginning of time, if indeed there was a beginning of time. We just don't know.


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