Clocks & Curvature: How Space-Time Affects Timekeeping

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Discussion Overview

The discussion revolves around the effects of curvature in spacetime on timekeeping, particularly in the context of gravity and hypothetical scenarios involving "negative gravity." Participants explore how different spacetime geometries influence the rate at which clocks run, referencing specific solutions in general relativity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that in regions of spacetime bent "inward," clocks slow down from an outsider's perspective, and questions what would occur in regions bent "outward."
  • Another participant clarifies the meaning of "bent inward" and "bent outward" using the Schwarzschild and Reissner-Nordstrom solutions, noting that proper time can be less than or greater than coordinate time depending on the parameters.
  • A participant asserts that gravity slows clocks down and speculates that "negative gravity" might speed them up, although they express skepticism about the realism of such a concept.
  • The same participant references their impression from cosmology that situations simulating "negative gravity" exist, specifically mentioning the inflation of the universe after the Big Bang.
  • Another participant counters that inflation did not involve curved spacetime and discusses how it addresses the flatness problem of the universe, while also mentioning "negative energy vacuum density" as a driving force, which could be informally likened to "negative gravity."

Areas of Agreement / Disagreement

Participants express differing views on the concepts of "negative gravity" and its implications for timekeeping. There is no consensus on the interpretation of inflation and its relationship to curvature in spacetime.

Contextual Notes

Participants note the complexity of definitions and the informal nature of terms like "negative gravity," which may not be widely accepted in the literature. The discussion also highlights the dependence on specific parameters in general relativity solutions.

Negeng
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In a place of gravity, where space time is bent "inward" clocks slow down from the prospective of an outsider. But what if you had a region of space time that was bent outward, what would happen to your clocks then?
 
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It's hard to know what you mean by "bent inward" or "bent outward." In the Schwarzschild solution, g00 = 1 - 2m/r, which is less than 1, and so for a particle sitting still at finite r the proper time is less than the coordinate time, consequently its clock runs slow. For the Reissner-Nordstrom solution, g00 = 1 - 2m/r + e2/r2, and so for certain values of the parameters (m=0 for example) g00 will be greater than 1, and clocks will run fast.
 
Simply put, gravity slows clocks down. Negative gravity would probably speed them up, but that doesn't sound realistic to me. :-p
 
harrylin said:
Simply put, gravity slows clocks down. Negative gravity would probably speed them up, but that doesn't sound realistic to me. :-p

I got the impression from the cosmology section that there are situations that simulate "Negative gravity" they bend space and time in the oppisate direction than gravity does. For example the inflation of the universe that happened soon after the big bang. Is this impression wrong?
 
Inflation did not involve curved spacetime...if anything it's this:

...Inflation answers the classic conundrum of the Big Bang cosmology: why does the universe appear flat, homogeneous and isotropic in accordance with the cosmological principle when one would expect, on the basis of the physics of the Big Bang, a highly curved, heterogeneous universe?

more here: http://en.wikipedia.org/wiki/Cosmological_inflation

But the driving force of inflation, "negative energy vacuum density", I guess could be informally described as "negative gravity" but I have never seen it referred to as such...currently it is usually called the cosmological constant or dark energy. I have not seen cosmological expansion described as resulting from "negative gravity"...but that could be an informal description since "negative energy" seems not so different..
 

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