# Clocks & Curvature: How Space-Time Affects Timekeeping

• Negeng
In summary, the cosmological expansion is the result of a "negative gravity" force that bends space and time in the opposite direction than gravity does.
Negeng
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?

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.

harrylin said:
Simply put, gravity slows clocks down. Negative gravity would probably speed them up, but that doesn't sound realistic to me.

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..

## 1. How does space-time affect timekeeping?

Space-time is a concept in physics that combines the three dimensions of space and the dimension of time into a single four-dimensional continuum. This means that the passage of time is not constant and can be affected by factors such as gravity and velocity. As a result, timekeeping can be impacted by these factors and may vary in different locations in the universe.

## 2. Can time be affected by gravity?

Yes, according to Einstein's theory of general relativity, gravity affects the curvature of space-time. This means that the closer an object is to a massive body, the slower time will pass for that object. This phenomenon is known as gravitational time dilation and has been confirmed through experiments such as the Hafele-Keating experiment.

## 3. How does velocity affect time?

According to Einstein's theory of special relativity, time is relative and can be affected by an object's velocity. As an object moves faster, time will appear to pass slower for that object relative to a stationary observer. This phenomenon is known as time dilation and has been confirmed through experiments such as the Hafele-Keating experiment and the famous twin paradox thought experiment.

## 4. How does the curvature of space-time affect the accuracy of clocks?

The curvature of space-time can affect the accuracy of clocks due to the phenomenon of gravitational time dilation. Clocks in stronger gravitational fields will appear to tick slower than clocks in weaker gravitational fields. This means that clocks in different locations in the universe will not be perfectly synchronized and may have slight variations in their timekeeping.

## 5. Is it possible to have a completely accurate clock?

According to the theory of relativity, it is not possible to have a clock that is completely accurate in all locations in the universe. The passage of time is relative and can be affected by various factors such as gravity and velocity. However, with advancements in technology and the use of atomic clocks, we can create highly accurate clocks that can account for these variations in timekeeping.

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