Quote:
Originally Posted by HydrogenBond
Has there ever been experiments placing clocks below sea level to make sure time will slow as we get closer to the center of the earth? We could lower a clock into the deepest sea trenches, within a hardened container so the internal conditions can simulate the space shuttle. We keep another clock at the surface and monitor changes.
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Previous responses to this post have done, I think, a good job of answering it, but I’ve some additional comments to contribute.
The best modern
atomic clocks, such as the NIST-F1 and others in the
TAI collaborative, are already sensitive enough that arithmetic correction must be made to their digital counters when their altitude is changed by an amount as slight as that experienced when they are moved from one floor to another of the same building.
Since all of the clocks in the TAI are above sea level, and since it was established as a standard in the 1970s, the TAI is for a clock at mean sea level, all of its clocks must be adjusted using Relativity. A less “geocentric” time standard is
BCT, a calculated time that would be measured by a clock infinitely distant from all matter in the universe (ie in truly gravitationally flat space) with exactly the velocity of the barycenter of the solar system.
NIST and other labs are putting a lot of effort, with good results, into making small, inexpensive atomic clocks, so the day is likely not far off when a typical high school class could use one to measure time differences between two clocks on different floors of its building and compare them to calculations made from the formulas of Relativity. Once these become commonplace, they’ll likely be so useful that they’re carried by submarines, making the experiment HydrogenBond describes practical.
Although you’d have to go considerably deeper than the bottom of the deepest ocean trench to begin to see An interesting question that came up in a string of posts ending with
Re: More correct, but more approximate, examples of grav time dilation in and around (these posts are about gravitational time dilation as one approaches the center of the Sun, but the principle is the same as with the Earth) is what gravitational time dilation would be experienced by a clock placed at the bottom of a shaft reaching all the way to the center of the Earth, where the net force of gravity relative to the surface is zero. Although one might expect (as I and an erroneous wikipedia article suggested) that such a clock might actually run faster than one on the surface, this is not the case. Gravitational time dilation is at a local maximum at the center of the Earth. Even at this maximum, the speed of a clock at the center of the earth relative to one at its surface is very nearly an unchanged 1, on the order of
.
To get large gravitational time dilations (and such a thing could be very useful!), you need either much more mass than can be had with a mere Earth-size planet, or even a star, or you need great, black hole or near black hole, density.
Atomic clocks and gravitational time dilation without and within planets and stars
