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Q & A: time dilation and gravity

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Most recent answer: 05/07/2016
Q:
Gravity and circular logicIf warped spacetime, with the time component being the major player, causes gravity, then why does gravity cause time dilation. Is this not a circular argument? What gives?
- Richard A Sullivan (age 63)
Forked River NJ USA
A:

The time dilation effect (time running slower downhill) is identical to the main source of gravitational path bending. (For light or other things moving at or near the speed of light in the reference frame of the massive gravity source, another major piece of the bending comes from space curvature.) So there is some circularity to the argument, as you say. If the Equivalence Principle (local undetectability of gravitational fields) is correct, then you can show that the time dilation implies bending paths and vice versa. But why accept the principle? Because the detailed implications of it are confirmed by experiments, including the recent spectacular observation of gravity waves from merging black holes.

Mike W.

Some old answers in which you might be interested:
http://van.physics.illinois.edu/qa/listing.php?id=31019

https://van.physics.illinois.edu/QA/listing.php?id=21717&t=gravitational-lensing-of-the-sun


(published on 05/07/2016)

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