# Gravity and time

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## Main Question or Discussion Point

Is it possible that gravity affects time by constricting motion? We know that gravity can redshift light so if time is measured by the vibration of cesium atoms might it be similar to the effect of a pendulum being slowed by adding weight. That is the dilation of time is caused by the force of gravity constricting the motion of our timepiece, whatever that is and this constriction acts universally at the atomic level and above.
It seems to make sense at the fringe where in a black hole time stops completely in a way that could be attributable to the intense force of gravity constricting all motion whatsoever. I swear this post has nothing to do with a bong just one too many documentaries.

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Orodruin
Staff Emeritus
Homework Helper
Gold Member
No. You need to stop trying to come up with your own explanation and learn what the theory that describes gravitational time dilation accurately says. You will not do so by watching popular science documentaries.

russ_watters
Mentor
Is it possible that gravity affects time by constricting motion?
No. Gravity does not "constrict motion".
...the effect of a pendulum being slowed by adding weight.
Uh...pendulums are not slowed by adding weight(mass). The period is a function of their length only (and g, but we're on Earth).
That is the dilation of time is caused by the force of gravity constricting the motion of our timepiece, whatever that is and this constriction acts universally at the atomic level and above.
...and this of course would not explain time dilation due to motion.

PeterDonis
Mentor
2019 Award
in a black hole time stops completely
No, it doesn't. This is a pop science misconception; as @Orodruin has already pointed out, you can't learn science from pop science sources.

I'm trusting you guys to think about the questions before you answer but look at some of the sloppy answers I got because you pooh poohed me without thinking.

1).No. Gravity does not "constrict motion

Increased gravity would increase the friction at the pivot of a pendulum thus constricting the motion of a pendulum.

2) The period is a function of their length only (and g, but we're on Earth)

My question was about gravity on any body so g is not a constant

3).and this of course would not explain time dilation due to motion.

It would explain time dilation due to acceleration since gravity cant be differentiated from acceleration.

4) You never addressed the point of gravity decreasing the period of light waves via redshift. If Gravity can do this isnt it plausible that it could decrease the period of electrons in a cesium atom used to measure time dilation.

5) You will not do so by watching popular science documentaries.

I actually no longer watch science documentaries as I cant tell what is true and what is bs. I've got to say in all humility you guys dont have a lot of patience for a layman trying to understand this stuff. May I suggest a separate section for people who work for a living but would like to understand the issues without being made to feel like an idiot? I dont have the education or the time to delve into calculus and I feel like a parishioner in 15th century France who doesnt know latin. There was a time when science was presented to the public in a form that someone who doesnt specialize could understand. I listened to Faradays lectures on the Chemistry of a burning candle, they are truly fascinating and Faraday would have been apoplectic to have it said that his lectures couldnt be trusted as science.

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Dale
Mentor
You were, in fact, given correct answers.

1).No. Gravity does not "constrict motion

Increased gravity would increase the friction at the pivot of a pendulum thus constricting the motion of a pendulum.
First, that would be friction constricting the motion, not gravity. And second, both the friction and the weight would increase with increasing gravity, so it is not clear that there would be any constriction of motion at all.

2) The period is a function of their length only (and g, but we're on Earth)

My question was about gravity on any body so g is not a constant
Fair enough, but increasing g makes a pendulum go faster, so it is the opposite direction from what is needed to explain gravitational time dilation. (As well as being the wrong magnitude, and not proportional to small changes in height)

3).and this of course would not explain time dilation due to motion.

It would explain time dilation due to acceleration since gravity cant be differentiated from acceleration.
No, it wouldn’t. Again, it is the wrong direction, the wrong amount, and the wrong dependency on height.

4) You never addressed the point of gravity decreasing the period of light waves via redshift. If Gravity can do this isnt it plausible that it could decrease the period of electrons in a cesium atom used to measure time dilation.
It increases the period, not decreases. And yes, it is not only plausible that atomic clocks experience gravitational time dilation, it has been experimentally confirmed thus validating GR which predicted the correct direction, magnitude, and dependence on height of the effect, as well as the motion dependence.

I've got to say in all humility you guys dont have a lot of patience for a layman trying to understand this stuff.
Speaking bluntly, in your posts above you do not appear as a layman trying to learn this stuff. You appear as someone who has already developed a personal theory on this stuff. This “I call BS” post furthers the impression of someone who is not interested in learning, but is more interested in pushing a personal theory.

We do not tolerate personal theories here, as is clearly stated in the rules. Most personal theories are, like yours, so fabulously wrong that they are a complete waste of time for all involved. They irritate the experts and the discussion does not further our educational mission even for the proponent of the personal theory. Very little is gained by having people correct personal theories, and the proposer frequently takes umbrage at the substantive criticism, as you have.

If you really are “trying to understand this stuff” then PF will be a tremendous resource for you. Feel free to ask questions about mainstream scientific theories. We will be glad to answer such questions and teach you physics. We will not, however, entertain personal speculation.