That Time Problem??

[InfiniteNow]

Originally Posted by Southtown

But the guy was asking about gravity. How could time pass by differently in orbit than it does on the surface. I can't answer, so I share in his desire to realize such an explanation.

It's more about gravitational potential.

Try starting here, and then come back with a more specific question.

Gravitational time dilation - Wikipedia, the free encyclopedia

[modest]

Originally Posted by Southtown

At present time, to me time is the flip-side of the space coin. Space is the distance between locations, and time is the distance between moments, however dynamic the relation amongst the things about which we know very little may be.

But the guy was asking about gravity. How could time pass by differently in orbit than it does on the surface. I can't answer, so I share in his desire to realize such an explanation.

According to the equivalence principle of general relativity there is no descriptive difference between an accelerating frame of reference and a stationary frame in the presence of a gravitational field.

This means a person on a rocket ship with constant acceleration will feel like they are standing on the surface of a planet. In either case a person feels weight. Also, someone in an elevator that is free falling toward a massive body like earth will feel weightless just like someone who is stationary in deep space outside the influence of any gravitational field.

In fact, general relativity proposes that someone who conducts experiments of special relativity in a free falling elevator will get the same results as someone who does the same experiments in a stationary elevator in deep space.

This idea can be used to derive all the laws of General Relativity including gravitational time dilation. GR tells us that if we are on earth's surface looking up at a clock higher in the gravity well then the clock will appear to run faster than our clock.

To derive this with the equivalence principle we must consider what would happen in an accelerating frame (or elevator) with no gravitational field. Let's say we are in a very large elevator and there is a clock on the ceiling. The elevator is undergoing constant acceleration like a rocket. It is in deep space. Every second the elevator goes faster.

To make this situation simple we can consider the clock on the ceiling to simply be a strobe that is programmed to blink sixty times per second. Our own clock is also programmed to blink sixty times per second. If you consider this situation you will realize the person on the floor will not see the strobe on the ceiling flash sixty times a second but faster than that. Because the entire elevator is accelerating there is a Doppler-like effect where the strobe flashes are observed more quickly from flash to flash by the time they get to the floor. The change in velocity from the time of emission to observation accomplishes this.

The important things are:

1. If the equivalence principle of general relativity is true then the time dilation I just described for our accelerated frame must extend to gravitational potential as well.
2. Can this be described mathematically and applied to gravitational fields.

Number one has been found true and verified by atomic clocks (such as GPS)

Number two - mathematically, a person can use accelerated coordinates such as the Rindler metric:



This can be used to describe the situation above and it can also be used to derive gravitational time dilation and redshift which is done here:

Gravitational redshift - Wikipedia, the free encyclopedia

So, I believe the reason for gravitational time dilation can be shown as a result of gravity as "curved spacetime". Actually, it was predicted on that basis. Why gravity curves spacetime?

-modest

[Southtown]

Originally Posted by InfiniteNow

It's more about gravitational potential.

Try starting here, and then come back with a more specific question.

Gravitational time dilation - Wikipedia, the free encyclopedia

Hmm... ok, why does gravity affect time?

[Southtown]

Originally Posted by modest

So, I believe the reason for gravitational time dilation can be shown as a result of gravity as "curved spacetime". Actually, it was predicted on that basis. Why gravity curves spacetime?

-modest

Thank you sir for explaining that so eloquently. Ps why the "eye of Ra" in yer sig?

[InfiniteNow]

Originally Posted by Southtown

Hmm... ok, why does gravity affect time?

You will have to bear with me. I only learned some more about this yesterday thanks to a post elsewhere by Janus. In other words, I'll try to answer correctly, but may misspeak and my comments should be checked.


We know that acceleration results in time dilation/length contraction.
We know that gravity is indistinguishable from acceleration.

Now, in this example, when time is dilated in one reference frame relative to another, it is because there is greater "gravitational potential."

There ya go.



From the wiki link I shared:

Gravitational time dilation is the effect of time passing at different rates in regions of different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes.

<...>

Gravitational time dilation is manifested in accelerated frames of reference or, by virtue of the equivalence principle, in the gravitational field of massive objects. In more simple terms, clocks which are far from massive bodies (or at higher gravitational potentials) run faster, and clocks close to massive bodies (or at lower gravitational potentials) run slower.

It can also be manifested by any other kind of accelerated reference frame such as an accelerating dragster or space shuttle. Spinning objects such as merry-go-rounds and ferris wheels are subjected to gravitational time dilation as an effect of their angular spin.

This is supported by the general theory of relativity due to the equivalence principle that states that all accelerated reference frames possess a gravitational field. According to general relativity, inertial mass and gravitational mass are the same. Not all gravitational fields are "curved" or "spherical"; some are flat as in the case of an accelerating dragster or space shuttle. Any kind of g-load contributes to gravitational time dilation.

[Southtown]

I read that page. And I understand that time dilation happens by either gravitation or acceleration. But the OP asks how it happens mechanically, and I can't answer. I imagine that both acceleration and gravitation act upon atoms in the same manner. Though I admit, the speed of light being observed equally in all inertial frames of reference kinda tweaks my noodle.

[CHADS]

Would I be right in thinking that as an object accelerates its kinetic Energy increases .. and its this Energy which Contributes to its Gravitational potential?

So the faster an object travels the more mass it seems to have so gravity and velocity are similar in some fashion?

Whilst moving at large velocities or in greater gravitational wells ;The whole clock and its working mechanisms and moments are dimensionally restricted in doing what it would do if it was on earth. The clocks Mechenisms and moments on Earth would be the comparible clock.

Now in comparison on Earth to a clock taken away at 90% speed of light Its Mechanisms and moments would be restricted litrally in dimension. Like a funnel .
A snooker ball can whirl around the top of a funnel .. but one that is deeper in the funnel is heavily restricted in its movement and could only make smaller whirls in relation to the ball at the top of the funnel.

So when the ball Travelling at 90% C at the bottom of the funnel returns to earth
Which is represented at the top of the funnel It has only been moving at small circles ... in comparison to the clock on earth ... So Shows a lesser time.

The ball has mass so cant pass straight through the funnel but a photon is massless and can occupy the stem of the funnel .

Hope this Abstract concept helps in explaining something.

[InfiniteNow]

Originally Posted by Southtown

I read that page. And I understand that time dilation happens by either gravitation or acceleration. But the OP asks how it happens mechanically, and I can't answer. I imagine that both acceleration and gravitation act upon atoms in the same manner. Though I admit, the speed of light being observed equally in all inertial frames of reference kinda tweaks my noodle.

I don't have the words be explain it myself, but I will ask, do either of these help?


TimeDilation

LengthContract




More below:

Introduction to special relativity - Wikipedia, the free encyclopedia

This article aims to give a gentle, non-technical introduction to the theory based on geometrical intuition and explain some of the terminology and formalism involved. A more advanced, encyclopedic description will be found in the parent article Special relativity. It will be helpful to approach relativisic mechanics by first studying some properties of the classical (Newtonian) picture.

Animations:

1. MichelsonMorley
2. TimeDilation
3. LengthContract
4. ContractInvisible
5. Simultaneity
6. TwinParadox
7. Foucault
8. Precession

[Moontanman]

Modest: Also, someone in an elevator that is free falling toward a massive body like earth will feel weightless just like someone who is stationary in deep space outside the influence of any gravitational field.

Now this sounds like a real time problem, to one of these people what time it is will be far more important than it will be to the other. Hmmm.... I guess time really is reletive I couldn't help my self Modest, it just seemed so obvious that time would indeed be a probelm in this context. On the other hand if the gravity well was deep enough (black hole) it wouldn't matter to either one of them would it? Both situations would last forever from each others point of view.

[CHADS]

Infinite!

Those Animation where great .. thanks for taking the time .... But im starting to get Scared ... Why does our Universe Have to be this way?

If PI measured just 3 .. Then i suppose we would take it for granted .