Simple hypothesis on gravity.

[Wanderinggiraffe]

Hello potential illuminators.

I like to have thought experiments every now and then, and when I had questions about gravity I couldn't find appeasing answers. SO I thought about it and here is what I came up with.

/Bear with me/ The nonsensical answer, gravity is the cumulative struggle to maintain existence. boom. nah, that sucks. But seriously though. Gravity is the pressure caused by displacement of "space." Best way to visualize it for me is expanding a balloon under water, the water wants that space back.

In this hypothesis space and time are together, spacetime, woo. Anyway, therefore the area around the object that has displaced spacetime has a higher density/concentration of just that, meaning that if you traveled further out, you would be crossing more spacetime and that could explain time dilation as well. Isn't that cool.

What do you guys think about this, I really want to have a discussion, but I live in a city in South Africa and my family just gives me a nod here and there.

[ajb]

You have presented a loose description of general relativity, gravity is the 'local shape' or 'geometry' of space-time. Test particles under the influence of just gravity follow geodesics, which is the straightest possible path on a curved space-time. We also know how to explain gravitational time dilation within general relativity.

 

My advice would be to read up on the basics of general relativity. How much physics and mathematics do you know already?

 

Just as a side note, I met your fellow countryman George F. R. Ellis a few weeks ago, he is a world leading expert in general relativity!

[DanMP]

... We also know how to explain gravitational time dilation within general relativity....

 

Really? How? Like this: https://www.academia.edu/9724931/Gravitational_time_dilation_explained_for_beginners_ ?

 

If so, what if the photon movement is up-down? How the "path"/time increases than?

And how this apply to (affect) a real clock?

 

Sorry if my questions are off-topic here. Please redirect me/them to a proper place.

[Strange]

 

Really? How? Like this: https://www.academia.edu/9724931/Gravitational_time_dilation_explained_for_beginners_ ?

 

I can't access that so can't comment on it.

 

If so, what if the photon movement is up-down?

 

You might want to read about the Pound-Rebka experiment, which looks at exactly this.

https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment

[ajb]

Really? How? Like this: https://www.academia.edu/9724931/Gravitational_time_dilation_explained_for_beginners_ ?

The effects of a gravitational well (ie. the Schwarzschild geometry) on clocks should be covered in any book on GR. For example, you can consult the lecture notes of Carroll.

 

If so, what if the photon movement is up-down? How the "path"/time increases than?

And how this apply to (affect) a real clock?

I am not sure what you are asking.

[swansont]

If so, what if the photon movement is up-down? How the "path"/time increases than?

And how this apply to (affect) a real clock?

 

Real clocks run faster when they are higher in a potential well. This has been tested; there's the Vessot Maser-on-a-rocket experiment, there's GPS, and there's the continual reporting of clocks at different elevations to the BIPM

[DanMP]

I can't access that so can't comment on it.

Enter the site and scroll down. It explains gravitational time dilation imagining a light clock (2 mirrors ...) in which the light paths become longer closer to a gravity well due to spacetime deformation.

 

You might want to read about the Pound-Rebka experiment, which looks at exactly this.

https://en.wikipedia.org/wiki/Pound–Rebka_experiment

Pound–Rebka_exp. is a gravitational redshift experiment. How it can explain gravitational time dilation? Try again my link to see what I meant.

 

 

Real clocks run faster when they are higher in a potential well. This has been tested; there's the Vessot Maser-on-a-rocket experiment, there's GPS, and there's the continual reporting of clocks to the BIPM

This is not what I'm questioning. I totally agree with all that GR predicts.

 

I just want to see/read a proper explanation, if possible ...

 

 

... you can consult the lecture notes of Carroll. ...

Here? I searched for "clock" and found nothing.

Edited February 3, 2016 by DanMP

[swansont]

 

Pound–Rebka_exp. is a gravitational redshift experiment. How it can explain gravitational time dilation? Try again my link to see what I meant.

 

Time dilation is a frequency shift. They are the same thing, just explained from different perspectives. If the frequencies are different, then the accumulated phase (i.e. the elapsed time) will be different.

[imatfaal]

Dan - get yourself a better guide to General Relativity. That is a post by a school boy - it is great for a school boy - but you can do so much better than that. If your maths is up to it look up Sean Carrol's notes - they are superb; and if your maths is not upto that standard then you will struggle to get a really good handle on what is at its foundation a mathematical and geometrical idea.

[DanMP]

 

Time dilation is a frequency shift. They are the same thing, just explained from different perspectives. If the frequencies are different, then the accumulated phase (i.e. the elapsed time) will be different.

 

In the same place we have both redshift and blueshift, depending on the light source beeing down or up. How exactly does this explain time dilation in the light clock above, or in any clock?

Dan - get yourself a better guide to General Relativity. That is a post by a school boy - it is great for a school boy - but you can do so much better than that. If your maths is up to it look up Sean Carrol's notes - they are superb; and if your maths is not upto that standard then you will struggle to get a really good handle on what is at its foundation a mathematical and geometrical idea.

My "maths" is not so good I hoped that there is a simple, logical explanation. I'll try to read Sean Carrol's notes next day(s).

[ajb]

Here? I searched for "clock" and found nothing.

102p of the 1997 lecture notes available on the arXiv discuss this using the equivalence principal and a Newtonian potential. You can also derive these results in GR properly, but maybe you do not need this right now.

[swansont]

In the same place we have both redshift and blueshift, depending on the light source beeing down or up. How exactly does this explain time dilation in the light clock above, or in any clock?

 

You don't have a blueshift and redshift in the same place — the detectors (clocks) are not co-located. The upper detector sees a redshift. The lower detector sees a blueshift. Or, viewed another way, the upper clock runs fast while the lower one runs slow, relative to the light.

[imatfaal]

My "maths" is not so good I hoped that there is a simple, logical explanation. I'll try to read Sean Carrol's notes next day(s).

 

To properly understand this is difficult - this is not taught in any depth until a fair distance through a physics degree . To get a rough view - try hyperphysics. Or Search on John Baez - his notes are a bit easier going and less mathy.

 

One problem is that gravity isn't amenable to a simple logical explanation - Newton might well have been one of the brightest people who ever lived; his explanation was simplish, not very logical, and had limits of applicability (which your questions are beyond). Einstein could also lay claim to that honour - and his explanation has the same failings and is MUCH MUCH harder to understand.

[Mordred]

Here is a free open end user textbook. Yes it's SR as opposed to GR however the mathematical level is easy to handle.

 

http://www.lightandmatter.com/sr/

 

the Beaz site already mentioned is also good

[DanMP]

I created a new topic for time dilation discussion I started above:

http://www.scienceforums.net/topic/93360-simple-explanation-for-time-dilation/

(here it was off-topic)