Kip Thorne's take on Gravity

[geordief]

I came across this idea on a BBC documentary last night -already put out on Youtube.

 

https://www.youtube.com/watch?v=75ESo5IPpBs

at I hour 25 mins and 15 seconds onwards

 

Although the idea does resonate with me , I am unable to discuss this intelligently and am hoping someone on this forum can see if the idea has merit.

 

To me it seems to be putting (or seeing) gravity in a back to front way in regards to its relationship with the workings of time but I do not have a good grip on the processes involved.

 

Here is the passage in the book that Khalili was clearly reading from ("The Science of Interstellar" by Kip Thorne)

 

 

"Everything likes to live where it'll age the most slowly & gravity pulls it there."

 

https://books.google.ie/books?id=PbWYBAAAQBAJ&pg=PT62&lpg=PT62&dq=%22everything+likes+to+live+where%22&source=bl&ots=h7L5wczpdS&sig=NUYtfOqzJltUpVUbc89WZ6FZI3U&hl=en&sa=X&ved=0ahUKEwjHiquzxvvSAhVPFMAKHSZGBfwQ6AEIGzAA#v=onepage&q=%22everything%20likes%20to%20live%20where%22&f=false

Edited March 29, 2017 by geordief

[koti]

"Gravity that we experience on earth is due to the slowing of time on earth"

I must say that I have no idea what this is about. I have admiration and respect for Kip Thorne so I assume its a either a poor word choosing or theres some more meaning to this. I dont get it.

[Bird11dog]

I addressed this idea back in 2014 here.

 

http://www.scienceforums.net/topic/83655-time-gravity/

Edited March 29, 2017 by Bird11dog

[geordief]

"Gravity that we experience on earth is due to the slowing of time on earth"

I must say that I have no idea what this is about. I have admiration and respect for Kip Thorne so I assume its a either a poor word choosing or theres some more meaning to this. I dont get it.

That quote is from the video,isn't it? It is Kip Thorne who says those words.

 

I think Kip Thorne is attributing that assertion to Einstein(I have no idea where Einstein may have said it:perhaps others do) and the claim seems to be that that the need for an object to minimize its passage of time somehow causes the phenomenon we experience as gravity. (any connection with the principle of least action? ) http://yima.csl.illinois.edu/psfile/ECE553/FeynmanLecturesOnPhysicsChapter2-19.pdf

 

I think Bird11dog did indeed bring up a very similar idea in the thread he mentions.

http://www.scienceforums.net/topic/83655-time-gravity/

 

From my limited understanding I think that it may not be possible to disentangle time dilation from spatial contraction.

Edited March 30, 2017 by geordief

[MigL]

Are you familiar with Fermat's principle of least time ( for massless particles ), and the more general principle of least action by De Maupertius?

It forms the basis of modern ( Lagrangian and Hamiltonian ) mechanics and even GR.

[koti]

That quote is from the video,isn't it? It is Kip Thorne who says those words.

 

I think Kip Thorne is attributing that assertion to Einstein(I have no idea where Einstein may have said it:perhaps others do) and the claim seems to be that that the need for an object to minimize its passage of time somehow causes the phenomenon we experience as gravity.

 

I think Bird11dog did indeed bring up a very similar idea in the thread he mentions.

http://www.scienceforums.net/topic/83655-time-gravity/

 

From my limited understanding I think that it may not be possible to disentangle time dilation from spatial contraction.

Yes, Kip Thorne says that in the video and I think he also says that hes quoting Einstein. I agree that time dilation cannot be seperated from spatial contraction and actually from gravity as well but I must admit that I was not aware that gravity itself is caused by time dilation? Im having trouble parsing this. Edited March 30, 2017 by koti

[geordief]

Are you familiar with Fermat's principle of least time ( for massless particles ), and the more general principle of least action by De Maupertius?

It forms the basis of modern ( Lagrangian and Hamiltonian ) mechanics and even GR.

I think we cross posted . That is what I was wondering about in my Edit ,I think (the Feynman lecture http://yima.csl.illi...Chapter2-19.pdf).

[koti]

Are you familiar with Fermat's principle of least time ( for massless particles ), and the more general principle of least action by De Maupertius?

It forms the basis of modern ( Lagrangian and Hamiltonian ) mechanics and even GR.

Both least time and least action was mentioned in many of the pop science books Ive read but I couldnt say Im familiar with it.

[robinpike]

"Gravity that we experience on earth is due to the slowing of time on earth"

I must say that I have no idea what this is about. I have admiration and respect for Kip Thorne so I assume its a either a poor word choosing or theres some more meaning to this. I dont get it.

 

I think this refers to the suggestion that if objects with mass were to 'prefer' to be in a state with the least rate of time, then this would cause objects with mass to move towards other objects with mass. Since mass bends space-time, and time runs slower the nearer the objects are to each other, thus the attraction attributed as gravity could be just the objects moving so as to be in a state of lesser time. I don't know if this idea has any merit.

[koti]

 

I think this refers to the suggestion that if objects with mass were to 'prefer' to be in a state with the least rate of time, then this would cause objects with mass to move towards other objects with mass. Since mass bends space-time, and time runs slower the nearer the objects are to each other, thus the attraction attributed as gravity could be just the objects moving so as to be in a state of lesser time. I don't know if this idea has any merit.

Sure. Mass causes the curvature of spacetime which causes gravity or like Swansont once said "gravity is spacetime curvature" i always assumed that tme dilation is the result of gravity not its cause.

[geordief]

Is this idea that bodies in movement naturally choose the path of the least passage of time in spacetime equivalent to the idea that they will choose the path that requires the least energy?

 

They have a "budget" of energy that only allows them one path ?

 

 

" i always assumed that tme dilation is the result of gravity not its cause "

 

 

 

Have we read too much of a cause/effect into this? Are the two phenomena interdependent without it being possible to separate chicken from egg (except mathematically as part of a model)?

Edited March 30, 2017 by geordief

[koti]

Have we read too much of a cause/effect into this? Are the two phenomena interdependent without it being possible to separate chicken from egg (except mathematically as part of a model)?

I agree with you 100%. Its just that Kip Thorn's words resonate with me and I still cant parse them:

"Gravity that we experience on earth is due to the slowing of time on earth"

[StringJunky]

I agree with you 100%. Its just that Kip Thorn's words resonate with me and I still cant parse them:

"Gravity that we experience on earth is due to the slowing of time on earth"

It makes no sense to me either because time and gravity are effects resulting from the interaction between space and mass-energy.

Edited March 30, 2017 by StringJunky

[koti]

It makes no sense to me either because time and gravity are effects resulting from the interaction between space and mass-energy.

Right? I hope its just momentary poor word choosing from Kip Thorne, especially that hes saying that hes quoting Einstein.

Edited March 30, 2017 by koti

[mistermack]

My own take on gravity is that the Earth is sucking in inertial frames, so that at the surface, we are accelerating through them at a rate of 32ft per sec squared. The force is provided by the chair I'm sitting on.

If I fall off a cliff, I temporarily stay motionless in one of those inertial frames, till I and the frame hit the foot of the cliff. At which point, the inertial frame keeps going, whereas I stop dead. (literally).

[Bird11dog]

Inertial frames are time dependent. The vibration of atoms obviously have very short and energetic inertial frames except at absolute zero.

[Bill Ryan]

Sorry for joining a year late.  I just joined this site. I was surprised Kip Thorne was so tentative in that video.  On another site a similar conversation started with reference to this link: 

 

 

This is the best attempt I've seen to support a physical intuition of the causal relation between curved time and gravitational attraction. On Earth (modest gravity/ normal speeds) Earth's mass produces a time dilation gradient that is way more important than space curvature. Our progress through time is like light moving through a prism - the drag increases toward the  thicker part of the prism and the light bends. 

I think this is in line with Bird11dog 2014 thread as far as I understood it.

Excerpting from the other site, I said this:

This is how I see the video. Everybody knows that when you are mowing the lawn and hit the sidewalk at an angle the difference in the resistance between grass and concrete makes the mower change direction towards the grass. Similarly, when light passes through a retarding medium with angled surfaces ( a prism) the right and left differences in the amount of glass as opposed to air makes the light change direction towards the thicker glass. Exotically, as an object is traveling through time in any gravitational field (for instance near the earth's surface) the modestly greater retardation in such progress that any object, even a point particle, experiences on its high and low flanks (as a result of gravitational time dilation) shifts the direction in space of its progress through time. Thus, if unsupported, it falls. Time dilation is responsible for what we experience as gravity in normal low velocity settings. But when something is traveling through space at a speed equivalent to how we are all progressing through time, (like light) then the curvature of space shows dramatically and the total effect, space plus time, is double what we normally experience. If Newton thought light had mass he would have predicted the same starlight curvature around the sun that Einstein mistakenly originally predicted before he figured out the double effect above. In this sense you can think of Newton gravity as the equivalent of time curvature without space curvature. I am without credentials so will now let the physicists have their way with me.

Reference https://www.physicsforums.com/threads/does-gravitational-time-dilation-cause-gravitys-attraction.881449/

And then BepiIT (who sounds like he might be a physicist), said this:

The GR metric for Newton's gravity is obtained from the Schwarzschild metric by assuming non relativistic velocities (v^2/c^2 << 1) and weak gravitational field (GM/Rc^2 << 1). In Cartesian coordinates It reads

ds^2 = -(c dt)^2(1-2GM/rc^2) + (dx^2 + dy^2 + dz^2)(1+2GM/rc^2)

so it does contain a time deformation term g_00 = (1-2GM/rc^2) (causing gravitational time dilation) as well as a space deformation term (1+2GM/rc^2). For non relativistic velocities, the time deformation is c^2 times larger than space curvature, because of the c^2 term in (c dt)^2.

Therefore, to leading term Newtonian space is flat. And in fact the equation of Newtonian motion derived via a least action principle do not make use of the spatial term of the metric.

Newton gravity originates from the g_00 term, as its spatial gradient (as Pervect wrote), and may be intuitively understood as a differential motions described by Bill Ryan (in fact gravitational force is the gradient of the potential, which in the above metric corresponds to the g_00 term). Space curvature is relevant for relativistic motions, e.g. by doubling the light deflection effect in the weak field limit (whereas for strong gravitational fields the space curvature term becomes dominant). Space curvature is also important for non relativistic motions if the measure is very accurate, e.g. by opening the orbit of planets and causing a precession like that measured for Mercury.

Therefore the visual exemplification of a rubber sheet curved by a heavy ball (the Sun), with smaller marbles orbiting around due to space curvature, is essentially wrong, because Newtonian space is flat. Eugene Khutoryansky's video is thus correct as far as I understand. The problem is that no GR book discusses this explicitly, but leave the point rather implicit (see for example the discussion on Newtonian metric in Hartle's "Gravity"). Only exception I know is this book: http://www.relativity.li/en/epstein2/read/ by David Eckstein. Hope this helps a bit. 

Reference https://www.physicsforums.com/threads/does-gravitational-time-dilation-cause-gravitys-attraction.881449/

 

 

 

 

 

Edited May 1, 2018 by Bill Ryan

[beecee]

2 hours ago, Bill Ryan said:

Reference https://www.physicsforums.com/threads/does-gravitational-time-dilation-cause-gravitys-attraction.881449/

The first reply from your link to that forum says it all.....

Quote

"A YouTube video is not an acceptable reference. You will need to find a textbook or peer-reviewed paper. A quick Google search does not turn up any actual papers by this person".

and then gave you some proper reference thus....

https://arxiv.org/abs/gr-qc/9712019

 

 

[Strange]

4 hours ago, Bill Ryan said:

Therefore the visual exemplification of a rubber sheet curved by a heavy ball (the Sun), with smaller marbles orbiting around due to space curvature, is essentially wrong, because Newtonian space is flat.

1. It is not Newtonian space, so that is irrelevant.

2. It is an analogy to curved space-time not curved space

3. It is just a really bad analogy

4. You can't falsify a scientific theory by criticising an analogy

5. You seem to have ignored all the valid responses in that other forum that point out why you are wrong

 

Edited May 1, 2018 by Strange
5

[MigL]

K Thorne could be making an analogy...

Consider a 2D representation of 3D space, and stack these sheets, or foliations, on top of each other in the third dimension ( as time advances ).
If time is advancing at different rates in different areas of these 2D foliations, we notice a 'depression' in the stack of foliations where time is advancing slower.
In effect, the top of the stack of foliations, with its depression where time is advancing slower, resembles the stretched rubber sheet with a bowling ball analogy of gravity.

.

[koti]

On 3.05.2018 at 5:56 AM, MigL said:

K Thorne could be making an analogy...

Consider a 2D representation of 3D space, and stack these sheets, or foliations, on top of each other in the third dimension ( as time advances ).
If time is advancing at different rates in different areas of these 2D foliations, we notice a 'depression' in the stack of foliations where time is advancing slower.
In effect, the top of the stack of foliations, with its depression where time is advancing slower, resembles the stretched rubber sheet with a bowling ball analogy of gravity.

.

Your above analogy visualizes time and it looks good. Kip's statement does something else, it implies causality between time dilation (cause) and gravity (effect) I think it's just momentary bad choice of words, I can't imagine him sticking to this if asked, it's just plain wrong. 

[smokequitterv2]

Things like apple falling down is due to gravity ,

Things like earth not falling down is due to gravity

The only thing i understand about gravity is newtons law's

Even though i have been staring into these , i have no idea what it is .

 

 

 

Edited May 4, 2018 by smokequitterv2

[Doozel]

I didn't see the video mentioned in the OP since it's been removed, but this is what Kip Thorne wrote in the book: "Time, he realized [referred to Einstein], must be warped by the masses of heavy bodies such as Earth or a black hole, and that warping is responsible for gravity.", and again: "The greater the slowing of time, the stronger gravity's pull.".

I think that, since space and time are linked together, to make the explanation cleaner he simply uses the slowing of time to indicate space-time curvature. Don't forget that "The science of Interstellar" is mainly a divulgative book and indeed after these statements he continues his exposition talking about how the slowing of time is important in Interstellar.

[geordief]

On 5/3/2018 at 4:56 AM, MigL said:

K Thorne could be making an analogy...

Consider a 2D representation of 3D space, and stack these sheets, or foliations, on top of each other in the third dimension ( as time advances ).
If time is advancing at different rates in different areas of these 2D foliations, we notice a 'depression' in the stack of foliations where time is advancing slower.
In effect, the top of the stack of foliations, with its depression where time is advancing slower, resembles the stretched rubber sheet with a bowling ball analogy of gravity.

.

Have we lost Mordred's answer to your post ? He said that Kip Thorne seems to have just got it wrong if I recall right.

 

Edit:it seems to be koti's post I was looking at . Thought it was Mordred's .My mistake.

Edited May 4, 2018 by geordief

[swansont]

I haven't looked at the details, but since there is a relationship between gravitational time dilation and length contraction/curvature, I don't find it all surprising that one could parameterize equations and re-cast gravitational attraction in terms of gravitational time dilation (or a time dilation gradient).

 

However, "The greater the slowing of time, the stronger gravity's pull." is incorrect. Time dilation is dependent on the gravitational potential, not directly on the strength of gravity. Someone inside of a uniform spherical mass shell feels no gravity, but would experience time dilation.

 

Janus runs through another example here https://www.scienceforums.net/topic/113821-the-logical-solution-to-the-twin-paradox-explained-comprehensively/?tab=comments#comment-1042761