Gravity: The why and the how:

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Oct 24, 2015.

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Our best and most accurate description of gravity we have of course is Einstein's GR and curved spacetime.
An excellent analogy that gives us a mental picture of this is the stretched rubber sheet analogy.
Although an excellent analogy, it needs to be said that all analogies are constructed to help visualise how gravity works, and more Importantly that they all have limitations in what they are describing.
Here is another I found that helps explain "How gravity makes things fall"

What do you think?

The video is 4 minutes long.

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5. danshawenValued Senior Member

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The video does respond to the question of 'how'. It makes no attempt to explain an answer to the question: 'why?'

Inertialess spacetime is not a sliding board, nor a rubber sheet, which is really no more advanced an explanation than was Robert Hooke's direct proportion celestial spring clockwork universe which he proposed as a counterproposal to Newton's inverse square law of gravitation. Spacetime may behave 'like' it is a rubber sheet that is basically a spring, but this would be an analogy, not an explanation.

Atomic structure gets its inertial mass from interaction with the Higgs mechanism (2%), and the other 98% of mass/energy that is a result of energy interactions from strong force between quarks, gluons, and color charge exchange. This mass/ energy likewise results from quantum energy fluctuations seething in the vacuum. Bound energy is the same as mass. Since E=mc^2.

Explain how this acts like an elastic rubber sheet without inertia acting between particles of bound energy, and you might be onto something worth explaining.

Last edited: Oct 25, 2015

7. arfa branecall me arfValued Senior Member

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I think gravitational lensing is a better gravitational 'analogy'.

Instead of the rubber sheet with a dent in it from a gravitational source, we have a four dimensional space with curved light in it in three of the dimensions, of which we get two in the two dimensional images from Hubble:

The four bright objects around the central one are more distant than it, and are images of the same object which is a quasar. I think it's like, a really long way away, and it must therefore be an image from the early history.

But, the stretching of a rubbery sheet shows up anyway, because that's what a two dimensional image (of a gravitationally lensed object) will look like from anywhere else, according to the special theory!

Note that, of course, the lensed galaxy's motion is sped up considerably . . .

And how much it resembles a black sphere moving on the surface of a (viscous) liquid, the image of the galaxy would be a reflection on the same surface of a dark fluid with enough viscosity to support the black sphere.

Last edited: Oct 26, 2015
8. KilljoyKlownWhateverValued Senior Member

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Interesting, mass of any kind warps space/time and we call it gravity. This warping of space/time has an effect on just about everything else in reality. At least I can't think of anything that isn't affected in some way by gravity. It has been considered one of the 4 major forces that govern our reality. But if it is in fact just a warping of space/time. Is it a true force?

9. arfa branecall me arfValued Senior Member

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That animation is presumably a faithful representation of a black hole moving in front of a galaxy, and it's got me thinking you could probably reproduce it with a real sheet of dark shiny rubbery material (I don't know where to get any though), a large ball bearing painted matte black, and a projector. Controlling the speed would be a bit tricky.

But it's what you call a heuristic, a way to visualise it in a plane which is coincident with motion. Add reflectivity to a sheet of dark rubber and you're away.

But wait a sec, all those ideas seem to have something exactly backwards: space isn't a dark reflective fluid, and the galaxy being a reflection has a problem with the projected image lying across the black sphere.
The ball needs to have a lower density so the fluid can support it, and it will sink into the fluid some, unless there is near-perfect surface tension.

The image of the galaxy is distorted in the above animation because the surface of an abstract fluid is distorted by a ball which we are comoving with, this doesn't depend on whether the galaxy image is inside the fluid or outside it and reflected off the fluid's surface.

The surface is determined by the relative motion of the galaxy and the black hole; does the black hole "touch" this surface at all, even at a single point? The disc absorbs all the light from the galaxy behind it in your line of sight, and in the analogy where the galaxy's image is reflected off a surface, the black sphere doesn't reflect any of that image.

Aha, so punch a circular hole in some sheet metal and make a nice hemispherical depression around the hole. With a bit of a paint job that gives you a nice reflective surface (black of course), you can distort the reflected images of distant objects and take photos that look like gravitational lensing.

Last edited: Oct 26, 2015
10. arfa branecall me arfValued Senior Member

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Actually, the hole has to be at the bottom of a fluted part of the metal; the hole has a finite diameter but the fluted part (of the warped spacetime) has to extend to the event horizon, but what determines how far this is? And this is what passes in front of a more distant galaxy from one point of view.

11. danshawenValued Senior Member

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Light bends in a medium like glass whenever it slows down, and we make use of this fact to make curved lenses out of glass that bend the light in a manner that can produce larger images.

Light also slows down in the vicinity of gravitational lensing, and the effect seems to be exactly the same as if it were refracted through something like a curved glass lens. The only difference between the two effects is, if you were measuring the speed of light in the vicinity of the gravitational lens, you would theoretically see no difference in the measured speed of light locally anywhere along its curved trajectory.

This is in part because light is affected by relativity's time dilation effect in the same manner that energy bound as matter is. Gravity is the cause of both the time dilation and the bending of the light.

But even if you had a sensitive interferometer local to where the gravitational lensing caused the curvature, no experiment you cold perform locally would reveal that any change in time dilation in the path of the bending light was occurring, including red shifting. Nor could you detect that the light had deviated fron its straight line path until and unless both you and the light had traveled a very great distace from where it had curved.

It's because time, energy, and rotation of the propagation of energy is all that exists. There is no space, no spacetime. EVERY dimension you observe in this universe is the dimension of time. Perfect rotation in every direction of the single temporal dimension, and the fact that time proceeds at different rates everywhere is what provides the illusion that other dimensions of space exist, and also allows energy to become bound as matter.

It's the reason relativistic mass seems to increase with increasing kinetic energy, and also the reason time dilation seems to increase in 'regions' where there is a higher concentration of bound energy, and the only way this can happen is if energy becomes bound. This is WHY there appears to be curvature of 'space', and, as implied by the way it is dealt with in the video, the reason really has nothing to do with 'space', and EVERYTHING to do with time, and time dilation. Forget coordinate systems; there never was any such thing as an origin for anything other than time, and time cannot be used as a Euclidean coordinate system because it proceeds at different rates everywhere, literally, in the real relativistic universe.

There is only time and energy that is bound or unbound. Bound energy rotates. Unbound energy propagates at the speed of light. The instant of 'now' is the same everywhere, but time proceeds at different rates everywhere.

It is a consistent view, which is one reason I don't seem to be able to forget about it. No rubber sheets, rubber rooms, or strait jackets, if you please. If you don't like the idea, just forget it. I won't attack you, and I don't even care if you understand.

Last edited: Oct 26, 2015
12. danshawenValued Senior Member

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Any coordinate system you try to construct using time and the speed of light will be a flawed and a crooked one, nor will any amount of mathematical description of such a thing avail a better understanding of how it curves on a larger scale and yet does not curve on a smaller one which includes all we are capable of measuring. Space that requires two observers to do simple geometry is nothing like the conception of Ancient Greece.

Using Pythagoras to try and dig mathematics out of its crooked hole would be humorous if so many did not believe that Minkowski had any concept of what he was doing. Time and space don't mix like that. Where is the description of scale? There is only time, and energy.

Last edited: Oct 26, 2015
13. The GodValued Senior Member

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If there is no space then what do you mean by time proceeds at different rates everywhere ? What is everywhere ?

I am not a fan of spacetime.....but certainly (rather intuitively) time has no meaning without space and vice versa...I am afreaid something is flawed in your reasoning....And how does variable rate of time everywhere of yours (which is not space as per you) makes the energy bound...... Energy cannot bind itself, it has to be associated with something to be called as bound energy, and what is that ?

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14. The GodValued Senior Member

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Not necessarily, the Galaxy might as well be moving or both of them are moving.....thats about absence of frame, but otherwise,

This animation which is suggestive of Black Hole Moving in front of Galaxy is meaningless. Firstly with respect to the motion of Black hole and secondly, a BH which could cause so much distortion in the path of light, would create mayhem for the structure of the Galaxy..

15. The GodValued Senior Member

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Gravitational Lensing (GL) by a Galaxy has an unanswered question...If it can distort the light, the all powerful massless light, then the Gravity should be strong enough to slowly start pulling in periphery stars and collapse soon, but it does not happen.

I tried to find out the maths, for a small deviation in the path of light due to gravity, what would be rotational parameters (mass and angular speed) for the periphery star to continue remain in the orbit without collapsing. None was available or I could not trace, but a solar mass periphery star would be required to rotate at a very high angular speed, unimaginably high speed to maintain its orbit....

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16. The GodValued Senior Member

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Understanding the spacetime curves locally, is an issue, barring of course funny data from GP -B.

But you cannot flaw the coordinate system which uses speed of light, in fact I feel that should be the most preferred frame if you discount the space, which anyway you are doing. What I mean is, to measure the speed of any object, a 'c' frame is the best candidate, you know CMB stuff, even if its origin is not what is proposed, it is light travelling at c.

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The gravity distorts nothing other than the topology of spacetime.
As you have been told before, light simply travels in geodesic paths in that curved spacetime.
Gravitational lensing of course is adequately explained according to GR.
Your quoted part that I include is probably the most convoluted, misunderstanding I have come across of gravitational warping and lensing. But you as an Electrician, I suppose I shouldn't be too hard on your lack of understanding.
I will try and get up another tutorial on the achievements of GP-B, and gravitational lensing and spacetime curvature to help you in that regard.

Last edited: Oct 26, 2015

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Funny data from GP-B?? And what data would that be? Or is this just another attempt by you to preach your anti mainstream cosmology, that has no basis in observation, experimentation or fact.

Of course as we all know, talk is cheap, and anti mainstream nonsense such as yours, is only tolerated on this forum, which begs the question, How many other forums have you been banned from due to your crank approach to science.
But of course maybe it is simply that I and other forum members just do not understand the level of your claims, and your apparent certainty in what you are claiming.
Why not then write up a scientific paper on your new cosmology for proper peer review? Instead of preaching it evangelistic style on a science forum open to any Tom, Dick or Harry?

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Light does not slow down, period. When light traverses curved spacetime, it follows geodesic paths that are slightly longer than the path it would follow in flat spacetime and so has a longer distance to travel.
Even photons from the local frame, passing through a medium maintain "c" always. From an outside frame though, it "appears" to be slower, due again to longer distances to travel due to refraction/absorption.

The speed of light/photons is always "c"

Space separates everything. Time stops everything from happening together.
We see it [spacetime] as a 4 dimensional construct against which we conduct our experiments.
https://einstein.stanford.edu/content/relativity/q411.html
What is a space time continuum?
In 1906, soon after Albert Einstein announced his special theory of relativity, his former college teacher in mathematics, Hermann Minkowski, developed a new scheme for thinking about space and time that emphasized its geometric qualities. In his famous quotation delivered at a public lecture on relativity, he announced that,

"The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. henceforth, space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality."

This new reality was that space and time, as physical constructs, have to be combined into a new mathematical/physical entity called 'space-time', because the equations of relativity show that both the space and time coordinates of any event must get mixed together by the mathematics, in order to accurately describe what we see. Because space consists of 3 dimensions, and time is 1-dimensional, space-time must, therefore, be a 4-dimensional object. It is believed to be a 'continuum' because so far as we know, there are no missing points in space or instants in time, and both can be subdivided without any apparent limit in size or duration. So, physicists now routinely consider our world to be embedded in this 4-dimensional Space-Time continuum, and all events, places, moments in history, actions and so on are described in terms of their location in Space-Time.

Space-time does not evolve, it simply exists. When we examine a particular object from the stand point of its space-time representation, every particle is located along its world-line. This is a spaghetti-like line that stretches from the past to the future showing the spatial location of the particle at every instant in time. This world-line exists as a complete object which may be sliced here and there so that you can see where the particle is located in space at a particular instant. Once you determine the complete world line of a particle from the forces acting upon it, you have 'solved' for its complete history. This world-line does not change with time, but simply exists as a timeless object. Similarly, in general relativity, when you solve equations for the shape of space-time, this shape does not change in time, but exists as a complete timeless object. You can slice it here and there to examine what the geometry of space looks like at a particular instant. Examining consecutive slices in time will let you see whether, for example, the universe is expanding or not.

Some of that makes a lot of sense, particularly the non absolute comments about time, but to somehow disengage that from space, and spacetime, is totally beyond my comprehension.
That is totally contradictory. How are you going to communicate your instant of now, with the instant of now to your cousin in M31?
There is no universal now.
It certainly is not a consistent view, and somehow [I don't really mind that much] it has totally gone off track to what I started the thread for. ie: One of the best analogies for how gravity operates that I have seen.

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20. danshawenValued Senior Member

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"Everywhere" is any point in any rotational direction in which energy can propagate, given a sufficient amount of time. The description of a "point", as well as "everywhere", as you have observed, is superfluous, as in not necessary to the description of a coordinate at all.

21. danshawenValued Senior Member

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Space is simply an artifact of time and the propagation of energy. Light travel time. Sorry, but the 2D rubber sheets really have to go.

22. John ConnellanValued Senior Member

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At the atomic scale, gravity is almost negligible.

To answer that, you would need to first ask yourself, what exactly is a force?

23. danshawenValued Senior Member

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The speed of light will not appear to change in the locality of a gravitating body because "proper time" dilates to accommodate any local curvature. The trajectories of light are as crooked as hell around gravitating bodies. Anyone sufficiently distant enough to see gravitational lensing can verify that. Lensing also happens for light that is skirting the rim of the Earth and the rim of the Sun, and a great deal of it bends in ways our instruments cannot even monitor because the instruments themselves are being operated within the same curved region of 'space', with the same time dilation effects causing subtle changes in local measurements to make it appear as though the light is still traveling at c along a perfectly straight trajectory. This is not the reality of the situation, but the only way for us to know this for certain is to observe it from a much greater light travel distance.

Spacetime curvature isn't LITERALLY spacetime curvature. It is the effects of time dilation acting on and because of proximity to energy that is bound. There is no 'space' curvature that is associated with distortion or dilation of time. That's the REAL answer to the question: "why?"

Any region of space which has time dilation associated with it also has mass and inertia, whether there appears to be any actual mass there or not, EXACTLY as it would be if the mass of a gravitating body extended into the surrounding "space' responsible for the gravitational lensing. This same argument also applies to galaxies and to dark matter. Time dilation is your "non-baryonic" or dark matter, that seems to just "hang around" gravitating bodies, galaxies included. A rubber sheet model of the situation cannot possibly explain this consequence of time dilation.

The Higgs mechanism alone would account for an additional 2% of such dark matter, but I have reason to believe the curvature / time dilation we routinely see indicates is much more than a mere 2% additional mass/energy.

Last edited: Oct 27, 2015