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What's Up With Gravity And Spacetime Curvature?

general relativity.

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#1 Moronium

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Posted 10 May 2018 - 03:13 PM

According to some, gravity is not a "force" at all and it is the curvature of spacetime that causes objects to necessarily follow non-euclidean paths toward the center of the earth.

 

We've all seen the "cannon ball on a rubber sheet" analogy to "explain" this.  Problem there is, it presupposes a "force" of gravity, it seems.  Why else would the cannon ball "sink into" the rubber sheet, thereby creating a depression which unsuspecting objects are forced to fall into, then follow?  Without a force of gravity, why would they even "fall in" to begin with?

 

According to this "ask a physicist" website:

 

 

Q: Why does “curved space-time” cause gravity?

 

The curvature of space alone has almost no effect on the movement of objects until they are moving really fast.  With the exception of only the most extreme cases (black holes), space is very, very close to flat.  For example, the total stretching of space due to the Earth amounts to less than 1cm. In almost all cases the vast majority of an object’s movement is tied up in its forward movement through time.

 

 

 

http://www.askamathe...-better-answer/

 

Less than one centimeter?  By the whole earth?  That doesn't seem to correspond to anything like a cannonball on a rubber sheet, eh?

 

According to this guy, it's not the "space" part of spacetime, but rather the "time" part, which forces objects around.

 

How does that work, exactly?  How can a completely abstract concept like "time" force objects to move?  What in the world does it even mean to claim that an object has "forward movement" through time.   Time is not a space, which you can move through, is it?

 

I don't get it.

 

And how does time "point?"  Does it have fingers to point with, or something?  This guy says:

 

...time pointing slightly down is entirely responsible for the motion of the planets, and every other everyday experience of gravity.

 

 

So "pointing" by "time" in the direction of "down" is ENTIRELY RESPONSIBLE for planets moving, etc., eh?  Can anyone make any physical sense (as opposed to graph paper sense) out of this?  If so, can you explain it to me?  I don't get it, for some damn reason.

 

Edit: Should be obvious--I meant "gravity" in the thread title, eh?


Edited by Moronium, 10 May 2018 - 08:21 PM.


#2 Dubbelosix

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Posted 11 May 2018 - 06:11 PM

Yes gravity is a pseudo force, it's not technically a force from the first princples of relativity and so I have been arguing for a while that graviton or total quantization of gravity is wrong.


Edited by Dubbelosix, 11 May 2018 - 06:12 PM.


#3 Dubbelosix

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Posted 11 May 2018 - 06:12 PM

I won't be answering the rant afterwards though.


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#4 Moronium

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Posted 12 May 2018 - 12:23 AM

Yes gravity is a pseudo force, it's not technically a force from the first princples of relativity and so I have been arguing for a while that graviton or total quantization of gravity is wrong.

 

Well, gravitons may well not exist, but they would at least provide some kind of physical explanation for gravity if they did.  But that wasn't my question, nor was it "Is gravity a pseudo force?"

 

The "curved space" explanation is clearly misleading.  So the question is how time, a mere abstraction, can cause the planets to orbit the sun, can cause a guy stepping off the roof of a 50 story building to scatter his brains half-way across town when his head hits the sidewalk and busts like a watermelon, etc.  How does time do that?  Do clocks get together and team up to boss people around, or what?

 

Anybody understand that?


Edited by Moronium, 12 May 2018 - 12:36 AM.


#5 OceanBreeze

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Posted 12 May 2018 - 02:01 AM

Under dimensional analysis,  gravity is acceleration, having the dimensions of m.s-2

 

A gravitational force exists only in the presence of a mass. Then the dimensions are kg.m.s-2

 

 

 

 



#6 OceanBreeze

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Posted 12 May 2018 - 02:03 AM

Yes gravity is a pseudo force, it's not technically a force from the first princples of relativity and so I have been arguing for a while that graviton or total quantization of gravity is wrong.

 

so you say.



#7 Dubbelosix

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Posted 12 May 2018 - 07:20 AM

Well, gravitons may well not exist, but they would at least provide some kind of physical explanation for gravity if they did.  But that wasn't my question, nor was it "Is gravity a pseudo force?"

 

You said what is the deal with gravity not being real, I gave you an answer. You say you want a physical explanation.... the spacetime curves, that's all you need to know.

 

A question, you would not take, the Euler force, or the Centrifugal force and quantize them to explain them in a ''physical way'' so why do it to gravity when gravity is in the same family or class of pseudofields?


Edited by Dubbelosix, 12 May 2018 - 07:21 AM.


#8 Dubbelosix

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Posted 12 May 2018 - 07:21 AM

Under dimensional analysis,  gravity is acceleration, having the dimensions of m.s-2

 

A gravitational force exists only in the presence of a mass. Then the dimensions are kg.m.s-2

 

Not only the presence of mass, but all types of energy as well that contribute to the stress energy tensor.



#9 Moronium

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Posted 12 May 2018 - 07:31 AM

 You say you want a physical explanation.... the spacetime curves, that's all you need to know.

 

 

Heh.  And, as Moliere noted, opium induces sleep because it contains a dormative power, eh?

 

Me, I kinda get an image of Time (a really big guy who looks like Big Ben), also known as "Clockface," swaggering around sayin "Imma make your sorry *** bite the curb, punk!"  Then he "points downward" with his big fingers and, next thing you know, your teeth are all lying in the gutter.

 

I try to make sure that I'm on Time's side, kinda like the Rolling Stones, ya know [Time, time, time...is on my side, yes he is].


Edited by Moronium, 12 May 2018 - 01:19 PM.


#10 Moronium

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Posted 15 May 2018 - 01:29 AM

So "pointing" by "time" in the direction of "down" is ENTIRELY RESPONSIBLE for planets moving, etc., eh?  Can anyone make any physical sense (as opposed to graph paper sense) out of this?  If so, can you explain it to me?  I don't get it, for some damn reason.

 

 

Despite my facetiousness, this was a serious question, which no one has addressed.

 

Can anyone explain, or attempt to explain, how the "curvature" of "time" causes gravity?  I mean in some physically meaningful way, of course, not just by reference to some correlation in the abstract, followed by a raw assertion, in effect, that correlation = causation.

 

It is quite curious that clocks slow down when subjected to  increased gravity, but that explains nothing in itself.  First of all, clocks are not "time," but even if they were, how would slowed clocks "cause" gravitational effects?  That makes little sense, although one might coherently speculate that "gravity causes clocks to slow down," rather than vice versa.

 

I could see some third connection tying together the correlation between slowed clocks and increased gravity.  For example, gravity could "slow down" the ticking of clocks by affecting internal atomic motion, just as decreased temperatures can slow down physical processes.  But, if that's the explanation, I would be hard pressed to conclude that "curved spacetime causes gravity."


Edited by Moronium, 15 May 2018 - 01:52 AM.


#11 Moronium

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Posted 15 May 2018 - 02:03 AM

Just kinda "thinking out loud" here.  Einstein's equivalence principle says acceleration is "the same" as gravity.

 

So, one might say, I guess, that acceleration "causes" gravitational clock retardation.

 

There is also a correlation between acceleration and clock retardation in SR, but that's all it is (a mere correlation).  It has repeatedly been shown that acceleration, in itself, does nothing to affect the slowing of clocks with increased speed.  Acceleration does not "cause"  clocks to slow down (or speed up).   But there is a correlation.  Acceleration can cause a change in speed.  It is the change in speed, not the acceleration, which causes moving clocks to slow down.

 

Not sure how that would relate to gravitational clock retardation, though.  But it seems there might well be some connection.  Being deeper in a gravitational well and travelling at higher speeds seem to "cause' the same type of effects (the slowing of physical processes, including, but not limited to, those pertaining to the rate at which clocks tick).  Therefore, it is not unreasonable to suggest that they might well have a similar cause.

 

But, that said, it still makes no sense (to me) to say that "time" causes gravity (and is therefore "responsible for" the movement of planets, etc.).  What's "time" got to do with any of it?


Edited by Moronium, 15 May 2018 - 02:15 AM.


#12 Moronium

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Posted 15 May 2018 - 02:36 AM

Another connection between speed and gravity emerges with clock rates on earth.  Increased speed causes clocks to slow down.  Increased altitude causes clocks to speed up, so the effects can be offsetting.  And, in the case of the earth's surface, they are almost "exactly" offsetting.  This seems unlikely to just be some wild coincidence.

 

Clocks at the equator travel at a higher (rotational) speed, and therefore tick slower.  But (due to the fact that the earth is a spheroid rather than a true sphere) equatorial clocks are also farther from the earth's center of mass than are clocks at other latitudes, For that reason, they tick faster.  As far as clock rates go, the combined effect is reversed at higher latitudes.  There clocks tick faster than clocks at the equator, due to less rotational speed. But, on the other hand, they also tick slower due to being closer to the center of gravity.

 

The net effect, quite curiously, is that, at sea level, clocks tick at the same rate, regardless of latitude, all over the planet.

 

The identity of gravitational mass with inertial mass was long thought to be just some inexplicable coincidence.  But the equivalence principle explained "why" that's the case.

 

There must be some similar explanation for the fact that clocks can be synchronized all over the planet, I figure.


Edited by Moronium, 15 May 2018 - 02:47 AM.


#13 Moronium

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Posted 15 May 2018 - 03:39 AM

Some interesting excerpts from a paper which adopts the view that "gravity" is NOT due to spacetime distortions, but rather to the "inflow of space into matter:"  Obviously, this view is different from that presented by GR (which is incompatible with quantum theory).

 

 

Abstract

 

The new Process Physics provides a new explanation of space as a quantum foam system in which gravity is an inhomogeneous flow of the quantum foam into matter. An analysis of various experiments demonstrates that absolute motion relative to space has been observed experimentally by Michelson and Morley, Miller, Illingworth, Torr and Kolen, and by DeWitte. The Dayton Miller and Roland DeWitte data also reveal the in-flow of space into matter which manifests as gravity. The in-flow also manifests turbulence and the experimental data confirms this as well, which amounts to the observation of a gravitational wave phenomena. The Einstein assumptions leading to the Special and General Theory of Relativity are shown to be falsified by the extensive experimental data. Contrary to the Einstein assumptions absolute motion is consistent with relativistic effects, which are caused by actual dynamical effects of absolute motion through the quantum foam, so that it is Lorentzian relativity that is seen to be essentially correct.

 

_____

 

Absolute Motion and Quantum Gravity

 

Absolute rotational motion had been recognised as a meaningful and observable phenomena from the very beginning of physics. Newton had used his rotating bucket experiment to illustrate the reality of absolute rotational motion, and later Foucault and Sagnac provided further experimental proof. But for absolute linear motion the history would turn out to be completely different. It was generally thought that absolute linear motion was undetectable, at least until Maxwell’s electromagnetic theory appeared to require it. In perhaps the most bizarre sequence of events in modern science it turns out that absolute linear motion has been apparent within experimental data for over 100 years.  It was missed in the first experiment designed to detect it and from then on for a variety of sociological reasons it became a concept rejected by physicists and banned from their journals despite continuing new experimental evidence. Those who pursued the scientific evidence were treated with scorn and ridicule.

 

As argued in early sections space is a quantum system continually classicalised by on-going non-local collapse processes. The emergent phenomena is foundational to existence and experientialism. Gravity in this system is caused by differences in the rate of processing of the cellular information within the network which we experience as space....What has become very clear is that the phenomena of gravity is only understandable once we have this unification of the quantum phenomena of matter and the quantum phenomena of space itself

 

__________

 

Conclusions

 

We have shown here that six experiments so far have clearly revealed experimental evidence of absolute motion. As well these are all consistent with respect to the direction and speed of that motion. This clearly refutes the fundamental postulates of the Einstein reinterpretation of the relativistic effects that had been developed by Lorentz and others. Indeed these experiments are consistent with the Lorentzian relativity in which reality displays both absolute motion effects and relativistic effects. As discussed in detail in [1] it is absolute motion that actually causes these relativistic effects. As well these absolute motion experiments have given experimental support for a new theory of gravity....Of course no such quantum description of gravity is derivable from quantising Einsteinian gravity itself....it also appears that even the seemingly well-founded Newtonian account of gravity has major failings. The denial of this possibility has resulted in an unproductive search for dark matter. Indeed like dark matter and spacetime much of present day physics has all the hallmarks of another episode of Ptolemy’s epicycles, namely concepts that appear to be well founded but in the end turn out to be illusions, and ones that have acquired the status of dogma.

 

 

 

https://arxiv.org/pd...ics/0306196.pdf


Edited by Moronium, 17 May 2018 - 09:07 AM.


#14 Moronium

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Posted 16 May 2018 - 01:36 PM

You said what is the deal with gravity not being real, I gave you an answer. You say you want a physical explanation.... the spacetime curves, that's all you need to know.

 

 

1. I did not say that gravity wasn't real

2. Uttering, or SHOUTING, "the spacetime curves" is not any kind of physical explanation, but it certainly doesn't surprise me that you imagine it to be.

3.  "All I need to know," eh?  This is your method of "supporting" your pronouncements with facts, discussion of theory, rational argument, etc.  The old ipse dixit "proof."

 

No wonder you find it so easy to imagine that you "know it all," if that's your idea of substantiating your claims.


Edited by Moronium, 16 May 2018 - 01:37 PM.


#15 Moronium

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Posted 02 June 2018 - 08:23 AM

No wonder you find it so easy to imagine that you "know it all," if that's your idea of substantiating your claims.

 

 

"Education, n.: That which discloses to the wise and disguises from the foolish their lack of understanding." (Ambrose Bierce)

 

 

Here are a few excerpts from the blog of physicist Jonah MIller. Like some others, he has a strong affinity for the spacetime concept of GR.  That said, he is not one of the "foolish" that Bierce refers to above:

 

Regarding the graviton: I’d say that whether or not gravity is a true “force” is up in the air....You can turn the metric into a quantum-mechanical wave function, and if you do this, you’ll get a graviton that carries gravitational force. Doing this is paramount to saying that you believe quantum mechanics more than you believe general relativity, since you’re giving up Einstein’s beautiful geometric interpretation of gravity.

 

...As I said, no one really knows how to combine quantum mechanics and general relativity, and it’s not clear which one to trust more....Personally, I am very reluctant to give up general relativity’s geometric interpretation. But this is just my opinion and there’s no evidence that I’m more correct than the physicists who believe gravitons to be force carriers.

 

 

http://www.thephysic...-on-relativity/

 

I guess he isn't really that attached to spacetime.  If he were, he would just prove his preference by fiat, I figure.

 

P.S.:  While I'm here, let me ask again:  Can anybody provide some kind of explanation that I'm seeking?


Edited by Moronium, 02 June 2018 - 08:31 AM.


#16 andrewgray

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Posted 19 November 2018 - 03:46 PM

Yes, Moronium.  I have the answers you are looking for.

 

It is all about Einstein's Equivalence Principle!  As you recall, the mass m of a test object cancels out of both sides of Newton's force equation as it pertains to gravity.

Thus, all matter falls at the same rate (a pound of lead falls at the same rate as a pound of feathers! in a vacuum!) and follows the same path in orbits!  

So... this means that if one is in an elevator... one really cannot tell by dropping an object whether you are in an elevator

 

a ) that is stationary in Earth's gravity field ...or...

b ) whether you are in an elevator out in the middle of interstellar space being accelerated at 1 g.  

 

The object you drop will fall to the elevator floor in exactly the same way.  There is no way to tell where you are... (you cannot look out because there are no windows).

 

Now... suppose we are indeed out in interstellar space in an elevator accelerating at 1 g.., 

Then if we shine a laser beam across the elevator (parallel to the floor) the laser beam must bend into a curve

There is no way around this. There is no argument about this from( just about) anyone.  

 

But now comes the 1,000,000 dollar question!!!  If we are on Earth in a stationary elevator...

"Does a laser beam shined across this stationary elevator on Earth bend into a curve in the gravity field???"

 

If your answer is "yes", then you are FORCED into spacetime curvature and you believe in a strong equivalence principle.

In this case gravity cannot be just a force, because it is bending light. "Spacetime must be curved because light always

follows a straight path, but the path is curved"... 

If you answered yes... You are FORCED into General Relativity (GR).  GR mimics Newton almost exactly but also allows

for light to bend and to red-shift.

 

BUT!  If your answer is "no" then you have no need for spacetime curvature and you believe in a weak equivalence principle.

You are done.  Gravity is just a force that just so happens to cancel out of both sides of Newton's force equation.

You will have to argue with the "Eddingtons" of the experimental world, but their results are so minuscule,

your conscience can handle it. (You can have "force" gravity waves, and gyroscopes precess the same

in "force" gravity if you turn "Newton into Coulomb"). You will have to argue over the "Precession of Mercury", and

the Pound-Rebka experiment..  and others....  But many have....

 

Andrew Ancel Gray


Edited by andrewgray, 19 November 2018 - 04:00 PM.


#17 GAHD

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Posted 19 November 2018 - 08:36 PM

Eh, that trampoline bendy bit is a decent visualization. You can also think of it as concentric shells of stiffer and softer jello-o slowing down things closer to barycenter more because it's "thicker" and has more resistance. or you can look at it as a type of charge imbalance. All those are just analogies. It's like giving an amputee crutches and saying they can "walk" now..."close enough"
 


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