Is there any experimental or observational confirmation of curvature of spacetime?

Well would I be right to say that when we talk about a curvature in our spacetime model that this curvature is always a curvature with respect to an observer at some point(event) on that model ? **

For simplicity I imagine this observer is at an origin.

The model that is curved is a model that is constructed by an observer ,is it not.? Is there always an implied observer whenever statements are made about spacetime ,whether in Special or General Relativity?

I am familiar with the idea that the rubber sheet analogy is not to be taken literally and I hope I have not fallen into that kind of a trap (there are so many others

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)

** I mean if the observer is at a considerable distance from a black hole then "events " that happen near the black hole will seem to follow curved spacetime whereas for a second observer who is actually at the event horizon the curvature of spacetime in his immediate vicinity will be different (even not curved at all perhaps?)

 

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I just do not believe you.

 

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No. Spacetime has been bending since time immeasurable, and is manifest in both gravitational lensing and orbital mechanics. It deos not matter where you observe from, or even if there is an observer.

 

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I dont know you, but maybe you can deliver some sophisticated and logical inputs to the main topic of the thread based on your deep expert insight in physics. It would be nice.

By the way it seems that you have the right type of knowledge for this discussion:
"I studied cosmology, but I essentially left academia post PHD. I looked at a lot of tests for GR and at cosmology as a test for GR & other theories."

 

Thanks, but would the degree of curvature so depend?

If there were two different observers of light coming from the same distant source and one observer had a massive body between him and the source whereas the second observer did not, would the second observer say that the light he was observing was following a lesser curvature than would the first observer?

I realize my level of understanding is poor and so if I am wrong (or have poorly expressed myself) ,I will not continue argue the point.

 

It seems like quite complicated example and it is off topic in this thread. Maybe you should consider to open a new thread with more detailed description of what you want to discuss.

 

OK, I'll bite.

Here's some serious evidence for the bending of spacetime, not merely the bending of light. In studies of the light from distant type 1A supernovae, we find that there is not merely a redshift in their light, but also the expected time dilation. (Goldhaber et al. THE ASTROPHYSICAL JOURNAL, 558:359-368, 2001 September 1) That we find this change in time as well as a change in the path of the light is a significant challenge to any claim that there is no real spacetime change. Another great result is the time dilation found in multiple images of quasars created by intervening galaxies. (Dar, Arnon THE ASTROPHYSICAL JOURNAL, 382:L1-L4, 1991 November 20) There is a component to the time delay that is contributed by the mass distribution of the lensing body, and this is something that one can observe and measure in these phenomena. (Not an easy observation to make, since the time dilation difference can be more than a year separation.)

 

No problem

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There is experimental confirmation, but it isn't what you think: it's optical clocks run slower when they're lower, and your plot of such clock rates is not linear.

I'm afraid a photon only has an effective mass when it's going slower than c. It has a non-zero inertial mass, but this is really a measure of energy. IMHO it's better to say the bending of light is caused by a concentration of energy (usually in the guise of a massive star) which "conditions" the surrounding space, altering its properties, this effect diminishing with distance in a non-linear fashion. Because of this the speed of light is spatially variable, and because of this, light curves. Here's Einstein saying so:

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Matter is also affected, but the GR deflection of light is twice the Newtonian deflection of matter. IMHO this can best be understood by thinking of the wave nature of matter and relating that to light going round a square path. Only the horizontals curve downwards:

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We apply the label gravity to all this, but IMHO saying the bending of light is caused by gravity doesn't really say enough.

True. But curved spacetime isn't curved space and curved time, instead it's a curvature of the metric. It's like a curvature of your plot of measurements. Like a curvature in your plot of optical clock readings at different altitudes.

 

People who haven't seen Farsight before are in for a treat. Farsight is almost completely ignorant of Einstein's science and he is not competent at the relevant mathematics. He does, however, love cherry-picking quotations from Einstein in an attempt to make himself look smarter than contemporary scientists and to elevate love of Einstein (but not Einstein's actual work) to some sort of religious position.

When people wonder how someone can get tired of crackpots flinging around their own half-baked ideas, I point them to Farsight and his decade of internet history. (Including getting banned from forums fro not answering questions and being extremely hostile to people.)

 

All: best ignore PhysBang. His only contribution to a thread like this is abuse. Do not feed the troll.

Yes there is. See what Einstein said above, and note that optical clocks run slower when they're lower. See this from NIST: "If one clock in one lab is 30cm higher than the clock in the other lab, we can see the difference in the rates they run at". Note that an optical clock doesn't actually measure the literal flow of time. There is no time flowing through it. When it goes slower, it's because light goes slower. Not for any other reason.

 

This is the best advice Farsight can offer. I hope he does ignore me and not engage in his other regular tactic of going off on a tangent with some wild claim in order to distract from the subject at hand.

This is a nice idea, but it doesn't actually make sense. Farsight is, as usual, ignoring what Einstein actually says about time in GR. It is not about clocks at all, it is about what we expect from the same physical system transported to a different location. We have evidence that physical systems behave differently under transport and under the conditions of their location. Clocks are a convenient way to do our measurements.

It doesn't matter if light is involved even, since we can have physical interactions where no light is involved whatsoever and we do not have any evidence that interactions without light behave differently, with respect to their timing and displacement, than any other system.

Of course, Farsight has the religious belief that everything is made of light. Despite many people pointing out the flaws in his reasoning, he sticks to this conviction regardless of the sense of it.

 

I could find the full text of the first paper:
http://iopscience.iop.org/article/10.1086/322460/fulltext/53448.text.html

These data also produce compelling evidence that the observed explosion of the supernova itself isslowed20, due to a dilation effect, by the factor 1 + z.This provides independent evidence for cosmological expansion as the explanation for redshifts.Although this hypothesis has proved to be consistent with observation for over half a century, persistent doubts are still occasionally expressed (e.g. Mari

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, Moles, & Vigier 1977; Chow 1977;La Violette 1986; Arp 1987; Arp etal. 1990, 1994; Narlikar & Arp 1993).Surprisingly, until recently very few direct tests of this expansion have been performed. A test by Sandage & Perelmutter (1991), who calculated the surface brightness of brightestcluster galaxies over a range of redshifts, showed compelling evidence for expansion but did not reach a definitive conclusion because of possible systematic errors.An argument has also been made that some gamma-ray bursts (GRBs) should be at cosmological distances because of the observation that for the "longer GRBs," the length ofthe bursts was inversely correlated to the brightness of the GRBs (Piran 1992;Norris et al. 1995). The discovery of GRBs at cosmological distances strengthens this argument (see,e.g., Metzger et al. 1997); however, since the intrinsic length of a given GRB is unknown, this remains a qualitative argument (Lee, Bloom, & Petrosian 2000).

My comment: It seems to me, that it is primarily about the confirmation of cosmological expansion and I dont see any part directly correlating with the topic of this thread - observational confirmation of curvature of spacetime.

Regarding the second article, it seems to be about time dilation which I have never doubted and I dont see anything about curvature of spacetime. I couldnt find full text version, just this shortened version.

http://adsabs.harvard.edu/abs/1991ApJ...382L...1D

 

Well said.

 

It has been experimentally confirmed yes......
Check out GP-B

There are many experiments that confirm that spacetime is bent/warped/curved/twisted/waved in the presence of mass: So what you know is absolutely wrong and probably because you have a pre-conceived agenda.

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Firstly thanks for confirming my initial perception of you having an agenda.
Secondly, a photon has no known mass, but does have momentum, thirdly the bending of light is caused by the fact that it travels in geodesics and follows the curved spacetime which exhibits the effect we know as gravity.

Reasonable confirmation? You didn't try hard enough.

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Let me add also that if you are asking for "proof" [as is the way of most agenda laden anti science cranks] physics/science does not deal in proofs. It deals with the data gathered from observations and experiments and models accordingly..
I see somewhere where you claim to have studied cosmology?
As others have expressed, I find that hard to believe.
And even if true, you obviously do not have access to the many state of the art probes etc that are at the disposal of the expert professionals in this game.

 

Frames of References is an important postulate of SR/GR and the fact that each FoR is as valid as each other frame.
eg: If you are standing off at a safe distance watching me approach the EH of a BH, you will literally see me gradually red shifted beyond your viewing capabilities and even that of your infrared "scope. You will never see me cross the EH.
From my position though, everything appears as per normal: I approach the EH and ignoring tidal gravity effects, cross it and proceed onwards to the Singularity. Obviously also as you have presumed, I will not personally notice or feel any spacetime curvature, BUT, I certainly will see the effects of that spacetime curvature in the effects it has on the light coming from more distant objects behind the BH and evidenced in extreme gravitational lensing.

 

Tsk.

Ultron, a photon has a non-zero inertial mass, which is why "radiation conveys inertia between the emitting and absorbing bodies". See Einstein's E=mc² paper for that.

In addition light doesn't "follow the curved spacetime". Curved spacetime relates to the Riemann curvature tensor and the second derivative of potential, which relates to tidal force. See this book. The first derivative of potential relates to the "force" of gravity. Light curves more where the force of gravity is strongest, not where the tidal force is strongest. You can understand this more readily by thinking about a marble rolling across a curved sheet. Its path curves more where the slope of the sheet is steeper, not where the sheet is more curved:

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I'm afraid you need to ignore paddoboy too. He peddles popscience misinformation with a mixture of arrogance, ignorance, and abuse, and he absolutely will not read the Einstein material or other robust references.

 

Be as afraid as you like.

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Your own ridiculious claims that you have a TOE, your many infractions and bannings here for posting nonsense, and your permanent bannings elsewhere on other forums, certainly is good evidence of who or who not should be ignored.
How are the sales on your book going?

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http://relativity.livingreviews.org/Articles/lrr-2006-3/

http://relativity.livingreviews.org/Articles/lrr-2006-3/download/lrr-2006-3BW.pdf

The Confrontation between General Relativity and Experiment
Clifford M. Will:

Article Abstract
The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eötvös experiment, tests of special relativity, and the gravitational redshift experiment. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, and the Nordtvedt effect in lunar motion. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and other binary pulsar systems have yielded other tests, especially of strong-field effects. When direct observation of gravitational radiation from astrophysical sources begins, new tests of general relativity will be possible.


7 Conclusions
We find that general relativity has held up under extensive experimental scrutiny. The question then arises, why bother to continue to test it? One reason is that gravity is a fundamental interaction of nature, and as such requires the most solid empirical underpinning we can provide. Another is that all attempts to quantize gravity and to unify it with the other forces suggest that the standard general relativity of Einstein is not likely to be the last word. Furthermore, the predictions of general relativity are fixed; the theory contains no adjustable constants so nothing can be changed. Thus every test of the theory is either a potentially deadly test or a possible probe for new physics. Although it is remarkable that this theory, born 90 years ago out of almost pure thought, has managed to survive every test, the possibility of finding a discrepancy will continue to drive experiments for years to come.


Living Reviews in Relativity is a peer-reviewed, open-access journal publishing invited reviews on all areas of relativity research. Articles are regularly updated by their authors. All reference information is collected in a free online database.
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The above reputable paper of course is yet to be updated and with inclusions re the aLIGO results and gravitational waves confirmations from merging BH pairs.