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

[Ultron]

Curvature of spacetime is important interpretation of equotations of General relativity, but what I know this is just an interpretation without any experimental confirmation.

Many people, even many educated people believe, that curved spacetime of GR is confirmed by observed bending of light around Sun and also by bending of light in gravitational lensing observed in astronomy, but what I know, this is not true.

Bending of light is caused by gravity, because photons have effective mass (not invariant mass), it is also predicted by Newton gravity theory. GR just gives more precise level of bending which is in line with observed bending and accounts for relativity effects like time dilation. In other words bending of light is not confirmation of curvature of spacetime.

So I couldnt find any reasonable confirmation for curvature of spacetime apart from obvious confirmations of Lorentz factor change in line with predictions of SR and GR. But maybe somebody here will know better.

 

[DaveC426913]

GR does not simply provide a more precise value for the bending of light; it provides the correct value. Newtonian gravity predicts a specific value, it just predicts a value that is half of what is observed.

The Newotonian model suffers - not from a measurement error - but from a model error.

 

[PhysBang]

Curvature of spacetime is important interpretation of equotations of General relativity, but what I know this is just an interpretation without any experimental confirmation.

I don't know how you could possibly determine that. Since the core of the theory is the change in geometry, and "the curvature of spacetime" is this change in geometry, it seems impossible to have GR without the curvature of spacetime.

Perhaps you want to introduce some hidden theory behind GR, a theory that makes the universe just look like GR is correct but GR is really wrong. Well, nobody can ever prove that wrong. However, since you have no support for this hidden theory, we can all move along like it doesn't exist.

Many people, even many educated people believe, that curved spacetime of GR is confirmed by observed bending of light around Sun and also by bending of light in gravitational lensing observed in astronomy, but what I know, this is not true.

Well, if you have knowledge without any education, why ask us?

Oh, right, you're not really asking, you're telling. You're telling us in the manner that makes it most clear that you are an asshole with your own special theory to preach.

Bending of light is caused by gravity, because photons have effective mass (not invariant mass), it is also predicted by Newton gravity theory. GR just gives more precise level of bending which is in line with observed bending and accounts for relativity effects like time dilation. In other words bending of light is not confirmation of curvature of spacetime.

You have just told us that you prefer the scientific conclusions that are less accurate.

 

[Ultron]

GR does not simply provide a more precise value for the bending of light; it provides the correct value. Newtonian gravity predicts a specific value, it just predicts a value that is half of what is observed.

The Newotonian model suffers - not from a measurement error - but from a model error.

Generally I agree with you, but when we would like to be really exact, GR provides value which is confirmed by observations within error bar, there nothing like absolute final confirmation in physics. It can happen in future that there will be some upgraded gravity theory which will be confirmed in even bigger detail.

Regarding Newton theory, I just wanted to make sure that everybody understands that Newton theory also predicts bending of light by Sun, it is not some special feature of GR based on the idea of curvature of spacetime.

 

[geordief]

Why did GR predict that the geometry of spacetime would be affected by things like mass and energy?

I realize the answer may be far to hard for a layman to understand but any help in understanding this specific point would be appreciated (I do kind of appreciate why the geometry of spacetime is affected by relative and relativistic motion in SR but this GR thing seems like a different beast)

 

[geordief]

Regarding Newton theory, I just wanted to make sure that everybody understands that Newton theory also predicts bending of light by Sun, it is not some special feature of GR based on the idea of curvature of spacetime.

I didn't know that ,so thanks.

 

[Ultron]

I don't know how you could possibly determine that. Since the core of the theory is the change in geometry, and "the curvature of spacetime" is this change in geometry, it seems impossible to have GR without the curvature of spacetime.

Perhaps you want to introduce some hidden theory behind GR, a theory that makes the universe just look like GR is correct but GR is really wrong. Well, nobody can ever prove that wrong. However, since you have no support for this hidden theory, we can all move along like it doesn't exist.

Well, if you have knowledge without any education, why ask us?

Oh, right, you're not really asking, you're telling. You're telling us in the manner that makes it most clear that you are an asshole with your own special theory to preach.


You have just told us that you prefer the scientific conclusions that are less accurate.

Actually I like the relaxed approach in sciforums, but I dont like how some people unnecessarily insult other people without any obvious provocation. You had some bad day or what?

 

[DaveC426913]

Generally I agree with you, but when we would like to be really exact, GR provides value which is confirmed by observations within error bar, there nothing like absolute final confirmation in physics. It can happen in future that there will be some upgraded gravity theory which will be confirmed in even bigger detail.

Yes but what does that have to do with this?

We have observations, and we have a theory that models those observations. There is nothing wanting.

 

[PhysBang]

Actually I like the relaxed approach in sciforums, but I dont like how some people unnecessarily insult other people without any obvious provocation. You had some bad day or what?

I just get tired of cranks who think that they know a little physics and some "common sense" and have delusions of grandeur. I get a little sad about their mental health, too.

 

[The God]

Well, if you have knowledge without any education, why ask us?

Oh, right, you're not really asking, you're telling. You're telling us in the manner that makes it most clear that you are an asshole with your own special theory to preach.


You have just told us that you prefer the scientific conclusions that are less accurate.

Reported for unprovoked foul language...

 

[The God]

GR does not simply provide a more precise value for the bending of light; it provides the correct value. Newtonian gravity predicts a specific value, it just predicts a value that is half of what is observed.

The Newotonian model suffers - not from a measurement error - but from a model error.

The observed bending is certainly closer to GR value, but the error bars are troublesome. The error bars are significantly higher.

 

[Ultron]

I just get tired of cranks who think that they know a little physics and some "common sense" and have delusions of grandeur. I get a little sad about their mental health, too.

Most cranks do not really care about experiments and observations. I really do care and I have studied thousands of papers about experiments over time. But I dont take established interpretations like god given scripture.

Maybe I have the biggest delusion of grandeur ever, but if I would try some theory it would have to fit to existing experiments and observations. This is extremely hard work, but Im trying and I like it. And discussions with reasonable people can be very enriching and helping me.

So to reply to your previous post: Curvature is in the core of GR, but it could be just wrong. It is like you would say, that you can use derivation for computing speed of car and this means that the speed of car is caused by derivation. No, the speed of car is caused by engine accelarating it.
GR is saying that curvature expressed in tensors is causing gravity and Im asking is there some experimental or observational data which is supporting this?

 

[DaveC426913]

you are an asshole with your own special theory to preach.

I just get tired of cranks who think that they know a little physics and some "common sense" and have delusions of grandeur. I get a little sad about their mental health, too.

Phys, have you had prior dealings with Ultron outside this thread? This reaction seems premature at best.

 

[DaveC426913]

GR is saying that curvature expressed in tensors is causing gravity and Im asking is there some experimental or observational data which is supporting this?

The experimental support is the observation of the curvature that is predicted by the model.

If GR predicts an outcome and that outcome comes to be, then GR cannot be falsified using this observation. Any alternate theory would do no better at modeling gravity. One would have to find a different test that the alternate theory predicts differently than GR, and see which one passes.

 

[Ultron]

The experimental support is the observation of the curvature that is predicted by the model.

If GR predicts an outcome and that outcome comes to be, then GR cannot be falsified using this observation. Any alternate theory would do no better at modeling gravity. One would have to find a different test that the alternate theory predicts differently than GR, and see which one passes.

There is experimental support for bending of light, which is not the same as curvature as explained in OP. What I know curvature of spacetime was never directly observed.

 

[DaveC426913]

There is experimental support for bending of light, which is not the same as curvature as explained in OP.

Yes, but there is no experimental support for what makes the light bend.

It is impossible, even in principle, to directly observe the curvature of spacetime, just like it is impossible to directly observe gravity. In both cases, our evidence is witnessing the effect it has on the path of light and mass.

There is no direct observation of Newtonian gravity; there is only its effects - which we model.

 

[geordief]

When describing the concept of curved spacetime can we say that ,starting from a given origin the lines that we might draw to show equal values in space and time with respect to that origin are curved from the perspective of an observer at the origin ?

And that curvature increases as the points(events) in question are in greater proximity to mass/energy?

 

[Ultron]

It is impossible, even in principle, to directly observe the curvature of spacetime, just like it is impossible to directly observe gravity. In both cases, our evidence is witnessing the effect it has on the path of light (and other phenom) - and that is all we can hope for.

The model we had where light was bent due to gravity did not explain the observations we see.
The model we have where light travels along a geodesic (a straight line in curved spacetime) does explain the observations we see.

Thanks, this is really helpful.

Lets sum up how I understand it now:
Because tensors in equations of GR are interpreted as curvature of spacetime and this interpretation is one of the major building blocks of GR, it is interpreted in that way, that if the mathematical/geometrical model is giving correct predictions, it is considered as indirect confirmation of curvature, which cannot be observed (and confirmed) directly.
But on the other hand it also means, that if somebody comes with some upgraded theory with same equations as in GR and extended by some new equations, but with different interepretation than curvature, it means that there is no experiment or observation which would confidently rule out this different theory just because it would give different interpretation than curvature of spacetime. The rule would be out, until this new theory would provide some new predictions different to GR and would be confirmed by experiments or observations.

 

[Ultron]

When describing the concept of curved spacetime can we say that ,starting from a given origin the lines that we might draw to show equal values in space and time with respect to that origin are curved from the perspective of an observer at the origin ?

And that curvature increases as the points(events) in question are in greater proximity to mass/energy?

Im not sure about what you are asking, but it seems that you have the rubber sheet example in mind. This is just a very simplified model and unfortunately the real math is quite complex and most people including me struggle to visualise it properly.

 

[DaveC426913]

Thanks, this is really helpful.

Lets sum up how I understand it now:
Because tensors in equations of GR are interpreted as curvature of spacetime and this interpretation is one of the major building blocks of GR, it is interpreted in that way, that if the mathematical/geometrical model is giving correct predictions, it is considered as indirect confirmation of curvature, which cannot be observed (and confirmed) directly.
But on the other hand it also means, that if somebody comes with some upgraded theory with same equations as in GR and extended by some new equations, but with different interepretation than curvature, it means that there is no experiment or observation which would confidently rule out this different theory just because it would give different interpretation than curvature of spacetime. The rule would be out, until this new theory would provide some new predictions different to GR and would be confirmed by experiments or observations.

Correct. A new theory would have to explain all the observed phenom at least as well as GR.

The question then becomes: what purpose would it serve, unless it explained observed phenom better than GR? Which then asks the question, in what way is GR inadequately explaining it? (Note the error margins are in the data, not in the theory. Any other theory would have the same problem.)