Resultant time dilation from both gravity and motion

JesseM

You seemed to think it was relevant before when you said "Do you now understand what my objection is to your citing the inappropriate material for answering Dmitry7's OP?" The problem is that rather than sticking to a single criticism, you keep changing your line of attack, never really admitting that you made any mistakes in your previous attacks, as if you somehow believe that as long as you can show kev was wrong in some way, you have "won", even if the way you finally decide he is wrong had not even occurred to you at the moment you started attacking his post. Your latest criticism in post #41 about angles isn't any better than your previous attacks. The Schwarzschild metric is spherically symmetric, so although the fact that [tex]\theta[/tex] only ranges from 0 to [tex]\pi[/tex] means you can't have a full orbit with constant r and [tex]\phi[/tex], the time dilation equation is only talking about the instantaneous rate a clock is ticking relative to a clock at infinity over an infinitesimally short section of its orbit. It is certainly possible to have a circular orbit which for one half of the orbit has [tex]\theta[/tex] varying from 0 to [tex]\pi[/tex] while r has a constant value of R and [tex]\phi[/tex] has a constant value of [tex]\pi/2[/tex] (so for any infinitesimal section of an orbiting object's worldline whose endpoints lie on this half of the orbit, [tex]dr[/tex] and [tex]d\phi[/tex] would be 0), while the other half of the orbit also has [tex]\theta[/tex] varying from 0 to [tex]\pi[/tex] and r having a constant value of R, but now with [tex]\phi[/tex] having a constant value of [tex]-\pi/2[/tex] (so for any infinitesimal section of an orbiting object's worldline whose endpoints lie on this half of the orbit, [tex]dr[/tex] and [tex]d\phi[/tex] would still be 0). kev's derivation would work just fine in this case.

starthaus

His derivation is a hack and you've been doing your darnest to defend it. Why is it so difficult for you to admit that it is wrong?

Please read here. Sorry, but no matter how hard you may try, [tex]\omega[/tex] is not [tex]\frac{d\theta}{dt}[/tex]
We are talking about rigotous derivations, not about hacks, right?

espen180

Everything in that post has been adressed above.

Regarding "hacks", I would like to hear your definition of one, and why you think using algebra is "against the rules" if they don't conform to your rules (also state those rules, please).

starthaus

You mean using algebra badly? Like in truncating the metric by missing non-null terms? You claimed that you knew the metric by heart.
Like in using the wrong definition of angular speed?

JesseM

But currently your only basis for saying it's wrong is the argument in post #41. Regardless of whether that argument is valid, can you not admit that all your previous unrelated arguments which had nothing to do with [tex]\phi[/tex] vs. [tex]\theta[/tex] were on the wrong track?
Yes, I already did read that post, it's the same argument as the one I was responding to when I referred to "Your latest criticism in post #41 about angles". It is perfectly "rigorous" to consider a circular orbit which has constant r=R and constant [tex]\phi=\pi/2[/tex] for one half, and constant r=R and constant [tex]\phi=-\pi/2[/tex] for the other half, so that for any infinitesimal section of the object's worldline on either half, [tex]dr = d\phi = 0[/tex]; do you deny that such an orbit should be physically possible in the Schwarzschild spacetime? It may be true that for the purposes of a derivation, it might be a bit more "elegant" to consider a different orbit where r and [tex]\theta[/tex] remain constant for the whole orbit, but there's nothing physically wrong or non-rigorous about the way kev did it.

starthaus

What about the missing terms in [tex]\phi[/tex]? What about the [tex]v=r\frac{d\theta}{dt}[/tex]. Wouldn't it be easier for you to admit that you are backing the wrong formulas rather than patching in all kinds of special pleads? I gave you the correct general formula, it does not agree with kev's formula. I gave you the general derivation, it does not agree with the pervect/kev derivation. Can you at least decide which is right and which is wrong?

Isn't this the problem that needs to be solved? Isn't this the problem I solved at post 2?

espen180

In #2 you gave the metric, which of course is at the heart of all the results suggested in the thread. Personally I am unsure where the problem is. For my part, I choose dr/dt=0 and theta=pi/2 at the beginning of the derivation, but the argument here was that keeping these zero is not neccesary. The calculation is just as valid, for example at the apogee of the particle's trajectory, is what I think JesseM meant.

The other disputes have been focused on individual pieces of the derivation, like how to treat the metric or how to define certain variables.

JesseM

It's true that kev did not write out the full metric, but given that he was assuming an orbit where for any infinitesimal segment you'd have [tex]d\phi = 0[/tex], those extra terms would disappear anyway so this wouldn't affect his final results. And kev never claimed he was starting from the full metric, he said in post #8 that he was "Starting with this equation given by pervect", and pervect had already eliminated terms that went to zero.
What about it? That would appear to be an equation for Schwarzschild coordinate velocity (as opposed to kev's 'local velocity') for an object in circular orbit with varying [tex]\theta[/tex] coordinate, as with the type of orbit I described--again, do you agree that the type of orbit I described is a physically valid one? If you agree there would be a valid physical orbit with that type of coordinate description (with [tex]\phi[/tex] having one constant value for half the orbit and a different constant value for the other half), do you disagree that the above equation would be the correct coordinate velocity for an object in this orbit?
I think you don't understand what special pleading is, the fact that I and others respond to each of your various arguments with counterarguments, resulting in you continually abandoning your previous arguments in favor of new arguments you have invented on the spot, does not qualify as "special pleading". Yes or no, do you acknowledge that the arguments you made against kev's derivation prior to the new argument you've made in the posts here and here were flawed?
kev's formula is not intended to be a "general" one for arbitrary motion, it deals specifically with the case of an object in circular orbit. And since the OP was asking about whether total time dilation was a sum of gravitational and velocity-based time dilation, I thought it would be interesting to point out that for this specific case, total time dilation was actually a product of the two (whereas your more general formula does not relate in any obvious way to the formulas for gravitational and velocity-based time dilation)
Do you deny that the general formula would reduce to the specific formulas found by pervect/kev in the specific case they were considering, namely an infinitesimal section of a circular orbit where the radial coordinate and one of the two angular coordinates are constant?
If a general formula reduces to a more specific formula under the specific conditions assumed in the derivation of the specific formula, I'd say that both are right.

starthaus

Are you even reading what I am writing? Can you re-read posts 2,6,39,47?

starthaus

No, you are missing a lot of terms.

JesseM

Post 47 was by espen180, and as to the others, yes you derived equations for special cases that were closer to a product of gravitational time dilation and something else, but since you didn't use the concept of local velocity the "something else" (i.e. the second part of the product that didn't look like the gravitational time dilation equation) didn't look very much like the SR velocity-based time dilation equation. Since espen180's original post was asking about the total time dilation in relation to the gravitational time dilation and velocity-based time dilation formulas, I thought kev and pervect's equations were relevant to the OP. Again, I'm not saying your equations are wrong in any way, but you haven't made a convincing case that kev's are wrong either--if you still maintain that, please answer the questions in my previous post.

starthaus

Because it isn't. Both effects are GR effects, in fact, there is only one effect. There is no such thing as an SR effect. The effect falls out the Schwarzschild metric.I have already explained this here

I have answered your questions, I would like you to answer mine.

JesseM

This is a strawman, I didn't say anything about "SR effect", I just said that the formula for total time dilation of an orbiting object calculated using GR (not SR) broke down into the product of two formulas that look like the formulas for gravitational time dilation for a stationary object and velocity-based time dilation for a moving object in SR.
What questions of yours have I not answered? You didn't even ask any questions in this post! Anyway, there are several questions in that previous post #59 that I have asked variations on in the past and you have not answered, such as "again, do you agree that the type of orbit I described is a physically valid one?" (referring to the type of orbit I mentioned earlier in post 56) and "Yes or no, do you acknowledge that the arguments you made against kev's derivation prior to the new argument you've made in the posts here and here were flawed?" and "Do you deny that the general formula would reduce to the specific formulas found by pervect/kev in the specific case they were considering, namely an infinitesimal section of a circular orbit where the radial coordinate and one of the two angular coordinates are constant?" If you are interested in good-faith debate here, please answer the questions I ask you (and I will do likewise of course) rather than just picking one part of my post to criticize and ignoring everything else.

Passionflower

That does not exclude the possibility to identify them as separate things.

For instance in the Gullstrand–Painlevé chart you can readily identify the Lorentz factor for relative motions.

But in non-stationary spacetimes this will obviously be a very daunting task.

starthaus

Because, contrary to kev's claims, the term [tex]\frac{dr/dt}{\sqrt{1-r_s/r}}[/tex] does not represent "local velocity". It represents nothing. We had a very lengthy discussion in another thread, if you want the correct formula for local velocity you can find it in my blog, in the file "General Euler-Lagrange derivation for proper and coordinate acceleration".



Because it doesn't. Because it has absolutely nothing to do with any "SR velocity-based time dilation".

One very basic one: that the derivation and the result I gave are the rigorous, complete ansers. Yes or no?

Sure I did, you need to look at the sentences ending with question marks.

If you are happy with hacks and with formulas that are correct for restrictive conditions , like only in the equatorial plane, the answer is yes. Happy?

JesseM

What thread did you discuss it? Do you also dispute DrGreg's derivations which he linked to in post #8?
"Has to do with" is a rather ill-defined phrase. I'd say that if it uses the same equation as "SR velocity-based time dilation", then it "has to do with" it in at least some limited sense.
Your derivation seems rigorous but you'll have to define what you mean by "complete". Do you just mean that it's the most general case, and that all more specific answers would be derivable from it? If so then I agree. But if you're saying that from a pedagogical point of view it's "complete" in the sense that there's no point in discussing any more specific cases, I disagree, the more specific cases may be more helpful for gaining physical intuitions than the more general equation.
When I said "in this post" I meant the post I was responding to (the one where you said 'I have answered your questions, I would like you to answer mine'). There were no sentences ending with question marks in that post. If there were questions in other posts that you think I didn't address and you'd still like answers to, just point them out.
Not completely, because your comments about "hacks" and "restrictive conditions" still seem to imply you think there is something better about your own suggestion here that we should set [tex]d\theta[/tex] to 0 rather than [tex]d\phi[/tex], when in fact this would be every bit as restrictive in terms of the set of circular orbits that would meet this condition--do you disagree that both are equally restrictive? Anyway, as I think espen180 pointed out earlier, because of the spherical symmetry of the Schwarzschild spacetime, for any circular orbit you can always do a simple coordinate transformation into a coordinate system that still has the same metric but where the circular orbit now meets this condition, so in fact kev's final equation should apply to arbitrary circular orbits. If you're familiar with the phrase without loss of generality in proofs, kev could have said "without loss of generality, assume we're dealing with a circular orbit where [tex]d\phi[/tex] = 0" and a physicist would understand the implied argument about why the final results should apply to all circular orbits.

starthaus

Here

DrGreg's time dilation formula is a subset of mine, so "no". The point is that the quantity in discussion ([tex]v[/tex]) is not what you and kev claim it is. The correct formula can be found in my blog.


That's what you said. And I explained to you that it has nothing to do with any "SR-based time dilation. ".

It either is or it isn't. Can you answer with yes or no, please?

Good. This is what I meant.


Absolutely.[tex]d \theta=0[/tex] means no motion along the meridian whereas [tex]d \phi=0[/tex] means no rotation, contradicting the problem statement. Why are we even discussing this?

Of course I do, how many posts do we need to waste on this obvious issue?

That's not the point. [tex]\phi[/tex] and [tex]\theta[/tex] are not intechangeable. They have different meanings , both mathematically and physically. They have different domains of definition, [tex]\omega[/tex] is [tex]\frac{d\phi}{dt}[/tex] (and not [tex]\frac{d\theta}{dt}[/tex]). If you insist on interchanging them, you would need to exchange their domains of definition ([tex]\theta[/tex] would need to be in the interval [tex][0,2\pi][/tex]), you would also need to rewrite the Schwarzschild metric. This is not what kev did in his hack.



This is incorrect, since [tex]\phi[/tex] and [tex]\theta[/tex] are not intechangeable.