Time dilation: Gravity force vs Gravitational potential

[Schneibster]

Can someone please explain what YMMV means? Is it offensive? (yes, I know - I have led a sheltered life. For years I thought that Paris Hilton was a French hotel!)

Seriously though. Let's cut out the personal remarks and fighting - no purpose is served thereby, it wastes the site's bandwidth allowance and does not make interesting reading. While we're at it, let's keep links (and verbatim quotes therefrom) to a minimum - we all have internet access and a search engine (incidentally, I use StartPage which is free, cross-platform and as secure as you can get these days).

What do you say?

I hope you didn't take this personally; it wasn't aimed at you. I was commenting on someone calling you a poser, actually, which is, as I said, going outside the box to try to win the argument with you on grounds other than merit.

 

[Q-reeus]

Can someone please explain what YMMV means? Is it offensive? (yes, I know - I have led a sheltered life. For years I thought that Paris Hilton was a French hotel!)

https://www.allacronyms.com/YMMV
The trouble with rarely used acronyms - one has to guess between multiple choice.

Seriously though. Let's cut out the personal remarks and fighting - no purpose is served thereby, it wastes the site's bandwidth allowance and does not make interesting reading. While we're at it, let's keep links (and verbatim quotes therefrom) to a minimum - we all have internet access and a search engine (incidentally, I use StartPage which is free, cross-platform and as secure as you can get these days).

Agreed StartPage is THE preferred search engine if online privacy is at all valued.

What do you say?

Agreed. I will confess to having allowed personal anger over recent behaviour and actions to 'colour' exchanges here with one poster in particular.

 

[Q-reeus]

I hope you didn't take this personally; it wasn't aimed at you. I was commenting on someone calling you a poser, actually, which is, as I said, going outside the box to try to win the argument with you on grounds other than merit.

That lie I will not pass over. Given you must have read both my #18 and #26, there is no excuse. Confirm that you are accusing me of lying in #26. Yes - that's a specific request for a straight answer! Refusal to do so will be automatically taken as an admission of guilt on your part!

 

[rpenner]

#1 Ultron; Example one misunderstands surface gravity as the cause of gravitational time dilation as opposed to depth in a gravity well and comes to the wrong conclusion to how time dilation works in a centrifuge. The second example seems without basis. [Be ashamed]

#2 Q-reeus → Ultron; Correctly identifies problems with first example. Unclear if a solution is presented — it looks unworkable to me.

#6 Schneibster → Ultron; Incorrectly ignores tangential velocity of the centrifuged space clock in example one. Repeats Ultron's assumption that acceleration matters in GR time dilation problems. [Be ashamed]

#7 Schneibster → Janus58; Correctly takes issue with Janus58's logic as to size of centrifuge. Continues misapprehension as to source of time dilation in GR.

#11 Schneibster → Ultron → Q-reeus → Confused2; Mistates GR concepts.

#13 Schneibster → Ultron; Continues to Mistate GR concepts.

#15 Schmelzer → Schneibster; Correct statement of GR time dilation for clocks at rest with respect to one another.

#16 QuarkHead → Schmelzer + Schneibster; Inquires about where #7 and #15 diverge.

#18 Q-reeus → Confused2 → QuarkHead; Attacks QuarkHead for not parsing Schneibster's posts, #6, #7, #11, #13. Attacks Schneibster for not apologizing for "errors of logic" which have not been spelled out. [10 points]

#26 Q-reeus → QuarkHead; Admits that he made post #18 unnecessarily vexing and confusing by not naming Schneibster. Half-apologizes for not taking QuarkHead's content as written.

#28 Schneibster → QuarkHead; Passively-aggressively trolls Q-reeus in the style of Q-reeus' post #18. Added the American English acronym for car-culture jargon "Your Mileage May Vary" which metaphorically distances himself from his claim Q-reeus has no answers. [10 points]

#41 Schneibster → QuarkHead; Does not explain YMMV, misstates the party which post #18 calls "poser".

#43 Q-reeus → Schneibster; Heatedly accuses Schneibster of misreading posts #18 and #26.

 

[Q-reeus]

#2 Q-reeus → Ultron; Correctly identifies problems with first example. Unclear if a solution is presented — it looks unworkable to me.

Maybe you took into account my #9, maybe not. No way of knowing from that line. At any rate, while not in pretty LaTeX font, I'd say #9 makes it quite workable, if a little brief perhaps.

#18 Q-reeus → Confused2 → QuarkHead; Attacks QuarkHead for not parsing Schneibster's posts, #6, #7, #11, #13.

I 'attacked' QuarkHead in #18? It was purely an expression of surprise, given his mathematical expertise and I had assumed familiarity with basic principles of GR.
There was no intended insult, putdown, or such involved on any reasonable basis, though I can see how it could be initially taken that way. The charge of 'attacked' is therefore a severe value judgement imo. Particularly given the continual out-and-out trolling by certain members who suffer no evident penalty in pursuing such 'sport' here.

Attacks Schneibster for not apologizing for "errors of logic" which have not been spelled out. [10 points]

Against the continual misinfo of Schneibster this thread yes I will wear the charge of 'attacked', appropriate imo given there was never any admission to any of a string of exposed errors presented authoritatively as 'facts'. But ok if I went too hard, then I will just have to cop 10 points, but.....skipping to #28 below

#26 Q-reeus → QuarkHead; Admits that he made post #18 unnecessarily vexing and confusing by not naming Schneibster. Half-apologizes for not taking QuarkHead's content as written.

That last sentence is out of place - in fact I was simply being diplomatic. It would be unwise to press the specifics, but if you wish to, it's all clear enough.

#28 Schneibster → QuarkHead; Passively-aggressively trolls Q-reeus in the style of Q-reeus' post #18.

Really? In my style of #18? No clear distinction between an objectively valid if overly sharp criticism there, to the WILLFUL MISREPRESENTATION in #28? Wow.

Added the American English acronym for car-culture jargon "Your Mileage May Vary" which metaphorically distances himself from his claim Q-reeus has no answers. [10 points]

A generous, single interpretation, given my linked to article established one alternate version is "You Make Me Vomit". And Schneibster's subsequent 'that wasn't directed at you' suggests the last one - but I won't argue it was so for sure.

#41 Schneibster → QuarkHead; Does not explain YMMV, misstates the party which post #18 calls "poser".

Just misstates? How about; a second, clear WILLFUL MISREPRESENTATION! And as per my Report, such comes under the category of 'behaviour that may get you banned'. Yeah - 'may'.

#43 Q-reeus → Schneibster; Heatedly accuses Schneibster of misreading posts #18 and #26.

No, I accused him of LYING and given the sequence of postings, obviously he further implied I was in turn LYING in #26! Misreading would actually be an excuse i.e. dyslexia or some such.

To suggest some sort of 'moral equivalence' in all of above whereby we both deserved 10 points each is 'interesting'. This is SF.

 

[Schneibster]

Hi rpenner, not sure where you think I ignored tangential velocity in #6, though I didn't use that term. I did say:

The observer on the space module would see one time dilation (due to their velocity, not the fictitious centrifugal force) at one side of the rotation, and the opposite time dilation on the other side.

Emphasis not in the original.

In #7, I said

that is due in acceleration's case to the changing velocity

which is what I understood the PhysicsFAQ to say about why acceleration creates time dilation; it is not due to the acceleration per se but to the standard velocity-related time dilation, and is completely accounted for on that basis in SRT. I didn't link the PhysicsFAQ page because it introduces the centrifuge experiment without explaining it, and I feel this is a defect in its explanation that can lead to the misapprehension that results in confusion regarding whether acceleration introduces time dilation or not; acceleration does, but only due to the infinitesimally changing velocity which is completely accounted for in SRT. There is no additional effect due to the acceleration itself. Please correct me if this was wrong.

In #11, in GRT, due to the equivalence principle, it is my understanding that the effects of acceleration will appear in the metric tensor, just as the effects of gravity do; however, this does not conflict (due to the clock postulate) with the statement that this effect in the metric tensor is completely accounted for by the SRT velocity-related transform, with no additional effect from acceleration itself. Please correct me if this is wrong.

In #13 I don't see where I misstated anything at all, or even where it could be misinterpreted. I said that it seemed to me (inviting correction by Ultron) that he was wondering how something could be in the middle of a gravity well but still not experience time dilation; I explained that since there was no net gravity at that point, there was no reason to expect time dilation. Please correct me if this is wrong.

I will not address #28 or #41 here since they are apparently moderation issues and most sites don't want those discussed on the fora.

 

[Confused2]

Any chance of starting again from #1?

 

[QuarkHead]

What? No points for me? I am aggrieved!

 

[Ultron]

Actually I was surprised by complexity of discussion initiated by my question. Next time I will try to have simpler examples which will not open several topics in discussion.

By the way, I have opened new, slightly related thread in Alternative theories:
http://sciforums.com/threads/time-dilation-in-rotating-non-inertial-system.156267/

 

[rpenner]

In #13 I don't see where I misstated anything at all, or even where it could be misinterpreted. I said that it seemed to me (inviting correction by Ultron) that he was wondering how something could be in the middle of a gravity well but still not experience time dilation; I explained that since there was no net gravity at that point, there was no reason to expect time dilation. Please correct me if this is wrong.

You are wrong. Ultron is wrong. See post #15.

 

[danshawen]

Wrong.

Time dilation of a clock at rest in some system of coordinates is defined by $g_{00}$. Which is, for weak fields (like the Earth's) approximately defined by the Newtonian potential by $g_{00} \sim 1+ 2\Phi$, see for example formula (18.15c) of MTW.

How the Newtonian potential looks inside the Earth one can see, for example, https://en.wikipedia.org/wiki/Gravitational_potential

Correspondingly, $g_{00}$ has its lowest value, thus, we have the highest time dilation, at the center. Even if there is no gravitational force at the center at all. The curvature is, instead, some expression depending on second order derivatives of the metric. I'm too lazy to compute this for this metric, but a simple modification makes clear that the time dilation has nothing to do with curvature.

We simply have to make a large enough hole in the center of the Earth. Then the potential looks like fig. 2 of http://teacher.pas.rochester.edu/PHY235/LectureNotes/Chapter05/Chapter05.htm and is simply constant inside the hole. Thus, the whole metric will be approximately constant too, and curvature zero. But the time dilation will be nonetheless much greater than outside.

Thanks for going out on a limb to present this, and I believe your analysis is correct.

A gravity physicist who regularly publishes in the Royal Society journal however disagrees with this interpretation. We had some arguments about it. He had a bid in to redo the Cavendish experiment in orbit, but it lost out to other experiments on the last days of the space shuttle and the experiment got indefinitely delayed.

I had a couple of topological arguments to reach the same conclusion. Cut the Earth in half along an axis perpendicular to the equator. Position an atomic clock where the center was in each half. Those will both have time dilation, right? Now put the halves back together. Why should time dilation change? If you wish to make time dilation increase even more at the center, simply increase the density of the planet.

For bound energy that is matter, time dilation simply depends on proximity to other bound energy.