Talk:Gravitational time dilation

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[edit] Magnitude of gravitational time dilation at the surface of the Earth

My own meager calculations led me to the conclusion that here on earth our gravitational time dilation is equal to 1.00000000009 days for every 1 day that passes to an observer outside the system. These were based on what is thought to be the current size of the black hole (299,460,000 km in diameter) at the center of the milkyway and our 26,000 light year distance from the black hole. Feel free to check my math, it's probably a off since i used the windows calculator. I felt obligated to put something here since no one else has yet.

(Note: unsigned commment 10:38, 6 December 2005 71.254.97.250. In future, 71.254.97.250, please use ~~~~ to sign your posts--- it helps alot in keeping track of who said what in talk pages, which can sometimes become very long and complicated! And of course this is even more helpful if you have a static IP address or register an account (possibly under a pseudonym), but that's up to you.)

Interesting, but not possible to confirm. We can't yet observe from somewhere outside of our relative position in the Milky Way. Jeff Carr 11:52, 21 January 2006 (UTC)

[edit] Well, for starters, the very first sentence is wrong

Increasing the intensity of a gravitational field in a region reduces the effective rate of timeflow in the region? Not true. This doesn't even make sense. Time flows at the same rate everywhere, or in geometric terms, lapse of proper time corresponds to arc length along a timelike curve.

What the author should have said is that spacetime curvature can cause the divergence of null geodesics as they move outward from an isolated massive body. That means that a distant observer monitoring time signals from an second and much closer observer who uses his rocket engine to hover over the massive body will find the recieved signals to run slow relative to his own clock.---CH 21:09, 10 December 2005 (UTC)

[edit] Section The equation(s) for Gravitational Time Dilation is misleading

These formula only apply to:

  • Schwarzschild exterior, i.e. static and spherically symmetric vacuum, so don't apply to field outside a nonrotating disk, outside a rotating black hole, outside a charged nonrotating spherically symmetric black hole, etc.
  • a pair of static observers, one at Schwarzschild radius r and the other "at spatial infinity", so don't apply as stated to say an Earth-orbiting satellite and someone standing on the surface of the Earth.

Suggest a careful and thorough rewrite.---CH 21:17, 10 December 2005 (UTC)

[edit] Organization

Oh boy, oh boy, I dunno how this article got in this state, but it needs a complete rewrite before it can be called a reasonable encyclopedia article. See the todo list for hints.---CH 21:25, 10 December 2005 (UTC)

[edit] Mischaracterization of meaning of the Schwarzschild radial coordinate

Ooops, just noticed another serious mistatement: Note that in General Relativity, the circumference of an orbit is less than 2π the radius due to a mathematical consequence of the spherical spacetime geometry surrounding gravitating bodies. Of course, by definition, in any spherically symmetrical static spacetime, in the Schwarzschild coordinate chart, the radial coordinate accurately represents circumference and area of nested spheres (constant r). However, differences in r value do not correspond to radial distance (along radial spacelike geodesics with constant t). ---CH 22:37, 10 December 2005 (UTC)

--Kmarinas86 07:24, 11 December 2005 (UTC)I found a link that I think you might agree with: http://www.mathpages.com/rr/s6-04/6-04.htm

Perhaps the equation Gravitational Time Dilation=1/sqrt(1-2GM/rc²) itself is misleading, because I have been taking it at face value before I have start on Calculus III (I've already taken I and II).

BTW, this is the kind of attention from an expert that I needed, so your points of view are appreciated. You have clarified a few points that I was not sure of, in particlar, the point about the r coordinate corresponding to that circumference.

--Kmarinas86 08:05, 11 December 2005 (UTC)"However, differences in r value do not correspond to radial distance (along radial spacelike geodesics with constant t)." I'll see whether the escape velocity in General Relativity corresponds to the r value or the radial distance. Also, I think you implied that t affects the geodesic and thus the radial distance. I hope I understood that right.

[edit] More nonsense

Someone wrote:

There exists a place of no time flow, and where impact velocity for mass equals the speed of light, where mass is compressed to its Schwarzschild radius. Such matter has passed a region where Gravitational Time Dilation approaches infinity, is greater than 10^100 and passes a layer where gravitational time dilation is "undefined".
Therefore, one remains aloof about this strange paradox, until he or she is given an explanation.

This is sheer nonsense. KMarinas, the article by C. Nave you cite is an example of telling a white lie to students who don't have the background to follow gtr. Like many authors of semi-popular articles, he mixes up Newtonian gravitation with gtr, which of course leads to nonsense if you pursue this line of thought very far. For a better semipopular account, try

  • Geroch, Robert (1981). General Relativity from A to B. Chicago: University of Chicago Press. ISBN 0-226-28864-1.  Leisurely pace, provides superb intuition for Schwarzschild geometry.
--Kmarinas86 07:35, 11 December 2005 (UTC)I understand how you are reacting to this, as it was sort of planned. It's a ironical statement, not that I actually believe there exists a place of "no time flow", I agree that it's nonsense. I just have catalyzed a demand to improve this article, since I found it to be uncomprehensive, even before I edited it. I have an Encyclopaedia Britannica from 1976 and I know what a real encyclopedia looks like, and the previous version of this article (before I edited it) was not an example of that. The quantum mechanics page on Britannica is really technical, but simple enough for me to understand it. Britannicas are way much better than World Book, or any other encyclopedia I have really looked into so far. It's obvious that I can't make it as good as the Britannica. Many of the articles on Wikipedia, but certainly not the majority, fit Britannica's standard. I want this article to fit that standard. I want it to be complete as well, not just a small inkling of what Gravitational Time Dilation is. Because if :that's all Wikipedia can provide about Gravitational Time Dilation, then we are left wandering in other websites trying to :find out what it is exactly.

Actually, KMarinas86, you are supposed to add your signature at the end of your comments, not the beginning, but I that you know this. Also, the hypens represent an optional dash, they not part of the syntax. So you can type just ~~~~ and you will get this. CH 23:12, 11 December 2005 (UTC)

Also, I advocate indenting comments for readability, by typing one more colons just before each paragraph to be indented. And when you say:

:''I understand how you are reacting to this, as it was sort of planned''

I understand how you are reacting to this, as it was sort of planned

please be careful to give the impression that you might be bragging about a successful troll. If your idea of improving the WP is to write deliberately misleading articles in hope of goading someone else into rewriting it (so that you can argue endlessly with them?), quite frankly I don't believe you are here to help the WP and in that case I would not regard your presence as welcome. And I certainly am not going to waste time talking to a troll.

Since you are apparently a newbie, I'll give you a chance to think over what you said and to consider promising to adopt more straightforward and honest behavior at WP. In particular, I welcome requests in talk pages for "experts" to improve articles on technical subjects, but you won't win many friends at WP by attempting to manipulate users. Ask, don't trick; it's more honest and in the long run it works better for everyone.---CH 23:12, 11 December 2005 (UTC)

AffirmativeKmarinas86 01:22, 12 December 2005 (UTC)

[edit] Exact equation for Escape Velocity in GR

--Kmarinas86 07:55, 11 December 2005 (UTC)I know that the equations for Escape Velocity of Einstein's theory and of Newton's theory are not the same. I will see whether I can dig that up tonight.

--Kmarinas86 08:55, 11 December 2005 (UTC) Mass cannot travel at c, therefore escape velocity cannot be c ;)..... someone please give me an rational rebuttal to this... I know that the event horizon travels at c, but of course, the radius of the event horizon does not change unless mass is added under this event horizon. So the event horizon must be spinning, of course, this doesn't escape the understanding that matter travels inside this event horizon.

This leads me to another question, what is the equation for gravitational time dilation surrounding a rotating black hole? I haven't found an answer to that so far. Note that I'm speaking of gravitation time dilation, which I defined exculsive of the effects of special relativity. Perhaps that's the wrong approach (wrong definition)? I know that the books say that the movement of a object of a gravitational field moving through a gravitational field induces a greater gravitational field. That would imply more time dilation. But that depends on the actual velocity of the object at that point in space - both do vary by the way. If the black hole is not spinning it will not drag space time along with it (no frame dragging right?), though matter may be coming at an angle, then I not so sure what it would do. I know that some black holes are said to be non-rotating. Can they be non-rotating and have a disk as well? Um......

--Kmarinas86 09:19, 11 December 2005 (UTC)I know that velocity time dilation and velocity redshift are two seperate equations that should not be confused. The equation which I have been using are only for the non-rotating, uncharged black holes (schwarzschild solution), and the r coordinate is not the radial distance along curved line to the center of the black hole. The equations for time dilation in other solutions to the Einstien's field equation should be added. For a chart of four different types of solutions, see Rotating black hole.

My other question still isn't answered, does escape velocity in GR correspond to the r coordinate or the radial distance?

You don't need to worry about rotating black holes and escape velocities in an article on gravitational time dilation. Escape velocity is irrelevant, and the Kerr metric (which describes the spacetime surrounding a rotating massive object) is too complex to deal with here.
BTW - Given a Schwarzschild spacetime and for the radial coordinate r in Schwarzschild coordinates (which is what you are using in this article), the relativistic and Newtonian escape velocity equations are the same. As you note above, this escape velocity is >=c at the event horizon and within a black hole. What this means is that you cannot escape from either.
Once more thing: The event horizon does not "travel". It is simply a set of positions in spacetime that cannot be passsed through from below. What travels are the objects falling through it. --EMS | Talk 18:57, 11 December 2005 (UTC)

[edit] Changed intro

The current editor of this page seems to be confusing gravitational time dilation with geodesic deviation. Gravitational time dilation can exist in the absense of a curved spacetime. All that is needed is to be in an accelerated frame of reference, and it appears. The source of the acceleration (such as the gravitational field of the Earth) is irrelevant. Similarly, the Albert Einstein quote does not belong here, since this is effect is a consequence of SR instead of being a refutation of it. (Of course, in the overall context of GR that quote does apply, but this article is not about GR itself.) --EMS | Talk 18:31, 11 December 2005 (UTC)

--Kmarinas86 18:43, 11 December 2005 (UTC)"All that is needed is to be in an accelerated frame of reference, and it appears." That object would have it's own gravitational field and thus it's own gravitational time dilation. But by having gravity, it curves space, so how can you have gravitational time dilation without gravity and gravity without curved space? Well it would would be linear motion, not spherical.

See the equivalence principle. An accelerating rocket ship in outer space will, for the people on the rocket ship, have a gravitational field. That this gravitational field is generated by the mechanical acceration of the rocket ship instead of curved spacetime is irrelevant to its being a gravitational field. Yes, this is a linear acceleration, but for the people on the rocket ship, gravitational time dilation is a reality all the same. --EMS | Talk 19:09, 11 December 2005 (UTC)

[edit] "The equation(s) for Gravitational Time Dilation"

To Kmarinas86 - This section is a joke, with its multiple renditions of the effect in a Schwarzschild spacetime. A proper treatment requires the situation to be examined in different situations. Examples:

  • In an accelerated box, the equation with respect to an arbitrary base observer is Td = 1 − gh / c2, where
    • Td is the time dilation at a distant position,
    • g is the acceleration of the box as measured by the base observer, and
    • h is the "vertical" distance between the observers.
  • On a rotating disk when the base observer is located at the center of the disk and co-rotating with it (which makes their view of spacetime non-inertial), the equation is T_d = \sqrt{1 - r^2 \omega^2/c^2}, where
    • r is the distance from the center of the disk (which is the location of the base observer), and
    • ω is the angular velocity of the disk.
(It is no accident that in an inertial frame of reference this becomes the familiar velocity time dilation \sqrt{1 - v^2/c^2}).

Do note that these cases do not involve spacetime curvature, which makes them all the more valuable in my opinion. In the meantime, your second version of the Schwarzschild solution time dilation is the only one needed for that case.

I will not be as down on you as CH is, but I will warn you that it is obvious that you do not quite know what you are doing here. I see you as having done as almost much harm as good here, but your willingness to leave my edits alone speaks of someone who wants this to be a good article, and who is not the territorial type. Let's see if you can take what I am feeding you above and build something decent using it. If you can learn and adjust a bit, you may be able to bring things to a state where CH will gladly remove the accuracy tag. --EMS | Talk 03:50, 12 December 2005 (UTC)

I see that you used a reciprocal of the version of time dilation equation that I use. I presume that you are doing that because you are giving the value of time dilation of the external position against the value of the accelerated position where the value is less than 1. For the equations I use, the value is greater than 1, but that's giving the value of the accelerated frame against distant frame (the reverse order).Kmarinas86 04:55, 14 December 2005 (UTC)
Td = 1 − gh / c2 is an approximation. http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/gratim.html makes this "newtonian" error. http://scienceworld.wolfram.com/physics/GravitationalRedshift.html says that Td = 1 − gh / c2 is approximate.Kmarinas86 15:49, 14 December 2005 (UTC)
Kindly indent your reponses. They are hard to notice otherwise. I have taken the liberty of reformatting them this time.
Time dilation refers to time running slower. If the distant obsrver has a time rate of 1, the for one deep in a Schwarzcshild gravitional field the time time dilation will be \sqrt{1 - 2m/r} where c = G = 1. At the least you are describing how the observer in the gravitational field perceives time for the distant observer, but that is not how it is usually done. --EMS | Talk 05:03, 17 December 2005 (UTC)

I noticed that you tried and then (thankfully) removed a section called "Analogues to gravitational time dilation" building on this. You are missing a very important point there: There are not analogs, but instead are bona-fide examples of gravitational time dilation. In each case, a gravitational field is present for the observer in that objects in inertial motion are being accelerated with respect to the observer. Gravitational time dilation is a feature and accelerated frames of reference, and it does not matter if the reason for the acceleration is spacetime curvature or the rocket firing its engines or ones choosing to spin around. --EMS | Talk 19:10, 13 December 2005 (UTC)

It appears that I should think about the equivalence principle more carefully before submitting my next revisions.Kmarinas86 04:55, 14 December 2005 (UTC)

[edit] From bad to worse

"Common mistakes" is a huge mistake!!! In an accelerated box, the acceleration perceived is a function of one's position in the box! Look at it this way: If the bottom accelerated at the same rate as the top as seen inertially, then the bottom would tend to move away from the top in thier own frame of reference because the inertial distance is actually subject to the Lorentz contraction. The only way to overcome this is with a' = a / (1 - aL/c^2). That makes the relationship consistent.

http://scienceworld.wolfram.com/physics/GravitationalRedshift.html Kmarinas86 21:22, 17 December 2005 (UTC)
http://en.wikipedia.org/w/index.php?title=Gravitational_time_dilation&oldid=31694780#Common_mistakes Kmarinas86 21:22, 17 December 2005 (UTC)
What is your point? Or are you just doing future readers the favor of seeing what we are talking about. (If so, then that is good, and thanks.) --EMS | Talk 16:27, 18 December 2005 (UTC)

I am going to find the last "good" edit of this article and revert back to it. That may actually be my own previous edit, but if I can give you some slack I will. In the future, if you have an issue with what I ask of you, please inquire on this page. --EMS | Talk 04:20, 17 December 2005 (UTC)

P.S. To Kmarinas86 - I think that it is time for you to stop editing this page. I gave you a chance to do better, and instead got a bunch of original research. I have done my best to put this page into a reasonable shape now. What you had here before I stepped in was totally unacceptable. --EMS | Talk 05:05, 17 December 2005 (UTC)

I previously added the more exact equation for Gravitational Time Dilation and it came from your edits on the proper time page. How does that constitute original research? I know myself some of what I did was original-looking, but I got some of those ideas from you. I added what I thought were some of your ideas and put them on there. Maybe this should be just a small article with not a lot in it?Kmarinas86 20:40, 17 December 2005 (UTC)
Your diatribe that the gravitational time dilation equation for the "Newtonian" case is self-contradictory was quite original, and that is what I am refereing to. You are not the first person to notice this, but since you cited no sources for it I am quite sure that you came up with it yourself. (In fact that apparent contradiction drove me up a wall at one point until I figured out the answer.)
As for the use of my own material: I do admit that doing so was not original research. However, you pasted it in without any formatting to make it "fit" into the article. You even had my "exercise 3" heading in there! So the intent was fine, but the implementation was not. In the end I had to choose between a significant amount of editting or just taking it back out, and I chose to remove it.
I for one would love to see someone else work on this article, but the result needs to be article that is clear, concise, and correct. After a the point I reverted back to, I found myself with looking at less and less of all three of those. I'm sorry if this is cruel, since I know that you are trying, but you seem to still be learning about relativity and to make matters even worse don't yet know how to sort the "wheat" from the "chaff". --EMS | Talk 04:10, 18 December 2005 (UTC)

[edit] From worse to good to better

The disputed material has been removed, so I'm taking down the dispute message.Kmarinas86 23:04, 25 December 2005 (UTC)

The layout I think is a little scatter brained. I'm going to see make the text clearer like how I attempted at gravitational redshift.Kmarinas86 23:08, 25 December 2005 (UTC)

I have taken the "Gravitational Redshift vs. Gravitational Time Dilation" section located in the history section of the Gravitational Time Dilation article and put it in the Gravitational Redshift article. Kmarinas86 16:52, 26 December 2005 (UTC)

I think that you are effectively "rearranging the chairs on the Titanic". You are obtaining a better grasp of the material, and for that I applaud you. None-the-less, this is still far from being a good article on the subject. The big offense right now are the terms "fast-acting" and "slow-acting": These are neologisms, and their use is prohibited by the no original research policy. Also, there is no need to use new terms when describing a well-known phenomenon. I therefore strongly call on you to get rid of those terms. (Besides, what is "fast" or "slow" is not the observers but rather the rate of proper time passage at their location.) --EMS | Talk 18:25, 26 December 2005 (UTC)

[edit] New accuracy tag

Here are my complaints:

  1. Time dilation is the result of a gravitational field, not the presense of a massive object. general relativity explains how massive objects generate gravitational fields, but that is not the only source of such fields. In Einstein's definition, a gravitational fields exists in an accelerated box, and gravitational time dilation most certainly does also. In addition, letting yourself spin like a top creates a world view with a gravitational field also, albeit one that is a function of your rate of spin.
  2. The Schwarzschild Solution is a good example of how gravitational time dilation is manifested, but it must be emphasized that this is for an idealized case (spherically symmetric non-rotating masses), and the equations for other cases (the accelerated box and the spinning observer) need to be dealt with also.

With my having gotten rid of a bunch of extraneous material, this article is now somewhat better than before. However, it still has a ways to go, and I will see if I can work on it sometime soon. --EMS | Talk 19:19, 28 December 2005 (UTC)

[edit] Experimental verification ???

Is there a source for the airplane atomic clock experiement? I've heard this claim before but have never been able to find sources. How did they tell that the clocks had drifted and how much did they drift? This lack of information on this experiment has bugged me for years. I'm starting to think it's just urban legend. Especially now that I know how hard it is to measure small amounts of time drift between clocks, I wonder how it was that someone measured the drift. Jeff Carr 12:31, 21 January 2006 (UTC)

Add also a request for a source that the GPS system uses this in it's calculation. I've also looked into that claim in the past and could never find verification. Jeff Carr 12:42, 21 January 2006 (UTC)
Further more, the white dwarf Sirius B and the Pound-Rebka experiment are both redshift experiments, not confirmation of time dilation. Jeff Carr 12:47, 21 January 2006 (UTC)

[edit] Merge with Time Dilation

These two pages should be merged, but I'm too new to the Wikipedia to know the correct process of merging pages. Jeff Carr 05:07, 22 January 2006 (UTC)

See Wikipedia:merge, but before you do that, kindly consider that these pages were originally together and another editor chose to split them. I myself an neutral on this. I think that having the proper contents is more important than the organization. However, do feel free to start a discussion.
BTW - New discussions are usually placed at the end of a talk page, and I will move this one down. --EMS | Talk 05:29, 22 January 2006 (UTC)
I "broke" convention by putting this at the top because both articles were tagged as needing expert attention. I'm still new to the wikipedia; it seemed appropriate to me. I was trying to save people's time. They both have almost identical content and both were in bad shape. These articles are the same: there is no difference between Gravitational time dilation or any other sort. The theory is premised on the assumption that gravity and acceleration are indestinguishable. Jeff Carr 21:40, 24 January 2006 (UTC)
I'm less bothered by your not knowing Wikipedia right now than I am at your not knowing relativity. (Velocity) time dilation and gravitational time dilation are not the same thing. Time dilation as introduced in SR is an effect of velocity with respect to a fixed observer. Gravitational time dilation is an effect that exists between fixed observers in a gravitational field. So one involves velocity, and the other acceleration, and there is a difference between those. --EMS | Talk 05:34, 26 January 2006 (UTC)

[edit] Edits by 87.217.89.114

87.217.89.114 (talk · contribs), aka the Jazztel triple play services anon from Spain, wrote "Gravitational in GR means Fictitious force. Gravitational time dilation can be manifested at any kind of accelerated reference frame, and by virtue of the equivalence principle, it will apeear also by the presence of large mass...". The first sentence doesn't make much sense and is arguably seriously misleading; most would say that in gtr, gravitational effectes are identified with curvature effects in a Lorentzian spacetime. I reverted the change, although I agree that this article could use much improvement. ---CH 23:24, 13 June 2006 (UTC)

[edit] Todo list

As a courtesy, I have removed the "expert" items from the todo list.

I am leaving WP and doubt anyone else will know how to implement the suggested improvements since this was mostly a note to myself.

Sadly, I am now abandoning this article to its fate. I emphatically do not vouch for anything you might see in more recent versions. Given past history, I have reason to believe that at least some future versions of this article are likely to contain slanted information, misinformation, or disinformation. Beware also of external links to other websites, which may be cranky.

Good luck to all students in your search for information, regardless!---CH 00:19, 1 July 2006 (UTC)

[edit] Error in section "Inside a non-rotating sphere"

The last sentence of the following extract is in error:

If one is inside the sphere, the sphere can be split in two parts: a hollow sphere above and a solid sphere below. One is weightless anywhere in the interior of a uniform hollow sphere. With respect to one's gravitational potential, it is as if the hollow sphere is not there.

It is true that with respect to the gravitational field (the gradient of the potential), it is as if the hollow sphere is not there. However, the potential inside the sphere is everywhere the same as that reached when moving inwards to the inner surface of the sphere. This is a standard textbook result.

The following paragraph is also incorrect:

The implication is that the gravitational time dilation reaches its maximum at the surface of the non-rotating massive spherically-symmetric object, and that the gravitational time dilation reaches its minimum at the center of the sphere.

The gravitational time dilation actually continues increasing to a maximum at the center of the sphere, so this is misinformation. I have seen a couple of cases in physics forums and newsgroups where people have been misled by this specific sentence in this article. This section therefore needs rewriting to correct this error.

Jonathan A Scott (talk) 11:28, 20 February 2008 (UTC)