Talk:Time dilation/Archive 4

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Errors in this subject.

Ok lets start off with the statement: Time dilation is not a function of speed, or at least only possibility a perceived effect and not a real one as in a kind of illusion.

Reasoning:

Ship a moving a some percent the speed of light traveling from point a to point b 17 light years apart:

Here is a table of the different effects of time dilation for different speeds:

A	B	C	D	E
66.00%	197863022.28	25.75757576	34.28557863	49.58%
67.00%	200860946.86	25.37313433	34.17896546	49.74%
68.00%	203858871.44	25	34.09654535	49.86%
69.00%	206856796.02	24.63768116	34.03890897	49.94%
70.00%	209854720.60	24.28571429	34.00680204	49.99%
71.00%	212852645.18	23.94366197	34.00114314	50.00%
72.00%	215850569.76	23.61111111	34.02304549	49.97%
73.00%	218848494.34	23.28767123	34.07384375	49.89%
74.00%	221846418.92	22.97297297	34.15512692	49.77%
75.00%	224844343.50	22.66666667	34.26877889	49.61%
76.00%	227842268.08	22.36842105	34.41702873	49.39%

The first number is the speed the ship is moving according to a person on the ship.
The second column is the actual speed.
The third column is the time in years to make the trip.
The fourth column is the time that will pass on point a or b before the ship will complete the trip.
Formula =C*(1/SQRT(1-((B*B)/(299792458*299792458))))
The last column is the speed a person at point a or b will calculate that the ship was moving.
formula = (speed of light)/D

So you can see by this that as the ship passes 71% the speed of light it appears to take long for a person at point a for the ship to make the trip and thus seams to be going slower.

If anyone can tell me where I am wrong I would be grateful as I'm assuming I must be doing something wrong as this is so widely excepted but from everyone I have talked to they all seam to agree with my statements.

The first number is the speed the ship is moving according to a person on the ship.

That speed would be about zero, since there is not much relative motion between the ship and the person on the ship.

It appears to me that column A is rather v/c, where v is the relative motion of ship and points a and b and c is the speed of light.

From a person at a or b 's point of view, column C would be the time experienced from departure until arrival of the ship.

The person on the ship actually sees the same velocity as the stationary observer; however, the distance is shortened (see length contraction) and therefore the time is shorter; multiply the stationary time by a factor of sqrt(1 - v^2/c^2), so column D should maybe be the travel time as experienced on the ship, which would be (in years) 19.35078, 18.83603 etc..

And there is also the relativity of simultaneity: An observer at a and an observer on the ship will not agree on what happened at b at the time of the ship's departure (I assume that e. g. there was an explosion at b at the time of the ship's departure, as seen in the reference frame of a; the observer on the ship will argue that the event was actually before the ship's departure).

For the full mathematical picture, see Lorentz transformations.

Icek 10:00, 2 June 2006 (UTC)

Another error, more serious I think since the time dilation contradicts in general the basic concept of special relativity. According to this article: "In special relativity, clocks that are moving with respect to an inertial system of observation (the putatively stationary observer) are found to be running slower. This effect is described precisely by the Lorentz transformations." Let us reverse the inertial systems and move the observer to moving object. Now from his point of view his inertial system is stationary while the other one is moving in another direction. Then the clocks in that system which is now moving should be running slower. But they aren't. According to Lorentz transformation they are running faster, because the Lorentz factor is now in denominator.

Let's go back to the article: "Time dilation would make it possible for passengers in a fast moving vehicle to travel into the further future while aging very little, in that their great speed retards the rate of passage of onboard time. That is, the ship's clock (and according to relativity, any human travelling with it) shows less elapsed time than stationary clocks. For sufficiently high speeds the effect is dramatic. For example, one year of travel might correspond to ten years at home. Indeed, a constant 1G acceleration would permit humans to circumnavigate the known universe (with a radius of some 13.7 billion light years) in one human lifetime. The space-travellers could return to earth billions of years in the future (provided the Universe hadn't collapsed and our solar system was still around, of course). A scenario based on this idea was presented in the novel Planet of the Apes by Pierre Boulle."

1G acceleration causes only 0.000075% time dilation which means that influence of general relativity is nonessential. So we may safely assume that the system of space shuttle is inertial. If the concept of special relativity is universal from standpoint of its passengers the shuttle is stationary, while the Earth is fast moving, then on Earth few years should elapse while the ship's clock should register billions of them. Can someone explain that?

There's nothing wrong with this article. I think there is something wrog with Lorentz transormation and it needs major rewriting. You can only have one clock running slower, on Earth or on fast moving object. You can't have them both. If we don't rewrite Lorentz transformation we can't use it on fast flying space ship. Greg park avenue 17:23, 28 August 2006 (UTC)

Look again at the Lorentz transformation. For a clock moving in the x direction at v with t = t' =0 at x = x' =0, you have x=vt for the moving clock. So the t Lonrentz transformation becomes

$t'=(t-vx/c^{2})/{\sqrt {1-v^{2}/c^{2}}}=t(1-v^{2}/c^{2})/{\sqrt {1-v^{2}/c^{2}}}={\sqrt {1-v^{2}/c^{2}}}$. So the moving clock runs slower. This math also is reciporical in that to the "moving" observer the "stationary" observer's clock runs slower.

On the matter of acceleration: 1G is 9.8 m/s², not 9.8 m/s. Over time, a constant acceleration builds up one's speed more and more. Now in relativity, coordinate and proper accelerations are different (since otherwise a constant acceleration could cause you to go faster than c), but even so the example given is valid. --EMS | Talk 18:58, 28 August 2006 (UTC)

Agreed with Lorentz transformation. Yet, only one clock can run slower than the other, not both simultaneously. This paradox known as twin paradox Einstein predicted in 1905 will be removed by general relativity. Unfortunately his prediction proved untrue for small and continous values of acceleration and deceleration like 1G. 1G is here the thrust of the space ship engines, not the actual acceleration, and is an equivalent to the gravity of Earth on its surface. Assuming that gravitational radius of Earth is 0.9cm ($r_{g}$), time dilation due to this thrust is given by

$t'=t{\sqrt {g_{00}}}=t{\sqrt {1-r_{g}/r}}=\left(1-0.00000075\right)t$

and is too small to recompense for much bigger time difference shown by clocks running on high speed space shuttle and on Earth, which should be down to zero after ship's return to Earth. All those theories based on assumption that clocks on returning vehicle run differently than on departing one are subject to the same paradox and Minkowski space diagrams simply don't apply here.

I would like to introduce new concept which perhaps would restore symmetry of Lorentz transformation without much headache. Let's replace four dimensional time space by six dimensions - three for space and three for time. Proper time (time on space shuttle) will be then projection of the time vector in three dimensional time frame on one of its axis. Transformation from a stationary integral system to moving one would be then nothing else than rotating the time vector about an angle which cosinus is Lorentz factor. Reverse transformation (from moving vehicle to stationary) will be also projection of this very same vector under the same angle, just like in regular coordinate system transformation by rotation. Lorentz transformation becomes then Gallilean only in six dimensional time space. Simple, easy and full symmetry is restored.Greg park avenue 16:50, 29 August 2006 (UTC)

Ah, you are proposing a novel theory of physics. By all means you should start a website of your own and advocate your theory. If your ideas are fertile, then soon the scientific community will flock to you. Wikipedia policy (like any encyclopedia's policy) is to represent exclusively those theories that have gone through the entire process of gaining wide support. This is called the no original research policy. --Cleonis | Talk 11:38, 30 August 2006 (UTC)

.Greg park avenue wrote:

... only one clock can run slower than the other, not both simultaneously.

The key word there is "simultaneously". Simultaneity is relative in relativity. Events which are considered to occur "at the same time" in one frame of reference are found to occur at different times in other frames of reference. Because of how time is offset as a function of distance between frames of reference in relativity, both observers can find the other's clock running slow with respect to the temporal coordinates in their own frame of reference. So Greg's complaint is actually a common mistake that relativity novices make. --EMS | Talk 15:30, 30 August 2006 (UTC)

Thank you for friendly advise, but why bother with page when this is only new form of expressing Lorentz transformation and very simple indeed? Perhaps as an expert on rotation would you take a little time to review this proposal below I would like to place in wikipedia as an extra chapter? It's kind of unique but that's what wikipedia is about and I don't think we break any rules. However, I wait for any suggestions.

To show symmetry in Lorentz transformation regarding time dilation and twin paradox, one can write it as an rotation of time coordinates in six dimensional time space $x$, $y$, $z$, $t_{1}$, $t_{2}$, $t_{3}$. System of two coordinates $t_{1}$, $t_{2}$ has been rotated around axis $t_{3}$ about an angle $u$ and has become $t'_{1}$, $t'_{2}$, $t'_{3}$ while $sinu=v/c$. Then $cosu$ is the reciprocal of Lorentz factor, and the rotation has the very well known form:

$t'_{1}=t_{1}cosu-t_{2}sinu$

$t'_{2}=t_{1}sinu+t_{2}cosu$

where $t_{1}=t$ and $v=x/t_{1}$. You can show this system of equations in another form:

$t'_{1}={\frac {t_{1}-t'_{2}sinu}{cosu}}$

$t_{2}={\frac {t'_{2}-t_{1}sinu}{cosu}}$

Now, when you substitute second pair of time coordinates for space coordinates x and x' along which the system moves as follows

$t'_{2}={\frac {x}{c}}$

$t_{2}={\frac {x'}{c}}$

then you get nothing else than Lorentz transformation

$t'={\frac {t-vx/c^{2}}{\sqrt {1-v^{2}/c^{2}}}}$

$x'={\frac {x-vt}{\sqrt {1-v^{2}/c^{2}}}}$

Note that the function transforming coordinates $t_{2}$ is inverse to function transforming coordinates x. I think it needs a bit explanation, there is also some problem of idiom but this is only a rough sample and any help would be appreciated. What do you guys think about it? Greg park avenue 19:47, 30 August 2006 (UTC)

You are proposing a novel theory of physics. By all means you should start a website of your own and advocate your theory. If your ideas are fertile, then soon the scientific community will flock to you. Wikipedia policy (like any encyclopedia's policy) is to represent exclusively those theories that have gone through the entire process of gaining wide support. This is called the no original research policy. --Cleonis | Talk 21:11, 30 August 2006 (UTC)

I must agree with Cleonis. This page is to talk about time dilation as it is known and in relation to this article, not as you think it should be. Wikipedia is not a soapbox. --EMS | Talk 22:47, 30 August 2006 (UTC)

Maybe you reconsider, EMS. I didn't propose major changes and full blown on Richter scale theory, just the simple explanation how the time dilation could be represented by equivalent of rotation of time vector. When you want full Lorentz transformation in 6 dimension metric then you got:

$t'_{1}={\frac {t_{1}-t'_{2}sinu}{cosu}}$

$t_{2}={\frac {t'_{2}-t_{1}sinu}{cosu}}$

$t'={\frac {t-vx/c^{2}}{\sqrt {1-v^{2}/c^{2}}}}$

$x'={\frac {x-vt}{\sqrt {1-v^{2}/c^{2}}}}$

Both pairs of transformation are reversing each other, something I have pointed before that it needed an explanation, that's why you won't get any time dilation when space ship returns to Earth. And full symmetry will be this way conserved which no theory explained that far. But we don't go that far in wikipedia, are we? By the way, it's only a discussion, so don't get upset too much. I was only asking. Greg park avenue 00:00, 31 August 2006 (UTC)

*Sigh* You don't need six dimensions. The LT are a "rotation" of space and time which physically is a change of velocity. The standard spatial rotations are also technically Lorentz transformations (as together with the x-t transformations they form a group known as the Poincaré group). This does in four dimension what you want to do in six. Besides, your proposal is original research, and Wikipedia has a very proper ban on that. --EMS | Talk 00:33, 31 August 2006 (UTC)

You definitely need six dimensions to compensate for time dilation which is only an illusion, especially, when experimental data agrees with that. Look, when you bring in the resultants

$T={\sqrt {t_{1}^{2}+t_{2}^{2}}}$

$T'={\sqrt {t_{1}'^{2}+t_{2}'^{2}}}$

and the first pair of the above system of equations express by them, then this part of transformation becomes Gallilean again T' = T and x' = x - vT, while the second part stays unchanged. T is the real time we are experiencing, while t = $t_{1}$ is only its component. And that's it.

When you still claim that this is an original research, why don't you send it to Physical Review? It's only one page or two and your scientific language skills to argue with types from Brookhaven are sufficient to do that. Mine are not. Otherwise, it will stay on this back burner to the Judgement Day. Besides, time dilation is your baby, not mine. Just to be on fair side and not to take full credit, call it somehow in my memory. Greg_park_avenue transformation is OK with me. Greg park avenue 14:04, 1 September 2006 (UTC)

Dear Greg, Wikipedia is not a place for original research. That said, the two theories of relativity conform very well with the physical reality we can measure, and is does not, as you try to assert, contain contradictions. This discussion ends here. If you want to persue this quest outside of Wikipedia, feel free to do so, but I suggest you follow a course in General Relativity first. Shinobu 16:06, 4 September 2006 (UTC)

I would recommend taking course in simple relativity first. If you went to general first you might be suprised to find out that the shift of the Mercury perihelion in Schwartzschild metric was three times bigger than the same shift calculated on the basis of Kerr metric while the colapsar moment M → 0. That's a contradiction inside general relativity, but it's too big for wikipedia. What I suggested was a simple logic which even a high school student would comprehend but let me put it in more simple words yet. If we assume that the 4 dimensional time space may be curved, we must go up at least one dimension higher or two. Just like two dimensional sphere may be curved but only in three dimensional Euclidean space. This, as simple logic as that, ought to be inserted in every school book and science manual wikipedia nothwithstanding. And that's what I was trying to do. Why serve the kids with outdated theories like Minkowski space diagrams with its ict-axis? If time coordinate was an abstract number, than in case of g0i # 0 (Coriolis interactions), ds would contain an abstract number too, and then the energy and momentum which, as having been a differential mdxi/ds, would not even be real. What about the Hamilton Jacobi equation? And you call this simple logic an original research? You don't wait for the blessing of some smooth talking professor from MIT or anothor Ivy League joint. Them pompous asses killed even cold fusion without bothering to send a representative to the great state of Utah to check Fleischmanns - Pons findings and see how it was done and get to know how to properly repeat the experiment in their lab. They, the policy makers, have just said it cannot be done and that was the end of the latest major breaktrough in the history of mankind. And now you are one of them? If you can do nothing about this policy, at least don't confuse the kids. The last chapters of this article should be rewritten or removed because they contain major generic errors. If they remain like that I vote this article for not being neutral.Greg park avenue 19:55, 6 September 2006 (UTC)

Shinobu, I don't agree. Having read Greg's statement "Just like two dimensional sphere may be curved but only in three dimensional Euclidean space", I think that a course in General Relativity would be a waste of time. Having seen him call Minkowski space diagrams with ict-axis "theories", I think that just about every kind of physics course would be a waste of time. DVdm 10:27, 7 September 2006 (UTC)

I see that you've been to private schools and speak the perfect French, and most probably took one of the courses in sarcasm - Sarc1, Sarc2 or Sarc3. I can only say I Am Charlotte Simmons after Tom Wolfe or Don't Bother after Shakira for that. But no matter what language you speak or how good you speak it, you can't explain the unexplainable. When math says "no" you can't say "yes" in physics. Physics cannot be neither biased nor corrupted. I think you are in wrong part of wikipedia, politics department would be more preferable. Greg park avenue 15:27, 7 September 2006 (UTC)

Shinobu, just like I expected, he also entirely missed the point I was making, but I will not bother explaining. So I fully agree with your ending the discussion. DVdm 18:23, 7 September 2006 (UTC)

Shinobu, don't take this bait - hook, line and sinker from this hardly to be trusted friend of yours of unknown heritage. This selfish person is not worth to be Hooking Up with or even hanging around. You can do better than that. Just say I am who I am and be proud of it. Greg park avenue 14:29, 8 September 2006 (UTC)

This discussion is OT as well as being OR. I call on everyone not to respond further and let it end here and now. --EMS | Talk 20:26, 8 September 2006 (UTC)

This is not a political convention nor a fraternity formal to call on everybody. If someone had questions about the math above like how the Hamilton Jacobi equation shall look in six dimensional time space or what differences if any were there between its expression in four and six dimensions, the Einstein equations, the metric, the conservation laws, thr trajectory equations, the action e.t.c., I will still be here and take time to explain it to him or her as best as I can, and evereone even you is welcome to do that. If you're not interested, speak only for yourself, not for the entire international scientific community, because that makes you ridiculous. I will repeat that line one more time. This is only a discussion and I have never inserted any original research into wikipedia except into its Talk page. My comments about insufficiency of Lorentz Transformations were not the original research. This problem has been known since over one hundred years as the twin paradox and hasn't been satisfyingly resolved until this day, capisce? Many scientists will second that opinion and they did. Greg park avenue 19:21, 9 September 2006 (UTC)

Explanation requested

I am a nonexpert "with some significant scientific background". Is it meaningful to ask what actually causes time dilation? To my understanding, the article doesn't do that. Is it something that just IS, or is there some underlying cause? I think I understand length contraction (optical illusion) and mass increase (all that kinetic energy), but time dilation gives me a headache. Clarityfiend 09:27, 9 June 2006 (UTC)

It has been a never-ending but largely suffocated debate, depending on different beliefs. For example, not long ago a paper appeared in the AJP that emphasizes that length contraction is physical, while you seem to have read other opinions. The opinion of Lorentz was that such effects are physical in principle, but partially an optical illusion due to our own (unknown) velocity relative to space ("the ether"). Einstein's thoughts were difficult to follow (at one time he seemed to believe in a kind of relative reality and "relative motion" as cause) - I would be interested if someone could cite him on this point. Nowadays popular is the idea that the cause is one's trajectory through "space-time".

As such ideas are not directly verifiable, it is wise not to expand on such in an article about physics. A special article about the philosophy/philosophies of "relativity" over the ages may be appropriate for that. Harald88 12:05, 9 June 2006 (UTC)

Clarityfiend - Time dilation is physically real, and experimentally verified. It does have an underlying cause, which is described in the section Simple inference of time dilation. I advise studying that and the animated GIF in the following section. BTW - I have at time considered rewriting this article to reconsolidate and clarify it, but have yet to do so in part because I have not yet figured out what the rewritten article should look like. Perhaps you may have some ideas, given what you are trying to get out of this article. --EMS | Talk 15:34, 9 June 2006 (UTC)

I wasn't suggesting that time dilation wasn't real. I was just hoping that there was some relatively intuitive explanation of why it occurs. I already knew about the derivation (I remember it from 2nd year physics). So, I guess the best that can be said is that it is a consequence of the speed of light being the same in all frames of reference.

Has anybody proposed an experiment to determine if length contraction is actual and not illusory? I thought it was because light from the front and back of an object reached the observer "out of sync" (so to speak). I need more aspirin. Clarityfiend 01:11, 11 June 2006 (UTC)

You can look at the finding of muons generated high in the atmosphere as proof of length contraction. Since the muons have a half-life which is to short for them to reach the surface of the Earth in the time it takes for them to do so, their experiencing time dilation explains this. But what about the same as viewed by the muons? In that frame of reference the muon's clock is OK. Only if the distance to the Earth is reduced is there time in that frame of reference for the muons to get down here before decaying. --EMS | Talk 05:23, 11 June 2006 (UTC)

Thanks. Now I need to order aspirin by the case...

As for how the article should be rewritten, my first suggestion is to provide a introductory description aimed at the layman. The first sentence already starts to use jargon that would discourage the average reader. How about: "Time dilation is one of the non-intuitive phenomena associated with Einstein's theories of relativity. An observer watching, for example, a spaceship moving at a high enough velocity, would be able to detect time passing at a slower rate for those aboard, at least from the observer's point of view. A person on the ship, however, would not notice any difference. The dilation is negligible in everyday situations, only becoming noticeable at high speeds. This effect has been verified by numerous experiments." Then throw in a table showing how much time appears to slow down as speed goes up. Next, you could describe the experimental results: the muons, GPS, etc. (and find some way to put Ives at the end to minimize the impact of equations on the great unwashed). This could then segue into the space flight (what, no mention of Heinlein's Time for the Stars?) and popular culture sections (which should be merged together). That would satisfy the general public. After that, you could go into the grisly details, starting with the simple derivation.

Minor quibble: It seems kind of arbitrary to say that the effect only becomes "important" at 0.1 c. Clarityfiend 17:13, 11 June 2006 (UTC)

The problem with trying to pick a threshold like this is that the definition of "important" will depend on what you're doing. It might be better to pick an obviously-arbitrary value (such as, "length, mass, and rate of time flow change by 10% at about 0.xx C"). Heck, you could even do a table with an order-of-magnitude scale (10%, 1%, 0.1%), if it weren't for the fact that this information likely wouldn't be useful enough to justify the space taken by the table. --Christopher Thomas 20:08, 11 June 2006 (UTC)

Clarityfiend - I don't think the your proposals quite work. For example, a time dilation table was present at one point, and man was it ugly! Yet this article does need to be rewritten. My advice is that one of us set up a sandbox version, and we will work together to revise it a ways. --EMS | Talk 00:34, 12 June 2006 (UTC)

Time dialation and experienced time to circle the universe

In the section entitled 'Time dialation and space flight' the sentence, 'Indeed, a constant 1g acceleration would permit humans to circumnavigate the known universe (with a radius of some 15 billion light years) in one human lifetime. ', is interesting. Plugging 82 billion light years into the t* equation gives an experienced time of a little more than 25 years. But if you replace g with a slightly lower value, say 1.5 m/s2 then you get an experienced time of a little more than 150 years. It seems a strange coincidence that the universe fits us so well; If we lived on a planet with less gravity and were therefore incapable of sustained exposure to anything like 1 g, or if our life spans were similar to that of a dog, or if the universe were only a few times bigger then we could never hope to circumnavigate it. Yet our life spans, the size of the universe and the gravitation of Earth are all unrelated variables.

Are these equations accurate? I had heard than even with a high constant acceleration and time dialation it was impossible to reach the centre of the galaxy in a lifetime.

198.103.34.97 17:58, 9 June 2006 (UTC)Eric Saumur

I will take your calculations on faith, as I know that a constant acceleration really does get up to near light speed (with respect to the starting frame of reference) within a few years. At that point, your clock is all but stopped. For the galaxy: Going to the center within a human lifetime now does seem viable (and back too). However, where are you going to get the energy from for the accelerations and decelerations necessary for pulling off that trick? As for circumnavigating the universe, there is a problem: the Hubble expansion. As a practical matter, you will never get even halfway around it. --EMS | Talk 05:26, 10 June 2006 (UTC)

The phrasing of the question was careful about avoiding the expansion problem, if I remember it correctly (specified a sphere with the diameter of the presently-observable universe, as opposed to our universe, or even a spherical volume within our expanding universe). Regarding the equations, I was considerig doublechecking it yesterday, but so far have been too lazy. I'll do this within the next couple of days here on the talk page, showing my work. There are at least three ways of setting up the problem, though: Applying a thrust of constant magnitude from a stationary observer's reference frame, applying a thrust of magnitude scaling with the relativistic mass of the ship from the stationary observer's reference frame, and considering the ship to apply constant thrust in its own reference frame. These will give wildly different answers for travel time (in fact, the second option might make you approach C in a finite time, with thrust approaching infinity, now that I think about it). --Christopher Thomas 17:34, 10 June 2006 (UTC)

End of the universe (as they knew it)

I just realized there's something missing. The effect helped demolish once and for all the old deterministic view of the universe, yet this isn't mentioned at all. Maybe it belongs in a higher level article on relativity, but a cursory examination doesn't show it discussed anywhere except the determinism article. Clarityfiend 04:32, 13 June 2006 (UTC)

???. I assure you that relativity is a deterministic theory. Observers may not agree on the ordering of events which are not causally related, but for causally related events they will. See Minkowski space#Causal_structure. --EMS | Talk 04:59, 13 June 2006 (UTC)

The word "relativity" isn't in the Determinism article. The most I can find is mentions of chaos and quantum mechanics. Scientific determinism doesn't contain it either. As EMS described, as long as you're not looking through a Cauchy horizon, observers will agree on what spacetime looks like, though they may disagree on how to draw coordinate axes on it. --Christopher Thomas 05:39, 13 June 2006 (UTC)

Okay, I must be using the wrong term. Before Einstein, it was assumed that all parts of the universe were in sync, that time moved in lockstep everywhere. What's the word I'm looking for? Whatever it is, it should be mentioned somewhere. Clarityfiend 03:31, 14 June 2006 (UTC)

This would be simultaneity. The effects of SR on simultaneity are described at relativity of simultaneity.--Christopher Thomas 03:45, 14 June 2006 (UTC)

Naah. That's too narrow a definition for what I'm talking about. Paradigm shift is such an overused, clumsy phrase, but it comes close I suppose. Dammit, I'm sure there's a better way to say it, but I just can't think of it. Clarityfiend 06:22, 15 June 2006 (UTC)

The best I can do for you is to call it a "proper time differential". Just be aware that this is a neologism, as I just made it up. So you cannot write a Wikipedia article on it per Wikipedia:avoid neologisms.

The confusion, Clarityfriend, seems to be coming from your use of "deterministic" and "determinism" (which are best known as terms in philosophy dealing with "fate" and "free will") whereas I think the word you wanted to use was "absolute." You're trying to point out the distinction between Newton's view of space and time as having an objective and invariant existence independently of whatever they "contain," as opposed to the Einsteinian view that certain physical principles, while acting according to fixed mathematizable laws, are determined not with reference to such an external absolute space, but rather with reference to the mutual relation of the particular (set of) objects in question: that is, solely with reference to their measured change of position relative to one another, not with reference to a shared common space in which they are both supposed to be embedded. This is traditionally called the contrast between "absolute space" and "relative space." Actually, it would be better put as absolute space, versus the rate of change of certain measurement attributes respecting the different reference objects, with the existence of a "background medium" being regarded as gratuitous metaphysics. (You can see why it isn't put that way.) This is the general Machian "viewpoint," with which Einstein was in sympathy (though not the actual Machian analysis of the situation, which as it happens does include, in effect, what Einstein sets aside). -Scott Dickerson --72.245.1.234 17:11, 5 July 2006 (UTC)

One thing this article needs

If there is one thing I think this article could do with it is a Graph, showing Time Dilation effects in relation to speed.

I saw a graph like this years ago in an old book and was always interested in it, it showed how much time would appear to slow down if you were in a spaceship travelling at various percentages of the speed of light. I assume the graph was made using the various formulas on this page, it would be really great if someone could create a graph like this for the article.

In case I'm not explaining this well, what I mean specifically is a graph with one axis as speed (in percentages of C), and the other axis as the lengthening of time (i.e. at zero speed 1 second = 1 second, at the Speed of light 1 second = Infinitely long time, at-least I think that's how it goes).

A graph like this would be very useful for people to see at what speeds Time Dilation really starts to affect things, like if I wanted to know say, what would be the dilation at 25% C, then I could just go look (instead of trying to calculate it with those formulas).

--Hibernian 05:53, 19 July 2006 (UTC)

Real slowdown?!

Someone added about time dilation in general: "The time slowdown is real".

However, such a remark may only be valid in special cases (such as the twin paradox), and depending on what one means with "real". In general, . Thus I object to the abovementioned statement. Either delete or rephrase! Harald88 12:16, 21 July 2006 (UTC)

I edited-in the phrase in question. The objection is validly made, but please consider the following: (1) There seems to be no way to say anything very close to what the common word "real" says without inserting so many qualifiers that the point of using it is obscured. (2) My purpose in using the phrase is to address what I perceive to be a source of confusion in understanding what the theory contends.

The principle competing view is that the phenomenon is "just" a product of the geometry of available measurement technique and should not, by implication or otherwise, be attributed to the state of the measured object. Whether or not this turns out to be the case, it is not an accurate characterization of the Special or General Theories of Relativity as enunciated by Einstein and accepted by his contemporary followers. The competing view does not seem to represent a genuine live controversy, but rather the contention of a small minority outside the physics mainstream--thus not appropriate to the overall approach taken in this article, per Wiki rules. This could change, of course.

It is not accurate to state that, per these theories, "what appears as slowdown in some frames will appear as speeding up in some other frames"--if one uses "frame" in a sense consistent with its prior use in the article, which only addresses constant relative velocity on the part of measurer and measuree. The time-acceleration involved with the twin paradox is assigned, by the theory, to the distinct case of mutual acceleration. (It occurs during the turnaround.) Note that my concern with the above-cited statement involves ambiguity in what the term-of-art "frame" is to refer to. But I think it illustrates the very sort of confusion that I am at pains to alleviate. As the special cases have their own articles, it seems this article ought to present generalities that illustrate the scientifically-revolutionary thrust of the Einsteinian view in its generally accepted interpretation.

And even considering the special cases, the time dilation effect is understood to be a real property of the moving object, and I maintain that it is important to acknowledge that--precisely because it is counter-intuitive.

I say this without prejudice as to the basic question of whether the theories are "truly valid." I wonder that myself. They may not be. Alternatives must receive fair consideration. But non-mainstream objections should not trump a presentation of the theory itself. -Scott Dickerson --69.3.132.12 18:27, 24 July 2006 (UTC)

I doubt that any textbook puts it as you do. making it not only inaccurate but also WP:OR. If I remember well, some books or articles put it as "physical in the corresponding reference frame". Would that convey what you were trying to say? Harald88 21:40, 24 July 2006 (UTC)

Some time ago I uploaded an animation to the wikimedia commons that illustrates the matter that is discussed here. velocity time dilation (This gif-animation is 110 KB in size)

Oops, I had forgotten that I had inserted that animation on this talk page back in january animation with helical worldline

The animation shows two spaceships, one following a straight worldline and the other following a helical worldline that corkscrews around the straight worldline. The animation as a whole is a Minkowski diagram that is co-moving with the object following the straight worldline. For the "blue object" a larger amount of proper time elapses than for the "red object".
However, it is theory dependent whether to state or not that the red clock is slowed down, or even that the time slowdown is real.
The very point of Einsteinian special relativity is that in the setup shown in that animation there is no meaningful correlation to be found between the plane of simultaneity of the blue spaceship and the plane of simultaneity of the red ship. The plane of simultaneity of the red ship cannot be spatially extended in such a way that it contacts the worldline of the blue ship in a selfconsistent way, which rules out a comparison.
Strictly speaking, it is beyond the scope of Einsteinian special relaivity to state whether the red clock is slowed down. All that the theory states is that when the two spaceships rejoin after having travelled on worldlines of differing length, they will on comparison see that the blue clock has counted a larger amount of proper time.

I like the animation, and would welcome it inside this article. BTW, I disagree with your last remark: in SRT the reference clock is in the inertial frame and compared to that the red clock has retarded. That is, in standard English, "slowdown". Even when looking at it from other inertial frames, the red clock has slowed down relative to the blue clock, and the blue clock hasn't changed its rate during the experiment. Therefore I agree with Einstein when he wrote that that clock "must go more slowly". Harald88 20:10, 25 July 2006 (UTC)

It is very common in physics writing to not adhere to strict formulation all the time, for that would disrupt the flow of language too much. Without the context, it cannot be assessed whether this Einstein quote is originally intended as a principal statement, or as physics shorthand in the flow of the narrative. --Cleonis | Talk 22:38, 25 July 2006 (UTC)

In view of my remark below about Einstein's relative reality, I agree that such remarks are open for interpretation. Which doesn't change the fact that in SRT that effect is "absolute" (in both meanings of that word). Harald88 06:28, 26 July 2006 (UTC)

Of course, this strictness is very awkward for writing introductory material about relativistic physics. I am keen to avoid teaching the beginner things that he must later unlearn again, but this ties me down on all sides. Some authors decide to oversimplify some things, in order to get at least something across. --Cleonis | Talk 15:37, 25 July 2006 (UTC)

That last sentence appies to my efforts, the point of dispute being the "over." It's a basic question regarding not only Wiki but encyclopediae in general--do you provide "in a nutshell" versions for the casual or nonexpert inquirer, or offer something more precise and technical--but definitely harder for the typical inquirer to grasp? My own suggestion is that both be provided--a simplified, Asimov-type intro, followed by a more technical, less summary presentation. As written so far, this article does do both, though (to partially address the objections raised above) it might be better to completely separate them as a "part One"/"part Two".

Commentators on Einstein (I recognize that that isn't a "cite") express his negative attitude toward ("gratuitous") metaphysics. Raising the "but is it real" question may cross the line. My question is: does this snippet of metaphysics lead the reader further from the theory than the alternative of allowing him to assume the more-intuitive converse?

No OR is presented here. My goal is to provide a fair and clear exposition of the specifically Einsteinian interpretation of the phenomenon: not just the math and experimental confirmations, but the significant change in the physical wordview following upon a fundamental-spacetime interpretation (the expressed view of Minkowski and Einstein) as opposed to an artefact-of-measurement interpretation.

I'll acknowledge, certainly, that the project of centering an article on "Time Dilation" on Einstein's theories is a defeasible choice. Let's see some "Be Bold" alternatives, and discuss them. -Scott Dickerson--69.3.132.12 18:10, 25 July 2006 (UTC)

It's my personal experience that oversimplification easily leads to long-lasting misinterpretation. In particular, I only started to correctly understand SRT after reading the original papers. Careful phrasing isn't necessarily overly technical or complicated.

Note also that Einstein had a peculiar understanding of "real": for him (in 1905), real is what one measures, even if (as with time dilation!) what one measures is in part stipulated by convention.

Moreover, why single out the rather obscure Einsteinian interpretation, and omit the Lorentzian interpretation which is much more straightforward and easier to understand?

To me it makes more sense to have a box with varying interpretations (Einstein, Lorentz, Minkowski) than overly simple explanations.

As you didn't comment on my suggestion, I'll try to modify the statement in question to something almost as simple but not self-contradictory (as it is now). - Harald88 19:19, 25 July 2006 (UTC)

I now changed it, but as I remained close to 69.3.132.12's version, it's perhaps more complex than needed. I hesitate to replace it by a remark that a change of speed of a moving clock results in a change of clock rate, according to all observers in uniform motion - only, there is disagreement about the sign and magnitude. That's more compact, and perhaps simpler to understand. Or, as another alternative, we may use Cleonis'animation and pinpoint that although it's "relative" between inertial frames, the velocity time dilation can be as "absolute" as gravitational time dilation. Harald88 20:12, 25 July 2006 (UTC)

No comments?? Aren't we discussing how to present this? Harald88 20:47, 28 July 2006 (UTC)