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This article looks a little too big for a stub tag, anyone object to removing it? pielover87 22:07, 18 October 2005 (UTC)

Two clocks experiment

When I do the two clocks experiment as a thought experiment using the consequences of relativity I get that both clocks have slowed down relative to a midpoint, and that gravity accounts for the discrepancy. The midpoint is where you'd stand to get the same result. at two quater points the further away one would appear slower than the near one. So under time dilation they both appear slow to each other, but should become roughly the same time once they are together, the discrepancy, being due to distances moved in the gravity well.

determining Newtonian gravitational constant G

When equal gravitational time dilation factors are applied, first to blue shift a photon to a maximum energy density (limit wavelength), and then to convert photon energy into gravitational field energy, each of the two factors is equal to the square root of [(3/2) exponent 1/2, times Planck time divided by two pi seconds]. (Note that when Planck time is expressed in seconds and divided by two pi seconds a dimensionless ratio is obtained.) This is a required condition if the electron is a gravitationally confined particle. When the Planck time is 5.391 times 10 exponent-44 seconds, the blue shift time dilation factor is 1.025 times 10 exponent-22 seconds per second. The critical or limit wavelength photon that has the energy density to materialize a pair of gravitationally confined particles, has energy equal to (2/3) exponent 1/2 times the Planck mass energy. This mass is 1.7775 times 10 exponent-8 kg. The limit wavelength is (3/2) exponent 1/2 times two pi times Planck length in meters. The quantized electron mass is equal to 1/2 of the mass energy of the limit wavelength photon when this energy is reduced by the gravitational time dilation factor 1.025 times 10 exponent-22 seconds per second. The product of 1.7775 times 10 exponent-8 kg and 1.025 times 10 exponent-22 seconds per second is 1.8219 times 10 exponent-30 kg. This mass times 1/2 is the electron mass, 9.1095 times 10 exponent-31 kg. The electron mass may then be defined as (h/4 pi c) times (c/3 pi h G) exponent 1/4 kg. From this equation and the known electron mass (9.1093819 times 10 exponent-31 kg) a hypothetical value for the gravitational constant (G) may be determined. This value is 6.6717456 times 10 exponent-11 m exponent 3,kg exponent-1, second exponent-2. This could be useful because the gravitational constant is the least precisely determined fundamental constant.

Author B.G.Sidharth has modeled the electron as a Kerr-Newman type black hole. This is consistant with the electron being described as a gravitationally confined particle. User: DonJStevens

See Black hole electron, See also Micro black hole

Can you please not reference this talk page in the article unless it's absolutely necessary? Many thanks. -- Graham  :) | Talk 01:05, 12 Mar 2004 (UTC)

question about relativity of time

This is just a question and I apologize if this is the wrong forum, I am trying to understand how time can be relative? Shouldn't time be constant, for example just because the Solar System is separated by millions of miles, it is the same time there as it is here. The distance in between should not affect the time, my point being on the previous page, "When one accelerates towards the speed of light, time slows down with respect to the rest of the Universe. That is, a stationary observer would see the traveling objects slowing down their activity (while still traveling fast). For them, time passes slower." So my point is time may seem to be passing slower but we are in fact all in the same instant or moment of time? No matter how fast one is traveling, is it not still "now"?

No. It turns out that two events that happen at different points in space can't be observed by two or more observers that move in relation to each other as happenning at "the same time" (and so the same goes for "now"). "The same time" has no physical meaning. It turned out to be only a human concept not having a counterpart in the nature.

The reason for it is a physical fact that the speed of light is the same for all observers regardless of their velocities and the information from any event can reach the observer only with speed of light at the best. It creates a situation that if one observer establishes that some two events happened "now" (in his time i.e. in the time measured by his clock) an obsever that moves in relation to the first one sees those events as happening at different times in his time. So "now" as related to certain events has meaning only for one observer in the universe and so it is only a subjective idea, valid only for this particular observer and therefore "relative". It can't be something "absolute" that would be valid for everyone. Jim 17:04, 2004 Jul 3 (UTC)

No matter how fast one is traveling, is it not still "now"?

Yes I do believe you are correct. I think the same myself and have yet to see a satisfactory explanation otherwise. To think time slows down or speeds up just because you are moving very fast is preposterous to me.

Hi, you bring up a very good point, one of the stranger predictions of relativity. I am just an amateur, and much of relativity is beyond my grasp, but I believe I can explain at least part of this. First of all, I agree that the notion of time slowing or speeding based on one's velocity does seem preposterous. This is because even at our top speeds, we travel so slowly compared to the speed of light that the time dilation is negligible. If one were to graph the amount of time dilation versus the speed, it would appear as a curve stretching up to infinity as one's speed approached c, the speed of light. However, if one just looks at the section of the graph that shows velocities we can currently attain, it would appear horizontal. The notion seems preposterous because our species evolved only achieving speeds on the beginning almost-flat part of the curve, and because we grow up and all of our experiences are at extremely low speeds (relatively speaking; no pun intended). In a similar manner, the idea that the Earth might be (approximately) spherical and not flat seemed preposterous to many people in its time; if you grew up in a small area and never traveled far enough to see the curvature, it would seem flat to you. In fact, the Earth still seems flat to us; however, we grow up learning that it is round, and we can take airplanes and such around the world which helps solidify the concept. Furthermore, globes, and now photographs of the Earth from space further help us to visualize this.

Of course, none of this establishes relativity as being accurate. However, this a good deal of evidence supporting time dilation. One comes from muons produced from cosmic rays. The half-life of muons is well-known and unchangeable by any known process. One can calculate that all the muons should decay well before they reach Earth's surface; yet we detect many of these high-speed particles hitting Earth. This is in perfect accord with special relativity; the muons are travelling close to the speed of light and for them, time is travelling more slowly relative to us. From their "point of view", they are surving the proper amount of time, but from our point of view it is taking them a lot longer to decay. A second confirmation has been multiple experiments where two atomic clocks are synchronized, then one is flown at high speeds on a jet while the other one remains on Earth. When they are reunited, the one on the jet is slow by exactly the amount predicted by relativity. The third example is the most tangible, it concerns the operation of the Global Positioning Satellite system launched by the United States. These satellites all carry atomic clocks on board which continually broadcast signals including the current time. Commercial and military receivers on Earth receive these signals; it takes a fraction of a second for the signal to reach them. They subtract the signal time from the current time to determine how long the signal took to travel and using the known positions of the satellite, can calculate their distance and therefore their position. However, this does not take relativity into account; a system implemented in this manner would not work. See, there are two influences occuring here. One is that according to general relativity, time proceeds more slowly in a stronger gravitational field; this would predict that the clocks on the satellites would run faster. But special relativity predicts that faster objects experience time more slowly, and therefore the satellite clocks would run slower. The precise variance can be calculated and these two influences do not exactly cancel out; the clocks on the satellites should run slower than Earth-based clocks. The satellites' programming takes this time dilation into account and adjusts the clocks accordingly. Incidentally, not everyone was sure if relativity was really "correct" when the satellites were being constructed, so they were built in with both normal and relativity-corrected programming that could be switched remotely. They originally were launched in "normal" mode but it was soon obvious that the clocks were all getting out of sync, and the relativity programming was activated. — Knowledge Seeker দ (talk) 08:17, 20 Feb 2005 (UTC)

In regards to the second example, does this mean that someone who does alot of air travel has moved forward in time a little bit (maybe its some minutely small amount)? Astrokey44 18:23, 19 October 2005 (UTC)

(William M. Connolley 15:31, 20 Feb 2005 (UTC)) The best way of thinking about this (IMHO) is to realise that things that are in principle unobservable have no place in science (this links relativity to quantum mechanics). When you think, "how exactly would I determine if two events are simultaneous" (which is the essence of defining time) you realise that there is no absolute way of doing this, in most circumstances. If you then decide that the best way of doing this is synchronising clocks via light beams, you end up with (special) relativity. If the speed of light were infinite, it would in principle be possible to sychronise all clocks, and (philosophically) we would be back to absolute time. And as it happens, the same happens in the mathematical formalism.

modifying "time dilation" description

I removed remarks that time dilation is relevant only in extreme conditions, since of course it is relevant always (the same as its results as "magnetic field" or "gravitational field"), and I removed the remark that velocity time dilation in satellites is negligible when compared with gravitational time dilation which is not true. Jim 17:04, 2004 Jul 3 (UTC)

symmetrical?

The effect is of course symmetrical: an observer fixed on the "moving" object sees the "stationary observer" slowing down.

This sentence is entirely contrary to logic, and also contradicts the last paragraph of the "Gravitational time dilation" section. -- 66.32.110.58 21:38, 18 Sep 2004 (UTC)

(William M. Connolley 22:31, 18 Sep 2004 (UTC)) You're wrong. I've added a link to twin paradox which I think explains it better. Grav TD is a bit different - the symmetry is missing.

it's still contrary to logic.

I suppose it seems that way. In fact, starting with a few basic assumptions (for instance, the speed of light is measured the same for observers in all intertial reference frames), and using just the laws of logic/math, one will arrive at this result. So it's really not contrary to logic; in fact, it is quite logical. It is, however, contrary to intuition. In an analagous manner, the ancients were able to use logic to surmise that the Earth was round, not flat. Others might object "Why don't people on the bottom of the Earth fall off?" and the answer would be that for them, they are upside up and we are upside down, hanging off the bottom of the Earth. Now this is perfectly straightforward to us today in an age where we can travel around the globe and view photographs from space. Doubtless if our great-grandchildren grow up in an era where relativistic speeds are commonplace, they will find it perfectly natural and will politely smile at our ignorance. — Knowledge Seeker দ 01:53, 8 Mar 2005 (UTC)

But if one person sees time slowing down for another person, they might watch them, say, standing still while the other person goes on to live their life, comes back and sees they've only managed to move one inch in that time.. the other person watching the first person would -have- to see that person living their life in fast motion, or the two events aren't simultaneous.. and aren't existing in the same continuity. For both to see the other slowing down while they themselves moved at normal speed means events between the two aren't synching up, and that's simply illogical, right? Everything has to synch up!

I'm not sure I understand your scenario, but one of the concepts we must give up in relativity is that of absolute simultaneity. That is, observers in different reference frames will disagree about simultaneous events. Observer 1 might measure A and B as occurring at the same time, while Observer 2 measures A to occur before B, and Observer 3 measures B occurring before A. In some ways, this is analogous to what Newton proposed: in classical (Newtonian) physics, the concept of a preferred reference frame or "absolute rest" was discarded. That is, you cannot say "absolutely" that two events occurred in the same place, but at different times. To one observer it may appear so, but to another observer they will appear to occur in different places. That's absolute location. Absolute time means that you could say that two events occured at the same time, but in different places. We normally take this for granted, like that of absolute location. We can do this because we move at very low speeds relative to the speed of light (so we can use absolute time) and at low speeds relative to each other and the planet (so we can use absolute location). However, according to physics, neither model is accurate, and will break down at higher speeds. Of course, I find it extremely difficult to grasp a universe without absolute simultaneity. So does almost everyone. That's what makes Einstein a genius. Of course, anyone can come out with imaganitive theories. But that his theories provide testable hypotheses which have so far always been borne out provides evidence that his model is more accurate than our classical model. Hope this helps, and if you can elaborate on the scenario I can try to help you with that. — Knowledge Seeker দ 21:10, 11 May 2005 (UTC)

Thank you. THAT makes sense.

time slowing down

The whole idea of time dilation is preposterous! How is it possible? A light-year is the distance light travels in one year! That definition contradicts the idea of time dilation! Light travels a certain distance in one year! If you were travelling at, say, 186,000 miles per second, you would cover about 11,160,000 miles per minute, at which you would cover about 667,600,000 miles per hour. Now if you travelled that far per hour, you would cover about 2,670,400,000 miles per day, at which you would cover approximately 18,692,800,000 miles per week. At that rate you would cover about 972,025,600,000 miles in one year. That's how much distance is covered in one light year. Of course, I needn't go into all that. Time is not something that can slow down! Time is always going at the same rate! You can't slow it down! There is absolutely no way! What evidence do they have for this crazy theory anyway? There's another thing. They say that if you travelled in one second the distance it would take 100 years to travel, and then you travelled back to Earth at the same rate, 200 years would have passed on Earth. Ha! What kind of nonsense is that? That would be saying that time actually sped up! It contradicts time dilation! I don't see why there would be any evidence for this theory at all! And don't give me a bunch of mumbo-jumbo about us only being able to go at certain speeds. It doesn't really matter how fast you are going! Time isn't going to slow down! And no nonsense about people-used-to-think-that-the-earth-is-flat-but-it's-really-round-therefore-just-because-we-think-that-time-dilation-doesn't-exist-doesn't-mean-it-doesn't! It sure DOES mean that! There's a world of difference between the earth being round and time dilation existing! One could easily see that when you leave the land, it dissappears over a horizon rather than dissappearing into a point! Time dilation ISN'T LIKE THAT! It's not as obvious! Think about it. What is time? Time is the space between two events. Let's say your birthday is next week. Well, let's say that something happens and so you move your birthday party to today. Well, that's not speeding up time. That's just moving the party to today. You can't make next week happen today! Simple as that! Scorpionman 20:08, 19 May 2005 (UTC)

There is evidence. To name a couple examples:

• clocks at the tops of buildings (gravitational dilation) and in airplanes and spacecraft (both gravitational and velocity)
• fast-moving muons (particles of cosmic radiation that decay rapidly) are observed to last longer than slow-moving ones

I really don't see what the speed of light or the birthday-party example has to do with anything.

Nickptar 21:10, 19 May 2005 (UTC)

Okay, explain those examples. How does that happen? Scorpionman 01:57, 20 May 2005 (UTC)

• Hello, Scorpionman; thanks for your questions. You're right, it is a crazy theory (but like they say, truth is stranger than fiction). If you haven't already, take a look at the discussions above with a couple other users who also had difficulty grasping relativity (don't worry, we all do). I agree with Nickptar's comments above, and I'm just an amateur, but I'll add a few more comments. Your conversion of light years to miles looks accurate, although I haven't checked the calculations and I'm not certain what relevance it has. It is true that relativity predicts that if one were to fly away from Earth at high speeds and then return, one would find that a great deal of time had passed on Earth while perhaps only a few days passed for the traveler. This is because according to relativity, an observer would measure time travelling more slowly for a clock (or person) moving at high speeds relative to the observer. So two centuries later, the ship returns to Earth, but since time was travelling more slowly for it, the traveler has only aged a few days. Of course, all of this would be speculation, but General and Special Relativity make specific predictions which are different than those of classical physics. Since we are currently unable to achieve high speeds, the effects are virtually unnoticeable. However, there are several situations where there would be a measurable difference, and so far every one tested is consistent with relativity and not with classical physics. A practical example is the very accurate atomic clocks in the satellites of the Global Positioning System. Under classical physics, they should keep time at the same rate as their counterparts on Earth. However, general relativity predicts that time goes more slowly in stronger gravitational fields (slowing down Earth-based clocks) and special relativity goes more slowly for faster-moving clocks (slowing down the satellite clocks). These effects don't quite cancel out; it is predicted that the satellite clocks should go slower than terrestrial ones. Sure enough, the GPS clocks have software that adjusts their time to account for relativity. It is a tiny difference at those slow speeds, but enough to affect the precision needed for GPS. The only matter that we observe or can accelerate to near the speed of light are atomic and subatomic particles. As Nickptar mentions, some of these are unstable and decay at a predicatable rate. It has been observed that these unstable particles last longer when travelling at very high speeds in particle accelerators, or when produced in our atmosphere by fast-moving cosmic rays. Does this answer your questions? — Knowledge Seeker দ 22:11, 19 May 2005 (UTC)

Somewhat, although I still don't understand how time can be warped. And how it can be warped by speed! How would travelling at the speed of light make time pass more slowly? Exactly how does this happen? And how, how would gravity affect time? Scorpionman 01:54, 20 May 2005 (UTC)

If you're asking for a mechanism, I'm afraid I don't know. It seems to be a property of spacetime itself. It's not so much that time is warped; it's that humans intuitively have an erroneous conception of space and time as separate, non-interchangeable dimensions. Here's a very bad example: Suppose there is someone who lives in a universe (make it two-dimensional, for clarity), where nothing can move around. He can look around, though, so he A little distance away is a stick five feet long, lying at an angle to him. You ask him to measure the stick. He surveys it and says: there is a stick which 4 feet side-to-side. He can also tell that one end is closer to him than another, and reports that it is 9 "distances" far (equivalent to our 3 feet, but he doesn't realize that). Those are both fixed as far as he knows. Now he develops a machine that gives him the ability to move a little. He moves to his left and the stick remains the same, but now it is at a different angle. He looks at it, and to his horror, the stick is now only 1 foot side-to-side! He measures its "farness" and finds it to be about 14.7 "distances" (4.9 feet)! He calls his friend to tell him; his friend does not believe him. How can farness be changed? Just by moving around? It's completely illogical! Our first guy can't explain it either. But he notices that if he uses the conversion factor 3 "distances" = 1 foot, then he can calculate a "true-length" parameter of the stick, by using the Pythagorean theorem, adding their squares and then taking the square root. Even though the side-to-side decreased, the farness increased, and they offset each other perfectly. In both cases the stick has a "true length" of 5 feet. I admit this example is highly contrived but I hope you can see the parallels. The ends of the stick are equivalent to two points in spacetime (for instance, a spaceship now, right in front of me and a 10 minutes later, 9 light-minutes from me). We measure the distance between the two points (9 light minutes) and the time between the two points (10 minutes) as completely separate quantities. Relativity says they are both dimensions in spacetime, and are related. If we use the speed of light, c, as a conversion factor, we can convert time into units of distance as well. For a reference frame moving at high speed relative to me, I would measure time as going slower (so the time dimension increase) while the distance was less (length contraction, so the space dimension increases). Using the Pythagorean theroem (and converting time to distance as mentioned before), we can calculate a "space-time interval". One will find that although time is increased, length has decreased, and the space-time interval is the same from all reference frames. Just as we can easily move around to see that "side-to-sideness" and "farness" are different aspects of the same thing, if we could easily move fast enough to directly observe the shifts between time and space, we would intuitively realize that the space-time interval was the true, constant, measure—but different reference frames would measure the time and distance dimensions differently. In simplifying I've left out some details; also, as I am an amateur, any physicist or someone well-versed in relativity is welcome to correct/expand on what I've said. Scorpionman, I also suggest you take a look at Special relativity for beginners—I found it quite interesting. If you have more questions, let me know. — Knowledge Seeker দ 08:12, 20 May 2005 (UTC)

Some simple answers:

• Space is not warped by speed. Instead what happens in the space and time get exchanged as one moved from one inertial frame of reference to another. So of what we perceived as being space becomes time and vice versa.
• Time is not slowed down per se. Instead how your clock ticks is slower in the frame of reference of another observer. Your time is just as valid as his. However, if you travel away from another observer and then accelerate and return you will find that you experienced less time. See the proper time and twin paradox pages for an explanation of this.
• Gravity affects time through acceleration. To stay at the same distance from the center of the Earth, you are always being accelerated upwards in the viewpoint of relativity. (This acceleration is due to massive objects such as the Earth warping spacetime. BTW - You can choose not to be accelerated: The result is freefall.) In any case, since being accelerated means constantly switching inertial frames of reference, your view of "at the same time" keeps being changed and so you find that clocks at higher potentials are ticking faster and clocks at lower potentials are ticking slower. (My apologies if I lost you on this, but GR is just plain wierd even in comparison to SR.)

--EMS | Talk 04:43, 26 May 2005 (UTC)

Faster than light travel

Lets say you use a constant 1g to travel to a star that is 100 light years away. The star will appear one light year away when your length contraction reaches 100:1. First of all, how long does it take for length contraction to reach 100:1 at constant 1g? But more importantly, where did the 99 light years go? How is it that a star that was 100 light years away is now only one light year away? From your frame, you have observed faster than light travel toward this star.

I'm just an amateur, so anyone more knowledgeable please correct me. By my calculations (solving ${\sqrt {1-{\frac {v^{2}}{c^{2}}}}}={1 \over 100}$) gives a velocity of 299,777,468 m/s, or 0.99995c. Dividing this by g (9.80665 m/s²) gives a time of 3.06×10⁷ seconds or about 354 days. Of course, for an engine to maintain a constant acceleration of 1g, it would have to massively increase its force as higher velocities were reached; the acceleration produced by an engine that outputs a constant force would drop as higher velocities were attained. While we have engines that could produce a constant 1-g acceleration at conventional speeds, none of ours could keep up the acceleration at high speeds. The 99 light years don't really go anywhere; space would appear compressed from your point of view. It would be as if I placed a rod in front of you, parallel to your line of sight. Then I turned it so it was almost on end, and you asked "where did 90% of its length go?" It didn't go anywhere; the actual length was always the same, but the dimension parallel to you decreased while the dimension perpendicular to you increased. In the same way, while the distance of the star has decreased, when you arrive you would find that a great deal of time had passed in that star system. The distance dimension decreased but the time dimension increased. (This part of the explanation is slightly inaccurate; it glosses over a few details). I understand your point about exceeding the speed of light, but you really haven't. From your point of view, the distance to the star has decreased; you would measure your speed as 0.99995c. Or, more importantly, forget the acceleration; suppose I steal a spaceship that could instantly attain 0.99995c. I take off in the ship and at the exact second I engage the high-speed drive, the people on my planet send a warning signal to the other star system. To my delight, I reach in only 16 years and I'm thrilled because I think I've somehow passed the speed of light; signals from my home system will take another 84 (100-16) years to arrive! Yet I'll be doubly dismayed; not only did the light signal arrive almost 44 hours earlier, but a century has passed for them while I've been travelling, and their technology easily captures my ship. It doesn't matter if it's time dilation or if I underwent hibernation for a century on a slow ship and thought I was going very fast—a light signal will still beat me. Make sense? — Knowledge Seeker দ 07:12, 25 May 2005 (UTC)

When using the origin frame of reference a close enough approximation is c/g. But the only useful frame of reference for 1g acceleration is that of the traveller. A 100:1 length contraction from the perspective of the traveller to the destination should take more than one, but less than 100 years. I understand the compression of space as a function of relative velocity. This is the symmetry: the traveller see a length contraction while the destination sees a proportional time dilation happening to the traveller. And this is the crux of the question. If the traveller observes the destination continuously while in transit, he initially observes the destination to be 100 light years distant. But the distance to the destination decreases as his velocity increases relative to the destination. Lets assume for simplicity since I have no idea how to do the math, that it does only take one year in the travellers frame to achieve 100:1 time dilation (length contraction) at 1g. Between the beginning of the trip and now, the traveller has observed that his destination which was 100 light years away is now less than one light year away. I can do this math: 100-1=99. The observer has travelled 99 times the speed of light, from his reference. --JackN 02:58, 26 May 2005 (UTC)

Those are some excellent points you bring up. Unfortunately, I no longer possess the mathematical abilities (nor have I ever understood the details of relativity in enough detail) to deal with continuously changing functions like this. Offhand, I can point out two difficulties with your argument. One, as I understand it, the reference frames described in relativity are inertial reference frames; your accelerating traveller is continuously jumping to different reference frames. My grasp of relativity is shaky for single reference frames, and tenuous at best when observers (instantaneously) jump reference frames. I lack the ability to properly calculate continuous changes like this, so hopefully someone else can answer. The other problem I see is that the traveller is using an improper technique to measure his speed. Picking a single object like that may work well at low speeds, but not at relativistic speeds. Had he chosen a farther star, he would observe it to move even faster. Had he chosen a closer to star, it would move more slowly. The speed of light principle applies to objects moving through spacetime, not the fabric of spacetime itself moving. In any case, a beam of light would beat our traveller by a considerable margin in this case. Anyone else care to correct my explanation or flesh it out some more? — Knowledge Seeker দ 04:37, 26 May 2005 (UTC)

For the case of an object undergoing a continuous proper acceleration of g (with "proper" meaning "locally perceived"), the speed of that object v with respect to an inertial observer given that v=0 at t=0 is

$v=cgt/{\sqrt {c^{2}+g^{2}t^{2}}}$.

For $gt\gg c$, this approaches v=c. One way to look at this is that the Lorentz Transformations also action on acceleartion, reducing it as v approaches c.

--EMS | Talk 04:56, 26 May 2005 (UTC)

Thank you, EMS. JackN, I was thinking about this issue today, and I think I realized the more fundamental problem here. I think the problem statement is "The observer has travelled 99 times the speed of light, from his reference." This is not true; the observer has travelled zero times the speed of light, from his reference. All speeds must specify a reference frame against which they are measured (except for the speed of light); if I say that an object travels at 100 km/s I must also state (or imply) the frame of reference measuring that speed. Measured from the traveller's reference frame (which is not an inertial frame, actually), he is travelling at exactly 0 m/s. Is there any reference frame in which he is travelling at 99c? Not that I can see. From the reference frame of the star? No, observers in that frame would measure his maximum speed as 0.99995c. The traveller was in error when he tried to measure his speed by comparing his changing distance to an object. This works fine at low speeds: I can measure the speed of my airplane by calculating the rate of change of distance to that mountain ahead, because at my low speeds, there is very little difference in the distance I'd measure to the mountain and the distance the mountain would measure to me. Therefore, I can assume that from the reference frame of the mountain/Earth, the same distance change is observed, so they would calculate the same speed. However, the interstellar traveller cannot make the same approximation. He measures different lengths to the star than the star would measure to him. He cannot assume that the distances he measures will be the same distances those reference frames will measure. Travelling at 99c? Relative to what? Even in Newtonian mechanics you must specify the reference frame. If he had picked a further star, perhaps he'd have measured a speed of 200c. A closer one, 20c. Even closer, 0.4c. His method of calculating speed is flawed—an approximation that works well at low speeds to which we are accustomed but breaks down at higher speeds when those very concepts no longer apply. Does that make sense? I hope I've been able to explain what I'm thinking. — Knowledge Seeker দ 06:11, 27 May 2005 (UTC)

Knowledge Seeker - I think that you have missed a more fundamental issue here: JackN is saying "I have gone 100 ly in 1 year", and therefore sees himself as having travelled at a rate 99c greater that c. However, the 100 ly is as measured in the pre-acceleration frame of reference, while the 1 year is in the accelerating frame of reference. A velocity must be as described using time and distance values in a single frame of reference. (There is something in relativity called "rapidity" which is distance travelled divided by proper time, and which is used to construct the relativistic velocity tensor. However, it is not be confused with an observed velocity.) So in the final accelerated frame of reference, the accelerated observer will find the place he started from to be less than 1 ly away due to the Lorentz Contraction. Then the proper time of the accelerated observer having only progressed by 1 year is fine, as his average speed as determined by himself with respect to the starting point remains <c.

This is one of the nuances of relativity: There is no absolute time, and therefore there is also no absolute instantaneous distance. The observers disagree on the distance covered by the time of flight of the accelerated observer, and on the spatial separation the flight created between the observers. These views can be reconciled throught he Lorentz Equations, however. Also, the observers will agree on the proper time of the accelerated observer's flight.

The bottom line is that any exercise of this sort must be done using the Lorentz Transformation and it derivative relationships (such as the relativistic addition of velocities formula). For instance, the speed needed to obtain a Loretnz factor of 1/100 can be computed, and views in the frames of reference for both observers determined assuming linear, inertial travel at that speed. This may help JackN to better see what is going on. (This can also be done assuming continuous acceleration, but the math is a lot messier and would be difficult for a relativity novice to follow.) --EMS | Talk 14:49, 27 May 2005 (UTC)

EMS - Thank you so much for the time you have taken to answer my questions. I am somewhat rusty with the Lorentz Equations since I have not had to use them since the late 70s, and math is not my strength. And thanks for providing an application of the Lorentz Transformation to acceleration, but the paradox still remains. At the beginning of the trip the destination is 100 ly. While travelling at continous acceleration toward the destination there is a Lorentz Contraction of 100:1. It seems to me that if I were to observe the destination during continous acceleration I would seem to be observing faster than light travel. I hope I am not sounding dense, but is there a good way to explain the actual mechanism? --JackN 03:09, 30 May 2005 (UTC)

You are using the Lorentz Contraction is exactly the wrong way. The distance to your destination at the end of your trip to it is zero. You have arrived, and the issue is now one of how far away the Earth is as you pass that place which in the inertial frame of reference of the Earth is 100 ly away from the Earth. The trick is that you are not in the inertial frame of reference of the Earth. To have reached this place after 1 year, your average inverse Lorentz factor must be 100, but your current inverse Lorentz factor should be greater! So you would look back at the Earth as you pass this star, and find that it is less than 1 ly away.

You could "hit the brakes" so that you are back at rest with respect to the Earth at this star, and now it would be 100 ly away, but so what? Throughout your trip, light signals from the Earth were passing you. They may have been red-shifted more and more (before you fired the retro-rockets), but they could still be received. Given that, you never went faster than the light with respect to the Earth. In fact, in the frame of reference of the Earth, you took over 100 years to get to the star. Your proper time is not Earth time.

It is known that time dilation can be used to get to distant stars in a reasonable amount of proper time. The issue is the energy needed to pull it off. BTW - If you turned around at this star and came back in another year of your time, you would find that over 200 years have passed on the Earth. (This stunt in known as the twin paradox.) So you have traveled 200 light years in over 200 years. Just how fast did you think that you were going again?

--EMS | Talk 03:54, 30 May 2005 (UTC)

EMS - Thanks a million! I am familiar with the twin paradox, but this is the first real explanation I've heard. I'll have to think about what you have said a few days to become comfortable with it, but I've got the gist. If I understand you correctly, the "proper distance" of a trip is dependent on the acceleration of the traveller.

You are getting there. How a distance is perceived is a function of the relative velocities of the observers. In the context of SR an acceleration is merely a change of velocity. So to be technical, you cannot say by what factor things have been time dilated and Lorentz contracted for your accelerating observer without specifying when the observation is made. Of course since time is relative in GR, you also need to specify by whose clock the time was determined. "C'est la vie."

I think that it may help you to get ahold of a good book on SR and refamiliarize yourself with it. Issues like how coordinates are defined in SR and how that behave under the Lorentz transformations will be very helpful to you. As for Wikipedia, I do not advise it as a good source on information on relativity. It is getting better step by step, but it still has a ways to go. Even this page needs more work.

--EMS | Talk 05:01, 31 May 2005 (UTC)

BTW: Na₂₂ is a natural emmitter of e⁺ which could be magnetically bottled in a good vacuum. The last time I looked at it, permitting the collision of e⁺ and e^- produces 2 γ particles at right angles to the path of the original e⁺ and e^-. The development of a proper γ reflector would provide enough thrust to enable a constant acceleration of 1g, to the stars. We would also need to develop a method to create Na₂₂ since it does not exist in nature. --JackN 04:20, 31 May 2005 (UTC)

It's an idea, but I would prefer to manufacture anti-hydrogen for this. That's a much more efficient fuel than Na₂₂. (You just need to be careful not to use up your whole rocket-ship as you go from star to star.) --EMS | Talk 05:01, 31 May 2005 (UTC)

Problems with Intro

After staring at it for some time, I decided that I had to revert the introduction. While I could work with the changes to the velocity section, the new introduction made imporper claims:

• It implied that time dilation is peculiar to clocks that are separated and later reunited. That is the twin paradox. Time dilation itself occurs with respect to the coordinate system defined by a given clock whether or not the other clock has ever or will ever be next to the clock defining the coordinate system.
• It called proper time a "perceived" measurement, placing it on the same level as the coordinate times. Proper time is not just perceived, it is the physical passage of time for that observer. Proper time also is not relative. Instead it is an invariant that all observers will agree on. (They may disagree over the parameters of a clock's worldline, but not on how much time that clock ticked off as it traveled that worldline.)
• "The faster one travels ..., the greater the time dilation relative to their origin": This is nonsense. An observer cannot travel with respect to himself, and therefore is never time dilated with respect to himself or with respect to his own temporal coordinate system. The effect occurs with respect to other observers and their temporal coordinate systems.

I am happy to work with others, and with edits that improve on my own work. However, the new intorduction was a solid step backwards for the reasons listed above. I regret the need to revert it.

--EMS | Talk 04:24, 26 May 2005 (UTC)

Special relativity, time dilation, and synchronization procedures

Synchronization procedures according to special relativity

Let there be a formation of three spaceships, A, B and C. The formation is in the shape of a line, and the distance AB is the same as the distance BC. The formation as a whole is moving inertially.

The ships of the formation are constantly monitoring their spatial separation by transmittng radio-signals (or they exchange lightpulses, or any other pulse that travels at lightspeed). As long as the transit times of consecutive relays stays the same they know their mutual distances are unchanging. The ships of the fleet maintain a standard fleet time. Since the ships do not move relative to each other the ratio's of proper time for the onboard clocks of A:B:C is 1:1:1, so maintaining standard fleet time is straightforward, only the transit time of the radio-signals needs to be taken into account.

Each radio-signal carries a time-stamp of the moment of sending. In a sense, the time-stamp is frozen in time. The receiver takes the time-stamp, adds the transit time of the radio-signal, and so reconstructs the standard fleet time of the fleet.

Now what if instead of photons muons are used? Suppose that beams of muons are used, and the muons are given a velocity of 0.866 of the speed of light with respect to the ships of the fleet. Suppose that the separation of the ships is such that out of a 100 muons 50 reach the receiver.

In that synchronization procedure the receiver needs to take more than just the transit time into account. For the bunch of muons some proper time has elapsed, but not as much as for the sender and reciever. In fact, the velocity of 0.866 of the speed of light with respect to the fleet corresponds to half as much proper time over the length of the transit as the amount of proper time of the fleet. In this example the decay rate of a large amount of muons serves as a clock.

Special relativity describes that the two procedures: using the decaying muons or lightspeed signals yields mutually consistent results. Special relativity also describes that if there is a second fleet of spaceships, D, E, F, that has a velocity v with respect to the A, B, C fleet, and both fleets use the muon beams procedure to maintain synchronized fleet time, then both fleets see in the other fleet the same ratio of muons beamed to muons received.

Graphical representation of synchronisation procedures. The blue lines represent light signals, the grey lines represent beams of particles moving slightly slower than light. The bottom half shows the timelines of the signals of the procedure of "the reds" as seen from the frame of reference of "the greens".

Graphical representation

In the graphical representation the blue lines represent the timelines of the pulses of light in spacetime, the grey lines represent the timelines of the muons. The green lines represent fleet A, B, C, at five consecutive points in time. The red lines represent fleet D, E, F, at five consecutive points in time.

The observers onboard the green fleet can choose to interpret the physics of the moving muons of the red fleet either from the perspective of their own fleet, or from the perspective of the other fleet: in both cases the distances and velocities come out such that the amount of proper time of the muons in transit is the same, so as seen from either perspective the expected percentage of muons that is lost to decay during the transit is the same.

In this particular example all the relevant motion is on the same line, which is represented as the horizontal axis in the graphical representation. The two fleets of ships have a particular velocity relative to each other, and that is represented as a rotation of their timelines with respect to each other.

This is somewhat like a rotation of a cartesian coordinate system, but the difference is that when a cartesian coordinate system is rotated the axes remain perpendicular. When the axes of a spacetime diagram are rotated, then the only consistent way to represent that is to have the axes move in a scissor-like way.

The motion of the green fleet is represented with a perpendicular grid and the motion of the red fleet is represented with a rotated grid. That is an arbitrary choice, it does not represent a measurable physical difference. All the observations from both the perspective of the green fleet and from the perspective of the red fleet are consistent with both the perpendicular representation and the rotated representation; there is nothing to measure a difference. (Notice that without relativistic time dilation there would be a measurable difference.)

Formula

The structure that relates all these phenomena is mathematically represented by the following formula:

$c^{2}(\Delta t_{g})^{2}-(\Delta x_{g})^{2}=c^{2}(\Delta t_{r})^{2}-(\Delta x_{r})^{2}$

As seen from the green perspective the formula can be applied as follows: $\Delta t_{g}$ (delta t) stands for a period of time of the Green fleet, and $\Delta t_{r}$ stands for the how much red-fleet-time elapses during $\Delta t_{g}$ (as seen from the green perspective). $\Delta x_{g}$ stands for distance traveled by green during $\Delta t_{g}$. $\Delta x_{r}$ stands for distance traveled by red during $\Delta t_{g}$. In this example, time is measured in seconds, and distance is measured in kilometers.

If you take the frame of reference that is stationary with respect to the green fleet, then in that frame of reference $\Delta x_{g}$, (the distance traveled by the greens), is zero. As seen from the green-stationary frame of reference the reds do cover distance, which corresponds to less proper time for the reds as seen from the green perspective. What is invariant from frame to frame is the spacetime interval: the square of coordinate time minus the square of coordinate distance travelled. ('Coordinate time' is the amount of time as seen from the frame of reference of the observer; coordinate distance is the amount of distance traveled as seen from the frame of reference of the observer.)

The spacetime geometry that is described by this formula is called 'Minkowski spacetime geometry'. The amount of proper time of one object/observer with respect to another depends of their relative velocity. In a sense two observers who have a relative velocity are cutting dissimilar slices through spacetime, and thes cuts, these slices, are in a sense rotated with respect to each other. (There is no upper limit to this. In special relativity, the following scenario is self-consistent: a spaceship accelerates to a velocity that is close to lightspeed with respect to the home-planet, then it releases a probe that itself accelerates to close to the speed of light with respect to the spaceship; the probe itself releases a sub-probe, etc etc.)

Why time dilation

Why there is such a thing as relativistic time dilation anyway? It is not clear whether it is possible at all to find an answer to that question. For a start: what would a universe without relativistic time dilation (have to) look like?

The speed of light can in a more general sense be seen as the maximum speed of information: the maximum speed of causality. In our universe the speed of causality is very high indeed: 300.000 kilometers per second. Because of the extremely hich velocity of causality, the relativistic time dilation was completely unnoticable until the high technology of the 20th century was developed. What if the speed of light would be trillions of kilometers a second? If the speed of causality would be even higher, then our universe would resemble a universe without time dilation much, much closer than our actual universe. A universe with infinite speed of causality would be a universe with total separation of time and space, a universe without time dilation. But can a universe with infinite speed of causality exist at all? If every location of the universe is instantaneously connected to every other location, then how can such a thing as distance even exist?

Mayby finite speed of causality is a price to pay for the very existance of spatial distance. And maybe the only self-consistent universe with a finite speed of causality is a universe with Minkowski space-time geometry.
--Cleon Teunissen | Talk 22:40, 31 May 2005 (UTC)

Wait, it doesn't make sence. If every location of the universe is instantaneously connected to every other location, what does it change to distance? Not cause light/information would get anywhere instantly that it wouldn't take you the same time anymore to walk from your home to your school --82.249.211.32 16:40, 14 October 2005 (UTC)

---

Responses to the synchronization description

Nice try, but you seem to have goofed. The tilted red lines should be in the upper diagram. The red lines instead should be straight across in the lower diagram. Also, in the lower diagram it is the green line that should be moving (albeit in the opposite direction as that of the red line).

Beyond that, I find this illustration to be overly complex. Time dilation arises from a very simple and illustratable mechanism: Let observer A send a light beam down a 1-light-second path. By his clock it takes that light beam 1 second to travel the path. Now let there be an observer B who is traveling in a direction perpendicular to the path of the light (as seen by observer A). For observer B, observer A and the place the light beam is going to are offset during the time of flight of the light due to their relative motion. Since observer B must see that light also travel at c, its time of flight must be $1/{\sqrt {1-v^{2}/c^{2}}}$ seconds. For the times of flight for the observers to be consistent, the clock for observer A must be running at a rate of ${\sqrt {1-v^{2}/c^{2}}}$ in the frame of reference of observer B.

Also, this page is about time dilation, not the relativity of simultaneity. (That one does need an article, but once again any illustration needs to be kept simple.)

--EMS | Talk 15:03, 1 Jun 2005 (UTC)

The way you describe it makes it sound as if the proper time of observer B is the absolute time, and that time-keeping of observer A is distorted with respect to the absolute time. I am looking for a way to present that the perspective of A and the perspective of B are symmetrical and reciprocal in all respects.

To do any time dilation exercise, some frame of reference has to be the "rest" frame. In this case, it was observer B's. Of course this is just as valid as A's observing a similar beam of light miving between B's spatial coordinates. --EMS | Talk 16:08, 2 Jun 2005 (UTC)

Also, you make it sound as if it only has to do with the propagation of light. I see as the essence of relativity that all procedures that involve keeping track of how much time has elapsed yield mutually consistent outcomes. There is:

1. Coordinate distance; the amount of distance to be travelled in a transit is different as seen from different frames of reference.
2. Coordinate time: the amount of time that the transit takes is different as seen from different frames of reference.
3. Coordinate time dilation: the amount of time dilation that is involved is different as seen from different frames of reference.

In the middle of all of that is the constancy of the speed of light. That is the most fundamental reason for time dilation. The goal of my little exercise is

1. to illustrate that connection, and
2. to create as simple as description as possible.

I encourage you to do an illustration of my exercise above in the same way as you did the spaceships exercise above, so that you can see how that works. That is also something that I want to place in the time dilation article itself. --EMS | Talk 16:08, 2 Jun 2005 (UTC)

The relative qualities: distance, time, time dilation, relate to each other in such a way that as seen from all frames of reference the physics taking place is the same physics. In the case of muons in transit: as seen from all perspectives, the expected amount of loss to decay during transit is the same.

So yes, the diagram/animation is quite complex, in order to represent the interconnectedness that is so typical of relativistic physics.

If you are going to teach people about relativity, then your article needs to be understandable. Hitting them in the face with the full interconnectedness of relativity is not that way to do that. Instead you need to feed someone digestable pieces. Also, while I know that the interconnectedness is there, but the relativity of simultaneity is not the subject to the time dilation article. There is no way for a novice to look at that diagram and gain an understanding of time dilation, much less relativity. Besides, your diagram has blatant errors in it:

1. In the lower diagram, the tilted red lines should be green. You are now in the red frame of reference, where the red simultaneity lines by convention are vertical. The lines that you colored red are actually connected events that are simultaneous in the green frame, and so should be green.
2. The dots on your red line moving change direction at the same time. That is not the view in the red frame. (Perhaps you are showing the green viewpoint on the red line?)
3. The sub-diagram with the moving red line is below the diagram for the red frame, in which it is the green frame that is in relative motion.

--EMS | Talk 16:08, 2 Jun 2005 (UTC)

In the case of the moving red line I had made the decision to depict the motion of the muons as seen from the red perspective. As seen from the green perspective the reds timing signals do not reach the ends simultaneously, as represented in the tilted (stationary) diagram. The moving red line is inconsistent with that, as it displays the motion of the muons as seen from the red perspective.

This mixing of perspectives has disadvantages, so I will change that. --Cleon Teunissen | Talk 11:58, 2 Jun 2005 (UTC)

I think that you have done a wonderful job of confusing as to which frame of reference in which and what is being viewed in each. You also have done a wonderful job of losing track of the scope of this article, which is time dilation. Also please note that even corrected that diagram is so complex that it is uninformative. Only someone very adept at relativity would understand it, and that is not (or at least should not be) the intended audience.

Don't try to be cute. Don't deal with metaphysics. Also, don't worry about any part of relativity here other than time dilation. If you want to contribute, then get down to brass tacks here, and help me by creating an illustration of how the constancy of c requires the existance of time dilation.

--EMS | Talk 16:08, 2 Jun 2005 (UTC)

The self-consistency of time

Let observer A send a light beam down a 1-light-second path. By his clock it takes that light beam 1 second to travel the path. Now let there be an observer B who is traveling in a direction perpendicular to the path of the light (as seen by observer A). For observer B, observer A and the place the light beam is going to are offset during the time of flight of the light due to their relative motion. Since observer B must see that light also travel at c, its time of flight must be $1/{\sqrt {1-v^{2}/c^{2}}}$ seconds. For the times of flight for the observers to be consistent, the clock for observer A must be running at a rate of ${\sqrt {1-v^{2}/c^{2}}}$ in the frame of reference of observer B. --EMS | Talk 15:03, 1 Jun 2005 (UTC)

I have made a GIF-animation that illustrates what you describe.

Time dilation in transversal motion.

The green dots in the animation represent spaceships. The ships of the green fleet have no relative motion, so for the clocks onboard the individual ships the same amount of time elapses, and they can set up a procedure to maintain a synchronized standard fleet time. The ships of the "red fleet" are moving with a velocity of 0.866 of the speed of light with respect to the green fleet.

The blue dots represent pulses of light. One cycle of lightpulses between two green ships takes two seconds of "green time", one second for each leg.

As seen from the perspective of the reds the transit time of the lightpulses they exchange among each other is one second of "red time" for each leg. As seen from the perspective of the greens the red ships cycle of exchanging lightpulses travels a diagonal path that is two lightseconds long. (As seen from the green perspective the reds travel 1.73 (${\sqrt {3}}$) lightseconds of distance for every two seconds of green time.)

One of the red ships emits a lightpulse towards the greens every second of red time. These pulses are recieved by ships of the green fleet with two-second intervals as measured in green time.

Relative

The time dilation is relative: the green perspective and the red perspective are in all respects mirror images of each other.

All physics phenomena that can be used to measure lapses of time yield outcomes that are consistent with each other. (Intriguingly, most forms of time-keeping can be readily seen to count time by counting cycles of some oscillation.) There are no exceptions known to this inner consistency of time-keeping. If there would be an exception, then inertial motion would not be relative in the way that is described by special relativity.

In this example the rate of time as measured by any sort of clock is seen to be consistent with a velocity of light propagation that is invariant across the entire range of inertial frames of reference. --Cleon Teunissen | Talk 00:36, 6 Jun 2005 (UTC)

YES! That is what I want. It is more involved that what I envisioned, but the extra details are such that they help to drive the point home. Unless someone objects, please place it and a description into the article as a sub-section of the velocity time dilation section. Perhaps call it "The physics of velocity time dilation". Be advised that I will edit your wording when I get a chance, but yours will do for now. Just start with a basic description of what the overall physics is, and then start refering to the GIF.

You may also want to do the same thing from the standpoint of the red fleet, with the green ship moving upwards to show the symmetry of this effect. However, only do this if you are comfortable with using it.

Once again, thank you for this fine illustrative GIF.

--EMS | Talk 14:18, 6 Jun 2005 (UTC)

Sounds good to me. Impressive GIF-fu :). --Christopher Thomas 23:09, 6 Jun 2005 (UTC)

The "spacetime geometry ..." subsection

Cleon -

That GIF looks great. Thanks again for it.

As you can see, I have already done an edit on your text. You wrote:

There is no physics phenomenon known that would allow either the greens or the reds to identify themselves as "the non-moving ones".

However, there in nothing wrong with being non-moving (or at rest) in relativity. You just have to specify what it is that you are at rest with respect to. In one part of your animation, at-rest is with respect to the green fleet; In the other part, at-rest is with respect to the red fleet.

Be warned that I (and maybe others) will tweak your text even more. Some work is needed to better describe the overall physics of what is being illustrated. As I see it what you earned with the GIF was the right to have the first crack at explaining it. You have now exercised that right, and the rest of us can now "play" with your work. Even so, I for one will take care in how it is editted: It may not be perfect, but you have done a good enough job that a sloppy edit will make the text worse instead of beeter.

--EMS | Talk 02:02, 9 Jun 2005 (UTC)

---

there is nothing wrong with being non-moving (or at rest) in relativity. --EMS | Talk 02:02, 9 Jun 2005 (UTC)

As so often you have found a way to misunderstand. I should have mentioned that I was referring to the following: "There is no physics phenomenon known that would allow either the greens or the reds to identify their own state of inertial motion as non-moving with respect to some overall absolute reference."

I think there is something you are confused about: any distinction between being at rest and being in inertial motion is meaningless in the context of special relativity.

No. It is not meaningless. It just is a relative concept, not an absolute one. If I see something as maintining its distance and orientation with respect to myself, then I will consider it to be at rest. Period. End of discussion.

Now mind you, the object that is "at rest" in my frame of reference could be a ball on the end of a string which is keeping the ball from flying away from me as I spin around and around in circles. However, note that since I am spinning with the ball it orientation with respect to my face is constant and the string is also keeping its distance constant. So by the formal definition of being at rest, it is. The issue is that this rest is not an inertial state of motion.

Then again, you are probably at rest right now with respect to your chair, and both you and the chair are in an accelerated frame of reference.

(Actually there is one way that being at rest is an absoute, but being at rest with respect to one's self is awfully trivial.)

The dichotomy 'being at rest'/'being in inertial motion' is ingrained in our language, but we need to get away from that dichotomy.

In order to perform calculations the greens apply a coordinate system that is stationary with respect to the green fleet, and then, and only then, it is possible to apply the relativistic laws of physics in calculating what frequency they will actually detect as they receive signals from the reds that are emitted at an agreed frequency, say the frequency of a characteristic line in an atomic emission spectrum. (Or they can calculate from the measured frequency shift the magnitude of relative motion.)

In special relativity, when you have two emitters/detectors with a relative velocity, and you want to calculate for both what they will actually measure, then you choose two coordinate systems, one that is stationary with respect to "the greens" and one that is stationary with respect to "the reds", and then transformations between those coordinate systems can be performed. A phrase like "the greens are at rest in their own coordinate system" is a meaningless tautology, for the only way to "deploy" any coordinate system is to first specify with respect to what that coordinate system is stationary.
--Cleon Teunissen | Talk 11:17, 9 Jun 2005 (UTC)

It seems to me that "stationary" and "at rest" are synonomous. So you have ended up saying the same thing that I am: Once you specify the coordinate system, you can specify the rest state(s) within it. Contrary to what you implied, the construction of a rest state is easy. That there is not abosolute rest is a different matter.

My issue with your text is that it implies that there is no such thing as being at rest. I have seen that kind of statement confuse others in the past. I wish to avoid that here. --EMS | Talk 14:40, 9 Jun 2005 (UTC)

New link

This new link, You Want a Clear Understanding of Time Dilation, appears to me to be a "vanity" addition which does not provide the promised understanding. My temptation is to delete it, but I see little need to do so instantaneously. So how do others feel about it?

(Note that I will not complain if someone else discards it. I just feel that this edit is not so egrgegous that it must be reverted immediately. I expect that the consensus will be to remove it, but in this case I prefer verifying that first.) --EMS | Talk 02:24, 18 July 2005 (UTC)

Understanding time dilation rightly proceeds from understanding the Lorentz transformation correctly.

*Shubert's derivation of the Lorentz transformation is not a "novel narrative or historical interpretation." Wikipedia guidelines are explicit: "Research that consists of collecting and organizing information from existing primary and/or secondary sources is strongly encouraged." - Perspicacious

It's about time that you popped up. There are two issue here. The first is the original research one. Do you have any primary publication sources for this? Web publication is not primary. That requires a relevant peer-reviewed journal. Otherwise, you are attempting to use Wikipedia as a primary outlet for your ideas, which puts Wikipedia in the position of being an original source for it. That is improper.

Also, I do not see how this adds to the article. Starting with Gallilean transformations and moving onto relativity is fine, but this article assumes (with good reason) the validity of the Lorentz Transformations. I truly do not see how this is enlightenning at all.

One more thing: Could you please sign your posts here with four tidles (also created by using the signature button at the top of the edit window). That will create a timestampted signature. Thanks --EMS | Talk 04:45, 1 August 2005 (UTC)

We agree that Wikipedia is not a primary source. *1. It is not the place for original research such as "new" theories. *1. The phrase "original research" refers to untested theories; data, statements, concepts and ideas that have not been published in a reputable publication; or any new interpretation, analysis, or synthesis of published data, statements, concepts or ideas that would amount to a "novel narrative or historical interpretation". *2.

I categorically deny that Shubert's paper is "original research." No relativist, research-level physicist or expert in special relativity would call *A Derivation of the Lorentz Transformation from Newton’s First Law of Motion and the Homogeneity of Time "original research."

What do you classify as original research in Shubert's paper? Shubert bypassing the popular use of "the cosmic everywhere present now" in deriving the Lorentz transformation can't be classified as research. It would be far more accurate to label it "exercising reasonable control while editing."

How is section 6, Shubert's explicit derivation of the time dilation formula from the Lorentz transformation, not pertinent to the article on time dilation? --Perspicacious 00:41, 2 August 2005 (UTC)

"'exercising reasonable control while editing.'" Have you everheard the expression "a rose by any other name ..."? The question of whether it is original is a matter of where is has been published! Kindly name a peer-reviewed journal which has published this. I strongly suspect that you cannot, in which case this is for Wikipedia original research. I also assure you that you are far from the first person who is shocked to have their valuable insight rejected link this (although this article appears to actually be of some real value for a change). (And no, being of value does not change things. If SR was brand new, we would not let it in here until it became controversial.)

My hat's off to Dr. Shubert though. That article is one of the better pieces of original research that I have seen, and I think that it should be submitted for publication. At the least, do realize that I needed to look at it for over a day before it was yanked for the first time. Also please realize that since then, others have been keeping ot off too (but perhaps out of respect for my opinion). Finally, I am less bothered by the derivation in section 6 as the torturous route taken to get there. --EMS | Talk 06:04, 2 August 2005 (UTC)

You are right. "A rose by any other name..." Mostly we disagree on Wikipedia's definition of "original research." You interpret Wikipedia's guidelines as disqualifying an unpublished synthesis of published and uncontested concepts and ideas even when it doesn't amount to a "novel narrative or historical interpretation." I'll just leave it at that. --Perspicacious 12:59, 2 August 2005 (UTC)

You need to realize that Wikipedia sees its job as being to document existing human knowledge. Your approach is not part of this knowledge, but virtue of its being an "unpublished synthesis". So I thank you for your understanding in the matter and sincerely wish you luck for the future. --EMS | Talk 17:04, 2 August 2005 (UTC)

Deleted

That actually is a neat article, but it is better suited to the Americal Journal of Physics instead of Wikipedia. It is bringing up new concepts and not directly dealing with time dilation. It also seems to be a kind of original research, which also disqualifies it.

In any case, it is gone. For now. --EMS | Talk 16:34, 19 July 2005 (UTC)

To Eugene Shubert

It's about time that you found the talk pages. Kindly get yourself a Wikipedia user-ID ASAP. It is difficult to correspond with an anonymous editor whose IP address keeps changing for whatever reason. You are also losing out on the ability to watch these pages for changes by not having a user-ID. Of course you can stay an anonymous editor if you like, but it is not as if we don't know who you are.

Look above for my prior messages on your attempt to place that link into the time dilation article. Myself and William M. Connolley (who has actually reverted your link more than I have) are interested is discussing the issue with you. --EMS | Talk 02:45, 25 July 2005 (UTC)

I also think it is a vanity addition. Interesting point though, that the theory of relativity is an entirely mathematical subject and cannot be expressed meaningfully with words alone. I agree with that general idea, and in my personal experience it was through watching relevant animations that I got some understanding of relativity. The Shubert article does not help me. I support the decision to remove, and keep removing, the reference to the Eugene Shubert article. --Cleon Teunissen | Talk 08:49, 25 July 2005 (UTC)

The article space is not for talk

Kindly realize that all that your attempt to make your case in the article space did was to paste a sign on the rear-end of your edits reading "revert me". Please discuss this matter here. You will get no respect otherwise. --EMS | Talk 05:01, 31 July 2005 (UTC)

FTL Travel

Science fiction has often featured faster-than-light travel. However, that's impossible with that troublesome time dilation getting in the way. Would hyperspeed be the only way to travel at FTL speeds without the shift in time? Scorpionman 02:57, 27 July 2005 (UTC)

It is not so much time 'dilation getting in the way', its rather that speed is not what we tend to think it is. The concept of "hyperspeed" does not apply, speed isn't like that.

Velocity is counted by dividing distance traveled by time elapsed. The tricky part is that distance isn't quite what we tend to think it is, and time elapsed isn't quite what we tend to think it is.

As it happens this slots in nicely with the previous entry. The mathematical formulas of relativity describe the behavior of space-time and so on. The explanations in words use imagery from everyday life, which does not apply in situations where relativistic effects are significant.
-Cleon Teunissen | Talk 05:26, 27 July 2005 (UTC)

Time dilation is a fundamental effect of relativity theory. As best I can tell, getting rid of it returns you to the rules of Newtonian physics. (Its either that or have an inconsistent theory.) In that case, any powerful enough rocket can go faster than light. Just give the object a kinetic energy of more than $mc^{2}/2$ in a given frame or reference, and there you go. Just realize that in special relativity, that kinetic energy only gets you going at 74.5% of c. --EMS | Talk 05:50, 27 July 2005 (UTC)

Your choice of words makes it sound very anthropocentric. God said: let there be light, an lo, there was light. Einstein said: let there be time dilation, and lo, there was time dilation.

It seems to me that it is better to phrase in such a way that there is not even a hint of a human involvement. I think it is better not to say: 'time dilation occurs because we use the theory of relativity'. Of course it is the other way round. Relativity is concieved the way it is in an attempt to account for the physics taking place. --Cleon Teunissen | Talk 08:14, 27 July 2005 (UTC)

I can't see what was anthropocentric about what I wrote. You cannot "get rid" of time dilation alone and still have a self-consistent theory. The Lorentz transformations will not allow that. It's not a matter of Einstein said, but instead is a matter of what Einstein found.

I noticed that JohnArmagh has edited the opening section.
He replaced "Time dilation is a consequence of Albert Einstein's theories of relativity" with "Time dilation is an effect described in Albert Einstein's theories of relativity".
In your revision you had opted for a very anthropocentric formulation, which has now been corrected. I think it is important to avoid anthropocentric wording. There are quite a lot of people who believe that the theory ofrelativity is fundamentally a theory of observer created reality and I think that as a precaution wording that appears to corroborate that metaphysical belief should be avoided. --Cleon Teunissen | Talk 08:27, 28 July 2005 (UTC)

I have corrected that openning line back to its previous form. I cannot see how the consequences of the theory become attached to the man who formulated it. Physicists are reporters of rules behind reality, not the creators of those rules. The new wording impressed me as being very weak and even misleading. Time dilation is not described in the theory but rather in the articles written on it. Hence the need for the use of the word "consequence". Also, I do not see how the naming the person who formulated the thoery makes the text anthopocentric. --EMS | Talk 22:28, 28 July 2005 (UTC)

No, of course the naming of the person doesn't make it anthropocentric. It is stating a causal relationship that determines whether a human factor is implicated. Compare the following two statements:

• Global warming is a consequence of carbondioxide emission.
• Time dilation is a consequence of Albert Einstein's theories of relativity.

The formulation strongly suggests a causal relationship. --Cleon Teunissen | Talk 09:25, 31 July 2005 (UTC)

Error in discussion of gravitational time dilation

Whoever wrote this section goofed. The author refers to an orbiting observer, presumably meaning a circular orbit, but there are no stable circular orbits that close to the event horizon of a Schwarzschild hole, so he must have computed the gravitational time dilation for a static who uses a rocket engine to hover outside the horizon. You fix this by introducing Hagihara observers who really do move in stable circular orbits. Then there are two competing effects, the kinematic and gravitational time dilation. This is in fact the easiest way to obtain the basic GPS correction (the one which is built in to GPS satellites to take account of the largest contributions from special and general relativity).---CH (talk) 23:58, 27 July 2005 (UTC)

Hi Chris, some time ago, in scouring the web for information, I came across a discussion written by Kevin Brown. It is a discussion of velocity time dilation and gravitational time dilation for satellites orbiting Earth, which I think is closer to home than black holes.

Kevin Brown 8 apr 1997 09:00
Newsgroup: sci.physics, sci.physics.relativity
Subject: Re: Relativistic time on satellites

Kevin Brown concludes:
Consequently, for an orbit at the radius R=3r/2 (about 2000 miles up) there is no difference in the lapses of proper time. [...]
For example, in a low Earth orbit of, say, 360 miles, we have r/R = 0.917, so the proper time runs about 22.5 microseconds per day slower than a clock at the North Pole. On the other hand, for a 22,000 mile orbit we have r/R = 0.18, and so the orbit's lapse of proper time actually EXCEEDS the corresponding lapse of proper time at the North Pole by about 43.7 microseconds per day.

I don't copy all of the text, you'd have to use Google to locate the original message. I think this terrestrial discussion of velocity time dilation and gravitational time dilation is more suitable than the black hole scenario. --Cleon Teunissen | Talk 05:40, 28 July 2005 (UTC)

What I like about the discussion by Kevin Brown is that he points out that it is a bit odd to calculate the velocity time dilation separately, using special relativity. Kevin Brown argues: since general relativity subsumes special relativity, there is no need to use the math of special relativity; the Schwarzschild metric implies both velocity time dilation and gravitational time dilation, in that sense there is no reason to refer to velocity time dilation as a contribution from special relativity. ---Cleon Teunissen | Talk 05:54, 28 July 2005 (UTC)

One more remark. Astronomical observatoria all over the world have a procedure to maintain synchronized time keeping down to nanosecond level. For all observatoria on Earth the amount of lapse of proper time is very close to each other. On the poles the gravitational time dilation is stronger than at the equator; at the equator there is a velocity time dilation that is not present at the poles. Overall, the sealevel surface of the Earth is a surface of equal lapse of proper time. I think that rather exemplifies what general relativity is about. --Cleon Teunissen | Talk 06:27, 28 July 2005 (UTC)

Chris -

I miseed the "orbit" nuance when I worked on this page a few months ago. Overall, I was looking at getting the foundations of it firmer, and I was not sure what to do with the chart. I finally decided that I was better off letting it sit there, since those were the correct values for an observer being kept at static rest with the aid of a rocket.

Perhaps it is time to just remove the offending material altogether. --EMS | Talk 23:23, 28 July 2005 (UTC)

-------------------------

Cleon -

I know that you are trying to help, but you are only bringing in a lot of very incidental material, to the extent that it is relevant at all. Chris is very expert at this stuff and is quite familiar with the nuances of time dilation. There is no need to try to explain it to him. I assure you that Hagihara observers involves somthing much more general than Kevin Brown's exercise, and which is much more relavant to this article than that exercise.

I also wish that you would not treat Kevin Brown's writings as some kind of general relativity gospel, which you can quote from as if from scripture. For example, the bit about GR subsuming SR is very important, but if you had understood what it really meant, you would have realized that it is implied throughout Chris' posting and therefore added nothing to the conversation.

I strongly advise making suggestions and observations using your own words in the future. All that quoting Kevin Brown is doing is setting Chris up to generate a response that you cannot comprehend. --EMS | Talk 23:23, 28 July 2005 (UTC)

reversion of edits by Jok2000

I am not terribly in love with this page as-is. However, I cannot see how those edits added any clarity or valuable content to this page. Instead I saw a bunch of GPS-centric content that raised more questions than it answered. --EMS | Talk 04:31, 19 October 2005 (UTC)

---

Why promote a cranky viewpoint? The GPS exists. Reword it if you must and add that nice "This article is in dispute" tag. Jok2000 11:07, 19 October 2005 (UTC)

---

I see yours as being the cranky viewpoint. The equivalence principle is not directly involved with time dilation, and the GPS is documented elsewhere. In addition, your GPS equations are just a bunch of handwaving, with the surrounding text being inadequate to explain what is going on. The situation is made worse for your edits by the fact that the gravitational time dilation effect has been moved to a seperate article.

I think that you are confused as to what time dilation is and how it arises. For that I refer you to the proper time article, where you will find a more technical discussion of the underlying issues. In addition, GPS makes for a terrible time dilation example since the GPS clocks run faster than ours.

I thank you for your interest, and am willing to work with you if I can. However, I cannot consider these edits to be helpful, and therefor feel obliged to revert your edits again. --EMS | Talk 14:58, 19 October 2005 (UTC)

P.S. Oddly, I didn't revert again. My thanks to William for beating me to the punch. To Jok2000: Remember 3RR. You can't win a 2-to-1 battle. I know that you are trying to help. Let's stop being "cranky" with each other and see if we can resolve this peacefully. --EMS | Talk 15:06, 19 October 2005 (UTC)

I seem to be fated to follow EMS around... anyway, I cannot understand Jok's "Why promote a cranky viewpoint?" - nothing in EMS's edits justifies that. Also the GPS seems too... specific. ps: I don't much like the animated gif either... but I can guess who did that. Also, jumping so soon into suggesting a dispute tag seems very premature. Please, Jok, will you try to give a serious answer to EMS's point? William M. Connolley 15:14, 19 October 2005 (UTC).

Be careful about who you credit with the animated GIF. It is indeed Cleon's work, but I requested it. What is needed IMO is a better explanation of it. I regret that I have not gotten around to doing that. --EMS | Talk 15:28, 19 October 2005 (UTC)

---

Serious answer? Sure, read the German version of the page. Jok2000 15:16, 19 October 2005 (UTC)

I will (once I can translate it that is). However, this is not a terribly useful answer even so. --EMS | Talk 15:28, 19 October 2005 (UTC)

I was just trying to save the readers a couple of bucks on a book. I actually reverted your revert of me completely by accident. I had the page open and was pondering rewording (or reverting -- hence the comment) it when my daughter came by and I hit the enter key by accident. Jok2000 16:18, 19 October 2005 (UTC)

Comments by mdf

Is this article about time dilation as it is observed, or is it about how the effect is modeled by theory X? One gets the strong impression that the argument(s) are about the models, not reality. As one example of this, look at the opening sentence of the article (as of the the time I sign this note):

Time dilation is a consequence of Albert Einstein's theories of relativity.

Either time dilation exists, or it does not. And if it does exist, it was not invented by Albert Einstein. Furthermore, all the babble in the article about "synchronization" and the like are completely beside the point: when the effect is observed, physicists are not tediously engaged on clock sync bureaucracy, but simply measuring the rate of a non-local clock compared to an equivalent local one. Aren't these "gedanken experiments" supposed to clarify matters, not obfuscate? Another example of the "battle of the models":

A legitimate question is how special relativity can be self-consistent if clock A is time dilated with respect to clock B and clock B is also time dilated with respect to clock A.

Again, nature doesn't care a damn whether or not the theory we call "special relativity" is self-consistent. And if the question is still considered relevant, then the plain fact that special relativity has been empirically demonstrated to be accurate to the N'th decimal place suggests that (as per my thesis here) that the real question is whether or not some people's viewpoints are consistent with starkly observed physical reality.

If you want to boil this mini-rant down to a single question: why is this article so long? mdf 18:24, 19 October 2005 (UTC)

To answer the last question first, I think that you will have difficulty creating a quality article which is much shorter. However, that is not to say that this article could not use a good, solid rewrite.

For the first question, whether this is time dilation as observed or as modelled: It is as modelled. Relativity is just a theory, albeit one for which there is ample confirmatory evidence. However, even though I 100% believe that relativity is correct, I do not see it as either appropriate or necessary that this article should announce that correctness. A section on relevant confirmatory effects may be worth adding, however.

For self-consistency: Nature does "give a damn". Nature, by its nature, is self-consistent. If a theory such as special relativity should lack that attribute, then it is not an acceptable model of nature.

Whether it is accurate of not, relativity is not reality itself but instead is a mathematical model of reality. Note that even if relativity correctly describes how Nature operates, Nature does not do the math but instead simply does. --EMS | Talk 19:28, 19 October 2005 (UTC)

No, nature doesn't give a damn what a bunch of humans think. I'll say no more about this, as the point is non-negotiable; argue with physical reality at your peril.

My point is that the current article is wasting the readers time and wikipedia's space by wandering around aimlessly in "model land", when it should simply stick to the plain facts of the situation. The quality article -- the holy grail -- would simply state what time dilation is, provide a brief description of the observed effect, a history (first prediction/discovery, by who, etc) and prominently list notable observations (or claims thereof). (e.g., muon decay, the air-transpoted clock experiment, etc.) At this point, links to the relevant sections of various theories would be appropriate; let them elaborate on "self consistency", the mechanisms that give rise to the observations, etc, as it is well within their scope, not this article. mdf 20:20, 19 October 2005 (UTC)

I must admit that I am amazed that you referred us to the German version of this article, which when translated is found to be longer and even more wandering around in "model land" than this one. For example, it includes a number of calculations that I placed into the proper time article.

You have a sense of how you want to see this article organized and where you want it to go. Given that, be bold. This is Wikipeida after all. Construct your version and let's see how people like it. I strongly advise starting it in you own user space and seeking comments before moving it out. I must admit that I find your POV on the issue of self-consistency to be interesting, but your comment that its coverage in this article may be somewhat OT is well taken (even though that is my text that you so dislike), and your proposed outline appears reasonable to me. In any case this page badly needs work! Please try your hand, and let's see what you come up with. --EMS | Talk 03:28, 20 October 2005 (UTC)

Please cite the place where I referred you to the "German article". I have absolutely no idea what you are talking about.

My apologies. That was Jok2000's doing. I sometimes lose track of who's who when I am having two conversations at once. --EMS | Talk 21:20, 20 October 2005 (UTC)

As for being bold: if this was an article on the Mossbauer effect, or automatic transmissions, then I would have been bold a long time ago. But this is relativity, and, as you must know (cf. your "I strongly advise" ...), there has been veritible cottage industry of kookishness on this subject for as long as the Internet has existed (e.g., see sci.physics or similar on USENET). It is unlikely any changes I make along the lines I set out would survive longer than a muon. Hours of time for a few minutes? Not a future I want to invest in, hence, at this time, I limit my role for this article to a mere critic. Since you and a few others appear to have accepted the role of the custodians for this article, I encourage someone in that set to at least consider changing that first sentence. I think even Einstein would find it an outrage. mdf 16:52, 20 October 2005 (UTC)

What the hell, I re-wrote the introduction. The plan is to ditch alot of the current 'explanation' -- it is rife with confusion -- and replace it with the substantially shorter, and much clearer, version as elucidated by A. P. French in his 'Special Relativity' (pages 105-109). If anyone objects, revert the change and I'll stick to bird photographs without a fight. mdf 20:20, 20 October 2005 (UTC)

I'd say that you did a good job. I will do some word-smithing with it, but overall this is an improvement. For the most part I would advise seeking to do a minimum of "damage", but do be aware that "you cannot make an omelet without breaking a few eggs". I still encourage you to reorganize this article. Just be careful not to overreach in terms of content if you are not totally comfortable with relativity. However, there is more to being a good editor than being an expert in the subject. As I see it, if you can establish the right superstructure, the rest of us can make it work. --EMS | Talk 21:20, 20 October 2005 (UTC)

I've added an experimental confirmations section (the name sounds clunky). I will attempt to obtain a copy of Rossi & Hall's paper to make sure I have the details exactly right (I'm summarizing the summary French gives in 'Special Relativity', op cit.), the others are either wikified, or links exist to the outside world. I happen to concur with User:Jok2000 that GPS is highly relevant to this topic. Mind you, I couldn't help myself re: the eccentric term stuff, and perhaps this section could be near the end, not the beginning. I need a line drawing similar to the one on page 107 of 'Special Relativity. One is tempted to just take a picture of it. mdf 22:49, 20 October 2005 (UTC)

I agree that the GPS is relevant, especially in the context in which you mentioned in. Your new section stands in stark comparison to Jok2000's edit: You paragraph on GPS communicates more on it and how time dilation affects it than Jok2000 did in an entire section. You also placed the GPS into its proper context. I assure you that both William and myself are willing to work with and support throughtful edits that add value to this article. You are very much showing that you can do that.

As for French's line drawing, DO NOT copy that into Wikipedia without its being released into the public domain first. Please see WP:Copyrights. Out of necessity, Wikipedia has gotten fairly strict about that. --EMS | Talk 04:09, 21 October 2005 (UTC)

Among physicists I have conversed with, A.P. French's Special Relativity, although a classic, is considered to be showing its age. I commend your recent changes, but lets let the dust settle before we bring Mr. French into the fray. Jok2000 03:20, 21 October 2005 (UTC)

More Jok2000

Jok removed

This effect is commonly thought of as being time slowing down for the time dilated clock. This is not the case. Locally, one's proper time always passes at the same rate. Instead what is slowed down is how that proper time passage is perceived by another observer.

with the comment Shorten article as per talk. See GPS, talk or German page or "An Introduction to Time" for reasoning. I find her habit of referring us elsewhere for the reasonnnig to be very annoying. I can't read German. I don't have the book. I don't want to go read the GPS page to find out why an apparently reasonable piece of the intro has been snipped here. William M. Connolley 09:07, 20 October 2005 (UTC).

To mdf: WMC's lower-school orthodoxy and EMS's anti-rationalist stance generated an equilibrium in this article surrounding observed vs. real time dilation. (Not that either is necessarily an honest adherent to their stated philosophies). It is an unfortunate, but I suppose necessary part of the magic that is Wikipedia. Jok2000 20:33, 20 October 2005 (UTC)

Recent edits by ems57fcva

First of all, it is somewhat ironic that I have remove the last paragraph of the the intro almost on the heels of Jok2000's failed attempt to do so. However, I really feel that it collides with what mdf did, and with mdf's text being better. I put that text in to clarify how I started this article. In the new intro, it is superfluous at best, and so I decided that it's usefulness was at an end.

I like the experimental confirmations section, but felt that it was in the wrong place. I think that you first do your best to tell the reader what time dilation is about, and then drive home the point that it has been confirmed. If nothing else I think that it is helpful for the reader to have had a chance to understand what it is that is being confirmed.

The table of time dilation values has always impressed me as being at best a little odd. I decided that the time had come to see about it's outright removal, and I think that the article benefits from it. --EMS | Talk 03:45, 21 October 2005 (UTC)

For what it's worth, that bit about circumnavigating the universe in a subjective lifetime irks me philosophically (not that I feel any motivation to change it -- its entertaining, I guess). It is the philosophical equivalent of death. The incoming energy from exploding super-novae and magnetar emissions from the blue-shifted side of one's travel would kill you before you could recognize that that was what was happening to you, or even, I suspect, before you got very far in your trip at all. We'd still be happily arguing here on wikipedia long after such a traveller had turned into radioactive slag.Jok2000 15:16, 21 October 2005 (UTC)

For the love of goodness, we appreciate your efforts, but I and many like me ARE those people who are not physicists who are trying to understand TIME dilation. Guess what? You've made it so very complicated and confusing. If this is inteneded to be an article for experts then fine. But if its to help those being introduced to time dilation. GET RID OF THE GRAPHS and the MATHS and explane it conceptulally so that a 12th grader with some high school maths can get it.

Also just explain time dilation please and nothing else. And give examples step by step from time dilation that occurs when driving as opposed to standing still to time dilation that occurs when flying to the faster speed of satalites and then onto light speeds. Show a slow understandable progression with everyday examples that are SOUND.

Don't then in the middle of an example say... OH and we've proved it with this math problem. or we've just got all this data that proves it so trust us.... No please just stick to conceptually having the reader USE REASON to work it out that you've guided them through. Use 10 different approaches so that different readers might click onto a certain one. But make them all straight forward and very well thought out.

Is this for a general audience? I hope so. If so, please keep it simple. Time dialation does not have to be so hard to learn or to teach. It's been said in hundreds of science conferences so start here.

thank you. Sorry for the rant. But it's like you wonderful scientists and students of physics start off simple and before finishing your thoughts in the article suddenly through in some fact from left field too early or unnessasarily.

Good luck. Keep this thing aimed, pinned and respectful of your audience.

Best

For the new bee to this stuff you hit them with all these terms with out explaining them. So leave them out or define each one.

1)temporal coordinate systems: thanks for explaining that 2)Einstein synchronization procedure: thanks for explaining that 3)tE = (t1 + t2) / 2. : thanks for not telling us that t1 = time one and t2 = time 2 and what is tE? 4)t0 calibrated to read 0 : so you mean time zero? and why calibrated? Why even mention this? I'm new and I'm on the 3rd or 4th paragraph and I'm LOST because you've thrown calibrated to read 0 with out explantion and my hunch is you never needed to say calibrated to reach zero for the newbee. Your audience. 5) elapsed proper time for every 2 seconds of coordinate time: thanks for that. We the newbee all just magically understand "proper time" and "coordinate time." I know these can be defined their and then or not used but replaced by a common wording.

6)The formula for determining time dilation involves the Lorentz factor and is:

   T_1 = \frac{T_0}{\sqrt {1- \left(\frac{v^2}{c^2}\right)}}

Fantastic...NOW IT SO CLEAR. No wonder people think it's all just made up . High school kids CAN GET time dialation but not if you start teaching them like this.

I can't continue because it's so full of the kind of over complexity that the notion of time slows down, or time speeds up has not even been put across properly to the reader. Please please try to unlearn what you know in order to put yourselves in the shoes of the student and explain from first principles. Start with the apple dropping out of the tree, and hitting newton on the head and move towards the more complex stuff at the end of the article. If its a new term that you must use. Please define it.

Thank you.

The audience. The student.

TRS

Sorry for the poor spelling but I was just like this article rushing and not slowing down or caring to fix all the typos.

PS. again. This rant is because I see how much you guys could help a world wide audience. The rant is because your attempt is worthwhile and admirable so keep it simple and use reason to explain the counter intuitive notion of time dilation. With reason and straight forward simple conceptual examples and teaching you may help the counter intuitive become intuitive and natural as newtonion physics. EG the apple drops and that's gravity. To say time dialation is harder to teach is just not true. It's only harder to explain if you make it harder to explain.

(Above by Anon) This is why they teach Relativity in university and not high school, I suppose. The basic problem is that laymen do not believe in inertial reference frames. I suggest when you find something on a wikipedia page that you don't understand, you click on it.Jok2000 18:01, 23 October 2005 (UTC)

You are sounding more and more like a high preist for relativity. Kindly remember that science is advanced by asking questions and not by declaring things to be some kind of Truth. The anon is right that it is the job of this article to explain time dilation as best it can, and not just his job to somehow comprehend it, or take a college level course first. --EMS | Talk 05:06, 24 October 2005 (UTC)

To the anon:

1. PLEASE sign your edits! This is done by typing ~~~~ at the end of the edit. This can also be done by pressing the 2nd button from the right above the Wikipedia edit window.
2. Please get an account. They are free and helpful in identifying people. Besides, you are not doing anything improper here.
3. Unlike Jok2000, I think that you have some good points here. Kindly note however that I need less ranting and more specifics. Saying "you need to communicate" is almost useless. Asking "what is t_E supposed to be?" is excellent!

Overall, I think that you are more right than Jok2000 is on how explainable time dilation is, but its operation is somewhat non-intuitive none-the-less. I look forward to your comments on my edits in response to what you wrote above, and to more comments and questions from you. --EMS | Talk 04:56, 24 October 2005 (UTC)