## Einstein's Theory To Go Beta Testing 326 326

pinqkandi writes:

*"This article over at CNN looks into the relativity of Einstein's theory of relativity (pun intended) as equipment becomes more and more precise. Soon atomic clocks will be placed in the International Space Station to analyze the accuracy of Einstein's theories. One of the lead researchers says that if Einstein's theory is not right, it will only need minor adjustments to account for changes in space-time, due to its deadly accurate precision."*
## There are 2 theories of relativity (Score:4, Informative)

If you don't understand either one, take a look

here [bartleby.com]:

## Re:There are 2 theories of relativity (Score:2, Informative)

## What's wrong with the older proofs? (Score:1, Redundant)

## Re:What's wrong with the older proofs? (Score:3, Informative)

## Re:What's wrong with the older proofs? (Score:5, Informative)

These tests have been performed on the ground recently by measuring the frequency of a clock as its direction relative to the stars changes due to the rotation of the earth. (For example, see Phillips, et al., Physical Review D 63, 111101 (2001) or Physical Review Letters 85, 5038 (2000)- showing off is always good.) In space, one could use the faster rotation of the space station as the atomic clocks in space which may substantially outperform ground based clocks.

## Re:GPS does velocity already!!!!!! (Score:2, Interesting)

It turns out, however, that a standard atomic clock such as those used in the GPS satellites is not sensitive to these effects. In the measurements Kostelecky is talking about and the measurements we have done on the ground, one looks not at the standard clock frequency (based on the hyperfine transition) but instead at an auxillary frequency (a Zeeman transition) which has a first order magnetic field dependence. This frequency is sensitive (in leading order at low magnetic fields ) to the effects Kostelecky's framework predicts.

Therefore, one needs to operate an atomic clock in a slightly unusual way to search for these effects. In the hydrogen maser measurements we have performed (the Phys. Rev. D paper I mentioned) we measure the standard clock frequency while "tickling" the Zeeman frequency and record the shifts. A similar technique is being proposed in space. I wouldn't think that such a technique would be realistic on the functioning GPS satellites.

## Or other existing equipment (Score:3, Insightful)

I guess the hammer and feather experiment just gets more expensive in proportion to the expansion of the beurocracy.

## Re:What's wrong with the older proofs? (Score:4, Interesting)

Hasn't this been proved already? What's wrong with those older proofs?You can't prove anything in physics, you can try to disprove something and fail, and thus you may have reason to believe that the theory was correct.

But there is always a posibility that your theory may be disproved later. (Which doesn't mean the theory is rendered useless. Newton's mechanics for example, stood for a very long time, until they were replaced by the theories of relativity. But they are still used, because in most "normal" conditions they work good enought, and the math is easier to work with.)

## Re:What's wrong with the older proofs? (Score:2)

I believe that his theory of general relativity was proved mathematicallySure, Einstein did that himself. (How the hell would he have dared to release the theory otherwise...)

But a matematical proof don't really prove anything in physics, math is just a model, and if you built your model on the wrong premises, well...

Experiment are the sole judge of any theory. Math is just a very important tool, it can help determin what might work.

But it can't prove

anythingin physics.## deadly? (Score:3, Funny)

## Old methods reapplied (Score:4, Funny)

in time.

The joke of it all is that after a year some journalist asked why they didn't just stick it on a regular commercial jet but they didn't think of it at the time.

## Re:Old methods reapplied (Score:3, Funny)

-JPJ

## OK - a serious scientific question (Score:2)

they got two atomic clocks and stuck one on a plane and after two years of the plane flying around aimlessly they found a minute differenceI've heard of this experiment, but I have a serious question about it that's always bothered me.

This assumes that Clock A is stationary at 0 mph and Clock B is traveling at 400 mph, right? But, given that the Earth rotates AND orbits the Sun that assumption isn't really true. Relative to a given point, sometimes they're going faster and other times slower. Also, since Clock B is ideally flying in a big circle (around the Earth) doesn't its velocity (in relation to a set point) average out to 0 as well?

I would think that this experiment would only work if Clock A was dropped off somewhere in space and Clock B was launched

in a straight linerelative to Clock A. Where am I wrong?## Re:OK - a serious scientific question (Score:2)

## There is no "direction"... (Score:2)

The acceleration along the path you each take determines who, if anyone, is ahead.

If your trips were mirror images of each other, then on the outgoing journey (accelerating away) you'd each see the other's clock slow down.

On the way back (accelerating towards one another), you'd each see the other's clocks speed up again until they were back in synch when you met.

If the trips were not completely symmetric, then there will be a discrepancy

## Re:Special vs General Relativity (Score:2)

Doug

## Re:Old methods reapplied (Score:2)

The joke of it all is that after a year some journalist asked why they didn't just stick it on a regular commercial jet but they didn't think of it at the time.Can you imagine the excess baggage allowance on an atomic clock?

## Too soon to go beta (Score:2, Funny)

While we might think that we are equipped to carry out the beta test on Einstein's theory, methinks we may not yet be ready.

Practically, what we understand from the Theory of Relativity is what we BELIEVE we understand, and that will influence what type of outcome we are searching for.

Plus, the equipments that we think are ready may not be ready.

Take the Atomic Clocks for instant

After all, the "ticks" of the atomic clock, no matter which type of "atoms" we base it on, still depends on the variable TIME - as "ticks per second".

## Re:Too soon to go beta (Score:2)

You should read it.

Einstein was a pretty good writer, and his examples are still used today.

Go to your library!

## Kostelecky's page... (Score:5, Informative)

## Zero gravity? (Score:2, Interesting)

I'd consider it a "weightless" environment, but not "zero gravity".

- Tony

## Re:Zero gravity? (Score:1)

Might it just have something to do with gravity?

## Re:Zero gravity? (Score:1)

There is also such a thing as a Lagrange Point [montana.edu].

Kierthos

## Re:Zero gravity? (Score:5, Informative)

Technically, you're never going to get zero gravity. And yes, you're right, ISS isn't anywhere near that -- it's in orbit, and uses gravity to stay that way. ISS and the like are weightless (or near weightless) because they are effectually in a free fall; this state is termed "microgravity".

## Re:Zero gravity? (Score:2)

Unfortunately part of the spacestation is closer to the Earth and another part is further away. This means that there will be small accelerations due to gravity pretty much everywhere in the station. Only the center of mass of the station is really at zero gravity.

## Re:Zero gravity? (Score:3, Funny)

Maybe it's just the way the guy was quoted in the article, but if they need to test in a "zero gravity" environment, how would the ISS be applicable?

I'd consider it a "weightless" environment, but not "zero gravity".

True, but I'm sure they've taken that into account. The problem is, when the results come back a certain way, the same persons responsible for this article will write another about how "Einstein was wrong" because they don't understand what was actually decided here.

It's like testing the lifespan of Goldfish in water. But I didn't have any water, so I used Tequila. By the way, it's 26 seconds, but after about 15 the fish started using emacs. But the example remains the same...you can "prove" or "disprove" anything depending on who's reading it. It's all relative.

## GPS Satelites know this ! (Score:5, Informative)

## Re:GPS Satelites know this ! (Score:2, Insightful)

## Re:GPS Satelites know this ! (Score:2)

Sounds pretty unscientific to me. Here's one researcher's papers on the subject, which conclude that the GPS systems aren't following relativity. http://www.stcloudstate.edu/~ruwang/ [stcloudstate.edu]

## Re:GPS Satelites know this ! (Score:2, Interesting)

And also from one of the links:

For GPS satellites, GR predicts that the atomic clocks at GPS orbital altitudes will tick faster by about 45,900 ns/day because they are in a weaker gravitational field than atomic clocks on Earth's surface. Special Relativity (SR) predicts that atomic clocks moving at GPS orbital speeds will tick slower by about 7,200 ns/day than stationary ground clocks. Rather than have clocks with such large rate differences, the satellite clocks are reset in rate before launch to compensate for these predicted effects. In practice, simply changing the international definition of the number of atomic transitions that constitute a one-second interval accomplishes this goal. Therefore, we observe the clocks running at their offset rates before launch. Then we observe the clocks running after launch and compare their rates with the predictions of relativity, both GR and SR combined. If the predictions are right, we should see the clocks run again at nearly the same rates as ground clocks, despite using an offset definition for the length of one second.

We note that this post-launch rate comparison is independent of frame or observer considerations. Since the ground tracks repeat day after day, the distance from satellite to ground remains essentially unchanged. Yet, any rate difference between satellite and ground clocks continues to build a larger and larger time reading difference as the days go by. Therefore, no confusion can arise due to the satellite clock being located some distance away from the ground clock when we compare their time readings. One only needs to wait long enough and the time difference due to a rate discrepancy will eventually exceed any imaginable error source or ambiguity in such comparisons.

This in the other hand sound pretty scientific and conclusive to me

## In other news today... (Score:5, Funny)

## Re:In other news today... (Score:2)

aredeadly accurate.## "Beta testing"? (Score:1, Interesting)

## Re:"Beta testing"? (Score:3, Funny)

This is just another fine-grained test.Agreed. This whole thing is a lot more like

benchmarking. Those geeks want to find a way to squeeze another nanosecond out of reality.## Re:"Beta testing"? (Score:2)

(I may have misquoted bits of the story, but you get the idea...)

## Re:"Beta testing"? (Score:2)

## Hasn't this been done before? (Score:2, Insightful)

But one thing is for sure: They won't 'prove' Einstein in any way by doing this - but they might *prove* him wrong. Only negative proof can be done by example.

## So sad (Score:5, Funny)

He would have made for one heck of a great match on Fox Celebrity Boxing 3 with Stephen Hawking.

## Re:So sad (Score:2)

## "deadly accurate precision." (Score:2, Funny)

## Re:"deadly accurate precision." (Score:1)

## Re:"deadly accurate precision." (Score:2)

## What is the CNN article saying?? (Score:2, Interesting)

The CNN article is not very clear as to what it says. This comes from the fact that There are two different theorys of relativity.

1 The special theory

2 the General theory.

The special theory concerns what happens to the laws of physics as a person is traveling at a constant velocity, whereas the general theory is concerned with bodys that are accelerating ( In general relativity acceleration and gravity are equivalent).

So since the ISS is in orbit it experences an outwards accerleration( the same as one experences as one goes round a corner fast in a car.) In space there is gravity on the ISS but it is very little. This means that the ISS will experence a slight change in the ticking rate that is recorded. But this is explained by the general theory of relativity and not the special theory.

## Gravity vs acceleration (Score:3, Informative)

whereas the general theory is concerned with bodys that are accelerating ( In general relativity acceleration and gravity are equivalent).

Common misconception. Acceleration and gravity are not equivalent in General Relativity. They are *locally* (that word is extremely significant here) indistinguishable. The fact of the matter is that Special Relativity can handle acceleration just fine by using calculus. General Relativity is only needed where spacetime is not flat (i.e. in the presence of gravity), since the two postulates of Special Relativity only hold in regions of flat spacetime.

## Re:Gravity vs acceleration (Score:2)

"All objects fall the same way under the influence of gravity; therefore, locally, one cannot tell the difference between an accelerated frame and an unaccelerated frame. Consider the famous example of a person in a falling elevator. The person floats in the middle of an elevator that is falling down a shaft. Locally, that is during any sufficiently small amount of time or over a sufficiently small space, the person falling in the elevator can make no distinction between being in the falling elevator or being in completely empty space, where there is no gravity.

We could imagine two apples floating on either side of the person; as the elevator approached the earth, the apples would approach eachother. This happens because their paths, both toward the center of the earth, eventually converge. But this is not an effect that can be detected in a local experiment.

This statement of the equivalence principle makes an important suggestion. In special relativity--and all classical mechanics--we are used to the idea that objects travel at constant velocity unless a force acts on them. Now, if we can't locally tell the difference between falling in a gravitational field and travelling at constant velocity, then, locally, they must be the same thing. The paths of free bodies define what we mean by "straight" and if we observe an object deviate from constant velocity, it must be because spacetime itself is curved.

Formally, we state the equivalence principle this way: in any and every locally Lorentz (inertial) frame, the laws of special relativity must hold. From this, we conclude that the only things which can define the geometric structure of spacetime are the paths of free bodies."

## Re:Gravity vs acceleration (Score:2)

So basically, everywhere in the known universe, except in our minds?

## Re:Gravity vs acceleration (Score:2)

## Re:What is the CNN article saying?? (Score:2)

Breaks in Lorentz and CPT symmetry would provide clues as to why time flows in only one direction?

And perhaps cough up data useful to extremely large scale cosmology?

## Backwards? (Score:1)

"If variations in the ticking rate were discovered, Kostelecky says, it would be a "striking signal" that the laws of nature may be based on fundamental theories other than Special Relativity -- or perhaps in addition to it."I thought this was precisely what special relativity

doespredict, that a moving observer experiences less passage of time than a stationary one, increasingly so as the speed becomes a significant fraction of the speed of light. If the ticking ratedoes notvary, then special relativity would be invalidated.## Re:Backwards? (Score:2, Insightful)

I thought this was precisely what special relativity does predict, that a moving observer experiences less passage of time than a stationary one, increasingly so as the speed becomes a significant fraction of the speed of light. If the ticking rate does not vary, then special relativity would be invalidated.You're correct about special relativity, but we're considering a different sort of effect.

Special relativity predicts (among other things, as you describe above) that the ticking rate of a clock,

when always viewed from its own rest frame,is independent of the clock's orientation and velocity with respect to everything else in the universe. We're studying this idea by watching very sensitive clocks as they rotate or change velocities. Any dependence of a clock's rate on its orientation would imply that some directions are different from others, i.e, it would show a violation of rotational symmetry, which is a subgroup of Lorentz symmetry.Chuck

## This just in . . . (Score:2, Redundant)

One of the lead researchers says that if Einstein's theory is not right, it will only need minor adjustments to account for changes in space-time, due to its deadly accurate precision.This just in, from a 1903 Einstein press release:

One of Einstein's lead researchers says that if Newton's theory is not right, it will only need minor adjustments to account for changes in space and possibly time, due to our upcoming theory's deadly accurate precision.

## Where does relativity fall short? (Score:2)

## Re:Where does relativity fall short? (Score:2)

For more details and clarifications, consult an appropraite source, not Slashdot.

## Re:Where does relativity fall short? (Score:2)

The problem of the quantum--classical transition (a.k.a. the measurement problem) is not really a physics problem. Read Gottfried's QM text for a pretty clear description of how physicists come to grips with it. The people working on quantum computing have to deal with this all the time, and as far as I can tell, quantum decoherence for them is an engineering problem, not a physics problem.

Strictly speaking, on very large length scales (like the size of the earth or larger), gravity is the most prevalent force, because matter tends to be neutral in large clumps. However, gravity is still relatively weak on those scales, so you don't need a full theory of quantum gravity to understand it---the weak gravitational fields can be treated accurately as an plain-old potential. Only in the neighborhood of a black hole, or trying to describe the entire universe being in a single quantum state, or trying to understand the first few moments of the big bang, does QM seem not to work.

## Gravity Probe B - A Most Stringent Test (Score:3, Informative)

## GPS measures relativity all the time (Score:4, Informative)

## Re:GPS measures relativity all the time (Score:2, Informative)

Chuck

## Wasn't this already tested? (Score:2)

## Scientist Practical Jokes (Score:5, Funny)

## Adjustments? (Score:2, Funny)

## I don't belive in Relativity theory anyway... (Score:2)

Does this mean my GPS will stop working now?

:)

## GPS: been there, done that (Score:2, Informative)

Actually, GPS knows about this and takes advantage of it. It is the only consumer relativity application I know of.

The GPS SV's are going about 3900 m/s which is a sufficient percentage of the speed of light for relativity to come into play. If relativity weren't taken into account and Einstein obeyed, you'd be off by ~100 meters.

The correction could be done in the receiver or the signal could be biased in the SV. Following the Principle of Alice's Restaurant:

Factoring this correction into the SV, the onboard clocks use a frequency of 10.22999999543 MHz and your GPS receiver uses 10.23 MHz. This simplifies the GPS receiver software immensely.

GPS was designed during the 1970's by some really smart forward thinking guys.

## Horrible (Score:2, Insightful)

## Questionable journalistic value (Score:3, Insightful)

In fact the opposite is the case. No one has any reason to believe that general relativity is in error, but as part of good science it is being tested anyway. One can never prove a theory; one can only disprove it. So the best you can do is test your theories with greater and greater precision as the opportunities present themselves.

It's a case where this is, in effect, a pretty mundane story (a very well-established theory is being routinely tested), but the journalist in question is implying that there is some doubt as to its validity. Of course, it's possible the experiment will reveal deviations from general relativity's predictions, which would indeed involve "minor corrections" to the theory since it is so accurate in other areas, but there is a definite spin being put on the story which isn't in the underlying facts.

## Re:it's truly relative (Score:1)

## Re:it's truly relative (Score:1)

If you can think of an oak tree which lives several hundred years, the analogy can be made as well. I do not deny the fact that we can measure "time" or the passage of such, just that in a cosmic sense, time does not exist.

## Re:it's truly relative (Score:2)

but what makes time any less valid than length, width and height?I don't think Einstein ever said that time was any less valid than length, width, and height. All are relative, according to Einstein's theory.

"Time doesn't exist" is an inaccurate representation of what Einstein said. Of course time exists, because we define it to exist.

## Re:it's truly relative (Score:2)

-metric

## Sad techie/pedant joke (Score:1)

My typical response is:

"An abstract system that allows one to distinguish sequences of events"I then laugh till I puke

## Re:Sad techie/pedant joke (Score:4, Funny)

-Oh, my goodness, is that the time?(Rik points at Mike's wristwatch)-No, time is an abstract concept. This is a wristwatch.But to be truly pedantic, you will have to distinguish between "What's the time?", "What's time?" and "Is it Miller time yet?". ;-)

## Re:Sad techie/pedant joke (Score:2)

I havn't seen "the Young Ones" in years. I want it on DVD so badly I could burst. That, Red Dwarf, the New Statesman and the Brittas Empire is all I ask for.

(rik Mayall is sooooo cool)

triv

## Re:Sad techie/pedant joke (Score:2)

Airplane...Kid:Can I ask you a question?Pilot:What is it?Kid:It's an interrogative statement, used to test knowledge, but that's not important right now, mister.McCroskey:We keep losing their radio.Burgess Meredith:McCroskey, give it to me straight, what's it look like?McCroskey:A radio? Well, about so big, green, with numbers, lots of knobs.## Re:it's truly relative (Score:3, Interesting)

Time most assuredly does exist. I am perceiving time, therefore I am perceiving something. Whatever this something is, I define as "time". Viola.

You may think you can wiggle out of this by claiming that what I'm perceiving is an illusion, but no such luck; I define your claimed illusion as "time" (without conceding your illusion point.) It doesn't matter how you try to do this, I can always go one meta-level higher. You can't win without throwing out logic, at which point I declare moral victory anyhow.

The parent is really a hidden instance of "overgeneralization".

youdon't understand something doesn't affect the universe. Hint 2: You can't go "Newtonian gravity is incorrect. Therefore, there is no such thing as gravity." It's the same form, honest.)Of course the universe cannot be totally explained and there's a lot of mystery out there. Indeed, that's exactly why

making up fake mysteryis a waste of time! There's plenty to exercise your sense of wonder on or whatever other reason your subconcious is rebelling at this message for; why make up fake stuff like this? You need all the help you can get; throwing out logic pretty much leaves you adrift, with no clue. You wanna be that way, fine, no skin off my nose, but don't suffer under the illusion that you're any more 'enlightened' then me.## Re:it's truly relative (Score:2)

## Re:it's truly relative (Score:2)

Just because a real-world triangle may consist of untold quintillions of super-strings doesn't mean the triangle doesn't exist, it just means your human mind can't hold both frames of reference at the same time. It's a human limitation, not a universe-al one.

## Re:it's truly relative (Score:2)

Time does not existThan what separates actions from one another? Beside that, there is a rules that no two items can be in the same place at the same time. If time didn't exist, than two things would either, be allowed to be in the same place (our perception just doesn't see it), or no two things can ever be in the same place. This latter part can further be extrapolated to say that no two things have the *ability* to be in the same place, ever. I believe both of these to be untrue, so time must exist.

## narcisstic sense of time (Score:2)

So, if I were to stop perceiving time, does it cease to exist? Things happen while you're sleeping, you know.Either this is a totally narcistic sense of time, or else this requies certain metaconditions, such as an immortal soul (or similar) with the ability to be unconscious. There could be the ability to connect/disconnect from various time streams, etc. But this goes into discussions that many folks find uncomfortable. And most such subject definitions of time do not try to integrate these other factors.

[shrug]

## Re:it's truly relative (Score:2)

## an article on this (Score:2)

## Re:Why do this again? (Score:2)

We've already got a bunch of atomic clocks circling the earth -- in the form of GPS satellites. The funny thing is, they don't need to compensate for relativity, when they clearly should.I'm not going to take the time to find a link, but I believe they are compensated. Of course, the change isn't very much as they're simply not moving all that fast.

## Re:Why do this again? (Score:2, Informative)

here [aip.org] if you want to read more regarding GPS birds and relativity

## Re:It will be proved wrong! (Score:2)

That's my bet.

Be cause I can't see, what happens with a circular train around the Earth. How does it shrink, when it's velocity approaches c?

Oh, Einstein was wrong because

youcan't see?Special relativity concerns only objects in uniform straight-line motion. A circular train around the Earth is not straight-line motion, so general relativity comes into play.

On a small scale, an observer would see the effects of special relativity on the train cars nearby (shrunken in the direction of motion, clocks appear slow) but on the scale of the earth, these effects would be offset by general relativistic effects.

## Re:It will be proved wrong! (Score:2)

If you think if the fact that you have a bunch of differnt rules, some apply here, some apply there, nothing really works all of the time.Just because *you* don't understand how it all fits together, doesn't mean it doesn't. The rules do work "all the time" - if they didn't, physicists wouldn't find them very useful. The rules of special relativity apply everywhere, all the time, but they only produce the unusual time/mass dilation effects in situations involving relative differences in velocity. Ditto for general relativity: as far as we know, it applies throughout the universe at all times; however, since it's based on the strength of the gravitational field at any point, its effects vary. If these rules *didn't* vary in their effects depending on the situation, it would either mean they were wrong, or the universe would be an incredibly static place.

This is because they came up with an idea, found an area that it didn't work in and had to invent rules that worked for that areaThis is completely wrong. When this has happened, it typically results in an improved theory which completely explains all areas in question with a single theory. Try reading Thomas Kuhn's "The Structure of Scientific Revolutions" for more on this.

As for your tangential link to terrorism, it's hard to see how ignorance is going to help to achieve international peace.

## Re:It will be proved wrong! (Score:2)

Unfortunately, while the effects of Special Relativity can be deduced in relatively (heh) simple algebra, the effects of General Relativity require

verycomplex math, which is why you're not going to get a good answer on Slashdot. There might be folks here that can figure it out, but they probably won't get back to you for a while.Best guess is that, if you're standing next to a hypothetical train going around the Earth at half the speed of light, you'll mostly just see Special Relativity effects - clocks on the train appear slow to you, the cars look short, and the mass of the cars is increased. Observers on the train (assuming the centrifugal force* doesn't turn them into chunky salsa) would see your watch running slow, and you would appear shortened, as would the tracks around the Earth.

The catch is, the circular motion around the Earth creates a pseudo-gravitational field** inside the train that has its own set of effects, and calulating how they are perceived by an outside observer is more difficult.

I think your earlier confusion was that if the train cars shrink as seen by an outside oberver, how does the train stay attached? The best answer that can be given in a few minutes on slashdot is that the General Relativity effects balance it out somehow. This is the same answer that has to be given for the Twins Paradox, except that that one isn't too difficult to explain since there's no rotation involved.

* - yes, I know centrifugal force doesn't really exist, but is an observational by-product of inertia.

** - the pseudo-gravitational field is the same as the acceleration caused by the centrifugal force that doesn't really exist.

## Re:It will be proved wrong! (Score:2)

But if nobody can show me how they do fit ...In the case of the circular train - how do they work? I am asking.

...Excuse me! How it works for the circular train?

I was replying to an AC with a strange view of the applicability of physical theories. ShavenYak has already given a reasonable answer to your train question.

To understand what happens with the circular train, I'd suggest first trying to understand how simple special relativity really is - the Lorentz transformations which form the basis of special relativity involve little more than a simple application of geometry. A high school kid could work them out from first principles, pointed in the right direction. One site which includes a form of this derivation is here [colorado.edu], and it has some good links to other sites.

Once you've understood that, you can then apply the Lorentz transformations in as much or as little detail as you like to satisfy yourself that the circular train example doesn't put the slightest dent in special relativity.

I'll give you a hint though: imagine that the Earth is transparent. You're standing next to a circular train travelling near the speed of light. Look below your feet, at the train on the opposite side of the planet. At that point, it's not travelling towards you, it's travelling perpendicular to you. This means that there is no length dilation in the direction towards you. Which means that the radius of the train is unaffected.

So let's take that a step further and ask what it would take for the dilation of the train's radius to take place. Well, it would have to be travelling at least partially in the same direction as its radius for that to be the case. But it's travelling in a circle, so by definition, the direction of its velocity vector is always tangential to the circle,perpendicular to the radius. At no time does any component of the train's velocity vector coincide have the same direction as its radius. Therefore, there cannot be any dilation of the radius. (For bonus points, show why this still applies for an observer on the surface of the earth, rather than at the center.)

Perhaps this gives you some flavor of how these things naturally work out to avoid contradictions. No special tricks or selective application of rules are required. In your original post, you talked about inconsistencies "popping out". The very fact that theories like special relativity are easily able to cope with every special case and test case that is thrown at them, is an indication of what solid theories they are (again, see Kuhn).

Much of this stuff, and especially S.R., is very accessible to anyone willing to take the time and make the effort to learn about it. If you haven't made that effort, though, claiming that it must be wrong because you don't understand it only demonstrates your ignorance, it says nothing about the universe or the validity of well-tested physical theories.

## Re:It will be proved wrong! (Score:2)

If you think if the fact that you have a bunch of differnt rules, some apply here, some apply there, nothing really works all of the time.Actually, General Relativity works all the time*. It's just that in the case of uniform motion, it's easier to use Special Relativity (which is just a subset of General). And, at low speeds, Newtonian mechanics is much easier than even Special Relativity.

And its great to wonder and explore, but maybe we should focus more on other problems?I hardly think the relatively (heh, heh) tiny amount of time, money, and thought put into this experiment would make a dent in any of the world's "real" problems. Besides, what are the scientists going to do, release a paper on how people should be decent to each other? That's been done before on several occasions by non-scientists, and the results have been arguably less than satisfactory. One of those "papers" has been used to justify 9/11, another was used to justify the Spanish Inquisition**.

* - except on very small scales where Quantum Mechanics gets invovled. Maybe someday this will read "String Theory (or the like) works everywhere, it's just that it's easier to use Relativity on big stuff and Quantum on small stuff and only use String to figure out singularities"

** - yes, I know the motivations behind these acts aren't entirely (or perhaps at all) religious. The point is that the books don't work to make their readers decent to each other.

## Re:It will be proved wrong! (Score:2)

## Re:It will be proved wrong! (Score:2)

#1 sign of a crackpot: they "know" what science will show in the future.The logic of this is very simple:

## Re:It will be proved wrong! (Score:2)

"Do satellites contract"? From the point of view of an observer, their dimensions appear to contract along the relative direction of travel. The satellite itself detects no such contraction in itself, although it detects such contraction in you.

"Does the network of them contract?" It depends on the relationship of the observer to the network. See my answer re the train example. The answer will be the same as for a single satellite, i.e. contraction along the direction of travel relative to the observer, if the entire network is moving toward or away from an observer. If the observer is being orbited by a network of high speed satellites, then as I've pointed out for the train example, it's easy to see that there can be no contraction of the radius. So where's the problem?

"Is it visible in principle?" Certainly. All of these phenomena are visible, repeatable, verifiable, and theoretically consistent. They have been observed and verified in various ways. The problem is that to see obvious dilation effects that don't require very sensitive equipment (like atomic clocks) to measure, you need objects travelling close to light speed, which is rather difficult to arrange. Nevertheless, verification of the theory has been successfully performed in all sorts of ways.

## Re:It will be proved wrong! (Score:2)

But NEVER a contraction has been observedGiven that this is because we haven't been able to construct a suitable experiment, what do you conclude from that?

Given the nature of the theory (which as I have pointed out, can be derived by a high school student), the fact that this one aspect hasn't been experimentally verified doesn't detract from the theory.

If the theory is wrong, then you should be able to come up with a thought experiment that challenges it. The circular train/satellite network is a nice try, but it doesn't succeed. So where does that leave you?

## Re:It will be proved wrong! (Score:2)

The conclusion, that there is no contraction (observable) is enough. It's against SR.If you expect contraction of the radius, it simply means you don't understand SR. It's hard to refute something you don't understand. How could the radius possibly contract, when there's no motion in that direction?

If you believe the radius must contract because of contraction of the length of the ring, you need to consider the effect of constant changes in direction, i.e. the effects of acceleration. You seem to be trying to apply SR in a single step to the system as a whole, completely ignoring the effects of the construction of the example. No wonder your results seem inconsistent!

For example, how are you accounting for the fact that at different points along the track, train cars or satellites are moving in *opposite directions*? Oh, you're not accounting for it at all? Bit of a problem, don't you think?

Do you think, that there IS observable contraction:- in this case?I'd have to do the math to figure out exactly what would and wouldn't be observable in this case. In general, I would expect observable effects, but certainly not to the same degree as the noncircular case. As has been pointed out, including by this page [bucknell.edu], general relativity has to be considered because of the constant and extremely high acceleration in this example, and this has a significant effect.

in the case of noncircular train?Yes, contraction in this case would be observable, because the motion is in a constant direction and thus the SR effect is not affected by continuous changes in direction; which means that GR can be ignored, incidentally making the calculation much easier.

I encourage you to try to work through the derivation of the Lorentz transformation, even in just one dimension. It will be much easier to understand all this once you've assimilated that.

## Re:It will be proved wrong! (Score:2)

I don't! Nor the contraction of the perimeter.So which of the postulates Einstein used are you rejecting: the constant speed of light, or constant physical laws in all inertial frames? Or have you found a flaw in the derivation? Otherwise, you're just blowing smoke.

You expect what?I expect the dimensions of the observation to be based on the spacetime path that light from the observed object follows to reach the observer. In the case of an object undergoing orbital acceleration, I expect contractions on a local scale, but the effects of GR are difficult to intuit. However, overall it's easy to see the cancellation effect, as I've pointed out.

But if we move out to the Galaxy dimensions - there is almost no acceleration.You're either orbiting, or you're not. If you're orbiting, acceleration has to be large enough to support that. There's a ratio there that can be expressed as an invariant.

How do you know, that you are not observing a circular case, watching ONE car?Playing with limits doesn't affect the overall equation. Any local effects would not affect the overall system, because of the factors I've already described. I'd be happy to accept a research grant to work this out in detail - it ought to be a straightforward calculation. A computer simulation of what an observer would sees ought to be quite possible.

It is ALWAYS some acceleration involved. The gravitation of a distant star - whatever. Do you suggest, that SR never holds?Orbital motion implies a special set of circumstances in which different factors cancel out. I'd expect a difference between the orbital case and a non-orbital case. The orbital case involves accelerations significant to the calculation, by definition. In non-orbital scenarios, the relative effect of acceleration would be less.

## Re:It will be proved wrong! (Score:2)

## Re:It will be proved wrong! (Score:2)

Take a curved surface, let's say the size of Earth. Now, look at it from the perspective of two-dimensional beings on its surface. Draw a circle centered on the north pole with a circumference of 1,000 miles. Now measure the radius of the circle - on the curved surface of the Earth - and you will get a value slightly greater than the ~159 miles you would expect, because you aren't measuring on a straight line. The circumference is less than 2pi*radius.

Incidentally, if a degree is defined as 1/360 of a circle, you still see 360 degrees. Keep in mind, you have to bend your protractor to measure an angle on the curved surface.

Another interesting fact: on a curved surface, the angles of a triangle don't add up to 180 degrees. If you draw a equilateral triangle on the Earth with one points at the North Pole, and two points on the equator, so that each side is 1/4 the circumference of the Earth, all three angles will be right angles, and the sum is 270 degrees.

This is exactly what happens with the circular train. The circular motion (which is equivalent to acceleration or gravity) curves space in such a way that the track is non-Euclidean and the circumference does not equal 2pi radius.

## Re:It will be proved wrong! (Score:2)

The problem arises, when all the wagons (let say 360 of them) are so contracted, that they _all together_ need only 1/100 of second to pass - instead 1/7.5!You can't measure the length of the 'wagon' by the time it takes to go by when it's going by at relativistic speeds, because time and space are getting mixed up. Events which appear simultaneous to you do not from the perspective of the train, and vice-versa.

Nor me, nor the lions don't see any weird geometry around us - which had to save the SR.And I don't see a train circling the equator at near-light speed. This is why relativity is hard to fathom - it doesn't match our normal experiences, because we don't generally see anything moving more than 0.001% of light speed. Nevertheless, every experiment ever performed to test relativity has indicated that these effects do occur.

There's a lot of great reference material on relativity on the web. You will probably learn a lot more searching it out than you will reading these replies on slashdot.

## Re:It will be proved wrong! (Score:2)

Of course I can. I see no reason why not. Why? Who says, I can't?Erm, Einstein, for one. You're forgetting that time and space have no independent existence in relativity, and some things just don't work out the way you'd like. For instance, when your car is driving at 100 mph, the speed of light from your headlights is still c, not c + 100mph. Both you in the car and the hitchhiker on the side of the road will measure the same speed c for your headlights. This is extremely counter-intuitive, but it has been experimentally proven (Michelson-Morley experiment, measurement of speed of light is independent of speed of earth's rotation + orbit around sun).

Of course we do. Distant galaxies travel with 0.3 c or more.But we don't interact with distant galaxies in a way that makes relativistic effects obvious. Besides, the expansion of the universe is in the GR realm, so the effects are a bit more involved than just time-dilation and shortening. Incidentally, the relativistic equation for redshift is different from the classical equation, and this provides yet another proof of relativity.

Which one indicated the shrinking?Plenty of particle accelerator experiments have shown reactions occuring over larger distances than they could if the particles were at rest, indicating that distances are different in the moving particle's frame of reference.

Since you are obviously quite interested in the subject, you ought to do some more research and reading. If you'd like, post some questions on sci.physics.relativity newsgroup - the folks frequenting that newsgroup are quite a bit more knowledgeable on the subject than I am.

## Re:The General Theory is Wrong (Score:2)

As I recall, it was proven wrong by the detection and acknowledged existence of Tachyon particles travelling at over the speed of light when detected...References? I somehow missed the scientific article on the detection of tachyons.

If you really want to test the theory, build an ion engined probe with small nuclear battery and atomic clock, transmitters, etc... and enough fule to acclerate to relativistic speeds.Oh, I'd love to, but I have to mow the lawn tomorrow, maybe I'll get to it next week. Um, don't you think if we could do that, we'd find something better to do with it than test relativity... say, fly to Mars?

The theory has to be wrong because we have observed multiple instances of the violation of conservation of energy and the hard and fast rules around C speeds.And I assume you have some references here as well?

## Re:The General Theory is Wrong (Score:2)

It's a common misconception that Einstein's theories prohibit FTL travel - they do not.Technically, no they don't. Practically, they might, because the transformation of time/space coordinates screws up causality. For example, we send a spaceship from Earth to Neptune faster than light. It leaves Earth at 1:00pm and arrives at Neptune at 1:06pm (Central Daylight Time, before you complain about time zones - we're launching from my backyard). In the frame of reference of an alien spacecraft moving past Earth at a high sublight speed, 1:06pm at Neptune occurs earlier than 1:00pm at Earth. This is because of the transformation of space-time coordinates. If the aliens have to wait for light from Neptune to get to them to see it, we're OK, but if they have some kind of subspace sensors that can see the event as it happens (in their reference frame), they can prevent the launch after they've seen the arrival at Neptune. Oops.

A good space-time diagram is worth a thousand words, so look here [purdue.edu] for more. The example he uses is different, but the idea is the same.

His site also has an explanation [purdue.edu] of how FTL might work without these paradoxes. It hypothesizes a special reference frame (subspace, of course) for objects traveling faster than light. This reference frame would match that of nearby massive objects (planets, stars, etc). In this model, the information that our ship had arrived at Neptune could not go backward in time relative to our solar system, so the aliens could not know the ship arrived at Neptune in time to stop it.

Incidentally, this means that a ship moving at sublight speed through a solar system would be able to use its subspace sensors to see things that have just happened in our reference frame, but are actually in the future in theirs. But, they can't do anything with the information to prevent the event before it happens.

Unfortunately, we have no way to verify any of this sort of speculation, and probably won't for the foreseeable future. It's clear that if relativity as we understand it is correct, then FTL travel can violate causality. Whether this means it's impossible, no one knows.

## Re:Relativity vs. Quantum Mechanics (Score:5, Informative)

_Special_ relativity and quantum mechanics have no trouble getting along. In fact, the so-called Standard Model of particle physics, based on relativistic quantum physics, is an enormously successful theory. The trouble lies in getting relativistic gravity (i.e., _general_ relativity) to play nice with quantum mechanics. This is where string theory comes in.

The good thing about string theory is that it allows gravity and quantum mechanics to get along. The bad thing about string theory is that there is absolutely _no_ experimental evidence for it, and there are almost no possible tests of it that could be conducted in the near future. Lorentz violation is a major exception:

The afore-mentioned Standard Model obeys a certain symmetry called ``Lorentz symmetry'', which lies at the heart of special relativity. However, string theory allows Lorentz symmetry to be broken. Thus, any experimental detection of Lorentz violation could be a great signature of string theory, and, maybe, quantum gravity. Moreover, there exist current experiments that are capable of detecting Lorentz violation to a very high precision.

To summarize: We are studying Lorentz violation because (1) It is a possible signature of quantum gravity, and (2) It can presently be studied to very high precision.

Chuck

## Re:Relativity vs. Quantum Mechanics (Score:3, Insightful)

Remember, none of this has totaly been proven.But remember,

nothingis even totally proven in science. The best we ever have is a theory that hasn't been proven wrong yet.