Can someone explain Einstein's relativity theory?

[JesseM]

What ever gave you the idea that I'm trying to grasp what SR is all about? I already know what SR is all about. I'm simply pointing out the fact that time must necessarily flow at different rates for different inertial frames. I don't think that SR denies this, on the contrary, the twin brothers paradox confirms it! If this wasn't true then time dilation would indeed just be an illusion and not at all objective. But it is objective.

Time does flow differently in different inertial frames, in the sense that within each frame, clocks in the other frame are running slower. However, there is no objective truth about whose clocks are really running slower. Do you disagree with this last part?

 

[russ_watters]

What ever gave you the idea that I'm trying to grasp what SR is all about? I already know what SR is all about.

No offense, but the part you keep saying you want to ignore is the key part of the theory - if you don't grasp that by ignoring it you aren't addressing SR, you don't grasp SR.

I'm simply pointing out the fact that time must necessarily flow at different rates for different inertial frames. I don't think that SR denies this, on the contrary, the twin brothers paradox confirms it! If this wasn't true then time dilation would indeed just be an illusion and not at all objective. But it is objective.

The point of the twins paradox is it confirms the fact that SR is symmetrical - the twins don't experience the same passage of time because their paths are not symmetrical.

The fact that either twin can be picked, randomly, to accelerate to meet the other twin and the results will be the same (ie, the twin chosen to experience the acceleration will be the one showing less time at the end) shows that SR is, indeed, consistent and the laws of the universe are universal.

 

[NeutronStar]

Time does flow differently in different inertial frames, in the sense that within each frame, clocks in the other frame are running slower. However, there is no objective truth about whose clocks are really running slower. Do you disagree with this last part?

Yes, I disagree with your statement; "...there is no objective truth about whose clocks are really running slower".

I think it's quite obvious when the twins get back together that the younger twin was the one whose clock ran slower. There can be no denial of this since that is the twin that is younger upon return. What else would cause this effect if it wasn't objectively true? Really.

 

[RandallB]

Forget about all the gory details. Look at it this way. In a lab there are two black boxes. One is marked A and the other marked B. You put objects into box A and bring them back out again and there is no apparent change. Put them into box B and bring them back out again and apparently they haven't aged as much. What's the conclusion? The physics in box B is acting differently from the physics in box A.

It's pretty simple and straight-forward if you ask me.

Sure that is simple; but don't leave out the most important little detail.
When you opened box B, the twin Clock you put in there WAS NOT THERE!
It is now miles, Km's or Light years away and still speeding away from your lab.
At best you might see a series of clocks chasing after it. You will of course see time directly viewed on those clocks as running faster than your lab clock. Yes I said FASTER - but don't concern yourself with that until your ready to work with the words synchronized and simultaneity.
The only way you can see the original twin clock again is if someone somewhere moves it over to box C. So when you open box C (yes it's clocks zipping by in the other direction appear to be running fast), when you can extract the returning twin clock it will be well behind the lab clock because the rate of time in both box B and C is slow as measured by your lab clock.

Now to confirm that speed makes all the difference put an extra lab clock in box D where it will travel after the clock that continues in box B at 3 times the speed in box B to catch up with it. (Note: vB + vB + vB = 3vB is not correct) When it catches up it will be even more behind the time on the traveling clock than the returning clock was behind the lab clock.

This is all true only because SR and "the laws of physics and the actual physics" is the same in every reference frame.

Note: The time dilation your looking for has nothing to do with doppler effect or acceleration. When working SR it is best to use 'Black Hole' accelerations that only take a very short time to get to the speed you want. In GR the time change on the accelerated clock is ZERO for just a second, which you can discard. thus you can consider the time in the frame your measuring based only on speed.

Work those out and let us know if ready to look at simultaneity.

 

[NeutronStar]

The fact that either twin can be picked, randomly, to accelerate to meet the other twin and the results will be the same.

I'm sorry russ, but what you've said here simply isn't true. If you pick the twin in frame A to accelerate back to meet the other twin, then twin A would need to undergo more acceleration, and travel at a greater speed than the other twin in order to catch up to the other twin.

So there is an absolute difference in which twin you pick to accelerate.

It's not totally symmetric as you claim.

 

[russ_watters]

Yes, I disagree with your statement; "...there is no objective truth about whose clocks are really running slower".

I think it's quite obvious when the twins get back together that the younger twin was the one whose clock ran slower. There can be no denial of this since that is the twin that is younger upon return. What else would cause this effect if it wasn't objectively true? Really.

This is a wording issue: before they are brought back together and the situation is symmetrical, neither can be said to be running faster or slower. Once they are brought back together, you can say one went faster/slower. But that's not the issue here: the issue is what that implies about the laws of physics. The fact that the outcome is not the same does not imply the laws of physics aren't consistent, because the conditions of each twin's journey aren't the same. More on that in a sec...

Lemme try a different tack here: it seems you agree with everything except the conclusion. All of it is here:

The twin that ages less may have undergone an acceleration, however, his or her clock continues to run more slowly relative to the non-accelerated sibling even after the acceleration has ceased. Therefore, the twin who has undergone a change in an inertial frame has also undergone a change in his or her fundamental laws of physics

First off, you seem hung-up on the part about acceleration (yet you say frame of reference is unimportant?) - the acceleration is what puts them in different frames.

You also seem hung-up on the outcome (and this is probably more important): you're saying that the fact that the clocks show different times means the laws of physics are different. But that's wrong. Lemme give an example: you have two identical rocks. You throw one and your little brother throws the other. But they don't move the same distance. Why not? The rocks are identical, the laws of physics are identical - why wouldn't they go the same distance? Well, you're stronger than your little brother - you pushed harder! So too with the twins paradox: the laws of physics are the same, its just that you're doing different things to the two clocks: one is being accelerated, the other isn't. What's more, after the rocks leave your hand, they are no longer accelerating - shouldn't they then go the same distance (just like the twins who are not accelerating...)? No, the acceleration is what makes their frames different and what makes them travel different distances.

This seems self-evident, but perhaps its a symptom of another issue: what you are saying implies the desire for Time to be an absolute like C. If the laws of physics said time is abslute, then yes, certainly there'd be a contradction. But the laws of physics don't say that.

 

[Phobos]

I've read a piece on his theory and I'm having a little difficulty understanding it. I've used the famous E = MC^2 in calculations before but I want to have more understanding of the theory behind it.

Any info would be great.

The Teaching Company's "Great Lectures Series" (college lectures on tape) has a helpful one introducing Relativity (geared toward non-scientists).

no, I'm not being paid by them to say that

They're expensive to buy but your local library may have it.

 

[JesseM]

Yes, I disagree with your statement; "...there is no objective truth about whose clocks are really running slower".

I think it's quite obvious when the twins get back together that the younger twin was the one whose clock ran slower. There can be no denial of this since that is the twin that is younger upon return. What else would cause this effect if it wasn't objectively true? Really.

I'm not asking about the twin, since he switched rest frames--I'm asking about clocks in the frames themselves. If in each frame the twin is traveling alongside a clock that does not accelerate, then obviously that clock will be ticking at the same rate as his clock while he's in that frame--if you conclude that the traveling twin's clock was objectively ticking slower than the Earth twin's, would you also say that this clock moving with him while he was in that rest frame was objectively ticking slower than a clock on earth?

 

[JesseM]

The fact that either twin can be picked, randomly, to accelerate to meet the other twin and the results will be the same.

I'm sorry russ, but what you've said here simply isn't true. If you pick the twin in frame A to accelerate back to meet the other twin, then twin A would need to undergo more acceleration, and travel at a greater speed than the other twin in order to catch up to the other twin.

No, the acceleration would be the same, because the velocity difference would be the same in each twin's own previous rest frame. If a twin is traveling away from Earth at 0.6c, then turns around and heads back to Earth at 0.6c, then from the perspective of the frame in which he was at rest during the outbound trip he will be moving at about 0.88c as he returns to Earth (using the equation for addition of velocities give here). Likewise, if the twin is traveling away from the Earth at 0.6c, and then the earth-twin gets in a rocket and accelerates until he is approaching the traveling twin at 0.6c, then in the Earth's frame the earth-twin will now be going at about 0.88c. The situation is completely symmetrical. So Russ is right--the choice of which twin to accelerate so they will meet again can be made at random, and whichever one accelerates, he will be the one whose clock is behind when they meet.

 

[jcsd]

If the worldlines of two observers are coincident at events A and B which one of them experinced the longest time between the two events is depednent on the 'length' of their worldlines between the two events. The maximal proper time between two events is experinced by an observer represented by a staright worldline (i.e. an inertial observer).

 

[Janus]

What ever gave you the idea that I'm trying to grasp what SR is all about? I already know what SR is all about. I'm simply pointing out the fact that time must necessarily flow at different rates for different inertial frames. I don't think that SR denies this, on the contrary, the twin brothers paradox confirms it! If this wasn't true then time dilation would indeed just be an illusion and not at all objective. But it is objective.

The point is that you don't grasp SR. All your arguments are more in line with what Lorentzian Relativity says. In Lorentzian Relativity, time dilation is caused by motion through the aether, and thus the Clock that has the highest relative velocity with respect to the aether is the clock that runs slower. The aether provides an absolute frame of rest by which all motion could be judged. In LR is is possible to say that one of the clocks objectively runs slower than the other.

In SR, this is not the case. There is no absolute frame from which motion can be judged. And there is no way to say objectively (in a way that all frames in relative motion to each other would agree), which clock actually runs slower than the other. This is not to say that they will not agree which clock will read less time when brought back together, but they will disagree as to why this is the case. And each frame's explanation as to what caused the difference is equally valid.

 

[NeutronStar]

The point is that you don't grasp SR. All your arguments are more in line with what Lorentzian Relativity says. In Lorentzian Relativity, time dilation is caused by motion through the aether, and thus the Clock that has the highest relative velocity with respect to the aether is the clock that runs slower. The aether provides an absolute frame of rest by which all motion could be judged. In LR is is possible to say that one of the clocks objectively runs slower than the other.

In SR, this is not the case. There is no absolute frame from which motion can be judged. And there is no way to say objectively (in a way that all frames in relative motion to each other would agree), which clock actually runs slower than the other. This is not to say that they will not agree which clock will read less time when brought back together, but they will disagree as to why this is the case. And each frame's explanation as to what caused the difference is equally valid.

You may very well be right. Even though I've taken several courses on SR I've probably always viewed the problems intuitively from Lorentz's point of view.

Why isn't LR taught in college classrooms? Is there anything inherently wrong with LR, or is it just not taught because of the principle of Occam's Razor? Personally, I have never agreed with Occam's Razor. If something can be comprehended intuitively by including an idea that may not be physically detectable I have no problem with that.

Heck, scientists today are postulating the existence of strings to explain particle physics. Yet it is believed that we may never be able to detect the existence of a string. Ironically, if string theory makes a prediction that can be tested in the lab then everyone will start believing in strings.

So what if Einstein had never existed, and instead Lorentz proposed his relativistic aether. Then when his predictions came true (which would have been the same predictions as SR) everyone would start believing in his aether.

I think the whole scientific community needs to start getting their act together.

Either follow the lead of Occam or not. I wish they'd make up there minds. They just aren't being consistent. With SR they hold to Occam's Razor. But when it comes to String Theory they toss Occam's Razor out the window.

 

[ohwilleke]

Why isn't LR taught in college classrooms?

Because it is very likely wrong.

 

[NeutronStar]

Because it is very likely wrong.

Well, just for the record, John Stewart Bell doesn't agree with you for one. The following is from a book called The Ghost in the Atom by Cambridge press, ISBN 0-521-30790-2. The book is a collection of interviews with famous scientists on various topics. The following is an excerpt from an interview with John Stewart Bell:

Interviewer:

"Of course the theory of relativity has a tremendous amount of experimental support, and it's hard to imagine that we can actually go back to a pre-Einstein position without contradicting some of this experimental support. Do you think it's actually possible?"

John Bell:

"Well, what is not sufficiently emphasized in textbooks, in my opinion, is that the pre-Einstein position of Lorentz and Poincare, Larmor and Fitzgerald was perfectly coherent, and is not inconsistent with relativity theory. The idea that there is an aether, and these Fitzgerald contractions and Larmor dilations occur, and that as a result the instruments do not detect motion through the aether - that is a perfectly coherent point of view"

Interviewer:

"And it was abandon on the grounds of elegance?"

John Bell:

"Well, on the grounds of philosophy; that what is unobservable does not exist. And also on the grounds of simplicity, because Einstein found that the theory was both more elegant and simpler when we left out the idea of an aether. I think that the idea of the aether should be taught to students as a pedagogical device, because I find that there are lots of problems which are solved more easily by imagining the existence of an aether,…."

These are the words of John Stewart Bell, not me.

Although, I obviously agree with him.

 

[NeutronStar]

Apology to OsiriS^

I would like to apologize to OsiriS^ for contaminating his thread with my controversial view on SR. That wasn't my original intent. My original intent was to simply mention that SR is based on two very simple postulates. Everything follows from those two postulates. However, as you can see from the controversy everyone doesn't necessarily follow the same logic.

In other words, you may or may not find Einstein's approach to be the one of your choosing. I do believe that it is healthy to know that other choices are possible that are still consistent with the original hypothesis.

As someone posted earlier, "The theory is the postulates". Many people do feel that way. However, if that is indeed the case then any legitimate conclusions that you can make while maintaining the postulates of relativity, that too, is relativity theory. At least this is true if you believe that, "a theory is its postulates".

The Teaching Company's "Great Lectures Series" (college lectures on tape) has a helpful one introducing Relativity (geared toward non-scientists).

no, I'm not being paid by them to say that

They're expensive to buy but your local library may have it.

I actually purchased that video lecture and then returned for a different course. The lecture was technically correct alright. But I found it very hard to watch because of the annoying style of the lecturer. He seemed to be trying to argue the ideas by repeating trivial things over and over again as if he felt that his audience simply wouldn't believe it. At least that was my perception. Like I say, he was technically correct. But his lecture style got a huge thumbs down from me.

Just to add a positive note, I have since then bought several other video lectures from The Teaching Company. They aren't on the topic of relativity, but they are much better lectures. The professors are active in their fields, and quite popular having been on other programs like NOVA. They are also involved with popular scientific discoveries.

Some of the video lectures that I am quite happy with and highly recommend are,..

http://www.teach12.com/store/course.asp?id=178&d=Understanding+the+Universe%3A+Astronomy+2003%2FUnderstanding+the+Universe%3A+Astronomy+%28Set%29"

I found this lecturer, Alex Filippenko, to be very positive, upbeat, and knowledgeable in his field. Big thumbs up! This video set contains 56 lecture hours.

http://www.teach12.com/store/course.asp?id=1247&d=Particle+Physics+for+Non%2DPhysicists%3A+A+Tour+of+the+Microcosmos"

This follow dances around a lot while lecturing and waves his hands continuously while talking. He's a riot to watch in fast forward!

But on a serious note, he really knows his particle physics. He covers it all including the Higgs particle. I'd call it a must-see video. His excitement and love of particle physics really shows. I've already watched that video three times and learn something new every time. His lecture style is very efficient and he covers a lot of material. There are 24 lecture hours in this course.

http://www.teach12.com/store/course.asp?id=1423&d=Joy+of+Thinking%3A+The+Beauty+and+Power+of+Classical+Mathematical+Ideas"

There are two mathematicians that teach this course. What can I say? Pure mathematicians are nuts! These guys are no exception! They don't fool around, but some of these abstract ideas are pretty far-fetched. They also make fairly efficient use of the lecture time (for the most part). I wouldn't call this one a "must see", but I do give it a thumbs up.

Don't expect to see any heavy equations. This is aimed at the general public. Its more about how to think mathematically than about the technicalities of mathematics. I found it interesting and thought provoking. And perhaps most important of all I found it enjoyable to watch.

I really wish I could give that Relativity course a thumbs up. But I just can't. Like I say, the course material is technically correct if you can stand the lecture style. But I found that trying to watch that guy was more than I could bear. He just sounded more like he was arguing his points rather than teaching them from an excited point of view. I actually asked the teaching company to let me know if they ever redo that lecture with someone like Pollock or Fillipenko teaching it. Then I'd give it a thumbs up I'm sure! The course material was great. It just wasn't fun to watch. But you can always watch it and then return it for another lecture.

Or maybe it was just me. You might enjoy it. Who knows?

 

[NeutronStar]

Getting back to basics,...

I've read a piece on his theory and I'm having a little difficulty understanding it. I've used the famous E = MC^2 in calculations before but I want to have more understanding of the theory behind it.

Any info would be great.

Here's a link to contribute to the original purpose of the thread,...

http://www.karlscalculus.org/einstein.html"

 

[jcsd]

The problem with Lorentz ether theory is that it's such an ugly ad hoc theory that once you are sufficently skilled in relativity there is no way that you would want to use it. From what I understand LET originally because of the singularity in the equations when v = c it postulated that the Lonretz transformations breakdown when v is approimately equal to c (in special relativity the singularity is simply explained as the fact that light has no frame of reference) and I'm not entirely sure that all the relativstic result can be derived from the original theory without essentially 'tacking them on' to LET.

 

[NeutronStar]

The problem with Lorentz ether theory is that it's such an ugly ad hoc theory that once you are sufficently skilled in relativity there is no way that you would want to use it.

I would agree with you from a purely mathematical point of view. However, I prefer a little meat with my potatoes when it comes to ontology.

What you have said about comparing Lorentz's aether theory the with Einstein's relativity could just as easily be said about comparing Lagrangian dynamics with Newtonian mechanics.

Lagrangian dynamics considers only the energy of systems and so makes the mathematics of dynamics much easier. However, that doesn't mean that concepts like force, velocity, acceleration, and momentum don't exist. In other words, we don't abandon the underlying concepts of Newtonian mechanics just because Lagrangian methods are mathematically simpler.

In a similar way we don't need to abandon the concept of an aether altogether in order to enjoy the mathematical simplicity of SR. I'm not suggesting that the mathematical tricks of SR should be abandoned completely. I'm merely suggesting that from an intuitive point of view tossing out the concept of an aether altogether is not necessarily the greatest idea. It's also not necessary.

It appears that the aether theory is sneaking back into physics via quantum fluctuations. We are discovering that there is no such thing as a complete vacuum anywhere in the universe. So the idea of an aether may very well be ontologically correct, and possibly even be detectable on the quantum level. I personally have always believed that the universe is ontologically aetheral based so the idea of officially rejecting an aether altogether does not sit well with me.

I think that one of the biggest setbacks to aether theories is the classical notion that it somehow has to be absolute in some way. In other words, when people think of an aether they often think in terms of a Newtonian absolute space. The existence of that type of aether has been disproved. To think that way would be like thinking in terms of a Ptolemaic astronomy.

A relativistic aether, on the other hand, is not so confining. A relativistic aether is malleable and changing with the expansion of the universe, it's not an absolute space, it's more like the dynamic fabric of an expanding universe.

In any case, I just wish that this idea of a relativistic aether would have been better explored by young bright university students during the last few decades. Unfortunately, when the classical aether was disproved that kind of put a lid on every mention of any type of aether theory. Personally I think that was a bad thing.

But just to recap,... I'm not suggesting that we toss out the mathematics of SR. That is certainly a valid mathematical framework just like Lagrangian dynamics is a valid mathematical framework. But just because Lagrangian mathematics works doesn't mean that we should toss out all of the fundamental Newtonian concepts that preceded it. The same goes for SR. Just because SR works doesn't mean that there can't be an aether description beneath it.

 

[jcsd]

The problem is I really don't see any advanatge at all from teaching LET and you might as (quantum fluctuations are unrelated to any concept of ether), but I see plenty of adavnatges in teaching special relativity and to avoid confusion it is much better to be consitent and to use common conventions.

 

[NeutronStar]

The problem is I really don't see any advanatge at all from teaching LET,…

Well, actually I agree with you that colleges shouldn't actually teach the aetheral theory in all its gory mathematical detail. Heaven forbid! Modern pedagogical thinking seems to be aimed at the concept that torturing students by making them work out every conceivable mathematical relationship is "teaching". I have a real bone to pick with that particular pedagogical method. But that's another story.

I'm not suggesting that the mathematics of an aetheral theory be taught in all its gory detail. All I'm suggesting, like John Stewart Bell had suggested in the interview that I posted earlier, is that the basic notion of a relativistic aetheral theory should be included in courses on Modern Physics. At least to the point of making sure that the students are aware that it is still a viable option without contradicting the postulates of SR.

(quantum fluctuations are unrelated to any concept of ether)

I strongly disagree with this statement,…

Let's see,… How can I show how strongly I disagree with it?

How about,…

 

[Hurkyl]

What you have said about comparing Lorentz's aether theory the with Einstein's relativity could just as easily be said about comparing Lagrangian dynamics with Newtonian mechanics.

It would be nice if they were analogous -- however, it seems the major impetus for believing an aether theory is precisely because one doesn't want to believe SR. The same is not true for your example of Lagrangian and Newtonian dynamics.

I'm merely suggesting that from an intuitive point of view tossing out the concept of an aether altogether is not necessarily the greatest idea. It's also not necessary.

I disagree. Virtually every person I've ever seen touting aether theories had a very poor grasp of the things that let you take advantage of the mathematics of SR. For instance, they tend not to grasp relativity of simultaneity. If you don't grasp that, then you have no chance of properly analyzing a problem in different frames.

The evidence suggests that adopting this "intuitive" (ha!) point of view seems to increase one's difficulty doing problems, rather than decrease it.


Quite frankly, I don't see how

Here is how I'm going to do measurements. It turns out that the equations of physics will be valid for any inertial observer who does measurements my way.

is any less intuitive than

I'm not going to tell you how I do measurements, but they're affected by the aether. I'm not going to tell you anything about the aether, except that it affects measurements. Oh, and it all conspires to make that SR guy over there think he's right.

 

[NewLocality]

Hi everyone

Can I invite you to visit: -
www.electrodynamics-of-special-relativity.com[/URL]

Let me know what you think.

NL

 

[NeutronStar]

It would be nice if they were analogous -- however, it seems the major impetus for believing an aether theory is precisely because one doesn't want to believe SR. The same is not true for your example of Lagrangian and Newtonian dynamics.

I can assure you that my reasons for believing in an aether have absolutely nothing to do with not wanting to believe in SR. What exactly does SR offer that could or couldn't be believed anyway? I mean, it really doesn't offer a mechanism for time dilation. There's nothing to believe or disbelieve. It's just a mathematical trick.

Besides, any aether theory that maintains the postulates of relativity is going to also predict all of the same conclusions. The only difference is that it will also offer a physical mechanism for how these phenomenon arise.

I mean seriously. You can use SR to make calculations of how things will behave. But can you use SR to explain the actual physical mechanism of time dilation? I think not. SR doesn't explain the mechanism of time dilation, it simple says that it must occur. However, an aether theory, coupled with some concepts in quantum mechanics, can actually offer an explanation of the physical mechanism of time dilation. To me, that is much more attractive than just doing engineering calculations using SR.

 

[russ_watters]

I can assure you that my reasons for believing in an aether have absolutely nothing to do with not wanting to believe in SR. What exactly does SR offer that could or couldn't be believed anyway? I mean, it really doesn't offer a mechanism for time dilation. There's nothing to believe or disbelieve. It's just a mathematical trick.

Wanting to believe that time dilation is "just a mathematical trick" (ie, not physically real), is, in my experience the primary reason ether theorists don't want to believe relativity (and length contraction second). They want to believe that time and space are absolute and SR takes that away. Trouble is, it can't be wished away by getting rid of Relativity: its data - its a real phenomena that needs to be dealt with via theory.

However, an aether theory, coupled with some concepts in quantum mechanics, can actually offer an explanation of the physical mechanism of time dilation.

So far I have seen no evidence of that: most ether theory is two steps behind - still trying to match observations with the desire for an ether.

 

[NeutronStar]

Wanting to believe that time dilation is "just a mathematical trick" (ie, not physically real),...

You obviously haven't been reading my posts in this thread. I completely accept the reality of time dilation. I have no problem accepting the conclusion of SR. I'm simply not satisfied that SR has given any physical explanations for the mechanisms of what physically causes these things to happen.

here's the stance of SR,…

1. Accept these postulates
2. You must accept these conclusions.

Period amen! SR doesn't offer any mechanisms for why they occur. In a very real sense this isn't much different from Newton's law of gravity that was also a mathematical description, but didn't offer an explanation for a mechanism.

Perhaps I shouldn't have called it a mathematical trick. Perhaps I should simply call it a mathematical description rather than an ontological explanation.

I think it's ironic that Einstein was so bent on explaining Newton's gravity in intuitive terms yet he didn't seem to be concerned about explaining his very own SR in the same way.

However, an aether theory, coupled with some concepts in quantum mechanics, can actually offer an explanation of the physical mechanism of time dilation.

So far I have seen no evidence of that: most ether theory is two steps behind - still trying to match observations with the desire for an ether.

First, when you refer to most aether theories I fear that you are including many classical aether theories which obviously aren't going to work. Classical aether theories are as dead as perpetual motion machines.

Secondly, far beyond the scope of this thread, there is the topic of Quantum Mechanics. Just like there is the aether theory controversy surrounding SR, there are also controversial concepts surrounding QM.

For example, do you believe that all of time and space are quantized? Or do you believe that only bound systems are quantized and space and time are a continuum in general. Just like the aether theory in SR, these two different schools of thought associated with QM have not been fully resolved either.

Just for the record, I am of the school that all of time and space is indeed quantized. Only this school of thought is useful for explaining time dilation (from my point of view). If you believe that time and space are continuums then believing in an aether probably isn't going to be of any use to you.

 

[selfAdjoint]

Einstein derived his SR in operational terms. He showed why the Lorentz transforms result from the assumption of Galilean relativity and the invariance of light speed. He showed this by exhibiting observers trying to coordinate their measurements with clocks and measuring sticks.

Source invariance of light speed in what is unexplained. The postulates are well motivated.

 

[NeutronStar]

Einstein derived his SR in operational terms. He showed why the Lorentz transforms result from the assumption of Galilean relativity and the invariance of light speed. He showed this by exhibiting observers trying to coordinate their measurements with clocks and measuring sticks.

Source invariance of light speed in what is unexplained. The postulates are well motivated.

So in other words, you're agreeing with me.

Special Relativity is basically the following:

1. If you accept these postulates.
2. Then you must accept these conclusions.

I accept both!

So in a sense I accept SR.

But at the same time I'd like to have a deeper explanation dog gone it!

 

[JesseM]

You obviously haven't been reading my posts in this thread. I completely accept the reality of time dilation. I have no problem accepting the conclusion of SR. I'm simply not satisfied that SR has given any physical explanations for the mechanisms of what physically causes these things to happen.

here's the stance of SR,…

1. Accept these postulates
2. You must accept these conclusions.

Period amen! SR doesn't offer any mechanisms for why they occur. In a very real sense this isn't much different from Newton's law of gravity that was also a mathematical description, but didn't offer an explanation for a mechanism.

Modern physicists don't really believe that "mechanisms" are important any more. Any mathematical rule we can describe could be a rule that nature uses in her "program". Check out chapter 2 of Feynman's book The Character of Physical Law, "The Relation of Mathematics to Physics", for a good articulation of the way most physicists think about this (also note that internet physics guru John Baez, on his Crackpot Index, awards 10 points 'for arguing that while a current well-established theory predicts phenomena correctly, it doesn't explain "why" they occur, or fails to provide a "mechanism"').

Secondly, far beyond the scope of this thread, there is the topic of Quantum Mechanics. Just like there is the aether theory controversy surrounding SR, there are also controversial concepts surrounding QM.

For example, do you believe that all of time and space are quantized? Or do you believe that only bound systems are quantized and space and time are a continuum in general. Just like the aether theory in SR, these two different schools of thought associated with QM have not been fully resolved either.

Just for the record, I am of the school that all of time and space is indeed quantized. Only this school of thought is useful for explaining time dilation (from my point of view). If you believe that time and space are continuums then believing in an aether probably isn't going to be of any use to you.

All quantum field theories so far have had the property of Lorentz-symmetry, and this is also true of string theory. Loop quantum gravity explicitly says that space and time are quantized, and in this article by LQG expert Lee Smolin, he discusses whether Lorentz-invariance would be preserved:

Instead, the predictions of loop quantum gravity concern the structure of space and spacetime at very short distances. In particular, loop quantum gravity predicts that the smooth picture of spacetime in classical general relativity is actually only a coarse grained approximation to a discrete structure, in which surfaces and regions can have only certain, discrete quantized values of areas and volume[10, 18, 74, 75, 17]. Loop quantum gravity makes specific predictions for the discrete quantum geometry at short distances. Furthermore, these predictions are derived from first principles, hence they are not adjustable. In this way loop quantum gravity is different from previous approaches which postulate some form of discrete structure as a starting point, rather than deriving it as a consequence of the union of quantum theory and general relativity.

It turns out that this has consequences for the question of whether special relativity, and lorentz invariance, is exactly true in nature, or is only an approximation which holds on scales much longer than the Planck scale[28]-[40]. Several recent calculations, done with different methods[36]-[38], yield predictions for modifications to the energy momentum relations for elementary particles. These are of the form,
E^2 = p^2 + M^2 + \alpha l_{Pl}E^3 + \beta l^2{}_{Pl}E^4 + ...

where predictions have been found for the leading coeffcients \alpha, which generally depend on spin and helicity[36]-[38].

This is then an area of disagreement with string theory. Further, these modifications appear to be testable with planned experiments[28, 30, 39, 40]. Hence the different predictions of string theory and loop quantum gravity concerning the fate of lorentz invariance offer a possibility of experimentally distinguishing the theories in the near future.

4 The near term experimental situation

The most important development of the last few years in quantum gravity is the realization that it is now possible to probe Planck scale physics experimentally. Depending on dynamical assumptions there is now good experimental sensitivity to the \alpha terms in (2) for photons, electrons and protons. Increased sensitivity is expected over the next few years from a number of other experiments so that it is not impossible that even if the leading order E^3 terms are absent, it will be possible to put order unity bounds on \beta, the coefficient of the E^4 term.

However it is crucial to mention that to measure \alpha and \beta one has to specify how lorentz invariance is treated in the theory. There are two very different possibilities which must be distinguished.

• Scenario A) The relativity of inertial frames is broken and there exists a preferred frame. In this case the analysis has to be done in that preferred frame. The most likely assumption is that the preferred frame coincides with the rest frame of the cosmic microwave background. In such theories energy and momentum conservation are assumed to remain linear.

• Scenario B) The relativity of inertial frames is preserved, but the lorentz transformations are realized non-linearly when acting on the energy and momentum eigenstates of the theory. Such theories are called modified special relativity or doubly special relativity. Examples are given by some forms of non-commutative geometry, for example, \kappa-Minkowski spacetime[32]. In all such theories energy and momentum conservation become non-linear which, of course, effects the analysis of the experiments. In some, but not all, cases of such theories, the geometry of spacetime becomes non-commutative.

He then lists some experiments which could potentially measure \alpha and \beta by 2010, and concludes:

We may summarize this situation by saying that a theory of quantum gravity that leads to Scenario A) and predicts an energy momentum relation (2) with \alpha order unity is plausibly already ruled out. This is shocking, as it was commonly said just a few years ago that it would be impossible to test any physical hypotheses concerning the Planck scale.

Anyway, you can see that Scenario B) preserves the idea that there is no preferred frame, even though it is discrete.

 

[pervect]

My $.02 on "LR". It's possible to do "LR" correctly and get the same answers as standard relativity theory, in which case it's just an interpretation of special relativity and not a different theory, as it makes the same predictions.

However, because LR focuses on what changes (space and time) rather than what does not change (the Lorentz interval), it is more difficult to get the correct answers with the "LR" approach than the one that is usually taught. This is a good enough reason for not teaching the "LR" approach, in my opinion.

Furthermore, many of the "LR" proponents you see in the newsgroups or on the webpages are seriously confused (probably, in part, due to the fact due to the aforementioned difficulties). They get results that conflict with standard relativity theory. To make matters worse, they don't always seem to realize when their results are different than standard results (even when this is pointed out to them very directly) - probably because they don't understand the standard approach.

The fact that many LR proponents don't realize when they are wrong has to a certain extent "poisoned" the name. There is at least a 50% chance that when someone talks about relativity in terms of "LR" that they are making predictions that are not compatible with standard relativity without realizing it -(or at least without admitting it) - a typical false claim of an LR enthusiast is that the ether can be detected.

 

[NeutronStar]

Modern physicists don't really believe that "mechanisms" are important any more. Any mathematical rule we can describe could be a rule that nature uses in her "program". Check out chapter 2 of Feynman's book The Character of Physical Law, "The Relation of Mathematics to Physics", for a good articulation of the way most physicists think about this

Yes, I know that this is true, and I'm not happy about it.

Just seems to me that physicist are giving up on physics and simply becoming philosophers instead.

(also note that internet physics guru John Baez, on his Crackpot Index, awards 10 points 'for arguing that while a current well-established theory predicts phenomena correctly, it doesn't explain "why" they occur, or fails to provide a "mechanism"').

So why should their be any argument? Whose arguing the other side? In other words who's arguing that science does explain anything. Why don't physicists just respond to the so-called crackpots by saying, "Oh we don't bother trying to explain anything anymore, we've all become nothing more than engineers. There are no physicists left. Physics has died and engineering is all that survived from it."There also seems to be a double standard here. I mean, everyone claims that Newton's mathematical description of gravity wasn't actually an explanation but Einstein's General Relativity explains gravity in terms of warped spacetime. Physicists seemed to like Einstein's explanation better than Newton's mere description, not merely because it is more correct, but also because it offers an intuitive mechanism.

Particle physics proposed the theory of quarks to explain particle physics. Now String theory is proposing the existence of strings to explain particle physics. But anytime someone wants to explain relativity all of a sudden explanations aren't important?

I don't get it. Seems to me like there are some real inconsistencies here on the attitude of the scientific community.

Seems like scientists don't need to explain things anymore. If someone insists on an explanation just call them a crackpot!