Can someone explain Einstein's relativity theory?

[OsiriS^]

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.

 

[dextercioby]

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.

I'm afraid it cannot be explained in one post from a frum...I would advise you to read the famous book:"A brief History of time" by Stephen Hawking.
You'll understand many things.

Daniel.

 

[marlon]

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.

Check out the text "string theory part 1" on page three in my journal. There is a short paragraphe on General Relativity. Ofcourse it is very introductory, but it sets the tone. Firther on i suggest you check the info on the web entry for further reliable references. The answer to your question cannot be given in a few posts. First question should be : "why the name RELATIVITY theory". What does relativity mean. The answer is in my text...

regards
marlon

here is the link https://www.physicsforums.com/journal.php?s=&action=view&journalid=13790&perpage=10&page=3

 

[theriddler876]

hmnnnn well einstein said something like " you sit next to a girl for an hour and it seems like a mintue, you sit on a hot stove for a minute, and it seems like an hour, that's relativity"

 

[NeutronStar]

Einstein based his special theory of relativity on two postulates:

The First Postulate

The laws of physics are the same in all inertial systems¹. There are no preferred inertial systems, or reference frames². When inertial reference-frames move with constant speed with respect to one another the laws of physics will be the same in both reference-frames.

The Second Postulate

The phenomenon of light is correctly described by Maxwell's equations. In other words, all observers will measure³ the speed of light in a vacuum to be a constant value c in all inertial systems.

Conclusions to the Special Theory of Relativity

Once given the above two postulates as premises, the theory of special theory of relativity pretty much falls out from normal intuitive reasoning. I won't go into the actual conclusions, other than to say that once you've accepted these postulates the rest of Relativity is fairly easy⁴ to deduce and accept.

Footnotes:

1. Inertial systems are reference frames that move uniformly and without rotation.

2. A reference frame is just another name for an inertial system.

3. Note that this postulate does not actually say that the speed of light is c in all reference frames, but rather it only requires that the speed of light is measured as c in all reference frames. This is a technicality that most physicists never seem to want to talk about. This is because for physicists, "to measure is to be". In other words, as far as physicists are concerned what you see is what you get, or only observables matter. They typically aren't interested in discussing the ontological implications of fundamental measurements.

4. While the conclusions are fairly easy to deduce, the postulates are not without contradiction with respect to these conclusions. For example, Postulate One states that the laws of physics are the same in all inertial frames. Yet, one of the conclusions of special relativity is that time passes at different rates in different inertial frames thus contradicting the first postulate that states that the laws of physics are the same in all inertial frames. The twin brother's paradox proves this inconsistency between the theory and its postulates. 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 (i.e. time passes at a different rate for that twin than for the first twin) So the theory does seem to be in direct contradiction with its very own postulates.

Personal Comment

It is not my intention to discredit Special Relativity in any way by stating the above facts. Special Relativity has indeed panned out quite nicely as a mathematical framework making unprecedented confirmed predictions. The mere fact that the theory itself seems to be in direct contradiction with one of the postulates from which is was deduced does not in any way prove, or even suggest, that the theory is incorrect (i.e. the postulates themselves are not really a part of the theory, they were merely stated as a basis for deducing the theory. Therefore the theory is not actually in contradiction with itself.) It does, however, cause one to ponder how a postulate can lead intuitively to a conclusion which denies the very postulate that gave birth to it.

 

[dextercioby]

Einstein based his special theory of relativity on two postulates:

The First Postulate

The laws of physics are the same in all inertial systems¹. There are no preferred inertial systems, or reference frames². When inertial reference-frames move with constant speed with respect to one another the laws of physics will be the same in both reference-frames.

The Second Postulate

The phenomenon of light is correctly described by Maxwell's equations. In other words, all observers will measure³ the speed of light in a vacuum to be a constant value c in all inertial systems.

Conclusions to the Special Theory of Relativity

Once given the above two postulates as premises, the theory of special theory of relativity pretty much falls out from normal intuitive reasoning. I won't go into the actual conclusions, other than to say that once you've accepted these postulates the rest of Relativity is fairly easy⁴ to deduce and accept.

Footnotes:

1. Inertial systems are reference frames that move uniformly and without rotation.

2. A reference frame is just another name for an inertial system.

3. Note that this postulate does not actually say that the speed of light is c in all reference frames, but rather it only requires that the speed of light is measured as c in all reference frames. This is a technicality that most physicists never seem to want to talk about. This is because for physicists, "to measure is to be". In other words, as far as physicists are concerned what you see is what you get, or only observables matter. They typically aren't interested in discussing the ontological implications of fundamental measurements.

4. While the conclusions are fairly easy to deduce, the postulates are not without contradiction with respect to these conclusions. For example, Postulate One states that the laws of physics are the same in all inertial frames. Yet, one of the conclusions of special relativity is that time passes at different rates in different inertial frames thus contradicting the first postulate that states that the laws of physics are the same in all inertial frames. The twin brother's paradox proves this inconsistency between the theory and its postulates. 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 (i.e. time passes at a different rate for that twin than for the first twin) So the theory does seem to be in direct contradiction with its very own postulates.

Personal Comment

It is not my intention to discredit Special Relativity in any way by stating the above facts. Special Relativity has indeed panned out quite nicely as a mathematical framework making unprecedented confirmed predictions. The mere fact that the theory itself seems to be in direct contradiction with one of the postulates from which is was deduced does not in any way prove, or even suggest, that the theory is incorrect (i.e. the postulates themselves are not really a part of the theory, they were merely stated as a basis for deducing the theory. Therefore the theory is not actually in contradiction with itself.) It does, however, cause one to ponder how a postulate can lead intuitively to a conclusion which denies the very postulate that gave birth to it.

Where did u get the "fotnotes"?Check this one out:

2. A reference frame is just another name for an inertial system.

I THINK THAT WIPES OUT 10 YEARS OF MR EINSTEIN'S WORK...And did a hella of a favor to QFT...


Daniel.

 

[Doc Al]

4. While the conclusions are fairly easy to deduce, the postulates are not without contradiction with respect to these conclusions. For example, Postulate One states that the laws of physics are the same in all inertial frames. Yet, one of the conclusions of special relativity is that time passes at different rates in different inertial frames thus contradicting the first postulate that states that the laws of physics are the same in all inertial frames. The twin brother's paradox proves this inconsistency between the theory and its postulates. 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 (i.e. time passes at a different rate for that twin than for the first twin) So the theory does seem to be in direct contradiction with its very own postulates.

This is nonsense.

 

[Galileo]

For example, Postulate One states that the laws of physics are the same in all inertial frames. Yet, one of the conclusions of special relativity is that time passes at different rates in different inertial frames thus contradicting the first postulate that states that the laws of physics are the same in all inertial frames.

No, time passes at a different rate in an inertial frame that is moving with a constant velocity with respect to your inertial frame.
The first postulate simply says that if you view the situation from the other reference frame, the physical description is exactly identical.

 

[JesseM]

Einstein based his special theory of relativity on two postulates:

The First Postulate

The laws of physics are the same in all inertial systems¹. There are no preferred inertial systems, or reference frames². When inertial reference-frames move with constant speed with respect to one another the laws of physics will be the same in both reference-frames.

The Second Postulate

The phenomenon of light is correctly described by Maxwell's equations. In other words, all observers will measure³ the speed of light in a vacuum to be a constant value c in all inertial systems.

Conclusions to the Special Theory of Relativity

Once given the above two postulates as premises, the theory of special theory of relativity pretty much falls out from normal intuitive reasoning. I won't go into the actual conclusions, other than to say that once you've accepted these postulates the rest of Relativity is fairly easy⁴ to deduce and accept.

Footnotes:

1. Inertial systems are reference frames that move uniformly and without rotation.

2. A reference frame is just another name for an inertial system.

3. Note that this postulate does not actually say that the speed of light is c in all reference frames, but rather it only requires that the speed of light is measured as c in all reference frames. This is a technicality that most physicists never seem to want to talk about. This is because for physicists, "to measure is to be". In other words, as far as physicists are concerned what you see is what you get, or only observables matter. They typically aren't interested in discussing the ontological implications of fundamental measurements.

4. While the conclusions are fairly easy to deduce, the postulates are not without contradiction with respect to these conclusions. For example, Postulate One states that the laws of physics are the same in all inertial frames. Yet, one of the conclusions of special relativity is that time passes at different rates in different inertial frames thus contradicting the first postulate that states that the laws of physics are the same in all inertial frames.

No. If you are traveling at velocity v in my frame, I will see your clock slowed by a factor 1/(1 - v^2/c^2); in your frame, you will see me traveling at velocity v, and you will also see my clock slowed by a factor of 1/(1 - v^2/c^2). So in each frame, a clock traveling at v is slowed by the same factor, thus the laws concerning time dilation work the same way in both frames.

The twin brother's paradox proves this inconsistency between the theory and its postulates. 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.

No, in the traveling twin's frame it doesn't run more slowly once the acceleration has ceased. After the acceleration has ceased, and the twin is returning to Earth at constant velocity, the traveling twin's clock is running slow in the earth-twin's frame, and the earth-twin's clock is running slow in the traveling twin's frame. In both frames, though, you can predict that the traveling twin's clock will be behind the earth-twin's clock when they meet; in the traveling twin's frame, this is because at the moment the acceleration stopped, his clock was way behind the earth-twin's clock at the same moment, so that even though his clock is "catching up" to the Earth twin's clock (since the earth-twin's clock is ticking more slowly in his frame), it still will be behind the earth-twin's clock at the moment their paths cross. In the earth-twin's frame the analysis would be different--at the moment the acceleration stopped, he would also say that the traveling twin's clock is behind his own, but by a smaller factor; but since the traveling twin's clock ticks more slowly in his frame, the difference between their clocks would increase rather than decrease. But things will work out so that each frame will have exactly the same prediction about how much the traveling twin's clock will be behind the earth-twin's clock at the moment they meet.

 

[s3nn0c]

In my opinion, one of the best popular explanations of the theory of relativity was written by Brian Greene in his "The fabric of the cosmos" book.

 

[JesseM]

Where did u get the "fotnotes"?Check this one out:

2. A reference frame is just another name for an inertial system.

I THINK THAT WIPES OUT 10 YEARS OF MR EINSTEIN'S WORK...And did a hella of a favor to QFT...


Daniel.

Actually, this footnote, along with the rest of his post up to footnote 4, is correct. The statement that the laws of physics work the same way in all reference frames is only true if you assume that we're only talking about the reference frames of observers who are moving inertially (ie moving at constant velocity relative to other inertial observers, not accelerating).

 

[dextercioby]

Actually, this footnote, along with the rest of his post up to footnote 4, is correct. The statement that the laws of physics work the same way in all reference frames is only true if you assume that we're only talking about the reference frames of observers who are moving inertially (ie moving at constant velocity relative to other inertial observers, not accelerating).

Nope,notice the degree of generality.He said "reference frame=inertial frame" ,but he didn't say the key words:"in SR".

Again,i'm convinced thatwas balloney.Either he invented the footnotes or took'em from a crack-pot source...


Daniel.

 

[JesseM]

Nope,notice the degree of generality.He said "reference frame=inertial frame" ,but he didn't say the key words:"in SR".

Even in SR, you can have accelerated reference frames, you just can't assume the laws of physics work the same way in these frames. But in context, I think that footnote wasn't talking about SR in general, it was just qualifying a statement he made in the first postulate, namely "There are no preferred inertial systems, or reference frames". So in that context, the footnote need not have meant "whenever a physicist uses the words 'reference frame' they always just mean an inertial system"--it could have just meant "when I use the word 'reference frame' in my statement of the first postulate, I'm just using it to mean an inertial system".

 

[NeutronStar]

--it could have just meant "when I use the word 'reference frame' in my statement of the first postulate, I'm just using it to mean an inertial system".

That's precisely what I meant to convey in that footnote. Sorry if it was taken to imply some kind of blanket definition for the term. That wasn't my intent. I probably should have added something like "when speaking in terms of SR, the term reference frame is generally taken to mean Inertial system.

Sorry for the confusion. Ironically I put in the footnote to avoid confusion and it seems to have backfired.

I probably should have also clarified that my original post refers only to SR. I assumed that since GR requires additional postulates, such as the equivalency of acceleration and a gravitational field, it wouldn't be necessary to mention the distinction.

 

[ohwilleke]

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.

Special relativity is much, much easier conceptually than general relativity. In special relativity you are basically talking about a small number of equations (the Lorentz transformations), in ordinary every day algebra like the rest of physics, that insure consistency in cases where there are high velocity motion while maintaining the speed of light in a vacuum as a constant.

General relativity is much deeper. To be crude to the point of being inaccurate but heuristically useful, general relativity explains gravity by explaining how mass-energy and its pressure and motion (customarily broken out into ten numerical quantities) affect the curvature of space. General relativity does so using "tensors" (which are basically matrixes from linear algebra), most notably the "Ricci Tensor" and the "Stress Energy" tensor (which contains the ten numbers describing the mass alluded to above).

Tensor math is good, because it through the form of the equations make it obvious that there can be no preferred reference frame, but to actually calculate them without major assumptions concerning how you choose your reference frame and symmetry is extremely difficult.

Among the major qualitative predictions of general relativity are that:

(1) E=mc^2
(2) Light is deflected by gravity.
(3) Gravity is a quadradic function of velocity. A first order term depends on mass (with various other assumptions in place), a second order term depends on velocity, and a third order term depends on the square of velocity. This creates effects such as "frame dragging" and an altered expected precession of Mercury.
(4) Gravity is capable of being so great that light cannot escape, creating a black hole.
(5) The equations of GR can be generalized to the universe as a whole with certain simplifying assumptions. This generalization leads to our notions of how much matter, dark matter, and dark energy is necessary to have a universe consistent with data on the Hubble constant, other data and the equations of general relativity. The fact that there appears to be "dark energy" in the universe can be explained through a disputed term in the equations of general relativity called the cosmological constant, which has little or no impact on events at the galactic scale and below.

A nice primer is here: http://math.ucr.edu/home/baez/einstein/einstein.html

The real short version of GR (from the Baez primer):

We promised to state Einstein's equation in plain English, but have not done so yet. Here it is:

Given a small ball of freely falling test particles initially at rest with respect to each other, the rate at which it begins to shrink is proportional to its volume times: the energy density at the center of the ball, plus the pressure in the direction at that point, plus the pressure in the direction, plus the pressure in the direction.

The reader who already knows general relativity may be somewhat skeptical of this claim. After all, Einstein's equation in its usual tensorial form is really a bunch of equations: the left and right sides of equation (1) are matrices. It is hard to believe that the single equation (2) captures all that information. It does, though, as long as we include one bit of fine print: in order to get the full content of the Einstein equation from equation (2), we must consider small balls with all possible initial velocities -- i.e., balls that begin at rest in all possible local inertial reference frames.

Before we begin, it is worth noting an even simpler formulation of Einstein's equation that applies when the pressure is the same in every direction:

Given a small ball of freely falling test particles initially at rest with respect to each other, the rate at which it begins to shrink is proportional to its volume times: the energy density at the center of the ball plus three times the pressure at that point.

Equation (8) here: http://math.ucr.edu/home/baez/einstein/node10.html is the Einstein Equation.

 

[NeutronStar]

No, in the traveling twin's frame it doesn't run more slowly once the acceleration has ceased.

I don't see how that can be correct?

Say we have three twins, A, B, and C.

Twin A stays on earth. Twin B and C both take off in rockets (separate rockets).

To keep things as simple as possible imagine that both rockets take off in the same general direction and accelerate to something close to the speed of light side-by-side. They both cease to accelerate at precisely the same time, still being side-by-side. Then they travel along for some extended period of time until twin B decides to decelerate and then re-accelerated to return back to earth.

When twin B gets back to Earth he or she will be younger than twin A by say, x amount of time.

In the meantime, twin C is still just drifting along at close to the speed of light at a constant velocity. Finally, after some arbitrary time twin C decides to decelerate and then re-accelerate back toward earth. (Note that in this experiment both rocket pilots experience precisely the same amount of acceleration)

Now when twin C returns to Earth he or she will be younger than twin A by y amount of time.

If acceleration was the only deciding factor for time dilation then x=y. In other words, twin B and C are precisely the same age. I don’t believe that this is what SR predicts. I believe that it predicts that B will even be younger than C. In other words, x will not be equal to y.

Therefore, time dilation must have been occurring during the non-accelerated part of the trip. This must necessarily be the case since twin B and C both experienced precisely the same amount of acceleration.

Is this right or wrong? I'm open to criticism?

 

[JesseM]

I don't see how that can be correct?

Say we have three twins, A, B, and C.

Twin A stays on earth. Twin B and C both take off in rockets (separate rockets).

To keep things as simple as possible imagine that both rockets take off in the same general direction and accelerate to something close to the speed of light side-by-side. They both cease to accelerate at precisely the same time, still being side-by-side. Then they travel along for some extended period of time until twin B decides to decelerate and then re-accelerated to return back to earth.

When twin B gets back to Earth he or she will be younger than twin A by say, x amount of time.

In the meantime, twin C is still just drifting along at close to the speed of light at a constant velocity. Finally, after some arbitrary time twin C decides to decelerate and then re-accelerate back toward earth. (Note that in this experiment both rocket pilots experience precisely the same amount of acceleration)

Now when twin C returns to Earth he or she will be younger than twin A by y amount of time.

If acceleration was the only deciding factor for time dilation then x=y. In other words, twin B and C are precisely the same age. I don’t believe that this is what SR predicts. I believe that it predicts that B will even be younger than C. In other words, x will not be equal to y.

Therefore, time dilation must have been occurring during the non-accelerated part of the trip. This must necessarily be the case since twin B and C both experienced precisely the same amount of acceleration.

Is this right or wrong? I'm open to criticism?

I didn't say that time dilation only occurs during acceleration--in fact I said that in the traveling twin's frame, the clock of the Earth twin is running slow (this would be true in both the outbound frame and the inbound frame).

The thing to keep in mind is that different reference frames define simultaneity differently. If I am moving away from the Earth at constant velocity, and my clock was synchronized with clocks on Earth when I left, then in my reference frame the Earth clocks are all running slow, so my clock will keep getting further and further ahead of what the Earth clock reads "at the same moment" in my reference frame. But then if I accelerate so I am now traveling towards the earth, I will have a new reference frame, and this reference frame defines simultaneity differently than my old one, so that now the Earth clock is far ahead of what my clock reads "at the same moment". The earth-clocks will still be ticking slower than my clock in this reference frame, so my clock will be catching up to the Earth clock, but the Earth clock was far enough ahead when I first entered this frame that when I arrive at Earth my clock will still be behind.

If you find this hard to understand, we could try plugging some numbers into your scenario above to show exactly how this works, and why the time difference between the clocks of A and B will be smaller than the time difference between the clocks of A and C when they reunite.

 

[Janus]

I don't see how that can be correct?

Say we have three twins, A, B, and C.

Twin A stays on earth. Twin B and C both take off in rockets (separate rockets).

To keep things as simple as possible imagine that both rockets take off in the same general direction and accelerate to something close to the speed of light side-by-side. They both cease to accelerate at precisely the same time, still being side-by-side. Then they travel along for some extended period of time until twin B decides to decelerate and then re-accelerated to return back to earth.

When twin B gets back to Earth he or she will be younger than twin A by say, x amount of time.

In the meantime, twin C is still just drifting along at close to the speed of light at a constant velocity. Finally, after some arbitrary time twin C decides to decelerate and then re-accelerate back toward earth. (Note that in this experiment both rocket pilots experience precisely the same amount of acceleration)

Now when twin C returns to Earth he or she will be younger than twin A by y amount of time.

If acceleration was the only deciding factor for time dilation then x=y. In other words, twin B and C are precisely the same age. I don’t believe that this is what SR predicts. I believe that it predicts that B will even be younger than C. In other words, x will not be equal to y.

Therefore, time dilation must have been occurring during the non-accelerated part of the trip. This must necessarily be the case since twin B and C both experienced precisely the same amount of acceleration.

Is this right or wrong? I'm open to criticism?

The problem you are having is that you aren't taking the Relativity of Simultaneity into account. Clocks that are simultaneous as measured in one frame will not be simultaneous in another frame that is moving with respect to the first, if the clocks are separated along the axis of relative motion. So, for instance, if there were clocks at Earth, the point where B turns around and the point that C turns around that are sychronized in the Earth frame, according to B and C, the clocks at the turn around points will read later
than the Earth clock while B & C are moving away from the Earth. Since the distance of separation affects how much the Clocks are out of sync, the clock at C's turn around will read later than the one at B's turnaround.

When B turns around he changes frames of reference. (now heading towards Earth). In this new reference frame it is the Earth clock that reads the later time. Thus, according to B, the Earth clock now reads later than his own (Before he made the change of frame the Eart clock read Earlier than his own). When he returns to Earth he will find that the Earth clock will still read more than his own. (even though the Earth clock ran slower than his own during th return trip). IOW, his Earth twin will be older than him.

When C turns around, he is much further from Earth, thus from his new frame, the Earth clock reads much later. Again, when he returns to Earth, he will find that much more time has passed on Earth for him than it did for B, who made the shorter trip.

 

[jdavel]

Neut,


"While the conclusions are fairly easy to deduce, the postulates are not without contradiction with respect to these conclusions."

Nonsense. The theory IS the postulates, and there are no contradictions among them and the conclusions to which they lead.

Consider another possibility: You don't know what you're talking about!

 

[NeutronStar]

I didn't say that time dilation only occurs during acceleration--

I'm sorry for misunderstanding you. I thought you said,…

No, in the traveling twin's frame it doesn't run more slowly once the acceleration has ceased.

That sounded to me like you were saying that time dilation ceases to occur once the acceleration has ceased

If you find this hard to understand, we could try plugging some numbers into your scenario above to show exactly how this works, and why the time difference between the clocks of A and B will be smaller than the time difference between the clocks of A and C when they reunite.

I never said that I find it hard to understand. Nor did I ever say that I don’t believe that it happens. I've taken modern physics and I've gone through all the calculations and the Minkowski diagrams. All I'm saying is that time does indeed flow differently in different inertial frames. I believe that Relativity actually bears this out.

The problem you are having is that you aren't taking the Relativity of Simultaneity into account.

I never even mentioned simultaneity. Neither was that concept important to the experiment that I spoke of. Never once did I talk about what might be happening "simultaneously" between the twins during the experiment.

"While the conclusions are fairly easy to deduce, the postulates are not without contradiction with respect to these conclusions."

Nonsense. The theory IS the postulates, and there are no contradictions among them and the conclusions to which they lead.

Consider another possibility: You don't know what you're talking about!

Actually you're right. Technically the postulate merely states that the laws of physics are the same in all inertial frames. And I suppose that is true.

What isn't the same is the actual physics.

In other words, imagine that two observers are in frame A. They both age by the same amount. One of the observers goes off into frame B. When they return to frame A they did not age as much as the observer that remained in frame A. Therefore the only possible conclusion is that time flows more slowly in frame B.

If time flows more slowly in frame B then the physics of frame be is different from that from A. However, the laws of physics may remain the same within that frame. So I suppose it isn't a contradiction of the postulate after all.

I kind of fell into the trap of thinking that the laws of physics and the actual physics were basically the same thing. They're not.

So you're right. Technically, Special Relativity doesn't contradict it's postulates after all.

 

[JesseM]

I'm sorry for misunderstanding you. I thought you said,…

No, in the traveling twin's frame it doesn't run more slowly once the acceleration has ceased.

That sounded to me like you were saying that time dilation ceases to occur once the acceleration has ceased

I was responding to your statement "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." The traveling twin's clock doesn't run more slowly in his own frame--the earth twin's clock runs slower, because he is the one who is moving in this frame. Again, time dilation works the same way in every frame--any clock moving at velocity v in a given frame ticks more slowly by a factor of \sqrt{1 - v^2/c^2}.

The problem is you are talking as if "time dilation" is something objective, when in fact it never is--whether a clock shows time dilation depends on which frame you're in.

I never said that I find it hard to understand. Nor did I ever say that I don’t believe that it happens. I've taken modern physics and I've gone through all the calculations and the Minkowski diagrams. All I'm saying is that time does indeed flow differently in different inertial frames. I believe that Relativity actually bears this out.

It depends what you mean by "time flows differently". Of course it flows differently in the sense that each observer sees the other one's clock slowing down. But it doesn't flow differently in the sense that there is some objective truth about which clock is "really" ticking more slowly, and your discussion of the twin paradox suggested you thought otherwise.

I never even mentioned simultaneity. Neither was that concept important to the experiment that I spoke of. Never once did I talk about what might be happening "simultaneously" between the twins during the experiment.

I didn't say you had mentioned it, but I brought it up because I think it is quite important in understanding the experiment--it shows why, even though the traveling twin sees the Earth's clock ticking slower as he returns, he still predicts that his clock will be behind the Earth clock when he arrives, because at the moment he began the trip back, the Earth clock was far ahead of his clock in his frame, so even though his clock is ticking faster the whole trip back it still won't have caught up by the time he returns. And the phrase "at the moment he began the trip back" in that last sentence depends on understanding how he defines simultaneity in his frame.

Actually you're right. Technically the postulate merely states that the laws of physics are the same in all inertial frames. And I suppose that is true.

What isn't the same is the actual physics.

In other words, imagine that two observers are in frame A. They both age by the same amount. One of the observers goes off into frame B. When they return to frame A they did not age as much as the observer that remained in frame A. Therefore the only possible conclusion is that time flows more slowly in frame B.

No, you could analyze this problem equally well from the perspective of frame B, and from that perspective time is flowing more slowly in frame A. You would get the same predictions either way--that's a direct consequence of the fact that the laws of physics must be the same in all inertial frames (I don't know what you think you mean when you say the laws of physics could be the same in all frames and yet 'actual' physics could be different--that's obvious nonsense).

 

[Janus]

I never even mentioned simultaneity. Neither was that concept important to the experiment that I spoke of. Never once did I talk about what might be happening "simultaneously" between the twins during the experiment.

No, you didn't mention it, and that's the problem. Taking the Relativity of Simultaneity into account isimportant to understanding what happens according to twins B and C.

 

[jdavel]

JesseM

"...even though the traveling twin sees the Earth's clock ticking slower as he returns...

Careful there! As the traveller returns, the doppler effect causes him to see the Earth's clock running faster than his, not slower.

 

[NeutronStar]

The problem is you are talking as if "time dilation" is something objective, when in fact it never is--.

Excuse me?

The fact that the returned twin is younger than the original twin isn't objective?

Yes, I most certainly hold that "time dilation" is objective. Please correct me if I'm wrong but isn't that also the conclusion of Special Relativity?

Time dilation really does occur. That is to say that it objectively occurs. It's not just some optical illusion during the trip. The returning twin really is younger objectively upon return. It's a "real" objective phenomenon.

So yes, I'm absolutely talking as if "time dilation" is something objective.

 

[JesseM]

JesseM

"...even though the traveling twin sees the Earth's clock ticking slower as he returns...

Careful there! As the traveller returns, the doppler effect causes him to see the Earth's clock running faster than his, not slower.

OK, I was using "sees" to mean what events are simultaneous in his reference frame, not the delayed image he gets from light signals.

 

[JesseM]

Excuse me?

The fact that the returned twin is younger than the original twin isn't objective?

Sure, but the returned twin did not stick to a single reference frame.

Yes, I most certainly hold that "time dilation" is objective. Please correct me if I'm wrong but isn't that also the conclusion of Special Relativity?

It's not objective in the sense that as long as two observers are traveling at constant velocity, there is no objective truth about whose clock is running slower. If you calculate things in A's frame then B's clock is running slower, while if you calculate things in B's frame then A's clock is running slower. Regardless of which frame you use, you'll get the same predictions about the readings on their respective clocks at the moment their paths cross.

Time dilation really does occur. That is to say that it objectively occurs. It's not just some optical illusion during the trip. The returning twin really is younger objectively upon return. It's a "real" objective phenomenon.

Yes, of course the twin's clock will show less time elapsed when he returns. But during either the outbound leg or the inbound leg, when he was moving inertially, there is no objective truth about whether his clock or the Earth's clock was running slower for the duration of that leg of the trip. You can calculate the results of the entire experiment from any of the three inertial reference frames--the Earth's rest, the outbound rest frame, or the inbound rest frame, and in each case you will get the same prediction about what each twin's clock read when the traveling twin returned to earth. For example, in the outbound rest frame, you'd calculate that before the twin accelerated it was the earth-twin's clock that was running slower, but after the twin accelerates he will now be moving even faster than the Earth in this frame, so his clock will run slower than the earth-twin's clock (which is still running slow in this frame) during the second leg of the trip. In the inbound reference frame the opposite would be true--the earth-twin's clock would run at the same slow rate for the whole time, while the traveling twin's clock would run even slower during the first leg of the trip, then it'd run at normal speed after accelerating.

 

[NeutronStar]

Sure, but the returned twin did not stick to a single reference frame.

I'm afraid that I don't understand what that as to do with the price of bananas. I never claimed that the returned twin stuck to a single reference frame. I did, however, maintain that twin A remained in a single reference frame, and that is very important to my argument.

It's not objective in the sense that as long as two observers are traveling at constant velocity, there is no objective truth about whose clock is running slower.

But I just proved that there is objective truth to this. My experiment proves it beyond a shadow of a doubt. Assuming my experiment holds water with respect to the calculations of SR, but I'm pretty sure that it does.

If you calculate things in A's frame then B's clock is running slower, while if you calculate things in B's frame then A's clock is running slower.

I'm not the slightest bit worried about calculating things in different frames. My experiment does not require intermediate results or predictions. I'm only interested in the beginning and the end results of the experiment, and I can measure all of that in frame A.

Yes, of course the twin's clock will show less time elapsed when he returns. But during either the outbound leg or the inbound leg, when he was moving inertially, there is no objective truth about whether his clock or the Earth's clock was running slower for the duration of that leg of the trip.

Again, I'm not the slightest bit interested about what happens during any particular leg of any trip. The sole conclusion of my experiment is to say nothing more than time must have been dilated during the non-accelerating part of the trip. That's the only conclusion that I'm interested in, and my experiment proves that.

Also, I want to point out again that I'm not claiming that time doesn't dilate during acceleration. I'm really not concerned about that. I'm only interested in showing that time must have been dilated during the non-accelerating part of the trip That's really all I need to show to claim that physics is behaving differently in different inertial frames even though the laws of physics may appear to be unaffected within that frame.

I'm totally confident that my conclusions are correct and in agreement with SR.

 

[JesseM]

I'm afraid that I don't understand what that as to do with the price of bananas. I never claimed that the returned twin stuck to a single reference frame.

And I didn't say you had. The point is that for any two inertial reference frames, there is no objective truth about whose clocks are running slower.

But I just proved that there is objective truth to this. My experiment proves it beyond a shadow of a doubt.

No, your logic makes no sense. There are three frames here, and there is no reason to say that time "objectively" runs slower in anyone of them.

I'm not the slightest bit worried about calculating things in different frames. My experiment does not require intermediate results or predictions. I'm only interested in the beginning and the end results of the experiment, and I can measure all of that in frame A.

But the beginning and end results can also be measured from frame B or frame C, and you'll get the same predictions. Any physical situation can be analyzed from any frame you choose, without your ever having to switch to a different frame.

gain, I'm not the slightest bit interested about what happens during any particular leg of any trip. The sole conclusion of my experiment is to say nothing more than time must have been dilated during the non-accelerating part of the trip. That's the only conclusion that I'm interested in, and my experiment proves that.

But it doesn't prove that time was objectively running slower in anyone inertial reference frame, so it doesn't conflict with any of the postulates of relativity as you argued earlier. There is still a complete symmetry between the perspectives of the three different inertial reference frames--each frame says that the clocks in the other frames are running slower than its own clocks.

Also, I want to point out again that I'm not claiming that time doesn't dilate during acceleration. I'm really not concerned about that. I'm only interested in showing that time must have been dilated during the non-accelerating part of the trip That's really all I need to show to claim that physics is behaving differently in different inertial frames even though the laws of physics may appear to be unaffected within that frame.

Which frame, in particular, do you think is behaving differently? Do you think the inbound frame is behaving differently than the Earth frame, for example? I can assure you that no matter which you pick, there is no difference, each frame says that a clock at rest in that frame ticks at the normal rate, and clocks in another frame moving at velocity v relative to it are time-dilated by a factor of \sqrt{1 - v^2/c^2}.

 

[Janus]

I'm not the slightest bit worried about calculating things in different frames. My experiment does not require intermediate results or predictions. I'm only interested in the beginning and the end results of the experiment, and I can measure all of that in frame A.

SR.

Again, that's a problem. If you really want to grasp what SR is about, you need to consider what happens according to all the frames.

 

[NeutronStar]

Again, that's a problem. If you really want to grasp what SR is about, you need to consider what happens according to all the frames.

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.

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.

Now send physicists into each of these boxes to perform experiments. When they come back out they confirm that all of the laws of physics are valid in both boxes. However, even though the laws of physics are the same in box B it should be quite obvious that the actual physics behaves differently relative to the physics that occurs in box A.

So physics is not the same in all inertial frames even though the laws of physics may appear to be the same within the frames individually. That's the only conclusion possible.

Nothing I have said here conflicts with SR in any way. At first glance it appears to conflict with the first postulate, but I was wrong about that because the first postulate merely says that the laws of physics are the same in all inertial systems. It doesn't make any claim that the actual physics is the same. In fact, the transformation equations of SR show quantitatively that the actual physics isn't the same in different inertial frames!

My mistake earlier was that I was confusing the laws of physics with actual physics. The first postulate of relativity doesn't say that the actual physics is the same in all inertial frames, it simply says that the laws must be the same. And that indeed is true. So I need to retract my statement that SR is in contradiction with one of its postulates. That's wasn't technically correct.

 

[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,…