1905 Special Relativity theory Time dilation

[Janus]

Originally posted by David
No it’s not. The phenomenon of the electron flow occurs when an electromagnet is used, even if there is no “relative motion”.

This is not germane to the discussion at hand

The “motion” is not what produces the electron flow, the variation in the magnetic field at the coil is what produces the electron flow.

Where do you get this notion That Relativity tries to replace variation in the strength of the magentic field felt by the electron with "motion"?

None of the sites you have provided say this.

What they do say is that after the discovery of the wave nature of light and prior to SR, theory predicted that the variation that the Electron saw would differ depending upon wheter the magnet or electron was moving. SR corrected this.

I don’t know about any errors in Maxwell’s point of view, but I have some old physics textbooks from the 1920s and ‘30s and they say the effect is caused by the changing magnetic field strength at the coil. They don’t say anything about this having anything to do with “relative motion”. They say it has to do with the changing field strength at the coil, and they say the same thing can be accomplished by using an electromagnet and by varying the voltage to the electromagnet, with no relative motion involved. There is no need to mention SR in connection with this Faraday discovery.

Again, you are fixating on the wrong thing and misinterpreting SR's contribution.

But this UCLA Physics Department website tries to make it appear as an Einstein discovery and an Einstein phenomenon:

LINK TO SOURCE

No it doesn't, It merely restates what II've been saying. You are reading meanings inot the post that aren't there.

And I don’t think this website is correct about the Lorentz force being involved, because it is my understanding that for a Lorentz force to be involved, a separate current has to already be flowing through the coil before the magnet is introduced.

Considering the lack of grasp of the subject you've displayed so far, I wouldn't put much weight in your understanding.

When I go to electrical websites, I get the stuff about Faraday and about the electromagnet. But when I go to some physics websites, I don’t. I just get the stuff about Einstein and the “relative motion”, but nothing about the electromagnet.

This is because these physics sites are talking about it on a different level. Thye feel no need to discuss Faraday etc, because they expect it to be common knowledge to the reader. (You don't review the rules of addition and subtraction in a discussion of Calculus.)

What is the reason for bringing SR and Einstein into this stuff? Galileo wrote about relativity. Newton wrote about relativity. Doppler developed a great theory based on his understanding of relativity. Poincare wrote about the relativity of motion in 1902. Lorentz wrote the first modern relativity paper in 1904.

People knew thousands of years ago that if person 1 moved toward person 2, while person 2 stayed still, they would get closer together. While if person 1 stayed still and if person 2 moved toward person 1, they would also get closer together. So I don’t understand the significance of Einstein’s “relativity theory” in these types of relative motion demonstrations. And of course “the laws of physics are the same everywhere”. But physicists have known that for hundreds of years.

Einstein made no claims as to inventing the Principle of Relativity(In fact he was opposed to calling his theory "The Theory of Relativity", this name was coined by others.)

And yes, the Principle of Relativity held sway for hundreds of years. But during that perod of time light was considered particulate in nature. But once the wave nature of light was discovered, a problem occured. What did light wave through? If there was a medium (the Ether) then that medium now represented an absolute reference to judge motion by. (For instance, magnets moving with repect to the Ether behave differently than ones stationary to it. ) Thus you should be able to measure your movement through space. This appeared to be a death toll to the Principle of Realtivity.

Many people tired to resolve this conflict but only uncovered pieces of the puzzle. Einstein was the first to put the right pieces together in a way that resolved things in a complete way, and along the way resurrected the Principle of Relativity.


I think Einstein did great work with General Relativity, and he deserves all the credit he can get for that. In fact, let’s give him a couple of more Nobel Prizes. But some of this other stuff about “special relativity” seems to be a lot of nonsense.
[/B][/QUOTE]

If it seems nonsense then you just haven't invested enough time in trying to understand it. You've just labeled it "nonsense" and rejected it.

 

[David]

Originally posted by Janus
If it seems nonsense then you just haven't invested enough time in trying to understand it.

Ok, ok, maybe I’m just stupid, so maybe you can explain something to me. Could you go to that UCLA physics website here:

LINK TO SOURCE

and read that page and read about what Lucy and Ringo both see.

Notice that Ringo sees no electric field and he sees a different law of physics being responsible for causing the electron flow in the coil, a different law than the one Lucy sees, while Lucy does see an electric field.

Now, since Lucy is moving with the coil, and Ringo is moving with the magnet, what would happen if Lucy stopped moving with the coil (while some other student takes over her job of moving the coil) and then Lucy goes over by Ringo and starts moving with him toward the coil?

Does this mean that the laws of physics change for Lucy and the electric field suddenly goes “poof” and disappears for Lucy, but not for the other students in the room?

If so, how do the coil and the magnet know that Lucy has changed positions? In fact, how do the coil and the magnet know what Ringo is doing?

How does nature know that it should change the laws of physics for Lucy when she changes position and motion orientation, but not change the laws for the rest of the students in the class?

What did Faraday say about the relative motion and position of himself and his fellow lab technicians when he was conducting his coil and magnet experiments?

 

[krab]

Originally posted by David
Does this mean that the laws of physics change for Lucy and the electric field suddenly goes “poof” and disappears for Lucy, but not for the other students in the room?

This is precisely the point. We believe the laws of physics do NOT change. That's called the principal of relativity. It was believed by Galileo as well. In 400 years, it has never let us down.

Since the laws of physics do not change, the observed effects (magnetic, electric fields and forces) MUST be due to one and the same law of physics.

 

[David]

Originally posted by krab
This is precisely the point. We believe the laws of physics do NOT change. That's called the principal of relativity. It was believed by Galileo as well. In 400 years, it has never let us down.

Since the laws of physics do not change, the observed effects (magnetic, electric fields and forces) MUST be due to one and the same law of physics.

Well, that’s just common sense in a modern world without primitive superstitions, but that UCLA Physics Department webpages says the laws of physics do change and are different for different observers. That’s why Lucy sees a field while Ringo does not. That’s why Lucy stops seeing the field if she joins Ringo, while the rest of the class sees the field. This is just plain nuts.

That’s why I’m asking people here about that webpage.

The UCLA webpage says their theory comes directly from Einstein’s Special Relativity theory, and in the first paragraph of his 1905 paper, he does mention the very same phenomena of one viewer seeing an electric field and another viewer not seeing a field at the same time, in the same room. This is not science, it’s superstition. And I’m asking, “Why is a major university teaching this kind of science superstition?“

 

[krab]

Originally posted by David
...but that UCLA Physics Department webpages says the laws of physics do change and are different for different observers. ... This is just plain nuts.

...“Why is a major university teaching this kind of science superstition?“

I read the web page and I really do not know what your problem is with it. Here is their conclusion:

The Conclusion: Electric and magnetic fields are not invariant entities themselves, but are aspects of a single entity, the electromagnetic field, which manifests itself differently to different moving observers.

In my previous post, I said basically the same thing, and you said that's just plain common sense. So what actually is your problem??

 

[David]

Originally posted by krab
In my previous post, I said basically the same thing, and you said that's just plain common sense. So what actually is your problem??

You did not say “basically the same thing”, and I think you are missing the point of what the UCLA website is trying to tell students. It’s not saying that students will see different phenomena from different points of view if they are moving. What the UCLA website is saying is not like saying one student will see one group of reflections in a mirror while another student in a different part of the room will see a different group of reflections, while the laws of physics are the same for all the mirror reflections. The UCLA website is saying that the laws of physics regarding mirror reflections are different for different students, because of their different positions and different motion orientations.

The laws of physics at a magnet and coil do not change, due only to an observer’s “relative motion” as an outside observer. By “outside” I mean, as long as the motion of the students does not in any way physically affect what is going on at the magnet and coil. If a student comes into the room with a larger magnet, and moves around with it, then that could affect what is going on at the original magnet and coil, but that has nothing at all to do with the student as an observer. It has only to do with the new magnetic field strength at the original magnet and coil.

The “electric field” inside that classroom does not disappear from the classroom for some students but not for others. To claim such a thing is only superstition and magic.

If a student sees a polarized-light reflection inside the classroom, and another student doesn’t see it because he’s wearing polarized glasses, that does not mean that the reflection “exists” inside the classroom for one student, while it “does not exist” in that classroom for another student or that the laws of reflection have “changed”. The reflection “exists” for both students, although one might see it and the other might not.

If there is an electric field at the magnet and coil in that classroom for some students, then there will be an electric field at the magnet and coil for all students and for all people on earth. The viewing and the motion orientation of the viewer has nothing at all to do with the law of physics that causes the electron flow inside the coil when the coil and the magnet are moving relatively. This law does not change just because someone in the classroom is walking around or not walking around.

 

[David]

Originally posted by krab
So what actually is your problem??

You don’t have any problem with the UCLA physics website saying:

With the coil moving:

“In case A there is only a magnetic field in the classroom"

With the magnet moving:

" but in case B there is also an electric field in the classroom. It is this electric field that is acting on the elections to cause the galvanometer deflection in case B.”

??

You don’t have a problem with the UCLA physics department saying there are two different laws of physics at work, one for Lucy and a different one for Ringo, although Lucy and Ringo have absolutely nothing whatsoever to do with the reason the electrons flow through the coil? You don’t have a problem with two separate and different laws of physics being at work on the magnet and coil for different groups of students inside the classroom, not two laws simultaneously, but two different laws that apply to certain students when they are moving in certain ways inside the classroom, or, for that matter, a thousand miles away from the classroom?

 

[ahrkron]

Originally posted by David
You don’t have any problem with the UCLA physics website saying:

With the coil moving:

“In case A there is only a magnetic field in the classroom"

With the magnet moving:

" but in case B there is also an electric field in the classroom. It is this electric field that is acting on the elections to cause the galvanometer deflection in case B.”

The problem you point at is precisely what motivated Einstein to develop SR. The site uses this problem so similarly motivate students to think about electrodynamics as seen from different inertial frames.

As you mention, there cannot be two different laws in action, which means that electric and magnetic fields must be two aspects of the same thing.

In SR, both fields are put together into the so called "electromagnetic tensor", a 4x4 matrix that allows you to extract the electric and magnetic components of the field for any frame you want. Once we do that, there are no "two laws" anymore, and we get a better understanding of the relation between the "two" fields (electric and magnetic).

 

[David]

Originally posted by ahrkron
The problem you point at is precisely what motivated Einstein to develop SR. The site uses this problem so similarly motivate students to think about electrodynamics as seen from different inertial frames.

As you mention, there cannot be two different laws in action, which means that electric and magnetic fields must be two aspects of the same thing.

In SR, both fields are put together into the so called "electromagnetic tensor", a 4x4 matrix that allows you to extract the electric and magnetic components of the field for any frame you want. Once we do that, there are no "two laws" anymore, and we get a better understanding of the relation between the "two" fields (electric and magnetic).

Einstein pretty much says that toward the end of Section 6 of his 1905 paper. Apparently, what he said in the opening paragraph was a legend left over from the 19th Century, and he tried to straighten it out in the Electrodynamical part of his theory.

But, that UCLA website tries to give the impression that the “electric field” is not in the classroom, when some students – just one student – moves a certain way, and that is wrong. That is “magic”, not science.

Read that website again, the professor who wrote the paper says there is no electric field when a student moves a certain way. The writer said, “In case A there is only a magnetic field in the classroom, but in case B there is also an electric field in the classroom.” But this is not true. The electric field can’t be made to appear and disappear just by the movement of the students.

This is a common myth that came out of Einstein’s error in the Kinematical part of the 1905 paper, in which he said that only “relative motion” could cause mechanical clocks to change rates. That can’t happen, because “relative motion” puts no “force” of any kind on the clocks.

He cleared up this error in 1918 when he added a gravitational field to the K’ frame, and that caused the frame’s atomic clocks to slow down.

His atomic clock slow-down theory came out of his 1911 gravitational redshift theory, and that turned out to be correct, because it is based on real physics electrodynamical effects that take place inside the atoms, but his mechanical clock “slow-down” due only to “relative motion”, in the 1905 paper, turned out to be a mistake, and he corrected that mistake later. But this UCLA professor is passing along that same mistake, by claiming that the relative motion of a single student can remove the electric field from the area of the coil and magnet, and that is not true. This is not the proper way to teach “relativity”, and it should not be taught incorrectly.

 

[ahrkron]

Originally posted by David
But, that UCLA website tries to give the impression that the “electric field” is not in the classroom, when some students – just one student – moves a certain way, and that is wrong. That is “magic”, not science.

Depending on how you move with respect to the field, you will observe a different decomposition of it into electric and magnetic fields. The physics is the same, what changes is the names we give to each part of the field. No magic here.

Before SR, people thought they were two different fields, and it was indeed peculiar that they transformed in such a way as to keep the observed effects the same.

However, Einstein cleared things up (starting not from electrodynamics, but from the much more basic notion of simultaneity), and showed how the same physical magnitude is seen differently by different observers.

In a (special-)relativistic formulation of electromagnetism, we don't talk about each field, but use instead the field strenght tensor

F^{\alpha\beta} = \partial^\alpha A^\beta - \partial^\beta A^\alpha

(where A is the four vector formed from the electric and magnetic potentials)

This contains both the electric and magnetic components. It allows you to easily transform from one reference frame to another, and to read the values of each field you will measure in the new frame.

Also, once written this way, Maxwell equations reduce to two nice tensorial equations which work in every inertial frame. No need for magic or for special treatment to any observer.

Read that website again, the professor who wrote the paper says there is no electric field when a student moves a certain way.

What happens is that, if that student uses some instruments, he will detect only a magnetic field. This is not magic, but a result of the way we defined electric and magnetic fields. In a sense, we can say that the limited understanding of the full picture led people to define detector devices that detect only a motion-dependent portion of the full electromagnetic tensor.

The electric field can’t be made to appear and disappear just by the movement of the students.

You do get different readings of the electric and magnetic fields depending on how you move. See, for instance, J.D. Jackson's "Classical Electrodynamics", 2nd ed., section 11.10 (page 552), or any book on electrodynamics.

There are invariant quantities related to the field-strength tensor that are frame-independent, but the electric and magnetic "views" will change.

They are akin to relative speed. If you move, the speed you measure from electrons around you will be different. Similarly, the electric field you'll read from your interaction with them will vary.

[Einstein] said that only “relative motion” could cause mechanical clocks to change rates. That can’t happen, because “relative motion” puts no “force” of any kind on the clocks.

Why should force be involved? time dilation is not an alteration of the behavior of your observed system, but a real effect on the quantities you will measure from it.

A simple example: in particle accelerators, the particles that come out of a proton-antiproton collision will have different speeds. If you want to measure the lifetime of a particular species of particle, you need to factor in time dilation. Otherwise, you would obtain results all over the place.

Gravity has nothing to do with it. In particle accelerators, all interactions take place at essentially the same gravitational potential, and you do see the effect of time dilation.

He cleared up this error in 1918 when he added a gravitational field to the K’ frame, and that caused the frame’s atomic clocks to slow down.

This is a different effect, which adds on to the SR part when you have a curved spacetime (i.e., a significant gravitational field).

His atomic clock slow-down theory came out of his 1911 gravitational redshift theory, and that turned out to be correct

You should say "it also turned out to be correct". Time dilation has been verified in many contexts. It is a real effect.

 

[Tarupak]

If math is the way to understand physics, why is it applied in a different way in SR?

in mechanics, it is taught
x = x0 + vt

dx/dt = v

x0 is constant and dxo/dt = 0

and in SR

x' = gamma(x - Vt)

So, why x in SR is changing?. This is an asumption that leads to Vx = V (the changing rate in x is equal to the separation speed of the 2 frames) What's the real reason for that equalty?

If we assume that x is constant we must derive it as a constant.

Or if Vx = V and we integrate the speed equation we must integrate V because it is equal to Vx.

 

[THE[>U<]DUDE]

Well I've just been reading Greene's Elegant Universe and am having a hard time getting my head around this time dilation between George and Gracie. It just doesn't seem to make sense to (uneducated) me.

Surely an observer's independent observations of clocks traveling at near to light speed are affected by the time delay of the light traveling to the observer to provide him with that information?

If the clock is traveling away from the observer at near light speed, then it's going to take longer for the light to reach the observer (because of the increasing distance traveled by the clock) and so the clock's apparent time will appear to have slowed down.

To me this doesn't prove time dilation exists. It just shows that at near light speed it will take longer for the 'back-travelling' light to reach the observer - and so the time readings will differ.

Does this make any sense?

 

[ahrkron]

Originally posted by THE[>U<]DUDE
To me this doesn't prove time dilation exists. It just shows that at near light speed it will take longer for the 'back-travelling' light to reach the observer - and so the time readings will differ.

Does this make any sense?

It does. It is a common problem when people learn SR.

The main point to make is that, even after accounting for the time it took light to reach George, there's still a difference between his time and Gracie's.

 

[russ_watters]

Originally posted by THE[>U<]DUDE
Well I've just been reading Greene's Elegant Universe and am having a hard time getting my head around this time dilation between George and Gracie. It just doesn't seem to make sense to (uneducated) me.

I've actually found that the problem isn't generally one of understanding but one of acceptance. Don't sell yourself short - you seem to understand it but are looking for ways it could be wrong because its difficult to accept. Everyone does it and its proof that you're thinking.

Surely an observer's independent observations of clocks traveling at near to light speed are affected by the time delay of the light traveling to the observer to provide him with that information?

If the clock is traveling away from the observer at near light speed, then it's going to take longer for the light to reach the observer (because of the increasing distance traveled by the clock) and so the clock's apparent time will appear to have slowed down.

This issue is why I consider GPS satellites to be the simplest (and therefore best) examples of time dilation. The satellites travel in fixed orbits so issues with their motion are easier to filter out than if you are just trying to communicate with a spaceship moving directly away from you.

If the satellite flies over the same spot every 90 minutes (slight oversimplification), then all you have to do is compare the time passage of the clock on the ground to the clock on the satellite. The clock on the ground says the satellite passed overhead 90 minutes ago. The satellite reports it passed over slightly more than 90 minutes ago (because of the combined SR & GR effects).

In actuality, gps satellite clocks are calibrated BEFORE LAUNCH to run slower than their terrestrial counterparts so when in orbit they will remain in sync.

 

[THE[>U<]DUDE]

Thanks for your replies; I'll try and figure it out!

On a similar vein, I wonder if you could clarify a few points...

Do clocks (or whatever we choose to measure time with) slow down increasingly with greater acceleration?

If so, is this only in areas of curved space or do the same rules apply out in the flat regions of interstellar emptiness (i.e. where mass hasn't warped space)?

Do we humans age at a slower rate in a gravity well than in regions of non-warped space?

If so, if we could 'un-warp' space around us (so that we were cocooned in a bubble of flat space) would we observe our Earthly surroundings moving in slow-motion?

Thanks for bearing with me.

 

[russ_watters]

Originally posted by THE[>U<]DUDE
Do clocks (or whatever we choose to measure time with) slow down increasingly with greater acceleration?

No- with greater speed.

Do we humans age at a slower rate in a gravity well than in regions of non-warped space?

Simple answer: yes. Complicated answer: no, we age at the same rate, but TIME ITSELF advances slower, causing us to APPEAR to age slower to an observer in a lower gravitational potential.

If so, if we could 'un-warp' space around us (so that we were cocooned in a bubble of flat space) would we observe our Earthly surroundings moving in slow-motion?

Sure, but before we can create a negative gravitational field (if such a thing even exists), we need to figure out how to create a positive one. An easier way would be to just fly to a place of low gravitational potential. A Legrange point for example.