Scenario:

we have a solid rail made of ....let's see...., titanium alloy.

this rail is 1 ly in length. and connects from point A to point B

On this rail we place a train that accelerates to the velocity of 0.6 c it is held to the rail by a set of wheels.

At a certain point in it's travel we take a snap shot of the train and the rail.

The rail is undilated and is our rest frame and the train is dilated and length contracted due to velocity (0.06c)

What impact does the trains dilation and length contraction have on the rail which maintains it's connection between point A and point B.

[The thinking is that the rail is also absolute space]

Hum,
you seem to have answered it already.

the snapshot would show a `contacted`train on a `uncontracted` rail...

does the rail experience any of the dilation or contraction effects of the train?

According to SR, it depends on the frame of reference. If the observer is on the train,
then the rail is contracted and not the train. QQ, I assume you knew this simple SR
statement, so I assume you are going somewhere with this.

According to SR, it depends on the frame of reference. If the observer is on the train,
then the rail is contracted and not the train. QQ, I assume you knew this simple SR
statement, so I assume you are going somewhere with this.

An interesting side note would be to ask yourself about the Rpm of the wheels.

From one frame the length of the rail is contracted but the train isn't, in the other the train is contracted and the rail isn't.

It would appear that there must be two different Rpm's at the wheels in contact with the rail.

Correct. The rpm measured in each frame will be different.

An interesting side note would be to ask yourself about the Rpm of the wheels.

From one frame the length of the rail is contracted but the train isn't, in the other the train is contracted and the rail isn't.

It would appear that there must be two different Rpm's at the wheels in contact with the rail.

Very good, MacM, perhaps you're starting to get it.

Do you think that this is a contradiction in SR?
Don't forget that you haven't proven that time is absolute...

I don't think so. I thought he was implying that the wheels need to different speeds 'at the wheels' (in the wheel contact frame of reference).

According to SR, it depends on the frame of reference. If the observer is on the train,
then the rail is contracted and not the train. QQ, I assume you knew this simple SR
statement, so I assume you are going somewhere with this.
There are a number of issues I wanted to discuss with this or see discussed.

1) the rail is physically connecting two points. A and B.

2) if the rail is contracted then how is the destination percieved from the train. Is it closer than it was due to rail contraction or is it the same.

3) this seemingly paradox is the most common dilemma for people wanting to study relativity. Intuitively it suggests that at least two realities exists in conflict with each other. ( ie multiple tick rates)

4) Because the train is in contact with the rail I wondered what effect the two objects had on each other. One being contracted and dillated etc and the other deemed not to be so.

5) if in contact with the rail at what point do we distinguish betweeen the train and the rail. a) at the wheels contact with the rail, b) at the wheels contact with the train or c) neither.

IT is not all that different to the "pole in the barn" Thought Experiment.

however in this scenario the train is alway in physical contact with the rail.

The main thrust of the question is actually one to do with reciprication [the effect each has on each other] between two objects, this being the rail and the train.

If the train is dilated so that its change rate (tick rate has slowed) what impact does this dilation have on the rail. if it's length is contracted yet it still maintains contact with the rail what does this cointraction impart to the uncontracted rail.



If we take the view that everything is in some sort of relationship with everything then it is the relationship between a dilated object and a non dilated object I wished to explore.

I would assume that the rail in this instance must be effected by the dilation of the train and there fore the rails tick rate or change rate is impinged upon by this dilation.

2inquisitive,

I know that you have an interest in Accelerators. Has there been stiudies into the impact that the accelerating particle has on it's environment. the tube that it is fired in, the vacumm or air that is it's ambience.

Just as an aside to this question but relevant to the issue of reciprication.
I am currently writing a sci fi novella, that involves the attempt to send a particle of dust back in time 50 years but the experiment fails to recognise that the confinement chambers' state in time is also effected.
The result of this time travel experiment is that the particle inside the chamber goes back only 25 years and the chamber and everything else around it goes back in time......25 yeasr also.

the idea is exploring reflective symetry, or reflective physics.....

What you do to one thing you inversely do to another. The cause is effected just as much as the effect is caused. The effect is also the cause.
so in this novella the particle stays where it is in time and unexpectedly the universe surrounding the particle has to go back in time as well causing a major time refraction........sc fi is fun hey?

when two frames are approaching each other at what moment do they become the one frame?

For me the nub of the issue is this:

Relativity requires the use of frames in performing it's functions. This has been quoted as essential many many times.

Take A's perpective or Take B's perpective.....etc etc.....but where I think things break down is the the inter-relationship between our two objects.

Example from A's perspective what effect does B have on A.
From B's perspective what inpact does A have on B....and so on.....

It seems that relativity [as I have come to know it] does not include the impacts of all objects on each other.

For example if I was relatively stationary and an object travelled pass me as the rate o 0.6c would I notice any change in my physical state......I would think yes to be a definite answer.

Another example, if an object requires an infinite amount of energy to travel at 'c' then the universe would cease to exist becasue that energy is taken from somewhere......and if teh universe ceases to exist then what is our object traveling in and if it is how could it possibly dtermine it's velocity as C when it is traveling in absolutely nothing any way.

Now It is all well and good to apply relativity but to do so selectively is I think a flaw.

If we propel an object of mass along a rail 0.6 c the impact on the surrounding universe [including the rail] would be enormous.
And as yet I have not seen how relativity describes the effect on the universe.

when two frames are approaching each other at what moment do they become the one frame?
The question doesn't make sense.

Frames don't approach each other.

You seem to be thinking of a frame as having some limited size, and changing in time - that's not the case. Any frame encompasses all space-time.

pete let me rephrase the question you are referring to .

When does the pole in the barn become just a pole in the barn or should I say what effect does the pole have on the barn?

The reason is that when you separate the frames you also separate the reality.

To take the position of the pole is an excersise in imagining you are the pole or imagining you are the barn, we are takling an imaginary perpective. No one could possibly be the pole and no one could possibly be the barn.

So when we choose a frame we are setting up an imaginary construct, simply because nothing is in isolation everything is part of the whole. [Machs principle for example]

I do understand that this is essential fo relativety to function but this is also why it is severely limited and possibly flawed becasue of this limitation ( not valid at quantum levels etc)

Einstien found his postulation about light by saying that no one could possibly ride a ray of light and yet as soon as he postulated a light frame as invariant he did just that....ride on a ray of light.....

so if and it is alway if.....we take A's perpective then B does this but we are isolating the objects in to two when they are always a part of the one.

I believe that relativity is severely limited in it's application because of this selective one frame emphasis.

For example if I was relatively stationary and an object travelled pass me as the rate o 0.6c would I notice any change in my physical state
No (unless it hit you, of course!)

If we propel an object of mass along a rail 0.6 c the impact on the surrounding universe [including the rail] would be enormous.
You are mistaken, unless you're talking about effects that were well described before Relativity was developed (heat dissipated by friction, collisions with particles in the environment, effect of exhaust gases, mining of fuel, etc).

QQ, you seem to under some serious misunderstandings regarding what reference frames are and aren't.

It is often useful in the context of explanations to talk about an observer in a particular frame, but it's not actually necessary. The presence or not of an observer is irrelevant to the predicitons of the SR model and to what happens in reality.

Choosing a reference frame does not mean to "ignore the whole" - all reference frames encompass all space-time.


Choosing a reference frame is much like choosing a zero point on an arbitrary scale, such as degrees Celsius and degrees Fahrenheit... does it matter which one you choose? Does it change the physical predictions of your calculations?

When does the pole in the barn become just a pole in the barn
I don't understand the difference between "the pole in the barn" and "just a pole in the barn".

what effect does the pole have on the barn?
None, unless they collide or interact in some other way.

“ Originally Posted by Quantum Quack
For example if I was relatively stationary and an object travelled pass me as the rate o 0.6c would I notice any change in my physical state ”

No (unless it hit you, of course!)

“ Originally Posted by Quantum Quack
If we propel an object of mass along a rail 0.6 c the impact on the surrounding universe [including the rail] would be enormous. ”

You are mistaken, unless you're talking about effects that were well described before Relativity was developed (heat dissipated by friction, collisions with particles in the environment, effect of exhaust gases, mining of fuel, etc).

Pete of course I am talking about real impacts of relativistic velocities........why would you want to talk about it with out real impacts?

Your post only demonstrates the abstract nature of relativity. If I was stationary and an object of mass travelled past me at relativistic velocities I woudl be severely impacted upon, the mere energy required to propell the object come from me in part. The em emmissions of the dilated object would be in conflict with what I would normally experience and so on......relativity is an apathied model in that it segregates objects with out reference to everthing that surrounds that model.

Relativity does not exist in a vacumm. An object traveling at 0.9 c is travelling in a very different universe and we and all other objects are a part of that universe.

If you say that the only frame that matters is the preferred frame, then you have relegated relativity to the realms of pure abstraction, thus limiting it's application to thought experiments almost exclusively.

To take the position that other perspectives ( frames ) are irrelevant is an excercise in imagination only as all frames are alway relevant in the real world.

The whole argument in the other threads is about perpective. Philosophically if a person relies exclusively on his own perspective we have a state of insanity. It takes the balance of all perspectives to give us a balanced view.

The same applies to the universe in general, all frames are relevant to all frames in some way and to elliminate that relationship is like a man relyng only on his own perpective ( insanity)

Object A and Object B are in a continuous relationship and to take the view that it is only a relationship by A's perpective is invalid.

If I was stationary and an object of mass travelled past me at relativistic velocities I woudl be severely impacted upon, the mere energy required to propell the object come from me in part. The em emmissions of teh dilated object would be in conflict with what I woudl normally experience and so on......relativity is an apathied madel in that it segregates objects with out reference to everthing that surrounds that model.

Sorry QQ, this looks like complete nonsense to me.

Why do you think that the object would suck energy from you?
What emissions are you referring to?
What exactly is implied in "and so on"?

Relativity does not exist in a vacumm. An object traveling at 0.9 c is travelling in a very different universe and we and all other objects are a part of that universe.
This doesn't seem to make sense... what exactly do you mean by "a very different universe"?

If you say that the only frame that matters is the preferred frame
There is no preferred frame

To take the position that other perspectives ( frames ) are irrelevant
Why do you think that anyone is taking that position? I think you misunderstant.

The whole argument in the other threads is about perpective. Philosophically if a person relies exclusively on his own perspective we have a state of insanity. It takes the balance of all perspectives to give us a balanced view.
The whole development of Relativity was about developing a model in which the same physical results are predicted from all perspectives. That's what reference frames are about - the same physical results are predicted no matter what frame you choose to work from.

Choosing Celsius or Fahrenheit doesn't affect the fundamental entity of Temperature even though the numbers are different.

Choosing a reference frame doesn't affect the fundamental entity of spacetime even though (and this is one step further than the temperature analogy) the quantities of space and time are different.

Why do you think that the object would suck energy from you?
What emissions are you referring to?
What exactly is implied in "and so on"?

If we refer back to the train and the rail thougth experiment.

Say the train is travelling at 0.9c. I don't know what sort of energy is needed to propel that train but I woudl assume it would be a large perentage of all energy available universally.

The rail is part of that universe.......the energy to propell that train is taken from the rail. The rail I would suggest would fail and the train would continue with out it.We talk about trains and rails but we seem to fail to consider the ramicfications of that trains velocity to the rest of the universe. ( the rail is part of that universe.

So maybe I should ask the question again.

What impact does the train have on the rail at 0.9c.?

And if you answer none then we are in lah lah land for sure....

Choosing a reference frame is much like choosing a zero point on an arbitrary scale, such as degrees Celsius and degrees Fahrenheit... does it matter which one you choose? Does it change the physical predictions of your calculations
using this analogy I could say "there aint much point using Celsius as a method when the person youare trying to tell only knows fahrenheit."

I ask a very simple question ?

According to relativity, is object A effected by Object B and vica versa?

And then,

If so does relativity include this impact when making calculation about the selected frame.


For eample two large masses with significant gravities travel past each other at velocity. does relativity include the reciprical effects of that gravity on the velocity of our two masses. Or do we take a relected frame and view it only from that perpective.

Very good, MacM, perhaps you're starting to get it.

Do you think that this is a contradiction in SR?
Don't forget that you haven't proven that time is absolute...

I'll only say that clocks record ONE time and that wheels only turn at ONE Rpm. Otherwise your speedometer reading must change. That is no longer just Relativity but Multiverse. :D

I know that you have an interest in Accelerators. Has there been stiudies into the impact that the accelerating particle has on it's environment. the tube that it is fired in, the vacumm or air that is it's ambience.

Interesting point QQ. If the circumference of the accelerator is contracted and it still contains not only the same rarefied enviornment (but not void) the density goes up along with the apparent mass of such particles.

No wonder it takes more energy to keep going faster. :D

I'll only say that clocks record ONE time and that wheels only turn at ONE Rpm. Otherwise your speedometer reading must change. That is no longer just Relativity but Multiverse. :D

I prefer not to waste time on this unrealistic example. No wheel still sit on the track at relativistic velocity. Why don't you guys think about something that at least sound probable?

Why do you think that the object would suck energy from you?

My impression was that he is projecting an analog from the arguement that at v = c requires an object to posses infinite energy as in requiring the energy of everything in the universe and that from that perspective some lesser relative velocity has taken some lesser energy from everything.

Is that your thoughts QQ?

MacM:

I'll only say that clocks record ONE time and that wheels only turn at ONE Rpm. Otherwise your speedometer reading must change.

Wrong again.

Speed is distance travelled divided by time taken. In the frame of the train, the distance between points A and B is shorter, and so is the time taken to cover the distance, by the same amount. Net result: The speedometer reading is the same as the speed of the train as measured by somebody standing still on the rails.

I prefer not to waste time on this unrealistic example. No wheel still sit on the track at relativistic velocity. Why don't you guys think about something that at least sound probable?

Just making a comment not side tracking the issue. But yours is an unresponsive position. You and others refer to all sorts of thought experiments but the minute you don't want to consider something you start with the keep it plausible.

Well, sir not one tought experiment concerning relavistic speeds is plausible so I guess we should just stop talking about it - huh?

MacM:

Wrong again.

Speed is distance travelled divided by time taken. In the frame of the train, the distance between points A and B is shorter, and so is the time taken to cover the distance, by the same amount. Net result: The speedometer reading is the same as the speed of the train as measured by somebody standing still on the rails.

I'm not going to hijack QQ's thread and argue with you here. But your assertions are unfounded.

by JamesR,

Speed is distance travelled divided by time taken. In the frame of the train, the distance between points A and B is shorter, and so is the time taken to cover the distance, by the same amount. Net result: The speedometer reading is the same as the speed of the train as measured by somebody standing still on the rails.
================================================== ==============

That is correct, JamesR. The traveller sees time pass normally in her frame of reference. Example: Jill takes a one light year trip through space, in a curved flight.
Turns out, Jill got pregnant the night before she left. She has her baby 9 months after
leaving Earth. Time passes normally in her frame of reference, correct? She was travelling at .95c. When she is approaching Earth at the end of the trip, her clock
reads a little over a year passing and her baby is over 3 months old. What happens to the baby when she steps off her rocket on Earth? In Earth's frame of reference, she
has aged less than 9 months during her trip, according to SR.

2inquisitive:

No. In the Earth's frame of reference, she has aged more than a year, but less than the people on Earth.

Maybe I wasn't clear. The one light year trip was from Earth's frame of reference. She was gone slightly over one year by the Earth's clock, also. Are you saying that the
clock on her rocket will never reach one year, that the time an Earth-based observer
sees on her clock will be the same as she sees on her own clock?

Speed is distance travelled divided by time taken. In the frame of the train, the distance between points A and B is shorter, and so is the time taken to cover the distance, by the same amount. Net result: The speedometer reading is the same as the speed of the train as measured by somebody standing still on the rails.

Interesting... this means that the wheels must also have a different circumference in the two frames, and that difference must correspond to the lorentz factor...

What's the equation for the circumference of an ellipse?

Ellipse circumference = PI √(long axis² + short axis²)

For the train wheels:
long axis = rest frame wheel diameter
short axis = long axis x lorentz factor

I haven't time to work this through, but it doesn't look like it will work out...

Interesting problem.

According to relativity, is object A effected by Object B and vica versa?
Relativity does not suggest any effects.

An object with low mass (to avoid gravitational effects), charge (to avoid electrostatic effects), and radiation (to avoid burning you) passing you at an aribtrarily high speed in a vaccuum will not effect you in any way.

Say the train is travelling at 0.9c. I don't know what sort of energy is needed to propel that train but I woudl assume it would be a large perentage of all energy available universally.
You're treating speed as an absolute again... everything is travelling at 0.9c in some reference frames.

The rail is part of that universe.......the energy to propell that train is taken from the rail.
What if the train is powered by rockets? The energy is not taken from the rail.

What impact does the train have on the rail at 0.9c.?
It depends on the mass of the train, the type of wheels, how much force the wheels exert on the rail, and so on. The answers are not found in relativity, but in materials engineering.

Possibly None.

What if the train is powered by rockets? The energy is not taken from the rail.
Pete the problem is the power needed to push a rocket at these sorts of speed are simply not contaned in the rocket the energy required is way too much. The universe is considered as finite, yet it is suggested that to approach v=c required infinite amounts of energy. SO I ask you were is teh energy obtained to propel a rocket a near 'c'......the universe of course.

The universe is considered to have a finite energy status yes?

well Infinite sounds a bit more than finite...... :)

Pete the problem is the power needed to push a rocket at these sorts of speed are simply not contaned in the rocket the energy required is way too much.
Can you prove it, or are you going on gut instinct?

I think your gut is misleading you on this one.

Relativity does not suggest any effects.

This is the answer I was expecting Pete and I can't argue with that.

The only question that is now evident is:

Does relativity as a model reflect reality?

Because I know that everything impacts on everything when dealing with the absolute and if relativity can not deal with this reciprication then it is severely limited as a model for use in real situations.

You're moving away from relativity theory anyway.

Did you know that there are other areas of science and engineering that are often used in conjunction with relativity to describe real situations?

“ Pete the problem is the power needed to push a rocket at these sorts of speed are simply not contaned in the rocket the energy required is way too much. ”

Can you prove it, or are you going on gut instinct?

I think your gut is misleading you on this one.

may be if I had teh math I would....ha

ok,say we have a 10 kg lump of iron. What amount of energy is needed to propel that object to 0.9c?

You're moving away from relativity theory anyway.

Did you know that there are other areas of science and engineering that are often used in conjunction with relativity to describe real situations?

I guess I am Pete and this is also part of what I wanted to discuss,
How can relativity be adpated to remaiin free of conflict with other fields of endeavour?

My impression was that he is projecting an analog from the arguement that at v = c requires an object to posses infinite energy as in requiring the energy of everything in the universe and that from that perspective some lesser relative velocity has taken some lesser energy from everything.

Is that your thoughts QQ?

Correct in essence. but not in words.

Another thing that stands out for me is that when I did some graphing about the dilation vs velocity issue I realised as you have no doubt already know that as you approach v=c time dilates almost to the infinite as well.

so at v=c time dilation is infinite as well as the energy needed.

so to take the absurd and extrapolate.

at v= 0.9999999999999 how long is the dilated second to Earths frame?

What I understand is that the seconds length is approaching infinite. or eternal. Now if that is the case the object will arrive almost instantaneously, or to the other extreme never regardless of the distance it has to travel.
So from my perpsective relativity is limited to small velocities probably below 0.1 c if i rememeber the graphing......may be someone can elucidate on this point a little.

What this tells me that our thought experiments are fundamentally a waste of time, and only playing a mathematical mind game especially when dealing with near 'c' velocities.

So,,,,we stop right here.....

What is really happening here is we have at least two frames of reference.
one is Petes perpective and the other is mine.

Pete represents orthadox thinought and I represent only myself.

the frames of reference for this discussion are in conflict not so much the content as such but the frames of reference for sure.

I am placing a question about teh limitations of science if it doesn't include teh inverse regards impacts, call it reciprication if you will. And Pete is saying this is nonsense and that it doesn't fall with in the realms of relativity.

I argue it is true , it is nonsense to relativity but not to science per se..... so we have a conflict of what we are actually discussing.....ha ...typical internet....forums.


Pete has discovered that I am trying to put relativity in perspective with other fields of science. Ok.......so I failed, to do this and it was my intent.....but the point is am I trying to discuss relativity or am I trying to discuss relativities reality. To discuss the reality of relativity means that a holistic approach to physics is needed and not focussed solely on relativity. But our two frames, petes and mine, are at cross purposes.

So the discussion can only do one thing and that is fail to deliver a conclusion.

I would suggest that by taking a single frame as your reference we will always end up in conflict. twins paradox, pole in barn paradox, train on rail paradox, etc etc etc.....

It was stated that the pole has no physical relationship with the barn I think and that is a big flaw in reasoning...I reckon....the same applies to our train the rail and the surrounding universe.

The reality is that if a theory creates a physical paradox and refuses to show how the two frames relationship is then as far as I am concerned that theory has low credibility.

A time dilated object must effect the state of another less or more dillated object.....cause and effect is not negated by relativity. Object A must effect object B and vica versa to state otherwise is justifying only a mind game and not the reality.....

But if that is the case then that is the case, I will argue no more.....

How can relativity be adpated to remaiin free of conflict with other fields of endeavour?
As far as I'm aware it doesn't need to be adapted. Why do you think there is a conflict?

It was stated that the pole has no physical relationship with the barn I think and that is a big flaw in reasoning
Why? Gut instinct?

The reality is that if a theory creates a physical paradox and refuses to show how the two frames relationship is then as far as I am concerned that theory has low credibility.

Relativity creates no paradoxes, as far as I know. Would you like to enlighten me?

What do you mean by "the two frames relationship"? Are you sure you know what a frame is?

Correct. The rpm measured in each frame will be different.

Thank you James. You have made my day. I would like to see your response to the fact that this statement is clearly false.

If you are speeding down the turnpike at 100 Mph, your wheels rotate at the appropriate Rpm to result in the measurement of distance traveled per unit of time and if calibrated proerly you can read this velocity on your speedometer as 100Mph.

Even to the state trooper hiding behind the billboard with a high power camera, he records your instrument panel (speedometer) as indicating 100 Mph and presents this to the Judge as evidence in your Court case.

The state trooper crusier which pulls up along side and is slowly passing you so as to cut you off and force you to pull over and stop sees through your window that your speedometer reads 100 Mph.

All of these views of your speedometer are from different frames of relative motion. None see anything but 100 Mph. The wheels did not alter their Rpm with relative velocity of the frame. Your speedometer consistantly displays 100 Mph.

This is a clear test done at a variety of speeds millions jof time each day and these test do not support your claim that the wheels change Rpm with frame of refereance.

This is indicative of all relavistic affect claims on physical reality such as clocks. This example is direct evidence that reality supports my view and not yours. the reality is that any frame view that differs from the local proper time is perception and illusion and not physical reality.

Interesting... this means that the wheels must also have a different circumference in the two frames, and that difference must correspond to the lorentz factor...

What's the equation for the circumference of an ellipse?

What happened to frames of reference cannot be rotated?

Example #3 Here

Pete I don't see any real value in argueing about frames.....no real value at all....I have asked the question "What does relativity descrivbe as the relationship between the train and the rail" I have recieved an answer and I have described my reservations and thoughts about the limitations of the model. which have been either misunderstood or decried for their naivity....I can accept all that ....no problems.....but maybe you can tell me why relativity fails at quantum levels. And if so why I should agree to think that relativity is still valid. Actually it is not Einstiens work it is the lorentz aspect that I think fails relativity.... length contractions and time dilations have significant problems when applied to extremes and I would think this is where the theories are tested as true or false. This is my opinion at the moment and I reserve the right to change it when ever I deem necessary.....


an interesting point raised earlier which may be of some use is that if an object of mass has the velocity of .999999 c it's tick rate is almost nil.... so for the time that it is travelling at .999999c it isn't moving.....in fact it is almost stationary......in it's frame it's tick rate appears normal but to the earth observer it isn't ticking at all.....and that poses a real problem, length contracted so that it has no where to travel and it has no time to travel it....hmmmmm.......sounds like good physics..... [I do hope I am wrong of course]

If you are speeding down the turnpike at 100 Mph...

There isn't enough time dilation at a relative velocity of 100Mph to register, Mac.

A wheel spinning at a constant rate is essentially a clock... if clocks runs slow in moving frames, then wheels spin slow as well. This should not change the display of the speedometer, which is measuring the rpm in the wheel's rest frame.

You can deny time dilation if you like... but you can't prove it's false by simply denying it.

What happened to frames of reference cannot be rotated?

Example #3 Here

Sorry, I don't see the relevance... can you explain, please?

There isn't enough time dilation at a relative velocity of 100Mph to register, Mac.

I anticipated this response. Let me suggest that even at sub-light speeds surely relativity can tell the differance between 100 Mph and 0 Mph which effectively the trooper along side has when he sees not change in your speedometer. My point is that this situation is directly applicable to clocks. As you say the wheel is a clock in this sense.

A wheel spinning at a constant rate is essentially a clock... if clocks runs slow in moving frames, then wheels spin slow as well. This should not change the display of the speedometer, which is measuring the rpm in the wheel's rest frame.

Exactly my point. The clocks in question will also continue to physically accumulate time at its local rate and are not varied by the observers view of the clock.

You can deny time dilation if you like... but you can't prove it's false by simply denying it.

You can continue to argue that clocks and wheels change rates as a function of an observers view but that provides no physical cause nor is it supported as can be seen on close investigation.

maybe you can tell me why relativity fails at quantum levels. And if so why I should agree to think that relativity is still valid.
It doesn't actually... but not enough is known about quantum gravity to make valid predictions under conditions where it is expected to have a significant effect.

You should note that Quantum Electrodynamics relies very much on special relativity.

You should only agree to think that relativity is valid if it is logical to do so... I can attempt to explain why it is logical to me, but I can't speak for you.

On an afterthought, what exactly do you mean by "valid"?

For me, it means "gives useful predictions". This makes Newtonian gravity and mechanics valid. Note that the Newtonian gravity and mechanics models are indistinguishable from Einstein's Relativity for most conditions we experience.

Or do you mean "fundamentally true"? That's a harder one... I acknowledge the possibility (probability) that Relativity (for example) is really a special case of something more fundamental, but for me that doesn't make it invalid.

You can continue to argue that clocks and wheels change rates as a function of an observers view but that provides no physical cause nor is it supported as can be seen on close investigation.
This is the same argument as before. Nothing new here.

This is the same argument as before. Nothing new here.


I have to agree you have provided nothing new in the way of support for your arguement other than some subjective view based jpurely on mathematics.

It doesn't actually... but not enough is known about quantum gravity to make valid predictions under conditions where it is expected to have a significant effect.

You should note that Quantum Electrodynamics relies very much on special relativity.

You should only agree to think that relativity is valid if it is logical to do so... I can attempt to explain why it is logical to me, but I can't speak for you.

On an afterthought, what exactly do you mean by "valid"?

For me, it means "gives useful predictions". This makes Newtonian gravity and mechanics valid. Note that the Newtonian gravity and mechanics models are indistinguishable from Einstein's Relativity for most conditions we experience.

Or do you mean "fundamentally true"? That's a harder one... I acknowledge the possibility (probability) that Relativity (for example) is really a special case of something more fundamental, but for me that doesn't make it invalid.

we do actually agree. Relativity does make useful predictions and yes until something better comes along it would be unwise to ditch it. However I am sure it will be argued that the theory being 'close' to the truth makes it very hard indeed to progress beyond to a greater truth. This is of course a fundamental process as well.

Philosophically it is often quoted that the closer you get top the truth the more ellusive it becomes. I guess this is the challenge you physisist face hey?
But to become complacent will only hinder growth of knowledge.

I am sure both you and JamesR have certain reservations about relativity and I am also sure that you woudl be reluctant to discuss those reservations due to political correctness issues.

I personally would love to here of them........it'd put my purile assesments to shame I bet... :)

I am sure both you and JamesR have certain reservations about relativity and I am also sure that you woudl be reluctant to discuss those reservations due to political correctness issues.

I have no reservations about Relativity as a useful model.
Why are you sure I do?

If I did, then politics wouldn't stand in the way. I'm actually quite passionate about that.

may be if I had teh math I would....ha

ok,say we have a 10 kg lump of iron. What amount of energy is needed to propel that object to 0.9c?

The jproblem I see with your question is that you don't have to propel the 10kg mass at all. It doesn't have to move. You can propel a single electron relative to the 10 kg mass and produce the 0.9c relative velocity.

There seems to be no association between a mass and its relative velocity since there is no absolute velocity, only relative velocity.

Sorry, I don't see the relevance... can you explain, please?

He states outright that the other frame must not rotate. A wheel in this case is rotating. You were considering the circumference differance reqired to accomadate a different Rpm I believe.

He states outright that the other frame must not rotate. A wheel in this case is rotating. You were considering the circumference differance reqired to accomadate a different Rpm I believe.
Yes... but neither of the frames (train and rail) under consideration are rotating.

Yes... but neither of the frames (train and rail) under consideration are rotating.

Agreed but you were calculating the change in wheel circumferance required to accomadate a variable Rpm. The wheel frame is rotating relative to the other frames.

the question that interests me is: if the traveling object (at say, .9c) was in slots or whatever on the rail, would it come out of the track due to contraction?

Regarding the rpm of a wheel, I think I made a mistake.

The number of revolutions per minute is the angular velocity, w, of the wheel. To calculate the speed of the outside of the wheel, we use v=wr, where r is the wheel's radius. This is how the speedometer determines the speed of a car or a train or whatever.

Looking at the measured speeds in two different reference frames, of the car and the ground, we have a bit of a problem, which makes this situation rather more complex than it appears initially.

In the frame of the rail (ground), every point on the wheel has a different velocity, since it is rotating. What we are interested in is the speed of the centre of mass of the wheel (the axle) relative to the ground. This is the only point on the wheel which moves in a straight line parallel to the track. The person on the ground can watch the centre of the wheel and come up with a speed v, which is equal to the speed of the train relative to the track. However, they cannot simply look at a random point on the outside of the wheel and use v=wr. Why? Because the wheel is not circular in the track frame. The train, and hence the wheel, is contracted in the direction of motion of the train, making the wheel elliptical rather than circular in the frame of the track.

Things are equally complicated in the train frame. If the train observer watches the track, the track moves in a straight line at constant speed, and that speed is -v (i.e. the same magnitude as the speed of the train as measured by a trackside observer). But from the train observer's point of view only one point on the wheel moves at constant velocity -v at any time. This is the point on the wheel which is momentarily in contact with the track. The train observer also sees a number of length contraction effects due to the motion of points on the wheel relative to him - to an extent where it is no longer true that the circumference of the wheel is equal to 2 pi times the radius. To properly describe this requires general relativity.

What all this means is that it is not necessarily true that a speedometer which relies on a particular relationship such as v=wr to calculate the speed, will work properly as speeds approach the speed of light.

To conclude, I am not sure whether the rpm measured by a trackside observer is or is not the same as the rpm measured by somebody on the train. This is a complicated problem with many factors contributing.

To simply assert that the rpm must be the same, without working through all the arguments, is naive to say the least.

wesmorris:

Length contraction only occurs in the direction of motion, not in directions perpendicular to the motion. Therefore, the train is unlikely to come out of slots.

Agreed but you were calculating the change in wheel circumferance required to accomadate a variable Rpm. The wheel frame is rotating relative to the other frames.

Mac, you're not paying attention.
I don't care about the rotating wheel frame - it's not under consideration.

I was considering how the wheel circumference is different between the train's frame and the rail's frame.

As it happens, the wheel circumference is a red herring anyway - it's only the accumulation of horizontal distance that matters - the vertical component of the wheel circumference is irrelevant.

wesmorris:

Length contraction only occurs in the direction of motion, not in directions perpendicular to the motion. Therefore, the train is unlikely to come out of slots.

Thanks James.

JamesR, you have probably already stated this but I'll put in my words,

If the wheel of the train has a magnetic insert in it circumference so that every time the magnet touches the rail the train registers 1 rpm and the track registers 1 rpm.

At velocity the track and the train now use the same magnetic insert to determine velocity.

At say 0.8 c do the track and the train agree on velocity of the train from the tracks frame and the rail from the trains frame?

[I will admit at this point that I had only included the wheels in the original scenario as a convenience and not intended as a matter of consideration - but it 'turns' out (excuse the pun) to be interesting afterall]

My own answer would be that the velocity is agreed as the true velocity however the train will record it in a dilated state and the rail will not.

Say the rail is an Earth frame the velocity of the train is recorded using Earth seconds.
The Train however is using it's train seconds.

We know that the velocity is the same but I guess the train woudl consider itself to be going faster. hmmmmmm.......longer second greater distance......yep faster than the rails record. ahhhh....I t'ink

Maybe JamesR this should become a new thread topic, would you care to start it?
I also would suggest that our train use a tractor mechanism or "wheel gearing to track" as part of it's propulsion so that Wesmorris's concerns could be addressed.
could be fun!

As it turns out it addresses my major concerns about the "reciprication between frames issue"...as the wheel is in contact with the rail at all times.

Mac, you're not paying attention.
I don't care about the rotating wheel frame - it's not under consideration.

I was considering how the wheel circumference is different between the train's frame and the rail's frame.

As it happens, the wheel circumference is a red herring anyway - it's only the accumulation of horizontal distance that matters - the vertical component of the wheel circumference is irrelevant.

I think I was paying attention. that is why I raised the issue about wheel Rpm in the first place. You also were involved in the Rpm portion of the discussion when you began to talk about the circumferrence of the wheel.

I find no apparent reason for your concern about wheel circumference unless you were trying to equate Lorentz Contraction of the rail to wheel Rpm.

If I assumed to much then what were your concerns with circumference.?

Length contraction means the wheel circumference is different in the train frame and the rail frame. Neither frame is rotating.

Length contraction means the wheel circumference is different in the train frame and the rail frame. Neither frame is rotating.

So you are saying that you were concerned about the wheel geometry and not its Rpm?

If you're travelling alongside the train, the wheels are perfectly circular. If you and the train are moving at 0.9c relative to an observer, the observer will see (assuming special equipment and a super-duper-hyper-high speed camera) elliptical wheels (and if the with-train traveller is me, he's looking a hell of a lot slimmer!)

So you are saying that you were concerned about the wheel geometry and not its Rpm?
I was concerned about the rpm too, since I was (incorrectly) thinking that measured speed would be the cimple product of rpm and wheel circumference.

The point that I feel you are making me labour far beyond its importance is that I was never concerned with the rotating frame of the wheel.

If you're travelling alongside the train, the wheels are perfectly circular. If you and the train are moving at 0.9c relative to an observer, the observer will see (assuming special equipment and a super-duper-hyper-high speed camera) elliptical wheels (and if the with-train traveller is me, he's looking a hell of a lot slimmer!)

Actually, what one sees (or what a camera captures) is actually quite different to the raw predictions of relativity because of signal delays.

The transforms of relativity do not include the signal delays that would affect the perception of an observer or camera.

It seems that the rail-frame observer would perceive the train, its wheels, and yourself as rotated, not contracted. To make conclusions about what was really happening, an observer would need to record their observations and perform calculations to remove the signal delay effects.

See Penrose-Terrell Rotation (http://math.ucr.edu/home/baez/physics/Relativity/SR/penrose.html), and Seeing Relativity (http://www.invisiblemoose.org/site_material/Seeing_Relativity/relativity.html).

I was concerned about the rpm too, since I was (incorrectly) thinking that measured speed would be the cimple product of rpm and wheel circumference.

The point that I feel you are making me labour far beyond its importance is that I was never concerned with the rotating frame of the wheel.

Fair enough.