Is Faster than Light travel impossible?

[jmallett]

There is nothing about train tracks or roads that makes them 'independent of relative motion'.


OK. I assume that they have some speed relative to each other.


What do you mean 'synchronize'? Note that relativity assumes that any frame of reference (each of the two ships, in this case) will measure the speed of any beam of light as moving with the same speed c with respect to that frame.


I have no idea what you are looking for.

OK, I'll step it back a little on the subject of synchronization.
Ship A creates white light.
Ship B creates white light

What color do they appear to be to each other ?

 

[matheinste]

Matheinste, Great questions, and this is something for the defenders of Einstein. By placing an observer in the picture they immediately specify that with, or without, force it must be so. The dictate is that light travels at a single and constant speed in any given frame of reference. It may, or may not, be true, but if it is true then you are right to ask - by what law, or force can the observer do this ?

The next part is the exciting part. No-one seems to be considering this, and Einstein certainly didn't, so you are beginning to think beyond the rote learning of the last 100 years.

I hope nobody else thought that was a serious question.

Matheinste.

 

[Doc Al]

Then by definition he sees the light in the train, and by seeing it and the train at the same time, then the speed of the light in the train is the same in the train as it is for him - (c + v) disappears and the observer in the train measures the train's length incorrectly.

Nothing magical happens when the observer 'sees the light'. The speed of light with respect to the outside observer is c. And the speed of light with respect to an observer on the train is also c.

(c + v) is not the speed of light. It's the rate at which the light and the train approach each other according to the outside observer. An observer on the train would describe things differently: he would say that the light approaches the train--his frame--at speed c.

Every frame sees the speed of light to be c with respect to their frame. (Not someone else's.) This is a tricky concept.

 

[matheinste]

OK, I'll step it back a little on the subject of synchronization.
Ship A creates white light.
Ship B creates white light

What color do they appear to be to each other ?

Isn't white light frequency shifted still white light.

Matheinste.

 

[Doc Al]

OK, I'll step it back a little on the subject of synchronization.
Ship A creates white light.
Ship B creates white light

What color do they appear to be to each other ?

"White" is not a good choice for a color, as it is a mix of frequencies. To understand how the frequency of light changes due to the relative speed of source and observer, look up the Doppler effect. I recommend you stick to one topic at a time.

 

[Doc Al]

I hope nobody else thought that was a serious question.

 

[jmallett]

I hope nobody else thought that was a serious question.

Matheinste.

Matheinste, It was a good question in it's obvious error, of course, and that's why it was a great question.
The answer is - there obviously is no mysterious force and therefore there is no way that an observer CAN force the light to the same speed.
Ergo those (like Einstein) who assume it to be the case need to demonstrate the existence of the force or dispense with the observer.
Einstein specifies it, but does not explain it's obvious fallacy.

I thought you were trying to be ironic, and used that irony to show that once you move down that road you are clearly in some particularly non-scientific territory.

 

[jmallett]

Isn't white light frequency shifted still white light.

Matheinste.

Whereby we are unable to determine red shift in the universe and therefore unable to determine it's rate of expansion ?

I'll let the physicists know about that one.

 

[jmallett]

Only the folks that believe in stationary observers got suckered into that. The rest used his original irony to indicate that it was, of course, an ironic question because it assumes observers with magical powers.

 

[jmallett]

Now is there anyone out there interested using relativistic mechanics in order to understand relativity ?

 

[jmallett]

"White" is not a good choice for a color, as it is a mix of frequencies. To understand how the frequency of light changes due to the relative speed of source and observer, look up the Doppler effect. I recommend you stick to one topic at a time.

It is, of course, the same subject, because the postulate at the moment is that light in a moving train is seen in one way in the train, but a different way by someone not in the train. It's just going back to some very basic stuff assumed by the experiment because there did not seem to be consensus in this forum on the understanding of the speed of light in a particular frame of reference, so I was trying, first, to define some basics which we might all agree on before jumping to the assumptions which we do not, apparently, agree on for the moment.

 

[jmallett]

It is, of course, the same subject, because the postulate at the moment is that light in a moving train is seen in one way in the train, but a different way by someone not in the train. It's just going back to some very basic stuff assumed by the experiment because there did not seem to be consensus in this forum on the understanding of the speed of light in a particular frame of reference, so I was trying, first, to define some basics which we might all agree on before jumping to the assumptions which we do not, apparently, agree on for the moment.

OK, pick a color, pick any color, hey you can even pick anything in the electromagnetic spectrum as far as I am concerned. I don't think we need to argue (yet) about the color of this light - that will change in due course anyway, although it's possible that we may disagree on the color it is going to be later.

 

[Doc Al]

It is, of course, the same subject, because the postulate at the moment is that light in a moving train is seen in one way in the train, but a different way by someone not in the train.

Nope. That might be your postulate, but it has little to do with relativity. Everyone sees the light traveling at the same speed with respect to them.

 

[jmallett]

Nope. That might be your postulate, but it has little to do with relativity. Everyone sees the light traveling at the same speed with respect to them.

No, definitely NOT my postulate.
Thank you for making the point.
It is the postulate of the stationary observer.

It is the postulate currently being made by a variety of people in this forum.

 

[Doc Al]

It is the postulate currently being made by a variety of people in this forum.

Nope, just you.

 

[jmallett]

Nope, just you.

Actually you have taken this position. Please bear with me for a moment, and please indicate at which po9int you disagree.

The "stationary observer" watched the observer take a measurement in the train.

He measured the speed of the train (in his reference frame)

He observed that the observers on the train incorrectly measured the length of the rod - when considered in the stationary observers time frame.

He then took the velocity information of his frame of reference, but used it together with the iength measurement made in another frame of reference, thereby confusing two sets of data.

Clearly he cannot derive the equation r(AB)/(c + w)

Now, why do I believe you have made that postulation ?
Because you assumed that the light in the train traveled faster than the light in the stationary frame yet both were in the same frame of reference.

OK, so let's then agree, right ? The stationary observer sees the light in the train traveling at the same speed as the light in his own frame. Do we agree ?

 

[jmallett]

It is, of course, the same subject, because the postulate at the moment is that light in a moving train is seen in one way in the train, but a different way by someone not in the train. It's just going back to some very basic stuff assumed by the experiment because there did not seem to be consensus in this forum on the understanding of the speed of light in a particular frame of reference, so I was trying, first, to define some basics which we might all agree on before jumping to the assumptions which we do not, apparently, agree on for the moment.

Oh, and by the way, any time someone says - "go back and read about..." it reminds me of the people you meet in various religions who when asked to give their view simply say - "you need to study Gospel x, chapter y"

I appreciate that you have your beliefs. I am still a skeptic. I am merely trying to understand how you believe your beliefs, because they are not to me self-evident

 

[Doc Al]

He then took the velocity information of his frame of reference, but used it together with the iength measurement made in another frame of reference, thereby confusing two sets of data.

Nope. The 'stationary' observer does not make use of any length measurements made in some other frame. All his measurements are made in his own frame.

Now, why do I believe you have made that postulation ?
Because you assumed that the light in the train traveled faster than the light in the stationary frame yet both were in the same frame of reference.

Nope. I've said as many times as possible: Viewed from any frame of reference, the light moves at the same speed. (Again, I have no idea what you mean when you talk of things being in 'the same frame of reference'.)

OK, so let's then agree, right ? The stationary observer sees the light in the train traveling at the same speed as the light in his own frame. Do we agree ?

I've been saying that all along: The 'stationary' observer sees all light travel at the same speed with respect to him (not the train!). A basic premise of relativity is that the speed of light is the same in every frame. Now if you switch to the frame of the train, then the speed of light is also c with respect to the train.

Where you are getting stuck is in not understanding how the stationary observer can see the light and the train close at a rate of 'c + v', even though both the stationary observer and the train both observe the light to move at the same speed c with respect to their own frames. This is tricky stuff.

 

[Doc Al]

I appreciate that you have your beliefs. I am still a skeptic. I am merely trying to understand how you believe your beliefs, because they are not to me self-evident

There's no requirement for science--especially relativity--to be 'self-evident'. Further, science is based on logic and evidence, not merely 'belief'.

Before calling yourself a 'skeptic' about something, why not first try to understand that something?

 

[matheinste]

Oh, and by the way, any time someone says - "go back and read about..." it reminds me of the people you meet in various religions who when asked to give their view simply say - "you need to study Gospel x, chapter y"

I appreciate that you have your beliefs. I am still a skeptic. I am merely trying to understand how you believe your beliefs, because they are not to me self-evident

If you accept the beliefs or postulates of relativity you arrive at certain logically derived consequences. You do not have to accept any postulates if you wish not to. However, you must accept the logical reasoning used. If you do not accept the postulate of light speed, which most agree is counterintuitive, so be it, but at least apply some logic in your arguments against it.

Matheinste.

 

[jmallett]

Nope. The 'stationary' observer does not make use of any length measurements made in some other frame. All his measurements are made in his own frame.


Nope. I've said as many times as possible: Viewed from any frame of reference, the light moves at the same speed. (Again, I have no idea what you mean when you talk of things being in 'the same frame of reference'.)


I've been saying that all along: The 'stationary' observer sees all light travel at the same speed with respect to him (not the train!). A basic premise of relativity is that the speed of light is the same in every frame. Now if you switch to the frame of the train, then the speed of light is also c with respect to the train.

Where you are getting stuck is in not understanding how the stationary observer can see the light and the train close at a rate of 'c + v', even though both the stationary observer and the train both observe the light to move at the same speed c with respect to their own frames. This is tricky stuff.

OK, so we are starting to agree.

"Viewed from any frame of reference, the light moves at the same speed. (Again, I have no idea what you mean when you talk of things being in 'the same frame of reference'.)"


I see that we agree there are various frames of reference.

When I say "same frame of reference" I mean a SINGLE frame of reference, for example the stationary observer has a single frame of reference. He can't see things (like light) behave differently at different times, because he can only exist in a single frame of reference, and everything he observes is now in the same frame of reference, that is to say his. This includes the various cars, trains, tracks, light, etc he has been observing throughout this discussion.

Are we on the same page ?

 

[Doc Al]

When I say "same frame of reference" I mean a SINGLE frame of reference, for example the stationary observer has a single frame of reference. He can't see things (like light) behave differently at different times, because he can only exist in a single frame of reference, and everything he observes is now in the same frame of reference, that is to say his. This includes the various cars, trains, tracks, light, etc he has been observing throughout this discussion.

Are we on the same page ?

Nope, not even close. For things to be 'in the same frame of reference' they must be moving together at the same speed. Note that anything--cars, trains, tracks, light--can be observed by anyone in any frame of reference. Just because someone in the track frame (that is, someone at rest with respect to the tracks) sees a train going by does not magically make the train somehow jump into the same frame of reference as the observer. The track frame sees the train moving (thus in a different frame); similarly, the train frame sees the track moving.

 

[jmallett]

If you accept the beliefs or postulates of relativity you arrive at certain logically derived consequences. You do not have to accept any postulates if you wish not to. However, you must accept the logical reasoning used. If you do not accept the postulate of light speed, which most agree is counterintuitive, so be it, but at least apply some logic in your arguments against it.

Matheinste.

First accepting the postulates or beliefs of anything is merely taking it on faith. We agree.

I fully accept the postulate of light speed, if we are talking about an observer will see light travel at speed c in his own frame of reference. I think you agree with that too.

Let's try to move to the logic part.

I will, for the moment, accept your stationary observer - we still agree.

We will both accept that the speed of light in the moving body is c.

We will now ask a question. As far as the train is concerned what is his speed ? Well probably he doesn't know, maybe doesn't care, right ? So what do we want him to do about that. The general conclusion is that his velocity relative to himself is 0 and therefore he can ignore his own movement.

Before going too further - any problems ?

 

[jmallett]

Nope, not even close. For things to be 'in the same frame of reference' they must be moving together at the same speed. Note that anything--cars, trains, tracks, light--can be observed by anyone in any frame of reference. Just because someone in the track frame (that is, someone at rest with respect to the tracks) sees a train going by does not magically make the train somehow jump into the same frame of reference as the observer. The track frame sees the train moving (thus in a different frame); similarly, the train frame sees the track moving.

Then the light in the train is not in the same frame of reference as the rod ?

 

[matheinste]

I do not wish to be drawn into the argument.

Matheinste.

 

[Doc Al]

We will now ask a question. As far as the train is concerned what is his speed ?

With respect to what? With respect to the train itself, the speed of the train is zero of course. The speed of anything is zero in its own frame.

 

[Doc Al]

Then the light in the train is not in the same frame of reference as the rod ?

The light is not part of any frame of reference. (There is no frame in which the light is at rest.)

 

[jmallett]

The light is not part of any frame of reference. (There is no frame in which the light is at rest.)

Then where is the frame of reference in which the train and the rod are at rest ?

 

[Doc Al]

Then where is the frame of reference in which the train and the rod are at rest ?

All of a sudden a rod appears. How is it moving with respect to the train?

 

[jmallett]

Then where is the frame of reference in which the train and the rod are at rest ?

Stationary with respect to the train, that's where we started and that's the postulate of Einsteins equations, although Einstein didn't actually need a train, he just had the rod floating. The train got introduced somewhere a few pages back, I think, but never mind, let's assume the rod and train are stationary relative to each other. The observer on the train is trying to measure the length of the rod just as Einstein had him do, but measuring the length of the train will do just as well.

 

[Doc Al]

Stationary with respect to the train, that's where we started and that's the postulate of Einsteins equations, although Einstein didn't actually need a train, he just had the rod floating. The train got introduced somewhere a few pages back, I think, but never mind, let's assume the rod and train are stationary relative to each other. The observer on the train is trying to measure the length of the rod just as Einstein had him do, but measuring the length of the train will do just as well.

OK. Rod and train are in the same frame.

 

[jmallett]

OK. Rod and train are in the same frame.

Good. We are on the same page. Now back a step -

Then where is the frame of reference in which the train and the rod are at rest ?

 

[darkhorror]

Good. We are on the same page. Now back a step -

Then where is the frame of reference in which the train and the rod are at rest ?

the train/rod are that frame of reference.

 

[Doc Al]

Good. We are on the same page. Now back a step -

Then where is the frame of reference in which the train and the rod are at rest ?

Moving along with the train, like any good reference frame. (Seriously, this is getting silly. Why not read that book I gave you the link for? It goes through all this in painstaking detail.)

 

[jmallett]

Good. We are on the same page. Now back a step -

Then where is the frame of reference in which the train and the rod are at rest ?

Then the observers on the train are measuring it's length at rest ?

 

[jmallett]

Moving along with the train, like any good reference frame. (Seriously, this is getting silly. Why not read that book I gave you the link for? It goes through all this in painstaking detail.)

Actually I did read a fair bit of that book, and here's some of the things I read:

- first question the book

- not being able to see your self in a mirror is IMPLAUSIBLE.
This hardly works for me because it is quite plausible, in fact sound works that way. It's possible for the statement to be right or wrong, but to dismiss it as implausible is not a particularly scientific approach, especially if we are going to draw some assumptions from that.

 

[jmallett]

Moving along with the train, like any good reference frame. (Seriously, this is getting silly. Why not read that book I gave you the link for? It goes through all this in painstaking detail.)

Sorry you see it as silly.

Einstein places the rest frame of the rod as the frame of the stationary observer. It is an explicit assumption that it is not at rest when moving in that frame, so we are stuck with a conclusion that is in it's rest frame when it is both in the train and when it is not moving relative to the stationary observer. Forget all the stuff about light.

He measures the length "at rest" and the length rAB is inherently the length when the "rod is at rest"

The length is therefore, in his experiment, inherently measured by the stationary observer.

 

[cfrogue]

Sorry you see it as silly.

Einstein places the rest frame of the rod as the frame of the stationary observer. It is an explicit assumption that it is not at rest when moving in that frame, so we are stuck with a conclusion that is in it's rest frame when it is both in the train and when it is not moving relative to the stationary observer. Forget all the stuff about light.

He measures the length "at rest" and the length rAB is inherently the length when the "rod is at rest"

The length is therefore, in his experiment, inherently measured by the stationary observer.

so what.

Make it happen in your mind.

They were at rest and measured the rod and then they were not at rest.

 

[Doc Al]

Einstein places the rest frame of the rod as the frame of the stationary observer. It is an explicit assumption that it is not at rest when moving in that frame, so we are stuck with a conclusion that is in it's rest frame when it is both in the train and when it is not moving relative to the stationary observer. Forget all the stuff about light.

He measures the length "at rest" and the length rAB is inherently the length when the "rod is at rest"

The length is therefore, in his experiment, inherently measured by the stationary observer.

You're getting all twisted in knots over the term 'stationary' observer.

Rather than use terms such as 'stationary' frame and 'moving' frame, let's call them the track frame and the train frame. No ambiguity there. If the train frame measures the length of the rod, then that's the length of the rod when the rod is at rest (with respect to the observer) since measurements are made in the frame where the rod is at rest. And if the track frame measures the length of the rod, then they measure the length of the moving rod since measurements are made in the frame in which the rod is moving.

OK. Now what?

 

[jmallett]

You're getting all twisted in knots over the term 'stationary' observer.

Rather than use terms such as 'stationary' frame and 'moving' frame, let's call them the track frame and the train frame. No ambiguity there. If the train frame measures the length of the rod, then that's the length of the rod when the rod is at rest (with respect to the observer) since measurements are made in the frame where the rod is at rest. And if the track frame measures the length of the rod, then they measure the length of the moving rod since measurements are made in the frame in which the rod is moving.

OK. Now what?

Now what is the equation the track uses to measure the length of the rod ?

 

[Doc Al]

Now what is the equation the track uses to measure the length of the rod ?

How would you like them to measure it? I suspect you'd like them to use a beam of light, else there wouldn't be much to talk about. So if they send a beam of light from one end (A) to the other (B), and they measure the travel time to be Δt, then the length of the rod in the track frame will be: L = cΔt.

 

[jmallett]

How would you like them to measure it? I suspect you'd like them to use a beam of light, else there wouldn't be much to talk about. So if they send a beam of light from one end (A) to the other (B), and they measure the travel time to be Δt, then the length of the rod in the track frame will be: L = cΔt.

Well, that's what Einstein said, so in terms of understanding Einstein's Special Theory of relativity this is going well.

But, the "stationary observer", the track observer we are talking about, sees something quite different from that, and relatively more complex, because he knows the speed v, and because he knows the speed of light c, therefore he needs to make 2 calculations, one to the front end, and one to the back end, and he has to take account of the fact that the rod is moving and that the speed of light is not instantaneous.

 

[Doc Al]

But, the "stationary observer", the track observer we are talking about, sees something quite different from that, and relatively more complex, because he knows the speed v, and because he knows the speed of light c, therefore he needs to make 2 calculations, one to the front end, and one to the back end, and he has to take account of the fact that the rod is moving and that the speed of light is not instantaneous.

And so?

 

[jmallett]

And so?

you don't see it ?

 

[Doc Al]

you don't see it ?

See what?

Depending on what the track frame measures, they can calculate the length of the rod with just one equation. If the train and the light beam are both moving to the right, the length of the moving rod according to the track frame will be L_track = (c - v)Δt_track.

See if you can derive that equation.

 

[jmallett]

See what?

Depending on what the track frame measures, they can calculate the length of the rod with just one equation. If the train and the light beam are both moving to the right, the length of the moving rod according to the track frame will be L_track = (c - v)Δt_track.

See if you can derive that equation.

That particular equation only works if the track can use the train's light, so it can't be valid in this useage. That's a simplification of what occurs. The track must use the track's light.

 

[Doc Al]

That particular equation only works if the track can use the train's light, so it can't be valid in this useage. That's a simplification of what occurs. The track must use the track's light.

Nope. There is only one beam of light that travels from one end of the rod (A) to the other (B). It doesn't 'belong' to the train or the track. Both frames can analyze the motion of that same beam of light.

 

[cfrogue]

That particular equation only works if the track can use the train's light, so it can't be valid in this useage. That's a simplification of what occurs. The track must use the track's light.

You can only say this if you have another theory of light.

DA presented a valid equation.

What is your theory?

 

[jmallett]

You can only say this if you have another theory of light.

DA presented a valid equation.

What is your theory?

That particular theory was the basis of the ether. Mitchelson Morely and a number of others disproved it. Einstein went forward with the assumption that light is relative to the frame of reference in which it exists, i.e. the train's light is not the track's light.

I don't yet have a full theory, just a whole lot of questions which I can't answer, but I am putting together some math on the subject.

Certainly in the situation Doc Al proposes we need to add in the distance deltaL which the rod passes through during the duration of the measurement. That's simple math and I will write it up for you. I hope soon to be able to share those equations, and I hope that someone will point out any errors I might have made. In addition to that I am working on an a demonstration with two bodies moving without reference to anything, i.e. truly relative, that use their own electromagnetic radiation (maybe light) to make a common measurement.

 

[Doc Al]

Einstein went forward with the assumption that light is relative to the frame of reference in which it exists, i.e. the train's light is not the track's light.

Nope--Einstein makes no such assumption. As I've already stated, light does not 'belong' to any reference frame. What Einstein does assume is that all light moves at the same speed with respect to any reference frame.

Certainly in the situation Doc Al proposes we need to add in the distance deltaL which the rod passes through during the duration of the measurement.

The equation I provided already takes into consideration the fact that the rod moves a distance vΔt_track during the time it takes for the light to travel from one end to the other.

(Note: Discussion of personal theories is not permitted.)