Is it Possible to Travel Faster than the Speed of Light?

[James S Saint]

Yes, I completely disagree with your post(s). My question was made to get you to realize the illogic of your assumptions. If you answer the question, you might see that there are problems with your assumptions.

i understand that was your intention and I will respect it, but not yet. I need to find out why people cannot see what I see so very clearly concerning "no absolute frame".

I have reduced the scenario to a simple case where there is no ground reference with which to use that equation because no one knows who is traveling.

The only things known are that there was 2Ls of distance and 1.333 secs later, there was none.

 

[James S Saint]

All of them are wrong. Assuming instant acceleration, the actual situation, in either of the ships' rest frames, is 0.86Ls being traversed in 0.9 secs.

So you disagree with (A), the very notion of relativity. I think therefore your input is a bit pointless.

And sorry, I had misread your reply just before.

 

[espen180]

So you disagree with (A), the very notion of relativity. I think therefore your input is a bit pointless.

And sorry, I had misread your reply just before.

The second part of A is wrong. The distances you report are not those observed by the ship observers, and the time is wrong according to ship observers. Of course I agree with relativity!

 

[James S Saint]

The second part of A is wrong. The distances you report are not those observed by the ship observers, and the time is wrong according to ship observers. Of course I agree with relativity!

EXACTLY what is in error with (A)?

The statements were;

1) Now the whole point to relativity is that there is no actual absolute frame, thus neither brother can claim to be the one traveling.

2) All we see is 2Ls of distance vanish in 1.333 secs.

The second sentence is the very setup to the story. (1) The brothers measured the 2Ls. (2) There was travel between them such that they both saw the distance vanish in 1.333 secs.

How can that be wrong?

 

[Doc Al]

1) Now the whole point to relativity is that there is no actual absolute frame, thus neither brother can claim to be the one traveling.

Either brother can (and does) view himself as being at rest and the other brother moving towards him.

2) All we see is 2Ls of distance vanish in 1.333 secs.

The second sentence is the very setup to the story. (1) The brothers measured the 2Ls. (2) There was travel between them such that they both saw the distance vanish in 1.333 secs.

Those measurements are only true in the ground frame. As soon as the brothers move, they are no longer at rest in the ground frame. They will use their own measurements of distance and time to measure how fast they move with respect to each other. (If you understand relativity, you can calculate what they will measure.)

 

[espen180]

EXACTLY what is in error with (A)?

The statements were;

1) Now the whole point to relativity is that there is no actual absolute frame, thus neither brother can claim to be the one traveling.

2) All we see is 2Ls of distance vanish in 1.333 secs.

The second sentence is the very setup to the story. (1) The brothers measured the 2Ls. (2) There was travel between them such that they both saw the distance vanish in 1.333 secs.

How can that be wrong?

Those starting conditions are physically impossible if reported in either of the ships' rest frames.

If reported in the ground frame, the correspond measurements the observers in the ships with make are the ones I gave above and in post #79.

 

[Borg]

i understand that was your intention and I will respect it, but not yet. I need to find out why people cannot see what I see so very clearly concerning "no absolute frame".

So you realize that the intention is to get you to see your illogical assumptions but, you're going to continue making statements that are based on those assumptions anyway? You aren't going to get anywhere with this so why not answer the question from post 76 while you're waiting for everyone else to see the light?

 

[James S Saint]

Either brother can (and does) view himself as being at rest and the other brother moving towards him.

Not so. Both brothers (and all observers always) see themselves as "the rest frame". That is what relativity is about. There is no actual rest frame for them to assume that they are the one traveling.

They will use their own measurements of distance and time to measure how fast they move with respect to each other. (If you understand relativity, you can calculate what they will measure.)

The only measurements that are made in this scenario is the 2Ls distance and the 1.333 secs duration. They both read the same time change. Neither knows who moved except that they moved with respect to each other.

Perhaps, from their perspective, one traveled at .9c and the other at .6c. Or perhaps one at .75 and the other at .75. They cannot know. They have nothing with which to measure such.

ALL they know is that there was 2Ls of distance and 1.333 secs later, there is none.

 

[James S Saint]

So you realize that the intention is to get you to see your illogical assumptions but, you're going to continue making statements that are based on those assumptions anyway? You aren't going to get anywhere with this so why not answer the question from post 76 while you're waiting for everyone else to see the light?

Note that you really aren't answering my questions either. I am trying to narrow exactly where I am actually wrong to one particular incorrect statement (at least). You are not helping with that. I understand that you might have a good point, but like I said. one train wreck at a time, please.

 

[James S Saint]

Those starting conditions are physically impossible if reported in either of the ships' rest frames.

If reported in the ground frame, the correspond measurements the observers in the ships with make are the ones I gave above and in post #79.

The physical impossibility of instant acceleration is not relevant. I could make the scenario where they backed off further and the ships merely took a little extra time to get up to speed. The question would turn out the same. It merely complicates the issue. How fast does a photon accelerate to get up to light speed when it leaves an atom? Certainly not instantly. So is the photon not traveling at the speed of light?

 

[espen180]

I'll sum it up in one sentence for you:
You are wrong in your assumptions that measurements are valid outside the frame they were made and that velocities may be linearly added together. You have been given the correct measurements and litterature where you can read about the theory but have ignored both.

 

[espen180]

The physical impossibility of instant acceleration is not relevant. I could make the scenario where they backed off further and the ships merely took a little extra time to get up to speed. The question would turn out the same. It merely complicates the issue. How fast does a photon accelerate to get up to light speed when it leaves an atom? Certainly not instantly.

The acceleration wasn't the point. My post is still valid regardless of how they get up to speed.

Also, a photon ALWAYS travels locally at c.

 

[Doc Al]

Not so. Both brothers (and all observers always) see themselves as "the rest frame". That is what relativity is about. There is no actual rest frame for them to assume that they are the one traveling.

What do you mean 'not so'? You just repeated back what I said.

The only measurements that make in this scenario is the 2Ls distance and the 1.333 secs duration.

According to what frame? Answer this or this thread is done.

They both read the same time change. Neither knows who moved except that they moved with respect to each other.

No one is talking about 'absolute' movement. All movement is relative.

Perhaps, from their perspective, one traveled at .9c and the other at .6c. Or perhaps one at .75 and the other at .75. They cannot know. They have nothing with which to measure such.

ALL they know is that there was 2Ls of distance and 1.333 secs later, there is none.

Again, according to what frame?

 

[James S Saint]

What do you mean 'not so'? You just repeated back what I said.

Oh oh.. I'm sorry. I read your post as "Neither".. my mistake.

According to what frame? Answer this or this thread is done.

The INITIAL frame, which is also the FINAL frame. It is in that frame that both measurements, both initial and final time and distance, get measured by both parties.

 

[Doc Al]

The INITIAL frame, which is also the FINAL frame. It is in that frame that both measurements, both initial and final time and distance, get measured by both parties.

OK, so what's the big issue? In the ground frame, the ships close at 1.5c. So?

Note that that says nothing about the relative speed of the ships when they are moving. If you wanted that speed, you can calculate it to be 0.96c.

 

[Mentz114]

But now there is where things seem to get a little confusing. The distance of 2 Ls between us got reduced to 0 in only 1.333 secs. That means that he traveled a 2Ls distance toward me in only 1.333 secs. That is 1.5 times the speed of light.

No, your twin only traveled 1Ls, because you meet at the sign. So you calculate that both of you traveled at 0.75c.

How did you double the distance traveled ?

This is how it looks from the sign's frame. This diagram is accurately to scale. You can read off distances and times and work out the time on your clock T² = t² - x² and divide by distance to get 0.96 !

 

[James S Saint]

OK, so what's the big issue? In the ground frame, the ships close at 1.5c. So?

Note that that says nothing about the relative speed of the ships when they are moving. If you wanted that speed, you can calculate it to be 0.96c.

What it says, because there are no "ground observers" (no absolute frame), the OBSERVED speed by the only observers present is 1.5c. Thus in the scenario pointed out, the observers, the travelers, would "see", by their measurements, that one of them traveled at 1.5c.

THAT is relevant.

The theory is that no such observation, measurement, could ever be made. "No observer will measure anything traveling faster than light."

But there is an even greater consequence.

 

[James S Saint]

No,
your twin only traveled 1Ls, because you meet at the sign. So you calculate that both of you traveled at 0.75.

How did you double the distance traveled ?

I am measuring the distance between the two travelers. Later in the thread, I removed the ground from the story all together leaving the only observers seeing only each other and thus measuring only that in 1.333 secs, a distance of 2Ls vanished. Thus they would measure 1.5c

 

[Tomsk]

The INITIAL frame, which is also the FINAL frame. It is in that frame that both measurements, both initial and final time and distance, get measured by both parties.

You have taken a distance measurement and time measurement (2ls and 1.333s) in one frame (the ground frame, which you're now trying to forget) and assuming those distances and times are the same in other frames (the traveler's frame and his brother's). This is not true.

there are no "ground observers" (no absolute frame)

Having no ground observers is completely different to having no absolute frame. The ground is a perfectly valid reference frame, it's not absolute.

 

[espen180]

What it says, because there are no "ground observers" (no absolute frame), the OBSERVED speed by the only observers present is 1.5c. Thus in the scenario pointed out, the observers, the travelers, would "see", by their measurements, that one of them traveled at 1.5c.

Nope. As has been explained, that's not the case.

 

[Doc Al]

What it says, because there are no "ground observers" (no absolute frame), the OBSERVED speed by the only observers present is 1.5c.

Again that's the closing speed only in the ground frame!

Thus in the scenario pointed out, the observers, the travelers, would "see", by their measurements, that one of them traveled at 1.5c.

Nope! If they used measurement made while they were moving, they would measure their relative speed as 0.96c. If they just use the measurements made in the ground frame, their closing speed would be 1.5c. In no frame is anything moving greater than c.

The theory is that no such observation, measurement, could ever be made. "No observer will measure anything traveling faster than light."

Given the statements you've made in this thread, I don't think you're in a position to tell us what relativity says.

But there is an even greater consequence.

Beware: Garbage in = garbage out.

 

[Mentz114]

I am measuring the distance between the two travelers. Later in the thread, I removed the ground from the story all together leaving the only observers seeing only each other and thus measuring only that in 1.333 secs, a distance of 2Ls vanished. Thus they would measure 1.5c

See the diagram I added. I think you are still miscalculating it by mixing frames.

 

[James S Saint]

Again only in the ground frame!

They are BOTH in the ground frame when they take their measurements.

If they used measurement made while they were moving, they would measure their relative speed as 0.96c.

But they didn't

If they just use the measurements made in the ground frame, their closing speed would be 1.5c. In no frame is anything moving greater than c.

Those two statements are contradictory. In the ground frame where they made their measurements, they measured 1.5c (not supposed to be possible). But then you said, "In no frame is anything moving greater than c.".

Make up your mind.

 

[Borg]

Well, this has been fun. I've got to go for now but, I'm definitely going to check back to see if:

A. My question from post 76 ever gets answered.
B. The thread gets locked.
C. James gets banned.
D. B and C.

 

[espen180]

But they didn't

They did. You just can't/won't realize it.

Those two statements are contradictory. In the ground frame where they made their measurements, they measured 1.5c (not supposed to be possible). But then you said, "In no frame is anything moving greater than c.".

Make up your mind.

Closing speed =/= velocity

 

[James S Saint]

See the diagram I added. I think you are still miscalculating it by mixing frames.

I think you missed my last point. There are only two measurements (now). There is a distance of 2Ls between two people. 1.333 secs later, there is no distance between them. To both of those people, the distance between them vanished in only 1.333 secs yet they both know tht light could have only traveled that distance in 2 secs.

From their perspective, one of them traveled at 1.5c.

 

[Doc Al]

They are BOTH in the ground frame when they take their measurements.

OK, then you admit that measurements are being made in the ground frame. Good!

Those two statements are contradictory. In the ground frame where they made their measurements, they measured 1.5c (not supposed to be possible). But then you said, "In no frame is anything moving greater than c.".

Make up your mind.

In the ground frame, the closing speed is 1.5c. That's obviously not the speed of the ships! That was given as 0.75c. Or have you forgotten already?

Please tell us what frame measures the speed of a ship to be 1.5c? Answer: No frame does!

 

[Austin0]

I am measuring the distance between the two travelers. Later in the thread, I removed the ground from the story all together leaving the only observers seeing only each other and thus measuring only that in 1.333 secs, a distance of 2Ls vanished. Thus they would measure 1.5c

If you understand logic then you must understand the limitations of abstractions.
Your assumption of 1.5 c is an abstraction based on a concept of distance /time that has no physical meaning. In any frame. No entity travels from your intial point to the other initial point i.e. 2 ls
It is no different that the faster than c sweep of a laser dot which also has no physical meaning because no single entity actually traverses the distance from the first point to the last.

 

[Bussani]

I'm just wondering if you're trolling everyone at this point. You're saying yourself that all your measurements are made from the ground's frame--that is, when everything is standing still before the experiment. You've been told again and again that from the ground's frame--from those measurements you took--you can conclude that the closing speed was 1.5c. You seem to think that means something, but it doesn't. All you've done is closed your eyes through part of the experiment, looked at the results from the ground's point of view, and come to the incorrect conclusion that one of you moved faster than light. This isn't what relativity talks about at all.

 

[James S Saint]

In the ground frame, the closing speed is 1.5c. That's obviously not the speed of the ships!

Not obvious to whom?? The only observers measure 1.5c.

That was given as 0.75c. Or have you forgotten already?

That was the reality. But from that reality, we get the only observers seeing a 1.5c speed. There is no observer who stands on any ground and watches the event so as to tell the travelers how fast they were going.

Please tell us what frame measures the speed of a ship to be 1.5c? Answer: No frame does!

You JUST said yourself that the 1.5c is measured from the ground frame!? "In the ground frame, the closing speed is 1.5c." == 1.5c as seen by the ONLY observers.