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

[Doc Al]

But I am getting that both would read that 2Ls would be traversed in less than light speed time.

You still don't get it. In the ground frame, the ships move 1 Ly in 1.333 s--a speed of 0.75c. You can calculate a closing speed of 1.5c, but nothing is actually moving at that speed.

 

[Sumo]

Nope. That doesn't apply. The distance is measured standing still.

But why do you insist on an absolute measure of distance? One of the premises that you agreed on was that this doesn't exist. Yet here you are talking as if the distance measured standing still is somehow the only real one.

 

[Doc Al]

Nono.. not only would you be presuming the outcome of a measure so as to make it "correct", but the theory is about the ability to observe anything traveling faster than light. We know from the outside perspective how it was that the distance got traversed in such short order, but THEY do not. They cannot know who was moving nor how much. Thus they observe a movement, speculated to be one of them, that they measure to be faster than light. The theory says that they could never get in that situation. Their measurements should always be less than light speed.

If the ships do not know anything about a ground frame or any measurements made in such a frame, then the best they can do is measure their speeds relative to each other. That speed, for the nth time, is 0.96c, not 1.5c. No one measures anything to move faster than light.

 

[James S Saint]

Nope. You have to stick to a single frame to get sensible results. According to the ship frame, they only traveled a distance of 0.66 Ly. So they measure the speed of the approaching sign to be 0.66/.88 = 0.75c. (Of course.)

From the ground frame, the ship moves 1 Ly in 1.333 s, again a speed of 0.75c.

The ships do not traverse a distance of 2 Lys according to any frame in this problem.

No
No
No
You cannot change what they already measured while they were standing still. They did not make a measurement while they were moving such as to perceive a shorter distance.

They measured standing "still" 2Ls. They looked at both clocks and got that the distance vanished in faster than light time. How much faster is all we were calculating.

THE ONLY FRAME OF MEASUREMENT IS THE INITIAL FRAME. They make NO measurements while moving. Thus the distance, as they calculate at the end and from the beginning remains at 2Ls. Granted the clocks slow down. But that only makes it seem faster.

 

[Mentz114]

THE ONLY FRAME OF MEASUREMENT IS THE INITIAL FRAME. They make NO measurements while moving. Thus the distance, as they calculate at the end and from the beginning remains at 2Ls. Granted the clocks slow down. But that only makes it seem faster.

No, if you use their clocks, you must use the corresponding contracted distance to calculate the velocity.

 

[Doc Al]

OK, I think this thread has gone on long enough. I don't see any progress being made here. You've said the same thing many times, and you've been corrected many times. Time to stop this merry-go-round.