Einstein speak

[undidly]

Did Einstein say nothing can travel faster than light or did he say nothing can be observed to be traveling faster than light?

[Strange]

He (or the Lorentz transform) says that nothing can travel faster than light.

Although that is a bit of simplification. Information cannot travel faster than light. Nothing with mass can travel at the speed of light. Nothing with real rest mass can travel faster than light. If hypothetical tachyons existed, then they could never travel at or less than the speed of light.

[antoniseb]

Did Einstein say nothing can travel faster than light or did he say nothing can be observed to be traveling faster than light?

I know you're looking for nuance and precision here, but it doesn't matter what words Einstein uttered. It only matters what his theory predicts. For that, Strange's statement is basically right, as long as you are observing locally, so that cosmic expansion is not part of your speed, and perhaps with other constraints, e.g. I don't know if frame dragging around a rotating black hole could result in something having a speed of c or more for an observer.

[korjik]

I know you're looking for nuance and precision here, but it doesn't matter what words Einstein uttered. It only matters what his theory predicts. For that, Strange's statement is basically right, as long as you are observing locally, so that cosmic expansion is not part of your speed, and perhaps with other constraints, e.g. I don't know if frame dragging around a rotating black hole could result in something having a speed of c or more for an observer.

IIRC, you should not be able to observe it while it is apparently travelling at more than c.

[caveman1917]

I know you're looking for nuance and precision here, but it doesn't matter what words Einstein uttered. It only matters what his theory predicts. For that, Strange's statement is basically right, as long as you are observing locally, so that cosmic expansion is not part of your speed, and perhaps with other constraints, e.g. I don't know if frame dragging around a rotating black hole could result in something having a speed of c or more for an observer.

Not locally, since locally (frame dragging or not), space is simply minkowskian. Perhaps you mean observing it further away to be travelling at >c, but in that case you don't need frame dragging or other fancy stuff, any rotating observer will see a distant star going >c. Or in different terms, for any object in any spacetime we can introduce an observer sufficiently far away and rotating sufficiently fast such that the object will have a speed faster than c. The only constraint is locality.

[ShinAce]

Einstein said that the speed of light is constant. He then said, it follows that anything travelling less than the speed of light cannot be accelerated to or beyond the speed of light. Whether or not tachyons exist and can be observed was not covered by Einstein, as far as I know.

That's about it for the special theory of relativity.

[pzkpfw]

Did Einstein say nothing can travel faster than light or did he say nothing can be observed to be traveling faster than light?

It's much the same as here: http://cosmoquest.org/forum/showthre...communications

...where you asked:

Did Einstein say that FTL communication was impossible because at that time it was?