One more ''traveling faster than light'' query. . .

[Undead_Dude]

*Originally posted by g8rguy *
More or less irellevant. In principle, relativity doesn’t say nothing can go faster than c, only that you can’t accelerate anything past c.

That’s not totally true. Relativistic equations don’t allow for a “real” mass for a particle moving FTL. So the first thing that needs to be tackled in the rather speculative and very unlikely realm of tachyons is to accept the questionable concept of “imaginary mass”. So that might not be an outright declaration of impossibility, but it is at least a very serious censure of the concept.
Tachyons

[John_Kentzel-Griffin]

*Originally posted by ***g8rguy **

Yes, I’m assuming we won’t be able to detect them, if they exist.

<snip>

Partially, by the way, the reason I assume that we won’t be able to detect them, ever, is that if they do have the ability to affect normal matter

If they can affect normal matter, then they could be detected. If, on the other hand, they cannot be detected, then in what sense do they exist?

Our notions of causility rule out detection. And something that cannot in principle be detected does not exist.

[g8rguy]

I almost entirely agree with you, DrMatrix, except that I would say that if you can’t detect something, it’s safe to assume that it doesn’t exist but that definitive pronouncements can’t be made. I guess that’s just quibbling over what “exists” means, though.

And yes, I agree that either energy or mass would have to be imaginary; either is rather hard to swallow. Interestingly, if Undead Dude’s link is correct, there would be ways for tachyons to interact with normal matter via, for example, scattering, which would certainly at first blush seem to be acausal and a very strong argument for their nonexistence.

[The_Great_Unwashed]

*Originally posted by bryanmcc *
**borschevsky and g8rguy,

Correct me if I’m wrong, but I believe that you cannot “collapse your particle” in a certain way. I.e., you cannot collapse it to “down” to make the other party’s particle down as well. When you collapse your particle by viewing it, it collapses in a random way to up or down. There’s no choosing which you will see. So yes, the other party’s particle(s) will also collapse, but their’s will be random, too. So you won’t be sending 'em any information other than that their particles have collapsed, and they won’t even be able to tell if it’s because they were collapsed by you, or because they are looking at them themselves.

I think.

Confusing enough for ya?

-b **

I am not a physicist, but I can tell you that you are wrong, the thing about these entangles pairs is that though the state of neither is “known”, they can be configured to be in opposite states (say one up, one down), observing one causes it to “collapse” into a particular spin, and simultaneously causind the remote paired particle to collapse into the corresponding (opposite) spin. This “action at a distance” is one of the very observable phenomena that put QM and GR at odds with each other – both cannot be right.

More info at The New Scientist

[The_Great_Unwashed]

Ah, I jumped the gun (or some strange Q effects occurred).

bryanmcc never suggested that AAAD doesn’t happen, but merely that no practical information sending applications/methods are immediately apparent that utilise this flavour of AAAD – I’d have to leave that to those who know.

Oops!

[bryanmcc]

The Great UnwashedP:

Yes, I certainly agree that Spooky AAAD occurs through tangled pairs. But, as you say, it is not immediately apparent how an observer on one end would be able to distinguish whether the particle was up because the other one had already been collapsed as down, or whether it was up because he/she just collapsed it by observing it.

-b