Bose–Einstein condensate

[swansont]

What does any of this have to do with BECs?

[ajb]

What does any of this have to do with BECs?

 

Sorry about this, again nothing to do with BEC's but Tachyons do not "defy" special relativity, but quantum mechanically they are ruled out. Just to clarify, things.

[Klaynos]

3. Photons have not yet been conclusively proved to be massless.

 

I'm sorry but I've just got to stop you there, despite being so tired I wasn't planning on posting today...

 

Photons ARE massless.

Photons travel at c.

 

The above are two known facts from various bits of physics.

 

This thread has taken a very strange turn.

[Pete]

in other words, it doesn't "slow down," it just traverses a greater distance.

 

I disagree. The optical path length is the same. The photons merely take rest stops along the way.

 

To be precise, there is a finite time between photon absorption and photon emission.

 

Photons ARE massless.

Photons travel at c.

 

The above are two known facts from various bits of physics.

To be precise a photon's proper mass has never been measured to be exactly zero. There is only an upper bound on it. Similarly with its speed in that it has never been proven to be exactly the same value in all inertial frames because all measurements to date have a non-zero margin of error.

Tachyons don't defy relativity. They are hypothesized particles that would conform to relativity' date=' but that requires imaginary energy or imaginary mass (and perhaps negative as well), and we don't know what that means, physically.

[/quote']

I've had a problem with these tachyons since I read the paper which postulated their existance. It is based on the assumption that p and E can be measured independantly. I've never heard an arguement which proves that to be true.

 

Pete

Edited July 13, 2008 by Pete

[iNow]

Thanks for the clarification on my point, Pete. However, it would be helpful if you could attribute the following two quotes to which you responded, as those did not come from me. Enjoy.

[Pete]

Sorry about this, again nothing to do with BEC's but Tachyons do not "defy" special relativity, but quantum mechanically they are ruled out. Just to clarify, things.

 

That's news to me. The article which postulted their existance did so using both relativity and quantum mechanics.

Thanks for the clarification on my point, Pete. However, it would be helpful if you could attribute the following two quotes to which you responded, as those did not come from me. Enjoy.

Well .. as you said ... I was being lazy.

 

I went back and corrected them.

 

Pete

Edited July 13, 2008 by Pete
multiple post merged

[ajb]

That's news to me. The article which postulted their existance did so using both relativity and quantum mechanics.

 

It is now well established that in (perturbative) QFT tachyons are an artefact of "choosing the wrong vacuum" to expand about. They are inherently unstable.

 

Maybe we should start a new thread on this rather than hijack this one.