Right handed or left handed,intrinsic?

[ShayanJ]

The helicity of a particle is right-handed if the direction of its spin is the same as the direction of its motion. It is left-handed if the directions of spin and motion are opposite.

from http://en.wikipedia.org/wiki/Chirality_(physics)"

As you can see this definition is depended on the motion of a particle which,of course,is not intrinsic so how can we call helicity,intrinsic?In fact what is the benefit of defining such a thing at all because every particle can move in any direction.
thanks

 

[DrDu]

Although helicity can be defined for any particle it is invariant only for particles with mass zero whose speed is always c in any reference frame.

 

[ShayanJ]

But helicity depends only on the direction of motion,not speed.

 

[DrDu]

Yes, I mean the following: In case of a massive particle you can change helicity by changing to a reference system which moves with a higher speed V than the particle in the original system v_0. In the Galilean case this would mean that v in the new system is v_0 -V. If V is greater than v_0, this means that you have changed direction.
In Einsteinian relativity this becomes impossible for massless particles as velocity is no longer additive and especially because c is always c independent of the system of reference.

 

[Vanadium 50]

So you can change the helicity of a particle. So what? You can also change the velocity. the energy, the momentum, and many other properties. Why does this one bother you?

 

[Meir Achuz]

from http://en.wikipedia.org/wiki/Chirality_(physics)"
so how can we call helicity,intrinsic?

I can't. Who is 'we'?

 

[IMP]

If I am reading that correctly: Chirality is intrinsic but helicity is not. Chirality is "handedness" but helicity is not...

 

[ShayanJ]

Handedness,by the definition I found in wikipedia,can't be intrinsic.Also particles can be found to be right handed or left handed.
If above lines are correct,its not reasonable to define handedness.But it is defined.
So I think there should be a problem with the first two lines.

 

[SpectraCat]

In chemistry, we treat chirality of molecules as intrinsic, but that is not strictly true since there are reactions that can change chirality. So for most things, you are correct that chirality and helicity are not invariant. DrDu has explained to you one example where helicity *is* intrinsic, namely photons:

Yes, I mean the following: In case of a massive particle you can change helicity by changing to a reference system which moves with a higher speed V than the particle in the original system v_0. In the Galilean case this would mean that v in the new system is v_0 -V. If V is greater than v_0, this means that you have changed direction.
In Einsteinian relativity this becomes impossible for massless particles as velocity is no longer additive and especially because c is always c independent of the system of reference.

Doesn't that answer your question?

 

[Meir Achuz]

Why didn't post #7 end this thread?

 

[haael]

So OK, if chirality is not helicity, then how do we measure it?

Suppose I have a left-handed electron, then I change the reference frame so it moves backwards. How can I determine if it is still left-handed?