Why can’t longitudinal waves be polarized?

[madmike159]

Why can’t longitudinal waves be polarized? I’m guessing its something to do with the particles oscillating in the same direction of propagation, but I can’t think of a explanation of why they can’t be polarized.
I have also been told that some transverse waves can’t be polarized. X-rays can but gamma can’t with current technology, is this because of the higher energy of gamma photons?

 

[olgranpappy]

longitudinal waves are "polarized" in the direction of propagation. transverse waves are polarized perpindicular to the propagation direction, since there is more than one direction perp to the propagation direction there can be more than one transverse polarization and we can filter for either x, or y polarization... but that's not true for longitudinal.

 

[Andy Resnick]

For electromagnetic radiation, 'polarization' refers to the direction of the electric field vector. Some EM waves do not have a well-defined polarization (optical vortices, near-field) for this reason. I suppose gamma waves could be polarized by grazing incidence methods, but I don't know enough about the technology.

Not sure about stress (longitudinal) waves. I suppose one could define a polarization direction if they are sufficiently well-behaved, but I'm not that familiar with the topic.