# Does light have a pressure wave

1. Oct 25, 2015

### Sachabloke

A seismic wave constitutes a shear wave and pressure wave. Does light have a pressure wave through the electrical field and could this be the way light "smells" it's way to where we can detect it?

Many thanks

2. Oct 25, 2015

### Staff: Mentor

No.
It does not.

3. Oct 25, 2015

### Justice Hunter

I think to elaborate more, it does sort of have this function, acting like a pressure wave, but instead, the pressure wave is just mathematical probability, and in total contrast has really nothing to do with pressure, which requires "extra parameters"

So really, if you shoot a photon of light out in space, its not actually moving in the form of a wave, but the mathematical probability that you could find it in a given location, is given by a wave-like distribution, where some regions have higher probabilities then others. This is analogous to a region of high compression (ie, a region that has a higher probability of finding the particle in a certain location then another), but is not a physical wave by any means.

Light also has additional wave like properties, where a photon is an oscillation between a magnetic field and a perpendicular electric field.

Now I'm not well versed on the subject, but i believe that the reason its not a shear or pressure wave, is because the wave is self induced, there is no pervading medium required for the oscillation to occur, which means no magnetic field in space would effect the photon, and neither would an electric field.

4. Oct 25, 2015

### Sachabloke

Many thanks justice hunter for the elaboration.

Many thanks to mfb for your contribution.

5. Oct 25, 2015

### sophiecentaur

A photon is not something that you can do that with. You would have no idea whether or when it was going to be emitted and certainly no idea which direction. It's only once it has been actually detected that you can identify it as having existed and carried energy from A to B.

6. Oct 25, 2015

### Staff: Mentor

There are single-photon sources where you can check that a photon has been emitted.

7. Oct 25, 2015

### Justice Hunter

Well, sure... but you could think of "shooting a particle" as just a vague way of saying that we are observing a photon sent from one place, to another place, I didn't feel like it was necessary to go into the nature of how it gets detected or emitted, for purposes of keeping the topic as simple as i could articulate it. But ya i don't disagree with you though, so were on the same page.

8. Oct 25, 2015

### sophiecentaur

I would think that it's pretty important, if you are introducing a quantum particle into an argument, it should follow the appropriate 'rules'. Your post was attempting to assign wavelike properties to a photon but isn't the whole point of QM that they are two separate regimes. It's easy to assume that introducing the word "photon" into an argument, somehow raises the level of things and implies some greater understanding of what's going on. I think the reverse is true. The wave approach does very well in describing pretty much all topics like this thread. (Anyone would think that wave calculations were 'easy' )
"Shooting a particle" implies things about photons that are not really appropriate in most cases. The single photon source is an exception which should be treated with care.

9. Oct 25, 2015

### nasu

I think the original formulation is misleading, to start with.
A seismic events creates longitudinal waves (called P waves by seismologists) and shear (transverse) waves. These are two kind of mechanical waves and they can both exist in a solid medium like the crust or other solid structures of the Earth.
It is not that the seismic waves have pressure waves so does not make sense to ask if light has the same.

Light in vacuum is a pure transverse wave but it may have longitudinal components in media.
However it can exert a pressure even it's purely transverse.

The smelling part is nonsense, of course.:)