Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: sleeping on 19/10/2012 09:04:03

Title: What happens when two EM waves collide in space.
Post by: sleeping on 19/10/2012 09:04:03
I understand that photons do not interact in free space. How about two electromagnetic waves in free space. For example, if you have two EM waves with differing frequencies colliding in space, will we get a third EM wave that is modulated by the two waves.

Thanks
Title: Re: What happens when two EM waves collide in space.
Post by: evan_au on 19/10/2012 11:09:24
There are some non-linear materials which will allow photons to interact in the manner you describe. Optical fibers will do this if the power levels get too high.

In a vacuum, electromagnetic waves will pass through each other.

However, if the photon energy gets high enough (like gamma rays), they can produce a pair of particles (like an electron and a positron) through their interaction.
Title: Re: What happens when two EM waves collide in space.
Post by: JP on 19/10/2012 16:22:30
However, if the photon energy gets high enough (like gamma rays), they can produce a pair of particles (like an electron and a positron) through their interaction.

Yep!  Photons can't interact because they only interact directly with things with charge.  Photons don't have charge, so they don't interact directly with each other.  However, they can interact with the vacuum because due to weird quantum effects, the vacuum can have a sort-of charge (through virtual particles).  If two photons interact with the vacuum, then through the vacuum they can secondarily interact with each other.
Title: Re: What happens when two EM waves collide in space.
Post by: sleeping on 19/10/2012 18:35:57
Thanks for the answers.

So, by theory if the 2 EM waves are high energy gamma rays collide, a third EM should appear. This 3rd EM wave would be modulated or have component freq of the previous two EM waves.