# What do electromagnetic waves look like in 3 dimensions?

1. Jul 23, 2007

### Joza

What do electromagnetic waves look like in 3 dimensions?

In my textbooks etc. they are always represented as the standard sine wave. But what about actual 3 dimensions?

Are there waves with smaller wavelengths than gamma waves?

2. Jul 23, 2007

### mgb_phys

3. Jul 23, 2007

### xez

b) They call high energy photons gamma rays, though
that's just a name. You could have arbitrarily high
energy photons with arbitrarily high frequency and
arbitrarily short wavelength. I don't recall that there's
a limit as to how short the wavelength can be and have
it still be something you could 'call' a gamma ray.
The main thing is that past certain limits it becomes
VERY difficult for gamma rays to be produced with any
higher energies. Nuclear reactions often produce gamma
rays. Matter and antimatter annihilations produce even
higher energy gamma rays.
And some very extreme cases involving things like
black holes, supernovae, etc. can produce quite intense
high energy gamma ray bursts:
http://en.wikipedia.org/wiki/Gamma_ray_burst

The practical 'limit' is essentially how high energy of
a matter-anti-matter collision you could have in the
universe, and above certain limits they just don't happen
often in ways we can (or would want to directly!) observe.

a) That gets 'complicated' well not really complicated, but
it's a matter of interpretation. You can view an
electromagnetic wave as a classical (classical physics E/M
theory) wave. The wave has an electric field strength E,
a magnetic field strength H, and the E vector is at right
angles to the H vector in free space. Being a transverse
wave E and H both are at right angles to the direction
of propagation in free space.
The E and H are just intensity vectors of field components,
at any given point in space and time, though, and
aren't really saying anything about the 'shape' of the
equations or information to say how E and H vary in
space to get the 'shape' of the field. How E and H vary
in TIME and SPACE, though, in areas free of SOURCES
of new EM waves is dictated by Maxwell's equations so
they'll tell you how an EM wave, once created, will
move in time and space.

However you can also look at EM fields as composed of
quantum particles called photons, and then you can use
QED theory to look at the 'shape' of the photons in
terms of their probability of having a given E or H
field intensity and detection probability at any given
point in space and time. There's no fixed 'shape' to
a photon since that depends on its emission process and
the environment it's traveling in. You could 'localize' a
photon inside a 'box' and of course see wave functions
and resonance type effects versus the size of the box and
wavelength of the photon.

can produce something like a continuous coherent
'plane wave' or almost 'spherical wave' of waves that
have fields that look like your classical smooth amplitude
perfectly coherent sine waves flowing outward forever.

Something like an atom that emits a photon from
spontaneous emission though will pretty much emit
a photon with some relatively discrete direction and
as a wave-train that is sort of like a damped sine wave,
initially strong then decaying to zero after a few dozen
sine cycles....

like

4. Jul 23, 2007

### Staff: Mentor

5. Jul 23, 2007

### gabee

This is a great site from MIT which shows videos of exactly what you're asking for.

http://ocw.mit.edu/OcwWeb/Physics/8-02TSpring-2005/Visualizations/detail/light.htm [Broken]

Last edited by a moderator: May 3, 2017