
Originally Posted by
.o:0|O|0:o.
Does anyone actually know how EM waves propagate through space?
They propagate just like any other waves. A wave in a solid is said to propagate due to motion of particles, but look deeper and you get down to electromagnetic field interactions in atoms that are "99% empty space". It's similar for an EM wave, only it's in "100% empty space".

Originally Posted by
.o:0|O|0:o.
They have alternating oscillating electric field and magnetic field components, they vary in frequency/ wave-length and have many curious behavioural characteristics (wave-particle duallity for photons), but while mechanical waves are effectively the result of particles being moved, that is, they require a medium (water molecules for the sea, air molecules for sound, etc.), there is no such material medium in space.
Actually EM waves don't consist of separate electric and magnetic fields variations, it's just the one field, the electromagnetic field. And think about pacing an oceanic swell wave in a helicopter. It's essentially a pressure pulse. In similar vein an EM wave is a stress-energy pulse in space.

Originally Posted by
.o:0|O|0:o.
Maxwell's Equations may describe the behaviour of EM waves, but I am not sure they describe the nature of EM waves.
Here's a couple of interesting papers:
http://arxiv.org/abs/0803.2596 and
http://arxiv.org/pdf/quant-ph/0604169. I don't quite agree with the dimensional aspect fo the latter, but it gets across the way a photon is a pulse of wavefunction, and that this has a physical reality. I'd say think of the photon as a soliton wave rather than a billiard-ball particle.

Originally Posted by
.o:0|O|0:o.
Does the Standard Model apply to an X-Ray without mass?
Yes. Mass is rest mass, light has no mass because it isn't at rest. Here's a paper that's well worth reading:
Light is Heavy by van der Mark and 't Hooft. It describes how a massless photon trapped in a mirror-box adds mass to that system. Open the box and the photon escapes, the system loses energy/momentum, and the mass is reduced. This is akin to Einstein's E=mc² paper
Does the Inertia of a Body Depend upon its Energy Content?.

Originally Posted by
.o:0|O|0:o.
When a wave travels towards us from the earliest times of the universe, do we explain it as a simple matter of a particle travelling without the obstruction of an atmosphere or is the wave interacting with the fabric of the universe at every stage of the way, allowing energy to be moved along and keeping it going?
The latter, though "fabric" isn't quite the right word. Space isn't nothing, it does sustain waves and fields, but it isn't a fabric or substance in the usual sense of the word.

Originally Posted by
.o:0|O|0:o.
If the latter hypothesis is the closest answer, where can I find out more? If anyone has some idea I would appreciate it.
It all comes back to displacement current. Think about vacuum permittivity ε0 and permeability μ0. These combine as vacuum impedance Z0=√(μ0/ε0), impedance being resistance to alternating current. They also combine as c=√(1/ε0μ0), this expression being akin to the mechanics expression v = √(G/ρ) where G is the shear modulus of elasticity relating to stiffness, and ρ is density. ε0 is like stiffness and μ0 is like density. Take a look at Mordehai Milgrom's
New Physics at Low Accelerations (MOND): an Alternative to Dark Matter at
http://arxiv.org/abs/0912.2678 and note this line on page 5:
"We see that the modification of GR entailed by MOND does not enter here by modifying the ‘elasticity’ of spacetime (except perhaps its strength), as is done in f(R) theories and the like."
I wouldn't say MOND was quite right, but this "strength of space" thing does feel like the best way to describe it. IMHO what's important is that an electromagnetic wave involves an EM field variation. The field can't vary without some form of current. There's no charged particle moving, so it isn't conduction current. Instead it's displacement current, and it's alternating. That's why impedance applies. What's waving in an electromagnetic wave? In a nutshell: space itself.