I'm not sure if this has been answered before, but I figured this would be the right forum to find out. I'm not by any means an expert in physics, just someone who's interested in understanding more about the universe.
I've heard it stated that light behaves like both a particle and a wave. Something about that statement bothered me, and I started thinking about it. Whenever we describe light (or to generalize, any type of EMR) we use its wave properties (frequency and wavelength). So what if, for argument's sake, we say EMR is just a wave and we discard the notion of it also behaving like a particle?
A wave must travel through a medium. But we know light can travel through a vacuum, so what is the medium? Could the medium be spacetime itself? We know that spacetime can be warped and stretched by mass, so why couldn't it vibrate?
Consider a tank of water. Low-frequency waves you would make by disturbing the surface don't penetrate the walls of the tank. But higher-frequency waves like sound can be felt/heard through the glass. To me, this is analagous to certain wavelengths of EMR being able to penetrate certain densities of mass - the way visible light doesn't pass through your body but x-rays do.
We say that photons contribute energy to atoms when they strike them. Could it be that the atoms are being excited by the vibration of spacetime, the way the sand on a beach is moved when a wave reaches the shore? Think about radio waves - the wave travels easily through less-dense media (air, houses, us) but when it reaches a denser "shore" (the antenna) the particles on the shore become excited and translate that energy into a different form (the movement of electrons through the antenna).