What happens when two photons collide? From a little research done it seems as though they would create subatomic particles (maybe electrons?)If so, would photon collisions technically create matter? Is this a widely thought of theory?
 A: Take a look at this question. The OP stated that he wanted the energy of the photons to be so low pair production wasn't possible. I bolded these two words because, yes, it is possible for two colliding photons to create particles, in this case specifically electrons and their antiparticles, positrons (which are like positively charged electrons). Note that their charges are opposite, so charge is conserved. You could also create muons and antimuons, and so on.
You seem to be bothered by the fact that we just "created" matter, as electrons have a mass of roughly $511 \mathrm{keV}$, which is about $9.1 \times 10^{-31}$ kg. However, recall that while photons indeed have no rest mass (which makes them move at exactly the speed of light), they do indeed carry momentum. So, Einstein's formula $E=mc^2$ is nice, but in it's full form it should be
$$
E^2=m_0^2c^4 + pc^2
$$
where $m_0$ is the rest mass and $p$ is the momentum.
So, photons carry energy. And from the equation you can see that mass is equal to energy, so they can be converted into each other. One electron-positron pair may just as well collide and produce 2 (or more) photons. This doesn't violate any fundamental physical principles like energy conservation, conservation of momentum etc. And if it's not allowed, it's bound to happen eventually, as Murphy's law states. Although that isn't exactly particle physics.
You could look into the Wiki article on pair production, Two-photon physics or check out the Feynman lectures; volume 3 eventually has something on this topic.
