Electromagnetic waves travel in space because their nature is to "leave" their point of creation.If we toss a rock into a smooth pond, ripples move out from where the rock come down.The rock gave kinetic energy to the water, and the water can't "hold" the energy stationary in one place.The energy moves away from where it was initiated.Light is a different critter in that it is electromagnetic energy, and, as such,it does not need a medium to travel through.It moves very well through the vacuum of space. But the idea that it won't stay where it was created makes it similar to the water wave.Wherever this little electromagnetic ray began,it didn't stay there.Light is electromagnetic energy, and it has an innate desire to move. Movement is actually part of what light is. Light is a moving electric and magnetic field. Both.At the same time, and at right angles to each other.