Question #8a8fa
2 Answers
Because light is a perturbation of the electromagnetic field.
Explanation:
Imagine empty space....there is nothing.
Now place a charge in it, for example, an electron. Space is still empty of matter (apart for the electron) but is full of the Electric Field generated by the charged electron. The field is not matter BUT it is all around the electron in space.
Next, let us consider the same electron but now moving at constant speed. During this movement there will also be a Magnetic Field around the now moving electron.
To summarize we have empty space and one electron moving at constant speed; around the electron and filling the space there will be an electromagnetic field.
Now we have the good bit!
Imagine that for some reason we ACCELERATE our moving electron. This acceleration will produce a perturbation in the electromagnetic field around the electron, a kind of ripple, that propagates outwards from the electron. This ripple will be our wave.
In the figure you can visualize the ripple (blue) observing the "deformation" of the field lines of the Electric Field around the electron at one instant. The ripple will move outwards with speed
No one knows the answer to your question.
Explanation:
Gio's answer is excellent and consistent with our current theories of Physics.
But a Field [ Gravitational, Electric or Magnetic ] is just an idea that explains what we observe. No one knows if it is true and thus no one knows why no medium is needed for EM energy to propagate from one location to another. We just know that it does occur; that is that radio signals work in outer space where the is no matter to carry the energy as there is with Sound and Water.
