the nature of light

Light is electromagnetic wave in nature. All electromagentic waves travel by mutual interaction of electric and magnetic fields. Vacuum itself permits both fields to establish, such that electromagentic waves can pass through.

In fact, vacuum offers the least "impedance" for the propoagation of electromagentic waves than any other media. From Maxwell's electromagnetic theory, the speed of electromagentic wave in a medium is given by,

c = 1/square-root[u.e]
where c is the speed of electromagentic wave in the medium, with permittivity e and permeability u.

Because the values of permittivity and premeability of vacuum are not infinite, they ave finite values. This shows that vacuum permits electromagentic fields to propagate through it.

The "vacuum impedance"(or impednace of free space) is found to be about 377 ohms, which is a finite value (i.e. not infinite). This finite impedance allows electromagnetic waves to propagate.

For information on free space impednance, you may visit the web-page below:

http://en.wikipedia.org/wiki/Impedance_of_free_space