Why light can't go faster then 300 000 km/s? What prevents it?

Question

Why can't the speed of light be faster then approx 300 000 km/s? What prevents it?

Answer 1

Lightspeed can be anything non-zero and finite for special and general relativity to work. Any medium, including vacuum, has a permittivity (electric field) and permeability (magnetic field). The permittivity ε and permeability µ of a medium together determine the phase velocity v = c/n of electromagnetic radiation through that medium,

$\varepsilon \mu = \frac{1}{v^2}$

If you can change one independently, you alter ligthspeed. This can be done on paper, and trivially so. Alas, it does not reduce to practice given the finite size of atoms and the direction in which the diddle operates - the Scharnhorst effect,

http://www.npl.washington.edu/AV/altvw43.html
http://arXiv.org/abs/gr-qc/0107091
http://arXiv.org/abs/quant-ph/0010055
Phys. Lett. B236 354 (1990)
Phys. Lett. B250 133 (1990)
J Phys A26 2037 (1993)