The speed of light may not travel through space at a constant rate after all, say two new studies. (Photo : REUTERS/Yuya Shino)

Thus far, textbook descriptions of the speed of light assume that the light is traveling in a vacuum.

Space, however, is not a vacuum.

According to the Alpha Galileo Foundation, two new studies slotted for publication in the European Physical Journal D demonstrate that the speed of light is actually variable.

The authors of the studies include March Urban of the University of Paris-Sud, along with Gerd Leuchs and Luis L. Sanchez-Soto from the Max Planck Institute for the Physics of Light in Erlangen, Germany.

A major part of the discussion in both studies is the nature of a vacuum, which on a quantum level is not, as most believe, empty. Rather, it is filled with the particle pairs.

First, Urban and his team propose that there are in fact a limited number of particle pairs including electron-positron or quark-antiquark pairs within a vacuum. This opens the possibility that the speed of light can then fluctuate at a level independent of the energy of each light quantom or photon. In other words, the speed of light would depend on the vacuum properties of space and time.

In their study, Leuchs and Sanchez-Soto found that variations in the speed of light can reveal the number of charged elementary particles in any given space. If correct, the value of the speed of light can then be combined with the value of vacuum impedance in order to determine the total number of charged elementary particles that exist in nature.

In all, the fluctuations in time are estimated to be somewhere around the realm of 50 attoseconds per square meter (scientists estimate that it takes 320 attoseconds for electrons to transfer between atoms) and may in fact be testable with the help of ultra-fast lasers. Up until this point, light was considered to move at a constant 186,000 miles per second.