The speed of light has long been calculated to be 299,792.458 km per second, but now new research from France and Germany indicates that light may not travel at a fixed rate after all, but instead can fluctuate.

A key component of Einstein’s famous E=MC2, the speed of light has been thought to be finite since 1676 after Danish astronomer Ole Rømer first established his findings while studying the motion of Jupiter’s moon Io.

Two separate studies by scientists from the University of Paris-Sud in France and from the Max Planck Institutes for the Physics of Light in Germany are disputing the long established belief concerning the nature of a vacuum.

Researcher Marcel Urban and his colleagues in France said they had identified a “quantum level mechanism” for understanding vacuum. Urban’s research indicates that a vacuum is not completely empty as long thought, but instead filled with pairs of virtual or ephemeral particles with varying levels of energy. Because of this, Urban asserts that since the characteristics of a vacuum fluctuate, the speed of light then must also vary as well.

Gerd Leuchs and Luis L. Sánchez-Soto, in their forthcoming paper for the Max Planck Institutes, are suggesting that certain physical constants (physical quantities with values that are thought to be universal in nature and remain unchanged over time) indicate that there are also a number of elementary particles in nature, including those that might be found in a vacuum. The physical constants they speak of could include properties such as the speed of light and another that’s known as the “impedance of free space” (varying levels of the electric and magnetic fields of electromagnetic radiation traveling through free space).

Physicists have long found that the concept of the vacuum is one of the most fascinating issues in their field of science. A vacuum, when viewed at the quantum level – at the smallest and most basic level – is not empty, but instead filled with particle pairs such as electron–positron or quark–antiquark pairs that are constantly appearing and disappearing. While these particle pairs are real particles, their lifetimes are extremely short.

If these findings are proved to be true, they could have an impact on current scientific theories that take the speed of light into consideration.

Both studies will be published in an upcoming edition of the European Physical Journal – D (EPJ-D).