The saying 'Nature abhors a vacuum' is meant to describe how energy and matter will try to flow from areas of high concentration to those of lower concentration. In quantum mechanics though the saying takes on new meaning as virtual particles continually pop into and out of existence within vacuum. Now researchers, as reported by Springer, have reason to believe that these particles actually cause the speed of light within a vacuum, the universal constant, to fluctuate.
Unlike many other values, the speed of light in a vacuum is defined, so any deviation from 299,792,458 m/s, as the result of refined measurement, actually results in a change to the meter. Part of the reason it is a defined valued is that it can also be found within the product of two other constants; vacuum permeability and vacuum permittivity. The researchers have found that these two constants may vary slightly within a vacuum because of a limit on the number of virtual particles within the space. However, the variance they introduce may be as small as 50 attoseconds or 0.00000000000000005 seconds, but with new ultrafast lasers, it may soon be possible to experimentally measure this.
Another team of researchers have also found that the impedance of a vacuum, which also impacts the speed of light, may be dependent on the number of charged particles within a vacuum, but not their mass. If correct, that means it could be possible to estimate the total number of charged elementary particles in the Universe.