# Fine-Tuning and the Speed of Light

Imagine living in a universe where balls, trees, cars, and all sorts of everyday objects simply popped into or out of existence. Or where those same objects *instantaneously* moved from one location to another distant location. That would be a bizarre universe indeed. Well, we live in such a universe, at least when looking on small-enough scales. The discipline of quantum mechanics says such things happen, and repeated measurements with the proper tools confirm their reality.

More significantly, many of the life-friendly characteristics of this universe *depend* on such bizarre behavior. For example, water serves as the life-sustaining fluid because of quantum mechanical fluctuations in its molecules. Quantum principles enable plants to convert the Sun’s radiation into energy reservoirs via photosynthesis. Quantum mechanics even influences fundamental ideas like cause and effect and particle masses. Two new studies show that these quantum mechanical fluctuations may ultimately determine the speed of light.

The speed of light is related to two other quantities, the vacuum permeability (μ_{o}) and vacuum permittivity (ε_{o}), that scientists consider fundamental constants (there is no variation in either space or time). New research shows that μ_{o} and ε_{o} may originate from the magnetization and polarization of the particle pairs (specifically fermions) that quantum mechanically pop into and out of existence (at microscopic levels) all the time in the vacuum of space. If true, one can model light travel as absorption and reemission by these pairs and calculate a finite velocity of light. Such a process would give a constant speed of light on scales much larger than the Planck length (statistics smooth out the quantum fluctuations) but a variable speed for short lengths.^{1} Remarkably, the technology to test this scenario is within reach.

Another study extends this research to show that the speed of light can be used to determine the number of fundamental, charged particles. Specifically, the impedance of the vacuum relies on this number and is critical to determining the speed of light. Although the researchers used an overly simplistic model (by their own admission), they constrain the number of fundamental particles to about 100.^{2}

What does this mean? This work ties so-called fundamental quantities like the speed of light, μ_{o}, ε_{o}, and the number of particles to the “strength” of quantum mechanical effects in our universe. Scientists now have some understanding of what would happen if that strength were greater or weaker. For example, changes in the quantum nature affect the range of tunneling rates available to organic molecules and the complexity and speed of communications. Either of these changes reduces the habitability of the universe. Scientists may find quantum mechanical explanations for many, if not all, the fundamental properties of the universe, but it is unlikely that all the universe’s life-friendly properties depend on such quantum properties in a coordinated way. In that case, we would expect to simply move fine-tuning arguments to a more fundamental level.

##### Endnotes

- Marcel Urban et al., “The Quantum Vacuum as the Origin of the Speed of Light,”
*European Physical Journal*D 67 (March 2013): 58. - 2. Gerd Leuchs and Luis L. Sánchez-Soto, “A Sum Rule for Charged Elementary Particles,”
*European Physical Journal*D 67 (March 2013): 57.