News of a potentially huge breakthrough in physics, that the Cosmic Speed Limit may have been violated, has taken the world by storm this past week. As a fan of science in general and physics especially, I am excited not only by the observations reported, but also by the fact that physics, of all things, is capturing the interest of the general population.
While we occasionally hear news reports on cosmology, updates on the age of the universe or beautiful glimpses at the jeweled treasures of our galaxy, and while the happenings at the LHC sometimes percolate up into the level of the general news, it is infrequent that these reports truly grab the attention and spark discussion among the wide population.
Yet the recent news that something has perhaps violated the ‘law’ that nothing can travel faster than light –a physical principle right up there with E=mc2, one which every child has known since they sat upon their mother’s knee– has been lighting up internet forums, social networking news-feeds, and office lunchrooms.
With this article, I’ll try to shed some light (har!) on the recent developments, and hope to share a bit of my enthusiasm (and skepticism) of the news.
The news has come that a group of scientists at CERN, the European Organization for Nuclear Research, have recorded observations where sub-atomic particles have been measured to travel faster than the speed of light. They fired neutrinos from Switzerland at a detector in Italy and clocked a time for the ~730km trip which was 60 nanoseconds (0.00000006 seconds) faster than light could have travelled that same distance in a vacuum (that will be important later).
As expected, an observation such as this has been met with considerable skepticism. Indeed the group of scientists at CERN (not the same CERN team that is doing physics at the Large Hadron Collider) have spent the past two months reexamining their experiment, trying to find a flaw in it which would explain the results without violating c (the speed of light in a vacuum). So far they haven’t been successful, but they’re still not willing to go so far as to say these neutrinos have travelled faster than c. Instead they are asking for help from the physics community, asking for their colleagues around the world to try to replicate the experiment, and perhaps find any flaws in the experiment which would preserve c as the cosmic speed limit.
Neutrinos are a very tricky species.
It’s important to realize the razor thin margin at which light speed was supposedly broken. The results point to a speed which caused the neutrinos to arrive 60 nanoseconds faster than expected, with a margin of error of 10 nanoseconds. The speed measured was just 0.002% faster than the exact value expected by all of modern physics. There are an extraordinary number of mundane explanations that could introduce such a tiny, tiny variance. For example, an error of only 18m in the calculation of the roughly 730km distance between the emitter and the detector would be sufficient to account for the faster than light claims.
Even if the distance between those two locations is known down to within 18m, there are a whole host of variables that come into play, each of which can affect the measured result. Not the least among these is the fact that neutrinos are a very tricky species. It is unfathomably hard to detect a neutrino. A neutrino will happily zoom through a light-year of lead with only a 50% chance of interacting, or ‘hitting’ anything. Experiments which deal with them have to make their measurements, not on individual particles as can be done with light, accelerated electrons/protons, etc, but rather they have to fire billions and billions of neutrinos at a detector before they can even hope to have one hit and be noticed. Some pretty hairy statistical analysis is then used to extrapolate what happened.
How is “c” different from “the speed of light”?
Depending on how often you peruse the science section of your news-aggregator of choice, you may somewhat frequently hear of events, particles, phenomena, etc that travel faster than the speed of light in a given medium (air, water, fibre-optic glass, etc). This could certainly cause confusion as to why this week’s news is any different. The confusion is caused by a bit of ambiguity in the language used in the reporting these various events.
The constant “c” is “the speed of light in a vacuum”. This is not the same as ‘the speed of light’ or ‘the speed that light travels’, because we know that light is often slowed from c by its medium.
Physics knows of and expects that light waves/photons can be slowed by the medium through which they travel. When light travels through air or water or glass, it is slowed from it’s ‘normal’ speed, c, by that material. We understand this physics very well, as it is necessary to explain how something as simple as a prism works (light of different energy/colours is slowed at different rates, resulting in a separation).
Some things can even move faster than light waves can move through a given medium, because they aren’t affected by that medium in the same way that light itself is. This physics is also very well understood, but even in these cases where things are traveling faster than light, nothing is travelling faster than c.
What’s so special about “c”?
What’s interesting about c is that it is a calculated constant which comes out of the math in Maxwell’s equations on electromagnetism. Indeed, it was the fact that the value for c is not dependent on physical measurements, that its value comes out of the equations themselves, that gave Einstein his lightbulb moment (har!), leading him to his theories of Special and General Relativity.
Einstein’s revelation was that, since the math dictates c, and since no matter where you are or how you’re moving, math will work the same way, then therefore light will always travel at c (when not slowed by a medium). Einstein’s brilliance was in how he interpreted the consequences of that basic principle.
Traveling faster than c simply breaks the math of Maxwell’s equations and the math upon which most of the past century’s physics has been built. Numerous predictions of physical reality have come solely out of the math contained in those equations. Some of these predictions, like those of relativity, at times can make the universe look like a funhouse mirror. Yet over and over, these mathematical predictions have been verified to occur in our physical reality via an incredible number of laboratory experiments, astronomical observations, and technological advances.
Why so skeptical?
Much of modern physics simply wouldn’t work if Maxwell’s equations and those derived from them weren’t able to stand up to the extremely rigorous poking, prodding, testing, and attempts to break them that have occurred over the past century as part of the progress we’ve made in just about every area of physics. Yet the idea that these neutrinos have travelled faster than c would mean that Maxwell’s equations are incorrect in a deeply fundamental way.
Superluminal speeds would lead the way to a new area, perhaps even a new era, of physics and technology.
While we’re certain that we have a lot more to learn about physics on the grandest and smallest scales, it is difficult to believe how this bedrock of modern physics could be so marvelously predictive and accurate in describing the universe around us, while at the same time being completely wrong about c as the cosmic speed limit.
Faced with the results of one experiment, an experiment in which the particles were measured to travel so very, very close to exactly the figure of c we expect, even one in which the scientists have been so careful, skepticism is the natural reaction to those who think rationally and scientifically.
That said, it would be absolutely wonderful if this were true. Superluminal speeds would lead the way to a new area, perhaps even a new era, of physics and technology. It would hallmark the arrival of a vast amount of fundamentally new knowledge of how the universe works.
I’d be willing to bet a large amount that this result turns out to have a mundane explanation. Though, I would dearly love to lose that bet.
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