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.
What happened?
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).
Scientists say they have fired neutrinos below-ground, faster than the speed of light from a laboratory in Geneva, to a laboratory 545 miles away in Italy.
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.
The speed of light in a vacuum is approximately 1.079 billion km/h
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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Beautiful article. Pauli’s Ghost once again smiling and throwing new challenges. These challenges makes Physics and science more interesting and attract young minds.
The whole idea that there is some speed limit on all things, is in my opinion, totally absurd nonsense! What is “speed”? SPEED is distance per time IN RELATION TO SOMETHING. There is no such thing as speed without a context. The statement that nothing can go faster than the speed of light hardly makes any sense. All speed is relative to something. There are quite likely objects on the outer reaches of the universe that are certainly at least approaching the speed of light in relation to this planet. So that means, we, on this planet are also approaching the speed of light in relation to something else. So does that mean we are restricted in someway, from going too much faster in a direction away from this distant object on the other end of the universe which is speeding away from us near the speed of light? Since to go faster than the speed of light is not allowed? Remember, we can’t go the speed of light, because as you approach the speed of light, well, your mass goes to infinity! And the energy required goes to infinity! And oh yea, it means our time goes slower and slower. So if there is something on the other end of the universe trying and trying to approach the speed of light away from us, that means we are going faster and faster in relation to it and our mass is approaching infinity, OH MY!!! The universe is going to explode!! Or at least we will, because after all, you can’t have infinite mass! You can’t go the speed of light and certainly cannot exceed it, irregardless of what this thing is that we are measuring the speed with respect to! It could be a piece of dust zipping along out a billion billion billion light years away!!
Oh, but the relativists will look to their sacred texts, and say, no, no that’s not what God, er, I mean, Einstein said. He said that that relative to those objects we would be restricted from going faster than light, and our mass would approach infinity. As observed by that distant object. Oh, ok, then gee it all makes sense now.
Phaedrus, I think you’re bumping into the very unintuitive reality that light’s velocity is not additive. All kinds of strange predictions come out of that supposition, some of which you’ve alluded to (some even weirder ones which you haven’t). The thing is that *every* experiment to test these strange predictions of relativity has wound up confirming them to be true.
Much of modern technology (everything from CRT televisions and computer monitors to GPS devices) simply wouldn’t work if not for these bizarre truths of the universe which relativity reveals.
I sympathize that it may make no sense, but you should bear in mind that, unlike the understanding we have developed about the everyday world around us, our species has had no need to develop an innate intuition or common sense for relativistic phenomena.
You are right that speed in [only] one sense is not limited to the speed of light, and that has to do with the rate planets move away from each other due to the expansion of the universe, however, with that exception set aside.
The point you make about speed being relative is exactly the point Einstein made, and like you, he did not believe his own conclusions either. One thought experiment you can do is as follows. Two observers, one on a speed-of-light ship, and one just floating around (stationary to both ships) are watching another speed-of-light ship coming toward the first one. The observer on the speed-of-light ship should see the other ship as traveling at twice the speed of light, whereas the outside observer should see each going at the speed of light but in opposite directions.
What if, both observers saw the other ship as only going the speed of light, rather that the ship based observer seeing the other ship at twice the speed of light?
What would be the ramifications.
One thought is that since Speed = Distance/Time. If speed is fixed, but distance is varied, time must also vary.
If this were true, is there anyway to prove it?
We don’t have to actually get to the speed of light to test this, we only have to be very accurate.
One experiment that has been done is to put synced atomic clocks on 2 planes, one going the direction of the earth, and one opposite so that they are traveling at substantially different speeds over the same distance.
If speed is linear then the clocks should stay in sync. If speed plateaus at some value then speed is not linear and the clocks should be out of Sync. Here is the experiment http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/airtim.html
The light-speed barrier provides a useful framework for considering how we observe phenomena. I think it is reaching to think that the effect extends to all objects/phenomena in a physical sense, it only provides for considering how a participant OBSERVES light from speeding objects from various frames/perspectives (just the light – like how we would observe objects falling past an event horizon – not the object).
We tend to photocentric in defining our understanding of nature, but should realise that photons are the limiting factor, and of course their maximum (or perceived maximum) is the upper limit for phenomena observed using photons.
Many here make the statement about ‘c’ being the so called speed of light …in a vacuum. However, let us make first the statement about terminal velocity. That is terminal velocity of a falling object in our atmosphere, which is about one hundred and twenty miles per hour. We can prate all we want to about the falling velocity being [integral]{{d(accel vector)/dt} + V0} whose resolution in three dimensions is -32 ft/(sec^2) which after a few seconds seems to yield fantasy…until we start to have to accept the reality that the Reynolds and d’Arcy Weisbach equations concerning the behavior of viscous fluids give rise to forces countering the gravitational acceleration differential equations of Newton. The acceleration forces are countered by the resistance forces in the viscous medium, air, through which any earthbound falling matter ‘falls’. In space is no different. Space is NOT empty, and has Reynolds, Froud, and other maybe undiscovered viscous resistances as well. There is no perfect vacuum….anywhere, so ‘c’ really is an imaginary number. As lightspeed is variable depending on media, its density, and other characteristics of media; and can actually be ‘stopped’ in certain circumstances like in Bose-Einstein media; so it can also be variable in supposed vacuums that are really highly dispersed plasmas, gases, liquids, and solids, and other states of matter yet undiscovered. Therefore what we perceive as ‘c’ is really an average of many differences on the resolution in multidimensional space of the discontinuous partial differential equations in many unknowns governing its travel from source to observer. Statistics! That is what has yielded what we popularly want to call ‘c’, because until we find something better, many of us ‘want to believe’ in Dr Einstein’s work simply because it has worked well so far, and one never gets fired, loses tenure, loses professional face, or loses promotability…for continuing to robotically support his work. For all we know, the functions governing ‘c’ may be akin to the tangent ratio, hyperbolically tending to infinity as one approaches true vacuum through decreaingly positive values.
Hi;
It occurs to me to wonder if the real constant of the universe is actually the speed of nutrinos, and that the speed of light is only very close to that speed….with our current “observer biases” we would conclude that lightspeed actually was the universal constant, and that any variances we’ve observed in our experiments to test it, were our own errors. Would any of the math we’ve based our calculations on, be significantly different if lightspeed were only a few nanoseconds out?
To set the record straight, everything in the universe travels through spacetime at the invariant speed c. Light itself is believed to travel through space at c, with zero travel in the time dimension. Earthbound humans, however, “use up” most of their speed allocation in the time dimension. For present purposes, light travels through space at exactly c, regardless of medium; it is not true that light slows down or speeds up depending on medium. Now, phase velocity is defined as c/n, where n is the frequency dependent index of refraction, but this is physically different than the speed of light. Phase velocity is due to the superposition of the direct wave with secondary waves radiated by electric charges within the medium; all of these constituent light waves travel with speed c. The secondary waves may be either retarded or advanced in phase relative to the direct wave, corresponding, respectively, to resultant phase velocities less than or greater than c. According to the Ewald-Oseen extinction theorem, the effect is as if the direct wave incident on the medium is extinguished and replaced by a wave of the same frequency but with a phase velocity c/n characteristic of the medium (this is the origin of refraction).