Saturday, September 24, 2011

On The Possibility of Superluminosity

The physics world is a-buzz this week due to a paper published by a group of scientists working at CERN that seems to show superluminal motion by neutrinos. To rephrase that for people who don't know what I'm talking about, the measurements made by a group of scientists seem to show some really tiny sub-atomic particle traveling faster than light. Which is to say, to be more concise, that Einstein would be wrong.

This is an intensely interesting time for physics, needless to say. According to the paper, neutrons produced at CERN in Geneva are detected at a detector called OPERA in Italy in such a manner that they seem to have made the trip in about 60 nanoseconds less than it would take light to make the same journey (light would be expected to make a trip the same length in about 2.43 milliseconds). Looked at one way, that's not very much, only about 1 part in 40,000 faster. But from another perspective, that amount is HUGE, because according to Relativity Theory, nothing that has mass (like neutrinos) should be able to travel faster than the speed of light in a vacuum, c. The constant c is an immensely important one in physics, equal to 299,792,458 meters per second, or about 186,000 miles per second (or 669,600,000 miles per hour). The whole “in a vacuum” part is very important, because particles with mass are known to move faster than the speed of light just about every day, but with a very important twist: it only happens in a medium such as air or water where the local speed of light is less than c. Nothing in nature has ever been observed to travel faster than c, more than 100 years since Einstein first advanced his revolutionary theories.

Until, possibly, now.

However, the safe money is still on the fact that this is a systematic error of some sort. I'm 99% confident that it will turn out to be something of the sort, and that there will be seen to have been no superluminal travel at all. Einstein's theories have been proven correct time and again for over a century now, and tie both into modern physics and back into classical electrodynamics with near-perfect fit. In fact, relativity makes it pretty difficult to accurately measure distances that are one-way only, because of the near-impossibility of establishing a consistent timeline; simply moving from one end of a measuring course to the other in order to clock how long it takes light to travel it causes your frame of reference to experience time dilation relative to an observer who is standing still. Ideally you'd measure the distance forward and back on the same track, but since there are only a few places in the world capable of producing neutrons like this, and the detectors to detect neutrinos don't correspond to them, that is unfortunately out of the question.

However. Having said that, there is still the fact that the other main support of modern physics, quantum mechanics, continues to not play nicely with relativity. And while I'm 99% sure this will turn out to be a measurement error of some sort, there's always that 1% chance that we are on the brink of a major revolution in physics. And I do mean major. This would overturn our conceptions of physics nearly as profoundly as did the introduction of relativity and quantum mechanics in the first place at the beginning of the last century. A whole lot of physics as we know it would have to either go out the window or be heavily modified. (The practical side of me notes that the job market for physicists might pick up dramatically if that were the case!) It's been several decades since the last really big, paradigm-changing discoveries in physics, and if history is any guide, we might be about due for a new one. The scientists who are reporting this are not some crack-pot theorists, and are as surprised at their findings as anyone. They've done some serious work at eliminating sources of uncertainty, and unless someone finds a pretty big flaw with their setup, it does look as if something is happening, whatever it may turn out to be.

Still, such speculation is putting the metaphorical cart before the horse at this point. As I said, this will most likely be resolved in a fairly pedestrian fashion, with no major implications. Although there is one possible solution that I thought of that would explain the results while still adhering to relativity, one that will be instantly familiar to anyone who's ever played Valve Software's beautiful gem of a game Portal. And that solution is, well, a portal. General relativity does allow the existence of wormholes, which are essentially the eponymous devices from Portal. Basically, something goes in one hole and immediately comes out the other, no matter the distance between them. As an example, consider taking a strip of paper 10 centimeters long and putting two dots, A and B, at either end. Next, fold the strip of paper over on itself so that the dots touch. Now while in two dimensions the dots are still 10 centimeters apart, in three dimensions there is very little distance between them, and if you poked a hole through both dots you would essentially have the equivalent of a two-dimensional wormhole (it would actually function in three dimensions, though). Similarly, general relativity provides us with four-dimensional space-time, and it's not inconceivable that it could be ‘bent’ in an analogous fashion.

(By the way, if you have never had the immense pleasure of playing Portal, you should remedy that as soon as possible. I don't have time for a full review right now, but I firmly believe Portal is one of the most innovative computer games ever made. It's a thinking person's game, which is one reason I love is so much. Basically you get to move the two ends of a wormhole around, and use it to solve puzzles in a first-person view that it is nearly impossible to describe in a manner that gives it credit without spending a couple hundred words on it. Which I will do in a later post.)

The reason we don't see wormholes all around us is because they are unstable; they require some sort of negative energy density to hold them open, or they collapse on themselves and close off. No one has yet figured out how to have such a negative energy density, so they remain as yet theoretical entities. Considering that the neutrinos passed through over 700 kilometers of the Earth's crust on their journey, it's highly unlikely they encountered any regions of negative energy density either, but it's an interesting idea...

Actually, one test that would be very, very helpful to run would be to send photons along the same path the neutrinos take and see if they, too, show up 60 nanoseconds earlier than they're ‘supposed’ to, which would mean that it's not the neutrinos moving superluminally, but some sort of bent-space effect. Alas, such an option is unavailable to us because while neutrinos can move almost unhindered through the solid rock of the mantle, light can do no such thing, so that test is sadly out of the question right now.

2 comments:

  1. I'm glad I'm not the only one who thought of Portal. :) Just so long as GLaDOS stays out of it...

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  2. Much obliged for your summary!

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