Detour: Scientists Break the Lightspeed Barrier


There once was a lady named Bright
Who traveled faster than light.
She went out one day
In a relative way
And returned on the previous night!

(With an acknowledgement to The Economist, which paraphrased this little limerick in their story on this very issue)

________________________________________

Thursday, September 22, 2011.  Will it go down in history as the day that Einstein’s theory of special relativity went down in flames?

Researchers working on the OPERA project at CERN in Geneva, Switzerland, announced that they have, over the course of three years and 15,000 experiments, measured the velocity of a beam of neutrinos traveling faster than the speed of light.

This is huge, since it may—and that’s a key word—overturn Einstein’s theory of special relativity.

It’s such a huge thing that it deserves comment, even here in a blog devoted to the best science fiction films.  Though I’ve pointed out that the most popular science fiction is not that interested in science, I am, so I’m going to go right on and talk about this.

Special Relativity

In order to understand why this unexpected experimental result matters, you need some background.  You need to know what the special theory of relativity is and how it works—and that’s a pretty complicated subject that I don’t fully understand myself.  Oh, I have a layman’s appreciation for the topic, and I’ll share that with you—but it’s likely that I don’t get all the nuances of the theory.

Back in 1905—that was a big year for Einstein, in which he published three groundbreaking papers which revolutionized modern physics—Einstein proposed the special theory of relativity.  Basically, it says that for cases of uniform motion—that is, unaccelerated motion and, as later refined, unaccelerated motion outside a gravitational field—all motion is relative.  There is no “correct” assertion that one of two moving bodies is at rest with respect to the other.  It’s special relativity because it applies only in the special case of uniform motion (Einstein formulated general relativity a bit later, and it applies to accelerated motion as well, thereby incorporating gravity).

An example will make this a little clearer.  Imagine, if you will, that Flash Gordon and Buck Rogers are astronauts in deep space.  This is, by the way, the modern formulation of the example, which I have most recently encountered in Brian Green’s The Fabric of the Cosmos—though I’m the one who decided it was Flash Gordon and Buck Rogers, since this is a science fiction blog.  Now, Flash is at rest—he’s not moving at all.  Buck, on the other hand, is traveling at a uniform ten miles per hour in a straight line on a course that has him passing a mere twenty feet from Flash.  What special relativity tells us is that, from Flash’s perspective, Buck is moving, but that from Buck’s perspective, you might as well say that Flash is moving at ten miles an hour, and that Buck is stationary.  There’s no way to tell the difference, and no way to tell which one is “right” about who is moving and who isn’t.

That all goes out the window the second one of them accelerates, mind you—that includes changing direction as well as speed.

It sounds unbelievable, but you experience (or can experience) this in every day life.  If you’re in a car traveling at a steady 60 miles per hour in a straight line, and you close your eyes, you can’t tell you’re moving until the car accelerates, decelerates, or changes direction—at least if the suspension is good.  Of course it’s dangerous to do that if you’re driving a car…elevators replicate the experience, too, during the part of the trip where the elevator is moving at a constant speed.  You don’t even have to close your eyes unless it’s a glass elevator.

It seems like all Einstein said was that there was no difference between uniform motion and the seemingly special case of uniform motion of zero, but there’s quite a bit more to it, with some intriguing subtleties.  Special relativity does away with the concept of absolute space, the idea that there’s some special reference frame from which to judge whether something is moving or not.  It replaces it with the notion of absolute spacetime, in which space and time are unified in a single entity—to be fair, absolute spacetime does owe something to Minkowski, who reformulated Einstein’s work using geometrical principles in 1908.

For our purposes, the most important consequence of special relativity is that nothing can travel faster than the speed of light in a vacuum (about 186,000 miles per second).

Some of the other consequences, by the by, include (1) relativity of simultaneity, so that different observers may report that events take place in a different order depending on their rates of motion; (2) the absolute nature of the speed of light, meaning that the speed of light is the same for all observers, regardless of their state of motion (which is really a doozy of a proposition, but among other things means that no one can ever catch up with a beam of light since it will appear to be moving at lightspeed no matter how fast they’re going); (3) matter-energy equivalence, expressed in the famous equation E = mc2; (4) lack of luminous aether, meaning that there is no medium through which light propagates; (5) time contraction, so objects traveling at high rates of speed relative to the speed of light travel more slowly in the time dimension (i.e., time passes more slowly for the fast-moving object); (6) Lorentz contraction, so objects traveling at a high rate of speed (once again, relative to the speed of light) get shorter; (7) a new relationship between momentum and inertia, so that objects gain in mass as they approach the speed of light; and (8) Thomas rotation, in which different observers may report different orientations (that is, different angles between an object’s direction of travel and its rotation or spin) of the same object as that object travels faster.

The list of consequences is probably only of interest to the physicist, but the important thing is that each and every one of these consequences of the theory of special relativity has been experimentally observed.  In other words, special relativity has had a spectacular success in the scientific arena; it’s absolutely correct in every respect that we can determine!*

Or it was…

It’s also the foundation for quantum electrodynamics, a highly successful theory in its own right.

Einstein got the entire theory and all of its predictions from two postulates, as he called them, and which we might term hypotheses.  The first is the principle of relativity, which states that the laws of physics are not changed by motion.  The second is the principle of invariant light speed, which states that light always travels at a fixed speed relative to a stationary set of inertial coordinates, regardless of the motion of the source of that light.

I guess that’s what a genius level intellect will be able to do—I sure couldn’t have done that!

So…if the OPERA folks are correct, and neutrinos do travel faster than light, one of the consequences of special relativity—that nothing can travel faster than the speed of light—is wrong.

The OPERA Experiment

So, what the heck is the OPERA experiment, and how did it generate so much hullaballoo?

Simply put, it’s an experiment designed to test for neutrino oscillation.  That may not tell  you much if you don’t know a little physics, like what a neutrino is, for starters.

Neutrinos (which in Italian would be “little neutral ones”) are fundamental particles in the Standard Model—electrically neutral subatomic particles which interact with other matter only through the weak nuclear force.  Because they interact so weakly, they generally pass through other forms of matter with no interactions (“like a bullet through a fog bank”); that makes them hard to find.  They’re a kind of lepton, like the electron, and as far as we know they aren’t made of anything (that’s why we call them fundamental).

There are three kinds of neutrinos, corresponding to the three families of matter in the Standard Model:  the electron neutrino, the muon neutrino, and the tau neutrino.  No one knows why the elementary particles come in three families, by the way, though string theorists have some ideas with some math behind them, so we might find out why, one day.  At any rate, now we’re getting to the heart of the neutrino oscillation phenomenon.

If neutrinos have mass, they could change from one type to the other, and this would have the added benefit of explaining why we can only detect one-third to one-half as many neutrinos as we think we should be able to coming out of the sun (this was called the solar neutrino problem, and it really bothered some folks for a while—it was used by Arthur C. Clarke in his novel Songs of Distant Earth, which Clarke stated was his favorite of his own works—postulating that something was very, very wrong with our sun, causing it to nova far earlier than expected).  That change is called neutrino oscillation.  Basically, if we’re only looking for electron neutrinos, and some of the neutrinos emitted by the sun are changing to muon neutrinos and tau neutrinos, we won’t see them unless we’re specifically looking for them…

Incidentally, if neutrinos do have mass, they will feel the effects of gravity, giving them another way to interact with other forms of matter.  Massless neutrinos would have to travel at the speed of light, while massy neutrinos could not, if special relativity is right.

In 1998, a neutrino detector in Japan proved that neutrino oscillations exist, so if the theories are right, then they have some mass.  We just don’t know what it is and no one has figured out a way to directly measure it.

The Kamiokande neutrino detector in Japan

So the OPERA (Oscillation Project with Emulsion tRacking Apparatus) experiment directs a beam of high intensity muon neutrinos (that’s the second family) from CERN in Geneva to an underground laboratory in Italy, where they attempt to detect tau neutrinos.  It’s about 450 miles, through solid earth, and it takes the beam about three milliseconds to make the trip.  It went active in 2008, and in May 2010 the experiment’s researchers announced their first tau neutrino candidate discovery.

Here’s the problem:  over the course of the three years the experiment has been in operation, with over 15,000 observations, the neutrino beam should have taken about 0.002419354 seconds to make the trip.  Instead, it took about 0.002419294 seconds.

Uh oh.

I realize that it doesn’t seem like a long time, and it’s not.  But light can travel the distance between the two laboratories more than 413 times in a single second.  These are speeds we’re not really equipped to understand; it seems instantaneous to slow human perceptions.

If the OPERA researchers are right—and to their credit, what they’ve said is that they want the rest of the physics community to look at their work and make sure it’s right, and to replicate the experiment themselves—then neutrinos travel faster than light.  By about 0.1%.

Where do we go now?

Obviously the next thing to do is to decide if the folks at OPERA have made some kind of mistake, and if they haven’t, if anyone else can do the same thing and come up with similar results.

So where and how could they have made a mistake?  The first possibility is that it’s some kind of measuring error.  If, somehow, the distance from the origination point in Switzerland and the ending point in Italy is wrong, it could make a difference in the computation of speed.  Or if the measurement of time is somehow mistaken, they could also be wrong.

Frankly, that sort of elementary mistake doesn’t seem all that likely, does it?  But a little math tells us that they’d only have to be off by about .0116 miles (the 6 x 10-8 second difference times the speed of light, 186,000 miles per second), which is really not much in terms of distance—about 58 feet (the margin of error on their measurements is about 2 cm, or something less than an inch).  Or somehow their clocks are off, which isn’t as far-fetched as you might think (again, 6 x 10-8 seconds, but the margin of error has been calculated to be 1 x 10 -8 seconds).

There’s another problem in all this.  CERN doesn’t actually manufacture a beam of neutrinos.  What they actually do is manufacture a beam of pions and kaons, extremely short-lived subatomic particles which decay into neutrinos.  The exact lifetime of pions and kaons is random.

As it turns out, the OPERA experiment uses GPS satellites to determine where the origin and ending points of the neutrino beam are located.  Some scientists have already stated that an accuracy of 10 nanoseconds—remember, the neutrinos were only 60 nanoseconds early—can’t be achieved using GPS satellites.

There’s at least one other reason to believe that this was some kind of measuring error.  Back in 1987, light from a supernova, SN 1987A, located in the Large Magellanic Cloud, reached the Earth.  So did the neutrinos from that explosion, and for the first time in history, scientists were actually conducting neutrino experiments and could catch some.  The light was a little bit behind the neutrino burst, by about three hours.  As it turns out, the light was delayed by collisions with the dust clouds, and it doesn’t get emitted until the shockwave from the explosion reaches the surface of the star, which gives a theoretical delay time of…you guessed it…three hours.  In other words, the neutrinos were right on time.

If the OPERA results are correct, the neutrinos should have arrived almost four years before the light did.  Of course, in 1983 we didn’t have neutrino detectors capable of finding the neutrino burst, but the point is that we did see a neutrino burst when we thought we should.

By the way, when we talk about a neutrino burst here, we’re talking about a grand total of twenty-four antineutrinos (which may simply be neutrinos with opposite spin, but nobody knows for sure yet) in a period of something less than thirteen seconds.  It’s a statistically significant result, mind you, and it agrees with theoretical models about supernovae explosions, but I wanted to be clear that we’re talking about a particle that is very hard to detect.

On the other hand…this isn’t the first time someone has observed neutrinos moving faster than the speed of light.  Fermilab, the American accelerator facility, has been sending beams of neutrinos to Minnesota, where the MINOS (Main Injector Neutrino Oscillation Search) detectors were located.  They also saw a similar result—but were uncertain enough about the exact position of the detector that they declined to consider the result significant.

Once we eliminate the measuring errors, of course, what we’re left with is new physics.

And no one, but no one, is speculating about that yet.

Or are they?  Turns out someone has been speculating about it—back in 1985 someone named Chodos proposed that neutrinos might be the elusive tachyons.  The explanations for whether or not that’s possible are way beyond me, though.

I’ll go out on a limb here, though, and say that if there is an effect, it won’t be that neutrinos always travel faster than light—there’s that SN 1987A data out there.  If it’s a real effect, it will turn out to have something to do with neutrino interactions with matter.

If any of this is proved to be true, maybe science fiction can get its faster-than-light drives and communication devices back.

________________________________________

*  I would be remiss if I didn’t mention one semi-popular criticism of relativity around on the web, Andy Schlafly’s contention that relativity is a liberal conspiracy to “encourage[] relativism and its tendency to mislead people in how they view the world.”  While Schlafly is a brilliant man with undergraduate degrees in computer science and electrical engineering, as well as a law degree, he’s simply wrong on this front.  Some of his proofs that relativity is wrong, such as the so-called Pioneer Anomaly, have been fully explained, and others, such as a distortion in the Moon’s orbit, have been cited as proof, not of relativity being wrong, but a large and unknown planet (dubbed Tyche in some research) existing beyond the orbit of Pluto.  Among other things, Schlafly credits Poincare and Lorentz with the creation of the theory of special relativity, instead of Einstein.  The entire scientific establishment seems to accept relativity—after all, it (along with quantum mechanics) underlies all of modern physics.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: