Thursday, September 29, 2011

How can OPERA's faster-than-light neutrino results make sense?

In my opinion, they can't make sense--I strongly favor the outcome that they made a mistake somewhere.  But for the sake of arguments, what *could* this result be saying?  There are a lot of loonies out there who are starting to stand up to say, "See, I told you so!  I've been saying Einstein was wrong for decades."  How long before we hear someone say, "This proves that you have to shut down the LHC!"  but I digress.

1. Neutrinos really do travel faster than light
Well, that would be something!  The Lorentz Transformations were derived towards the end of the 19th century in order to make sense of the Maxwell Equations of electricity and magnetism.  Our whole technological world is built on these equations, so anything that would allow the neutrino to go faster than light would have to be a small (very, very, very small) correction on these robust equations.  We would have seen this somewhere else by now, I think.

One way to keep everything in tact is to say that the neutrino has an imaginary mass.  (What is an imaginary mass?  How much would imaginary mass weigh in a gravity field?  Negative weight?  I have no idea.)  Then according to Lorentz, the faster the neutrino goes (beyond the speed of light), the lower its energy gets.  So infinitely fast neutrinos would have no energy.  But they would have infinite imaginary mass.  Is this dark energy?

2. Neutrinos fake going faster than light
This is the non-mistake outcome that I favor. Let's say that the momentum of the neutrino is very well known.  Then the Heisenberg Uncertainty Principle says that the position of the neutrino is uncertain.  What if there was some effect that enhanced the neutrino's position uncertainty in its direction of motion?  Then it would arrive slightly before it got there all along its direction of motion.  Maybe it has to do with the neutrinos' interesting spin signature.  We know that there is only one spin-type for the neutrino: left-handed spins for neutrinos and right-handed spin for antineutrinos.  Maybe the left-handed spin pushes the uncertainty forward a little bit, and the right-handed spin pushes it back.  This is easy (enough) to test at OPERA or here at MINOS.

This is, sort of, a combination of the Star Trek warp drive and the Hitchhiker's Guide infinite improbability drive.  I like it.

Friday, September 23, 2011

Neutrinos are weird, and wonderful

Actually, this astounding result is very good news for Fermilab! We have committed to studying neutrinos for the next 10-20 years. So when somebody asks, "Why should we care about neutrinos," the answer is easy!

If neutrinos can travel faster than light, this contradicts one of the very foundations of physics as we know it. Therefore, we need to understand how:
  • neutrinos can have this ability when no other matter in the universe does.
  • the equations of electricity and magnetism can include this result.
  • our understanding of Einstein's Relativity Theories ("Special" and "General") is affected, and neutrinos seem to be our way to do this.
And lastly, how come the Swiss are are so damn good at telling time? :-)

Observations of OPERA presentation

They have been sitting on this hyper-luminal neutrino for six months.

They initially did the analysis with intentionally inaccurate assumptions, while the various groups in OPERA made improvements on these aspects. For example, the biggest factors are
  • The distance between CERN and the experiment ("geodesy")
  • The measurement of the time the protons hit the target at CERN
  • The synchronization of the clocks between CERN and the experiment.
  • eight or ten other smaller effects
The thorough analysis with bad assumption led to neutrinos that were 1048 nanoseconds too fast. Then they "opened the box" on the more accurate systematic measurements. The corrections to the accurate results were 988 nanoseconds, leading to the 60 nanosecond too-fast result.

They "opened the box" six months ago, and they were clearly stunned. This collaboration of hundreds of scientists have considered possible mistakes in the analysis for this time.

An aside on the distance between the source and the experiment: They show a huge step function at the time of the Italian earthquake in 2009. This huge change in the distance was 7 centimeters!

This is an uncomfortably reasonable result--very precisely determined.

Neutrinos faster than light???

I've thought a lot about the CERN result that the neutrinos in the OPERA experiment travel slightly faster than the speed of light. This result is truly earth-shattering. A result is a result--first we have to see if there are any holes in it. The press reports say it is sound.

Here is what I know.

They see that the distance between CERN and the experiment in Italy is about 60 feet shorter, out of about 2.4 million feet (730 km) (or one part in 40,000), for neutrinos than what they measure it to be. (The result is that the neutrinos get there 60 nanoseconds early--I translated this into something more understandable). Their error-bars are 10 nanoseconds, which makes this a 6-sigma effect--quite believable.

The speed of light "speed limit" is not something to giggle at. A huge percentage of the understanding we have in the physical world would be toppled if this result is real.

Einstein came up with the "speed limit" after examining Lorentz's observation of the symmetries of the equations of electromagnetism (Maxwell's equations). Lorentz's work was in the 19th century. The constancy of the speed of light, and the inability of an object with mass to obtain the speed of light, is a consequence of the validity of the theories of electricity and magnetism. The fact that we are communicating by electronic computer is a pretty good testament to the validity of our understanding of E&M. Making Lortentz's equations invalid would mean that our understanding of E&M is wrong.

We measure the "speed limit" at Fermilab (and at CERN) every day. I could go on and on about this.

The normalized speed of a particle, beta, is equal to the square-root of (one minus the (the mass-squared over the energy-squared)). For beta to be greater than one would require an "imaginary" energy or mass (but not both). This is the definition of the hypothetical "tachion". An imaginary mass for the neutrino would be very interesting!

So, there are a few possible explanations for this results that I can think of, in order of plausibility (IMHO):
  1. The result is wrong, and there are several ways to satisfy this explanation.
  2. A neutrino has imaginary mass.
  3. There is some time/space/dimensional anomaly between CERN and the experiment, making the distance slightly shorter than it should be.
  4. Our understanding of physics is wrong
(Imaginary energy is what is required to create a stable wormhole, by the way.)

How could the result be wrong? We'll see what they have accounted for in their measurement.
  • Measuring the precise distance is very tricky. They are shooting the neutrinos through the earth, so this requires very precise knowledge of the shape of the Earth and the location of the source and the experiment.
  • Measuring the precise time is also very tricky. This, in particular, is what interests me. How do two places that are 730 km apart synchronize their clocks to this level of precision? Can GPS do that? (Of course, GPS technology RELIES on our understanding of E&M and the constancy of the speed of light. Ironic, eh?)
  • Exactly when and where are the neutrinos created? We think we understand the particle beam and its properties, but if this result is correct, then clearly we don't. (Another irony.)
In my lifetime, there have been two other times when there was a result of earth-shattering proportions:
I believe it is accurate to say that both of these were considered to be good experiments, but no one else has been able to verify the results. Thus, the community has considered these results to be flukes.