Thursday, October 06, 2011

Faster than Light

"We don't serve faster than light neutrinos in here" said the bartender. A neutrino walks into a bar.

The cognoscenti were abuzz -- Einstein was wrong! Relativity was debunked! European scientists at CERN in Switzerland and Gran Sasso in Italy had shown that the speed of light is not really the limit. Physicists, on the other hand, were mildly amused, one, even,
who promised to eat his shorts if the experimental result was correct. The great majority of physicists, a clear consensus, were skeptical of the results, thinking that there must be an experimental error.

Interestingly, no one in the physics establishment mentioned the consensus. No one accused the experimenters of being Relativity-deniers. No one tried to stop publication of the seminal paper in a prestigious journal. And no one claimed that the CERN-Sasso scientists were bigots – after all, Einstein was a Jew. In short, the physics community reacted not at all like the global warming community when confronted with contrary evidence.

So what was all the excitement about? The experiment, code named OPERA, was built to detect neutrinos, ghostly subatomic particles, which are produced at CERN and aimed towards Gran Sasso, 700kms away. There are several types of neutrinos and two of the species are called mu neutrinos (mu-nu) and tau neutrinos (tau-nu). The primary purpose of the experiment was to determine if any of the mu-nus from CERN had converted into tau-nus along the way. If so, this would help establish the idea that neutrinos have a finite (really tiny) mass that might account for the much-sought-after “Dark Matter” hidden in the universe. A sidelight was to measure the time of flight of the neutrinos and compare it to the time light would take to travel the same distance. Surprise! The neutrinos took less time, 60 nanoseconds less.

OPERA chief scientist Antonio Ereditato explained that “we are not claiming things, we want just to be helped by the community in understanding our crazy result - because it is crazy. And of course the consequences can be very serious.” Indeed, much of modern physics - as laid out in part by Albert Einstein in his Special Theory of Relativity - depends on the idea that nothing can exceed the speed of light (in vacuum).

Faster-than-light particles, so-called tachyons, have long been contemplated by theoretical physicists. If they did exist they could be used to send signals into one's own past, a clear paradox of causality -- and an explanation of the backwards joke at the beginning of this note. In fact, the most famous quip about “faster than light” has by now attained a venerable age (Reginald Buller in Punch, 12/19/23):

There was a young lady named Bright,

Whose speed was far faster than light;
She started one day
In a relative way,
And returned on the previous night.

The upheaval of known physics resulting from the discovery of tachyons would be momentous. A few astounding effects are discussed briefly in the Appendix.

In a related development, the 2011 Nobel Prize in physics has been granted for an experimental error! It was 1997 and Adam Riess was sure he'd spotted a blatant error in his results -- measurements of exploding stars implied that the universe was expanding at a faster and faster rate, instead of slowing down, as everyone expected. Indeed, astrophysicists believed that the rate of expansion of the universe -- set in motion by the Big Bang 13.7 billion years ago -- would be slowing down due to the influence of gravity. The goal was to figure out how rapid the deceleration was. What the scientists found, instead, was that the expansion of the universe was accelerating -- an observation that could be explained by the existence of a mysterious “Dark Energy” that acts like anti-gravity. Further experiments supported this finding and, even though no one knows what the Dark Energy is, the experimenters were awarded the prestigious Nobel Prize.

In breaking news (10/5/11): The Nobel Prize in Chemistry was awarded to Dan Shechtman, an Israeli scientist, for his discovery of quasi-crystals, a form of matter that was not thought to exist. Shechtman faced skepticism, even expulsion from his research team, before his discovery won widespread acceptance as a fundamental breakthrough. “The main lesson that I have learned over time is that a good scientist is a humble and listening scientist and not one that is sure 100 percent in what he read in the textbooks,” Shechtman, 70, told a news conference in Haifa, Israel.

These cases illustrate the way real science should work. It is not politically motivated, and is not right just because it is believed, no matter the consensus.


In classical physics, mass is independent of speed. In Relativity, however, Einstein showed that the mass of a particle is related to its velocity, v:

M = M0/sqrt(1- v2/c2)

where M0 is the particle’s rest mass (mass at zero speed), c is the light speed and sqrt(…..) signifies the square root of the quantity in brackets. As one tries to accelerate a particle, and its velocity increases, so does its mass because of the v in the denominator of the equation. That makes it harder to speed up the particle. The result is that for all normal particles (we might call the tardyons) the speed has an upper limit of c, the speed of light.

Note that for tachyons, if they exist, the term v/c exceeds one, and the term in the brackets is negative. Since the square root of a negative number is imaginary, the mass of a tachyon is a strange thing indeed.

Another curious effect is that, unlike ordinary particles, the speed of a tachyon increases as its energy decreases. In particular, energy approaches zero when v approaches infinity. Therefore, just as tardyons are forbidden to break the light-speed barrier, so too are tachyons forbidden from slowing down to below c, because infinite energy is required to reach the barrier from either above or below.



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