Science and Exploration

[JAGG]

Originally Posted by dreadgeek

Jagg:

I'll try to do my very best on this one. The answer to both questions require a little bit of background on what a neutrino is and why whether or not they can exceed the speed of light is an interesting question.

So neutrinos are very small, *very* weakly interacting subatomic particles. They are the result of atomic decay (called beta decay) and are electrically neutral. They are weakly interacting because the two forces that will act on neutrinos are either very weak or very short-range. The first is weak nuclear force which is responsible for atomic decay. It is very short-range falling off to nothing pretty much outside of the range of the nucleus of an atom. The other is gravity which is long range but very weak (gravity seems strong because gravity is caused by mass and the Earth has a LOT of mass but gravity is the weakest of the four foces). How rarely do neutrinos interact with other matter? A neutrino from the sun could pass through the the Earth without *ever* interacting with another particle. This would be true even if the Earth were solid lead and lead is very dense (which is why it's used for shielding)!

The other really interesting thing is that neutrinos have very little mass while not being completely massless. The mass of a neutrino is so small that it is measured in terms of its energy. It is 50 meV (megaelectron volts). To give you an idea of just how small a number this is equivalent to this portion of a gallon of gasoline 0.0000000000000000000607991. (Recall that Einstein demonstrated that you can convert energy to mass) The reason why it is interesting is that if the neutrino were precisely massless it would always travel the speed of light (because anything with zero mass will travel the speed of light). Since the neutrino appears to have a very small, but non-zero mass, this means it can accelerate toward but can never exceed the speed of light.

This is a consequence of the equation e=mc^2 because c^2 is the speed of light (c) squared (^2). Since the speed of light in vacuum is 186,282 miles per second that number squared is huge! To accelerate *anything* with mass to within a sizable portion of c would take infinite energy. Since infinite energy isn't to be had in a finite universe nothing with mass can accelerate beyond the speed of light.

Which takes us to the recent experiment and what it might mean. So, IF it turns out that these neutrinos were accelerated beyond the speed of light then that means that Einstein's special theory of relativity will have to be revised. That said, it's simply too early to tell. Measuring the speed of neutrinos is actually a statistical matter so they look at the number of detections within a certain period of time after the accelerator fires. It may be a measurement error. If so then these experimentalists do botch things sometimes. If, on the other hand, these results are confirmed then the principal researchers are all going to Stockholm to pick up a Nobel.

To answer your two specific questions:

The answer to whether or not the neutrinos can keep up their motion indefinitely, the answer would be yes for a given value of indefinite. Until it interacts with another particle a neutrino at any velocity will continue at that velocity.

As far as the speed of a neutrino under natural conditions they have been detected within the margin of error of the speed of light (so within .999999 percent of c) from sources like a supernova.

Cheers
Aj

I know what neutrinos are but thanks for the input and taking time to respond. I found the answers on some of the links and websites many of you pvt messaged me with. Thank you!