Friday, 16 March 2012

Not so fast with the neutrino mystery!

When I attended the village Harvest Festival supper last year, the news about neutrinos travelling faster than light had just hit the headlines.  Since it is known that I work in 'big physics', several friends confronted me with a smile, and various versions of the same question, dressed up as a statement.  "So! Physics is wrong then!"

At the time I was amused by this interrogation, and it reminded me that it was an opportunity to spread the word about how science progresses.  For very many people it is surprising to find out that being wrong is an opportunity to find something new.  It is sometimes said that physicists like nothing better than hearing what they already know.  This 'confirmation bias' is a feeling that we all have, for most of our lives.  We like to believe that we understand things, even if we are deluding ourselves. 

However, for most of us who work in science, the 'second best' thing in our professional lives is to find a surprising mystery that challenges our 'beliefs' and opens up the chance of learning something that nobody has ever known before.  The mystery of the neutrinos that might be travelling faster than light definitely falls into this category.  So much of fundamental physics points to the complete unlikelihood of the observation, but nevertheless the observation had been made. 

In actual fact I think almost every physicist was skeptical about the claim - and this would include those who had made the observation and who were calling on the broader community to explain where they might have gone wrong.  After all, we know exactly how fast ordinary neutrinos travel compared with light and would be surprised to think that those created by CERN would behave differently.  The very best and most sensitive evidence came from observations of a supernova known as SN1987A.  The light from this distant exploding star took 168,000 years to reach us and the burst of neutrinos arrived just 3 hours earlier.  We know for certain that the neutrinos came from the same direction and we understand how light can be delayed in its journey.  Light reflects and scatters from particles of matter on its way here - the neutrinos just go straight through.

SN1987A supernova - a great neutrino source!
Image from here

Even last October, the 'smart money' was on the likelihood of a subtle experimental error, and now, months later there are rumours that there are two possible candidates.  As it happens, these two tiny imperfections in a huge and complex experiment would have opposite effects.  One would make the neutrinos appear to be going even faster, and the other would make them seem slower.  Nobody yet knows which one of these dominates the measurement, but in May there is a good chance that they will find out.  At the moment, we just know that the error in the measurement is big enough to include the expected result that neutrinos do not break the light barrier.

So what does this reveal about the path of science?  I think that the openness of the scientific community, and the ease with which news can now be transmitted to the public, are strengths that we should celebrate.  The media exploits this openness for its own ends - namely profit.  However, at last the general public are able to see that science progresses in little steps, with our models of the universe getting closer to the truth each time.  Some of the steps take us backwards but they probably teach us something anyway.

The best comparison I can make to everyday life is that of seeing a delicious sausage being made.  It is perfectly OK if you are squeamish and decide not to watch what goes into the sausage, but if you don't watch then you are missing something about life, part of the path to true understanding of our universe.    In my own case I'm probably more squeamish about making a sausage than making science, but everyone is different!

Small note:  This has been written to go into a local magazine, but it was published here first!

1 comment:

krissthesexyatheist said...

(As you know) The beauty of science is that it is flexible and self correcting, unlike religion that "knows all the answers fer sure", but as time goes by...are wrong again and again. I didn't know you worked in physics (I'm new-ish here). Awesome.