[Marxism] Struggling to Get a Handle on the Flavorful Neutrino

Louis Proyect lnp3 at panix.com
Tue Oct 20 15:27:24 MDT 2015


NY Times, Oct. 20 2015
Struggling to Get a Handle on the Flavorful Neutrino
by George Johnson

It was 20 years ago that Art McDonald and I stopped at a Tim Hortons 
near Sudbury, Ontario, for coffee and doughnuts on our way to his job at 
the neutrino mine. Donning hard hats, we crowded into a rattling 
elevator cage and descended 6,800 feet to an underground laboratory that 
reminded me of the one in “The Andromeda Strain.”

The Sudbury Neutrino Observatory sat at the end of a long corridor at 
the bottom of a working nickel mine. In the tunnels above us miners dug 
and blasted through granite. Dr. McDonald was after a far less 
substantial ore.

Neutrinos are said to pass through Earth almost as easily as through 
empty space. During the flight, theorists believed, neutrinos were 
capable of changing their identity. Dr. McDonald’s job was to catch them 
in the act. It was six more years before he succeeded. Earlier this 
month he won a share of a Nobel Prize, a climax to a long and perplexing 
tale.

I had come to Sudbury on a philosophical quest. I wasn’t entirely sure I 
believed in neutrinos, which were invented in 1930 to fill a hole in 
physics. In a type of radioactive decay, experimenters had measured more 
energy going in than coming out.

That is supposed to be impossible, so the fix was to conjure forth an 
unseen particle with precisely the right characteristics to take up the 
slack. The particles had gone unnoticed, the argument went, because they 
had no handles for experimenters to grab onto — no charge and (it was 
believed at the time) no mass.

Sometimes this explanation seemed a little too pat. I knew neutrinos 
were eventually detected, but in ways so oblique that I wondered how 
physicists could be sure they weren’t just seeing what they needed to see.

By now neutrinos are woven so tightly into the mesh of physics that you 
would have to be a crank to doubt their existence. But when you start 
peeling away the layers of theory, reality can start feeling pretty 
abstract.

Of all the particles in the universe, the only ones our senses can 
directly register are photons — particles of light that strike the 
retina and send electrical signals to the brain. Our cruder senses 
respond to whole globs of matter — larger globs for touch, invisibly 
tiny globs for smell. Sound, for its part, is the vibration of matter, a 
rumbling of the ground or a reverberation of the air.

Revealing the existence of theoretical stuff like neutrinos means 
coaxing them into producing photons to be registered by our eyes or our 
instruments. It took a quarter century to figure out how to do that, and 
by a somewhat circuitous route.

Like other particles, neutrinos, the theory goes, have antimatter 
counterparts. When an antineutrino collides with a proton, it should 
transform it into a neutron while an antimatter electron is kicked out. 
It quickly strikes a regular electron, exploding into two photons flying 
in opposite directions — tiny flashes of light.

An instant later the neutron is sucked into the core of an atom, 
resulting in another flash. If the timing and energy of these 
scintillations are precisely in sync, you can say you have glimpsed a 
neutrino.

In the mid-1950s two experimenters, Frederick Reines and Clyde Cowan, 
put it all together. They measured neutrinos spewing from a nuclear 
reactor. The reward was a Nobel Prize.

Then things started getting messy. Now that it was possible to detect 
neutrinos, physicists had a way of testing their theory of sunlight — 
that it was generated by nuclear fusion. That meant neutrinos should be 
pouring from the sun in droves.

In the inverse of the reaction used by Reines and Cowan, a neutrino 
striking a neutron should transform it into a proton and an electron. If 
the neutron is contained within the core of a chlorine atom, it morphs 
into an argon atom and emits gamma rays. Gamma rays are very high 
frequency light.

With a vat of chlorine atoms (in the form of dry cleaning fluid), 
Raymond Davis Jr. was first to find this circumstantial evidence 
(resulting in yet another Nobel Prize). But his experiment is more 
famous for seeing only a fraction of the neutrinos required by solar 
theory — another hole in physics.

Maybe the sun wasn’t really powered by fusion. Or maybe neutrinos were 
eaten by a black hole lurking inside. By the time I met Dr. McDonald, 
theorists had rallied around a less radical thought.

By then there seemed to be three different “flavors” of neutrinos. Maybe 
as neutrinos streamed from the sun, they “oscillated” between the 
different types. Our instruments had been blind to all but one. That is 
where the Sudbury detector came in. It succeeded in registering all 
three flavors, as signatures of photons.

This solution to the solar neutrino problem required a troubling 
trade-off. For years physicists had celebrated the neutrino’s massless 
purity, which allowed it to pass at lightspeed through anything in its 
path. But for neutrinos to oscillate they had to be saddled with a tiny 
dab of mass. “That can’t be — it’s too ugly,” the great physicist Hans 
Bethe remarked when he heard the proposal. But in the end the 
alternatives seemed worse.

As I raise a doughnut and a cup of takeout coffee to Dr. McDonald and 
his crew, I still feel a little uneasy. Quarks, gluons, Higgs bosons — 
the story is the same. Behind the scenes, particles decay into other 
particles, until at the end of the tunnel you see the light. Whether 
we’re reading a meter or a computer screen, our knowledge ultimately 
comes down to photons.

On that trip to Sudbury, Dr. McDonald gave me a nugget of nickel ore. 
Solid as it seems it is made of atoms that consist mostly of empty 
space. It shimmers a silvery gold because photons strike hollow shells 
of electrons and ricochet into my eyes. All of our knowledge of the 
world is so indirect.

I find some satisfaction in Boswell’s famous description of Samuel 
Johnson disputing Bishop Berkeley’s contention that the world is all in 
our minds. Kicking a rock and maybe stubbing his toe, he declared of the 
theory, “I refute it thus.”



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