Why do we need neutrinos?
From pages 210-233, The Heavenly
TIme Machine
Photons to carry energy, electrons for making
chemistry upon which life depends and quarks to make solid matter
out of which we and all else are built – these three basic
components are all the universe needs. Yes, we need virtual messenger
particles to make forces, and there are all sorts of short-lived
entities that seem to do something, but these are just a way
to help the stuff that counts to do its job. The virtual and
short-lived particles are, in a sense of speaking, not even real.
These are sort of like the frosting on the cake. We cannot say
the same for the neutrino. It is one of the most durable and
stable particles around. To capture, affect or destroy a neutrino
is an almost impossible job. It would take light years worth
of lead shielding to stop a neutrino. The neutrino is here, but
what is it good for? Yes, it does perform a useful function to
carry away excess energy when an atom undergoes radioactive decay.
But there are other ways in which this bookkeeping trick could
be handled. Instead of emitting an electron and neutrino when
a neutron turns into a proton, how about emitting the electron
at a higher velocity to carry away the excess energy? Why does
the universe need a neutrino that hardly interacts with matter
in any way? It is a mystery.
Neutrinos were first hypothesized in the early
1930s by Wolfgang Pauli as a way to account for the missing energy
in radioactive decay. But the particle was not detected till
the 1950s, when vast numbers of concentrated neutrinos first
became available from nuclear reactors. The interaction of the
neutrino with matter is almost nonexistent, but not zero. Concentrate
enough neutrinos onto a detector and you will catch a few. There
are several different kinds of neutrinos and their antiparticle
versions, the antineutrino. All are characterized by almost zero
mass and near light-speed velocity. The neutrino is not affected
by anything except the force of gravity and the weak force involved
in the radioactive decay process. No one is sure how many neutrinos
there are in the universe. But there are theoretical grounds
to indicate that there are as many neutrinos as there are photons.
Neutrinos were created in the original big
bang process of the creation of the universe, and new ones are
constantly streaming out of stars and radioactive decay. The
mass of the neutrino is tiny, if any, so they do not contribute
appreciably to the content of the universe. They move at the
speed of light if massless, or at nearly that speed if there
is some tiny mass associated with the neutrino, as recent tests
indicate. The neutrino is like a photon with respect to mass
and velocity. But a photon serves an essential function as it
interacts with matter. We see by means of photons. We send radio
signals through photons. We transmit energy through photons.
Not so with neutrinos, because they do not interact with anything.
The sun shines down on the earth, and we see the light photons.
At night we see no photons because the sun is hidden from view.
But day or night is all the same for neutrinos because the earth
is transparent to them. A light year's width of lead is for an
electron-neutrino like a pane of glass for a light-photon. But
what is this thing good for?
Possibly there is no mystery involved. We
do need a mechanism to keep the energy before and after balanced
in the radioactive transformation process. The neutrino provides
a simple way to do this. Alternatively, the neutrino will perhaps
explain some very deep insight into science or Torah one day.
Too bad that this matter has to remain hidden at this time. But
possibly the secret has already been revealed to us in the supernova
process.
In 1987, the neutrino flux from a supernova
in the Large Magellanic Cloud, 170,000 light years away, reached
the earth. A total of 22 antineutrinos were detected (11 in Japan,
8 in the United States and 3 in the Soviet Union). It is estimated
that the neutrino flux emitted by the collapsing star was 10^58
neutrinos. Of these, 10^11 neutrinos passed through every square
centimeter on earth, and about 10^14 neutrinos passed through
every person. Twenty-two detector interceptions out of such a
large number shows how weakly the neutrino interacts with matter.
This is important for our health, because no one could survive
being hit by 10^14 interacting particles. It is good that neutrinos
don't interact much with matter, otherwise they would kill us.
But not having any neutrinos would also not kill us. So why neutrinos?
Possibly because neutrinos are a necessary factor in causing
a supernova explosion. And the supernova is a necessary factor
in the spreading of carbon. And carbon is essential to our existence.
So in this respect, it does seem as if we would not exist if
there were no neutrinos. But a flood of strongly interacting
neutrinos would kill us. Does this perhaps explain the purpose
of this mysterious weakly interacting particle? You decide.
The enormous gravitational pressure of a collapsing
star turns the iron core into pure neutrons. This means that
protons become neutrons, releasing a neutrino in the process.
This is where most of the neutrinos from the star come from.
Neutrinos are weakly interacting particles. But a neutron ball
is not ordinary matter. It is tremendously dense, compressed
matter that even the elusive neutrino cannot easily penetrate.
The neutrinos hit the neutron core of the star and bounce back
with great force. The star explodes spewing everything except
the neutron core, all over space. Among the debris of the star
is carbon, which was cooked in the nuclear furnace of the star.
A billion years later this carbon combines with other cosmic
dust to form a new generation star and new generation planets
where carbon is a common ingredient. Carbon is part of the planet;
it is part of the "dust of the earth" from which man
was fashioned. Having performed the job of exploding the star,
the neutrinos speed harmlessly on their way. In 1987, the creature
called man catches 22 neutrinos in traps devised by his ingenuity
an ingenuity which is uniquely ours as part of being created
"in the image" of Him who brought it all into being.
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