And like every Friday, the weekly column "A Taste of Physics" is back — number 41.
This time: a particularly strange particle that led to a Nobel Prize and nearly triggered a scientific revolution.
-
The neutrino is a peculiar particle.
It exists everywhere in such staggering quantities that 65 billion of them pass through every square centimeter of your body every second.
It is so tiny that it can travel through a steel wall one light-year thick (9.5 trillion kilometers), and there is still a 50% chance it won't interact with a single other particle along the way — emerging from the other side as if nothing happened.
-
The enormous facility shown in the video is a neutrino detector built in Japan at a cost of over one hundred million dollars.
It was constructed deep inside a mine, with 1,000 meters of rock shielding it from cosmic rays that could contaminate the experiment's results.
It contains 50,000 tons of water purified to an almost unimaginable degree — the concentration of foreign particles is measured in parts per trillion.
Its walls are lined with more than 11,000 light sensors so sensitive they can detect even individual photons of light.
-
Because the neutrino's mass is so incredibly small, it barely interacts with other particles at all.
It simply flies through them at speeds close to the speed of light and comes out the other side.
The detector's purpose is to capture the rare occasions when a neutrino strikes another subatomic particle.
When this happens, the struck particle absorbs energy and begins moving at high speed.
Because the particle is moving through water rather than a vacuum, it travels faster than the light it emits — a phenomenon known as Cherenkov radiation, a fascinating topic we'll explore another time.
This radiation is picked up by the light sensors, and by analyzing it, researchers can draw conclusions about the neutrino itself.
-
The reason such highly purified water is used is that in order to detect light from tens of meters away, the water must be completely transparent.
Moreover, even a trace amount of radioactive particles in the water could generate noise that would make it difficult to isolate the neutrino's signature.
-
Discovering the fundamental properties and mass of the neutrino earned the two scientists who worked on it the Nobel Prize in 2015.
The particle nearly triggered an enormous scientific revolution in 2011, when scientists at the CERN particle accelerator claimed — after 3 years of experiments — that the neutrino travels faster than light.
According to the theory of relativity, faster-than-light travel is impossible, because mass increases and space contracts to infinity.
The scientific world was gripped by genuine panic for several months, at the end of which it emerged that a fiber-optic cable connected too loosely to an atomic clock had caused an incorrect measurement of the particle's speed.
-
And one more interesting detail to close:
Most neutrinos come from the Sun and cosmic events, but our own bodies produce more than 300 million neutrino particles every day.
They are created through the radioactive decay of potassium, which is present in the human body in small amounts.
Shabbat Shalom 😊
#ATasteOfPhysics