(That is Half 3 of a collection on neutrinos, Majorana fermions, and one of many strangest open questions in physics. Learn Half 1 and Half 2.)
Neutrinos have mass. We all know this. And big particles — ALL large particles, as we established in Half 1 — flicker between left- and right-handed states. That flickering IS the mass. The fixed Higgs handshake, the limitless switching. That is the deal. That is what makes all of it grasp collectively.
However neutrinos do not flicker. Left-handed neutrinos keep left-handed. Proper-handed antineutrinos keep right-handed. No switching. No flickering. Nothing. And but they’ve mass.
So both every part we simply mentioned about mass is incorrect — and I am fairly assured it is not — or one thing very unusual is occurring with the neutrino.
Probably the most simple resolution is that this: the right-handed neutrinos ARE there. They exist. We simply cannot see them.
Here is why that works. Take into consideration the electron. The electron has two fully impartial methods to explain it. One: handedness. Left or proper. However we have discovered that for an enormous particle that is simply the flickering — transient, consistently altering. It isn’t a everlasting label. Handedness for an electron is sort of…incidental. It would not outline what the electron basically IS.
However there’s one other method to describe an electron: particle versus antiparticle. Electron versus positron. And THIS one is everlasting. Essential. Pinned open by electrical cost. An electron has cost. A positron has the alternative. In the event that they meet, they annihilate in a flash of pure vitality. The universe treats this distinction as sacred, as a result of cost is conserved, and the universe doesn’t fiddle with conserved portions.
So for the electron: handedness glints and would not actually matter. Particle versus antiparticle is locked and elementary and actually, REALLY issues. Two descriptions. One necessary, one not.
This offers us what we will fairly name the Dirac image — named after Paul Adrien Maurice Dirac, who first labored out the arithmetic of relativistic quantum particles. On this image, the neutrino works precisely the identical method because the electron. Two choices for handedness, two choices for cost. 4 complete combos.
Left-handed neutrino: we see them, the weak drive loves them. Proper-handed antineutrino: we see them too, the weak drive produces them in beta decay. These are the observable ones.
Then there are the opposite two. Proper-handed neutrino. Left-handed antineutrino. These exist within the idea. They only do not work together with something. Our germaphobic weak drive will not contact them — incorrect palms, bear in mind? They haven’t any electrical cost, so electromagnetism ignores them. No colour cost, so the robust drive ignores them. The one drive they EVER really feel is gravity. They’re, in probably the most full and complete sense conceivable, invisible. Not exhausting to detect. Not uncommon. Not shy. INVISIBLE. Utterly, completely, in-principle undetectable by any instrument we might ever conceivably construct.
They may very well be on this room RIGHT NOW and we’ve no method of detecting them.
And look — it really works. The maths is constant. It explains why we solely see left-handed neutrinos.
There’s even one thing genuinely stunning hiding in it. If these right-handed neutrinos exist and are ENORMOUSLY large — and I imply absurdly, nearly comically large, like ten to the fifteen instances heavier than a proton — then one thing elegant falls out of the arithmetic. Their mass and the mass of strange left-handed neutrinos find yourself inversely linked. Make the right-handed accomplice heavier, and the left-handed neutrino will get lighter. It is known as the seesaw mechanism. Push one finish down, the opposite goes up. And it might clarify why neutrino lots are so vanishingly, nearly insultingly tiny. The lightness of the neutrino could be a direct echo of the enormousness of one thing we will by no means straight observe.
That is good.
However here is the factor. Relating to the electron, its two descriptions — handedness and particle-versus-antiparticle — are saved impartial by electrical cost. Cost is what forces them aside. Cost is what insists that “electron” and “positron” are categorically various things that can not be confused or collapsed into one another.
However the neutrino has no electrical cost. Now we have bookkeeping units that preserve neutrinos distinct from antineutrinos in our equations — however not like electrical cost, they are not sacred. They don’t seem to be protected by any deep precept. They’re unintentional. The universe did not mandate these guidelines. They only fell out of the mathematics, as a result of we designed the mathematics that method.
Here is the factor: nothing is FORCING the excellence between “neutrino” and “antineutrino” to be elementary.
And that is the crack within the door that Ettore Majorana walked by.
In Half 4, we get to Majorana’s final paper — and the experiment that may lastly reply the query he left behind.
