Will protons last forever? Why do scientists look for signs of decay?
Will protons last forever? Why do scientists look for signs of decay?
By Don Lincoln | Published: 2024-11-05 15:57:00 | Source: Hard Science – Big Think
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The universe appears to be eternal, or close enough. Nearly 14 billion years ago, stars lived and died, galaxies rotated, and matter moved in majestic ways throughout the universe. This may not seem great at first, until you realize that this stability requires that ordinary matter not decompose.
This is not normal. Decay is common. Ask any homeowner: Just minutes after taking possession of your home, it may seem like you’re stuck in an endless cycle of fixing things that break. Even radioactive materials eventually decay. So, what keeps the universe’s matter stable on cosmic time scales? Scientists don’t know the answer to that, and they are I built Highly sensitive detectors to look for proton decay. So far, no proton decay has been observed, which certainly seems to go against the natural order of things.
To understand why protons are stable, we need to understand the material they are made of. Basic chemistry will tell you that matter is made of atoms, but the atoms themselves are made of smaller components: protons, neutrons, and electrons. As it turns out, protons and neutrons are made of smaller objects, called quarks. (We’ll get to quarks later.)
On the scale of atomic and nuclear matter, what is important is that protons, neutrons and electrons are stable. This applies exactly to protons and electrons, but not to neutrons. Although neutrons buried within the nucleus of atoms can live forever, this is not true for isolated neutrons. If you could extract a neutron from the center of an atom and put it in an empty bottle, the neutron would decay in less than fifteen minutes, which is much shorter than the universe’s 14 billion years.
Conservation laws
What saves protons and electrons from decay is a combination of so-called “conservation laws.” The term “conservation law” simply means that there is a property that does not change no matter what happens.
We can use regular Lego pieces to explain what this term means. Let’s say your child has a collection of 10,000 Lego pieces. As any parent knows, kids can make endless things out of Lego: a building, a bridge, or a duck figurine for a kid with enough artistic talent. The child can use some or all of the pieces in his artwork; However, no matter what the kid creates, what remains the same is that he still has 10,000 Lego pieces. The number of pieces is maintained.
For particles such as protons, neutrons, and electrons, several conserved properties determine whether the particles are stable or not. These are energy, electric charge, baryon numbers and the more mysterious leptons.
Energy is a measure of motion, such as a thrown ball, or effort, such as a coiled spring. However, due to Einstein’s most famous equation E = mc2which is also a measure of mass. In fact, for an isolated, stationary particle, the particle’s mass is its entire energy. In the context of particle decay, conservation of energy means that a subatomic particle can decay into a lighter particle, but not the other way around. If a heavy particle turns into a light particle, the amount of energy stored in the mass becomes less; However, the remaining energy can cause the daughter particle to move. Under this scenario, the total amount of energy does not change after decay. In contrast, if a lighter particle decays into a heavier particle, there will be more mass – and thus more energy – after the decay than before. This would change the amount of energy, which would violate the principle of conservation of energy.
Electric charge is another conserved quantity. A proton has an electrical charge of +1. If a proton decays, the sum of the electric charges of all the decay products must also add up to +1. The electron, which has a mass of about 0.05% of the mass of a proton, has a charge of -1. The positron, the antimatter cousin of the electron (and the same mass), has a charge of +1.
Thus, on the basis of conservation of energy and charge, a proton (heavy, charge +1) can decay into a positron (very light, charge +1) and a photon (very light, charge 0); However, this decay is not seen. The reason centers on the last relevant conserved quantities: the lepton number and the baryon number. Particles such as the proton and neutron are baryons. It is heavy and contains three quarks. Particles like the electron are leptons. They are light and do not contain quarks.
All baryons have baryon number B = +1, while all leptons have lepton number L = +1. Antimatter versions of particles have the opposite lepton or baryon number. Some particles that are neither leptons nor baryons have zero leptons and baryons.
This explains how a neutron (charge 0, mass 939.6 MeV, baryon number +1, lepton number 0) can decay into a proton (charge +1, mass 938.3 MeV, baryon number +1, lepton number 0), an electron (charge -1, mass 0.511 MeV, baryon number 0, lepton number +1), and a particle called a neutrino. Antimatter electron (charge). 0, mass 0 MeV, baryon number 0, lepton number -1). If you check each saved quantity, you will find that everything is working fine.
As for the proton, it is simply the lightest baryon known. Because of the conservation of energy, in order for it to decay into a lighter particle, a lighter baryon must be present. Since there are none, the proton is stable. For the electron, there are leptons lighter than the electron (neutrinos), but there are no lighter charged particles. The absence of any combination of particles that will simultaneously obey all the laws of conservation is an obstacle to electron decay.
Are protons eternal?
Does this mean that protons and electrons are eternal? Will they last forever? This is an empirical question, not a theoretical one. It is certainly possible to imagine some theory governing matter that violates conservation laws and allows protons to decay; However, scientists have built large detectors, weighing tens of thousands of tons, to look for proton decay, and none have been observed. These experiments determine the minimum lifetime of protons, which is about 2 x 1034 Years, or about a trillion trillion times longer than the age of the universe. If protons decay, they exist for a very, very long time.
However, scientists continue to search for proton decay in experiments designed for other purposes. If proton decay were observed, it would tell us something new and important about the laws of nature. the Deep underground neutrino experiment (DUNE) is a large experiment being built to study the behavior of a subatomic particle called… Neutrino. While its primary purpose is neutrino studies, scientists will also exploit the detector to look for proton decay. Sand dunes It is currently being built and is expected to begin operations at the end of the decade.
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