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December 12, 2015 at 6:56 pm #45426StevenModerator
In atoms, they spend all their time around the nucleus doing the orbit and never seem to get tired. So I guess so. And they get front-row seats to the demise of the universe . . . S
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Electron “Lifespan” is at Least 5 Quintillion Times the Age of the Universe
George Dvorsky
12/11/15 5:30pmElectron “Lifespan” is at Least 5 Quintillion Times the Age of the Universe
Basic physics suggests that electrons are essentially immortal. A fascinating experiment recently failed to overthrow this fundamental assumption. But the effort has produced a revised minimum lifespan for electrons: 60,000 yottayears, which is get this about five-quintillion times the current age of the Universe.
Thats a Yotta Years
An electron is the lightest subatomic particle that carries a negative electric charge. It has no known components, which is why its considered to be a basic building block of the universe, or an elementary particle.
An international research team working on the Borexino experiment in Italy were looking for signs of electrons decaying into lighter particles, but as expected, they came up short. This is actually a good thing because it affirms what physicists have suspected for a long time. Had they found evidence that electrons decay into photons and neutrinos even lower-mass elementary particles it would violate the conservation of electrical charge. Such a discovery would suggest an entirely new physics beyond the Standard Model.
But the research team did manage to come up with the most accurate measurement yet of the lifetime of electrons. Their calculations suggest that a particle present today will still be around in 66,000 yottayears (6.6 × 1028 years), which, as Physics World puts it, is about five-quintillion times the current age of the universe. The details of this work now appears at the science journal Physical Review Letters.
An article in APS Physics explains how the scientists came up with such an extreme figure:
Borexino consists of a shell of petroleum-based liquid that lights up when a neutrino, a nearly massless neutral particle, knocks an electron loose from one of the liquids atoms. The detectors roughly 2000 photomultipliers then amplify and sense the emitted light. [The] researchers calculated the sensitivity of the detector to photons produced via hypothetical electron decays into a photon and a neutrino…They then looked for photon events above this background with energies near 256 kilo-electron-volts, an energy corresponding to half the electron rest mass.
After looking at 408 days worth of data, they found….nothing. But they did manage to determine a mean electron lifetime.
A New Lower Bound
Now, this doesnt imply that electrons will live that long. First, the Universe probably wont exist by then. And even if its still around say after a Big Rip scenario the fundamental properties of particles like electrons will likely be entirely different.
Second, and more to the point, the new measurements move up the previously estimated lower bound on electron longevity. The new figure is 100 times greater than the previous lower limit, which was determined in a similar experiment back in 1998. Put another way, if such a reaction occurs, it must happen less than once every 6.6 × 1028 years.
No Signs of Decay
The reason for the hideously long lifespan has to do with the fact that scientists cannot be completely certain that electrons are immune to decay. The observations made by the Borexino researchers or rather the lack of observations suggests that, because we havent seen electrons decay by now, their lifespans must be at least as large as the new calculations suggest.
Sean Carroll, a research professor in the Department of Physics at the California Institute of Technology, explained it to Gizmodo in an email:
Decay is very natural in particle physics; heavier particles tend to decay into lighter ones. A neutron left all by itself, for example, will decay into a proton, an electron, and an anti-neutrino in just a few minutes. Its just the elementary-particle version of the decay of a radioactive nucleus like uranium.
But there are some things that seem to never happen, which we describe by conservation laws. For example, the total electric charge doesnt change. Also the baryon number (total number of protons plus neutrons, minus the number of anti-protons plus anti-neutrons), and the lepton number (electrons plus neutrinos, minus their antiparticles). Notice this is satisfied by the neutron decay. Before decay we have one neutron, which is charge = 0, baryon number = 1, and lepton number = 0. Afterwards it is also charge = 0 (proton = +1, electron = -1, anti-neutrino = 0), baryon number = 1 (proton = 1, electron and anti-neutrino = 0), and lepton number = 0 (proton = 0, electron = 1, anti-neutrino = -1).
Baryon and lepton number have never been seen to change in any experiment doing so would be Nobel-Prize-worthy but on theoretical grounds we think they possibly could change, and probably did in the early universe. (That would help explain why there is more matter than antimatter in the current universe.)
But nobody expects charge to change, which is a more robustly conserved quantity.
It would be one of the most surprising things ever if electric charge was not conserved, said Carroll. Thats why everyone thinks electrons dont decay.
Carroll said the only particles that are lighter than electrons are electrically neutral: neutrinos, photons, gluons, gravitons. If there were other light charged particles, we should have detected them by now. This suggests theres nothing for the electron to decay into.
But we should still look! Its a lottery ticket very unlikely that you will find anything, but if you do, you get rich, said Carroll. Sadly, they didnt find anything, but null results are an important part of good science.
December 13, 2015 at 12:41 am #45427ubiquitin442ParticipantDecember 13, 2015 at 9:17 pm #45429c_howdyParticipantI received a telephone call one day at the graduate college at Princeton from Professor Wheeler, in which he said, “Feynman, I know why all electrons have the same charge and the same mass” “Why?” “Because, they are all the same electron!”
-RICHARD PHILLIPS FEYNMANThe one-electron universe postulate, proposed by John Wheeler in a telephone call to Richard Feynman in the spring of 1940, states that all electrons and positrons are actually manifestations of a single entity moving backwards and forwards in time.
-https://en.wikipedia.org/wiki/One-electron_universe -
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