Do Electrons and Positrons Have a Finite Lifetime?

[iced199]

I am pretty sure they don't, but Wikipedia says that their lifetime is about 10^26 years. Then it says they are stable because they are the lightest particle to have an electric charge. I am confused now. It can't decay because if it did, it would violate charge conservation, since two lighter particles - photons and neutrinos, are both neutral.

 

[someGorilla]

It says "at least" 10^26 years, not "about" 10^26 years. "At least" is consistent with not decaying at all.

 

[Morgoth]

There ain't a thing such as "infinity" in experimental data.
These data are taken by running models at the PC, and as everyone knows the CPUs do not recognize infinity, but rather very large numbers. Those years are practically "infinite", and so the process is unobservable, because 10^26 years is some times the magnitude of the Universe's lifetime. The stability of the electron is saved!

 

[rwooduk]

so in 10^26 years what would an electron decay into? i understand that 10^26 might as well be infinity, BUT why then list the lifetime?

please could someone clarify a little further?

thanks.

 

[phinds]

Hm ... this is interesting. Since an electron is an elementary particle, I don't see how it could decay. If an electron can decay, does that mean a quark can decay? As you ask, what would it decay into?

It all seems unlikely, but I'm no expert.

 

[jtbell]

i understand that 10^26 might as well be infinity, BUT why then list the lifetime?

It's NOT an actual lifetime! It indicates the "state of the art" of our experimental techniques in attempting to determine whether the electron really does decay after all. If we continue to improve those techniques, without actually finding electron decay, that number will become larger.

It may be listed in a table of lifetimes, but that's just a convention. It saves us from having to put together a separate table for lower limits. Any time you see something like "> 10²⁶ years" in a table of lifetimes, with a ">" sign, it's intended to be interpreted as described above.

what would it decay into?

That's an interesting question. Either there would have to be a (negatively) charged particle with less mass than the electron, or charge conservation would have to be violated. The latter would obviously be verrrrry interesting because it would represent physics beyond the Standard Model. Here's a paper about a search for a charge-conservation-violating decay:

Search for electron decay mode $e \rightarrow \gamma + \nu$ with prototype of Borexino detector (Physics Letters B)

 

[rwooduk]

thats great, many thanks!

 

[dauto]

That's an interesting question. Either there would have to be a (negatively) charged particle with less mass than the electron, or charge conservation would have to be violated. The latter would obviously be verrrrry interesting because it would represent physics beyond the Standard Model.

A charged particle lighter than the electron is not possible. If it existed it would be easily produced by pair production and would already have been observed.

 

[willem2]

I am pretty sure they don't, but Wikipedia says that their lifetime is about 10^26 years.

Where does it say that?

Since electrons are the lightest negatively charged particle, there isn't anything for them to decay into. Protons decay, and the result is gammay rays and a positron, which will combine with and eliminate an electron.

 

[Drakkith]

Hm ... this is interesting. Since an electron is an elementary particle, I don't see how it could decay. If an electron can decay, does that mean a quark can decay? As you ask, what would it decay into?

It all seems unlikely, but I'm no expert.

Muons are elementary particles, yet they decay very quickly.

 

[phinds]

Muons are elementary particles, yet they decay very quickly.

Damn ... I KNEW that and just didn't connect the dots with this thread. Thanks.

Interesting that an elementary particle (no internal structure) can decay into OTHER elementary particles (an electron and 2 neutrinos). Who would'a thunk it ?

 

[rwooduk]

Where does it say that?

http://en.wikipedia.org/wiki/Particle_decay

so in an attempt to wrap this up, in theory they could decay but their lifetime is such that we will never see it and if they do decay we are unaware of the particle that they would decay into, except to say that it would be negatively charged with less mass than the electron.

 

[ChrisVer]

In the current theory, I don't think they can decay...
Their decay will ask for new physics, such that they would eg violate charge ...

 

[rwooduk]

thinking outside the box, and i may sound like a complete idiot here, but if electrons have an intrinsic energy and they are able to hold their energy for eternity then wouldn't that be equivalent to perpetual motion? so in that respect they must decay?

 

[ChrisVer]

thinking outside the box, and i may sound like a complete idiot here, but if electrons have an intrinsic energy and they are able to hold their energy for eternity then wouldn't that be equivalent to perpetual motion? so in that respect they must decay?

they can still interact/annihilate

 

[phinds]

thinking outside the box, and i may sound like a complete idiot here, but if electrons have an intrinsic energy and they are able to hold their energy for eternity then wouldn't that be equivalent to perpetual motion? so in that respect they must decay?

The continuing existence of the electron doesn't violate any laws. You are perhaps thinking of a perpetual motion MACHINE, which is something that is impossible because it does work in a closed system forever with no application of external energy. The electron isn't doing any work just by virtue of existing.

 

[dauto]

http://en.wikipedia.org/wiki/Particle_decay

so in an attempt to wrap this up, in theory they could decay but their lifetime is such that we will never see it and if they do decay we are unaware of the particle that they would decay into, except to say that it would be negatively charged with less mass than the electron.

No. The electron most likely doesn't decay at all. But if it does decay than it decays into neutral particles and charge isn't conserved. Our expectation that charge must be conserved is the reason it most like doesn't decay. A negatively charged particle lighter than the electron is impossible period. Charge non-conservation is extremely unlikely, probably impossible, but we cannot say it for sure.

 

[rwooduk]

The continuing existence of the electron doesn't violate any laws. You are perhaps thinking of a perpetual motion MACHINE, which is something that is impossible because it does work in a closed system forever with no application of external energy. The electron isn't doing any work just by virtue of existing.

interesting. i was thinking along the lines of if an electron has inherent energy then it must continue to lose that energy. but as you say if no work is done then it could simply 'hold' its energy. still kind of amazing to think that something can exist forever, but I am now taking a tangent that doesn't help with my physics degree at all lol

thanks for all the help!

 

[ChrisVer]

The proton lives forever too (up to now unfortunately), and it's not even elementary...

 

[mfb]

Protons decay, and the result is gammay rays and a positron, which will combine with and eliminate an electron.

It is unclear if protons decay. So far, no decays were observed. Decays would violate baryon number conservation.
Some models predict a very large, but finite lifetime, and the observed baryon asymmetry in the universe is a strong hint that baryon number can be violated, but currently we don't know.

Interesting that an elementary particle (no internal structure) can decay into OTHER elementary particles (an electron and 2 neutrinos). Who would'a thunk it ?

All elementary processes are like this - particles transform into and/or absorb/emit other particles.