Atoms. Best before XXXX

LuxFerum

Philosopher
L
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Dec 19, 2002
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I dont know if someone told me this our I read it somewhere, but here it is.

" Atoms dont last forever, It may take bilhons and bilhons of years, but they will colapse"

I know this is true for some atoms, like plutonio.
but what about the others? Are they perfectly stable and will last forever?
 
There has been some debate in the past as to whether or not the proton decays (I don't know if that has been resolved one way or the other) which, if it does, would mean that normal matter is unstable. Also, pretty much all element have radioactive isotopes with varying half-lives, but outside of proton decay I can't see how, say simple Hydrogen (one proton, one electron) would decay (what would it decay into?).
 
In think it was in one of my physics textbooks, where they mentioned electron decay and said that it took approximately 10^18 seconds.

This is about 2.31 times the current age of the universe so I doubt that it is an issue of any real consequence.
 
Crossbow said:
In think it was in one of my physics textbooks, where they mentioned electron decay and said that it took approximately 10^18 seconds.
Click to expand...

How did they get that number?
And what is the main reason of this "instability"?
 
Crossbow said:
In think it was in one of my physics textbooks, where they mentioned electron decay and said that it took approximately 10^18 seconds.

This is about 2.31 times the current age of the universe so I doubt that it is an issue of any real consequence.
Click to expand...
So the half-life is 10^18 seconds? That would imply that a significant portion of the electrons originally created during the early big bang expansion are already gone.

What are electrons supposed to decay into?
 
Nah, electrons can't decay. They are the lightest charged particle, there's nothing lighter for them to break up into (while conserving charge).

Protons might decay, but as far as I know, there's no good evidence for it yet. Limits on proton decay are that the half life must be greater than 10^33 years I think. Here's a link
 
Proton decay was a big theory in the 1980's and some detectors were built to look for it, for example Kamiokande (in Kamioka in Japan; the NDE stands for nucleon decay experiment) and SuperKamiokande. These are the giant underground tanks of water.

They didn't find any, and the experiments were "repurposed" to look for neutrino oscillations. Atmospheric neutrinos were the primary background in the detectors. NDE was retronymed to "neutrino detector experiment" at that point. Neither detector has any solid evidence for nucleon decay, which puts a pretty severe lower limit on the half-life of the proton (you can never rule it out completely, so you put lower/upper limits on effects).

Fortunately, neutrino oscillation did work out; SuperK was the first solid evidence, and SNO confirmed it.
 
Yay! Particle Physics!

Finally, a question that I'm qualified to answer! (The fact that some other posters already did won't deter me.) I did my senior thesis on various experimental constraints of grand unified theories, and this is what I remember:

Some of the simpler candidates for grand unified theories predicted proton decay with an upper limit on the proton lifetime of 10³² years. There was hope for a while of confirming these theories (like SU(5)) by observing a proton decay. The Kamiokande experiments did not detect any proton decay, and put the lower limit on the proton lifetime at 10³³ years, as Azathoth said. So some of the nicer GUTs (Grand Unified Theories) are ruled out.

It was a fun thesis. I presented my work at the end of the year, and the conclusion of my talk was, "So basically, all of these theories are ruled out by experiment."
 
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