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Q & A: Lifetimes of neutrons and extra-galactic photons

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Most recent answer: 06/16/2015
I really don't get it,this book that i read is telling me that paticles lifetime isn't much and neutrons live too much(15minutes it says)if so ,every 15 minutes my atom should lose a neutron and that is not what i expect,in this condition,all atoms would be unstable and they would be decaying pretty much all the time.(i see how ridiculous my questions are but you gotta answer)and if photons die quickly how do i expect them to travel thousands of years to get to earth so i can see the far galaxies???
- ana (age 13)

Hi Ana,

Nice questions.   That number for the lifetime of the neutron, 15 minutes or so, is only for free neutrons.  Neutrons bound inside nuclei, like most of yours are, don't decay because conservation of energy won't allow them to.   There are a few odd-ball nuclei that will decay via positron emission, i.e.   C14 --> N14 + e- + anti-neutrino  but they are very rare and your body doesn't contain many of them .   See   for some more information.

As for your second question, photons don't decay.  They just keep on going forever unless they bump into something and scatter or get absorbed.  This allows astronomers to see objects at the far ends of the universe and the beginning of time.


(published on 06/16/2015)

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