# When does mass get converted into energy? [duplicate]

You know how energy is converted into mass in the sun, in particle accelerators and in nuclear bombs...Well mass gets converted into energy only in those situations (relativeley) and it doesn't happen in our day to day life...This makes it look like there needs to be a circumstance that the particles are in to get converted into energy...But in the situations that I've mentioned, the circumstances are different eg-

           particle accelerators- high speed

sun                  - high temprature


See what I mean? ... So my question is What is the general circumstance that a particle needs to be in, in order to get converted into energy?...Help will be valued...THANX

Well mass gets converted into energy only in those situations (relatively) and it doesn't happen in our day to day life.

Strange as this may seem your statement is incorrect.
In "our day to day life" what we do not notice is the very small changes in the mass of a system which is occurring all the time.

One important reaction in the Sun is the proton–proton chain reaction during which four protons are converted to a Helium-4 nucleus with the loss of $$0.7\%$$ of the mass of the original protons.
This mass has been converted into energy, in the form of gamma rays and neutrinos released during each of the individual reactions. The total energy yield of one whole chain is $$\approx 4\times 10^{-12} \,J$$.

A spring of mass $$100\,\rm g$$ which is stretched and stores $$1\,\rm J$$ of elastic potential energy increases in mass by approximately $$10^{-14}\,\rm g$$ which represents $$10^{-14}\%$$ of the mass of the spring, a change which cannot be measured.

So it is all down to a matter of scale. In nuclear Physics the changes in masses are significant when compared with the masses of the constituent particles whereas in "our day to day life" the changes in mass are insignificant compared with the system under consideration.

As to why all the mass cannot always be converted into energy that is how it is. For example there seems to be a law which dictates that the number of large particles (eg protons, neutrons etc which are collectively called baryons) has to stay constant. This means that a proton (baryon number =1) cannot spontaneously become energy. However a neutron (baryon number = 1) can dewcay into a proton (baryon number = 1) with the release of energy as the mass of a neutron is greater than the mass of a proton. However a proton (baryon number =1) together with an antiproton (baryon number =-1) can end up as energy. Note that you cannot create or destroy charge so an electron cannot just become all energy as the law of conservation of charge would be violated.

• Thanx for the answer but why does the energy of the spring get converted into energy...What was the circumstance that it had to be in, in order to get converted into energy and why did only a part of the energy get converted into mass? Why didn't the whole 1J get converted? Oct 8, 2020 at 12:38
• @alienare4422 I have added an extra paragraph to my answer to explain why it is that all mass cannot become energy. In the case of the spring the whole $1\,\rm J$ did get converted into mass. What could not happen is the whole spring becoming energy unless it net an equivalent spring made of antimatter. Oct 8, 2020 at 13:51
• good point but I still don't understand why it happens to only part of the total energy and not the whole thing...I know you said that thats how it is but thats my question. I value your trying though, thanx Oct 8, 2020 at 14:57

Interactions between particles which change a massive particle to massless ones tipically happen at high energies. Another possibility is the decay of a massive particle to a smaller-mass one. This happens for unstable particles, like heavy nuclei.

• yeah, but why does it happen at high energies? Oct 8, 2020 at 12:35

If by mass to energy conversion you mean particles with mass that interact to produce particles with no mass, then the first thing that comes into my mind is the particle - antiparticle annihilation. E.g. electron and positron can annihilate and produce two photons. Electrons and positrons are fermions (matter particles) and in the process of annihilation they decay into two massless bosons.