Did I say Particle Physics? I shouldn't have said that. I don't know much about it. But still, what I came upto recently was this :- I read somewhere that unstable nuclides can disintegrate in several ways, beta decay and positron decay being two of them. In beta decay, a neutron gets converted into a proton and an electron and in positron decay, a proton gets converted to a neutron and a positron. Now, also, an electron and a positron annihilate each other giving lots of energy. So... If I carry a beta decay with a neutron, I will have a proton and an electron. Then if I carry a positron decay with this proton, I will get my original neutron back, plus a positron. So basically, the situation amounts to getting a pair of an electron and a positron from nothing. Now if I make them react, I will get energy for free!! Isn't it a perpetual motion machine then? If not, what's the flaw?