Dear Ahmad,

Have you ever been surprised when the total mass decreases in a beta decay (more precisely, the decay of neutron)? The same thing works here! I think, you are comfortable with partial conversion, not total conversion!

But both are the same. Look, STR does not say 'how' mass is converted into energy; it just says don't be surprised if it happens!

When Dirac formulated Relativistic QM the idea of antiparticle came into play. To explain this, Dirac assumed an invisible sea of -ve energy electrons and when an electron is excited from the sea,it leaves a hole behind which appears as the 'positron'. Since there is always some perturbation in nature, a hole in the sea cannot sustain too long; the perturbation will make the electron to fill up the hole. When it does so, it leaves the energy behind.

This was the old idea, it may have explained some things but it had some problems. One of them was, we started with one electron and after solving Dirac eqn we arrive at infinite no. of electrons! How these electrons are 'created'?

The answer was finally provided by Quantum Field Theory (QFT) which gives us a mathematical way of creating and annihilating particles. It gives answers in terms of coupling: whether a process will happen or not depend on whether the particles in the process have the right couplings or not. And, till now, it has been quite sucessful in describing nature . For example, it says that electron and positron can annihilate, but electron and antimuon cannot.

One last comment, "Charge" does not always refer to the 'electric' charge, there are other kind of charges!

Best Regards,

Dipankar

Dear Dipankar,

Thanks for the reply. But you left me wondering, what are those different kind of charges? Can you please elaborate on that a bit.

And you were right regarding that partial conversion thing, I found it a bit surprising that the whole of the mass can get converted to pure energy.

Other charges includes, leptonic charge, baryonic charge etc. For ex. electron has a leptonic charge (electron) = +1 but positron has leptonic charge -1.

Thank you... :)

Few people recognize that mass is only a name for a form of potential energy. Electron positron pairs are formed from charge-less photons by an E-field assisted separation of the photon fields. The charge (DC E-field) of the pair, when separated, becomes the Coulomb potential energy and is measured by the combined mass. When they recombine, the DC charge is converted back to AC-fields (photons) during the acceleration of the pair in the Coulomb field that grows as they come together and approach the speed of light. Mass disappears as the Coulomb potential energy (and DC-field, charge) is used up. Remember that potential energy is relative; the Coulomb energy in (from r = 0 to infinity) actually goes from 0 to 2mc^2, not minus infinity to 0.

Unbalanced-mass charges can't resonate the same way to make the conversion.

A. Meulenberg, Universiti Science Malaysia

Hmmm, I doubt it ,but worth thinking about.

The uncertainty principle is used to explain why the electron in a hydrogen atom does not plunge into the proton. Should it not work the same way with a positron and electron?

The uncertainty principle is MISUSED to explain why the electron in a hydrogen atom does not plunge into the proton. I'm at IISc for the next couple of weeks (in the old physics bldg), if you all wish to get together to discuss it in detail ([email protected])

It is not true that the only difference between matter and antimatter is an opposite charge. Example: what about the neutron and antineutron?

Ramiz,

Anti-particles also have negative spin, isospin, and so on. It isn't just their charge which is reversed. 

>I mean how can the electromagnetic attraction make two particles lose all its mass and convert into energy?

It is *not* simply a matter of electromagnetic attraction causing the annihilation - this is a qualitatively different thing. And if you can explain it, there's a Nobel in the wings.

This is essentially because at the vertex of elementary particle interaction the total energy-momentum (4-vector) of incoming states is equal to that of outgoing states. Mass and energy are not conserved separately. In a classical interaction that would have been true. For example when two billiard balls collide in a classical collision process, to total incoming mass will be same as the total outgoing mass, and total momenta along X and Y axes will also be conserved.