kurious said:
These are rules but it is not proven why they work.
When I said negative energy photons I wasn't referring to time.I really mean photons which if they strike a normal mass would cause it to move towards the direction they came from...[deleted text]...However I won't say more because this isn't theory development section!
I agree not to make this into a debate...I don't want to stray too far from the original question, but since there were disagreeing responses, I'll just state what the standard understanding is for the record, and leave it for others to decide (or ignore) for themselves. First, I'll get to the punchline: there is no observation of negative mass-energy states, and to date, no reason for them to exist (there is a technical reason why "negative mass-energy states" can be in a theory at the level of the Lagrangian, but all propagating degrees of freedom [i.e., the observed ones] have positive energy about the stable vacuum state, so these particles won't be mediating any interactions, etc.).
In quantum field theory (which quantum electrodynamics is formulated in...an extremely well-tested theory), if you want conservation of a type of quantum number (e.g. electric charge), then it is a theorem that there must exist partner particles for every type of particle. These partners are called "antiparticles" since they have opposite quantum numbers relative to their partners. The photon is an example of a particle which is its own anti-particle partner. Both particles manifestly have positive energy in this framework. So where did this "negative energy" business originate?
Before people were doing proper quantization of fields, they noticed that when attempting to describe a relativistic electron (using a relativistic "Schrodinger equation" modified for a spin 1/2 particle), there were apparently states of the electron that had negative mass-energies, and that in quantum mechanics there is consequently a non-zero probability of tunneling from a positive energy spectrum of states to a negative energy spectrum of states. Thus there would be an instability in the energy of an electron: it would keep getting more and more negative energy with no stable state. Dirac attempted to solve the problem by saying that there are electrons filling the "negative energy sea", and since they are identical particles as well as fermions, the positive energy states are bounded below (i.e., the Pauli exclusion principle is in action). In other words, the mass-energy of an observed electron is the "Fermi energy" of the system. Later, it was suggested that instead the problem would be fixed by saying that there must be a particle that has positive energy but opposite quantum numbers to the electron (and the same mass); there are no negative energy particles to propose. This particle was discovered (the positron).
Thus, the negative energy interpretation and the later anti-particle prediction were ad-hoc band-aids that signaled a new theory (like the ad-hoc assumptions of the Bohr model to fix the problems there is a hind-sighted signal that there is a new theory underlying the description of the electron bound to the nucleus: quantum mechanics). This new theory was the quantum theory of *fields*, from which anti-particles are a necessary consequence if you want to have certain conserved quantum numbers...something that observation tells us we should have. This is the framework from which I was working in my repsonse to the original question. Using this framework, we *do* see how particles can attract (and repel) each other via mediators. In fact, you can construct a measurable (macroscopic) electrostatic potential with a basis of positive energy photons as we should be able to do if we are to make contact with the macroscopic world...this potential is the one coming from the classical Maxwell equations.
With regard to the rules I mentioned in the previous post are rules from quantum mechanics. Not knowing why the rules work is equivalent to saying that we don't know why quantum mechanics works...true, but it is well tested, so this is not really an issue. There isn't an alternative theory that works in which we *do* know why nature works that way. And quantum fields are what you get when you marry special relativity with quantum mechanics. Again, we don't know *why* quantum field theory should describe nature, but its predictions are well tested, so as far as we have seen it *does* describe nature.
Cheers.
