Consider a high energy photon travelling through space. A photon cannot spontaneously change into mass because of the conservation of momentum. The momentum part of the photon is assimilated into the nearest mass object, a nucleus for example. It cannot be imparted as momentum into the newly created electron/positron pair because there is not enough energy (I will cover the maths of this in another post).
In a previous post I tried to explain an odd relationship involving Kepler's 3rd law of planetary motion. This came about from looking at the photon/mass interaction. One thing that came out of this post was Newton's law may actually extend all the way down to Planck lengths.
(I appreciate that there is currently experiments under way to test Newtons equation of gravity. For now though I am going to proceed with the idea that it is still intact. It being subject to modification when we get into the large gravity arena when general relativity takes over.)
A photon needs something to hit in order to dissipate its momentum. Now you may be thinking the following;
Surely, if you fire to high energy lasers at each other then you could get two photons travelling in opposite directions to interact. This would then cancel the momentum while allowing mass to be created? Just like to billiard balls travelling in opposite directions.
I am afraid not, in classical electrodynamics theory it is known that waves pass each other without interference. From Quantum Electro Dynamics (QED) it appears that photons cannot interact with each other because they do not carry charge.
NOTE: the previous paragraph will be explained in another post. The bit about QED is not strictly true, but will do for now.
I have highlighted a line there for two reasons. QED is the most accurate theory we have to date, so deserves some respect. Also it says that photons cannot interact because they do not carry charge. I take this to also mean that in order for mass to change to energy or vice versa according to
$E = m c^2$ ...(1)
we need charge. So while we always talk about the amount of energy we need to create mass, or the amount of energy that is liberated when mass is converted into energy, we actually need charge to be present? So, which is it? mass or charge or both? Of course, where there is charge there is mass.
In an earlier post I used a photon and mass to derive (1), this is very common. Imagine though, that this is just a consequence, what is really important is the amount of energy required to create charge, mass being a by product. Ages ago I did a post on conservation. Energy is conserved and so is charge and momentum, linear and angular.
What if the energy to create mass is actually the energy required to create charge?
why can't we have a neutral version of an electron much like a neutron? the nelectron! no that is not a typo. So a photon would just convert into a single nelectron, like so
$ \gamma \to e^0$
This never happens.
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Aside: When it comes to photons creating electron/positron pairs, we argue that two particles have to be produced in order to balance the charge. Consider the neutrino/proton interaction.
$\bar{v_e} + p^+ \to n^0 + e^+ $
$\bar{v_e} + p^+ \to [p^+ + e^-] + e^+ $
The electron then binds to the proton to create a neutron and the positron is liberated?
$p^+ + e^- + e^+ \to n^0 + e^+ $
All this happening under the hood?
I'll do some research and then I will be doing a later post on about this.
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In positronium, the electron and the positron recombine and annihilate each other, converting into two or more photons, note that they NEVER annihilate into a single photon. Once again this is because of the conservation of momentum. Do we need mass/charge available in order for this to occur in addition to that provided by the electron and the positron? In other words, if the electron and the positron were out in the vacuum of inter galactic space (which is about the best vacuum you are going to find) would they still recombine and annihilate. My current understanding is that yes they would.
Let's try running it backwards and see what happens (after all Feynman said that a positron is just an electron traveling backwards in time, more on this later). In this case we would see two photons come together, create an e/p pair that then recombine into a single photon.
Hold on a minute, there are two problems here. The first is that we have already stated that two photons cannot interact to form an e/p pair. Second at the end of the process e/p annihilation cannot create a single photon.
So this is not a symmetrical process. By looking at the results you would know if you were watching the film in reverse or not. I can't help thinking that there is something important here that I am missing.
One thought did occur to me while writing this post, is it the case that whenever there is a energy to mass conversion there are at least 2 charges created, one positive and one negative? For a mass to energy conversion we destroy one positive and one negative charge? I like the idea, but can it be true?
A photon with enough energy being converted to mass will do so in the presence of charge. Is it the charge that creates +/- charge pair, or the photon itself? If my understanding of QED, which is very little, is correct then a photon in the electromagnetic field causes an excitation in the electron/positron field creating the charge pair. (Need to learn more about this I think.) So the electron/positron field creates the charge pair after being excited by a photon from the electromagnetic field? In which case we would always expect +/- pairs to be produced.
Does this mean we also have a muon/antimuon field and a tau/antitau field. I'm not buying that I'm afraid, the universe is much to elegant for such profligacy.
When an electron/positron pair annihilate they are in the presence of their own charge. Is this the reason they can annihilate? When the e/p do annihilate they cause excitations in the electromagnetic field in the form of photons. You might be tempted to argue that the neutron and anti neutron both have no charge and happily annihilate each other. But this is not strictly true because they are made up of quarks and anti quarks that do have charge (supposedly).
So to finish this post. The conversion of energy into mass and vise versa is dependent on conditions and other events happening in addition to the requirement given by equation 1. I am convinced that the solution will be far simpler than we think. Will let you know if I get anywhere.
Wrote this while listening to this.
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