If you watch “Mock the Week” you will be familiar with the format. In this case the discussion is about whether the question is “What is 2+3?” or “What is 4+1?” This discussion has been going on for at least a hundred years, with no resolution in sight. String theorists swear by 2+3. Woit says that is “not even wrong” and claims it is obviously 4+1. Normally in a conflict between Woit and string theory I find myself on the side of Woit. But not in this case. I am now convinced that in this instance Woit is not even wrong, and “not even wrong” is right.
You see, the main question about particle physics is “Why 2+3?”, or in technical terms, why is the gauge group of the nuclear forces SU(2) x SU(3)? There is a related question about the charge on the up quark: “Why 2/3?” There is no mention of 4+1 anywhere in particle physics. But it was only once I started to consider the question “How 2/3?” that I started to make progress in understanding what is really going on behind the scenes.
That is because I found the answer in the equation tan(2W) = 3/2, where W is the “weak mixing angle”, which is without a doubt the most important angle in the whole of particle physics. So after that I could turn my attention to the questions “Why 2/3?” and “Why 2+3?”. Or, to be more precise, to the question “What is 2+3”?
And I found that the answer is 5 Maxwell equations. The 3 Maxwell equations in here are the ones that relate the magnetic field to the current. These are the most important equations in the whole of pre-nuclear energy. They are the most important equations in the whole of pre-quantum technology. They are still the most important equations today, because you can’t run a wind farm or an electric car without these three equations.
If we write the equations in “natural” units, so that the vacuum permeability and the vacuum permittivity are both 1, then the speed of light is also 1, and the equations are written in vector form as curl(B) = J+dE/dt, where B is the magnetic field, J is the current, and E is the electric field. The rest of the equation is the mathematics that describes how the magnetic field varies in space (curl), and how the electric field varies in time (d/dt).
There is another companion equation that describes how the electric field varies in space, that is div(E)=Q, where Q is the electric charge (or technically the charge density). That gives you 1+3 Maxwell equations. Normally you would add another 1+3 equations div(B)=0 and curl(E)+dB/dt=0, but these are equivalent to Lorentz symmetry of the electromagnetic field, so if we assume the symmetry, then we don’t need the equations.
But we do need one more equation, that is conservation of charge. Electric charge cannot be created or destroyed, it can only move around, or cancel out. The equation that enforces this physical property is div(J)=-dQ/dt. Or is it dQ/dt=-div(J)? We know what the answer is, but what is the question? It shouldn’t matter, really, should it? Multiplying the equation through by -1, doesn’t change the equation, does it? Well, yes, actually it does. It doesn’t change the answer, but it does change the question. And therefore it is important. It is the same as the difference between the questions 4+1 and 2+3.
We know that the ultimate question of particle physics, the universe and everything is 2+3, so this is the question we must ask. And it tells us to write the equations in 5×5 matrix form with the differential operator (1, d/dt, del) acting on the columns (0, Q, J), (-Q, 0, E) and (J, E, -B) to produce the answer (0, 0, 0). That means that in the matrix form, Q and B are antisymmetric, while J and E are symmetric.
Now when I was taught Maxwell’s equations, back in the dark ages (1970s), I was taught that E is antisymmetric, not symmetric. This is wrong because if E is antisymmetric, then spacetime is Euclidean, not Lorentzian. Of course, I didn’t know that at the time, but I do now. The difference between 4+1 and 2+3 has nothing to do with this, it is the difference between Q being symmetric (and therefore J antisymmetric) or antisymmetric (and J symmetric). And the fact that charge can be quantised, but current cannot, implies that Q is mathematically a circle, not a straight line, which means it is antisymmetric, not symmetric.
So there we have it. The ultimate question is “What is 2+3?” The reason why Einstein failed to answer this question is because he thought the question was 4+1. So what I want to do now is explain what Einstein would have done in 1915 if he had realised the question was 2+3. To be fair to Einstein, there was no real reason to think the question was 2+3 until much later, when quantum theory was sufficiently developed to make it clear that the gauge group of a quantised entity had to be compact. It could in principle have been deduced from the Dirac model of the electron in 1928, but it wasn’t really until the 1950s that there was enough evidence to reconsider the question, by which time it was too late, as 4+1 had been set in stone.
As you know, the biggest obstacle to answering any question is asking the wrong question. And if you are fixated on answering 4+1, when the correct question is 2+3, you will just go round and round in circles, bashing your head against a brick wall, if that’s not a mixed metaphor. Once you know the question is 2+3, and the answer is 5 Maxwell equations, then it isn’t hard to imagine that to include momentum and energy as well as current and charge, you just have to extend the equations from real numbers to complex numbers, so that the imaginary part gives you five Einstein equations for gravity.
These equations are rather different from the Maxwell equations, because the symmetric/antisymmetric dichotomy is reversed by the extension to Hermitian/anti-Hermitian matrices. In particular we get some anti-Hermitian diagonal matrices, which make things more complicated, since there are no anti-symmetric diagonal matrices in the Maxwell case. The first equation to consider is conservation of energy, which is div(p) + d(p0)/dt = m, where p is the momentum, p0 in the energy (I can’t use E again, because that will cause confusion), and m is a type of mass. If this equation doesn’t make sense to you, then don’t try to think of m as being something you already know, think of this equation as being a definition of m, whose properties we then have to work out as we go along. It’s a Lorentz scalar, so mass is the obvious interpretation.
The second equation is div(g) = p0 + d(m0)/dt, where g is the Newtonian gravitational field. In Einstein’s language, E=mc^2, so that p0 replaces the Newtonian mass as the source term for gravity. But what on earth is this extra term d(m0)/dt doing here? It is an extra source of gravity that actually does exist in Einstein’s theory, although it is not easy to interpret it physically. It is not just a mass term, but a change-of-mass term. In standard gravitational theory, mass cannot change except by moving. But this is not true in reality, because mass is not conserved in the weak interaction. So the d(m0)/dt term cannot be ignored, and creates a genuine mixing between the weak force and gravity.
The importance of this remark cannot be overstated. I’ll pause a while to let it sink in.
The two diagonal terms m and m0 are two different types of mass, one of which is constant, while the other changes over time. Newtonian gravity assumes they are equal, which is of course logically impossible. Einsteinian gravity does not assume they are equal, but still assumes that there is only one type of mass, which is still logically impossible. Einsteinian gravity and the weak force are incompatible.
But if (as is obvious) we do not understand what type of “mass” m0 is, we can take the equation as a definition of m0 in terms of the gravitational field. That is, m0 is the time-integral of div(g)-p0, so it can be calculated from the gravitational field and the energy. That means it is a Machian type of inertia. But m is a Newtonian type of mass.
Now listen carefully – m0 is only defined up to a constant of integration. So you can choose your constant of integration to ensure that m=m0 and there is only one type of mass. However, m is constant (by definition) and m0 is not (also by definition), so over time m0 will drift away from m, and they won’t be equal any more. By reading the literature carefully I have worked out that the calibration m=m0 was carried out in the period between 1971 and 1973, and I have worked out how far m0 has drifted away from m in the past half-century or so.
And I also know why nobody has noticed this drift. It is because it only affects gravitational measurements, and does not affect the standard model of particle physics in any way. The Dirac equation edits out the gravitational field, and shunts this variability (which is physically real) off into some variables that cannot even in principle be measured. So it is logically impossible to detect this drift in particle physics experiments. It can only be detected in gravitational experiments.
And once you know this drift is physically real, you can detect it in the measurements if you look closely enough. You can detect it in Cavendish-type measurements of the Newtonian gravitational constant G. You can detect it in inconsistent measurements of the gravitational mass of copies of the International Prototype Kilogram. You can detect it in pre-1969 experiments to measure the electron/proton mass ratio, before the ruthless dictatorship of the Dirac equation came into force, and suppressed all opposition from the Machian gravitational party.
And just because I live in Birmingham I can’t resist mentioning the Lunar Society, which was a major force in the advancement of science, technology and philosophy in the second half of the 18th century. They regulated their activities by the phase of the moon, because it was only safe to walk around Birmingham at night if the moon was full. But they made progress in many endeavours by communicating across boundaries, sharing ideas, and thinking outside the box. They were not crackpots or lunatics, they were lunar luminaries.
Progress in science today also depends on communicating across boundaries, sharing ideas and thinking outside the box. Preferably by the light of the moon. And it was the light of the moon that shone on a very faint trace of a 19-year oscillation in the m0/m relationship. And it shone a gravitational light on the neutral kaon (weak) eigenstates. And it shone clearly on the charged/neutral kaon mass ratio. And on the charged/neutral pion mass ratio. By the light of the moon, walking fearlessly across boundaries and thinking outside the box, I have seen things you wouldn’t believe. I know, you don’t believe them. You think I am crackpot or a lunatic. But I am not. I am a lunar luminary.