Federated Republic of Sean @freakazoid@retro.social

The (simplified) idea is that what we actually have is a bunch of massless particles that always move at the speed of light and get bounced around in proportion to how strongly they interact with the quantum vacuum. This is akin to photons' slowing down when they travel through glass. You can view them as having acquired rest mass or as getting constantly absorbed and reemitted.

Anyway, what I've been trying to get at is that maybe there are *only* null worldlines. That would mean that, to propagate slower than c, a particle would have to do a lot of backtracking. I'm not sure if this is really meaningful, if it's just restating something obvious, or if it's wrong in some way.

This is related, incidentally, to the idea that mass is an extrinsic property that arises due to interaction with the quantum vacuum.

I used the term null worldline earlier without explaining it. It's a path along which the spacetime interval is zero, i.e. the path a photon takes. Anything on such a path is moving at the speed of light. Spacetime interval is sqrt(dt^2-dx^2-dy^2-dz^2) using the same units for both, so multiply time by c or divide spatial distance by c.

Four-momentum and four-position are complementary variables, which means the product of their uncertainty (standard deviation) has a lower bound. This is supposedly just a consequence of the wave-like nature of quantum objects, but the wave function is also just a statement about statistics; it has no physical realization. So they're really just two ways of saying the same thing. https://en.m.wikipedia.org/wiki/Uncertainty_principle

Rest mass is not one of the elements of four-momentum, but can be computed from it with a formula similar to the formula for spacetime interval: sqrt(E^2-px^2-py^2-pz^2). I'm using c=1 here for simplicity.

You can get velocity from it as well, but I'll just link to the Wikipedia page for that explanation: https://en.m.wikipedia.org/wiki/Four-momentum

All four elements use the same units by dividing energy by an extra factor of c (or just setting c to 1), because the value of c is just a consequence of our choice of units for distance and time; there's no reason you can't use the same units for both, which makes c go away.

People generally think of this as particles occasionally "jumping" or tunneling around. But I think that the Heisenberg uncertainty principle is more fundamental than that, and you can't think of particles as behaving "normally" most of the time and jumping around some of the time.

Special relativity combines energy and momentum into a 4-dimensional vector called four-momentum.

Anyway, what I'm getting at is that maybe "motion" is not a concept we can really apply to the quantum world. There are quantities we call energy and momentum that are conserved, but things happen that should require more energy/momentum than a particle should have, as long as the time (for energy) and distance (for momentum) don't exceed a certain limit.

The physics we observe in the macroscopic world comes from the average behavior of numbers of particles that are so large that there is nothing in our experience we can draw on to think about it. Heck, we can barely grasp the size of the human population. The same is true of the scale differences.

A lot about the way we're taught about particle physics primes us to think about it as if it's mostly like macroscopic physics, right down to the word "particle". We're taught that "particles" sometimes act like particles and sometimes like waves. We are shown diagrams that have protons and neutrons in the nucleus depicted as spheres packed together, because even though we know this is not correct, we don't have a better model.

If you think it sounds like the apparent existence of gauge bosons could really just be a consequence of the interaction rules for different particles, you're right. It does sound like that. But that takes one down a very deep rabbit hole, because there's not really a dividing line between gauge bosons and "real" bosons. And Bose statistics apply to anything with integral spin, even if it's made of fermions.

You could say the massive gauge bosons don't actually have mass unless and until they exceed their range limit, which they can only do if they acquire enough energy to achieve their mass. For our purposes, they are massless and move at the speed of light but unlike photons have limited range.

You might think this model breaks down when you try to take into account gauge bosons that have rest mass, because things with rest mass can't move at the speed of light and therefore can't have null worldlines. But all gauge bosons really behave as if they're massless. Their measured mass comes from the Higgs mechanism.

Then Einstein took them and asked why we still needed an aether.

Anyway, in this model, the reason electrons repel one another is because they are directly exchanging momentum with one another. Their various properties determine how they can exchange momentum, through various symmetries and conservation laws. The exchanges looks like they're trading photons.

This wouldn't be the first time someone took an effect that was predicted due to one theory and flipped it around to say it made the original theory unnecessary. This is exactly what Einstein did with the Lorentz transformations. Lorentz came up with them to explain how it was that light should appear to move the same speed to every observer despite propagating through a a stationary Aether.

Now, the idea that the Unruh effect means that there's Unruh radiation is controversial. But Hawking radiation is not particularly controversial. It has also been speculated (though this is considered a fringe idea) that Unruh radiation might even explain inertia and gravity.

The Unruh temperature is the same as the Hawking temperature (in fact it's sometimes called the Hawking-Unruh temperature). The Unruh effect, incidentally, is the prediction that an accelerating observer will see black body radiation where a stationary observer sees none. An accelerating observer even sees an event horizon.

Energy is still conserved, as is CPT symmetry, so this looks like (and is the same as) an antiparticle coming out of nowhere and annihilating with the original particle, producing a shower of other particles.

This is also an explanation for "virtual particles". It also explains the Unruh effect, which incidentally is the same as Hawking radiation and was predicted independently at around the same time.

But the universe conspires to prevent us from using this fact to learn anything useful about the future (or the past for that matter) through this bidirectional propagation of information. This is in part because both the past and future directions have a source/sink of last resort. And particles can spontaneously change temporal direction.

Ok, continuing from my phone while the kids aren't doing too much property damage.

Redefining "local" as any point on the past or future light cone doesn't make fields disappear as a useful tool, it just makes it clearer that they are only tools and not real things.

It also has the implication that information can propagate in either direction in time, which I've addressed before: it does.