[logfromblammo]

I have a hypothesis, unsupported of course, that everything has a fixed spacetime velocity. As beings with mass, we perceive the universe as having three spatial dimensions and one temporal dimension. We move relatively slowly in the spatial dimensions, and we find it easy to change direction. As a result, we are hurtling incredibly fast in the temporal dimension.

A photon, on the other hand, moves incredibly fast in the spatial dimensions, and finds it difficult to change directions in them. From its perspective, the spatial dimensions might as well be one dimension, represented by its vector of movement in space. It moves relatively slowly in our temporal dimension, however. And that leads to the question.

What if we only perceive time as a single temporal dimension because we are moving so fast through time that we have so far been unable to perceive any other temporal dimensions or change temporal direction?

It may be that if a human were to accelerate close to the speed of light in the known spatial dimensions (thus decelerating in the temporal dimension) it would become possible to perceive additional temporal dimensions, and maybe alter one's course through time. Our current understanding of causality assumes that one's movement through time does not change direction.

If time does have additional dimensions, a massless particle could execute a u-turn in the temporal dimensions, and it would appear to us as though it turned itself into its antiparticle. If the u-turn was in any way imperfect, the particle probably could never intersect any point in spacetime that it has ever previously passed through and interact with itself in a way that could create a paradox. Or maybe all electrons and positrons really are the same particle, endlessly interacting with itself as it bounces around in spacetime, and all paradoxes become self correcting, since causality flows in multiple directions.

TL;DR: Our assumptions about causality may be wrong.

[jerf]

"We move relatively slowly in the spatial dimensions, and we find it easy to change direction. As a result, we are hurtling incredibly fast in the temporal dimension."

There exists an invariant such that you can look at anything and sum its spatial and temporal velocities in a certain manner to obtain c, but it's not a very useful observation because you end up with only two categories: Things moving at c, and things not moving at c. You don't have "slow" or "fast" things because that all depends on your frame of reference. For instance, from an object's frame of reference, it is always at rest.

(This is also why old sci-fi about a drive that can push you to FTL if you get "close" to the speed of light is gibberish. Your velocity is always zero relative to yourself. You can never get close to c because you can't even get closer to c. It is always and forever c beyond you.)

[logfromblammo]

That seems like a form of solipsism for intergalactic travelers. Wherever you go, there you are.

If you have a point of origin or a destination, you can define your speed relative to either of those points. And if you are at rest with respect to another object, you will both have the same velocity vector for (x,y,z,t) = (0,0,0,c) or maybe (0,0,0,-c). You both move at the same velocity through time, so you age at the same rate.

Now, if you throw that object away from you, in your frame of reference, you are at (0,0,0,c) and the object is satisfying something like sqrt(x^2+y^2+z^2-t^2)=c (real physics is more complicated, naturally). You age normally, and the object ages more slowly. From the object's frame of reference, it is aging normally, and you age more slowly, because you're the one moving fast.

Now as that spatial component approaches c, it becomes more and more difficult to hang a left at Betelgeuse. So you can usually treat all the dimensions that square to a positive number as the magnitude of their combined vector (let's call it s). The dimension that squares to a negative number, t, could be the magnitude of a vector in multiple dimensions that all square to a negative number (let's call them u, v, and w).

So a photon might prefer to see its spacetime vector as (s,u,v,w) = (c,0,0,0) or maybe (-c,0,0,0), provided that x^2+y^2+z^2=s^2 and u^2+v^2+w^2=t^2 (or similar equivalent constraints that change the signs around). And whatever happens that might appear to us as though the photon is traveling at less than c is actually the photon stepping sideways through temporal dimensions orthogonal to our own hard-to-divert movements through time.

If you look at dual quaternions or geometric algebra, the math for systems with dimensional signatures (+,+,+,-) and (+,-,-,-) are often nearly identical, with a few sign flips here and there. And it would allow for odd things like imaginary mass and imaginary energy. We simply might not notice the additional temporal dimensions, for the same reason that it is difficult for us to change the direction of a massless, chargeless photon without touching it.

[ceejayoz]

If it's unsupported it's a hypothesis, not a theory. Conflating the two is what gives us the "but it's just a theory!" statement people try to make.