It is kind of circular - which suggests there is nothing unique about time. "The only evidence for time is change". Not "change (of particle position say) is one evidence of time passing". No - the ONLY evidence is change - the change in particle position for Barbour's simple examples. Therefore, do away with this extra baggage of time, and just look at particle positions. After all, we tell time (and motion) by the position of hands of a clock, the position or angle of stars, or the oscillation in position/momentum of atoms.
What no one has done is understand consciousness or reduce biology to physics much at all. The math behind the above is extremely well known and ironed out. That is why some physicists now put the challenge on biologists and psychologists. The personal or subjective flow of time we all experience is theorized to be recreatable from this (timeless) framework. After all, all you have access to is a single snapshot and memories. Sensorial data and brain states. Registering and firing of nerves and neurons. Momenta of particles...why not? Just particle momementa in a table in some kind of sequential form (e.g. worldines in 4D spacetime block universe).
I completely agree this may end up being an impossible challenge, or that it's later shown to be misguided. But there are accomplished philosophers and physicists behind it, or at least sympathetic to it.
> It is kind of circular - which suggests there is nothing unique about time. "The only evidence for time is change". Not "change (of particle position say) is one evidence of time passing". No - the ONLY evidence is change - the change in particle position for Barbour's simple examples. Therefore, do away with this extra baggage of time, and just look at particle positions.
Well, you've eliminated one step: you can't just look at particle positions, you need to measure change in particle positions in relation to X if you are to explain the world. Simply saying "static state 1", "static state 2" doesn't explain anything, unless you have some kind of relation between state 1 and state 2.
In the end, the very basic purpose of physics is to be able to tell, given state 1, what state 2 will be.
> In the end, the very basic purpose of physics is to be able to tell, given state 1, what state 2 will be.
Totally. But I would say your idea of predicting is still unnecessarily involving a "flow of time"; of things "becoming" or changing in themselves. Relations can hold without this notion of change or "becoming". A carpet with a regular pattern does not evolve in time, yet it has patterns. The patterns could be analogues to the laws of physics. The pattern tells you what can be in adjacent portions of the carpet, just like the laws of physics take input and tell you what will or can happen next. The carpet never changes though. You can imagine a separate observer tracing out a line in the pattern from one section to another and seeing it "change", but again the carpet never changed.
Fitting consciousness into this model is very hard I admit. There would be no outside observer tracing out lines in the carpet seeing them change. Instead, the flow of time (the feeling of us persisting from one moment to the next; not being entirely new objects at each instantaneous slice) would have to be a conscious illusion. But so is redness and warmth I could say. Maybe a brainstate is just your memories. And having a sequence of memories gives the illusion you existed prior to this instant. And this process* is done at every instant.
*Process as in timeless patterns on a carpet or timeless laws of physics. This process does not "take time", it's just action of particles behaving the laws of physics - in a timeless/carpet sense. Consiousness is given at every instant by the relation of particles, like the imagine on a movie screen is given at each instant from the photons of the projector. It's just that our screen "consciousness" feels persistent due to having memories.
If anyone wants a more cogent explanation read Tegmark, Barbour, and Harvey Brown. Here is Harvey https://youtu.be/CA-YsWXRSHU
The problem is that there is no change or any notion of time flow in physical models. They describe a static 4-D universe. So there is no particle but there is a one-dimensional world line in the equations with no difference between points. Surely time has a particular property that is reflected in the equations that one can predict across time and not space. The notion of that world line reflects this. But this does not tell why we perceive those world lines point by point.
I.e. a physical model is like a set of frames for a movie with particular relations between frames. But it does not tell why if we see the movie we perceive the motion and not, for example the whole movie at once. Or why the perception is across time and not space.
And since these being discussed in various forms since at least Parmenides and Buddha I doubt this will be resolved any time soon.
> The problem is that there is no change or any notion of time flow in physical models.
What do you mean by this?
When I write x(t) = x0 + (dx/dt) * t + (d2x/d2t) * t^2, time is right there in the equation.
In relativity, it is even self-evidently different from the 3 spatial dimensions: s = sqrt(x^2 + y^2 + z^2 - (ct)^2).
There is even a somewhat intuitive interpretation for the special-ness of the time dimension: all matter is constantly moving along the ct axis of space time at speed c, unless acted on by some force, trying to follow the shortest distance between the past and the future (so the trajectory bends towards the center of mass of any other matter it finds on the way).
That equation describes a curve in 2 dimensional space with no differences between points with each point having particular time and space coordinates. And you can even resolve it to express time as a function of space. But we do not interpret that as a flow of space.
Sure, but you still can't explain it without adding an extra dimension to your model, and that extra dimension is not symmetrical with the space dimensions. In fact, there is no physical model that I am aware of that makes time and any space dimension interchangeable.
The fact that our mathematical models generally seem to allow movement backwards and forwards in time is in stark opposition to observed physics. This obviously suggests that the models are wrong, and there is something about time we are not capturing well enough. Relativity does somewhat fix this, by essentially postulating that everything is moving with speed c in space-time, but that is a somewhat unsatisfying explanation, since it seems natural to ask why.
The extra dimension does not explain the movement or change. The world line corresponding to the equation is static. It does not show at all why when one looks at a particle, one perceive the movement and change in the position, and not, for example, the whole world line at once.
I am not saying that time and space are the same in physical equations. The point is that they do not describe the perception of time flow, not that there is no difference between time and space.
As I wrote the structure of equations (equations are parabolic or hyperbolic, not elliptical, the sign of the time dimension in the metric tensor is opposite to the space coordinates) reflects that one can predict across time but not space. I.e. the equations reflects that from a picture of a room one can tell what will happen in one hour or what did happen one hour ago. Shadows from the Sun will move, a sleeping cat will not be there, but things will be mostly the same. But try to tell what is in the rest of the room from a one-hour long video of the wall. It is not possible.
But this difference tells nothing about perception of “now” or the time flow.
In a sense the equations reflects how memory operates. We remember a sequence of events and we can focus on a particular moment or select events in an arbitrary order similar how we can select a point or points on the world line of a particle. But the memory does not have “now” and so the equations reflecting the notion of the world line tell nothing about the time flow.
What no one has done is understand consciousness or reduce biology to physics much at all. The math behind the above is extremely well known and ironed out. That is why some physicists now put the challenge on biologists and psychologists. The personal or subjective flow of time we all experience is theorized to be recreatable from this (timeless) framework. After all, all you have access to is a single snapshot and memories. Sensorial data and brain states. Registering and firing of nerves and neurons. Momenta of particles...why not? Just particle momementa in a table in some kind of sequential form (e.g. worldines in 4D spacetime block universe).
I completely agree this may end up being an impossible challenge, or that it's later shown to be misguided. But there are accomplished philosophers and physicists behind it, or at least sympathetic to it.