Descartz2000 said:
A future state is not an inherent future from all viewpoints. Some viewpoints might claim it to be a present and past state.
ConradDJ said:
There is pretty strong evidence that there is no "wall of change sweeping across" the whole universe at once. I think what relativity tells us is that the present moment "now" is local to every point of view.
Agreed, the basics facts of relativity have to be factored into anything being said here. One observer can judge two events to be simulataneous, which to another observer follow one after the other, etc.
But this is why I like a thermal approach to time - it recognises, as Conrad says, that it is not a simple dimension, but complex. A simple view of time is that it is another geometric dimension - measured in terms of distance covered. But a complex view recognises that time can be ticked off in two kinds of units - thermalisation (cooling, entropification) as well as distance (expansion, motion). There is a duality here as these two physical processes are two sides of the same coin.
So getting back to my argument that the temperature of the universe does act like a universal clock, a global wall of change sweeping through, imagine looking up into the night sky and making a visual reading of its prevailing temperature. Registering photons.
Light cone logic applies of course. So that is a strict locality constraint. But so too does a transactional interpretation of QM, which admits thus an essential nonlocality. Individual events have a "timelessness", or rather, they turn indeterminate spatiotemporal potential into some actual crisply decohered event.
Anyway, looking up at the stars, we are catching energetic photons from all directions. But there is clearly a powerlaw relationship. In general, the stars are all equally bright, but distance makes them dim. And also further away in time, in our "past".
But from a transactional QM point of view, nothing has "happened" until the star has "decided" to emit a photon and my eye has "decided" to accept it. The connection is formed across time in some fundamental (nonlocal) sense. Once it has "happened" of course, it is a fixed part of the universe's history. It is woven into the history of the universe.
Note also that such events are always (excepting a non-zero but vanishing degree QM uncertainty) entropic - they go in the direction of a thermal gradient. My eye may emit photons of its own, but they will be way down in the weak infrared, never climbing back up the gradient to be hot like a star's emissions.
So looking up at the night sky, I am seeing photons over every distance (and hence distance back in time). But every individual event is also timeless in that it required me, as the decohering, wavefunction collapsing, observer to anchor one end of a transaction that is in fact "making time". Creating an act of communication, ie: thermalisation.
Of course, the conventional view is that the star emitted a particle, a photon, and it crossed vast regions of space, red-shifting as it went, before smacking into my retina. This is a realist view based on strict locality. It is a convenient way of modelling the situation perhaps, but contradicted at a fundamental level by QM, and the reason why some more subtle and complex model of time is actually needed.
Anyway, that is the situation. I look out at the stars and make thermalising connections with hot radiation sources over an incredible range of spatiotemporal "distances". The majority are in fact "near to" - the closer stars in the same galaxy. But in powerlaw fashion, photons could reach me from any distance within the visible universe.
So this admits that the "now" here is my now. But it is a complex now because my now is directly (nonlocally) part of some time-distant star's "now". The whole path of that photon exchange was a collapse of a wavefunction that put the star, my eye, and everything along the way, in a strict temporal order (and strict thermalisation order, as part of what happened was the red-shifting as well).
But there is also a global wall of change in this story as well. When I look out at the night sky, in every direction, over every distance and hence timescale, the sky looks pretty black. Stars (located thermal bodies) are the exception. And 98% of what I see is the global coldness, the weak thermal sizzle of the cosmic background radiation. This is a pure measure of the universes thermalisation, or cooling due to expansion and consequent red-shifting.
So mostly, my interactions are ruled by a global clock - the CMB. Just as to one side of me, there is an important heat source, the sun, to the other, there is a vast heat sink. And this is the entropy gradient that even makes it possible for us to exist as located, complex, observers.
What does this all say about the issue of "now"? Well, first up, GR alone is only a partial model. QM and thermodynamics are needed for a more complete story. As well as distance (GR), there is entropy (thermodynamics). And as well as locality (GR), there is nonlocality (QM).
Second, most of our temporal relations are either warm and short-range (the sun is only minutes away), or cold and distant. So our "now" is quite tightly defined in fact by a fairly precise position on an entropic gradient (hot foreground, cold backdrop). We can of course have thermal interactions over incredible distances (and hence times measured in distance). But these become vanishingly weak and do very little to nudge our otherwise quite tightly determined location on a thermal scale (the one locating us at some point between our dominant heat source and our dominant heat sink).
Third, it seems that thermo considerations are in fact a better way of thinking about time as a dimension. Time can be equated with distance (as distance is thermalising in practice - expansion causing red-shifting even without anything else happening). But if we equate time with change, and change with gradients, and gradients with entropification, then "now" can be seen in thermal terms. It becomes a measure of potential action.
My past is the past because that is a gradient already run down (and star light is not in my past until it has become an event registered as part of my now - and that star's now too). My now is where I happen to be on the gradient (the one between my dominant heat source and dominant heat sink). And my future is all the distance yet to slither down that entropy gradient towards the ultimate blah of a universal heat death.
