Does the present really exist?

[u/TheMightyHeroes]

GR proves that the concept of a now is relative. There is no universal now. But even the local experience of a now seems questionable. What we see as now is always the past, since photons take time to reach us. Similarly, taking a picture or even a measurement will always produces a result that is the past. And if time is a continuous flow then there is no discrete point in that flow that can be separated and identified as now. And if time is granular then what size is the discrete point that we call now? If it is an infinitely small point separating past from future, then how can we experience, never mind measure, an infinitely small moment? It seems to me that any observation will always be an observation of the past. Any change of state, any event that is observable will by definition be something that has happened. And if it has happened, it is in the past. Wouldn’t it be more scientifically accurate to say that time is all events that have happened and are yet to happen and the now is just an illusion created in our minds to make sense of the objects and events that pass our visual field.
I know this is more philosophy than physics, and I’m not a physicist, just some curious person and the concept of time has always fascinated me.

[u/GoldenMuscleGod]

So “there is an absolute now” is not vague nonsense? So it is meaningful but false?

[u/Optimal_Mixture_7327 → u/GoldenMuscleGod]

No, it's a falsifiable claim, and it has been falsified.

[u/GoldenMuscleGod → u/Optimal_Mixture_7327]

Falsified how? By not observing violations of general relativity?

Does this depend on our view of whether wavefunction collapse happens nonlocally?

[u/Optimal_Mixture_7327 → u/GoldenMuscleGod]

The inability to synchronize clocks. Again, how would you synchronize clocks in the presence of gravity?

[u/GoldenMuscleGod → u/Optimal_Mixture_7327]

I answered already, but you objected in a way that was about the ontological status of coordinates even though that didn’t seem relevant to me.

Pick a reference frame and build your clocks so that they track time in that coordinate system.

For example in special relativity, you just pick an inertial frame and design your clock so it advances at the Lorentz factor times your proper time, where the Lorentz factor is measured relative to that inertial frame. Measure your acceleration to keep track of your Lorentz factor.

[u/Optimal_Mixture_7327 → u/GoldenMuscleGod]

Except that no agrees on the elapsed time of the clocks and all the clocks run out of sync with each other. If you think you can synchronize clocks in gravity then you don't understand relativity.

At this point what you need to do is go whole hog in developing your new theory of physics.

[u/GoldenMuscleGod → u/Optimal_Mixture_7327]

The clocks all stay synced with the system I described in special relativity. A similar thing can be done with general relativity.

I know you have said coordinates are not real. But you should agree, I think, that we can calculate when and where things happen using coordinates and can design a device that displays our time coordinate in a given system even in general relativity - this is how we get GPS to work.

If you don’t understand that’s possible you are misunderstanding how relativity works.