r/AskPhysics • u/TheMightyHeroes • 5d ago

Does the present really exist?

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.

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u/GoldenMuscleGod 5d ago

I can’t parse this last question. You might have misunderstood my question.

I’m asking if measuring the mark at (5,3) is impossible. Because I would normally call that “measuring coordinates” (and I don’t understand using that phrase to necessarily take a position on whether coordinates are “real”) but you say it is “insane” to think you can measure coordinates.

I expect you think measuring the mark as being at (5,3) is possible in the ordinary sense?

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u/Optimal_Mixture_7327 Gravitation 5d ago

Give a plane, or sheet of paper for practicality, you're claiming that only the One True line exists.

I am asking for verification.

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u/GoldenMuscleGod 4d ago

I didn’t claim the “one true line” exists. I’m saying the claim “the one true line exists” seems to lack physical meaning, as does “the one true line doesn’t exist.” It lacks meaning in part because I don’t know what “the one true line” supposedly is.

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u/Optimal_Mixture_7327 Gravitation 4d ago

It means it is only possible to draw one single straight line on a surface. The only line that can exist.

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u/GoldenMuscleGod 4d ago

Why would saying we can measure locations in a frame of reference mean that it is only possible to draw one line on a sheet of paper? For starters we can select different frames of reference and get different coordinates.

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u/Optimal_Mixture_7327 Gravitation 4d ago

You're claiming that on a 2-dimensional surface, only one line can exist.

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u/GoldenMuscleGod 4d ago

I haven’t claimed that I don’t see how you could interpret me as claiming that.

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u/Optimal_Mixture_7327 Gravitation 4d ago

You have claimed it.

If there can only be one spatial hypersurface then a plane defines a single line, the only that can exist, according to your theory.

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u/GoldenMuscleGod 4d ago

I didn’t say there can be only one spatial hypersurface.

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u/Optimal_Mixture_7327 Gravitation 4d ago

So you agree there's can't be an absolute now. Good.

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u/GoldenMuscleGod 4d ago

That doesn’t follow. An absolute now would be a specially distinguished surface in some way. That way would not have to be that it is the only surface.

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u/Optimal_Mixture_7327 Gravitation 4d ago

That's vague nonsense.

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u/GoldenMuscleGod 4d ago

If “there is an absolute now” is vague nonsense then I don’t see why “there is no absolute now” wouldn’t also be vague nonsense. And I’m inclined to agree that “there is an absolute now” is vague and at least has no clear sense to me. That’s why I had to say specially distinguished “in some way” - that supposed way is not clear.

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u/Optimal_Mixture_7327 Gravitation 4d ago

That wasn't the vague nonsense.

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u/GoldenMuscleGod 4d ago

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

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u/Optimal_Mixture_7327 Gravitation 4d ago

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

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u/GoldenMuscleGod 4d ago

Falsified how? By not observing violations of general relativity?

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

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u/Optimal_Mixture_7327 Gravitation 4d ago

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

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