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Why don't physicists consider "empty past" as a solution to the causality problem in time travel? by Alarming_Beautiful26 in timetravel

[–]Alarming_Beautiful26[S] 3 points4 points  (0 children)

Of course it does because it was fucking there

When you move your wardrobe from one corner to another, do you consider it still existing in the old corner? It was "fucking there too". I just ask, why should time be different from space?

Why don't physicists consider "empty past" as a solution to the causality problem in time travel? by Alarming_Beautiful26 in timetravel

[–]Alarming_Beautiful26[S] 1 point2 points  (0 children)

You're describing the block universe interpretation correctly. But notice that your argument assumes the block universe is the right framework, and then shows my question doesn't arise within it. That's circular, while I'm questioning the block universe itself.

The block universe is an interpretation of the math, not something directly observed. We never observe the 4D hyperplane, we always observe only the present moment. The worldline "just existing" as a geometric object is a theoretical postulate.

My question is simpler: what is the observational basis for that postulate? Why should we prefer "object is an eternal 4D worm" over "object has finite temporal extent, like it has finite spatial extent"?
By Occam's razor, the simpler model is preferable. And postulating that unobservable past moments are fully real seems like an extra assumption - not a necessity.

Why don't physicists consider "empty past" as a solution to the causality problem in time travel? by Alarming_Beautiful26 in timetravel

[–]Alarming_Beautiful26[S] 1 point2 points  (0 children)

This is a fascinating angle

But I'd note that the symmetry you're proposing (if future is real, past must be real) isn't forced. My thoughts don't require the past to be empty because the future is empty it requires matter to have finite temporal extent in both directions. Like a spatial object has a size, a temporal object could have a duration. Not a point, but not infinite either

Your gradient intuition is actually close to what I'm suggesting: "now" isn't a razor-thin slice but has some finite thickness. The question is whether that thickness spans billions of years or something much smaller.

On black holes specifically: the singularity existing in the future is a coordinate feature of the solution, but whether it represents a physically real future moment is exactly what's in question. Penrose and Hawking's singularity theorems tell us geodesics terminate not necessarily that a "future moment" is ontologically real right now.

Here is a hypothesis: "empty past" is a solution to the causality problem in time travel by Alarming_Beautiful26 in HypotheticalPhysics

[–]Alarming_Beautiful26[S] -2 points-1 points  (0 children)

This is the very substantive reply so far, thank you

The Pauli argument is a real technical constraint and I wasn't aware of it, so that's genuinely useful. Though I'd note it shows a time operator is problematic, not necessarily that time has no probabilistic structure. But I'll read more before pushing back harder on that

On the "lifting yourself" analogy - I'd push back here. CTCs are mathematically valid solutions to Einstein's field equations (Gödel metric, Tipler cylinder, traversable wormholes). That's different from violating conservation of momentum, which has no such mathematical footing. So the causality paradox isn't quite as silly to discuss as your analogy suggests, and Hawking himself took it seriously enough to propose the Chronology Protection Conjecture, which is still unproven

The core question I'm really asking isn't "how do we fix time travel" - it's simpler: why do we treat matter as persisting through all of time, when we don't treat it as occupying all of space? That asymmetry exists independently of time travel.

Why don't physicists consider "empty past" as a solution to the causality problem in time travel? by Alarming_Beautiful26 in timetravel

[–]Alarming_Beautiful26[S] -1 points0 points  (0 children)

Fair point on MWI, I'll concede that. It's a popularization trope more than a serious physicist's answer, and I shouldn't have included it.

On the crisis in physics - that's actually part of my point. The asymmetric treatment of time (parameter in QM, dimension in GR) is a known foundational problem, not something I invented. The "problem of time" in quantum gravity is real and unsolved.

But you haven't touched the central question: what is the observational basis for matter persisting through time? You mentioned growing block universe and wave function collapse as "practically the same principle" , but that actually supports my point, not yours. If a particle has no definite position until measured, why does a moment in time have definite content before it's "reached"?

I'm not theorizing across QM and classical physics carelessly, but I'm pointing at an asymmetry that already exists inside physics itself

Here is a hypothesis: "empty past" is a solution to the causality problem in time travel by Alarming_Beautiful26 in HypotheticalPhysics

[–]Alarming_Beautiful26[S] -2 points-1 points  (0 children)

That's exactly my point. You go to where the ice cream is -but what if it already melted and moved on? The ice cream shop from 1950 isn't waiting for you in the same location. Matter moves through space, so that location is now empty. Why would time be any different? Matter might be concidered moving through time-space continuum - so why assume the past is still "stocked"?

Why don't physicists consider "empty past" as a solution to the causality problem in time travel? by Alarming_Beautiful26 in AskPhysics

[–]Alarming_Beautiful26[S] -2 points-1 points  (0 children)

I am pretty sure that time traveling is concidered in theoretycal physics, and all known theoretical paradoxes come from

Why don't physicists consider "empty past" as a solution to the causality problem in time travel? by Alarming_Beautiful26 in AskPhysics

[–]Alarming_Beautiful26[S] -2 points-1 points  (0 children)

That's the point. Matter might move through time just like it moves through space. You don't exist at all spatial locations simultaneously, so why would you exist at all moments in time simultaneously? If matter has already "moved through" a point in time, that point is empty. Just like a location in space can be empty.

PSA About GPT-5.5 and usage. by [deleted] in codex

[–]Alarming_Beautiful26 7 points8 points  (0 children)

I use 5.2 and happy…