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Comment by brwck | Hacker News Reader

It's not just a matter of our subjective experience of time, it's a matter of the laws of thermodynamics and entropy. Time moves in one direction is another way of saying entropy always increases. If time could move in the opposite direction, then entropy decreases which breaks our understanding of physics.

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The direction of causality should also be reversed from what I can tell. Instead of a bullet slowing down as it hits air molecules and pushes them out of the way, the air molecules push on the bullet because the bullet will be sucked into the barrel in the future.

More on topic, I think our existing theories of reality tell us that the future probably affects the past, or at very least, is predetermined. If you know the solution to a differential equation, you know the state at any point in time. There's no going off the rails, so to speak. And if the system is constrained in any dimension (i.e. it's nonholonomic) then the state at any given moment relies on the full trajectory up to that point, as opposed to just the previous state. But you can flip that on its head and say that the future state determines the present trajectory. E.g. to turn a bicycle left, you have to first turn right.

but what about reverse falling cartridge? Will spacetime around Earth change from "hole" to "hill"?

That's not going to be necessary.

I think it's the same thing. The future energy state of the cartridge is that it's in the chamber, so it gets sucked up. It's problematic though, because the direction of gravity doesn't change.

It's really interesting to think about how we struggle to express the idea of the future having a causal impact on the past. I reckon this is because our language and our understanding of time are limited.

Our brains like to process events in a linear sequence, from past to present to future, but this view of time might not fully capture how everything in the universe is interconnected. It's possible that our language just can't handle these complex concepts.

So, I don't think anything mentioned in this thread contradicts the idea that "time always moves in one direction" and "entropy always increases".

Right. "Time only moves in one direction" is not saying much more than "our consciousness experience time moving in one direction". The very idea that time "moves" is entirely related to our vantage point. If our perception were not bound to time, then the nature of cause and effect might look completely different.

Just commented about interpreting the Probability Law as sort of "Inverted 2nd. Law of Thermodynamics".

I'll expand here how if the arrow of time actually doesn't exist, the future could change the past without breaking our - current - understanding of physics (tragiclly because we will probably have maybe hundred of years till we change our minds about what are the properties of the universe).

In a range or probabilities of one event, one of the probabilities will always be the one is going to actually happen. Closer to the event to occur the most certain you can be about which one of those, could be the one that will happen.

Here's the catch, you have to change your mind a bit, in our current understanding of physics, the information of the future event which has not happen yet, already exists here in the past for that event.

Now, if you know - and you know - the outcome of an event, you most certainly will be able to choose if you go along that path, or you choose to change the future event to something else. Whoalá, the future changed the past.

Brains of earth continously do this, every second of our entire lives, animal brains do this too, almost all life on Earth has some neurological, physiological, chemical predictive mechanism in place.

An example, you're about to walk across a street, you see a car coming, now your brain "predicts" you'll be hit by that car if you just keep walking, you stop walking to avoid certain death, done, the future changed the past. The information - really close to 100% of probability of death - extracted by the brain from the sheer reality of the universe, allowed you to survive.

And no current understanding of physics got harmed anywhere along the way of the future changing the past.

I don't think the idea that "the future can influence the past" is the same thing as saying that entropy decreases or that time can move in the opposite direction. I think these are different concerns

The "arrow of time" conception of entropy: 1) does not work locally and only works at large enough scales, and; 2) is essentially isomorphic to the concept of time.

So no, it's not at all incompatible with retro-causality. When you think about retro-causality, the idea that time "moves" is completely superfluous. Time is probably not even a real thing.

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