Sorry for the late reply. Don't know if you'll still be reading this, but...
> This is getting a bit meta, maybe even off-topic. But I think this is fairly simple to explain: you can't remember states you haven't been in. Generalized memory implies some record of a state that has occured - states that have not occured cannot be remembered.
In a discussion about the arrow of time, this is somewhat begging the question! The difference between a state that you've "been in" and a state that you "will be in" is exactly the subject that we're discussing. How do you precisely define "been in" or "occurred" in a way that doesn't reverse under a transformation from t <---> -t?
The answer I've provided elsewhere in this thread is along the lines of: Other than melting icecubes and scrambling eggs, the only other difference you can notice between the past and the future is that you can remember the past, but you cannot remember the future. If you could remember the future just as well as you remember the past, you probably wouldn't have strong opinions about which way time goes (or which direction is "clockwise"). If you, Merlin-like, could only remember the future then you'd probably be here asking why you always observe entropy decreasing in closed systems, and complaining that they got the second law of thermodynamics backwards.
On a fine-grained scale causality works just as well in a rewound video, although it is full of spontaneous-seeming coincidences with surprising macroscopic effects. There are only two things that establish an arrow of time:
* The universe has an entropy gradient along the "time axis", with one direction (which we can call 'P') having lower entropy and the other ('F') having higher entropy.
* We (and other physical systems) are able to form memories in one direction, but not the other. Because of this, we perceive a sense that time progresses "from" the direction that we can remember. This happens to be the direction of increasing entropy. Because of this ability to remember only along one direction of the entropy gradient, we call 'P' the past and 'F' the future.
This is not a coincidence. Memory operates on systems of increasing entropy, so you'll always only remember the past having less entropy than the present. [1]
>In a discussion about the arrow of time, this is somewhat begging the question!
Not really. "Been in" isn't meant to imply a temporal relationship. If a system has been in microstates A, B and C, then it can potentially remember states A, B and C. It cannot remember state D. That doesn't stay anything about whether or not A preceeded B, or C preceeded A.
I agree with your last two paragraphs, but not the formulation in the middle para. "you cannot remember the future" ... this just seems like an non-useful observation to me. I think the problem comes from this line:
>We (and other physical systems) are able to form memories in one direction, but not the other.
I think this is wrong. The issue is that our memories are of macrostates, and macrostates are subject to the entropy gradient. If we could form memories of microstates, we'd effectively be able to remember events that had no arrow of time associated with them. But then you say this yourself in your final line. And Maccone's concept seems fine to me (as if that matters :)
> This is getting a bit meta, maybe even off-topic. But I think this is fairly simple to explain: you can't remember states you haven't been in. Generalized memory implies some record of a state that has occured - states that have not occured cannot be remembered.
In a discussion about the arrow of time, this is somewhat begging the question! The difference between a state that you've "been in" and a state that you "will be in" is exactly the subject that we're discussing. How do you precisely define "been in" or "occurred" in a way that doesn't reverse under a transformation from t <---> -t?
The answer I've provided elsewhere in this thread is along the lines of: Other than melting icecubes and scrambling eggs, the only other difference you can notice between the past and the future is that you can remember the past, but you cannot remember the future. If you could remember the future just as well as you remember the past, you probably wouldn't have strong opinions about which way time goes (or which direction is "clockwise"). If you, Merlin-like, could only remember the future then you'd probably be here asking why you always observe entropy decreasing in closed systems, and complaining that they got the second law of thermodynamics backwards.
On a fine-grained scale causality works just as well in a rewound video, although it is full of spontaneous-seeming coincidences with surprising macroscopic effects. There are only two things that establish an arrow of time: * The universe has an entropy gradient along the "time axis", with one direction (which we can call 'P') having lower entropy and the other ('F') having higher entropy. * We (and other physical systems) are able to form memories in one direction, but not the other. Because of this, we perceive a sense that time progresses "from" the direction that we can remember. This happens to be the direction of increasing entropy. Because of this ability to remember only along one direction of the entropy gradient, we call 'P' the past and 'F' the future.
This is not a coincidence. Memory operates on systems of increasing entropy, so you'll always only remember the past having less entropy than the present. [1]
[1]: https://phys.org/news/2009-08-physicist-solution-arrow-of-ti...