Comment by lisper | Hacker News Reader

Comment by lisper | Hacker News Reader

Here's another take on the topic:

http://blog.rongarret.info/2014/10/parallel-universes-and-ar...

The TL;DR:

"The punch line is this: the statement that we can't time-travel into the past is exactly the same as the statement that we can only remember the past. It is not the case that one causes the other, it is that the two things are logically equivalent. Your perception of "traveling through time" emerges from your mental states and not the other way around. You feel like you are "traveling forward through time" because your mental states have this natural order to them. You can remember the past and not the future because whatever you remember is your past. The laws of quantum mechanics (and entanglement in particular) insure that what any given instance of you remembers appears to be a continuous and coherent sequence that behaves according to regularities that we call the laws of physics. But in fact you do not travel through time, because at root there is no you, and there is no time. There is only the wavefunction, from which both you and time emerge as an approximation."

so how does quantum mechanics explain the continuous and coherent (more or less) sequence that is perceived even in a non-physical dream?

In exactly the same way. Dreams are just the brain "remembering" internally generated stimuli.

if it's exactly the same, that would imply that quantum mechanics and decoherence effects are equivalent for both internally generated imaginary stimuli, and external stimuli based on "real" physical objects. but it seems like a stretch to suggest that if i dream that i am flying, that the same quantum mechanical effects that contribute to Time's Arrow in that dream are in play in the "real world", where such a thing would be impossible physically.

I think you're missing something really fundamental. Decoherence happens at the sub-microscopic level -- unless things are very, very cold, in which case you can get macroscopic quantum effects. But at room temperature, by the time you get up to the molecular level things are already more-or-less classical. By the time you get to the level of a neuron they are (as far as we know) indistinguishable from classical. From the point of view of QM, there is no difference between being asleep and being awake. All of your mental processes are indistinguishable from classical.

yes i understand decoherence at different scales, but my point is that the Arrow of Time exists for both a real physical object, such as someone falling off a cliff, but also a non-real object, such as someone dreaming of falling off a cliff. decoherence can explain the first, but since there is no physical cliff or object in a dream (at either the micro- or macro- scale), how can it explain Arrow of Time that is observed in interactions between non-physical imaginary objects?

But your perceptions of real and non-real objects (and hence your perception of time) comes from the same source: the pattern of neurons firing in your brain. It ultimately doesn't matter whether those neuron firings are caused by external stimuli from real objects or internal stimuli from imaginary ones. The nest result is the same: your perception of the passage of time runs in one direction because your mental states form a totally ordered sequence of accreting memories. Decoherence insures that those memories remain self-consistent with each other and with the "real world".

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