My point is that talking about history supervening only makes sense if the math describing that behavior has been demonstrated to be applicable to the real world.

It is applicable.

QM works when applied to reality. It’s spectacularly successful. Physical systems behave as expected based on the evolution of their wavefunctions.

Time-reversibility is simply a mathematical fact about the evolution of those wavefunctions — they retrace their steps when the appropriate time-related variables are negated.

If a wavefunction evolving forward in time produces a state sequence Q0, Q1, …, Qn-1, Qn, you can take nothing but Qn and by time-reversing the evolution of the wavefunction, you will get Qn, Qn-1, …, Q2, Q1, Q0. Time-reversing the wavefunction produces the same state sequence in reverse.

If you can generate the correct causal history from nothing but Qn, it shows that the causal history is implicit in Qn. Where else could it be coming from?

Patrick: Just because the math works doesn’t mean anything in reality.

Indeed. Science uses math to model reality. The search is for better models. Reality is time-dependent unless one thinks of the block universe.

I find mulling over the reality of time and whether the way we experience and model it is flawed or illusory far more compelling than wondering if I’m a brain in a vat.

keiths: If you agree that we cannot judge the likelihood of this “utter failure”, …then it follows that we are no position to claim that our “sensorimotor systems” are delivering accurate information to us.

But as nothing follows from allowing that our model of the world that we build up from our shared experiences may be illusory, we can justifiably continue to behave as if that information is reliable. And of course the overwhelming majority* of humans live their lives as if their lives were real.

*I’m assuming Keiths has some extra dimension to his life that follows from his mantra that we can’t be certain of anything. To which the riposte, still unanswered, is…

My point is that talking about history supervening only makes sense if the math describing that behavior has been demonstrated to be applicable to the real world.

It is applicable.

QM works when applied to reality. It’s spectacularly successful. Physical systems behave as expected based on the evolution of their wavefunctions.

Some of QM has been demonstrated to accurately model reality. The time reversibility has not (again, as I understand it).

Time-reversibility is simply a mathematical fact about the evolution of those wavefunctions — they retrace their steps when the appropriate time-related variables are negated.

If a wavefunction evolving forward in time produces a state sequence Q0, Q1, …, Qn-1, Qn, you can take nothing but Qn and by time-reversing the evolution of the wavefunction, you will get Qn, Qn-1, …, Q2, Q1, Q0. Time-reversing the wavefunction produces the same state sequence in reverse.

If you can generate the correct causal history from nothing but Qn, it shows that the causal history is implicit in Qn. Where else could it be coming from?

The fact that the math allows for this does not mean that in reality the history of a particular macro state can be uniquely determined, even in principle. That remains for empirical verification. My understanding is that current results do not support the idea.

Some of QM has been demonstrated to accurately model reality. The time reversibility has not (again, as I understand it).

There’s a reason I emphasized the word ‘mathematical’ in this sentence:

Time-reversibility is simply a mathematical fact about the evolution of those wavefunctions — they retrace their steps when the appropriate time-related variables are negated.

Even if Q0 through Qn had nothing to do with physical states, and were merely mathematical abstractions, it would still be true that the entire state sequence is implicit in Qn. That’s a mathematical fact, not a physical one.

So if the actual physical states going forward in time match the sequence Q0 through Qn, then the argument is complete. There is no need to find some aspect of reality that corresponds to the time-reversed sequence.

Patrick,

It

isapplicable.QM works when applied to reality. It’s spectacularly successful. Physical systems behave as expected based on the evolution of their wavefunctions.

Time-reversibility is simply a

mathematicalfact about the evolution of those wavefunctions — they retrace their steps when the appropriate time-related variables are negated.If a wavefunction evolving forward in time produces a state sequence Q0, Q1, …, Qn-1, Qn, you can take

nothing but Qnand by time-reversing the evolution of the wavefunction, you will get Qn, Qn-1, …, Q2, Q1, Q0. Time-reversing the wavefunction produces the same state sequence in reverse.If you can generate the correct causal history from

nothing but Qn, it shows that the causal history is implicit in Qn. Where else could it be coming from?Indeed. Science uses math to model reality. The search is for better models. Reality is time-dependent unless one thinks of the block universe.

I find mulling over the reality of time and whether the way we experience and model it is flawed or illusory far more compelling than wondering if I’m a brain in a vat.

But as nothing follows from allowing that our model of the world that we build up from our shared experiences may be illusory, we can justifiably continue to behave as if that information is reliable. And of course the overwhelming majority* of humans live their lives as if their lives were real.

*I’m assuming Keiths has some extra dimension to his life that follows from his mantra that we can’t be certain of anything. To which the riposte, still unanswered, is…

“so what!”

Some of QM has been demonstrated to accurately model reality. The time reversibility has not (again, as I understand it).

The fact that the math allows for this does not mean that in reality the history of a particular macro state can be uniquely determined, even in principle. That remains for empirical verification. My understanding is that current results do not support the idea.

Alan,

See this.

Patrick,

There’s a reason I emphasized the word ‘mathematical’ in this sentence:

Even if Q0 through Qn had nothing to do with physical states, and were merely mathematical abstractions, it would still be true that the entire state sequence is implicit in Qn. That’s a mathematical fact, not a physical one.

So if the actual physical states going forward in time match the sequence Q0 through Qn, then the argument is complete. There is no need to find some aspect of reality that corresponds to the time-reversed sequence.

Patrick, on another thread:

I addressed that in my previous comment.