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Wiseman comments on Collapse Postulates - Less Wrong
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Comments (60)
4 points:
If collapse actually worked the way its adherents say it does, it would be: 1. The only non-linear evolution in all of quantum mechanics. 2. The only non-unitary evolution in all of quantum mechanics. 3.... WHAT DOES THE GOD-DAMNED COLLAPSE POSTULATE HAVE TO DO FOR PHYSICISTS TO REJECT IT? KILL A GOD-DAMNED PUPPY?
Not a valid argument. The physics of the universe are what they are, at the microscopic and macroscopic levels. If it so happens that there is some non-GR-violating non-locality going on (don't complain, just cause you can't imagine it, doesn't mean it's not possible), then your list above simply would be wrong, and there would be no violation of "traditional physics" to complain about.
In any case, since from the perspective of each world we have non-determinism, and the only world we are acting on is our own, why is it necessary to explain many worlds for the purposes of AGI?
Well, first: Does any collapse theory have any experimental support? No.
Neither does MW, they are both interpretations.
I'm going out on a limb on this one, but since the whole universe includes separate branching “worldsâ€, and over time this means we have more worlds now than 1 second ago, and since the worlds can interact with each other, how does this not violate conservation of mass and energy?
Wiseman left ages ago, but I'm taking a stab at this question because 1) I want to know if my answer is right, and 2) other people who read it might want to know the answer too.
As far as I can tell from this sequence, the number of worlds that exist over time, or at least the total amplitude, is constant. Multiple "past" configurations contribute amplitude to the same "present" configuration. Any given "past" configuration also contributes amplitude to multiple "present" configurations. The scare quotes are because neither the question nor the answer makes much sense if one considers timeless physics.
If you take the MWI literally, each world splits all the time, so the number of worlds would increase. Of course, there is no point counting what we cannot observe, not even in principle.
Depends on what you mean by that. But yes, one can certainly express the MWI in a way that preserve unitarity over multiple worlds.
Probably not in this sense. The world splitting process ought to be a tree graph, with no cycles. Scott Aaronson explains it better.
You may want to ponder how rational it is to refer to an exciting idea that was never fleshed out as if it were a real physical model.
My understanding is "Yes, but only if the resulting 'present' configurations are identical, which basically never happens when things get big."
That's what Scott says, yes. There is related to Poincare recurrence, something that happens probably just as often as two worlds combining.
The "number" of worlds increases, but each world is weighted by a complex number, such that when you add up all the squares of the complex numbers they sum up to 1. This effectively preserves mass and energy across all worlds, inside the universal wave function.
Even if this were true, conservation of energy across the worlds is not a good argument for or against MWI. There is no reason it should be conserved over non-interacting entities. Also note that energy in our expanding Universe is not conserved (or even well-defined) globally.