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quantum mechanics has two different laws that describe how a system changes in time. Rule 1 says that except during a measurement, the wave evolves smoothly an
by platz 8y ago
quantum mechanics has two different laws that describe how a system changes in time.
Rule 1 says that except during a measurement, the wave evolves smoothly and deterministically, exploring every possibility.
Rule 2 says that during a measurement of position, the wave collapses around the position where it's seen, with a probability proportional to the square of the height of the wave, before the collapse.
It is only Rule 2 that mentions probabilities at all.
And, Rule 1 and Rule 2 are in catastrophic tension with each other.
Rule 1 says that there are always all possible outcomes.
Rule 2 says there is only 1 outcome and it's picked out with some probability rule.
It's pretty contradictory - is there one outcome or all outcomes?
> youtube.com/watch?v=Zri9gS1w5ok Perimeter’s Lee Smolin will argue that the problems that have bedeviled quantum physics since its inception are unsolved and unsolvable for the simple reason that the theory is incomplete.
- rohit2412 8y agoAnd I never understand what is a "measurement". Has it something to do with a human being observing it? Isn't any measurement just electromagnetic or gravitation forces acting on it, which act all the time?
- platz 8y agoI think one development that occurred since the late 80's, is that most physicists don't think conciousness is required at all, developing the idea of "decoherence" instead. Not that resolves the measurement problem in any way, of course.
- cygx 8y agoA measurement is an interaction that crosses the Heisenberg cut separating the quantum from the classical world. Eg you prepare an atom in a superposition of states relative to some 'quantization axis' determined by a Stern-Gerlach apparatus. The state will randomly 'collapse' into one of the available final states, resulting in a macroscopic dot on some screen. You and all your physicist buddies will agree on the placement of the dot. There is no agreement on how this happens, complicated by the fact that there is no such thing as a classical world I alluded to above, ie any interactions with the apparatus and the conscious observers supposedly obey the laws of quantum mechanics.