flink@umcp-cs.UUCP (Paul V Torek) (12/23/85)
Many moons ago, Ken Rimey posted an explanation/endorsement of the Many Worlds interpretation of QM. I tried to mail to him, but no luck. I noticed he's still around today, so here's my reply: >You may have noticed that, in describing a theory in which the >universe is deterministic and measurement is not a fundamental >idea, I sure refer to measurement and probability a lot. The >point is that these ideas are involved only in the interpretation >of the mathematical object that represents the state of the universe. >They don't clutter up the theory of how to calculate that object. >In particular, in the Many-Worlds view, wave functions don't "collapse". Then what do measurements measure, in the Many-Worlds view? Are "position" and "momentum" fictions? >Many-Worlds is indistinguishable experimentally from the more popular >variant of quantum mechanics that talks about wave functions >collapsing. Then why is Many-Worlds interesting? Indeed, Many-Worlds >is less a theory than an argument that some of the conventional >postulates of quantum mechanics are not fundamental. What do you mean, "some of the ... not fundamental". And why is it important to argue that point? > Many working >physicists will, if you ask them, express doubt as to whether quantum >mechanics is really applicable to cats and such. And one interpretation of QM has it that it doesn't, because macroscopic objects like cats and such involve entropy (i.e. when the cat dies, entropy is increased, thus an irreversible process has taken place). Why should I prefer the Many Worlds view to this view? (Or, if you don't think we have to choose a single view: why should I even *bother* with the Many Worlds view.) >On the other hand, it is often suggested that quantum mechanics is >incomplete. The problem is that the rules for how a system changes >state when it is measured seem to be central features of quantum >mechanics, and yet these rules make explicit reference to measurement, >as if the observer played a distinguished role in the universe. This >difficulty motivates much crackpot physics. Yeah, the "Copenhagen Interpretation", but there's a similar view (which I just described) that does not give comfort to the crackpots. On the "incompleteness" charge -- I assume you refer to the EPR thought- experiment -- how does the Many Worlds view answer the misgivings of EP&R? How about the Bell theorem (does that pose any problem for the Many Worlds view)? > Ken Rimey > rimey@dali.berkeley.edu --Paul V Torek, umcp-cs!flink P.S. Sorry for the tone of some questions, but I'd really like to get to the bottom of the business of interpreting QM.
rimey@ernie.BERKELEY.EDU (Ken &) (01/13/86)
> Many moons ago, Ken Rimey posted an explanation/endorsement of the Many > Worlds interpretation of QM. I tried to mail to him, but no luck. I > noticed he's still around today, so here's my reply: > > >You may have noticed that, in describing a theory in which the > >universe is deterministic and measurement is not a fundamental > >idea, I sure refer to measurement and probability a lot. The > >point is that these ideas are involved only in the interpretation > >of the mathematical object that represents the state of the universe. > >They don't clutter up the theory of how to calculate that object. > >In particular, in the Many-Worlds view, wave functions don't "collapse". > > Then what do measurements measure, in the Many-Worlds view? Are "position" > and "momentum" fictions? Nothing different. See the following quote. > >Many-Worlds is indistinguishable experimentally from the more popular > >variant of quantum mechanics that talks about wave functions > >collapsing. Then why is Many-Worlds interesting? Indeed, Many-Worlds > >is less a theory than an argument that some of the conventional > >postulates of quantum mechanics are not fundamental. > > What do you mean, "some of the ... not fundamental". And why is it > important to argue that point? What I mean is that it is unnecessary to postulate that wave functions collapse during measurements. Measurements are ordinary physical interactions of matter with matter, and are adequately described by ordinary equations of motion. The reason to argue this point is to clarify that quantum mechanics does NOT indicate that "observers" play a special role in the laws governing the universe. > > Many working > >physicists will, if you ask them, express doubt as to whether quantum > >mechanics is really applicable to cats and such. > > And one interpretation of QM has it that it doesn't, because macroscopic > objects like cats and such involve entropy (i.e. when the cat dies, entropy > is increased, thus an irreversible process has taken place). That is not an interpretation of QM. It is simply wrong. > On the "incompleteness" charge -- I assume you refer to the EPR thought- > experiment -- how does the Many Worlds view answer the misgivings of > EP&R? How about the Bell theorem (does that pose any problem for the > Many Worlds view)? > > > Ken Rimey > > rimey@dali.berkeley.edu > > --Paul V Torek, umcp-cs!flink No, the analysis of these thought experiments is independent of whether you use the Many-Worlds viewpoint or not. Ken Rimey
kort@hounx.UUCP (B.KORT) (01/14/86)
Perhaps my level of understanding is a bit naive, but don't the wave equations encode our state of knowldege (uncertainty) about the state of affairs prior to measurement? Also, don't we have the basic problem that measurement involves interacting with the thing being measured, thereby perturbing it from its state prior to measurement? When the probability wave collapses (e.g. by peeking inside the box to peer at Schroedinger's cat), aren't we simply experiencing a quantum jump in our state of knowledge (a discrete reduction in uncertainty)? Isn't our state of knowledge merely the cumulative result of bits of information coming in through the sensory channels linking our knowldege reservoirs to the location of measurement events? If this view is sound, then the wave equation is not so much a description of what's "out there" as it is a description of "what we know" about that which is "out there." -- Barry Kort ...ihnp4!houxm!hounx!kort A door opens. You are entering another dementia. The dementia of the mind.
rimey@ernie.BERKELEY.EDU (Ken &) (01/16/86)
In article <501@hounx.UUCP> kort@hounx.UUCP (B.KORT) writes: >Perhaps my level of understanding is a bit naive, but don't >the wave equations encode our state of knowldege (uncertainty) >about the state of affairs prior to measurement? Also, don't >we have the basic problem that measurement involves interacting >with the thing being measured ... ? When the probability wave >collapses ... aren't we simply experiencing a quantum jump in >our state of knowledge? ... >If this view is sound, then the wave equation is not so much >a description of what's "out there" as it is a description of >"what we know" about that which is "out there." > > -- Barry Kort > ...ihnp4!houxm!hounx!kort Well said, but I don't think it's true. Consider a lone free particle. In general, we don't know where it is, so we invent a wave function to give the probabilities of it being here or there. But in the real world, this wave function does not behave as if it described a distribution of hypothetical positions of a classical particle. Instead: 1. It's evolution in time is entirely self-determined. There is no "velocity" that can be specified independently of position. 2. The values of the wave function are complex numbers who's squared magnitudes are the aforementioned probabilities. As the wavefunction evolves, it can destructively interfere with itself. If quantum mechanics did nothing but quantify our ignorance about what we are looking at, how would it explain, say, the discrete energy levels of atoms? Ken Rimey rimey@dali.berkeley.edu ucbvax!rimey