On Fri, Nov 21, 2014 Bruno Marchal <[email protected]> wrote: >> Yes the Schrodinger Wave Equation is easily reversible (and it's >> continuous and deterministic too), but with regard to the reversibility of >> time that's a irrelevant fact because the SWE is a unobservable >> abstraction. >> > > > To be sure I was reasoning assuming the usual non relativistic SWE. Then > it is reversible in the same unitary sense that quantum computer gates are > reversible, which includes the usual notion of time. >
That is incorrect because computer gates are observable but the SWE, both relativistic and non relativistic, are unobservable, only the square of the wave is observable and then only as a probability. So the SWE may be reversible but it's square is not; if 4 is the product of two integers there is no way to know if they were 2 or -2, so you can't reverse things and find the previous probability, much less get back into the actual previous state with 100% certainty. John K Clark > > > > > To get something real that you can actually see > > > I am a platonist. If I see something, I very much doubt it is real ... > > > > > > you must square the amplitude of the SWE of a particle at a point and that > will give you the probability you will observe the particle at that point, > and probability, unlike the SWE, is something that you can observe and > measure. > > > Only from a first person perspective. It is psychologically real, but that > does not exist at the ontological level (that is the spirit of both > computationalism and Everett's QM). > > > > And Schrodinger's equation has complex values, that means it has a "i" > (the square root of -1) in it, and that means very different quantum wave > functions can give the exact same probability when you square it; and if X > and Y both produce Z then things are not reversible, if you're in state Z > there is no way to know if the previous state was X or Y. > > > There are equivalent up to a global phase factor. > > > > You get all sorts of strange stuff with i, like i^2=i^6 =-1 and > i^4=i^100=1. And in the macroscopic non quantum world if the probability > of me flipping a coin and getting heads is 1/2 and the probability of you > flipping a coin and getting heads is 1/2 then the probability of both you > and me getting heads is 1/4, but in Quantum Mechanics that's not > necessarily true because now you must deal with i and complex numbers. I > think you could say that mathematically it's the existence of that damn i > in the SWE that makes Quantum Mechanics so weird. > > > I am not so sure. I am actually teaching quantum computation, mainly to > illustrate quantum weirdness and the many-worlds, and I can manage to do > that without using complex numbers. (the audience is not all well versed in > mathematics). The real Pauli matrices (sigma_x and sigma_z) are enough. > That is not new, David Albert does the same in his little book "QM and > experience". > > I am forced to consider the wave as real (ontologically), because it > interferes even when I don't look at it (especially if I don't look at it > actually), so that when I want to "measure" the probability (by taking the > square of the amplitudes) I get the correct numbers. > > Bruno > > > > > John K Clark > > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > > > http://iridia.ulb.ac.be/~marchal/ > > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
