In article <XcHUi.153401$%k.295389@twister2.libero.it>,
scerir@libero.it says...
> "Gerry Quinn"
> > So, what precisely is the measurement protocol he is using to make wave
> > or particle like measurements on the particles constituting each beam?
> > Has anyone got a link, because the article doesn't say, and googling
> > failed to find anything? If we knew that, we could write down the sort
> > of statistics we would expect from a successful 'bilking' experiment,
> > and perhaps that would considerably elucidate the situation (most
> > likely by proving that bilking is actually undetectable).[/color]
>
> Only this one
>
http://faculty.washington.edu/jcramer/Nonlocal_2007.pdf[/color]
Thanks!
> As far as I remember (?) you need few photons (something
> like 50 or less) to realize if it is a diffraction
> pattern or an interferential one. But you also need
> a very clean source of entangled photons imo.
>
> There is an interesting paper here
>
http://www.arxiv.org/abs/quant-ph/0506027
> about that 'bilking' or, to say it better,
> once the future has unfolded, it cannot change
> the past.[/color]
Yes. I find the argument quite convincing. It does raise some
interesting questions with regard to quantum computation.
The authors propose that you cannot go back in a time machine and shoot
your father because, essentially, the observation of your own existence
demands that a chain of events, no matter how unlikely, led up to it.
If you try to do it, you will perhaps shoot someone you think is your
father but actually isn't, or your gun will misfire, or some such
possibility.
>From now on I will revert to the traditional experiment of shooting[/color]
your grandfather, as it somehow seems less brutal than simple
patricide. Anyway, I propose the Grandfather Computer (TM),
constructed using a grandfather, a time machine, pen and paper, and a
deadly weapon of some kind.
You travel back in time, locate your grandfather, and demand that, on
pain of death, he write down the answer to some difficult computation,
say the factors of a large number (incidentally, you don't need to tell
him the number). If you have so arranged matters that this is the only
remotely possible way he could survive, it seems like a way to leverage
the evolution of the wave function of the universe to carry out this
computation; in short, it is a form of quantum computer.
Probably the flaw in the this scheme is the difficulty of actually
removing all feasible alternative courses of events that will lead to
your grandfather's, and thus your, survival. In reality it will not be
possible to remove all low-probability events (weapon malfunction,
mistaken identity, a random police visit, etc.) that will still be much
more likely than his correctly guessing the answer to the computation.
I wonder if this argument can be extended to investigate the
possibility of quantum computation in general. While I know that
devices have been built that are technically working quantum computers,
there are none that can do general computations that are not feasible
by other means. For example, the system using caffeine molecules needs
a lot of molecules, and does not perform better in practice than a
classical molecular computer based on simple parallel computation.
My feeling is that quantum computation as usually advertised is also a
sort of 'bilking' attempt, albeit not exactly in the same sense as
Cramer's experiment. It might be that both forms of bilking are
impossible, and that the reasons are related. Ways in which you might
be born despite your grandfather not solving the computation are the
equivalent of errors in typical quantum computation schemes. Both can
be seen as resistance on the part of the wave function of the universe
to being squeezed into a very narrow range of selected outcomes after a
considerable amount of complex unitary evolution.
- Gerry Quinn