On 23-Dec-08 22:01, Warp wrote:
> andrel <a_l### [at] hotmailcom> wrote:
>> On 23-Dec-08 19:27, stbenge wrote:
>>> Darren New wrote:
>>>> Shay wrote:
>>>>> 1. The universe is made of particles which behave in predictable ways.
>>>> Errr, no. The particles behave in ways that are only statistically 
>>>> predictable.
>>> Particles are individually unpredictable (to us) because we still do not 
>>> have a complete understanding of physics. Very tiny particles may appear 
>>> to do random things, but until we have determined the what the smallest 
>>> particle is -- the true quanta -- we can't say for certain that truly 
>>> random events actually happen. They look random to us because of our 
>>> incomplete understanding.
> 
>> That looks suspiciously as if you believe in a hidden variable type 
>> theory. I think it was proven that reality has no underlying hidden 
>> variables. It is however some time ago that I did really study physics 
>> and reading http://en.wikipedia.org/wiki/EPR_paradox it is clear to me 
>> that I need a refreshing course.
> 
>   If I'm not mistaken, the currently most accepted theory is that it's
> *impossible* to predict certain quantum phenomena exactly. And this
> "impossible" doesn't mean "we don't yet have the technology to do it",
> but "there's a feature of the universe which simply makes it impossible".

To be somewhat precise: Bell's theorem says that *if* there is a local 
variable that we don't know (yet) but that does determine the state of 
the system and what we see is only statistical because we have not the 
equipment (yet) to measure it exactly *then* a certain measurement will 
on average never exceed a certain value. If however the uncertainty is 
more fundamental than that, i.e. if really is as absurd as quantum 
mechanics predicts then that value can be higher than that value.
People done the experiment and within experimental errors the 
measurements agree with QM and either there is no local hidden variable 
or Bell is wrong (i.e. one has to prove that Bell used an faulty axiom).

As I said reading that EPR piece on wikipedia it might be tiny bit more 
complicated than that. But probably the above is good enough for any 
non-specialist.

>   Theories can be wrong, of course (luminiferous aether anyone?), but
> as long as we don't have evidence of the contrary, we have to assume that
> that is how things work.

Bell's theorem is much more solid than that even. Then again it is a 
theorem not a theory.

>   As a side note, I find it amusing (and in some ways a bit sad) that some
> people seem to think that physics is about belief. They will say something
> like "I don't believe that black holes really exist", or "I can buy black
> holes, but I don't believe in singularities", or "I don't believe that c
> is the maximum achievable speed". And mind you, this by people who only
> have rudimentary layman-level knowledge about physics.

Or: I don't believe that the universe is so weird that we really can't 
measure the spin of a particle. Surely the equipment can be improved 
somehow someday (sorry sam ;) )

Or: we don't know what conscience is and we can't predict what the spin 
of a particle will be, so these things must be related (sorry new agers 
out there ;) )

>   Physics is not about belief. Physics is not about people trying to
> sell you ideas, and you believing them or not, depending on whether you
> find those ideas plausible and logical or not.
> 
>   Perhaps a bit counter-intuitively, physics is not about the "truth".
> Religions sell you the "truth", physics (and science in general) doesn't.
> What physics is all about is determining how the Universe works by measuring
> what can be observed and formulating scientifically sound postlates based
> on those measurements. Physics doesn't try to "sell" you anything. Physics
> simply tells you what we have found so far, with the technology and knowledge
> we currently have. It's not a question of belief. It's about what we know
> currently. (What we know may be partially false, but that's not really the
> point. If it's false, then new evidence and new measurements will eventually
> tell us so, so we can update what we know.)
> 
>   In other words, physics doesn't tell you "this is the truth". Physics
> tells you "this is what we currently know". You not believing it has zero
> effect on the fact for as long as you can't provide any evidence of the
> contrary. (If you can, then usually expect a Nobel prize, or at least
> worldwide recognition.)

Often even, like in the case of QM, the only claim is that if you follow 
the procedures you will arrive at a value that is close to what can be 
measured. In other words, we don't even pretend to know or understand 
anything at all.

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