AI and cognitive psychology rant (getting more and more OT - tell me if I should shut up)
mis6 at pitt.edu
Sun Nov 2 18:46:18 CET 2003
Stephen Horne <steve at ninereeds.fsnet.co.uk> wrote in message news:<l4h9qvgon62pdf3fem1i5974v35t1r3u97 at 4ax.com>...
> Superfluid helium is a macroscopic phenomenon - it may be explained in
> terms of QM effects, but that doesn't make it a quantum effect in
> itself any more than more everyday macroscopic effects (which can also
> be described in QM terms). If superfluid helium is your only clue, it
> will tell you no more about quantum effects than e.g. lightening tells
> you about the properties of an electron.
It is true that superfluidity is described by an effective field theory
which is not directly related to the properties of a single electron;
but still it is a (non-relativistic) *quantum* field theory, so the fact
that it is "quantum" is relevant. Things are different in ferromagnets,
for instance, where a lot of properties can be derived from classical
very unrealistic models (such as the Ising model) due to the universality
property. But not ALL properties. Anyway, I do understand that you have
in mind quantum effects related to the wave function collapse, and
I don't think superfluidity is of big help on these issues, so I must
agree with you on that point. Unfortunately :-(
> It was quite a revelation to discover that the physics of the cosmos
> were actually the same physics we experience on the ground.
> The centre of a black hole exists, in a sense, but we can never
> observe it because it is inside the event horizon, and as time itself
> stops at the event horizon (from the perspective of any outside
> observer) there is even good reason for claiming that the space inside
> the event horizon doesn't exist.
> >Michele is a better one for this topic.
It is interesting to notice that the region *inside* the event horizon
is a perfectly physical region and can be relatively well understood.
For instance, an observer can fall inside the horizon and live relatively
well if the black hole is large enough and the tidal forces are small
enough; we can perfectly compute how much time s/he will live and what
s/he will see. It is true that external observers cannot see the poor guy
enter in the black hole, because of the infinite time dilatation, but
this does not mean that the guy does not enter in the black hole, according
to its proper time.
There is only one point (of a set of points if the black hole is
rotating) which we cannot understand, i.e. the singularity.
Near the singularities general relativity fails and we don't know
what happens. It is interesting to notice that Hawking proved
that GR necessarely implies singularities: this means that we know
for sure that GR is certainly not a complete
theory of Physics ;)
> I read a book about string and brane theory some time ago - I guess
> possibly the same one, though it has vanished into book-borrowing
> space as all the best books do so I can't tell you the title.
> Lots of theory about possible geometries and topologies of many
> dimensional space-time and how they could change from one another.
> They didn't address the issue of how they could change at all, given
> that time existed within the geometry rather than outside of it, and
> for that among other reasons my impression was that it was a
> fascinating read that nevertheless left me with no more clue than I
> had to start with.
That's normal ;)
> I would at least have appreciated a definition of supersymmetry,
> rather than the usual 'its too abstract for your puny mind' copout.
Supersymmetry is a much simpler concept than branes or strings:
unfortunately it is still too abstract to explain, unless one has
expertise in quantum field theory :-(
Modern physics is so difficult than you can happily spend your entire
life on a subject such as string theory and never understand it.
That's life !
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