A post on the
ASP.NET forums recently went a little crazy by shifting from a
perfectly normal question on how to get the response
object from a class that doesn't derive from Page or
Control (to which the answer is to use
HttpContext.Current.Response) to quantum mechanics and
the multiverse theories.
I happen to know a few things on quantum mechanics,
dating back from my PhD, so I can shed some light on
these subjects (or make them even more obscure, we'll
see).
Here are a few things that have been said in
this thread
and a few comments:
"Light will act like a wave until observed, at which
time it collapses to a point."
It would be more precise to say a photon, or quantum
of light, that is, the minimum quantity of light you
can get.
"wherever an elemental "decision" is made (whether the
light went through the top or bottom hole of the
twin-hole experiment; or whether Schrodinger's cat is
alive or dead), the universe splits to accommodate
both decisions."
That was the original idea of the multiverse, but
we'll see that there may be a much better and simple
explanation.
"Another "solution" to the riddle proposed by
Schrodinger's cat is the idea that light travels
backwards in time, just as it travels forward."
For that to solve any problem, all particles would
have to be able to travel back in time: light is not
the only way to transmit information. As a matter of
facts, virtual particles are able to travel faster
than light, but there's no way to observe these
directly, so they can't convey any information. As far
as we know, no faster than light phenomenon can
transport any information. Another way to say that is
that no signal can travel faster than light. If it
travels faster than light, it's not a signal. One
example uses a pulsar as a beacon: the pulsar sends a
jet of particles in some direction which rotates with
the pulsar (like a beacon). Imagine now some enormous
projection screen (interstellar gas clouds play this
role very well) that is able to emit some light when
the particle jet hits it. If the screen is far enough
from the pulsar, the spot of light it projects on the
screen can move well above the speed of light (its
speed is the angular rotation speed of the pulsar
times the distance from it to the screen). The
explanation is that the spot of light you see at one
point in time was not created by the same particles as
a little later. In other words, what you see is not an
object moving, what you see is a succession of
different objects that give the illusion of movement
(the real movement is perpendicular to the screen,
whereas the one you think you see is parallel to it).
A similar phenomenon gives the illusion that a
particle can quantum-tunnel through a barrier faster
than light. It's a little trickier to explain but in
this case too, no faster than light signal can be
transmitted.
"I know that the multiverse theory has moved on from
that, and rather than splitting universes there are
now bubbling multiverses and virtual multiverses"
True, now it's a completely different theory, based on
string theory. It states that there is only one
universe (which is the definition of the universe
after all) that has different, causally disconnected
regions in which the laws of physics are different.
These new "bubbles" can appear when a region of an
existing bubble tunnels into a state with a lower
vacuum energy, which results in the rapid expansion of
this bubble as the extra energy is transformed into
space, so fast that it disconnects it from the bubble
that formed it. There's
an excellent article
about that in the
September issue of
Scientific American.
"I mean Schrodinger was trying to explain the role of
the observer in deciding the quantum state of a
particle. In his experiment he assumed that the only
observer was the experimenter that opened the box -
until the box was opened the particle was 'in' a state
of quantum uncertainty. But, what I always say when
someone mentions the experiment - what about the
cat???!!! Surely, it knows whether it is alive or
dead!"
Absolutely, this is what makes Schrödinger's cat
thought experience completely bogus as it's usually
told: the cat is an observer and is classic enough to
collapse the particle's state. It's never half-dead,
half alive.
But there are real Schrödinger's cats that actually
fulfill exactly the original prediction. The
difference is that they are not cats, but rather small
lumps of matter. Scientists are now able to make these
lumps bigger and bigger, but it will always be
impossible to do the experiment with an actual cat.
What happens when you measure a quantum phenomenon has
been fascinating since it was discovered, more than
any other aspect of quantum physics. The reason is
clearly that it is the only case in modern physics
where pure chance seems to have a role: it looks
undeterministic. Of course, this has been hastily
interpreted by many as the finger of God, or as what
enables us to have free will. I'll get back to that as
soon as I've exposed a more modern theory of quantum
measurement that seems to give very good results while
making it all deterministic again. I can't find the
references of papers about this so I'll rely on my
memory here. If someone reads this and knows where to
find the relevant papers, please drop me a note.
The idea is that a measurement device is a quantum
system (like everything) that has many degrees of
freedom and that a measurement is actually a complex
interaction with such an object. What happens is that
this interaction results in the quantum object to
collapse into a classical state. This theory is able
to predict the time that it takes the object to
collapse, and how complex an object has to be to cause
the collapse. Experimental data seems to confirm this
theory (I think the experiments were done at the Ecole
Normale Supérieure de Paris).
So according to this theory, there is nothing strange
or random in a measurement, it's just one quantum
interaction like everything. In a way, the chaos of
the state of the device replaces chance. And
everything is deterministic again.
Including the human brain.
So where does that leave our freedom of choice? Well,
we would have none, obviously, if we are made of
quantum particles like the rest of the universe. But
that's not a problem, the illusion of it is enough.