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starship-design: Re: This and That.
The issue you bring up-- about getting information from a particle
without affecting it-- is a good example of some dilemmas in current
quantum theory. As you say, quantum mechanics is a well-established
principle of physics, but it's a well-established principle that will
probably change radically over the next decade or so. We should be
watching developments to see if the forthcoming interpretation allows
any of the ideas we're talking about for spaceship design. My feeling,
though, is that the "new quantum" will turn out to dash a lot of hopes.
Either way, though, the Copenhagen Interpretation is almost assuredly on
the way out.
The first two "Questions" you have about your thought experiment concern
Wave-particle duality, and you're absolutely right that it doesn't make
sense. There are plenty more examples where "wave-particle duality"
leads to all sorts of dilemmas. Whatever new theory of quantum
mechanics emerges, that is one aspect that will almost certainly
disappear. Another thing that will (hopefully!) disappear is the
concept of "collapsing a wave function" - the issue that any measurement
knocks a particle into an "observable" reality. Once this has been
replaced with a new theory, there won't be any conceptual problem with
"measuring" a particle without interacting with it. It merely doesn't
make sense in the current quantum framework-- that's not to say it
doesn't make sense period.
So - how to reformulate quantum without these current problems? It
turns out we'll probably need to replace it with reverse-causality on
the quantum scale. Reverse-causality comes with a lot of its own
problems, namely paradoxes. But there's an elegant theory being batted
around that nature won't allow paradoxes. If there's somehow a
fundamental law of nature that paradoxes are banned, that would finally
draw the line between the quantum (microscopic) and macroscopic world
that physicists have been trying to define for nearly a century.
Strange "Quantum" effects happen when reverse-causality does not lead to
a paradox. If reverse-causality DOES lead to a paradox (i.e. changing
something in the past that has already been determined), you've just
entered the everyday-world regime, and the reverse-causality shuts off.
If correct, these new versions of quantum theory will say something
about the FTL communicator you mentioned (and ANY FTL system) -
Macroscopic FTL means macroscopic time-travel (or at least time-
communication). And macroscopic time-travel means Paradoxes. But if
you can't use quantum effects to make a paradox, then the whole scheme
will fail. There's simply no way around it.
Apart from all this brand-new, unproved theory, I personally don't
believe it's possible to construct a Pure Paradox. From first
principles, a pure paradox is a contradiction of itself, and (for me,
anyway) that in itself proves that paradoxes are impossible. If there
can't be paradoxes, there can't be time-travel, and therefore there
can't be FTL. The only possible way out (besides discounting free will)
is if there are an infinite number of possible universes: an idea I find
very disturbing. I'm not saying FTL's impossible, but there is a
certain intellectual coherence of the concept of reality: the concept
that once something "happens", nothing can change the fact that it did,
in fact, happen. FTL begins to unravel this whole concept of what
reality is, and my confidence in reality is why I'm very skeptical that
anything along those lines will ever be possible.
And if it is, spacetravel will probably be the least of humanity's
I agree with your advice to Kyle; let's tap the ZPE and forget FTL. At
least I can philosophically handle the consequences of stealing energy
from a vacuum.