In contrast to the arbitrarily complicated evolution of a (nonintegrable) classical system, all a quantum state ever does is move in circles.
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FQXi Prize winning essay What if Time Really Exists?, 2008.Sean M. Carroll
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Does life in some way make use of the potentiality for vast quantum superpositions, as would be required for serious quantum computation? How important are the quantum aspects of DNA molecules? Are cellular microtubules performing some essential quantum roles? Are the subtleties of quantum field theory important to biology? Shall we gain needed insights from the study of quantum toy models? Do we really need to move forward to radical new theories of physical reality, as I myself believe, before the more subtle issues of biology — most importantly conscious mentality — can be understood in physical terms? How relevant, indeed, is our present lack of understanding of physics at the quantum/classical boundary? Or is consciousness really “no big deal,” as has sometimes been expressed?
It would be too optimistic to expect to find definitive answers to all these questions, at our present state of knowledge, but there is much scope for healthy debate...Roger Penrose
The Schrödinger equation, which is at the heart of quantum theory, is applicable in principle to both microscopic and macroscopic regimes. Thus, it would seem that we already have in hand a non-classical theory of macroscopic dynamics, if only we can apply the Schrödinger equation to the macroscopic realm. However, this possibility has been largely ignored in the literature because the current statistical interpretation of quantum mechanics presumes the classicality of the observed macroscopic world to start with. But the Schrödinger equation does not support this presumption. The state of superposition never collapses under Schrödinger evolution.
Ravi Gomatam
Two features of QT are commonly taken to be fundamentally non-classical: the absolute randomness of single events in the atomic regime, and the need for a permanent record of the experiment obtained using a macroscopic experimental arrangement…QT can also be applied to the larger system consisting of the original atomic system plus the macroscopic experimental arrangement. In this case, however, the larger system needs to interact with another stage of macroscopic recording. Since this procedure can continue ad infinitum, and is decisively terminated only when the result of an experiment is interpreted by a conscious observer, some noted quantum theorists have promoted the view that the quantum theory has some nexus with the consciousness of the observer...
Ravi Gomatam
It seems to me that we must make a distinction between what is "objective" and what is "measurable" in discussing the question of physical reality, according to quantum mechanics. The state-vector of a system is, indeed, not measurable, in the sense that one cannot ascertain, by experiments performed on the system, precisely (up to proportionality) what the state is; but the state-vector does seem to be (again up to proportionality) a completely objective property of the system, being completely characterized by the results it must give to experiments that one might perform.
Roger Penrose
Certainly we do not need quantum mechanics for macroscopic objects, which are well described by classical physics – this is the reason why quantum mechanics seems so foreign to our everyday existence.
Alain Aspect
Carroll, Sean M.
Carroll, Tom
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