punkypink (imported) wrote: Fri Dec 16, 2011 6:51 am
It's amazing stuff. Although I do remember reading somewhere that in quantum mechanics, just the act of observing what happens, causes reality to change. Will that be a factor?
It's not so much that measurement (observing) causes reality to change on the quantum level, there is no reality without observation. A particle, an electron for instance, only exists as a probability wave until it is observed. If that there is no reality on the quantum level until a measurement is made blows your mind, don't feel bad. Even Einstein resisted this idea, but it has consistently been proved through experimentation.
The Heisenberg uncertainty principal says that one can never know both the location and velocity of a particle. If one measures its location, one cannot know its velocity, while if one knows its velocity, one cannot know its location. A hydrogen atom consists of one proton and one electron, but that electron isn't a single electron whirling around the nucleus, as atoms were pictured when I was a kid. It exists as an electron cloud of possibilities until it is measured.
Albert Einstein (
http://en.wikipedia.org/wiki/Albert_Einstein), himself one of the founders of quantum theory, disliked this loss of determinism in measurement (
http://en.wikipedia.org/wiki/Bohr-Einstein_debates). (A view paraphrased as "God does not play dice with the universe.") Einstein held that there should be a local hidden variable theory (
http://en.wikipedia.org/wiki/Local_hidd ... ble_theory) underlying quantum mechanics and that, consequently, the present theory was incomplete. He produced a series of objections to the theory, the most famous of which has become known as the Einstein-Podolsky-Rosen paradox (
http://en.wikipedia.org/wiki/Einstein-P ... en_paradox). John Bell (
http://en.wikipedia.org/wiki/John_Stewart_Bell) showed that the EPR paradox led to experimentally testable differences (
http://en.wikipedia.org/wiki/Bell%27s_theorem) between quantum mechanics and local realistic theories. Experiments (
http://en.wikipedia.org/wiki/Bell_test_experiments) have been performed confirming the accuracy of quantum mechanics, thus demonstrating that the physical world cannot be described by local realistic theories.[40] (
http://en.wikipedia.org/wiki/Quantum_me ... te_note-39) The Bohr-Einstein debates (
http://en.wikipedia.org/wiki/Bohr-Einstein_debates) provide a vibrant critique of the Copenhagen Interpretation from an epistemological (
http://en.wikipedia.org/wiki/Epistemological) point of view.
The Everett many-worlds interpretation (
http://en.wikipedia.org/wiki/Everett_ma ... rpretation), formulated in 1956, holds that all the possibilities described by quantum theory simultaneously occur in a multiverse (
http://en.wikipedia.org/wiki/Multiverse) composed of mostly independent parallel universes.[41] (
http://en.wikipedia.org/wiki/Quantum_me ... te_note-40) This is not accomplished by introducing some new axiom to quantum mechanics, but on the contrary by removing the axiom of the collapse of the wave packet: All the possible consistent states of the measured system and the measuring apparatus (including the observer) are present in a real physical (not just formally mathematical, as in other interpretations) quantum superposition (
http://en.wikipedia.org/wiki/Quantum_superposition). Such a superposition of consistent state combinations of different systems is called an entangled state (
http://en.wikipedia.org/wiki/Entangled_state). While the multiverse is deterministic, we perceive non-deterministic behavior governed by probabilities, because we can observe only the universe, i.e. the consistent state contribution to the mentioned superposition, we inhabit. Everett's interpretation is perfectly consistent with John Bell (
http://en.wikipedia.org/wiki/John_Stewart_Bell)'s experiments and makes them intuitively understandable. However, according to the theory of quantum decoherence (
http://en.wikipedia.org/wiki/Quantum_decoherence), the parallel universes will never be accessible to us. This inaccessibility can be understood as follows: Once a measurement is done, the measured system becomes entangled (
http://en.wikipedia.org/wiki/Quantum_entanglement) with both the physicist who measured it and a huge number of other particles, some of which are photons (
http://en.wikipedia.org/wiki/Photon) flying away towards the other end of the universe; in order to prove that the wave function did not collapse one would have to bring all these particles back and measure them again, together with the system that was measured originally. This is completely impractical, but even if one could theoretically do this, it would destroy any evidence that the original measurement took place (including the physicist's memory).
In 1925, following pioneering work with Hendrik Kramers (
http://en.wikipedia.org/wiki/Hendrik_Kramers), Heisenberg developed matrix mechanics (
http://en.wikipedia.org/wiki/Matrix_mechanics), which replaced the ad-hoc old quantum theory (
http://en.wikipedia.org/wiki/Old_quantum_theory) with modern quantum mechanics. The central assumption was that the classical concept of motion does not fit at the quantum level, and that electrons (
http://en.wikipedia.org/wiki/Electrons) in an atom did not travel on sharply defined orbits. Rather, the motion was smeared out in a strange way: the Fourier transform (
http://en.wikipedia.org/wiki/Fourier_transform) of time only involving those frequencies that could be seen in quantum jumps.
It's not just that the physical restrictions of our measuring devices prevent us from measuring both the position and velocity of an electron, it's that an electron never possesses both in the manner we would think from a classical concept of motion. In other words, one cannot think of an electron as a ball traveling on a particular path.
