Quantum Physics: rethinking the microscopic world

The development of the Quantum Theory

Origins of the Quantum Theory

The Photoelectric effect

Atomic Models from Aristotle to Schroedinger

Heisenberg Uncertainty Principle

Schroedinger's cat

Quantum tunneling and other useful quantum effects

Differences between quantum physics and classical physics

Classical physics embraces determinism, the notion that everything is preordained by that which came before and that there are laws that can always state with certainty the results of certain actions.

Quantum physics is the essence of uncertainty: not only are both future and past indeterminate and malleable, even the present is uncertain and sometimes unknowable. Sometimes particles zig, sometimes they zag -- and nobody can say when or why or what shall come of it.

To classical physicists, things are either possible or impossible; to quantum physicists, everything is some shade of probability, and anything is possible if done fast enough.

Classical experiments are infinitely repeatable; identical conditions always yield identical, observable results. With quantum experiments, identical conditions are impossible to measure accurately and only probability determines the results, which cannot be observed without somehow being altered.

Reality, in classical physics, is outside, the ultimate frame against which anything can be observed objectively; in quantum physics, reality changes constantly, and objective observations are not possible.

In classical physics we can imagine ourselves outside of nature but our actions are nonetheless bound by determinism; in quantum physics we are intricately connected to nature and thereby gain freedom of choice.

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Humerous interlude

Snow White and the Seven Quarks

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So, what's it all mean?

Opinions vary on the overall meaning of quantum physics. Here are four interpretations:

The Copenhagen Interpretation

The observer's mind is what collapses the wave function; science is not about what nature actually is but what we know about it. Thus Schroedinger's cat neither lives nor dies until the watching human mind registers its state.

The Princeton Interpretation:

The human mind creates reality; the universe happened the way we see it now because we are here to observe it.

The California Interpretation:

Every time a particle could either zig or zag it does both, creating infinitely many infinitely diverging worldlines. If we cultivate our ESP, we can consciously determine which way an event happens on our worldline.

And last but not least, the unofficial Feynman interpretation:

The rules of nature are hard enough to determine as it is; we should not be so arrogant as to presume that they make sense to us as well.

Back to the Physics Multiverse

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