10 Greatest Ideas in the History of Science
Classical Mechanics Fails to Describe Small Particles

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‹‹ Symmetry Quantifies Beauty The Universe Is Expanding ››

The classical physics of Isaac Newton and James Clerk Maxwell work reasonably well for most everyday applications. But classical physics is limited in the sense that it does not quite accurately depict reality.

The first inkling that something was seriously wrong came from analysis of blackbody radiation. Imagine a hot stove: It first starts out red, then turns white as it gets hotter. Classical physics was incapable of explaining this. Max Planck, however, had an idea: Perhaps the released energy came in little packets called "quanta." Instead of energy taking on continuous values, it instead takes on only discrete values. (Think of the difference between a ramp and a staircase; a person standing on a ramp can take on any height, while a person standing on a staircase only has certain discrete heights from which to choose.) As it turns out, these "quanta" of light energy are today known as photons. Thus, it was demonstrated that light, which until that time generally had been thought of as a wave, could also act like discrete particles.

Then along came Louis de Broglie who extended the concept: All particles can act like waves, and all waves can act like particles. Slam-dunk evidence for this idea came by way of the famous double-slit experiment, which conclusively showed that photons, electrons and even molecules like buckyballs exhibit wave-particle duality. (A lab confirmed the results of this experiment yet again in May 2013.)

These two concepts, quantization and wave-particle duality, form the core of the discipline known as quantum mechanics. Two other core concepts include the uncertainty principle (i.e., the inability to know various pairs of characteristics of a system with precision) and the wavefunction (which, when squared, gives the probability of finding a particle in a particular location). And what does all that give us? Schrödinger's cat, which is simultaneously dead and alive.

No wonder Stephen Hawking always reaches for his gun.

Source: Galileo's Finger: The Ten Great Ideas of Science by Peter Atkins

Image: Epzcaw/Wikimedia Commons

‹‹ Symmetry Quantifies Beauty The Universe Is Expanding ››

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