If beyond the slits there is a fluorescent screen, we can easily calculate what the quantum state "at the screen" will look like: It will have the peaks and troughs characteristic of interfering water waves.įinally comes the interaction with the screen. If the electron is shot at a screen with two slits in it, then the quantum state will behave similarly to a water wave that hits such a barrier: circularly expanding waves will emerge from each slit, and there will be constructive and destructive interference where those waves overlap. In the case of the electron mentioned earlier the dynamical equation is relevantly similar to the dynamical equation for water waves, so we can visualize the quantum state as a little plane water wave moving in a certain direction. These equations have names like the Schr ödinger equation (for nonrelativistic quantum mechanics) and the Dirac equation (for relativistic quantum field theory). The second part of the mathematical apparatus is a dynamical equation that specifies how the quantum state changes with time so long as no observation or measurement is made on the system. The wave function for the electron is "spread out" in space. But for the moment, this simple visualization works. Although this visualization works for a single particle, it does not work in general, so care must be taken.
In the case of a single particle it is common to visualize this wave function as one would a water wave: as an object extended in space. For example, if one prepares in the laboratory an electron beam with a fixed momentum, then the quantum state of each electron in the beam will be something like a sine wave. If one is doing an experiment or observing something, one must first associate a mathematical quantum state or wave function with the system under observation.
#QUANTUM PHYSICS DEFINITION HOW TO#
To illustrate the second point, we have the equally oft-cited remarks of Niels Bohr, "Anyone who says that they can contemplate quantum mechanics without becoming dizzy has not understood the concept in the least," and of Richard Feynman, " have always had (secret, secret, close the doors!) we always have had a great deal of difficulty in understanding the world view that quantum mechanics represents." How could both of these circumstances obtain?įor the purposes of making predictions, quantum theory consists in a mathematical apparatus and has clear enough rules of thumb about how to apply the mathematical apparatus in various experimental situations. To take an oft-cited example of the first point: The theoretically calculated value of the anomalous magnetic moment of the electron using quantum electrodynamics matches the observed value to twelve decimal places, arguably the best confirmed empirical prediction ever made.
Quantum mechanics has the distinction of being considered both the most empirically successful and the most poorly understood theory in the history of physics.
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