Consider the double-slit patterns obtained for electrons and photons in. Let us explore what happens if we try to follow a particle. It is somewhat disquieting to think that you cannot predict exactly where an individual particle will go, or even follow it to its destination. Formulated by the German physicist and Nobel laureate Werner Heisenberg in 1927, the uncertainty principle states that we cannot know both the position and speed of a particle, such as a photon or electron, with perfect accuracy the more we nail down the particle's position, the less we know about its speed and vice versa. Those who developed quantum mechanics devised equations that predicted the probability distribution in various circumstances. There is a certain probability of finding the particle at a given location, and the overall pattern is called a probability distribution.
After compiling enough data, you get a distribution related to the particle’s wavelength and diffraction pattern. However, each particle goes to a definite place (as illustrated in ). The idea quickly emerged that, because of its wave character, a particle’s trajectory and destination cannot be precisely predicted for each particle individually. Both patterns are probability distributions in the sense that they are built up by individual particles traversing the apparatus, the paths of which are not individually predictable.Īfter de Broglie proposed the wave nature of matter, many physicists, including Schrödinger and Heisenberg, explored the consequences. The overall distribution shown at the bottom can be predicted as the diffraction of waves having the de Broglie wavelength of the electrons.ĭouble-slit interference for electrons (a) and protons (b) is identical for equal wavelengths and equal slit separations. Each electron arrives at a definite location, which cannot be precisely predicted. ) The building up of the diffraction pattern of electrons scattered from a crystal surface. Repeated measurements will display a statistical distribution of locations that appears wavelike. But if you set up exactly the same situation and measure it again, you will find the electron in a different location, often far outside any experimental uncertainty in your measurement. Experiments show that you will find the electron at some definite location, unlike a wave. What is the position of a particle, such as an electron? Is it at the center of the wave? The answer lies in how you measure the position of an electron.
Matter and photons are waves, implying they are spread out over some distance. Explain the implications of Heisenberg’s uncertainty principle for measurements.
Use both versions of Heisenberg’s uncertainty principle in calculations.
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