We can't easily measure its position, but by noting the time of exposure and measuring the streak, we can tell how fast it's going. We can take a picture with a normal camera, and see a streak on the film where it passes. Whenever we measure a particle, we always (by definition) use some sort of filter that gives us the position and velocity of the particle to some degree, and these degrees of error are inherently dependent on each other.Īnother way to see it: Think of a photograph of a bullet in flight. And where a step function tells you something about magnitude, it is homogeneous over time, and cannot be pinned down anywhere. The problem is that while a pure impulse is accurate in position, its area is indeterminate. When you take the velocity, it looks like a step function. When you take the position of your particle, it looks like an impulse. And since people use oscilloscopes to measure this stuff anyway, it's probably pretty close to the truth. I found that an explanation based on control systems helped me the most. The HUP also explains why a transporter will never work (though those tricky people at Star Trek mention something about a Heisenberg Compensator. Now, instead of classical determinism, we can do no better than quantum determinism - meaning if it's at all possible to write such equations then they will have to come in the form of the probabilities where particles could be. But Uncertainty broke down the movement of particles to probability functions (known as wave functions). In the Newtonian world, it was still possible that the grand equation for all particles could be written out starting at the beginning of time and and tell exactly what things would be like in the future : determinism. At least not in my house ( young man!).)Īs for the Romantics, though Heisenberg didn't begin the Downfall of Scientific Method, he did, however, end classical determinism. The effect is symmetrical so attempting to measure velocity we'll naturally affect direction (roughly equivalent to the seed bouncing off your knife or something - though I don't think tomato seeds ever reach such high velocities. In other words, the measurement of position directly affects velocity (being speed and direction). Well, what happens, as soon as you locate their position ( you poke 'em) they start to move. Let's say that tomato seeds are our metaphorical particles and in order to determine their position you must touch them with your knife. The best metaphor I've heard for the HUP is: tomato seeds. The overall distribution shown at the bottom can be predicted as the diffraction of waves having the de Broglie wavelength of the electrons (CC BY 4.0 OpenStax).*giggle*. 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 (Figure 1.9.1 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. Heisenberg made the bold proposition that there is a lower limit to this precision making our knowledge of a particle inherently uncertain. Newtonian physics placed no limits on how better procedures and techniques could reduce measurement uncertainty so that it was conceivable that with proper care and accuracy all information could be defined. Until the dawn of quantum mechanics, it was held as a fact that all variables of an object could be known to exact precision simultaneously for a given moment. The Heisenberg Uncertainty Principle is a fundamental theory in quantum mechanics that defines why a scientist cannot measure multiple quantum variables simultaneously. In 1927 the German physicist Werner Heisenberg described such limitations as the Heisenberg Uncertainty Principle, or simply the Uncertainty Principle, stating that it is not possible to measure both the momentum and position of a particle simultaneously. However, this possibility is absent in the quantum world. In classical physics, studying the behavior of a physical system is often a simple task due to the fact that several physical qualities can be measured simultaneously.
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