We are making the positions of the photons more precise. So, when we are narrowing down the slit, we are narrowing down the possible positions of the photons in the slit. We are narrowing the width of the beam at the slit, which results in narrowing the width of the light received on the screen. Experiments show that if we narrow the slit, at first the light that lands on the screen also narrows.

Let’s consider a laser that shoots its beam through a single slit (see image to left). 5 Example of Heisenberg’s Uncertainty Principle The HUP is not just about our knowledge of atoms. The HUP is a law of nature which makes atoms possible. The quantum particle would fly out of the atom.

If the electron were pinned down to the tiny space of the nucleus rather than the cathedral, its momentum would vary so wildly, due to the HUP, that the positive electrical attraction could not hold it. And why the electron, instead, occupies a space around the nucleus that is analogous to a cathedral when viewed by a grain of salt. He is explaining why the electron does not, in fact, limit itself in position to a small space like the nucleus. While Al-Khalili uses the word “knowing” in his explanation, he is explaining more than our lack of exact knowledge. Quantum particles simply could not be imprisoned inside the nuclei.” 4 This corresponds to its momentum being too erratic for the attractive force of the protons to keep it there for long. “Heisenberg’s uncertainty principle tells us that trapping a quantum particle within the tiny confines of a nucleus would imply knowing its position to high accuracy. He explains why the negatively-charged electron doesn’t fall into the positively-charged nucleus. Jim Al-Khalili, a leading quantum physicist, gives an example of the uncertainty principle at work.

In particular, you must allow that the particle may have large momentum.” (italics per original) (Note: Werner Heisenberg in developing his principle originally addressed position and momentum later his principle was expanded to include properties additional to position and momentum.) In another description of the principle, Wilczek writes, “According to the Heisenberg uncertainty principle, in order to have accurate knowledge of the position of a particle, you must let that particle have a wide spread in momentum. The Nobel Laureate, Frank Wilczek, puts it this way, “According to the original uncertainty principle, to pin down the position accurately we must live with a large uncertainty in momentum. The HUP applies to each individual particle. In summary, we will get different measurements if we measure the momentum first than if we measure the position first. And vice versa: If the position is measured and then, momentum is measured, the position measurement will have been invalidated and rendered inaccurate due to the position having changed. This is because the particle will now have a new momentum. And vice versa.įurther, if the momentum is measured and then, the position is measured, the original measurement of momentum is no longer accurate. To the degree the position of a particle is precise, to that degree the momentum is imprecise. Indeed, the particles do not have precisely defined momentum and position at the same time.

For example, it is not possible to discover with precision both the momentum and the position of a quantum particle simultaneously. The Heisenberg Uncertainty Principle (HUP) is also called the “Indeterminacy Principle” or simply, the “Uncertainty Principle.” It says that some of the properties of atoms and the components of atoms have an inherent fuzziness.

Heisenberg principle