A man by the name of Werner Heisenberg proposed the uncertainty principle in 1927. Heisenberg was a German theoretical physicist whose main contributions were to quantum mechanics, the study of the atomic and subatomic world. His principle of uncertainty took a while for people to accept. The main idea is, the more precisely you measure the position of a particle, the less precisely you can know its motion (momentum or velocity) and vice versa.

Heisenberg was debating the implications of quantum theory, a weird new way of understanding how atoms behaved that had been created during the preceding decade by physicists such as Niels Bohr, Paul Dirac, and Erwin Schrödinger. Quantum theory argued that energy was not continuous but rather arrived in discrete packets, which was one of its many counterintuitive concepts. Light can be thought of as both a wave and a stream of these quanta. Heisenberg uncovered a flaw in the way basic physical properties of a particle in a quantum system might be assessed when fleshing out this radical viewpoint. In one of his regular letters to a colleague, Wolfgang Pauli, he hinted at a notion that has since become a key component of the quantum description of the world.

Suppose the position of a particle is known to very high precision, such that **x **is exceedingly small. The uncertainty principle shows that **y **must be large, i.e., the momentum is not known precisely. Furthermore, because neither uncertainty nor momentum can be precisely measured, neither position nor momentum can be precisely measured. For instance, consider an example where we measure the position of an electron, and we must collide it with a photon and then return to the measuring device to do so. Photons hold some momentum, so a transfer of momenta will occur here. This will then cause the momentum of the electron to increase, and attempts at measuring the position of a particle will increase the uncertainty in the value of its momentum.

The uncertainty principle is inherent in the properties of wave-like systems and arises in quantum mechanics simply due to the wave-like nature of quantum objects. We clearly see this principle in atoms, where negatively charged electrons orbit a positively charged nucleus. Intuitively, they should attract each other, but this principle holds. If an electron gets too close to the nucleus, its position in space would be precisely known, and the error in measuring its position would be infinitesimal. The error in measuring its momentum would then have to be immense, triggering the electron to move extremely fast.

The uncertainty principle played an important role in many discussions on the philosophical implications of quantum mechanics, in particular in discussions on the consistency of the Copenhagen interpretation, a collection of quantum mechanics interpretations. Uncertainty should not be confused with the observer effect, which is that measurements of certain systems cannot be made without affecting the system. This principle limits us greatly in understanding all there is to know about particle physics.

Writer: Golda Abs

Editors: Rana Alqahtani/Lamar Albukhari

## References

1- Howard Wiseman Professor in Physics. “Explainer: Heisenberg’s Uncertainty Principle.” The Conversation, 2 July 2021, theconversation.com/explainer-heisenbergs-uncertainty-principle-7512.

2- “Uncertainty Principle.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 1 June 2021, http://www.britannica.com/science/uncertainty-principle.