# Why Does the Universe Depend on Planck's Constant?

By: Patrick J. Kiger & Austin Henderson  |

In the year 1900, Dr. Max Planck introduced a mysterious number to the world of physics. This number, now known as Planck's constant, would become the cornerstone of quantum mechanics and eventually help save the day in a popular Netflix series. But what exactly is Planck's constant, and why is it so crucial?

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## Classical Mechanics vs. Quantum Mechanics

Quantum mechanics deals with the tiny particles that make up our universe and the interactions between them. Planck's constant is essential in defining the behavior of these particles.

But to truly appreciate its importance, we first need to understand the difference between classical mechanics, which describes the motion of everyday objects, and quantum mechanics, which dives deep into the universe's microscopic scale.

### Classical Mechanics

This physics branch, which Sir Isaac Newton described in the late 1600s, deals with the observable world, explaining how apples fall from trees and planets orbit stars. If we think of energy as water, then in classical mechanics, we can pour any amount of water continuously.

### Quantum Mechanics

Enter the realm of the bizarre and unexpected! In quantum mechanics, energy behaves a bit differently. Instead of pouring water continuously, it's like adding sugar cubes to a coffee cup. We can add one, two, or three sugar cubes, but not half or a quarter.

This discrete nature of energy is a fundamental concept in quantum theory, and it's where Planck's constant steps in.

## Planck's Constant in Quantum Theory

Planck's constant defines the amount of energy a photon (a particle of light) can carry, based on the frequency of its electromagnetic wave. This relationship between photon energy and electromagnetic radiation is crucial in understanding phenomena like the photoelectric effect.

Electromagnetic radiation and elementary particles "display intrinsically both particle and wave properties," explains Fred Cooper, an external professor at the Santa Fe Institute, an independent research center in New Mexico, by email.

"The fundamental constant which connects these two aspects of these entities is Planck's constant," he says. "Electromagnetic energy cannot be transferred continuously but is transferred by discrete photons of light whose energy E is given by E = hf, where h is Planck's constant, and f is the frequency of the light."

## Why Small Changes in Planck's Constant Matter

One of the intriguing aspects of Planck's constant is that its value has seen slight changes over time. While these tiny adjustments don't cause the Earth to stop spinning, a significant deviation in its value could lead to a universe where atoms are larger than stars. Talk about a cosmic shake-up!

And for those trivia enthusiasts, the size of a kilogram now relies on Planck's constant. Yep, this tiny fundamental physical constant plays a role in defining weight.

## Did 'Stranger Things' Get It Right?

If you're a "Stranger Things" buff, you might recall a scene from season three involving Planck's constant. But there's a twist! The showrunners used the 2014 value for Planck's constant instead of the 1985 one, a little hiccup in their otherwise meticulous attention to detail.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.