# Heisenberg Uncertainty Principle: Importance & Background

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

In this lesson, we will learn about the Heisenberg uncertainty principle. Why is it important, what is the history that surrounds it, and how was it received? Test your knowledge with a quiz.

## What is the Heisenberg Uncertainty Principle?

The Heisenberg uncertainty principle is a physical law that forms part of quantum mechanics. It says that the more precisely you measure the position of a particle, the less precisely you can know it's motion (momentum or velocity). And the more precisely you measure a particle's motion, the less precisely you can know its position. This is contrary to our everyday experience of life, where these measurements are independent of each other, and can be measured as precisely as we'd like. When it was introduced in 1927, it took a while for people to accept.

It may not be easy to understand this principle, but it is even harder to explain it. One way Heisenberg tried to explain it to people was to say that the act of observing something affects the outcome.

Imagine that you are in a laboratory, trying to observe an electron through a microscope, in order to measure its position and velocity. The light that you are using in this observation bounces off the electron, and reaches your eyes. That's how you can see it. But the light affects the electron when it bounces off it.

Light contains tiny particles called photons, and those particles have a certain amount of momentum. This is a quantity that fast and heavy objects have lots of: a football player running has a lot of momentum, which is why it's hard to stop them. In the case of light, its amount of momentum depends on the wavelength (color) of the light waves, which can be controlled in a laboratory.

If the kind of light we use for our observation has photons with a lot of momentum, then we can easily see where the electron is (its position). It's like shining a really bright light into the microscope. But because they have a lot of momentum, they'll transfer it to the electron when they bounce off it, causing it to speed up. This will make it hard to know how fast it is moving (its velocity). Our observation has affected the electron's velocity.

But if the kind of light we use has photons with hardly any momentum, we can't easily see where the electron is (its position). It's like using a microscope in a dim room. But since the photons have little momentum, they won't affect the electron's speed, making it easier to know how fast it is moving (its velocity).

The better we know the velocity, the harder it is to know the position. And the better we know the position, the harder it is to know the velocity. That's the uncertainty principle.

## Heisenberg and Quantum Mechanics

Quantum mechanics explores the physics of the tiny, subatomic world. It turns out that on these tiny scales, things act quite differently to the way they do in our everyday lives. The foundations of quantum mechanics were laid out by people like Einstein and Planck at the turn of the 20th century. But then a lot of work lay ahead: turning ideas into equations and laws. That work would take a few decades, and Heisenberg was a key figure during that time.

Heisenberg started work on the principle in 1925, when he suggested that electrons in an atom don't travel in precise orbits, and their motion is random and hard to predict.

To unlock this lesson you must be a Study.com Member.

### Register to view this lesson

Are you a student or a teacher?

#### See for yourself why 30 million people use Study.com

##### Become a Study.com member and start learning now.
Back
What teachers are saying about Study.com

### Earning College Credit

Did you know… We have over 160 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.