Heisenberg’s uncertainty principle tells us that it is impossible to simultaneously measure the position and momentum of a particle with infinite precision. In our everyday lives we virtually never come up against this limit, hence why it seems peculiar. In this experiment a laser is shone through a narrow slit onto a screen. As the slit is made narrower, the spot on the screen also becomes narrower. But at a certain point, the spot starts becoming wider. This is because the photons of light have been so localised at the slit that their horizontal momentum must become less well defined in order to satisfy Heisenberg’s uncertainty principle.

I based this video on one by Prof. Walter Lewin of MIT: http://bit.ly/100Wk2K

Henry (MinutePhysics) has previously made a video about Heisenberg’s Uncertainty Principle where he treats it as less spooky and more a consequence of waves: http://bit.ly/TV3xO5

Sixty Symbols has a great video on Planck’s constant: http://bit.ly/11upebY

Thanks to the University of Sydney for hosting this experiment, especially to Tom and Ralph for their assistance getting it working.

Music: Kevin McLeod (Incompetech.com) Mirage and Danse Macabre

source

I'm a visual learner, so I liked the video graphics you have, much better way for me to learn. Dr. Dorian Canelas at Duke Univ has a link to you from the Intro to Chem course on Coursera. Glad she gave us student this link!

Very nice sir.

Thank you very much

How can you know that the particle emited from laser is the same particle that reaches the screen?

It’s a particle that is causing a wave. Was that so hard now…. Walter…, thank you. Stan

While observing the double slit experiment, we somehow measure speed and position with our eyes. After all, observing means having a certain amount of speed and location information. Since we cannot know the position and velocity at the same time due to the uncertainty principle, shouldn't there be small deviations as in the measurement result even in the case of the observer effect?

That’s insane

I am not sure if I understood this correctly, but isn't this just like something to try to "fit" this wave-like behavior of light into the particle-like behavior?

I have a doubt, what happens when u don't use slits and directly observe the light with same same cross-section as the slit is directly hitting the screen..

hey give me credits now

No one good tool than estein

"Photons…must veer to the left or to the right to ensure we don't break Heisenberg's uncertainty relation" is NOT explaining anything. Nothing in nature works to avoid human conceived rules.

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I FINALLY UNDERSTOOD THIS. OMG. I CAN'T THANK YOU ENOUGH FOR THIS. YOU ARE THE BESTTTTTTTTTTTTTTTT.

Why? if i find a higher probability of finding an electron in position x on time t and then in y on t2. then y-x/t2-t will give me exact speed. and i also do have exact location X and Y. but if you try to do this just by fourier analysis finding position and speed on a single spot only then uncertainty is true. but that's a mathematical limitation but not a limitation set on quantum particles. its more like seeing an object with one eye doesn't changes the object in 2D, it just shows you one perspective. Then why all the scientist says uncertainty is a fundamental property of quantum particles? i never understood.

Thank you

That's an awesome example!!!

After watching janardan sir's video, I am here

Awesome video. Thanks for sharing!

Really weak explanation

is h/2 equal to h/4π which one is true in this princible some people using first some of them using second when they explaining heisenberg's uncertainty princble