Heisenberg's Uncertainty Principle Explained
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it as a concrete, visual illustration of the uncertainty principle and of why light diffracts through a slit.
Recommended by 3 people across 3 different months, 2016 to 2022.
What it is
A 4-minute Veritasium demo of Heisenberg's uncertainty principle using a laser shone through an adjustable narrow slit. As the slit narrows the spot on the screen shrinks, then widens again once the photons are localised enough that their horizontal momentum becomes less well defined. Based on a Walter Lewin lecture demo and filmed at the University of Sydney.
What people said
Strong rec Shishir Maharana · 2019-08 · Physics Stack Exchange · on “Diffraction: What actually happens in the slit”
You should really go see Veritasium's video ( [this video] ). He explains the Uncertainty Principle using slit diffraction. It can give you a fair idea of what is actually going on in the slit. The slit is not actively participating in the experiment and so it is not causing any fringe pattern. It is the wave nature of the photons as they diffract through the slit that is causing the fringes on the screen. In my opinion, You should also watch Eugene Khutoryansky's video on this ( [LINK] ) to get a reasonably good analogy.
Recommends Yaman Sanghavi · 2017-12 · Physics Stack Exchange · on “Is Heisenberg's Uncertainty Principle applicable to light?”
Using wavelength you can find only the magnitude of momentum $\sqrt{P_x^2 + P_y^2 + P_z^2}$. For finding its direction you will need its wavevector $\vec{k}$. Heisenberg's Uncertainty principle applies to each component of momentum and the corresponding component of position, for example, you can't find simultaneously $P_x$ and $x$. Heisenberg's Uncertainty Principle in vector form: $\Delta\vec{P}.\Delta\vec{r} =3\frac{h}{4\pi} $ There is a nice demonstration of this in an experiment of diffraction of light through single slit in this video by Veritasium: [this video] In the experiment, when the light is allowed to pass through a thin slit, it's position is being confined to the slit. So as the s
Recommends Devansh Mittal · 2019-12 · Physics Stack Exchange · on “Why does light spread out?”
So we know the light that's emitted from a torch (flashlight) must be moving in straight lines, so why does it spread out when moving? Why does it cover larger area? The reason for such spreading out lies in the idea of "Diffraction". You can read more on diffraction at this resource [LINK] . The following are some useful points for a quick understanding. [LINK] [LINK] The roots of why Diffraction happens lies in "Heisenberg's Uncertainty Principle", which you can understand at the following two resources. Heisenberg's Uncertainty Principle Explained by Veritasium. [this video] Heisenberg's Uncertainty Principle in action! by Dr. Walter Lewin. [LINK] Following is a quick summary of Diffraction on
Recommends Devansh Mittal · 2019-12 · Physics Stack Exchange · on “Why does a wave actually diffract?”
The roots of why Diffraction happens lies in "Heisenberg's Uncertainty Principle", which you can understand at the following two resources. Heisenberg's Uncertainty Principle Explained by Veritasium. [this video] Heisenberg's Uncertainty Principle in action! by Dr. Walter Lewin. [LINK] Following is a quick summary of Diffraction on the basis of Heisenberg's Uncertainty Principle. 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 sc
Cites Ameet Sharma · 2016-01 · Physics Stack Exchange · on “Question about heisenberg uncertainty principle and single-slit diffraction”
My question relates to this [this video] video illustrating the Heisenberg uncertainty principle. The video shows light being shot through a slit forming a spot on a screen. As the slit narrows, the width of the spot narrows, until eventually the width of the spot starts increasing. The person in the video says this is counterintuitive. I'm slightly puzzled as to why this is counterintuitive . Isn't this just like classical single-slit Fraunhofer diffraction, which would work with water waves? So what I'm guessing is the experiment is counter-intuitive using a particle view of light? So does this mean Heisenberg's Uncertainty principle is somehow equivalent to wave-particle duality? Looking to cl
Cites anna v · 2017-12 · Physics Stack Exchange · on “Is Heisenberg's Uncertainty Principle applicable to light?”
The Heisenberg Uncertainty principle [LINK] , HUP, is a basic quantum mechanical observation, modeled by the commutation relations of the appropriate operators. Light is the name of classical electromagnetic radiation, described by Maxwell's equations. It can be mathematically shown that light, (classical electromagnetic waves,) is emergent from an enormous number of photons of energy h*nu where h is the Planck constant and nu the frequency of the classical EM wave. The HUP is only relevant for elementary particles and their composites, like atoms and molecules. Photons as individual elementary [LINK] particles obey the Heisenberg uncertainty principle when their momentum and position is det
Cites Amit Kumar Goldy · 2022-10 · Physics Stack Exchange · on “Given Heisenberg's uncertainty principle, why do we not see random colors when monochromatic light passes through a narrow slit?”
I was looking at this experiment by Veritasium. [this video] Here he shines a green light through a narrow slit and we see the light smear as the slits becomes narrower. Momentum of a photon is $h/\lambda$ . Since $h$ is a constant, shouldn't the uncertainty in momentum manifest as uncertainty in wavelength instead of position on the screen? So instead of the light smearing, shouldn't we see random colors on the screen instead of the smeared, steady, green?