What Heisenberg's Uncertainty Principle *Actually* Means

Let's talk about one of the most misunderstood but awesome concepts in physics. The Heisenberg uncertainty principle. Or maybe it should be the Heisenberg 'fuzziness' principle instead? Would that confuse less people?

[ScienceAsylum]

I love how you represented likelihood in position with faded particles. Brilliant!

[ZardoDhieldor]

German here, "Unschärfe" is a term from photography meaning *blurriness*/ "unfocusedness." I don't know whether this is where Heisenberg got the name from but maybe the idea is that you can't focus on two different objects simultaneously if they have a different distance to the camera. One of them will always be out of focus.
Also, in German there are two names for the HUP, "Unschärferelation" (= blurriness relation) and "Unbestimmtheitsrelation". "Unbestimmtheit" means indefinite (or vague). I think *indefiniteness* is a much better name to describe this phenomenon than uncertainty.

[PointyTailofSatan]

I used to believe in the Heisenberg Uncertainty Principle. But now I'm not so sure.

[EckhartsLadder]

For me, the confusion came from Stephen Hawkin’s explanation in A Brief History of Time

[tone]

Took a couple days to get to this one (Sorry!) but this really clarified the uncertainty principle for me. I went with 3 at the start, but there were definitely some mechanics I didn't really understand. Looking forward to the more technical video, although who knows if I'll understand it...

On the homework, wouldn't measuring the momentum put the position back into flux, so that if you measured position afterwards it'd be in a random place again? Otherwise you'd have simultaneous exactly-accurate information for the location and momentum, and the fact that you can't do that is kind of the point of the principle in the first place.

Also, I had a question on the equation: If you've just measured the location of the particle, isn't ∆x zero, at least momentarily? there's no uncertainty at all: it is where your result just said it was. And if it's zero, then no matter how large ∆p is, the product of the two is zero. Assuming I didn't just overturn almost a century's worth of quantum theory, what stops that from being the case? Does a little bit of uncertainty remain, even when measured? or do we just use an arbitrarily small non-zero number to represent no uncertainty, instead of zero?

[marcellveiner]

Just finished my high school studies and done a final from higher physics. As particle physics is partly in the curriculum, we covered this topic too, I remember that we specifically learned the second explanation.
However, I always fellt this part too slippery, and all our theachers were very unsure when asked for another explanation. I'm not surprised that this (among a few others) came out to be false. There are a lot of cases when because of simplifying we are taught the wrong answer.
Welcome back!

[le_scienceall]

I like calling it the "spreading" principle instead, e.g. a particle state is necessarily spread in position and/or momentum space.

[alicraftserveur]

Damn, I picked 1. because I was picturing the equation in my head lol
That σ_x.σ_p ≥ ħ/2
I interpreted 1. like "when the error on x is small, the error on p is large"

[ELYESSS]

I don't remember subscribing to this channel, but a big thanks to past me for doing it

[GaryWardatCoastalBliss]

The uncertainty principle is an artifact of probability theory being applied to a physical system: Chebyshev's inequality.

[justus]

I think the best way to translate Unschärfe is blurry or "blurryness".
Image you try to see underwater, it's hard to clearly tell where exatly stuff is and the vision is blurred.
In German, when Unschärfe is used, it is mostly referred to vision too.

Great video, thank you :)

[Fransamsterdam]

I don't know you, I am not sure who you are, but I like you.

[ethendixon]

Looking Glass, you are so awesome! You deserve more subs, or a shout out from 3B1B or Minutephysics or something.

[resonarc]

Thank you so much for your videos. This really cleared up questions I had when I hear about the HUP (at least the way it's usually described).

[Morberticus]

This video wades back into the swamp of "interpretations of quantum mechanics", so there is bound to be disagreements.

Most people would agree that description 2 is inaccurate, and glosses over the intrinsic, fundamental role the HUP (or more generally, non-commutation) plays in QM.

But the question of whether or not a system has a property prior to measurement has different answers for different interpretations. The Copenhagen interpretation, for example, only concerns itself with what measurement devices report when they correlate with quantum systems. It makes no propositions about the ontology of an unmeasured quantum system, and limits itself to an epistemic understanding of experimental outcomes and their correlations.

Under my favourite interpretation (Decoherent Histories), however, we can make statements about the properties a system has without the context of a measurement. We can say a particle has a position whether or not it is measured, and we can say a particle has a momentum whether or not it is measured, provided we are careful with our syntax. Unlike hidden variable theories, the Decoherent Histories interpretation uses the vanilla Hilbert spaces of QM and doesn't introduce any new mathematical structures.

tl;dr Different interpretations of QM map the formalism of QM to different propositions about reality. Therefore, for better or for worse, different interpretations will map the HUP to different propositions about reality. So pinning down what the HUP means is difficult.

[ildisiri]

Angelic voice and explanation that is exactly, what we call "layman's terms". Very nice, you have a new subscriber and fan!

[misjacarbo]

Hi Mithuna!
So great to have found you again on Youtube!
Will be telling my 12s to watch your channel!
Where are you based at the moment and what are you up to?
You can use my school email to answer. Still the same! 10 years later!
Mr Carbo

[chitranshitiwari]

you are great your explaination was very good help me in coming out from misconception of hesinburg uncertainity

[TalysAlankil]

I feel like there's something amazing about using Alice iconography to talk about quantum mechanics, a subject so keenly tied into complex numbers, when it's been theorized that Alice in Wonderland was Lewis Caroll's jab at complex numbers for being…well, as mad as the inhabitants of Wonderland. I love it and I'm loving your videos so far.

[JoJoModding]

German here. The translation for "Unschärfe" is blurryness. A blurred photo is "ein unscharfes Photo" in german.