My favorite explanation comes from Greg Egan[0]:

"The uncertainty principle is the inability of a quantum system to possess sharply defined values of certain pairs of variables, such as position and momentum. Unfortunately, this simple fact is sometimes shrouded in confusion, some of which probably dates back to a famous thought experiment of Heisenberg’s in the 1920s. Heisenberg pointed out that, because light comes in quanta with a minimum amount of energy and momentum for any given wavelength, even if an electron was a point particle straight out of classical physics, we could never illuminate one in order to see where it was without disturbing it to some degree in the process. This is a perfectly true statement — but it’s a true statement about a hypothetical alternative universe, because electrons aren’t classical point particles. A correct description of an electron, whether as a wave function in ordinary space or a state vector in a Hilbert space, shows that it doesn’t need to be “disturbed” by anything in order to be subject to the uncertainty principle. It simply can’t possess an exact momentum and an exact position at the same time, any more than a musical note can be a perfect middle C, giving it a well-defined frequency, while lasting for a billionth of a second, giving it a well-defined location in time."

[0] http://gregegan.customer.netspace.net.au/FOUNDATIONS/04/foun...

> A correct description of an electron, whether as a wave function in ordinary space or a state vector in a Hilbert space, shows that it doesn’t need to be “disturbed” by anything in order to be subject to the uncertainty principle.

This is, in fact, a result of the uncertainty principle of Fourier analysis. See https://en.wikipedia.org/wiki/Fourier_transform#Uncertainty_...

I'm not following how "uncertainty" principle is a bad way of putting it. No matter what we do, we cannot know the position and velocity precisely at the same time. If you know position precisely, velocity is uncertain. From what I understand it's not a matter of velocity is "as yet undetermined", if we know the location precisely, then the velocity has many values and will collapse to one value if observed precisely (at which point position will have gone from precise to many valued).

Or should I not be physics-ing in the morning.

"Uncertainty" suggests that the position might, in some way, be defined with 100% precision, but it's us, the observers, who are uncertain what the actual value is.

"Unschärferelation" suggests the value coming out of the system (position, impulse, etc) is in a fundamental way not pinned on a single value fixed with 100% precision, but instead it's spread out over a distribution function.

Oh, I got it. It's the difference between "I am uncertain" and "It is uncertain". That makes sense.

First discussion that happens in an undergrad quantum mechanics class.

Teacher: "It is uncertain" Student: "Can't we measure it better?" Teacher: "No, it is unknowable, no matter what" Student: "Wtf?"

Unscharf (the adjective to Unschärfe) can be translated to "out of focus" or "blur", which kind of describes the phenomenon figuratively.

The article's problem with "uncertain" is that it has connotations of some intelligence comprehending the observed value. When I say, "velocity is uncertain" it seems to mean something like "I am uncertain what the velocity is", but when I say that "velocity is undefined" or "velocity is fuzzy" then it is more clear that I am talking about the velocity itself.

I think "uncertain" is fine. Of course, the particular words are not really that important if you just tell people to read the definitions and equations used in the theory.

"undefined" has a very specific scientific and mathematical meaning that would place it at risk of being very, very wrong if conflated.

"Uncertain" also has a meaning outside the uncertainty principle. When we say that a measurement has uncertainty, we usually mean that it has some fixed value, but our tools are not capable of measuring it beyond some limit.

Almost all terms in mathematics and science are overloaded in ways like that. For example, what is the "basis" for a mathematical space?

Good point. Uncertainty colloquially does admit the possibility of "no true value" embarrassingly as a scientist, I forgot the stat definition.

I agree. Uncertainty principle is a great word for it. Not sure the authors points are really valid, and the "mongolian" language metaphor he used is a stretch.

VERY capable physicists have been happy using the term uncertainty principle just fine in English and have no misunderstanding of what that means.

I thought exactly the same thing. ΔpΔv > k is exactly "the uncertainty in p and the uncertainty in v cannot be zero.

It sort of is a bad way in that "uncertain" means that an answer exists but we don't know it, whereas the answer really doesn't exist.

However, this is a really minor nitpick and since statistics is used all the time with QM "uncertainty" is just fine. The article is making a mountain out of a semantic molehill.

I have encountered people, in person, that spout new-agey nonsense based largely on the word "uncertainty" in this uncertainty principle. I'm sure they would latch onto other things were it not there, but this definitely feeds into that stuff.

Yes, "unsharp" or "the principle of non-sharpness" or something like that, inspired by some German terms used, would be much less prone to misunderstandings and myths. "It's not sharp, but it's OK." Can't be reduced to "stupid scientists are so uncertain."

> new-agey nonsense

One of these hippie types went so overboard that he even made a "hand wavy" coat of arms to go along with his lateral comments about Buddha and Laotze [1] and question our very ability to fully comprehend an objective reality.

[1]: https://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Co...

Unwinnable battle, that one.

new agey nonsense comes out of every popsciification of physics, this isn't new. Its also still a minor thing IMO.

> which transliterates to “unsharpness relationship,” but as there is really no such term in English

Seems like there is: "unsharpness relationship".

> "Unbestimmtheit" (Indeterminacy) was on the part of the observer: not realizing certain aspects of nature at this stage in our knowledge—rather than proof that nature itself is fundamentally undetermined and uncertain.

And yet Bell's theorem and Aspect's experiment show there are no hidden variables.

If I understand this guy right, he's basically saying that the uncertainty principle is just a statement about our ability to measure things, rather than a statement about the actual reality about what variables (hidden or not) are stored by each particle.

I used to think the same, and intuitively this still seems right to me, but apparently there's been a bunch of experiments based on the Bell Inequality that prove that we're wrong.

> If I understand this guy right

Trivia: This guy was actually pretty famous in the 90s for "Kais Power Tools"[1], a set of very popular image manipulation plugins with - at that time - unrivaled features. Later his company also released Kais Power Goo, Bryce, Poser and more.

[1] https://en.wikipedia.org/wiki/Kai%27s_Power_Tools

No, I do not think that you are understanding him correctly. What makes you think that?

Just one example from the article:

> rather than stating that either position or momentum are "as yet undetermined", it became common usage and popular wisdom to jump to the conclusion that there is complete "uncertainty" at the fundamental level of physics

Can you explain how you drew any other conclusion from the article? The whole thing is driving at this one point.

His position is ‘that either position or momentum are “as yet undetermined”’. That means that the ‘uncertainty’ is not due to our ability to measure things, but ‘rather […] a statement about the actual reality about what variables (hidden or not) are stored by each particle’. :)

Is there actually a thing in physics where you change the measurement by observing it?

I do electrical engineering, and as far as I know, the uncertainty principle means that as the signal in the time domain gets more localized, the signal in the frequency domain gets more spread out (and vica versa). I think ( I don't know for sure) position can be thought of as time domain and momentum can be thought of as frequency domain (or it might be the other way around).

I'm not sure if this relationship actually leads to the Futurama "No fair, you changed the outcome by observing it!"

I could research this to find an answer, but it would take me way too long.

> as far as I know, the uncertainty principle means that as the signal in the time domain gets more localized, the signal in the frequency domain gets more spread out (and vica versa).

That is exactly right.

And you can also tell a similar story for the position-velocity relationship: if you make a wave by throwing a rock into a pond the resulting wave front will be circular, i.e. the position of origin of the wave is well defined (it's where the rock landed), but its direction of travel is not.

By way of contrast, if you want to make a wave with a well-defined direction of travel, the only way to do it is to make a very wide wavefront, i.e. one whose position is not well determined.

A simple example of a "measurement effect" is the quantum zeno effect [1]. You can steer a system by making a series of measurements and gradually transitioning the measurement axis from aligning with the initial state to aligning with the target state [2].

For example, placing a diagonal polarizer between a horizontal and vertical polarizer will allow light to pass through [3]. As you use more and more polarizers that gradually transition from horizontal to vertical, you converge on a mechanism for rotating horizontally polarized photons into vertically polarized photons without loss.

1: https://en.wikipedia.org/wiki/Quantum_Zeno_effect

2: http://algorithmicassertions.com/quantum/2015/10/26/Quantum-...

3: https://youtu.be/PJHCADY-Bio?t=6m45s

Coming from an audio background, this explanation clicked immediately. You can't determine anything about frequency from a single audio sample. And conversely, you can't determine anything about signal phase from a frequency spectrum.

Is this just an apt analogy or is it basically the same concept at work in QM?

Observer effect.

Thanks :) That gives me something concrete to google

My favourite scientific mistranslation: Alien hand syndrome.

https://en.wikipedia.org/wiki/Alien_hand_syndrome

The original French is "Syndrome de la main étrangère", which should be called "stranger's hand" and describes a condition where brain injury may result in unwanted movements of a hand.

https://fr.wikipedia.org/wiki/Syndrome_de_la_main_%C3%A9tran...

"Alien" often just means "foreign" anyway. https://en.wiktionary.org/wiki/alien#Adjective

In what sense this a mistranslation? If you conflate alien with extra-terrestrial?

In current usage, people almost exclusively use "alien" to refer to ETs. The only ones who use it in the sense of "foreigner" are immigration bureaus, and this becomes a source of hilarity whenever they speak to the outside world.

Would you ever say "I had some aliens in my home last night for dinner" and expect someone to interpret that to mean immigrants/tourists/strangers? At best, they would criticize you for using that term to refer to them.

Illegal Alien gets quite a few hits on google.

https://www.google.com/#q=illegal+alien

Perhaps I should have said "immigration law enforcement" instead, but the same point. Outside the that context, "alien" means ET.

It isn't a literal mistranslation, it's a context error. In english the proper word in this context would be stranger, not alien. But that's still a mistranslation. Had this been something to do with immigration or visas, then alien might have been appropriate.

Merriam Webster's definition 1A for "alien" is belonging or relating to another person, place, or thing : strange. I think it fits the context very well.

http://www.merriam-webster.com/dictionary/alien

But if you take Webster’s definition, alien is still overbroad. A person OR place OR thing is a much wider scope. 'Stranger' only describes persons and so is still the appropriate word in the context.

> But if you take Webster’s definition, alien is still overbroad.

That it could perhaps encompass other meanings than the intended one does not make it incorrect for the intended meaning.

> 'Stranger' only describes persons and so is still the appropriate word in the context.

"Stranger's" would be more specific than "alien", and wouldn't be a bad translation, but "alien" is likewise not a bad translation (and, actually, has almost exactly the same breadth in English as "étrangère" does in French; so its arguably the most exact translation, since it uses a word that both admits the specific sense intended within its scope and which has a pretty similar breadth of association as the source.)

Its also the idiomatic word in English for describing something which provokes a feeling of distance from the speaker in a way which is quite appropriate for the subject matter, so its probably the best translation idiomatically.

Overbroad? "Étranger", in French, is just as broad as "alien". It can be used for people, places, things, and more. Save for the ET meaning, any use of "alien" or "foreign" can be translated to "étranger", and vice versa. It is a very broad word.

This may be a case where the translation ends up more accurate. 'Observer' is really just any other wave/particle. So, this is in terms of all outside perspectives not just machines/scientists.

I remember the first time someone explained to me that the uncertainty principle was just a fact of waves. Decomposing a single event into frequency space makes no sense, and neither does the inverse, taking a frequency (a succession of regular events) and expecting it to have instantaneous meaning.

When I heard this I felt a profound sadness. After I was told it seemed obvious, simple, intelligible, and the idea of a great cosmic darkness, Chaos disordering and underpinning the universe, had vanished and been replaced by a plain mathematical relationship. Alack.

How odd. When I grokked the uncertainty principle (and later, entanglement) I felt a profound sense of euphoria and peace, because the world suddenly made sense. Can you elaborate on why achieving this understanding made you sad? Why is it so important to you to have chaos and disorder?

Hard to say - it was a visceral reaction that mostly manifested as a brief resistance to the idea ("no, that can't be right"). I imagine some component of my thought wants a space in the universe that is claimed by mystery. I enjoyed reading Heisenberg's "Physics and Philosophy", where he discusses the quixotic nature of the double-slit experiment and so on, notably things like observation collapsing the wave function and removing the diffraction pattern. Heisenberg definitely colors these things with an air of mystery, the idea that the operation of the universe flies in the face of what we think of as sensible. I'm someone who has always enjoyed being on the margins, questioning, overturning, poking at consensus. Before I understood the uncertainty principle I think it was a door to a much blacker mystery, and thus a much greater rejection of the notion that "we understand", which I think is something I have always associated with evil, hubris, and folly.

I think the OP is conflating matters that were originally conflated by the theoretical community. Aspect makes the point that until '82 even Feynman did not note the distinction between wave/particle duality and entanglement (only the latter demands non-local aka "spooky" action.) It was only after Bell, et al that e.g. in '82 Feynman recognized the distinctions and per Aspect "typical Feynman he then invented Quantum Computing".

The theory of relativity is an misleadingly phrased concept - it should be the "theory of absolutivity" - because the relativeness is not the new part (galilean and newtonian relative reference frames had been around for centuries) it's reconciling it with the absolute speed of light which was the new part, the part that introduces tricky math and "strange" concepts that don't jive with our day-to-day sensory experiences in physics.

I can't agree with the argument that "relativeness is not the new part"--since relativity introduces the idea that measurements of time and space (and mass, electric fields, magnetic fields, etc.) are relative to the reference frame. Classical mechanics only admits relative measurements of velocity (and energy, momentum, etc).

But if you want to rename it, Einstein said that he should have named it the Theory of Invariance. I'm fond of "relativity" because it admits adjectives like "relativistic". We can say, "At relativistic speeds."

well popularly (non-scientifically) relativity is thought to mean that a measurement is relative, and that's generally an older concept than Einstein, even though classical mechanics have a more limited scope of quantities that are measured relatively (position, velocity). There are still things in einstein's theory of relativity that aren't relative, even which would have been relative in the classical system (the speed of light). And the initial math outlays (lorentz transformations) are exactly as I described them, shutting down the possibility that the speed of light is relative, creating an "absolute" measurement.

What you are describing as "absolute" is described in the literature as "invariant", which might help if you are doing web searches for more information. "Absolute" usually has a different meaning.

I remember when I first learned that it actually literally meant that two events could be simultaneous in one frame of reference, but non-simultaneous in another. Blew my damn mind.

"theory of subjective simultaneity" sounds awesome.