Monday, November 28, 2016

This isn’t quantum physics. Wait. Actually it is.

Rocket science isn’t what it used to be. Now that you can shoot someone to Mars if you can spare a few million, the colloquialism for “It’s not that complicated” has become “This isn’t quantum physics.” And there are many things which aren’t quantum physics. For example, making a milkshake:
“Guys, this isn’t quantum physics. Put the stuff in the blender.”
Or losing weight:
“if you burn more calories than you take in, you will lose weight. This isn't quantum physics.”
Or economics:
“We’re not talking about quantum physics here, are we? We’re talking ‘this rose costs 40p, so 10 roses costs £4’.”
You should also know that Big Data isn’t Quantum Physics and Basketball isn’t Quantum Physics and not driving drunk isn’t quantum physics. Neither is understanding that “[Shoplifting isn’t] a way to accomplish anything of meaning,” or grasping that no doesn’t mean yes.

But my favorite use of the expression comes from Noam Chomsky who explains how the world works (so the modest title of his book):
“Everybody knows from their own experience just about everything that’s understood about human beings – how they act and why – if they stop to think about it. It’s not quantum physics.”
From my own experience, stopping to think and believing one understands other people effortlessly is the root of much unnecessary suffering. Leaving aside that it’s quite remarkable some people believe they can explain the world, and even more remarkable others buy their books, all of this is, as a matter of fact, quantum physics. Sorry, Noam.

Yes, that’s right. Basketballs, milkshakes, weight loss – it’s all quantum physics. Because it’s all happening by the interactions of tiny particles which obey the rules of quantum mechanics. If it wasn’t for quantum physics, there wouldn’t be atoms to begin with. There’d be no Sun, there’d be no drunk driving, and there’d be no rocket science.

Quantum mechanics is often portrayed as the theory of the very small, but this isn’t so. Quantum effects can stretch over large distances and have been measured over distances up to several hundred kilometers. It’s just that we don’t normally observe them in daily life.

The typical quantum effects that you have heard of – things whose position and momentum can’t be measured precisely, are both dead and alive, have a spooky action at a distance and so on – don’t usually manifest themselves for large objects. But that doesn’t mean that the laws of quantum physics suddenly stop applying at a hair’s width. It’s just that the effects are feeble and human experience is limited. There is some quantum physics, however, which we observe wherever we look: If it wasn’t for Pauli’s exclusion principle, you’d fall right through the ground.

Indeed, a much more interesting question is What is not quantum physics?” For all we presently know, the only thing not quantum is space-time and its curvature, manifested by gravity. Most physicists believe, however, that gravity too is a quantum theory, just that we haven’t been able to figure out how this works.

“This isn’t quantum physics,” is the most unfortunate colloquialism ever because really everything is quantum physics. Including Noam Chomsky.

39 comments:

driod33 said...

Is the main thing that suggests space-time is quantum,that you cannot have a infinitely small unit of either?

Sabine Hossenfelder said...

No, it's that the combination of quantum physics with non-quantum gravity leads to mathematical inconsistencies.

Sabine Hossenfelder said...

I explained this here: Why quantize gravity?

Chris Sonnack said...

I'm pretty sure what is meant, both by "rocket science" and by "quantum physics" in this case is understanding the topic -- i.e. being able to "do the math" and to be knowledgeable about the topics within the field. :)

Unknown said...

No, everything is NOT just quantum physics (plus some theory of gravity).

There is also statistical physics. The world would be a very different place if protons had spin zero or one, and not because of the "quantum" properties of
angular momentum, but because of the statistical properties of angular momentum,
which affect chemical equilibrium through the entropy part of Gibbs free energy.
Reactions involving water would be a quantitatively different thing!

Uncle Al said...

Somebody is days time-gapped separately shown two halves of a dense random dot stereogram and names the image - eidetic memory. Child prodigies, idiot-savants. Explain them, Noam.

A two-color photon works like indeterminate orthogonal polarizations. It has a different taste.

Somebody high on boo drove up a winding mountain road, was sloppy making ergot derivatives or dipeptides, placed an opaque lump in a light beam and saw a bright spot centered in its shadow. Create more such events, Noam.

Sabine Hossenfelder said...

Unknown,

Statistical mechanics is the prime example for an emergent theory. You can derive it from quantum physics. Well, maybe you can't, but you could. I don't know what issue you have with the spin of the proton. Best,

B.

Ori said...

So if I don't understand the world, is it because I don't understand enough quantum mechanics?

nicolas poupart said...

Logic does not require quantum theory. The existence of the logic gates "AND", "OR" and "NOT" is sufficient to describe the set of recursively enumerable languages (level 0 of the Chomsky hierarchy). Any imaginable universe, independently of the laws of physics of this universe, making it possible to realize the logical gates "AND", "OR" and "NO" makes it possible to realize the whole Turing computability, that is to say, the set of the deterministic phenomena. Thus, quantum theory is only an accidental way to achieve Turing computability. Logic is transcendental, physics is immanent and accidental.

Louis Tagliaferro said...


I understand your point that most physics come down to quantum physics when extrapolated deeply enough. However to be fair, the contextual meaning I most often see for the saying is more along the lines that the mental capacity involved to make a milkshake is many orders of magnitude less than what is required to learn and understand Quantum physics (it's usually about mental effort and requirements). I've personally have never interpreted the saying as implying quantum physics is not underlying in all physical phenomena.... except gravity (for now?).

Henning Dekant said...

I may have to steal some quotes from this blog post (properly attributed of course), to explain to investors how you can be a Big Data and Quantum Computing play at the same time.

Joe Perry said...

I think you misunderstood Chomsky's point there. Key line is *everything that's understood* about human beings. That is to say, not very much.

Sabine Hossenfelder said...

Joe,

I count all of neurobiology, medicine, much of molecular biology, economics, and sociology to 'what's understood about humans'. That includes also peace and conflict studies, international relations, and parts of the political sciences. It also includes, for example, the sociology of science. Believing that all of this can be understood by not thinking too much dismisses a lot of research (not to mention researchers) as useless. Having said that, I didn't read the book, and quite possibly it contains statements that are not nonsense. Best,

B.

Sabine Hossenfelder said...

Louis,

I was hoping it's clear that this blogpost isn't meant seriously.

Sabine Hossenfelder said...

Nicolas,

Logic, as any other part of mathematics, is realized by the execution of certain functions in your brain or in a computer. Which means - guess - it's quantum mechanics. You seem to be referring to platonic ideals of mathematical structures, but in reality we use their representation in certain subsystems of the universe. Best,

B.

Sabine Hossenfelder said...

Ori,

That you could theoretically understand the world by quantum mechanics doesn't mean it's a very practical way. Best,

B.

MarkusM said...

"From my own experience, stopping to think and believing one understands other people effortlessly is the root of much unnecessary suffering. Leaving aside that it’s quite remarkable some people believe they can explain the world, and even more remarkable others buy their books, all of this is, as a matter of fact, quantum physics. Sorry, Noam." - I'd love to see a reference to the reasearch (experimental please !!!) where that is shown.

akidbelle said...

Hi Sabine,

about the list you enumerate, I think they are plain wrong about "driving drunk". :-)

I'll also bet that the 27th century physicists will see quantum physicists as drunk drivers (looking at the history of quantum physics, chances are 50/50 if physicists are still there). No offense meant, because in any case there is no other choice at present.

J.

PS: sorry to make the subject a bit more serious.
PS: unknown, how do you make any valid statistics without a constant of action?

Sabine Hossenfelder said...

Markus,

I hope we agree that there's plenty of evidence that quantum mechanics and quantum field theory is correct. Everything else follows from that. That it's possible to come up with a law of nature that does not follow from the fundamental laws but is still mathematically consistent is an extraordinary claim that requires extraordinary evidence. The problem is that the people who typically make such claims don't realize they're making an extraordinary claim. Best,

B.

akidbelle said...

Hi Sabine,

I think the assumption in your response to Marcus is that QFT is fundamental law (or maybe I don't read properly). Meanwhile the previous sentence state that it is "correct". This is a huge difference; 19th century chemistry is "correct" but not fundamental. But at the time there was an unbreakable atom which was fundamental...

Of course the claim that QFT is not fundamental is also extraordinary... but a lot more "business as usual" when looking at the history of physics.

Of course nobody knows, but as far as I can see nobody seriously wants to know; and except for a few physicists in their old age who are not happy with QM, everybody shuts-up (and calculate, at least from time to time).

So I have questions: assume that QFT is not fundamental; how would you address this problem? (*) What predictions or results should it give?

Thanks,
J.

(*) even if in a not so serious manner :-)

Sabine Hossenfelder said...

akidbelle,

QFT is *for all we presently know* fundamental. But that it might eventually be replaced by something more fundamental doesn't mean it'll become wrong. It will just no longer apply to everything. If so, then you could say there are things that are not quantum physics. I don't know what predictions it would lead to if QFT wasn't fundamental. To make predictions one would first have to have a theory for that.

In any case, all the examples that I mentioned would still be quantum physics... Best,

B.

Rob van Son (Not a physicist, just an amateur) said...

Sabine, Noam Chomsky is the last to use the phrase "it's not quantum physics". His linguistic theories are more complicated that quantum physics (try to get a good explanation of X bar theory). Contrary to Quantum Physics, his theories have little support in reality. His theories have been described as being little more than interesting mathematics.

(I might not be a physicist, but I am a linguist of sorts)

driod33 said...

I have read the article, but it doesn't yet click in my mind.(sorry a bit slow)When you say "Physicists therefore interpret the singularities in general relativity as signs that the theory is no longer applicable and must be corrected."
Maybe there is something else that they have not thought of that doesn't preclude infinities?

Sabine Hossenfelder said...

driod,

You are right, the singularities are an issue which is often mentioned, but they are not strictly speaking inconsistencies. Singularities are believed to be nonsense, but mathematically they're perfectly fine. The problem is how to combine GR with the standard model consistently. If you have any theory that does that, you're in the game. It is widely believed however that such a theory will also remove the singularities. Best,

B.

MarkusM said...

"I hope we agree that there's plenty of evidence that quantum mechanics and quantum field theory is correct." - Sure, but it's right exactly for those situations where it has been tested and these are many, indeed. But when gravity is involved or in the case of living systems the evidence is less clear, at least to me. (Actually nobody seems to know what life is in the first place).
I find it conceivable that gravitation will remain a purely classical phenomenon (cf. Dyson, Penrose) and the same could be true for life (at least for all practical purposes). I have to admit that I am not a Platonist, i.e. QM for me is just yet another recipe allowing my advanced animal brain to make predictions under certain circumstances. As it so happens the quantum formalism also works for human decision processes (quantum cognition), suggesting there is nothing ontological to QM.

"The problem is that the people who typically make such claims don't realize they're making an extraordinary claim." That's right, on the other hand people who claim that everything is just quantum mechanics tend to ignore certain problems, like the measurement problem or the hard problem of consciousness which seem to have no convincing solution within the formalism of orthodox QM.

Joe Perry said...

Saying we don't understand humans is very different to saying that work that goes into trying to understand humans is useless, or indeed easy to grasp. And you'll note the parenthesis after that bit too ('how they act and why') - he's talking about human beings' everyday behaviour. I really don't think it's unreasonable to characterise this as poorly understood (so that a lot of what is understood is grasped intuitively by most people - unsurprisingly seeing as understanding how humans act is something that humans have evolved to do!)

Also to Rob van Son - can assure you that Chomskyan linguistics is substantially easier to understand and work with than quantum physics, and that while they fail in large part to describe language (as do all linguistic theories which do not predict a large quantity of unrealistic linguistic systems), they are a real attempt trying to understand the human linguistic system on the basis of the real languages - not just a mathematical curiosity.

As for a good explanation of X-bar theory, I can have a go... As originally formulated, it's that lexical categories (nouns, verbs, and adjectives) can all be associated with two adjacent phrases, called a specifier and a complement, which behave alike in certain ways. This was used, for instance, to derive the parallel meanings in phrases like 'The enemy destroyed the city' and 'the enemy's destruction of the city'. Here 'the enemy('s)' is the specifier in both cases, and '(of) the city' is the complement. The theory was subsequently generalised to functional categories (grammatical items like articles, conjunctions, and tense-markers). Full arguments for *why* you'd want to have these parallel structures relies on quite subtle empirical arguments about grammaticality in English. An alternative hypothesis, current at the time, for the parallel phrases I mentioned above, for example, posited that the noun phrase was simply derived from the verb phrase. Chomsky showed that this couldn't be the case in a 1970 paper called 'Remarks on Nominalisations', on the basis of various facts of English grammar. X-bar theory isn't generally considered to be the correct way of doing these things anymore, but was an useful model proposed on the basis of empirical data to capture linguistic facts.

Sabine Hossenfelder said...

Markus,

We're talking past each other. I'm telling you that there's no known way to consistently AVOID that systems made of many small things are also described by what the small things do. It is, for all we presently know, not possible. There's no theory that does away with reductionism. If there's no consistent theory, it's not possible, regardless of whether you have tested a regime. You are claiming the impossible is possible. So I am asking, how do you want to do that?

As I said above, it's a big claim, and you don't seem to realize how big a claim that is. Best,

B.

Rob van Son (Not a physicist, just an amateur) said...

@Joe Perry
"Full arguments for *why* you'd want to have these parallel structures relies on quite subtle empirical arguments about grammaticality in English. "

Except, X-bar theory was a theory of HUMAN language, not just English. Also, Chomsky did not do empirical research (that was functional linguistics).

The description you gave was on the level of popular science descriptions of the Heisenberg Uncertainty principle. When you start to apply these principles to actual language and have to account for null operators and hidden movements in Generative Syntax, things are not that simple anymore.

When I tried to follow Generative Grammar talks, I quickly became nostalgic to my quantum physics courses.

Unknown said...

The universe is purely mental: http://www.nature.com/nature/journal/v436/n7047/full/436029a.html

CapitalistImperialistPig said...

Let's not forget Chomsky's actual point. Evolution has equipped most of us with mental tools that allow us to (albeit imperfectly) analyze the motives and intent of other people's behavior. Unlike quantum physics, which requires years of study and exceptional talent to master, we almost all develop these human talents in our natural environment.

Not only that, but the human talents are actually pretty effective in analyzing other people, while quantum mechanics is worse than useless for that purpose.

driod33 said...

Thank you,mathematics seems to point to deeper ideas, antimatter, neutrinos,and the Multiverse. But maybe that does not apply to singularity's.

Sabine Hossenfelder said...

CIP,

That's a fair point - if you are dealing with a group of 100 people whose main long-distance communication channel is smoke signals. Evolution has not even remotely equipped us to understand what happens in systems of billions of people tightly connected in social networks. Best,

B.

John Loop said...

..Trying to digest your and Markus conv... Great blog! But I would say there is hope for you. :) My take: "..it’s quite remarkable some people believe they can explain the world" This is maybe a "religious"/maybe even.. a conservative belief. It is charming that a physicist says this about physics. I find it amazing that it would NOT apply ...in spades... to the non physic(al) world, especially believing this. Love ya. John

Pfogle said...

Human behaviour is emergent on many levels - particularly the individual and the group. We may well have evolved with all the tools to understand others' actions, but that does not make them any more predictable, especially where large groups are involved.

As with QM, we can see the possibilities, perhaps calculate probabilities, but we can't ever say with certainty what's going on inside someone else's head!

Don Foster said...

I understand you are not quite serious here, but there is something that should be clarified. You seem to be putting Quantum Mechanics in the role of causal agent. There is an actual physical universe out there that I expect would manage to carry on without our physics, quantum or otherwise, and perhaps even without Noam Chomsky.

Uncle Al said...

Macroeconomics bloodily illustrates the follies of centrally administered national economies. No quantitative analytical tool usefully models positive feedback, corruption, regulatory avoidance (including taxation), and Beltway lobotomite procedural abuse.

Quantized gravitation is on no firmer ground for not first questioning its own assumptions that "must" be true for convenience, beauty, and clean traces. Two pairs of black holes merged classically, within a small fractional second to equilibrium, releasing less than 5 mass-% binding energy. Scientific socialism is no more believable.

CapitalistImperialistPig said...

Bee,

For sure, our instincts lose a lot of skill when dealing with billions of people, however connected.

I haven't seen any evidence that QM or even statistical mechanics can improve on them though.

Joe Perry said...

Rob:
Tried to post a comment, but it was too long. So I've only posted my reply to the second half of your post here, which is probably more interesting than the rest of my reply (I hope!)

"The description you gave was on the level of popular science descriptions of the Heisenberg Uncertainty principle. When you start to apply these principles to actual language and have to account for null operators and hidden movements in Generative Syntax, things are not that simple anymore."

Ok, but you wanted a good explanation of X-bar theory, not all of generative syntax! The description of X-bar theory I gave was more or less complete except that I left out the detail that a category forms a unit with its complement to the exclusion of its specifier. It's worth noting that X-bar theory, as originally developed, had the effect of *reducing* the numbers of transformations and abstract elements. In fact, some of Chomsky's students at the time went all the way to abolish transformations altogether - that's how we get nontransformational generative models like LFG and HPSG (which are much easier to implement computationally than current Chomskyan syntax, but are, in my view, much too powerful as linguistic theories: they don't really restrict the range of possible grammars at all).

Thing is, though, *all* models of syntax need some analogue of movement: we need to be able to explain why items realised in one part of a sentence behave like they're located in another part of the sentence (for example, why question words at the beginning of a sentence might function as an object, which is usually located after the verb). Similarly, we need to explain why elements that seem not to be present on the surface can apparently nonetheless have an effect on the objects around them (for example, why sentences without surface subjects behave like they do have subjects with respect to things like the distribution of reflexive pronouns). Once you admit this kind of machinery into the theory (movement and empty categories aren't the only ways, but something on the same order of complexity is required) I don't think it's surprising that they're applied to a wide range of phenomena, sometime productively, and sometimes less so. These strategies are most useful, I think, when they succeed in unifying apparently disparate phenomena in a wide range of languages. I can go into more detail on some ways I think this has been productive if you're interested?

"When I tried to follow Generative Grammar talks, I quickly became nostalgic to my quantum physics courses."

I always thought QM provided a nice analogy to the hidden things that go on in syntax. You generally can't observe the wave-function of a particle directly, but you need it for the theory to give the right predictions. Same is true of movements and empty categories and even phrase structure.

As for the relative difficulty, I'm someone who understands generative syntax pretty well but not quantum mechanics, so I probably can't be trusted. But just from trying to learn a bit of quantum mechanics on my own, I'd say it's pretty clear that the amount of intellectual labour required to do QM is an order of magnitude or so more than to do GS.

And I'd say comparing a talk to a course isn't exactly apples to apples!

Sabine Hossenfelder said...

Don,

The universe would go on whether or not we understand quantum mechanics. It wouldn't go on without quantum mechanics. Best,

B.