[timr]

Except it isn't "completely wrong". The article the OP links to says it explicitly:

> “What actually causes lift is introducing a shape into the airflow, which curves the streamlines and introduces pressure changes – lower pressure on the upper surface and higher pressure on the lower surface,” clarified Babinsky, from the Department of Engineering. “This is why a flat surface like a sail is able to cause lift – here the distance on each side is the same but it is slightly curved when it is rigged and so it acts as an aerofoil. In other words, it’s the curvature that creates lift, not the distance.”

The meta-point that "it's the curvature that creates the lift, not the distance" is incredibly subtle for a lay audience. So it may be completely wrong for you, but not for 99.9% of the population. The pressure differential is important, and the curvature does create lift, although not via speed differential.

I am far from an AI hypebeast, but this subthread feels like people reaching for a criticism.

[avs733]

the wrongness isn't germane to most people but it is a specific typology of how LLMs get technica lthings wrong that is critically important to progressing them. It gets subtle things wrongby being biased towards lay understandings that introduce vagueness because greater precision isn't useful.

That doesn't matter for lay audieces and doesn't really matter at all until we try and use them for technical things.

[kybernetikos]

The wrongness is germane to someone who is doing their physics homework (the example given here). It's actually difficult for me to imagine a situation where someone would ask ChatGPT 5 for information about this and it not be germane if ChatGPT 5 gave an incorrect explanation.

[avs733]

The predicate for that is you know it is wrong, that wrongness is visible and identifiable. With knowledge that is intuitive but incorrect you multiply risk.

[timr]

I grant your broader point, but extrapolating from this marketing copy is not a great example.

The real question is, if you go back to the bot following this conversation and you challenge it, does it generate the more correct answer?

[jdhwosnhw]

I would still say its completely wrong, given that this explanation makes explicit predictions that are falsifiable, eg, that airplanes could not fly upside down (they can!).

[JamesSwift]

I think its valid to say its wrong even if it reaches the same conclusion.

If I lay out a chain of thought like

  Top and bottom are different -> god doesnt like things being diffferent and applies pressure to the bottom of the wing -> pressure underneath is higher than the top -> pressure difference creates lift

Then I think its valid to say thats completely inaccurate, and just happens to share some of the beginning and end

[carabiner]

It's the "same amount of time" part that is blatantly wrong. Yes geometry has an effect but there is zero reason to believe leading edge particles, at the same time point, must rejoin at the trailing edge of a wing. This is a misconception at the level of "heavier objects fall faster." It is non-physical.

The video in the Cambridge link shows how the upper surface particles greatly overtake the lower surface flow. They do not rejoin, ever.

[timr]

Again, you're not wrong, it's just irrelevant for most audiences. The very fact that you have to say this:

> Yes geometry has an effect but there is zero reason to believe leading edge particles, at the same time point, must rejoin at the trailing edge of a wing.

...implicitly concedes that point that this is subtle. If you gave this answer in a PhD qualification exam in Physics, then sure, I think it's fair for someone to say you're wrong. If you gave the answer on a marketing page for a general-purpose chatbot? Meh.

(As an aside, this conversation is interesting to me primarily because it's a perfect example of how scientists go wrong in presenting their work to the world...meeting up with AI criticism on the other side.)

[carabiner]

Saw you were a biologist. Would you be ok if I said, "Creationism got life started, but after that, we evolved via random mutations..."? The "equal transit time" is the same as a supernatural force compelling the physical world act in a certain way. It does not exist.

[timr]

I am a biologist (biochemistry, but close enough). I don’t have a problem with what you wrote.

It’s not the same thing at all, though. We don’t know what “got life started”, and that’s the realm of faith.

This is more like saying that “evolution is due to random mutation”, which is technically wrong, but close enough to get the point across.

[adgjlsfhk1]

right, the other is that if you remove every incorrect statement from the AI "explanation", the answer it would have given is "airplane wings generate lift because they are shaped to generate lift".

[timr]

> right, the other is that if you remove every incorrect statement from the AI "explanation", the answer it would have given is "airplane wings generate lift because they are shaped to generate lift".

...only if you omit the parts where it talks about pressure differentials, caused by airspeed differences, create lift?

Both of these points are true. You have to be motivated to ignore them.

https://www.youtube.com/watch?v=UqBmdZ-BNig

[tatjam]

But using pressure differentials is also sort of tautological. Lift IS the integral of the pressure on the surface, so saying that the pressure differentials cause lift is... true but unsatisfying. It's what makes the pressure difference appear that's truly interesting.

Funnily enough, as an undergraduate the first explanation for lift that you will receive uses Feynman's "dry water" (the Kutta condition for inviscid fluids). In my opinion, this explanation is also unsatisfying, as it's usually presented as a mere mathematical "convenience" imposed upon the flow to make it behave like real physics.

Some recent papers [1] are shedding light on generalizing the Kutta condition on non-sharp airfoils. In my opinion, the linked papers gives a way more mathematically and intuitively satisfying answer, but of course it requires some previous knowledge, and would be totally inappropriate as an answer by the AI.

Either way I feel that if the AI is a "pocket PhD" (or "pocket industry expert") it should at least give some pointers to the user on what to read next, using both classical and modern findings.

[1]: https://www.researchgate.net/publication/376503311_A_minimiz...

[ummonk]

The Kutta condition is insufficient to describe lift in all regimes (e.g. when the trailing edge of the wing isn't that sharp), but fundamentally you do need to fall back to certain 2nd law / boundary condition rules to describe why an airfoil generates lift, as well as when it doesn't (e.g. stall).

There's nothing in the Navier-Stokes equations that forces an airfoil to generate lift - without boundary conditions the flowing air could theoretically wrap back around at the trailing edge, thus resulting in zero lift.

[timr]

The fact that you have to invoke integrals and the Kutta condition to make your explanation is exactly what is wrong with it.

Is it correct? Yes. Is it intuitive to someone who doesn’t have a background in calculus, physics and fluid dynamics? No.

People here are arguing about a subpoint on a subpoint that would maybe get you a deduction on a first-year physics exam, and acting as if this completely invalidates the response.

[boombapoom]

except we were promised to have "PHDs in our pocket" which would mean that this falls short on the sales expectations...

[ttoinou]

I would say a wing with two sides of different length is more difficult to understand than one shape with two sides of opposites curvatures but same length