# How Many People Actually Understand QM?

1. Apr 12, 2007

### Giuseppe Mayart

What I mean to ask is, are there any statistics that detail the percentage of people on the planet who have the capacity to understand quantum mechanics?

I ask because I’ve heard a lot of people, who are very smart, say that they’ve attempt to work out the math of QM and were completely stumped. Perhaps logistical/mathematical understanding is not their strong suit and the show their intelligence in other areas. But still I’m just curious, what is it like, 2% or 1% (perhaps less) of the world’s population can understand QM?

2. Apr 12, 2007

### robphy

"I think, I can suggest, that nobody
understands the quantum mechanics." - Feynman

http://www.aaas.org/programs/international/caip/isc/Bauer/I.pdf [Broken]

Last edited by a moderator: Apr 22, 2017 at 4:57 PM
3. Apr 12, 2007

### Mike2

Actually, it is the essence of logic itself. The most obvious thing we could say about nature is that all things exist in conjunction. For obviously the chair that you are sitting on exist, and the floor holding up the chair exists, and the walls exist and the door exists, etc. This even applies to things we don't observe such as things in the other room. Though we assume they exist in conjunction with what we do observe, we have some uncertainty about the likelihood that they are still there. So we naturally assign some probability to the existence of things we haven't observed yet. For that matter, we might also assign some probability to things we do observe. Are things that we see exactly what we think they are?

And if we start with the presumption that all things are consistent, and each thing that exists does not prove the non-existence of any other thing that does exists, then again this is equal to saying all things exist in conjunction.
For

~(A->~B)=A*B

where "~" is negation, "->" is implication, and "*" is conjunction. Then the development I outlined (link below) proceeds logically to the path integral formulation of QM.

Since we have A*B=(A->B)*(B->A), and a probability is assigned to conjoining new facts, then implication, "->", can be seen as a path with an amplitude that is the square root of a probability (See Link).

So starting from the premise of logical consistency between all facts (whatever they might be) the path integral formulation of QM can be derived.

We're not allowed to talk about the details here since it is not on the arXive yet. Until then, see:

http://news.killfile.org/index.cgi?group=sci.physics.foundations&number=698 [Broken]

Last edited by a moderator: Apr 22, 2017 at 4:57 PM
4. Apr 12, 2007

### christianjb

Nobody understands QM to its full extent, but lots of people know enough to make calculations that are in accordance with expt., which is what we expect from any theory.

Off the top of my head, I would estimate that 5-10% of people have enough 'smarts' and aptitude to use QM as a useful tool. That probably translates to 75% of people on this board.

Basically, just about anyone who's smart enough to be interested in QM is probably smart enough to use QM.

However, if you're talking about the number of people smart/creative enough to develop the fundamental theories of QM in useful, novel and interesting ways not previously explored... That's maybe closer to 5% of 5%.

I can use QM as a tool without any great strain on the noggin- but I'm probably not skilled enough to really make much progress in questioning the fundamental foundations of QM in any new/interesting way.

5. Apr 12, 2007

### Ki Man

really? for soemthing on that level, i thought it should be something more to the likes of .0003% of all people when it comes to pioneering the science

6. Apr 12, 2007

### christianjb

Perhaps, but neither of us have any data. It may be that most of these smart people are concerned with other problems at the moment.

7. Apr 12, 2007

### masudr

Those who think we don't understand quantum mehcanics should ask, "who understands classical mechanics?"

The principle of least action is at least as mysterious (if not more so) than the path integral formulation, in my opinion.

8. Apr 13, 2007

### Thrice

Define "understand" and you can answer the question. Otherwise this is just empty talk.

9. Apr 13, 2007

### masudr

Use Oxford English Dictionary, Webster etc.

10. Apr 13, 2007

### Jimmy Snyder

OED gives 14 senses for the word 'understand' and most senses have several subsenses. Which one did you have in mind?

11. Apr 13, 2007

### masudr

I can't access the OED online until I'm back on the College network. I'm moving back on Sunday.

Anyway, my point was that if we "understand classical mechanics", then whatever sense we mean by understand in that phrase, we can probably also apply that sense to the phrase we "understand quantum mechanics," hence making it irrelevant which sense I meant.

Besides, I'm not the OP. What sense did they mean when they said "understand"?

12. Apr 13, 2007

### Jimmy Snyder

Or "Quantum Mechanics". It covers a number of areas so large that I doubt any single person is even aware of all of its aspects, let alone understand them.

The OP wasn't really interested in knowing how many people understand the physics, they were asking how many can understand the math. I'm pretty sure they meant the math in an introductory text. When Feynman said no one understands QM, he didn't mean to imply that the authors couldn't do the math in their own books. In my opinion, anyone who is not mentally handicapped can understand an introductory QM text like Shankar's by the simple act of applying themselves to the task. However, lack of interest will prevent most people from commiting themselves for the amount of time it would take.

Last edited: Apr 13, 2007
13. Apr 13, 2007

### setAI

computer scientists

14. Apr 13, 2007

### Careful

I think it is safe to say that our understanding'' of classical mechanics is strongly motivated from experience with everyday objects whose objective existence is not questioned. Now, you were alluding to the variational principle : to my feeling the Newton laws are much more understandable than the Lagrangian formulation. Also, one can reformulate QM in terms of forces, where the wave function becomes a (rather strange) fluidum.
So, what we really do not understand in QM is the lack of an objective reality attached to either the wave and the particle, but we already knew this for long time .... :uhh:

15. Apr 13, 2007

### reilly

One difficulty in this thread is, what is "understanding?"

For example, the famous Feynman quote, and masudr's comments seem to me to be dealing with the very essence of things -- why is Nature the way it is? Why does QM work? Nobody has a clue; nobody understands...

But that's clearly not the whole story. I've known a couple of low-temperature experimentalists, who barely got through their theory courses. Yet they knew their stuff, QM and vacuum pumps, and knew it well. And, of course, their understanding was highly intuitive, feed by hands-on work. They were not particularly articulate nor demonstrative about their knowledge; they just did stuff, and they knew stuff.

I have absolutely no difficulty in saying that I understand QM. Prior to teaching QM. I might not have been so bold. I should append the word "practical" to "understand." Why the Schrodinger eq. why photons? Why the standard probability interpretation? Not to worry for your day job. Once you begin to master the mechanics of QM, you also learn about it's power to describe incredibly disparate phenomena. You learn by doing; you build an understanding based on practical experience. christianjb says much the same thing.

The DOL http://www.bls.gov/oco/ocos052.htm [Broken] article says there were roughly 16,000 working physicists in the US in 2004. The adult US population then was 218 million. So a generous estimate says that physicists comprise 1/100 of a percent of the adult population. Let's be generous and say another 16,000 are capable of doing QM with practical understanding, and we get up to 2/100% of the US adult population capable of working with and understanding QM.
Regards,
Reilly Atkinson

Last edited by a moderator: Apr 22, 2017 at 4:58 PM
16. Apr 13, 2007

### lalbatros

It all depends on what you mean by understanding.
If the math and the logic and the rules are involved, really many people understand QM.

But QM pushes our brain irremediably in some indeterminate state,
we get the impression that there is much more to understand,
but we even don't understand what.

17. Apr 14, 2007

### reilly

With the change of a word or two, you might as well be describing the human condition.

With all due respect, you encounter this intermediate state because you choose to. I say choose beause there are many physicists like me who take a very pragmatic approach to physics, and try to avoid indeterminacy in our thinking, at least about physics. So we don't worry about things like :why is the electrons's charge ? why spin?, why quarks; why does mass attract mass(substitute energy if you want,), why do Newton's Law's work; why do accelerating charges radiate?

Are these questions any less profound than, say, why does the Schrodinger eq. work? The plain fact is that it's all a big mystery, a cosmic crap shoot. To paraphrase Wigner's famous dictum; why in the hell should anything work?

The choice, then, is one of approach: pragmatic or formal, if you will. They are both certainly valid ways to procede. In the pragmatics world we say, "Sure, we understand QM, it works", in the formal world, they say,Of course we don't understand QM-- it may work, but why?

In today's informal language, QM is outside the box, the formalists want to get it inside the box we've already got; the pragmatisits say, grow the box as needed.

Regards,
Reilly Atkinson

Last edited: Apr 14, 2007
18. Apr 14, 2007

### tehno

IMO,this has been probably the best answer to OP's question so far!

19. Apr 15, 2007

### lalbatros

reilly,

I have this pragmatic approach too (I work as an engineer in the heavy industry).

However, everybody has come some day on strange questions in QM.
Strange but not necessary useful practically.
I am sure you know many of these questions, as you cited some of them.

For myself, the strange questions came right from the beginning.
I learn QM first in 1976. The teaching approach was based on the famous postulates.
The measurement process has a special place in this introduction to QM.
I had not yet studied the hydrogen atom, but I was already puzzled.
Why would the SE not be able to describe the measurement process?
Some years later, I even bought a collection of paper on this topis, edited by JA Wheeler.
I read a lot about it. I finally concluded this is a futile topic.
Well, still I would like to present QM in another way and show why and how the measurement postulate in useless.
I think I could not do that convincingly. Even with a toy model of the Stern-Gerlach experiment.

I just looked a bit at "Consistent Quantum Mechanics" by Griffiths on his web site.
Maybe I missed the right page, but I could not convince myself that this book could close this futile topic.

So, that illustrates how QM makes me (and others) wandering.

Michel

Last edited: Apr 15, 2007
20. Apr 15, 2007