What is the hardest question to ask a quantum physicist?

[realblonde]

My friend thinks he can answer any question related to Quantum physics (although he claims he won't be able to answer known unknowns i.e 'the mass of the Higgs-Boson particle'). However, I would like to challenge him with a series of the hardest questions anyone on this forum can put to him.

I promise to post his answers up on this blog for you to see what he comes back with.

Many Thanks!

 

[Char. Limit]

Why do you study this stuff?

Just kidding, although I have always wondered that.

 

[Matterwave]

What is the fine structure constant (really)? And why is it very nearly 1/137?

Iono, there's some weird stuff in Quantum that'd be pretty hard to answer...

 

[humanino]

A good one is to prove mathematically that gauge theories with spontaneous symmetry are renormalizable.

 

[jtbell]

"Which interpretation of QM is the correct one?"

 

[Demystifier]

Is the moon there when nobody looks?

 

[Mr confusion]

i also think this is a challenging one-is the moon there when nobody looks?
ie. the epr paradox.

 

[conway]

It's really a matter of degree. The deep metaphysical questions that people have posted are really not on target to my way of thinking. The problem is that you don't have to get very deep into the subject at all before the calculations become excruciatingly difficult. I would say that if your friend is capable of doing the standard calculation of the energy levels for the Hydrogen atom (the actual wave functions, that is: not the simplified Bohr atom) with nothing but a pencil paper (no look-ups except for the fundamental constants h and q etc.) then his claim has at least a grain of truth to it.
If he can calculate the ground state energy of the helium atom, then he is pretty good. If he can calculate the first excited state of helium, then he is at the very highest level. We should forgive him if he cannot readily calculate the boiling point of water or the electrical conductivity of copper.

 

[Nuno Amiar]

Is the moon there when nobody looks?

Why is that such an hard question?

 

[peteratcam]

Your friend obviously knows very little, to have claimed he knows so much.

I would ask him to solve the hydrogen atom by path integral methods, and explain clearly why Feynman wasn't able to do it. If he can do this then he is arrogant and clever, rather than arrogant and stupid.

(This is not a known unknown - Kleinert did it in 1979 so it is certainly doable, but you can imagine that if it left Feynman stumped, it is not an easy problem even though the H-atom is almost the first bit of QM anyone studies.)

 

[tiny-tim]

hmm … just quote to him what both Bohr and Feynman said …

"Anyone who thinks he understands quantum mechanics, doesn't understand quantum mechanics" ​

 

[Demystifier]

Why is that such an hard question?

Because it can be reduced to "Is electron there when nobody looks?", which is a hard question because it is not known (or at least there is no consensus) what is the correct interpretation of quantum contextuality, entanglement and nonlocality.

 

[Demystifier]

hmm … just quote to him what both Bohr and Feynman said …

"Anyone who thinks he understands quantum mechanics, doesn't understand quantum mechanics" ​

And what about those who think that they do not understand quantum mechanics?

 

[lightarrow]

"I send a single photon through a thin slit. Tell me the exact point where this photon will hit a screen after the slit".

I'm impatiently waiting for the answer...

 

[LukeD]

If he claims to know so much, why don't you just ask him something you want to know? Try to expose him by legitimately taking him up on his offer.

Ask him to explain the EPR "paradox" and its solution.
Ask him to explain why quantum cloning is impossible. (it violates conservation of probability)
Ask him to explain non-commuting variables and what they mean for the uncertainty principle.
Ask him to explain the quantum harmonic oscillator and its energy spectrum.
and I could go on..

Any physics grad should be able to talk about those.

If he knows something, he should be able to talk meaningfully about these.
Otherwise, you'll have exposed him as the fraud he is.

 

[Nuno Amiar]

Because it can be reduced to "Is electron there when nobody looks?", which is a hard question because it is not known (or at least there is no consensus) what is the correct interpretation of quantum contextuality, entanglement and nonlocality.

Well can it be reduced to that question? What is to look at an electron? Isn't it basicly interacting with it? Independently of anyone "looking" at the moon or not, the moon itself is always a system of interacting particles wether it be the photons emitted from the sun or the moon particles themselves. As far as my interpretation of QM goes, the moon is always "being looked upon" wether it be by a conscious being or not. Is this interpretation correct?

 

[conway]

I'm starting to wonder why everyone seems so intent on exposing the individual in question as a fraud. Are there no circumstances wherbey someone could reasonably claim to have a proficient overall grasp of the subject, to the point where any reasonably posed problem should have a calculable solution? I previously gave the example of a helium atom: if someone can look at the problem and write down the correct differential equations, and set up some reasonable program for seeking out numerical solutions, then can he not claim to be able to have answered the question?

I also have the impression that there are plenty of people who post regularly to this discussion group who feel they are qualified to "answer any question relating to quantum physics". Again, why do we assume that the person in question is any different?

 

[humanino]

I'm starting to wonder why everyone seems so intent on exposing the individual in question as a fraud. Are there no circumstances wherbey someone could reasonably claim to have a proficient overall grasp of the subject, to the point where any reasonably posed problem should have a calculable solution? I previously gave the example of a helium atom: if someone can look at the problem and write down the correct differential equations, and set up some reasonable program for seeking out numerical solutions, then can he not claim to be able to have answered the question?

I also have the impression that there are plenty of people who post regularly to this discussion group who feel they are qualified to "answer any question relating to quantum physics". Again, why do we assume that the person in question is any different?

I think answering the question I raised requires a much deeper understanding of quantum theory that even calculating numerically the atomic spectrum of Helium. In fact maybe showing that "gauge theories with symmetry breaking are renormalizable" is maybe too much to ask, and your proposal is more reasonable/realistic. I also do not make the claim that we could not find another even more difficult technical question. But I certainly agree that asking "interpretational" question is not a well posed problem. Nobel prizes and world known experts in general do not agree on interpretation anyway.

 

[atyy]

Is reality deterministic?

 

[tiny-tim]

Is reality deterministic?

I knew someone was going to ask that.

 

[atyy]

I knew someone was going to ask that.

I mean apart from fish being able to predict the future!

 

[tiny-tim]

It's elementary fishics!

Preserve the bowliverse! ​

 

[Mentz114]

It's elementary fishics!

Preserve the bowliverse! ​

Ta-rah !(Cymbals clash)

 

[Haelfix]

A good one is to prove mathematically that gauge theories with spontaneous symmetry are renormalizable.

That's just mean!

 

[TMFKAN64]

"Which interpretation of QM is the correct one?"

I would have gone with "But what does it all mean?" which is essentially the same question.

 

[Dmitry67]

For the given number of Protons and Neutrons, calculate the lifetime of nuclei

 

[Demystifier]

Well can it be reduced to that question? What is to look at an electron? Isn't it basicly interacting with it? Independently of anyone "looking" at the moon or not, the moon itself is always a system of interacting particles wether it be the photons emitted from the sun or the moon particles themselves. As far as my interpretation of QM goes, the moon is always "being looked upon" wether it be by a conscious being or not. Is this interpretation correct?

I could answer this in another thread, but here I would like to leave the answer to the friend of the thread starter.

 

[lightarrow]

Well can it be reduced to that question? What is to look at an electron? Isn't it basicly interacting with it? Independently of anyone "looking" at the moon or not, the moon itself is always a system of interacting particles wether it be the photons emitted from the sun or the moon particles themselves. As far as my interpretation of QM goes, the moon is always "being looked upon" wether it be by a conscious being or not. Is this interpretation correct?

Your is a conjecture that you cannot prove experimentally = with physics.

 

[Nuno Amiar]

Your is a conjecture that you cannot prove experimentally = with physics.

I am not conjecturing. I am simply stating that the act of observing (measuring) is such that it happens all the time around us.

 

[Count Iblis]

Suppose a physicist in northern Greenland falls and tunnels through the Earth to end up in Antarctica. Compute the probability distribution for the subjective time the tunneling takes as experienced by the physicist.

 

[jostpuur]

One of the most surprising things I was forced to learn during my QM studies, is that physicists do not yet know how to compute spatial probability densities of quantum particles in order to predict interference patterns and other patterns you encounter if you shoot particles to a detector wall or film.

So I would ask a following question: Suppose we have a source approximately at origo (0,0,0), a detector plane orthogonal to the z-axis, at location z=L (means a plane (x,y,L)_{x,y\in\mathbb{R}}), and suppose we know the time evolution of the wave function \Psi(x,y,z,t), which starts at t=0 approximately at origo, and then proceeds as a wave packet towards the detector wall. What is the probability density \rho(x,y) for the particle's observation point on the wall?

IMO this is an unknown unknown so it qualifies as a question to the realblonde who didn't want known unknowns.

 

[conway]

People continue to scoff at the purported claim for all the wrong reasons. Why is it unreasonable to claim that one can "answer any question" about quantum mechanics?
Obvioulsy this is out of the question if we interpret it as meaning that you could calculate anything to any desired accuracy. But how unreasonable would it be to say you can "explain any phenomenon" involving quantum physics?

Let's turn it around and consider what this claim might mean if you applied it to classical physics. Because I would venture that most of us think we basically understand all of classical physics. But to take an example, does that mean we can all calculate the velocity distribution of molecules in an ideal gas, as Maxwell did 150 years ago? Probably very few people could. And yet there is no deep mystery as to how the equilibrium comes into being, once you have thought about the collision of two billiard balls essentially creating a new, random distribution of velocities under the constraints of energy and momentum conservation. Apply this to millions of particles and it is easy to believe that eventually a velocity distribution will be created which is in a sense more random than all other possible results. In this way you can reasonably claim to understand, and even "explain" what is happening, without being able to do the actual calculation.

What is really different about quantum mechanics is that even for relatively straightforward questions, like the energy states of the Helium atom, there are very few people that feel they have a solid idea of what exactly is going on physically, regardless of the actual calculation. In fact, for a lot of people who have acheived some proficiency, there are probably more problems for which they can do the detailed calculations that problems for which they can actually "explain" what is going on. This is the opposite of the situation with classical physics.

 

[marthkiki]

My friend thinks he can answer any question related to Quantum physics (although he claims he won't be able to answer known unknowns i.e 'the mass of the Higgs-Boson particle'). However, I would like to challenge him with a series of the hardest questions anyone on this forum can put to him.

I promise to post his answers up on this blog for you to see what he comes back with.

Many Thanks!

Unify quantum mechanics and relativistic physics in a perfect theory.

 

[Count Iblis]

How to do computations in http://insti.physics.sunysb.edu/~siegel/parodies/atchoo.html" ?

 

[Phyisab****]

A good one is to prove mathematically that gauge theories with spontaneous symmetry are renormalizable.

Clearly the best of all the questions posed. So many ill posed/philosophical/unknown questions here it makes my head hurt! Is the moon there if you don't look at it? The moon isn't even a quantum particle, and it's not a reasonable question if it was.

 

[heldervelez]

How to derive the value of Mass property of particles?

 

[Demystifier]

The moon isn't even a quantum particle,

But it is made of quantum particles, isn't it?

 

[amir11]

a bit late but I think very simply ask him what the photon is.
probably every one knows the famous answer by einstien!

 

[humanino]

a bit late but I think very simply ask him what the photon is.

It's a quantum of the photon field. You may as well say "but what is the photon field ?", however one can play this game with any question. Same game could be played with "but what is a quantum, really ?". My point is : within QED, a photon is a well-defined mathematical concept, and if you want to go into "but what is it really ?" the only answer you will get is that QED works fine as far as experiment is concerned.

 

[Count Iblis]

It's a quantum of the photon field. You may as well say "but what is the photon field ?", however one can play this game with any question. Same game could be played with "but what is a quantum, really ?". My point is : within QED, a photon is a well-defined mathematical concept, and if you want to go into "but what is it really ?" the only answer you will get is that QED works fine as far as experiment is concerned.

That's why all physicists should believe in Tegmark's ideas about reality being purely mathematical in nature: All that exists is only abstract math, and thus our universe is the mathematical model that describes it and nothing more.

 

[Frame Dragger]

The same question parents and teachers have struggled with forever! "Where do baby Quantum Physicists come from?"

 

[torquil]

That's why all physicists should believe in Tegmark's ideas about reality being purely mathematical in nature: All that exists is only abstract math, and thus our universe is the mathematical model that describes it and nothing more.

Since I'm reading Penrose's "Road to Reality" at the moment, I've been exposed to a lot of discussion about the "nature of reality". However, I find the concept of "reality" to be much less well-defined than the physical theories that are used in practice.

For me it is not sufficiently well-defined to talk about the nature of reality.

What is great however, is that the ability of physics to describe/predict our observations of all kinds of phenomena is improving with time, independently of how one wishes to define "reality".

Torquil

 

[yoda jedi]

not only quantum physicists

Is the moon there when nobody looks?

i like it !
easy one !

"Which interpretation of QM is the correct one?"

i like it !

Your friend obviously knows very little, to have claimed he knows so much.

I would ask him to solve the hydrogen atom by path integral methods, and explain clearly why Feynman wasn't able to do it. If he can do this then he is arrogant and clever, rather than arrogant and stupid.

(This is not a known unknown - Kleinert did it in 1979 so it is certainly doable, but you can imagine that if it left Feynman stumped, it is not an easy problem even though the H-atom is almost the first bit of QM anyone studies.)

well said !

 

[amir11]

It's a quantum of the photon field. You may as well say "but what is the photon field ?", however one can play this game with any question. Same game could be played with "but what is a quantum, really ?". My point is : within QED, a photon is a well-defined mathematical concept, and if you want to go into "but what is it really ?" the only answer you will get is that QED works fine as far as experiment is concerned.

As far as I know a photon has not got any clear description even in terms of QED. I ment the quot by einstien
: "All the fifty years of conscious brooding have brought me no closer to the answer to the
question: what are light quanta? …..…… Of course, today every rascal thinks he knows the
answer, but he is deluding himself.”

 

[Living_Dog]

My friend thinks he can answer any question related to Quantum physics (although he claims he won't be able to answer known unknowns i.e 'the mass of the Higgs-Boson particle'). However, I would like to challenge him with a series of the hardest questions anyone on this forum can put to him.

I promise to post his answers up on this blog for you to see what he comes back with.

Many Thanks!

Is the cat alive?

 

[Frame Dragger]

Is the cat alive?

Do that one better and ask him about 'Wigner's Friend'.

EDIT: If you want to trip him up with something obvious, ask him what the difference is between the 'Sum Over Histories' for a particle, and the "Path Integral" for a particle. If he says anything other than, "same thing", shoot him, he's an alien.

 

[torquil]

As far as I know a photon has not got any clear description even in terms of QED. I ment the quot by einstien
: "All the fifty years of conscious brooding have brought me no closer to the answer to the
question: what are light quanta? …..…… Of course, today every rascal thinks he knows the
answer, but he is deluding himself.”

What was Einsteins objection to the description of the photon in QED? Is it simply related to his general objection to quantum physics and its non-local measurement aspects?

Or is it related to technical aspects of QED, e.g. regarding the definition of an asymptotically free single photon in/out state, in the presence of vacuum fluctuations? Or maybe problems with convergence of perturbation theory?

Btw, do these technical aspects pose any problem in pure QED?

Torquil

 

[humanino]

As far as I know a photon has not got any clear description even in terms of QED. I ment the quot by einstien
: "All the fifty years of conscious brooding have brought me no closer to the answer to the
question: what are light quanta? …..…… Of course, today every rascal thinks he knows the
answer, but he is deluding himself.”

Again, the photon is well defined mathematical concept in QED. It's actually quite funny that you decided to use a quote from Einstein to justify your attitude, because Einstein himself came up with the idea of a photon. So you might as well have used a quote from Planck rejecting Einstein's idea of the photon.

 

[jtbell]

As far as I know a photon has not got any clear description even in terms of QED. I ment the quot by einstien
: "All the fifty years of conscious brooding have brought me no closer to the answer to the
question: what are light quanta? …..…… Of course, today every rascal thinks he knows the
answer, but he is deluding himself.”

It's been more than fifty years since Einstein died! Don't you think there might be a possibility that we might have learned a few things about photons since then?

 

[DrChinese]

The same question parents and teachers have struggled with forever! "Where do baby Quantum Physicists come from?"

LOL