No experiment can be repeated? (2 questions)

[moe darklight]

1) Hey, so I just started reading the Feynman lectures. In the second chapter he has a small intro to quantum and he says:

Another most interesting change in the ideas and philosophy of science brought about by quantum mechanics is this: it is not possible to predict exactly what will happen in any circumstance.

For example, it is possible to arrange an atom which is ready to emit light, and we can measure when it has emitted light by picking up a photon particle, which we shall describe shortly. We cannot, however, predict when it is going to emit the light or, with several atoms, which one is going to.

ok, so far so good, I was aware of this part. But then he goes on to say:

You may say that this is because there are some internal ‘wheels’ which we have not looked at closely enough. No, there are no internal wheels;

this is just the intro of the book so he might go into more detail later, but it caught my attention— I always figured that there were "internal wheels" and we just haven't discovered them yet, and that this is why we can't predict (or that the wheels were simply unobservable)...

but his statement implies there are no wheels at all?? is this actually the case? it seems weird that reactions would happen without rhyme or reason yet still follow a semi-predictable pattern. How do we know that there aren't any internal wheels that we are yet to discover?
Maybe I misunderstood what he meant (most probably :-) ).
2) (EDIT) I realize now my second question reads kind of stupid because I didn't really explain that well what I meant... I meant, since the lectures are pretty much the outline of a physics class, if in the same physics class now a days there would be any subject that is not mentioned in the books due to recent advancements.

I've read next to nothing on it, but I that know string theory is pretty new, even though some physicists find it to be loopy (haha end with a pun! everyone loves a pun, right? ... r-right?)

 

[Demystifier]

Moe, your point 1) is a good one.
The claim that "there are no internal wheels" is nothing but one of quantum myths discussed in
http://arxiv.org/abs/quant-ph/0609163
(See in particular Sec. 4)
The fact is that we really do not know if internal wheels exist or not. A more common name for such internal wheels is "hidden variables". What we do know, however, is that if hidden variables exist, then they must have some strange properties, such as nonlocality and contextuality. (In the paper above you will also find more detailed explanations of these properties.) These strange properties make some physicists believe that they do not exist, but nobody knows with certainty if they exist or not.

 

[Anonym]

R.F:” For example, it is possible to arrange an atom which is ready to emit light, and we can measure when it has emitted light by picking up a photon particle, which we shall describe shortly. We cannot, however, predict when it is going to emit the light or, with several atoms, which one is going to… You may say that this is because there are some internal ‘wheels’ which we have not looked at closely enough. No, there are no internal wheels.”

his statement implies there are no wheels at all?? is this actually the case? it seems weird that reactions would happen without rhyme or reason ...How do we know that there aren't any internal wheels that we are yet to discover? Maybe I misunderstood what he meant.

Sure. R.F. has in mind two fundamental properties of quantum systems: 1) all atoms, electrons and photons considered are the same (indistinguishable); 2) time in the quantum world has size (HUR). When you perform the measurement, you are looking at quantum world using classical eyes. In the classical world time have no size, the quantum size tie up to the same single point. All you may say is that all photons were emitted within that delta t and this is consistent with the fact that the identical particles are indistinguishable (otherwise you may distinguish them using time tag). The emitted photons are the wave packets. If you will measure delta E, you may calculate delta t (for example). Sure that in this measurement you must use repeatability. Notice that I did not use any internal “wheels” and I do not understand what is weird here. The R.F. example describes the transition from the upper energy state to the lower energy state exactly as in classical physics.

The answer to your second question is yes.

Regards, Dany.

 

[moe darklight]

The answer to your second question is yes.

Sweet, so QM somehow proves that everyone loves a pun! So from the pdf (I read the sections that talked about the randomness) in a nutshell I get that there could be hidden variables, some physicists believe that there probably aren't, so I'm guessing, from his comment, that Feynman was in that group.

I guess what confused me was that his wording seems to imply that we know for a fact that there aren't any hidden variables, which seems counter intuitive to me (and physics are often counter intuitive so I wanted to make sure).

Like I said I just started reading the book so I have a long way to go until I can understand this in more detail, but that statement kind of struck me so I wanted to get it out of the way (it was bugging me all day actually lol).
I realize now my second question reads kind of stupid because I didn't really explain that well what I meant... I meant, since the lectures are pretty much the outline of a physics class, if in the same physics class now a days there would be any subject that is not mentioned in the books.

 

[JesseM]

For fermions we can say that there are no internal variables if we assume they obey the same quantum rules as all observable variables, because the Pauli exclusion principle, which implies that even if we hadn't discovered some variables yet we could tell if the set of variables we had so far was incomplete. But this doesn't rule out hidden variables which fail to obey the same rules as measurable variables.

 

[Anonym]

I guess what confused me was that his wording seems to imply that we know for a fact that there aren't any hidden variables, which seems counter intuitive to me.

The assumption about existence of the “hidden” variables that describe the quantum world as the classical world is so counter intuitive to me that I never read even one paper in that direction (at least did not finished reading to the end). Similarly, for example, the assumption that the universe is described by SE seems to me outrageously stupid.

I realize now my second question reads kind of stupid because I didn't really explain that well what I meant...

Now I see that I understood your second question correctly and I did not consider it stupid.

Regards, Dany.

 

[Anonym]

Perhaps it is worth to add something.

so I'm guessing, from his comment, that Feynman was in that group.

In addition, it is pretty good group: A.Einstein, E. Schrödinger, W. Heisenberg, P.A.M. Dirac, J. von Neumann, etc. For me the case was closed after J. von Neumann discussion (I consider the statement made by youngster J.S.Bell as simply unmannerly kid).

If you intend to prove that somebody is wrong you will not have time to do something positive in your life.

Regards, Dany.

 

[moe darklight]

Well I'm obviously not anywhere near the level of being able to understand arguments on either side. My understanding of QM is superficial at best, so my comment also came form a purely superficial point of view.— The idea of something being random is very hard for me to understand, harder than other "weird" concepts like infinity and extra dimensions, I just can't fit it in my head.

By the way, you listed Einstein, I thought he did have a problem with the idea (the whole "god does not play dice" thing).

Well, I hope I'll get a bit clearer picture once I get to the 3rd book that has all the QM stuff.

 

[Demystifier]

In addition, it is pretty good group: A.Einstein, E. Schrödinger, W. Heisenberg, P.A.M. Dirac, J. von Neumann, etc. For me the case was closed after J. von Neumann discussion (I consider the statement made by youngster J.S.Bell as simply unmannerly kid).

Einstein was definitely NOT in that group. He never accepted that nature is probabilistic and that QM is a complete description of nature.
Schrodinger was also not in that group, he never accepted the concept of "quantum jumps".
The case was definitely NOT closed by Neumann, while your statement on Bell is simply meaningless.
Nevertheless, it would be interesting to see what words would you choose to characterize the contribution of D. Bohm.

 

[Demystifier]

1. The assumption about existence of the “hidden” variables that describe the quantum world as the classical world is so counter intuitive to me that I never read even one paper in that direction (at least did not finished reading to the end).

2. Similarly, for example, the assumption that the universe is described by SE seems to me outrageously stupid.

1. Who said that hidden variables are classical? We know for sure that they must have at least one nonclassical property - nonlocality.

2. So, the universe is described neither by hidden variables, nor by SE. Then, how it is described?

 

[Anonym]

Well, I hope I'll get a bit clearer picture once I get to the 3rd book that has all the QM stuff.

I don’t know what your current background is. The Feynman Lectures on Physics are extremely difficult since they are extremely deep (in addition they are the experiment of the one-to-one translation of R.P. Feynman volume of knowledge of the mathematics into English). Certainly, it is not good introduction (the anecdote say that the students that were able to pass his exams successfully were accepted to be his Ph.D. students). When you will complete your degree and in order to check whether you also understood something you may return to the Lectures. There are number of excellent modern introductions in QM, for example, S. Gasiorowicz “Quantum Physics”.

The idea of something being random is very hard for me to understand, harder than other "weird" concepts like infinity and extra dimensions, I just can't fit it in my head. By the way, you listed Einstein, I thought he did have a problem with the idea (the whole "god does not play dice" thing).

So, you are in pretty good group (see above). Notice, that in my post (#3) I did not use the statistical interpretation either.

Nevertheless, it would be interesting to see what words would you choose to characterize the contribution of D. Bohm.

I agree with A.Einstein:” It, in my view, cheap consideration”.

Regards, Dany.

 

[Demystifier]

I agree with A.Einstein:” It, in my view, cheap consideration”.

Although I am an adherent of the Bohmian interpretation, I agree with Einstein that this interpretation is very cheap. But, unlike Einstein, I take it as a virtue, not as a drawback. For me, cheap means simple, and I prefer simple interpretations, not "deep" and "mysterious" ones.

 

[Anonym]

The universe is described neither by hidden variables, nor by SE. Then, how it is described?

To the best of my knowledge the state-of-art description of the universe (large scale phenomena) is given in terms of A.Einstein general theory of gravitation. Indeed, a more complete description will be achieved in future by the kids like moe darklight.

But, unlike Einstein, I take it as a virtue, not as a drawback. For me, cheap means simple, and I prefer simple interpretations, not "deep" and "mysterious" ones.

I think that the point here is that you ignore the fact that laws of nature are defined by God and not by you. And A.Einstein had better experience with that compare with you.

Regards, Dany.

 

[DrChinese]

I think that the point here is that you ignore the fact that laws of nature are defined by God and not by you. And A.Einstein had better experience with that compare with you.

Kind of an odd comment. I am not sure how you would know this about Demystifier.

 

[Demystifier]

Kind of an odd comment. I am not sure how you would know this about Demystifier.

That's easy: Everybody is less clever than Einstein, so Demystifier is less clever than Einstein too.

 

[Demystifier]

To the best of my knowledge the state-of-art description of the universe (large scale phenomena) is given in terms of A.Einstein general theory of gravitation. Indeed, a more complete description will be achieved in future by the kids like moe darklight.

And what about the small scale phenomena of the universe?

 

[Anonym]

I am not sure how you would know this about Demystifier.

What do you mean? That Demystifier is not a God or that laws of nature are not defined by him? I do not know. It is interpretation and as you know I am very weak in interpretations. Therefore, I asked your help in Why don't the Slits collapse the wave function? The paper written not clears enough for me. I am still waiting your even comment.

Regards, Dany.

 

[moe darklight]

Indeed, a more complete description will be achieved in future by the kids like moe darklight.

I doubt this since the degree I'm going for is digital film production , I just really enjoy science (I was torn between biology and film, but I chose film as a career). So the best I could offer is a very accurate science fiction movie some day :rofl:

I have heard about the third book being hard, so I'm expecting a challenge.. I'm not in a school setting and I don't have the pressure of deadlines and exams, so I can take as long as it takes for me to understand it.

Thanks for the explanations

 

[paw]

So the best I could offer is a very accurate science fiction movie some day :rofl:

I'd be satisfied with that. We could use accurate sci-fi's in place of the garbage we generally get from Hollywood.

 

[rewebster]

I'd be satisfied with that. We could use accurate sci-fi's in place of the garbage we generally get from Hollywood.

Who knows for sure about the garbage?

Without the TV series "Quantum Leap" there MAY not have been string theory!



(everything's connected )

-----------------------------------------------
and before TV, Well's "Time Machine" was written just a couple years before relativity came out.

 

[Anonym]

I doubt this since the degree I'm going for is digital film production... So the best I could offer is a very accurate science fiction movie some day... I'm not in a school setting and I don't have the pressure of deadlines and exams, so I can take as long as it takes for me to understand it.

I think you intend to choose a wrong way. It is not a matter of amount of time invested. Never, the entrance door is closed. The physics is Guild. To offer an accurate science fiction movie too much knowledge of mathematics and physics is required. Instead, you will convince yourself that you understood enough. Much better, I guess, to take the professional scientific adviser to your team and listen to him. You have plenty even here, in PF. From your side, don’t take it too serious. Keep smiling.

Regards, Dany.

 

[Anonym]

How to build a universe ?!
First step: Start at the beginning of time.
Step Two: Apply the laws of physics.
Step Three: Sit back, and watch the universe evolve.
Step Four: Cross your fingers and hope that it comes out looking something like the one we live in.

Demystifier, now you have a clever adviser also:

Finally, we have now a new set for building a universe.
Step One: look around you.
Step Two: Find the set of all possible histories that end up as a universe like the one we see.
Step Three: Add them together, and create a history for yourself.

Notice that the original question was:” How can we get number "9" by addition?”

Regards, Dany.