GROUP READ - Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality

Hi everyone! This quarter, the Science, Religion, and History group are going to be reading Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality, by Manjit Kumar. Everyone is welcome to join - this is an equal opportunity group read. :)

This group read will take place from July through the end of September, and will have an informal discussion throughout.

Thanks for setting this up, and the reminder. I just put the book on hold with the library--should be here the beginning of next week, right on time.

I finished it last night. It was just right for my level of knowledge of these things, and it was very readable. I'll keep it at hand as the discussion progresses.

Robert

Thanks for setting this up Rachel. Will you be posting the weekly reading assignments/portions?

Oh, no...it's a read-at-your-own-pace sort of thing. Otherwise there's no way I'd be able to participate! :)

#5 Sure :)

I've just reserved a copy through ILL. I'm looking forward to reading it.

I started this a few days ago and despite having had a feverish cold that's kept me off the computer for the last week or so, I have to come here and say I'm having trouble putting this down. I was a little concerned in the first chapter or so following the initial experiments, but since then, the author has been excellent at formulating concepts that I can at least almost wrap my mind around, and the people are simple fascinating.

#8 My experience has been much the same, I have been making good progress on the book. It is like High School Physics revisited with all the cool stuff that was missing in those textbooks. Manjit Kumar has done a great job tackling this otherwise overwhelming topic.

It is so good to read your comments, ronincats and PiyushC! I'm all but set to get into the book (I read the author's acknowledgement, haha!, and really liked his style). Can't wait!

Karen O.

Read the first 5 chapters of the book, till "When Einstein met Bohr"! Even the title of the chapter sounds amazing, doesn't it?

I've just started. I found the first chapter a bit of a struggle. I really wish I remembered more physics!

I'm halfway through the second chapter, where Einstein is introduced. This material seems more familiar. Einstein's dislike for the German Reich at the turn of the century has me reading a bit of pre-WWI German history.

That first chapter was really the only place I did end up struggling, so carry on!

Since I now have an iPad with Kindle ap, I will start reading this tonight or tomorrow.

48. Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality - Manjit Singh

My Review

4/5

I've now read four chapters, and find it amazingly easy to follow. I may even finally be beginning to get a general idea of what quantam physics is about. At least it will be good to understand why it got started in the first place.

Let me know if you have any quantum questions - I sorta do this stuff for a living. :)

Gave you a thumbs up on your review, Piyush.

Several years ago I had someone explain some quantum thing to me, and he lost me immediately. I'm sure his explanation made sense to me, but I take most of it on faith.

From Piyush's review: It is like High School Physics revisited with all the cool stuff that was missing in those textbooks.
Well, this got me to order the book.

#17 Jim, I will take you up on that offer, can you shed some light on the Leggett Inequality?

#18 Thanks Roni :)

#20 I am sure you will like it as well, Katherine, I will stay tuned for your review of this one.

Let's see what I can do...

Ok, so without question, the world we see around us is different from the quantum world. I can reliably sit on a chair without worrying about my butt tunneling through the chair. As Einstein said, the Moon is still there even when nobody's looking at it.

The microscopic world is very different. Particles diffract like waves; waves are absorbed and emitted like particles. A quantum state is a mathematical description of something like a hydrogen atom - that is inherently statistical in nature. As such, we can only pin down, say, where a particle is when we do something to observe it. But the very act of observing it changes the thing we want to observe. In between observations, a particle is defined as this weird combination of all possible quantum states it could be in.

So for the universe to make sense, we need to understand how a very large number of microscopic quantum things make up a macroscopic thing like a chair. This is called the quantum-to-classical transition and is one of the fundamental problems of quantum mechanics. And this problem was one of the chief issues Einstein had with quantum mechanics.

Leggett developed a description of a classical-type object that resembles a quantum description using the idea is states. His rules were that the object must be in one definite state at all times and that measurements made of the state of this object do not affect the state of the object. The idea was that quantum mechanics was a simplified expression of a deeper theory that was non-local (particles can communicate without exchanging signals like light) and contained "hidden variables" that weren't observable but made particles look quantum. In doing this, he developed equations (technically inequalities) that showed a relation between observations of the state of this object made at different times. If a system obeys these inequalities it exhibits the property of "realism", meaning it follows the rules earlier in the paragraph.

One can actually test this sort of thing at a quantum level very easily, and it's clear that microscopic systems violate these inequalities, and so are not "realistic" in the sense above. Back in the 2007 timeframe, some experiments were conducted on big objects that demonstrated even everyday show quantum effects and not "realism". This means that even though it is unlikely in the extreme, it is still theoretically possible for my butt to slip through a chair every time I sit down! It's just that the very large number of particles involved drives everyday objects to behave in realistic ways.

How's that?

#22 That is very good and very helpful.

From the failure of Leggett's inequality, is it safe to assume that Einstein's famous euphemism "God doesn't play dice" through which he basically wanted to establish causality and dependence not valid? I am of course assuming that the "realism" referred by you, is causality and dependence.

What is your take on one of the thought experiments of Einstein in which he tries to measure both position and momentum by collision and through law of conservation of momentum and maintains that measurement of one particle doesn't affect the measurement of another particle at a great distance (local reality)?

The failure of Leggett's inequality at the microscopic level is definitely one of the things that put to rest his comment and others like it. Experiments confirming this are conducted every time we use, for instance, transistors in electric circuits. That, of course, hasn't stopped people from trying to incorporate "realism" - causality and dependence - into the theory as hidden layers. The EPR experiments - Einstein's thought experiments on "realism" - kicked off an extensive research topic that is one of the most active areas of physics today, quantum entanglement.

So when, for instance, two particles are created in a reaction, these particles are described by a joint quantum state that captures all the possible combination of parameters for the particle. For instance, one property of an electron is intrinsic angular momentum, called spin. This spin is characterized by a direction - spin up or spin down. In a reaction where two electrons are created, the two electrons must always have opposite spin; when measured, one will be spin up and one will be spin down. There are two theoretical possibilities here: (a) the spin for each is always well defined even though we may not know it until we make a measurement, or (b) the spin state of each electron is a combination of all the possible spin states and not definitized until a measurement is actually made. It turns out that mathematically, these two possibilities are very different, and experiments can determine which is true. And sure enough, (b) describes what happens in experiments. So until I make a measurement of the spin state of one of the electrons, neither are definitely up or down. Once I make a measurement of one electron and find that it is, say, spin up, the other has to be spin down. So by affecting one particle, I have mysteriously affected the other instantaneously and without energy exchange. This is called quantum entanglement and is one of the bigger puzzles in physics. And it really happens - experiments happen to measure this effect often, and it's a core concept of quantum computing. Quantum entanglement is the thing that resolves the EPR paradox in the sense that we can show the paradox doesn't exist in nature, and Einstein's ideas about "realism" were wrong.

#24 Understood, many thanks for the lucid explanation. Quantum entanglement is quite counter-intuitive, isn't it?

I can imagine why Einstein would be spooked by the violation of local reality and information travelling faster than light, which again shouldn't be possible (since it violates relativity) or am I missing something?

Nope, you're right on target. Entanglement does break the classical concept of relativity. As best we can measure, it appears to be instantaneous communication not limited by the speed of light and this is what Einstein struggled with. In fairness to Einstein, it's not that he was a curmudgeon and wouldn't jump on the quantum bandwagon. He had a successful theory of how things in the macroscopic world move and how gravity works, and quantum theory is vastly different.

Oh, I would never call him names - his photon theory of light, theory of relativity and his work on the Brownian motion were all ground breaking achievements and more than vindicate him of any accusation of prudishness. Moreover, it wasn't as if he was against the quantum theory as a whole, he felt it was incomplete and just because the theory in its current form couldn't incorporate causality and dependence, didn't mean they didn't exist.

And it would have been great if he could have finished his Unification theory.

To be honest, the Copenhagen interpretation does have the feel of a patchwork, trying to take the best out of both worlds to answer criticisms, a model custom made to answer questions on paper, but which lacks the feel of it being a "real life" model.

And finished!

I really enjoyed this book. I still don't pretend to understand quantum physics, but I do feel that now I can read discussions of it more intelligently.

Einstein's Mistakes by Hans C. Ohanian contains some unnecessary and distracting polemics and some faulty connections in some non-scientific assertions. That is unfortunate because it is an informative book. It is more a story of Einstein's development of his ideas in the context of the scientific milieu of his time with some history behind that development back to Newton and sometimes further. There is an emphasis on where he went wrong, and that emphasis sometimes feels awkward as if pasted in to justify the premise of the book.

Nevertheless I can recommend this book to supplement Kumar's book with emphasis rather on what Einstein was doing than on what the quantum guys were doing at the same time. There is some discussion of how Einstein's personality played into his opposition to God's playing dice.

Robert

I've started this, but doubt I'll finish by the end of the month/quarter.

Finally finished! My review:

In 1900 Max Planck described the theoretical derivation for electromagnet radiation emitted by a blackbody. In 1905, Albert Einstein proposed that light is a particle, not a wave. So began science's great journey into the strange subatomic world now described with quantum mechanics—a world so foreign that standard Newtonian physics fell completely by the wayside and scientists debated the very existence of matter.

This book elaborates on the history of quantum thought contributions by dozens of scientists—many who won the Nobel prize. In the end it cam down to two schools of thought-- that of Niehls Bohr and Albert Einstein who held opposing views on the subject . To quote the book:

“For Bohrs there was no 'quantum world', only an 'abstract quantum mechanical description.' Einstein believed in a reality independent of perception. The debate between Einstein and Bohr was as much about the kind of physics that was acceptable as a meaningful theoretical description of reality as it was about the nature of reality itself.” (p332)

This book was a fascinating but not un-technical look at the history of quantum thought. It took me months of reading in small snatches while I thought through variations of theories and how they were wrong or right. I feel I learned a lot from it, but would not recommend it to those without a strong interest in science and perhaps at least some background understanding of quantum physics.

I was quite interested in the political environment of Europe and how the World Wars and anti-Semitism affected the scientifc community. Coincidentally, the next book up for my real life book club is Einstein: His Life and Universe by Walter Isaacson so I'll get a chance to compare and perhaps to solidify some of this material.

31: Congrats! I set it aside after Planck because I wasn't in the mood to concentrate, but I do intend to finish by the end of the year...