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For February 2020, we will be reading Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime by Sean Carroll.

Please use this thread to post questions, comments, and reviews, at any time.

Looks interesting!

Glad I bought this a few days ago. Can't wait.

I placed the book on hold at the library over a month ago. We will see when it arrives. :-)

I'm 100 pages in... so far so good! I'm looking forward to seeing how Carroll explains the approach to Quantum Gravity without "quantizing" gravity, but instead using the concept of gravity emerging from the wave function of the universe (or something like that... haven't finished the book yet LOL).

I’ve just picked up a copy from the library!

“If a tree falls in a forest and no one hears it, does it make a sound?��
Just finished the prologue, it brought to mind the contention of Daniel J. Levitin in This Is Your Brain on Music: The Science of a Human Obsession that no, the tree only makes a sound if it is heard, detected.

I own this book! I will join in on the discussion after I've finished reading for my other book clubs :)

Joan wrote: "“If a tree falls in a forest and no one hears it, does it make a sound?��
Just finished the prologue, it brought to mind the contention of Daniel J. Levitin in [book:This Is Your Brai..."

That sounds like a fascinating book, Joan! Thanks for sharing.

I’ve finished Chapter 4 and I understand how I should NOT think about wave function and uncertainty- but I don’t understand how I should.

I just started it...finally. ..and suddenly understand what good imaginary numbers are. it mad me mad as a kid to have to learn about them, since they aren't real so why torture us with them? now I see they're a tool. I'm a little confused though how an amplitude can be less than zero.

On the Bohr vs Einstein debate on quantum physics: interesting that Schrodinger, whose cat-in-the-box has tormented us for the past century, came down on Einstein's side vs. the Shut-Up-and-Calculate school of Bohr and Heisenburg.

Nancy, When the amplitude is negative that just means your wave is dipping below the axis. I think of the Y and X axes like property lines. If I take 3 steps into my yard that’s an amplitude of +3. If I take three steps into my neighbor’s yard that’s an amplitude of -3.

I found this a very interesting listen (audiobook version), but a lot of the material was new to me, and left my head spinning. Could anyone recommend anything that may be more of a beginner’s guide to the subject of quantum mechanics, or is this as introductory as it gets?

Joan wrote: "Nancy, When the amplitude is negative that just means your wave is dipping below the axis. I think of the Y and X axes like property lines. If I take 3 steps into my yard that’s an amplitude of +3...."
Thanks, Joan, but I'm still confused ... I not really up on wavelengths and amplitudes and such, so what exactly do the x and axes represent? I just can't see how a measurement can dip to below zero. and what even is the units we use to measure amplitude?

jj wrote: "I found this a very interesting listen (audiobook version), but a lot of the material was new to me, and left my head spinning. Could anyone recommend anything that may be more of a beginner’s guid..."

jj, this one /book/show/1...

is the best I've found yet. It all gives me a bit of a headache, trying to figure it out, but Jim Al-Khalili actually made me understand it .... sort of ;-)

Nancy wrote: "jj wrote: "I found this a very interesting listen (audiobook version), but a lot of the material was new to me, and left my head spinning. Could anyone recommend anything that may be more of a begi..."

Thank you very much for the recommendation Nancy. Book obtained, and will attempt to grasp the concepts. Here come the headaches. :)

Nancy wrote: "Joan wrote: "Nancy, When the amplitude is negative that just means your wave is dipping below the axis. I think of the Y and X axes like property lines. If I take 3 steps into my yard that’s an amp..."

Nancy, I’m puzzled too. I think he means we can measure whatever we choose- velocity, position, acceleration, spin. Each characteristic has values depending on how it is measured and how we assign the values: I expect quantum physicists have agreed on how to assign the positive and negative.
so for position if we just use 2-dimensions could be positive if right of the nucleus and negative if left.
acceleration could be positive if speed up and negative if slowing
Velocity could be positive if moving away from the nucleus and negative if moving toward
for spin - up could be positive and down negative or left positive and right negative. I think spin is an either/or characteristics, like a traffic light is red, green or yellow - the colors alternate in jumps rather than with a smooth wave, the spin is either up or down.
In chapter 4 he seems to say that the use of the word “WAVE�� is unfortunate because all this is not really about waves, butI don’t see why his vectors are any clearer.

I'm still in the dark. so far he's mentioned spin but hadn't gone into any detail about it. I'm not clear at all on what Schrodinger 's equation means. And I can't even type it because my phone doesn't have greek letters. the psi letter means wavelength. how do you find the wavelength? how do you know H, the Hamiltonian? which of these are variables? what are we trying to solve for? the rate of change of the wavelength is inversely proportional to the plank constant times i? × the Hamiltonian times the wavelength? if the wavelength is changing, doesn't it's energy change too? what is this equation supposed to do for us?
Will this stuff become clear later in the book? because so far, the only part I get is the joke about Heisenburg getting pulled over by the cop.

Nancy wrote: "I'm still in the dark. so far he's mentioned spin but hadn't gone into any detail about it. I'm not clear at all on what Schrodinger 's equation means. And I can't even type it because my phone doe..."

Nancy, I admire you for continuing to read and try to make sense of this. I was too chicken to even try.

Betsy, you made a wise decision! It only gets worse ....

Nancy wrote: "I'm still in the dark. so far he's mentioned spin but hadn't gone into any detail about it. I'm not clear at all on what Schrodinger 's equation means. And I can't even type it because my phone doe..."

Nancy, here is a way of thinking about Schrodinger's equation. The equation describes the behavior of a wave function. Here is an analogy from everyday life. Think of a stiff string under tension; maybe a spring, or a guitar string. Pluck it, and a fast camera could capture the string's position at a particular instant in time. But your eye isn't fast enough to track the string's motion, and you see a blur. The blur corresponds to the probability that the string is in some state over a period of time.

There is a wave equation that describes how the plucked string behaves. The solution of that equation can be squared and averaged over time to give the probability that the string is at any one place, corresponding to the shape of the blurred image in your eye. Likewise, the solution of Schrodinger's equation, when squared, gives us the probability that a particle (or a system of particles) is in some state.

thank you David! this vaguely reminds me of something I read about chaos theory. But Schrodinger seems to be saying the string is nowhere until we pinpoint its position. also, I don't have the book in front of me but I do remember the equation and am wondering where you get the variables to plug into it.

Nancy, the principle factors that you plug into the equation are the mass of the particle(s) and potential energy. The potential energy is derived from knowledge of the force(s) involved, such as the electric fields produced by the charges of protons and electrons. As with all differential equations, you also need to know the boundary conditions.

In my example above for a wave equation for, say, a plucked guitar string, the boundary condition is that the string is held stationary at both ends.

David,
I’m having a hard time relinquishing the particle image - for me the guitar string has a definite position - the blur is my uncertainty about where the string is. Carroll seems to be saying that’s the wrong way to think about the wave function.

I can’t get my head around his statements:
“We are most definitely NOT saying that there is an electron with some position and velocity, we just don’t know what those are, so the wave function encapsulates our ignorance about those quantities�� chap 1

“The way to break out of our classical intuition is to truly abandon the idea that the electron has some particular location�� (or spin, or velocity or whatever).

And then in Chap. 7 parsing the definition of probability, he asks us not to think of probability as how often something happens but as what he calls credence or epistemic.

My brain is spinning up/down, left/right and forward/backwards - superposition indeed.

Joan wrote: "David,
�� ... We are most definitely NOT saying that there is an electron with some position and velocity, we just don’t know what those are, so the wave function encapsulates our ignorance about those quantities�� chap 1 ..."

Joan, yes, Carroll is saying that the uncertainty principle is not that there is some uncertainty in simultaneously knowing a particle's position and momentum. It is that a particle does not simultaneously have a definite position and momentum.

This is non-intuitive because it is so different from classical physics, which is based on our everyday experiences.

David,
Fundamentally, I don’t understand what he is trying to explain.
As I read more of the book Carroll seems to be saying that our notion of the electron having velocity & position is erroneous - that the electron doesn’t really have characteristics like that - we impose those concepts because those are things we can measure.
And then he seems to say that the wave function doesn’t describe how the electron behaves because the wave function is the electron (and everything else).

I’m fascinated by the book but I think I’ll be reading it a second time - maybe it will be clearer then.

I just finished reading the book. The book seems to be aimed toward the layman; but I don't see how a non-specialist can appreciate the subtle arguments that are presented. After reading the book, I can definitely understand the difficulties others are having with the book. Here is my review.

Chapter 8:
I think I understand Von Neumann’s explanation about when systems are entangled we can only talk about the wave function for the combined systems, not the individual...
BUT
If 2 systems are entangled doesn’t that mean they each put constraints on the other so orderliness increases and entropy decreases?