This article presents a very inaccurate view of the realist approach. The universe does not "split" when you make a measurement.<p>The measurement problem is a solved problem. The solution is that measurement and entanglement are the same physical phenomenon. Measurement is just entanglement extended to a macroscopic system through a process called "decoherence". The net result is that, when you do the math, you recover classical behavior by taking "slices" of the wave function (the mathematical operation is called a "trace"). This has been known for decades now, and provides a coherent and easy-to-understand picture of what is "really" going on. It is astonishing to me that the physics community still bifurcates into two camps: those who think this is common knowledge, and those who are completely unaware of it (or think it's a crazy idea).<p>References:<p><a href="http://www.flownet.com/ron/QM.pdf" rel="nofollow">http://www.flownet.com/ron/QM.pdf</a><p><a href="https://www.youtube.com/watch?v=dEaecUuEqfc" rel="nofollow">https://www.youtube.com/watch?v=dEaecUuEqfc</a> (The same content in a video)<p><a href="http://blog.rongarret.info/2014/09/are-parallel-universes-real.html" rel="nofollow">http://blog.rongarret.info/2014/09/are-parallel-universes-re...</a><p><a href="http://blog.rongarret.info/2014/10/parallel-universes-and-arrow-of-time.html" rel="nofollow">http://blog.rongarret.info/2014/10/parallel-universes-and-ar...</a>
Relevant for those who are interested in the topic:
Two rather unusual interpretations if quantum mechanics:<p>- De Brogle-Bohm theory: <a href="https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory" rel="nofollow">https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory</a><p>- Gerard 't Hooft - The Cellular Automaton Interpretation of Quantum Mechanics: <a href="https://arxiv.org/abs/1405.1548" rel="nofollow">https://arxiv.org/abs/1405.1548</a> (see also <a href="https://en.wikipedia.org/wiki/Superdeterminism" rel="nofollow">https://en.wikipedia.org/wiki/Superdeterminism</a>)
Let me give example why physics is hard, using most simple example.<p>Ever encountered term observer (like observer in inertial frame)?<p>Well, it turns out, observer in physics means whole laboratory with established procedures of measuring time and length, not observer as you would mean in everyday life. And established procedure, what is that? Say, how do you measure time when certain event happened? It turns out, you can measure time only locally, and for this you need to have synchronized clocks spread out in your lab in points of interest. Some more philosophically inclined physicist would say that time means synchronized clocks. And how do you synchronize clocks? Well, it has to do with speed of light but I will stop here.<p>And this is for the most simple term. Imagine something more complicated. Now imagine hundreds of people writing papers and books with only partial understanding, and signal to noise ratio :-)<p>End of rant :-)
I know that Eliezer Yudkowsky is <i>very</i> controversial and some of his statements cannot be taken seriously, but I really liked his sequence of articles on QM. It made it a little bit more accessible to me, who knows very little about it.<p>I cannot judge how accurate it is; but from googling around, it doesn't seem he does any strong errors. Also he makes some very strong statements in the end which I found preposterous (mainly, that Bayes reasoning is better than scientific reasoning, and that Bayes reasoning must lead to Many Worlds theory).<p>The sequence is here<p><a href="http://lesswrong.com/lw/r5/the_quantum_physics_sequence/" rel="nofollow">http://lesswrong.com/lw/r5/the_quantum_physics_sequence/</a>
This is a really good description of the measurement problem. It takes all the sides of the debate seriously, which is hard for most physicists to do. If you think about quantum mechanics all day every day, you're almost bound to settle on one interpretation as your working model, and it becomes hard to take the others seriously.
Weinberg mentions the quote by Eugene Wigner regarding the importance of consciousness in the section on instrumentalists. However, I see it is being fundamental to realist's interpretation also. I subscribe the the realist approach, which I view as meaning nothing special happens when a human makes an observation - it is just quantum mechanics as usual. This has interesting implications. The key is that the observer is not outside the system, he is a part of it. His wave function becomes entangled with the system when the measurement is made. But what makes this difficult to analyze is that we don't know what it means for the observer to say "I see the result was *". What physical process allows the observer to be aware of the measurement?<p>We can make a simplifying and unsatisfying assumption - the observer has a register in his head which records the result of the measurement. Here, it is easy to imagine this register is part of the wave function just like the object being measured. As mentioned above, the wave function for this register is entangled with the object being measured so the measurement and register value are correlated. In our model this corresponds to the person independently thinking each of the possible results, which some people call multiple universes.<p>But this simple register is not what goes on inside the brain. Not knowing this makes it difficult to accurately model the measurement process.<p>EDIT: for clarity
What is wrong with the Pilot Wave Theory intepretation? I'm ok with FTL information transfer, and so Bell's inequalities are satisfied.<p>And anyway the other interpretations DO NOT rule out FTL information transfer. For example if one entangled electron flies into a black hole then we would be able to know its spin by measuring the other one even if light from it won't reach us.<p>Also there is this:<p><a href="https://en.m.wikipedia.org/wiki/Wigner's_friend" rel="nofollow">https://en.m.wikipedia.org/wiki/Wigner's_friend</a>
It seems that the scientific method has led us to a theory that is beautiful, accurate, and yet utterly incomprehensible. Until we can explain exactly what happens during a wave function collapse, I think QM will remain that way.
> In this musical analogy, the act of measuring the spin somehow shifts all the intensity of the chord to one of the notes, which we then hear on its own.<p>People can accept that measurements and observables are operators which act on the wave function (which can be expressed as a linear combination of eigenstates of the operator in question). People can even accept that some observables cannot be measured simultaneously, because they do not commute, and cannot share eigenstates.<p>People cannot accept that particles can <i>only be found in eigenstates</i> of the observable in question, without some mechanism to explain why this happens. If a particle's measured value can only be one of the eigenvalues of the operator, it begs the question "which eigenvalue is it going to show us?". Alternatively, if nature let us measure the <i>expectation value</i> instead of "one of the eigenvalues", then quantum mechanics would not be "weird" at all. Too bad, nature isn't like that, or maybe, be thankful that it is.<p>> But if the corrections to quantum mechanics represented by the new terms in the Lindblad equations (expressed as energies) were as large as one part in a hundred million billion of the energy difference of the atomic states used in the clock, this precision would have been quite lost. The new terms must therefore be even smaller than this.<p>I always see people (physicists) complaining about String Theory, etc. because they play around in regimes which are too small for us to actually work with. We have observed macroscopic effects which are due to a build-up of quantum mechanical effects (superconductivity, solid state, etc.). It would be expected that a correction to quantum mechanics would also make macroscopic predictions...