Monday, September 30, 2013

Shut up and think

Quantum mechanics is peculiar in that many people think that it has faulty foundations, and others do not and wonder why so many people expend so much effort philosophizing about misguided questions.

Pablo Echenique-Robba writes a paper with the title: Shut up and let me think! Or why you should work on the foundations of quantum mechanics as much as you please:
If you have a restless intellect, it is very likely that you have played at some point with the idea of investigating the meaning and conceptual foundations of quantum mechanics. It is also probable (albeit not certain) that your intentions have been stopped on their tracks by an encounter with some version of the "Shut up and calculate!" command. You may have heard that everything is already understood. That understanding is not your job. Or, if it is, it is either impossible or very difficult. Maybe somebody explained to you that physics is concerned with "hows" and not with "whys"; that whys are the business of "philosophy" --- you know, that dirty word. That what you call "understanding" is just being Newtonian; which of course you cannot ask quantum mechanics to be. Perhaps they also added some norms: The important thing a theory must do is predict; a theory must only talk about measurable quantities. It may also be the case that you almost asked "OK, and why is that?", but you finally bit your tongue. If you persisted in your intentions and the debate got a little heated up, it is even possible that it was suggested that you suffered of some type of moral or epistemic weakness that tend to disappear as you grow up. Maybe you received some job advice such as "Don't work in that if you ever want to own a house".
When people argue about whether an issue is a scientific question, then it is a good bet that it is not. For a truly scientific question, someone can propose a way for physically resolving it. Most of this quantum philosophy is just people complaining about issues that were scientifically settled 80 years ago.

R.P. Feynman supposedly said "shut up and calculate", but actually wrote in his textbook:
So we must talk about what we can predict. (Feynman, 1963a, p. 2-3)

The basis of a science is its ability to predict. To predict means to tell what will happen in an experiment that has never been done. (Feynman, 1963a, p. 2-8)

The problem has been raised: if a tree falls in a forest and there is nobody there to hear it, does it make a noise? A real tree falling in a real forest makes a sound, of course, even if nobody is there. Even if no one is present to hear it, there are other traces left. The sound will shake some leaves, and if we were careful enough we might find somewhere that some thorn had rubbed against a leaf and made a tiny scratch that could not be explained unless we assumed the leaf were vibrating. So in a certain sense we would have to admit that there is a sound made. (Feynman, 1963a, p. 2-8)

So at the present time we must limit ourselves to computing probabilities. We say "at the present time", but we suspect very strongly that it is something that will be with us forever -- that it is impossible to beat that puzzle -- that this is the way nature really is. (Feynman, 1963a, p. 10-1)
The quantum philosophers blame Feynman for being content with a lack of understanding of quantum mechanics, but that is not what he said. He is saying that quantum mechanics may be counter-intuitive, but that is because nature is counter-intuitive.

They believe that quantum mechanics would be more understandable if it were supplemented with a theory of hidden variables. But it appears that the hidden variable concept is just wrong, and contrary to nature.

Update: Lumo also attacks the above paper, and agrees with Feynman:
The discovery of the framework of quantum mechanics is the most important advance in physics of the 20th century – and probably the most groundbreaking development in the history of science – and Feynman just summarized one of its key properties. ...

And the argument that no need for a probabilistic description was found before quantum mechanics? It's partly true, partly false – the microscopic understanding of thermodynamics, statistical physics, makes it necessary to think in terms of probabilistic distributions and probabilistic interpretations of statements – but even if we decided that quantum mechanics was the first theory that showed that the probabilistic reasoning was fundamental, there wouldn't be anything wrong about it. Every important insight is discovered for the first time at some moment. Quantum mechanics is the first scientific framework that makes probabilities fundamental. It's also the last one because there won't be any non-quantum framework in physics, ever.
I do not agree with that Feynman emphasis on probabilities.

1 comment:

  1. Renormalization. It isn't going away. It isn't mechanical. It isn't mathematically valid unless you think infinitely wrong answers are correct. Feynman himself thought it mathematically invalid, and he invented it. When you have to pretend you can trim infinity like a topiary, good chance your solution and model is not even wrong.
    Funny in QM how if you bury your BS deep enough, and don't understand it, and your teacher didn't understand it, and the inventor of the idea didn't understand it... 'it's ancient history', 'who cares', and 'its resolved' since you can apply a method that is not logically valid. This means that there is no 'mechanical' foundation to QM at all, and you have nothing to work with when things go wrong. Feynman evidently hated philosophy, easy to see why with his attitudes, he couldn't explain what he was doing, only show sleight of hand tricks (which he was immensely fond of). It does not matter if you make predictions that agree with experiment when you have no idea how you are doing it. You might as well be channeling the oracle at Delphi. In Science, how you got there is as important as where you are going, and no miracles are allowed.