Where does quantum mechanics come from?

If string theory is proved to be the correct quantum theory of gravity but it failed to explain where quantum mechanics came from can we still consider it a theory of everything?

Can we possibly discover a theory that explains reality in the sense that nothing is left unexplained (in principle)?

The origin of quantum mechanics is mysterious for me, I know that quantum states live in a Hilbert space and obey a deterministic law of evolution and we only have an algorithm of calculating probabilities but all of this seems so mysterious. I want to understand the why of quantum mechanics not only how to calculate.

Do you think that any theory that claims to be TOE have to address these questions?


closed as not constructive by Emilio Pisanty, Colin K, Waffle's Crazy Peanut, Qmechanic May 9 '13 at 7:27

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    $\begingroup$ Just reading the title, I felt very tempted to post this as an answer ... ;-P $\endgroup$ – Dilaton May 8 '13 at 22:18
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    $\begingroup$ @Dilaton: +1,... but I'm sure that instead of storing wavefunctions and quantum fields, it is much easier for the program to just store the position. P.S. 64 KB is hardly enough for a continuous spacetime. They must have infinite KB. $\endgroup$ – Abhimanyu Pallavi Sudhir Jul 15 '13 at 5:54
  • $\begingroup$ @Dimension10 Thanks ;-P, so the non existance of the infinite KB could give the LQG people a point ... :-D. The question is already closed and there is another similar one stated from a less philosophical point of view. If it were not, you could have casted a flag saying that this is rather philosophy than physics ;-) $\endgroup$ – Dilaton Jul 15 '13 at 14:46
  • $\begingroup$ @Dilaton: "Wait, this can't be right? The speed of light is determined before the universe - draw loop as random(c0,c0+F(frequency)); ? This is going to cause some serious confusion among humans about Lorentz invariance!". ... ' ' "Well, at least it isn't determined inside the universe draw loop!" "Well, that would have caused a bit of confusion when humans determined QFT?!... " $\endgroup$ – Abhimanyu Pallavi Sudhir Jul 15 '13 at 15:29

An "acceptable" theory of everything is quite a matter of taste.

Since all your experiences are grounded in classical physics, you feel that quantum mechanics is unnatural and seek to "understand" it, probably in terms of your classical notions. For eg: Do you ever question Newton's first law... why should objects have a property called inertia?

Some people have accepted quantum mechanics as the fundamental framework and that our naive classical notions are simply an approximation to quantum mechanics in some regime (day-to-day life). If that was your perspective, then there would be no need for a theory of everything to "explain" quantum mechanics. QM would be an obvious input and the theory would have to predict/explain everything else that you observe.

Roughly speaking, any physical theory has to have something you put in (axioms) and some thing you get out (theorems). At the moment, to me, it seems unlikely that we might be able to find a theory which is unique, compelling, and self-evident, without needing any axioms. It would be wonderful if such a theory existed and if we found it, but I think we're going to take a long while before we get a handle on the question of whether that's possible. But hey, that's just my opinion. The concept is definitely fun to ponder about ;-)

  • $\begingroup$ Note that we do know where classical probability theory comes from. It isn't a case of axioms at all - it can be shown that probability theory is the unique extension of propositional logic to cases where the truth value of a statement can be unknown (Cox, 1946). If you want you can see this as "putting in" Boolean logic and "getting out" probability theory. But we aren't able to "put in" something as basic as logic and "get out" quantum mechanics just yet. ... $\endgroup$ – Nathaniel May 9 '13 at 1:13
  • $\begingroup$ @Nathaniel, scottaaronson.com/democritus/lec9.html $\endgroup$ – Siva May 9 '13 at 1:15
  • $\begingroup$ I don't see the relevance. $\endgroup$ – Nathaniel May 9 '13 at 1:16
  • $\begingroup$ Anyway, to continue my thought: It is of course a matter of taste as you say, but since classical probability theory can be derived so elegantly from such minimal assumptions, and since quantum mechanics and classical probability are so similar to one another, accepting quantum mechanics as the "fundamental framework" just doesn't seem right. $\endgroup$ – Nathaniel May 9 '13 at 1:20
  • $\begingroup$ Scott Aaronson explains how you could uniquely end up with the notion of "quantum probability" -- if we decide to generalize the condition $\sum N(p_i) = 1$ to the $L_2$ norm $N(p) \equiv |p|^2$ rather than forcing the $L_1$ norm. $\endgroup$ – Siva May 9 '13 at 1:21

"Theory of everything" is not actually a theory of everything. Physical theories reach to the depths of matter, but they leave blank spots behind the front line of knowledge. That is, having studied the bricks in every detail, we could still not understand the buildings made of those bricks. There are such things as chaos and emergent phenomena possible, thanks to complexity of systems.

There are many such gaps known, it is more like they divide scientifically known areas to the island regions. Though we know quantum mechanics, we cannot connect it to the biological level, and then to psychics. There are similar gaps in physics itself: hydrodynamics is not yet understood on the molecular level, atomic nuclei are only roughly understood, and so on. The connection of classical and quantum mechanical phenomena is one of those gaps. It needs some better clarification than we have today, even if the underlying physics is fully described.

So, string theory or any other TOE does not claim to solve those problems at all. Those theories all address only the deepest level of matter, that is particles and their possible internal structure. Even if such theory is found, much work is left to be done for physicists and other scientists.

  • $\begingroup$ This is actually wrong (-1) . In principle, it is solvable, just not in practice (not even something as simple as the the Schrodinger equation can be solved for even something a s simple as the Helium Atom. . $\endgroup$ – Abhimanyu Pallavi Sudhir Jul 15 '13 at 5:50
  • $\begingroup$ +1 The vast majority of physics has nothing to do with any fundamental theory of everything. It is about achieving an understanding of physical phenomena, and this all comes down to figuring out which laws are important and which can be neglected. $\endgroup$ – user10851 Jul 15 '13 at 15:26

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