History has showed us that all physical theories eventually fail. The failure is always a complete failure in terms of some abstract perfectionist viewpoint, but in reality, the failure only amounts to small corrections. Take for instance gravity. Newton’s theory is absurd – gravity travels instantly, etc. But it is also simple and powerful, it predictions working well enough to put people on the Moon.

Quantum Mechanics, it would seem, has a lot of physicists claiming that ‘this time is different’ – that QM is ‘right’. Nature does play dice. There are certain details of it yet to be worked out, like how to apply it to fully generalized curvy spacetimes, etc.

Lets look at what would happen if it were wrong. Or rather, lets look at one way that it could be wrong.

QM predicts that there are chances for every event happening. I mean in the following way – there is a certain probability for an electron (say) to penetrate some sort of barrier (quantum tunneling). As the barrier is made higher and or wider, the probability of tunneling goes down according to a well defined formula: (see for example this wikipedia article). Now, the formulas for the tunneling probability do not ‘top out’ – there is a really, really tiny chance that even a slowly moving electron could make it through a concrete wall. What if this is wrong? What if there is a limit as to the size of the barrier? Or put another way – what if there is a limit to probability? Another way to look at this is to say that there is a upper limit on the half life of a compound. Of course, just as Newton’s theory holds extremely well for most physics, it may be hard to notice that there is not an unlimited amount of ‘quantum wiggle’ to ‘push’ particles through extremely high barriers.

Steven Weinberg has posted a paper about a class of theories that try to solve the measurement problem in QM by having QM fail. (It fails a little at a time, so we need big messy physics to have the wave collapse). I agree fully with his idea – that we have to modify QM to solve the measurement problem.

### 2 responses to All physical theories are wrong. Where will Quantum Mechanics fail?

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Most of my musings point to an incredibly high frequency for some fundamental wave that controls electromagnetism and QM. This works out to about 10-60 seconds or so. Looking at this time from the point of view of an uncertainty relation DE*Dt >= h, we get for a tiny Dt of 10-61 seconds, an energy of 10^27 Joules! Or about the energy released by the sun every second. That’s a lot of energy. So how could we approach that – not from a straight on experiment, to be sure. I look at this as sort of an upper limit to the validity of the Quantum uncertainty relations. Its likely much lower than this for other reasons. But to say that DE*Dt works all the way to Dt == 0 is highly unlikely, to put it mildly.

But look at some more subtle effects – an electron penetrating a barrier, for example. How big does the barrier have to get before we start seeing some deviation from the expected temporary quantum boost that gets an electron through a barrier that it could never cross classically. A barrier penetration experiment probes the edges of QM much better than a brute force attack. With a barrier experiment we are asking QM to use its magic to push an electron (or lead nucleus) through an ever higher, ever widening barrier. We then study the statistics of the survivors. Is there an unexpected cutoff in the numbers – now that would be a smoking gun.