I'm continuing to read Jim Al-Khalili's book(adsbygoogle = window.adsbygoogle || []).push({}); Quantum: A Guide for the Perplexed. I'm on page 190; today I just read a few paragraphs and page 176 about quantum tunnelling.

My question is this: what does it take to say that an electron, for example, has successfully and definitely tunnelled through a barrier? Or is there only the probability function of having done so?

Jim Al-Khalili explained quantum tunnelling in terms of the wavefunction. Does the wave function need to be collapsed by way of observation (a la Copenhagen interpretation) for the electron to definitely exist on the other side of the barrier?

I was thinking that if quantum tunnelling only occurs in terms of probability, then what happens after tunnelling becomes likely? Must we keep making our calculations using probability of quantum tunnelling to determine what the electron does on the other side of the barrier to interact with whatever is there? Is this to be added to and added to successively with each further interaction that takes place?

I would think perhaps not: One of the consequences of quantum tunnelling is decay of a nucleus, such as what happens in a fission bomb. Does the decay actually take place for sure, leading to the chain reaction that then detonates the fission bomb, or is it simply likely to occur? If so, then how does the fission bomb definitely detonate?

I bring this up because I know the fission bomb does really detonate -- for sure. (Of course, sometimes fission bombs are duds, which I think might have to do with the probability of nuclear decay.)

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# Probability of quantum tunnelling

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