Omkar Ghugarkar

Literature Review of Measurement Theory in Quantum Mechanics

Measurement is still an unresolved problem in quantum mechanics. Textbooks state that measurement leads to collapse of the wavefunction. But how does this collapse occur, at what time will this collapse occur, and what interactions lead to collapse is still not known. This project is a reading project to look at the ideas present in literature and explore new possible ideas to resolve the conundrum of measurement.

We discussed on various interpretations of Quantum Mechanics and tried to ideate on creating our own thought experiments to better understand various interpreataions.Initially we started with the famous electron and slit thought experiment which was explained by Richard Feynman. This experiment give us the understanding of what exactly collapse is. Then we had a discussion on the EPR paper. This paper believed that Quantum mechanics is incomplete and can be completed by some hidden variables which were unknown.Moreover, Einstein was firm on this idea of Completeness which says that nothing is uncertain. Further we had discussion on the Bell's paper which actually proved that there is no possibility of any hidden variable to be present by his famous Bell's Inequality and thus concluding that Quantum Mechanics is a complete theory and there is no presence of Hidden Variable in it. After Einstein's paper many Scientist tried out to find the presence of hidden variable and thus tried to detect their own way of dealing with the wave function. One of them was David Bohm. He published two papers regarding his theory. Still now we have discussed the first paper and are going to discuss the second paper in following week. In first paper, he tried to explain his views of Quantum Mechanics and tried to create his own theory with the help of Quantum Mechanical Potential defined by him. He then further tried to explain the various examples with his own theory We have completed the part one of Hidden variable theory by David Bohm. Further on we discussed the part two paper of the hidden Variable theory. This theory gave us a insight of the project. Afterwards, we had a look towards a review of the Hidden Variable theory. The review in some sense suggested that the Theory by David Bohm is actually better than the regular Quantum mechanics we use and it was able to explain some concepts which regular Quantum Mechanics is unable to do. This review very strongly supported the claim of Bohm's Theory. Further on we discussed a very Recent Paper by Daniela Frauchiger & Renato Renner stating the Non-Go Theorem. The title of Paper reads as "Quantum theory cannot consistently describe the use of itself". It is something out of Box kind of Paper. It tells that there is no Theory which can satisfy the three assumptions Q,C and S. It thus concludes that " Analysing the experiment under this presumption, we find that one agent, upon observing a particular measurement outcome, must conclude that another agent has predicted the opposite outcome with certainty. The agents’ conclusions, although all derived within quantum theory, are thus inconsistent". Further we discussed the MWI of Quantum Mechanics and then Qbism. We were more focused in finding a thought experiment which would be able to understand the various interpretations.