Cosmology and the many worlds interpretation of quantum mechanics

V. F. Mukhanov

Sektion Physik, Ludwig-Maximilians-Universitat

17.1 Introduction

Although the mathematical structure of quantum mechanics was understood within a few years after it was invented, numerous quantum paradoxes still disturb 'simple-minded' physicists. Most of them, as 'naive realists', would probably never take Bohr's own over-philosophical and over-complicated treatment of these paradoxes seriously if they realized the philosophical consequences of the Copenhagen interpretation. To make my meaning clearer, let me quote Bohr's answer to Professor Hoffding's question regarding the double-slit experiment [1]. Bohr was asked: 'What can the electron be said to be in its travel from the point of entry to the point of detection?' And he replied: 'To be? To be? What does it mean to be?' However, if one questions the existence of microscopic constituents of macroscopic bodies, then the next logical step would be to question the existence of the macroscopic bodies and even ourselves.

Needless to say, very few (if any) of us, when making experiments or analyzing their results, address the question of what it means 'to be' every time. Even in the context of elementary particles, probably nobody doubts that the particles exist and somehow travel from the point of entry to the point of detection. Moreover, within the accuracy allowed by the uncertainty relation, these particles can be localized and described just as well as macroscopic 'classical' objects.

If this intuitive point of view is correct, then everything is in perfect agreement with what we used to think about the world existing 'out there' and independently of us. Our feeling is that this world can be well described by physical laws which (within a limited accuracy) are in 'one-to-one correspondence' with reality.

Universe or, ed. Bernard Carr. Published by Cambridge University Press. © Cambridge University Press 2007.

However, this is not what Bohr's interpretation of quantum mechanics tells us. According to Bohr, '... any talk about what the photon is doing between the point of production and the point of reception is ... simply mere talk' [1]. The observer becomes an active 'player in the game', and the physical laws just serve the observer's needs, simply relating the outcomes of the measurements without addressing the question of what the world looks like 'out there'. In this case, quantum mechanics does not make much sense in the absence of observers.

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