It’s an idea so embedded in the Western imagination that it leaks from science fiction films into daily thought and conversation. In a parallel universe Elvis is an octogenarian, Oswald missed Kennedy, Hitler won the war. When we chose this over that, a version of us chose otherwise, splitting off to exist as successful, fulfilled and adored. Logan now discovers this theory is no more than an attempt to reassert the certainties of Newtonian physics on a quantum universe. Since quantum theory threatens to destroy the safe cage of a mechanistic worldview, simply multiply the cages, ad infinitum. Multiverse theory keeps our decisions unimportant, since the other choice is always simultaneously made. The observer opens both boxes, slits them, burns them, destroys them with a hammer. The waveform never really collapses; all realities exist.

2. The Hidden Variable Theory

This theory has the air of someone struggling with their homework. The indeterminacy of quantum physics is an illusion due to our ignorance. There are probably some hidden variables. If we could uncover these variables, and knew their values, all the insecure feelings that quantum mechanics invokes would instantly vanish.

3. The Copenhagen Interpretation

This one needs extra coffee. The wave function of matter is a theoretical concept, not a reality; it’s the probability distribution of all possible states. The collapse of possibilities into a single state occurs when a machine takes a measurement. So, say the Copenhagenists, we can’t say anything about quantum realities, because all we have are our observations. They throw up their hands and shrug. Blanket life’s mysteries as ‘beyond our ken’. The Copenhagen Interpretation gives quantum mechanics the flavour of God in the mouth of a newly appointed vicar, who nods at tragedy with homilies.

4. The Von Neumann Interpretation

Logan likes how it sounds like a thriller, rather than a mathematician’s chain of logic. Von Neumann asked what it is about measuring something that causes the waveform to collapse. He envisages this:

A box pair experiment set-up is linked to a measuring device. It exists in an indeterminate state – as a waveform of probabilities – until it is measured, at which point the wave collapses into a particular state. What collapses the wave function? Not the measuring device. Being physical, it too is subject to quantum mechanics and exists (until the wave function collapses) in an indeterminate state. Not the photons of light in the room, not the eyes, the nerve cells, the brain of the observer, nor the electrical signals that pass between them, for all are part of the physical world, and thus subject to quantum laws. Since the entire physical world is quantum mechanical, the process that collapses the waveform cannot be a physical one. There is only one non-physical link in the chain: the observer’s consciousness. On the quantum level, according to Von Neumann, consciousness does indeed create reality.