Maddox Wine Bar, W1
14 May 2003
sciBAr made a welcome return to Maddox Wine Bar on 14 May, with Quantum: An event for the perplexed. Our speaker was Jim al Khalili, author of Quantum: A guide for the perplexed, and one of the BA’s own recorders. The sciBAr differed slightly from our usual themes, being a great deal more theoretical and abstract. Jim spoke for a little longer than our speakers usually would, 10 minutes. He started by explaining the double slit experiment – the most basic illustration of quantum mechanics and gave a very brief history of physics.
The double slit experiment describes what is so perplexing about quantum mechanics – the wave/particle duality of atoms.
When a single atom is fired at a barrier with two slits in it – the atom will behave like a wave and pass through both slits. When a detector is placed next to one of the slits, the atom will only go through one of them, behaving like a single particle.
Jim concluded his potted history by giving examples of what some theorists think may be happening; multiple universes and time travel and with the view, held by many physicists today that we ought not to worry about what’s going on when we’re not looking – but just ‘shut up and calculate’ and use the knowledge we gain for practical purposes.
Jim stated that he wrote his book to explain what was so perplexing rather than to de-perplex, since no one is too sure exactly what is happening.
The audience was made up of a mixture of sciBAr regulars and newcomers and the discussion was interesting.
Initially people asked questions to get to grips with quantum mechanics and then the debate became more philosophical.
People asked questions on links between quantum mechanics and the paranormal, and on the observer effect.
The observer effect and the question of consciousness was a popular topic for questions throughout the evening. Jim explained the famous Schrodinger’s cat thought experiment, in which there is a fifty-fifty chance of a cat having been poisoned within a sealed box due to the release of a poison gas which is controlled by the decay of a radioactive atom. It is impossible to predict whether the atom will decay or not, therefore the cat remains in an indeterminate state, both alive and dead, until someone actually opens the box and looks inside.
Jim stated that physicists are now becoming more able to understand the significance of the cat thought experiment. While it is true that you cannot determine whether the cat is alive or dead, human consciousness as a process has nothing to do with what is actually happening in his view. The quantum world behaves in a certain way whether we are looking or not and it cannot be extended to the macroscopic world that we see around us. We need to ‘shut up and calculate’ – the equation that we would use to determine the state of the cat would only give us a method of expressing whether the cat is alive, dead or in between until we open the box and know for sure.
Attendees also asked about the potential applications of quantum theory and whether it could be used for ill. Jim stated that in his view knowledge was better than ignorance and we ought to keep studying!
Quantum theory is used to explain all of chemistry and helps us to understand the way things work on an atomic scale. It helps us to understand how light works, and led to the development of lasers. It also helps us to understand semi-conductors and led to the invention of microchips.
Moreover – if Quantum Theory and General Relativity Theory are united, we would have a theory of everything – what a way to end an evening!
An event full of thought provoking discussion. All attendees seemed able to keep up and were happy to question Jim if they wanted further explanations.