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Hello, if the most famous fruit in physics is an apple, the most famous animal in physics is a cat.

It belongs to Edwin Schurdiger, a theoretical physicist who in the early 20th century helped to develop the theories of quantum mechanics.

Schrodinger's cat doesn't actually exist. It's the subject of a thought experiment

in which the equations of quantum mechanics make it appear both dead and alive at the same time.

The problem of a cat that's both dead and alive illustrates the challenges of quantum physics and at the heart of this apparent absurdity is a thing called the measurement problem.

The measurement problem arises because we don't really understand how the particles that constitute our world behave.

They're fundamentally mysterious to us, even shocking, and they defy

our attempts to measure and make sense of them. Possible solutions range from the

existence of multiple realities to the rather more mundane possibility of an error in mathematics, but a solution if found could

transform our understanding of reality. We'd me to discuss the measurement problem, a Simon

Saunders, professor in the philosophy of Physics at the University of Oxford,

Basil Heily, Emeritus Professor of Physics at Birkbeck University of London,

and Roger Penrose, Emeritus Rausball Professor of Mathematics at the University of Oxford.

Basil highly, at the heart of the measurement problem, is a distinction between how we think of the world at the level of the very small,

and how the everyday world of large objects seems to be classical physics and quantum physics.

Can you outline the distinction between the two?

Yes, let's start first of all with the classical world and one example that I'm going to talk about where

we can see Newtonian mechanics actually in action is on the snooker table.

We have little balls moving in straight lines. We have balls which we push

against the cushion and bounce back again. And we're fairly familiar intuitively

...