Definition: Generate an appropriate title for the given text. The generated title must be short and include the main topic of the text. The preferred titles are under fifteen words.
Input: The idea may sound far-fetched but the "many worlds" concept is the subject of serious debate among physicists. It is a particular interpretation of quantum mechanics - which describes the often counter-intuitive behaviour of energy and matter at small scales. Prof Cox made the comments during an interview with Radio 4's The Life Scientific programme. In a famous thought experiment devised by the Austrian physicist Erwin Schrodinger, a cat sealed inside a box can be both alive and dead at the same time. Or any combination of different probabilities of being both dead and alive. This is at odds with most common perceptions of the way the world is. And Schrodinger's experiment was designed to illustrate the problems presented by one version of quantum mechanics known as the Copenhagen interpretation. This proposes that when we observe a system, we force it to make a choice. So, for example, when you open the box with Schrodinger's cat inside, it emerges dead or alive, not both. But Prof Cox says the many worlds idea offers a sensible alternative. "That there's an infinite number of universes sounds more complicated than there being one," Prof Cox told the programme. "But actually, it's a simpler version of quantum mechanics. It's quantum mechanics without wave function collapse... the idea that by observing something you force a system to make a choice." Accepting the many worlds interpretation of quantum mechanics means also having to accept that things can exist in several states a the same time. But this leads to a another question: Why do we perceive only one world, not many? A single digital photograph can be made from many different images superimposed on one another. Perhaps the single reality that we perceive is also multi-layered. The laws of quantum mechanics describe what happens inside the nucleus of every atom, right down at the level of elementary particles such as quarks, neutrinos, gluons, muons. The weird and wonderful world of quantum mechanics reveals that nature is at heart probabilistic. Nothing can be predicted with any certainty. "Everybody agrees about that" says Prof Cox. But where physicists don't agree is about how these facts should be interpreted. For decades, the Copenhagen interpretation of quantum mechanics, which allows for only one universe, dominated particle physics. But Brian Cox supports the many worlds interpretation and, he believes, more and more physicists are now subscribing to this view. Brian Cox is on The Life Scientific on BBC Radio 4 on Tuesday, 23rd September at 09:00 GMT.

Brian Cox: 'Multiverse' makes sense