Are we closer to a 'theory of everything'?The physicists' ultimate dream is the search for a "theory of everything", a unifying explanation that can make sense of the infinitely tiny as well as the infinitely large.
From the strange particles that are the terrain of atom-smashing machines such as the Large Hadron Collider (LHC) at Cern, to galaxies beyond our own, about which we're learning more and more through increasingly powerful telescopes and observatories.
Much of Stephen Hawking's new book, The Grand Design, makes his case for so-called M-Theory as the prime contender to be that elusive theory of everything.
But it's esoteric stuff. So, in his first television interview, Newsnight asked him how he would explain the importance of M-theory to the many people in the UK who have little interest in theoretical physics.
The Large Hadron Collider is helping in the quest
"M-theory is the theory of everything. It explains how the universe was created out of nothing in the Big Bang, and how it behaves now. It governs everything we think and do. Isn't that of interest?" Hawking asks.
Though he hasn't really tackled the important part of the question, it's clear from his answer that Professor Hawking is as dogmatic about M-theory as he is about God. Recall his quote from the book: "It is not necessary to invoke God to light the blue touch paper and set the universe going."
He deals with M-theory in a similar tone: "M-theory is the only (sic) candidate for a complete theory of the universe." He adds later: "M-theory is the unified theory Einstein was hoping to find."
But not all physicists agree that M-theory is the answer. The blogosphere has been almost as alive with chit chat from critics of his support for M-theory as it has over his views on God.
The thing about M-theory that most people find confusing is that its maths implies extra dimensions - not yet observed - that exist alongside the four dimensions of space and time that we have become familiar with in our everyday world.
The trouble with theories of everything, including M-theory, is that testing them in the laboratory is tricky - and that leaves them open to the charge that they're as much a leap of faith as religion. Theoretical physicist and broadcaster, Jim Al-Khalili, suggested as much on Newsnight last week.
But experimental evidence may be closer than some think. Atom smashers such as the LHC may one day "see" the extra dimensions that M-Theory implies, and London's Imperial College has published a paper in Physical Review Letters with a press release making the bold claim: "Researchers discover how to conduct first test of 'untestable' string theory."
Lead author Michael Duff tells me it's not quite as black and white as that and that the "test" is an indirect one, but it could have important implications for both string theory and M-theory - effectively an umbrella theory that embraces all five leading string theories.
The team from Imperial say they've found that string theory predicts the behaviour of entangled quantum particles - another mind-boggling area of physics. As this prediction can be tested in the laboratory, researchers say they can now test string theory.
"This will not be proof that string theory is the right 'theory of everything' that is being sought by cosmologists and particle physicists," Professor Duff explained.
"However, it will be very important to theoreticians because it will demonstrate whether or not string theory works, even if its application is in an unexpected and unrelated area of physics."
But Professor Hawking is not alone in his attachment to M-theory, or to the idea that our universe is just one world in a "multiverse" of worlds.
This is an idea which echoes work by the physicist Hugh Everett III in the 1950s on quantum theory. This was roundly dismissed while he was alive, but has enjoyed a late renaissance in recent years. Everett described the universe as having not one single history, but multiple histories, in his so-called Many Worlds, or Parallel Worlds, theory.
Though there's no direct link between Everett's many worlds theory and M-theory, Professor Hawking does describe how M-theory "allows for 10 to the power of 500 different universes, each with its own laws".
Hugh Everett's son, the musician Mark Everett, more famously known as E of the rock band Eels, has tried to grapple with some of this physics in an effort to better understand his difficult relationship with his father.
E, promoting his latest album Tomorrow Morning, tells me how he believes his father's withdrawn character was down to the early dismissive reaction to his work from other physicists.
"He was a 24-year-old genius that was brushed under the carpet, and that ruined his life," he tells me.
But Professor Hawking explains how Hugh Everett III contributed to our knowledge of the universe.
"Hugh Everett made an important contribution to our understanding of quantum theory," he said. "In classical theory the universe has a definite history but this is not the case in quantum theory, Instead Everett suggested we could think of it as if the history kept branching into alternative histories."
The struggle to understand our world, or worlds, will continue, and the concluding paragraph of Professor Hawking's book sets out a seductive insight into the drive behind that search.
"The fact that we human beings - who are ourselves mere collections of fundamental particles of nature - have been able to come this close to an understanding of the laws governing us and our universe is a great triumph... If the theory is confirmed by observation, it will be the successful conclusion of a search going back more than 3,000 years. We will have found the grand design."
Incidentally, the M in M-theory is variously said to stand for "membrane", or according to Professor Hawking, possibly "master", "miracle" or "mystery". And mystery it may well remain for those of us still trying to make sense of it all.
Watch Susan's film featuring interviews with Stephen Hawking and Eels musician Mark Everett on the BBC iPlayer and Newsnight website.
BBC - Newsnight: Susan Watts: Are we closer to a 'theory of everything'?
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