ENTROPY, VIRTUAL PARTICLES, black holes, baby universes and a bet that cost its loser a year's subscription to Penthouse magazine were just a few of the items on the agenda for more than 100 secondary school students last weekend. They were at a physics seminar, but one that was light years away from the kind of dry science lesson that can be delivered on an uninspired curriculum. This one was part of the Stephen Hawking roadshow, a run-up to a visit by the great physicist and author to Hong Kong University of Science and Technology next week. Professor Hawking, 64, who talks with the aid of a speech synthesiser and is confined to a wheelchair after developing amyotrophic lateral sclerosis - a neurodegenerative condition - when he was at Oxford University, is set to deliver the inaugural lecture at HKUST's Institute For Advanced Studies. Last Saturday's warm-up lecture, Professor Hawking and Black Holes: Earlier Work by Hawking and Related Astronomical Observations, was delivered in Cantonese by Michael Wong Kwok-yee, associate professor in the department of physics. Although there are seven seminars in the series, called Perspectives on the Origins of the Universe, including Professor Hawking's, only three are aimed at secondary school level. The other two are The Space-time of Hawking: a Brief Introduction on Hawking's Life, His Work in Physics, and his View on the Nature of Space and Time, by Professor Chen Tianwen, in Cantonese tomorrow, and How Our Universe Began - String Theory Perspective, by Professor Henry Tye Sze-hoi, in English, on Tuesday. Both are in the Lam Woo lecture theatre at HKUST. Dr Wong took students through the history of Professor Hawking's life, disability and career, focusing on his major scientific contributions. 'He is famous for Hawking radiation and combining quantum mechanics with general relativity,' he said. 'These two fields are the most important in 20th century physics but seem to have two separate sets of laws that don't have anything in common. Many scientists have tried to combine them.' Dr Wong said 'Hawking radiation', a concept the physicist developed to solve a black hole paradox, was a result of the combination. Black holes, which have such strong gravity that light cannot escape from them, threw up a problem with the second law of thermodynamics. 'One interesting thing he proposed is that black holes are very simple, what people now call the 'no hair' theorem. This means black holes can be described by just three parameters; mass, angular momentum and electric charge. If you throw complicated things like a computer or a television into a black hole, all their complexity will be lost. It caused a controversy because information and entropy is lost,' Dr Wong said. This was in contravention of the law of thermodynamics that says the entropy of material going from an organised state to a disordered one must increase. 'He resolved the paradox by equating the surface of a black hole as a measure of entropy. But it led to something that at first he couldn't believe and that was that black holes must radiate. If they have entropy, they must have a temperature, and if they have temperature they must radiate,' he said. Professor Hawking called this 'evaporation'. Dr Wong explained to students how Professor Hawking postulated that virtual particles were the answer. 'Virtual particles are created in pairs - particle and anti-particle - and will be constantly created and destroyed everywhere, although you can't observe them as real events because they annihilate each other in such a short period of time. Virtual particles are generated near the boundary of black holes and in some cases one particle from a pair will fall into the hole and the other will be emitted. 'This is how a black hole loses mass, against conventional wisdom. Up to that point even Professor Hawking believed that black holes could have no radiation, that they must be truly black,' Dr Wong said, adding that Hawking radiation was too weak to be observed in astronomy. 'Even though virtual particles haven't been proved for black holes, they have been seen in other systems. There is such a thing as the Casimir effect.' (This effect is described by Wikipedia as 'a physical force exerted between separate objects, which is due to neither charge, gravity, nor the exchange of particles, but instead is due to resonance of all-pervasive energy fields in the intervening space between the objects'). At one time, Dr Wong said, Professor Hawking thought that objects being sucked into black holes ended up in another dimension called 'baby universes' and that it may even be theoretically possible to use them for space or time travel - although anything falling into one would be 'spaghettified' - but added the physicist had now abandoned the idea. Although Professor Hawking was famous for combining quantum mechanics and general relativity regarding black hole theory, Dr Wong said he had also extended the thinking to cosmology. 'People believe that you need to combine these two for cosmology, a study of the early universe. In the early stage of the big bang, space was so confined and the density was so high that you have to consider both; relativity because you have high density and quantum mechanics because it is so small.' This worked toward a theory of quantum gravity. Dr Wong said that although it was Professor Hawking's work on black holes and cosmology that won him critical acclaim, his book A Brief History of Time, which was on bestseller lists for 237 weeks and translated into 40 languages, was largely responsible for his popular appeal - so popular, in fact, he even made a guest appearance in The Simpsons. There was also his sense of humour. Dr Wong told students by way of example how Professor Hawking reacted to the discovery of a possible black hole in 1971. The only way to detect one was with X-ray astronomy, when material from a partner star in a binary system was dragged into a black hole, producing a visible whirlpool effect. Such an incident was witnessed in the binary star Cygnus X-1 by the Uhuru satellite. Instead of rejoicing that he could be proved right, though, Professor Hawking bet his colleague Kip Thorne at Caltech that Cygnus would turn out not to be a black hole. This is how Professor Hawking recalls the bet in A Brief History of Time. 'This was a form of insurance policy for me. I have done a lot of work on black holes, and it would all be wasted if it turned out that [they] do not exist. But in that case, I would have the consolation of winning my bet, which would bring me four years of the magazine Private Eye. In fact, although the situation with Cygnus X-1 has not changed much since we made the bet in 1975, there is now so much other observational evidence in favour of black holes that I have conceded the bet. I paid the specified penalty, which was a one-year subscription to Penthouse, to the outrage of Kip's liberated wife.' The Hawking Hong Kong roadshow has been co-ordinated by HKUST dean of science Cheng Shiu-yuen, who organised the visit, and associate dean Ng Tai-kai, who planned the lecture series. Dr Ng said Professor Hawking had been due to come to Asia anyway to take part in an international conference on string theory in Beijing later this month, and HKUST decided to 'use this opportunity to get the views of a range of people in the subject area'. Topics ranged from a 'bottom-up approach' to cosmology by Professor Bernard Hu Bei-lok, of the University of Maryland, to a novel approach to the limitations of general relativity by Professor Robert Laughlin, from Stanford, now president of the Korean Advanced Institute of Science and Technology, who won a Nobel prize in 1998. Dr Ng said that although the lecture series started as a one-off project: 'We have had many requests asking us whether we are prepared to hold more events like this and are thinking very seriously about that.' He said 'the emergence of intelligence' was being considered as the next subject. Dr Cheng, who was first asked by Chinese University of Hong Kong mathematician Professor Yau Shing-tung if HKUST wanted to host Professor Hawking's visit, said the occasion was a high-point for him personally. 'As a big admirer of him as a great scientist and human being, I am delighted that the university supported this and we managed to pull it off.' He said Professor Hawking was not charging a fee and that a number of special arrangements had to be made for his visit. 'He has asked for a private room to rest in because he tires easily and he wants a particular kind of English tea,' he said. Dr Cheng said that although Professor Hawking's visit was a great scientific occasion, with about 2,000 people applying for just 600 tickets, the real lesson for youngsters was about determination and overcoming difficulties. 'He's a good role model for young people. Everyone wants success but there may be a number of roadblocks in life that you have to overcome. I think this is why people have been so enthusiastic. It's not just the science,' he said.