Earlier this year, nine atoms of anti-hydrogen were created when positrons spontaneously began to orbit anti-protons.Anti-hydrogen is a difficult substance to deal with, however. Its electrically charged components can be contained by magnetic fields, but the neutral atoms are free to move until they bump into ordinary matter resulting in mutual annihilation. Anti-matter and matter were created in almost equal amounts during the Big Bang at the start of the Universe. The two types of matter promptly collided with each other, leaving a background radiation which has been detected by instruments like the Cosmic Background Explorer (COBE) satellite. A slight imbalance – one part in 10 billion – resulted in all the matter in the universe today.

Cosmic ray measurements also indicate that there are no significant reserves of anti-matter for the corporate descendants of BP, Shell and Exxon to exploit.Anti-matter can be created, however. Large particle accelerators, such as Europe’s CERN and America’s Fermilab, have been producing anti-electrons (called positrons because they carry a positive electrical charge) for 60 years Anti-protons have been around for almost as long. While the idea of anti-matter engines is plausible, their practical applications may in fact be limited to laboratory curiosities. But he also notes that similar, common-sense assumptions about physics have been proven wrong in the past.So is there any Star Trek technology that physicist fans can point to as a real possibility? Perhaps the holodeck, introduced in the second series, Next Generation, is the most likely to see the light of day. In the series, crew members could instruct the ship’s computer to create a tailor-made virtual reality featuring their favourite people, places and things.

In reality holograms have become commonplace on credit cards and even some countries’ bank notes. The idea that a sufficiently powerful computer could fill a deck of the Enterprise with a three-dimensional virtual reality is a reasonable extension of today’s technology.But the holodeck also has solid matter, which creates more problems. Professor Krauss suggests that this technology, and the replicators that produce food and drink for the crew, are based on transporters. If transporters can reconstruct people from a stored digital pattern, surely a cheaper version of the device can reproduce innumerable copies of a bad cup of coffee from a single template. But if that is the case, they would suffer from the same objections about the amount of energy required.Discussions of energy bring us back to the anti-matter engines that power the Enterprise. The theory likely to answer the question, which would combine gravity and quantum physics, has yet to be worked out. Some physicists, including Professor Krauss, argue that the paradoxes that would arise – for example, if you were able to go back in time and kill one of your grandparents before you were born – imply that there is some, as yet undiscovered, law forbidding it.

In practice, the immense gravitational force of each of the black holes would pinch off the connection long before one could get through. The only way to keep it open would be to thread the wormhole with enough exotic material – a substance that gravitationally repels other matter – to keep it open. Hawking has suggested that such matter does exist around black holes.Whether time travel will ever be realised is hotly debated. It can be envisioned by going back to the two-dimensional sheet of rubber, folding it once, and poking a thin tube through each of the layers from opposite sides and feeling around until they meet up.In theory it would be possible to travel through such a wormhole in the real, four-dimensional universe to another point in space-time. The implication is that if you could bend the Universe, the very act would create a large mass.Extremely large masses are the stock in trade of Stephen Hawking. The theoretical work that made him famous was on black holes, stars which have run out of fuel and have collapsed under their own weight until they take up zero volume. His conclusion that time travel might be possible is also linked to this work.If two black holes were to “join” they would form a wormhole, like the one in the Star Trek series Deep Space Nine.