Last Updated: 9:01am GMT 08/01/2007
Prof Stephen Hawking is planning a space flight.
A zero gravity flight is what astronauts call the "vomit comet", in which an aeroplane flies in such a way that people inside are temporarily weightless.
Stephen Hawking is 65 today. He was struck down by motor neurone disease when he was 21 and given a year or two to live .
Prof Hawking's next step towards the cosmos then depends on the Virgin Galactic space tourism plans of Sir Richard Branson, whose SpaceShipTwo will carry six passengers into a low Earth orbit from 2008.
The craft will be launched at 50,000ft from a mothership and soar into space at around 360,000ft, reaching a speed of 2,500mph — more than three times the speed of sound.
At present, a flight costs about £100,000 but Sir Richard will sponsor Prof Hawking's mission.
The scientist plans a quiet celebration of his birthday today with his family and said he had no intention of retiring for the foreseeable future. "The retiring age in Cambridge is 67 but I shall continue working," he said.
He is the author of A Brief History of Time — which has sold 10 million copies — and is now busy writing two books.
"My children's book, George's Secret Key To The Universe, will be published this October and my book The Grand Design on the philosophy of science should be out next year," he said.
The occasion of Prof Hawking's 65th birthday has led Lord Rees, president of the Royal Society, to pay a fulsome tribute.
He said it was "astonishing and noteworthy" that Prof Hawking had reached such an age because he was diagnosed with motor neurone disease, MND, when 21 and given only a year or two to live.
In his tribute, published exclusively on the Telegraph website, Lord Rees writes: "Everything that has happened since then seems to him a bonus. And what a triumph his life has been so far.
"His name will live in the annals of science; millions have had their cosmic horizons widened by his best--selling books; and his unique achievement against all the odds is an inspiration to even more."
Prof Hawking, who is confined to a wheelchair by MND, now has to rely on a muscle below his right eye to operate — via a switch on his glasses — his voice synthesiser.
He told The Daily Telegraph that he had offered to give his DNA to a project to scan the human genetic code for clues to the cause, in an initiative backed by the MND Association.
"Motor neurone disease is as common as multiple sclerosis but it has received much less public attention and awareness," he said.
"This may be because it often kills its victims in two or three years from the first appearance of symptoms, so they aren't around to be noticed. I am one of a few long-term survivors, so I have a duty to call attention to this terrible disease and to press for research into its causes, so we can find ways of curing it, or at least preventing it in the future.
"We know that biological processes are controlled by DNA, so a natural first step is to study the DNA of those with motor neurone disease, and compare it to the DNA of those without. For this reason, I strongly support the Whole Genome Project, and will be contributing my own DNA."
At the moment, doctors do not know the cause of more than 97 per cent of cases, though they do know that genetic factors play an important role.
The trigger, Prof Hawking believes, is "likely to be the result of exposure to infection or toxins".
One of those heading the project is Dr Ammar Al-Chalabi of King's College, London. He said: "The problem is that the genetic information contained within our DNA is like having 200 volumes of a telephone directory — and we are searching for the equivalent of single spelling mistake.
"The 'Whole Genome Scan' is a means of narrowing the search to 'hot spots' of the equivalent of a few pages."
may the force be with you