They say it won't happen, at least not on Friday, but in the event the Mayan prophecy of the end of the world is right, scientists have foretold a raft of bloody and catastrophic fates for us all.
Dark comets, famine, super-volcanoes, catastrophic climate change, and a plague of cancers are just some of the ends that could fulfill the prophecy.
Astrophysicist Professor Jocelyn Bell Burnell, who discovered pulsars, believes the most likely disaster that could pencil Doomsday into Friday's diary is a black comet.
Such an end would match that of the dinosaurs who after walking the planet for about 165 million years - homo sapiens has been around for a mere 200,000 years - were killed off by a 10km asteroid or comet that slammed into the planet.
Professor Bell Burnell believes if the world as we know it is to end on December 21 it would have to be a dark comet that strikes.
Dark comets have little of the ice and snow that most comets have, and a lot more dust which makes it much more difficult to spot them as they speed through Space.
'Comets normally are big, dusty snowballs. A dark comet has not much snow and a lot of dust. They are much harder to get a handle on,' she said.
The collision itself, except for those near the point of impact, would be unlikely to be fatal to the world's population but it would throw up so much dust into the atmosphere that billions of people could expect a slow death.
Huge quantities of dust would bring on an 'eternal winter' in which the sun would be obscured and crops around the world would fail, leading to mass famine.
Dr Dave Rothery, a volcanologist at the Open University, foretells a similar end but he thinks the death-bringing dust would be put into the atmosphere by a supervolcano.
Hundreds of cubic miles of debris will be blasted into the atmosphere if a super-volcano erupts on Friday
A dark comet or a super-volcano would put so much dust into the atmosphere that there would be catastrophic crop failure
More than 240 cubic miles of molten rock and debris are blasted into the sky by super-volcanoes.
Much of it would remain in the atmosphere as volcanic dust which would, just as with a massive asteroid or comet, block out the sun and cause famine.
'It would put so much ash and sulphur dioxide into the atmosphere that photosynthesis may break down," he warned.
A similar, albeit less devastating, even took place in 1816 when a volcano in Indonesia erupted and put so much dust into the atmosphere that it became known as 'the year of no summer'.
Other scientists asked by The Times what cataclysms could bring on the end of the world on Friday, in line with what many people believe is foretold by the ancient Mayan prophecy, included Bryan Lovell, a former president of the Geological Society.
His favourite Doomsday scenario was a vast escape of methane caused by an undersea landslide.
Methane is a greenhouse gas but it is about 20 times more powerful in warming the world than is carbon dioxide.
Dr Lovell said a huge release of sub-sea methane deposits would accelerate man-made climate change and lead to 'catastrophic climate change not too many Fridays from now'.
But it is not just scientists who are putting forward theories as to how the world will end and they range from the unlikely to the fantastical.
Among the favourites is that a rogue planet, Nibiru, which has long been inhabiting the far reaches of the solar system, beyond even Pluto, is now on a collision course with Earth.
Scientists have dismissed the theory as ridiculous not just because no one has ever managed to detect it in the outer reaches of the solar system but because if such a large object was heading this way it would have been spotted by now
Scepticism on the part of experts, however, has done little to diminish the determination of thousands of people to find a safe haven from disaster.
Authorities have closed off the French village of Bugarach and its mountain in France as Doomsday devotees sought sanctuary there from the end of the world.
In France the authorities have had to bar New Age followers from travelling to Bugarach, a tiny village home to fewer than 200 people, and the 'mystical mountain' where it is located.
Doomsday fanatics have identified Bugarach as a place of safety on the grounds that aliens live hidden within the mountain and are waiting for the end of the world when they will rescue humans in the area.
'I have issued an order barring anyone from climbing the mountain. And those trying to get into the village will be stopped and asked what their business is,' said Regional prefect Eric Freysselinard.
The village and the mountain will only be re-opened to outsiders two days after the end of the world is scheduled to have taken place.
Forecasts that the world will end on Friday are based on an ancient Mayan calendar which ends on December 12, 2012
The Doomsday prophecy is based on an ancient calendar from the Mayan civilisation that was based in what is now Guatemala in in Central America.
The calendar lasts for more than 5,000 years but comes to an end on Friday, which has prompted fears it forecasts the end of the world.
Other favourite Doomsday scenarios include a vast solar storm which will flare out from the Sun and engulf the Earth.
An alternative doom-laden theory is that a rogue black hole will swallow up the Earth, or that a quirk of galactic alignments will trigger a disastrous reversal of the Earth's magnetic field.
Vivienne Parry, a former presenter of Tomorrow's World, suggested a cancer that starts in foxes but can be transmitted to humans.
Man's best friend? A plague of cancers passed from foxes to people via dogs is one way the world could end.
Dogs, she suggested, would cease to be man's best friend and instead become man's worst enemy because the cancer would be transmitted through them.
Foxes would bite the dogs, transmitting the cancer to them, and they would bite their human owners.
She said that were all dogs to be destroyed as soon as people realised they were passing on an untreatable cancer the end of the world for humans could be postponed.
But she suspects man's love of his canine companions would seal his fate because putting down every dog would be too much to ask.