From HG Wells to the latest Big Brother challenge, time travel has sparked the popular imagination. Now, an American scientist has broken his silence about his dream of time travel, with a book documenting his life-long struggle to build a time machine.
By Neil Bowdler
BBC News, science reporter
Time travel has long held a fascination for many of us. The idea that we could use science to see the past and the future has been with us since HG Wells penned The Time Machine at the end of the 19th Century. Since then, sci-fi comics and Hollywood have built an entire time travel industry.
Today, man is successfully probing deep into the mysteries of the universe. Can he penetrate the greatest mystery of all - time itself?
One young boy, growing up in the 1950s in the Bronx in New York, was especially interested in these tales. Ronald Mallett was just 10 when his father died of a sudden heart attack. And it was in science fiction that he found solace.
Author of the Time Machine, HG Wells
"Just about a year after he died, I came across HG Wells' book The Time Machine. And that is what saved me from going into a total depression - because I had this inspiration," says Mr Mallett.
"I thought: if I could build a time machine, the way HG Wells had suggested, then I should be able to go back into the past; and if I could go back into the past, I could see my father again and warn him about what was going to happen to him, and maybe save his life. So that became an obsession for me."
More than 50 years later Ronald Mallett has learned a lot more about science. He's now a professor of physics at the University of Connecticut. But time hasn't changed him. He still wants to build a time machine, and is seeking funding for his so-called Space-Time Twisting by Light project.
Of course, building such a machine was never going to be simple. And it isn't.
First, Dr Mallett has to prove the concept. And that's complex too. But it works something like this: we know that massive objects, such as stars and planets, can bend both space and time. Dr Mallett and others believe that light too, because of its inherent energy, can also bend what's called the space/time continuum.
Build yourself an extremely powerful ring laser, and pop some material - maybe even one day a human - in the centre of this vortex of light, and you might just be able to drag what's inside the machine back or forward through time.
"What you would see would be a cylinder in which you would have laser beams that would be intersecting in such a way that they would create this huge light tunnel. So if you imagine a tunnel, with this vortex of light circulating around in it."
Unfortunately, talk of time travel and vortices smacks of science fiction, sounding like something straight out of an episode of Dr Who. And that instinctively makes many a scientist uncomfortable.
Dr Mallett himself trod carefully for many years, hiding the true intent of his investigations, for fear that he'd be branded a crackpot by his peers. But Dr David Whitehouse, a writer and astronomer, believes science needs people like the professor.
"I don't think he's a crackpot. He may be wrong; he may be misguided. But there's nothing scientifically dishonourable in being wrong or misguided," says Dr Whitehouse.
Importance of wrong
"Much of the science being done today in many fields will turn out to be wrong. Being wrong is an essential part of investigating the universe."
Nevertheless, there are still many who say time travel won't work. If it did, why isn't the present filled with time travellers from the future? And then there's what's called the "grandfather paradox".
At Universal Studios, the Back to the Future ride is due to close
For instance, if you went back in time and killed your grandfather or your father, you wouldn't exist. Changing the time line is a paradox. People have suggested that the way the universe gets over that is either by making time travel impossible - or that, when things happen to change the universe, the universe splits into all possibilities.
Dr Mallett now admits he won't be meeting his father. He says that, even if he succeeds in completing his light vortex, it would only take him as far back as when the machine was first switched on. But he's convinced time travel will happen - and, when it comes, we'll all be wanting to take a trip.
"Who of us has not longed to change something in their past? What if I could have changed this? What if I could have told this loved one 'don't get into that car', or 'don't take that flight'?
"I think just this notion, this longing, of being able to change the past, or to know what is going to come next; what's it going to be like a hundred years from now, 200 years from now? These, I think, are just so ingrained in us - this notion - that I think it's fundamental."
Below is a selection of your comments.
Of course if one went back in time and altered events then the "new" future would be different anyway and time travel may never get invented in the first place...
Confused? You will be!
It is an interesting idea; but in my opinion it would be imposible to go back in time and have a physical effect in present or future like the "grandfather paradox".
But it might be possible to develop a device that would allow us seeing the past like video a taped footage.
Sinan, New York
The world's most respected scientists thought flight was impossible not too long before the Wright brothers made it happen (with some French guys not too far behind). My point is, many barriers we thought were unbreakable have yielded when investigated with creative, courageous, brilliant minds.
Ben Ross, Boulder, CO
I too have become obsessed by time travel, but in a much less obvious way. In fact I have only just realised myself. The things I long to do, the things that drive me are all about going back in time and seeing what the world used to be like. So, I have become a paleontologist, with the ability to time travel and reconstruct ancient lands and biological communities, and when I have any spare time I take photographs. Photographs to me are a way of time travelling. When I look at an old photograph, by Atget fro example, the feeling of wanting to be in the scene is sometimes overwhelming. The same is true about my fossils - what I wouldnt do to see the Miocene!
Seems to me there is another flaw in the idea of time-travel. Supposing Dr. Mallets' lab is on the 20th floor of a tower block. Should he travel back in time say 200 years he might well plunge 20 (non-existent!) floors to his death. But travel back 200 million years and his part of Connecticut could well be at the bottom of a very deep sea. 4500 billion years and he would find himself in vacuo! So unless he has a space-travelling submarine of great strength I recommend he stays at home!
Paul O'Brien, Plymouth, England
The "grandfather paradox" and associated theories demonstrate a complete lack of imagination on the part of many scientists today. It is important to bare in mind the point of view of the time traveler. He leaves behind a tunnel to his original location in time in space. There is always a path mapped from the start of his journey to his present location. Drop the old fashioned notions of "time lines" or multiple realitys. P.S I think the term consensus reality better describes where we exist.
When we can change the past, in accordance to our whims, then we will lose all forms of accountability.
Accountability, responsibility and experience is what helps us as humans to grow in maturity, if we take this away with the actions of time-travelling, then it will limit our growth and take us back to a society ruled by children. (Some say we are already there.)
Jacques, Frankfurt am Main, Germany
If someone had already invented time travel in the future, then probably we would have visitors of the future right here in the present. Isn't that proof that time travel will probably never exist? Or is it just that we can't see time travelers?
Pablo Cordero, San Jose, Costa Rica
Go Dr Mallet! This is what science is about-trying to find a way to do the nearly impossible. There is, of course, a third way for time travel, which is that, if you consider time a straight line, then any traveller to the past has already been there. Therefore, you cannot change the present, because it has already been affected by you, the "present" relies on you journeying there.
Anonymous man, Herefordshire
I agree wholeheartedly with Dr Whitehouse. Humanity needs visionaries and thinkers like Dr Mallett. That's how we progress, like kids stumbling - but eventually learning to walk.
On the issue of his theories becoming a reality, I think that is why we urgently need to raise the popular consciousness about discussions on the ethical use of new technology. Look how great petrol engines are. They've transformed our civilisation - but at great cost. We need to think all new technology through before leaping into it.
Dave Ratchford, Nottingham