Time travel.

In the Sun yesterday, (a fine British 'newspaper' that's a bastion of truth, understanding and unashamedly honest journalism), there was a deeply insightful piece proclaiming that 75% of us Brits believe that Doctor WHO style time travel will be possible in the future. I can see one pretty hefty argument against that. Don't get me wrong, I love my sci-fi and it'd be great to imagine a time where we can travel back and correct all the mistakes the human race has made, but therein lies the problem. Surely the biggest argument against the future discovery of a reliable method of travel through time is precisely the fact that it hasn't happened. If, a thousand years from now, time travel becomes possible then surely someone would've traveled back to, say the 1940's for example and prevented Hitler from marching across Europe and murdering Jews. Wouldn't a well meaning chap have popped back to warn those unlucky souls caught in the catastrophe of the recent Asian tsunami? Or, on the flipside, how come all of us here in the UK aren't speaking German? I find it hard to believe that, if some powerfull yet corrupt government were to discover the secret of skipping back through time, they wouldn't use it to alter things so they, in the future, or even the here and now, were in complete control.
So the very fact that none of these things have happened is surely proof that time travel will never be possible.