The Weekend's TV: Downton Abbey, Sun, ITV1<br/>Stephen Hawking's Universe, Sat, Channel 4

Polished act from the aristocrats

According to Stephen Hawking's Universe, time travel into the past simply isn't possible, though any television commissioner knows it can be done, if you're prepared to spend enough money.

Cough up for the steam train pulling into a rural halt, the vintage Roller and the telegram boy's uniform and before you know it, it's April 1912. And from the very beginning of Downton Abbey, Julian Fellowes' new upstairs-downstairs drama for ITV, we know that something momentous is heading towards the big house. The postmistress draws in a sharp breath and the second footman – ironing the morning papers so that his Lordship won't sully his fingers with smudgy ink – is having trouble believing the banner headline. The Titanic has gone down – a general tragedy that becomes sharply particular when his Lordship discovers that his careful arrangements to keep the estate in the family have just been holed below the waterline. His nominated heir and the son who was about to marry into the family are among the missing. "It's such a shame," says a tweeny. "It's worse than a shame," replies the housekeeper. "It's a complication."

It's a bit of a Titanic itself, Downton Abbey – glossy, ostentatiously luxurious and boasting a glittering passenger list of upmarket acting talent. It's also very far from unsinkable, though it's too early to say whether the commissioning editors are going to regret their investment. They certainly know that the essential design is seaworthy – because of the success of Upstairs, Downstairs – and they've employed a designer with an established track record to tweak it for contemporary tastes – Julian Fellowes, who won a scriptwriting Oscar for Gosford Park, the Robert Altman film about a murder investigation in a Thirties country house. Unfortunately, they haven't quite realised that with drama it may actually be the over-zealous safety measures that send the vessel down.

Take marmalade as a case in point. In Gosford Park, Maggie Smith (playing exactly the kind of fearsome dowager she reprieves here) had a fine moment when she lifted a jar up for inspection at breakfast and uttered the withering line: "Bought marmalade? Oh dear, I call that very feeble." Behind that remark lay a whole stack of social assumptions, none of which was explained. You just had to work it out for yourself. In Downton Abbey, on the other hand, no such chances are taken. It's full of people asking helpful questions so that oddities can be clarified (the reason for ironing the morning papers, for example) and the plotting is equally semaphored, sometimes to a risible extent. The scene in which the cook set up a potentially fatal confusion between brass polish and chopped egg for the kedgeree was unfortunately reminiscent of that Mitchell and Webb sketch about the laborious mishaps in bad sitcoms.

It doesn't have to be another Gosford Park to work, of course – and there are plenty of things to enjoy here – not least Downton Abbey itself (played here by Highclere Castle in Berkshire). Brian Percival, the director, showed off nicely at the beginning with a long tracking shot through the downstairs rooms, flitting from flunky to flunky as the vast machine of an Edwardian aristocrat seat cranked itself into operation for the new day. And there is promise in the scenes between Elizabeth McGovern as Cora, the Earl's rich American wife, and Maggie Smith as the Dowager Countess, women who have little in common but their strong aversion to handing the family fortune over to a stranger from – they can hardly bring themselves to utter the word – Manchester.

It's possible that some of the faults of the first episode – the melodramatic simplicity of the antagonisms and the crudity of the characterisation, with its hissable villains and vulnerable heroes, were symptoms of opening-night nerves, a clumsy anxiety to get the audience on board. Possible too that the narrative loops that Fellowes already has in place – romantic longings and romantic possibilities – will tighten around an audience so that they can't wriggle free. But on this evidence, ITV will have to keep their fingers crossed for a bit longer yet. One signal difference between Downton Abbey and the Titanic is that there's no shortage of lifeboats available for those who want to abandon ship, and it can be done at the push of a button.

There was a weird moment at the beginning of Stephen Hawking's Universe where he – or rather his voice synthesizer – said, "Check it out," a rather slangy invitation to spend just under an hour boggling your mind with speculations about time travel. "Let's indulge in a little science fiction for a moment," he said, which was a bit rich given that what followed was almost nothing but. I don't doubt, of course, that there are several blackboards' worth of scientific formulae to back up Professor Hawking's assertions, but even so their practical application seemed a bit of a stretch. If you want to travel into the future, for example, you can construct a railway circling the globe and then provide a train to run on it that will lap the world seven times a second. For those on board, time slows down (or is stretched out) so dramatically that after a week's travel they will emerge to find that the world has moved on a hundred years. The catch is that only one-way tickets are available. Once in the future your only option is to live there, or leap forward again. I think I'll get there the slow way.