"During the shooting I realised that we are rare and therefore valuable and quite remarkable and worth celebrating."
In the first programme, he takes us on a fast-track journey from monkey to the space station.
Tall but slight, Cox is a youthful 46, though his trademark fringe is beginning to grey. He was born in Greater Manchester to parents who worked in a bank and was privately educated at Hulme Grammar School in the 80s. He excelled in physics but got a D in his maths A-level (he was "more interested in New Order and The Smiths"). Today, he lives in London with his wife, the American television presenter Gia Milinovich, their 5-year-old son and her son from a previous relationship.
The Wonders of the Solar System, in 2010, was the TV series that tipped him over the edge into mass appeal, and since then he has fronted, among others, The Wonders of the Universe and Stargazing Live. His shows have aired in New Zealand on TVNZ 7.
Cox acknowledges the confidence shown in him by the BBC, but he's not lacking in confidence himself.
"You make things for yourself ultimately and the biggest mistake you can make in television is to make it for somebody else. If you start to second guess what an audience wants, you're on a road to formulaic television. So I've really no interest in people who say, 'Well, we've had some focus group meetings and this is what we think'. They should go and work on baked bean packaging. And even then they'll make the wrong baked bean packet."
He laughs as he says this, but he's being serious. "If someone gave [the first programme] a one-star review, I'd think, 'You're an idiot.'?" He laughs again. "It's not meant to be cocky. What I'm saying is that I'm happy with it as a piece of television. Hopefully it's a Reithian thing - it educates, informs and it entertains. That's what television should be."
Cox is, before anything else, a scientist and still does research and gives an annual lecture course.
"I'm a Manchester academic. I don't do TV because I want a career in the media. Science is very important. It's undervalued and underinvested in and it's a force for extreme good in education, in society and economically. So there's a polemical element to what I want to do, but I enjoy making these films. I like learning curves and it's brilliant to work with creative people."
When I suggest that he might be out of his comfort zone in the latest series because he isn't dealing exclusively with physics, he disagrees.
"Science is going in the other direction, actually," he says, adding that there is now a multi-disciplinary, rather than compartmentalising, approach. The Institute of Biology has made him a fellow, for example, and a lot of particle physicists are starting to work in medical physics. Particle beam therapies, such as that being used to treat Ashya King, the 5-year-old whose parents removed him from an NHS hospital to Prague, are "potentially one of the main new cancer treatments".
He argues that there is a "special status to scientific knowledge" and that it is a necessary framework within which we can discuss wider questions of existence.
Take inflationary cosmology. "There may have been more than one Big Bang and probably, in these theories, there are an infinite number of universes being created all the time. So what does that mean? What does it mean that our existence is inevitable, that the universe may have been around forever?"
He hasn't got the answers but he wants a debate. "These things have not been discussed widely; they need novelists and artists and philosophers and theologians and physicists to discuss them."
When I ask him how God fits into his understanding of the universe, Cox says: "It doesn't at all. I honestly don't think about religion until someone asks me about it." And that's because, he explains, science is not about asking grand questions but very simple ones. The way to find out answers to big questions is "almost accidentally".
Using physics that is beyond me, Cox explains how his fridge shows that there is no afterlife (thermodynamics, apparently). But then he qualifies himself. "Philosophers would rightly point out that physicists making bland and sweeping statements is naive. There is naivety in just saying there's no God; it's bollocks," he says. "People have thought about this. People like Leibniz and Kant. They're not idiots. So you've got to at least address that."
He suspects that another civilisation exists in the observable universe, given that it contains 350 billion galaxies. But they would be so far away that we'd never make contact. "In our galaxy, the question is really, 'Are there any now that we could communicate with?' And we could easily be the only one at this moment. Are we the only one ever to have existed? That seems less likely, but it's possible. I wouldn't be surprised if a flying saucer appeared - in that it's possible - but I actually think civilisations are probably rare. For biological reasons, primarily."
The next big discovery, he believes, might involve finding life on Mars.
Are we, though, making as much progress in science as we should? Cox has a two-part answer. In one sense, it's remarkable how far we've come. We've moved, he says, from thinking the Earth was at the centre of the universe to walking on the moon in 400 years.
"But if you ask the question now, 'Can we do better?', then obviously we can."
Where, amid all his grand theorising, does Cox derive meaning in his own life?
"I used to think about meaning a lot when I had a secondhand overcoat, wandering around Manchester listening to Smiths albums aged 16, drinking Woodpecker cider," he jokes.
Now that he's a rockstar scientist, how has he coped with stardom? "It's a process - you learn to be famous. If you don't, you end up going crazy."
He has, he says, changed his habits.
"Do I walk down Oxford St on Saturday? No. I don't tend to get on the Tube. I probably could, actually, but I don't like it. I don't mind people staring at me if I'm walking in an open space, but I don't like getting enclosed with a load of people because then they start talking and taking pictures.
"You end up knowing people who've been through similar experiences, so you get to know more famous people. If you're balanced, you don't really want to talk about yourself. It's quite nice sometimes to go and be friends with people who also don't want to talk about themselves, which tends to be people who have a lot to talk about. The balanced person who handles life in the public eye is the person who doesn't really find themselves particularly interesting."
Music and physics
• Professor Brian Cox, 46, grew up in Manchester, the son of bank workers.
• In the 1980s he was keyboard player with the band Dare and later played for D:Ream, who had several hits in the UK charts, including the No 1 Things Can Only Get Better.
• He studied physics at the University of Manchester.
• He has appeared in a string of science programmes for BBC radio and television.
