Horizon: What is Reality?, BBC Two

Horizon took a funny turn this week. The new series started off gently enough – there was a nostalgic look back at 60 years of science on the box, then an exploration as to what makes us clever (the fun this entailed when vaguely well-known people sweated through a series of IQ tests). But last night it wanted us to get to grips with something very slippery indeed, so slippery that even the eminent scientists responsible for unleashing some of the more frontier theories in particle physics readily admitted their conceptual limitations in understanding their own formulations.

So when the off-screen interviewer tentatively suggested that she thought she was beginning to understand something called the Holographic Principle (how the universe was a hologram?) she was quickly slapped down: “If you think you understand, then you don’t,” said the eminent scientist Leonard Susskind (the brains behind String Theory and the possibly even stickier Holographic Principle), before adding, disarmingly, “because nobody does.”

So. Reality. Is it, as Dr Johnson believed, simply what we see with our eyes, feel with our hands and trip over with our feet? Or does it, as Bishop Berkeley expounded, come into being only when it’s perceived? (Does the moon disappear when we’re not looking at it, as Einstein himself once puzzled?) And how does one corroborate such perceptions with other perceivers? And might not this, in fact, be all a dream? Or, perhaps, a Matrix-like nightmare?

We saw kids kicking a ball about in a park, each kick a possible act of Johnsonian refutation of the immateriality of the universe. And we were falsely lulled by the soothing, avuncular tone of actor Bernard Hill, narrating as if he were reading us a quirky little tale before bedtime. And then we were even treated to a bit of gentle geek humour: “Reality is a set of things we know to be the case,” began one scientist. “Reality is full of facts. Facts such as, ‘It’s difficult to get a date on a Saturday night’.” See, we were being told, these scientists really aren't scary at all – they are just like you and me.

But then we were transported to Reality HQ, and this is where it all started to get fuzzy. Reality HQ is Fermilab in Chicago, which specialises in high-energy particle physics. Here you’ll find the Tevatron, the giant underground particle accelerator where particles get bashed about at great velocity. The hunt is still on for Higgs boson, which will add one more piece to the protean jigsaw of our understanding of reality (but who can tell you whether we should be holding our breath or not?).

Then it was off to Vienna to learn something about the Double-Slit Experiment (with Professor Anton Zeilinger, main picture) which sees photons behaving strangely, and thence back to the US for a very brief history of parallel universes (via Professor Susskind's elusive holograms). Here one can imagine infinite universes and infinite versions of oneself. Actually, this was the point at which I relaxed again. I really liked cosmologist Max Tegmark, who seems to have a very poetic, Platonic take on the world.

But otherwise it was all a bit heavy. As heavy as being sucked into a metaphorical black hole. It was all so much simpler (relatively) when reality  was the preserve of philosophers rather than mathematicians and theoretical physicists. It was even simpler when it was the preserve of God. But, still, it was good of Horizon to have given it a shot.

Next week, a particle physicist attempts to explain relational aesthetics in contemporary fine-art practice. He’ll probably make a pretty good fist of it, too.

• Watch Horizon: What is Reality? on BBC iPlayer