Lighting Up the Dark: Jim Al-Khlalili on The World According to Physics

12 May

Jim Al-Khalili’s presentation for the Swindon Spring Festival (online) was a bit of a tease; a clever and fabulously clear description of all that’s currently wrong with Physics but without telling us what needs to be done about it.

For that you need to buy his new book, The World According to Physics.

That won’t be a burden for me. I already own three or four Al-Khalili’s and admire his clear writing, his innovative TV explanations and his inspiring Life Scientific on the radio. I’m a bit of a fan and so hearing him almost tell me what was in his new book was a genuine treat.

What we got was ‘an exploration of the shoreline of our island of knowledge in the ocean of our ignorance’. Exhibit 1 was dark energy. I well remember reading about this myself, for the first time, in the late 1990s and thinking (in Rabi’s famous words concerning an earlier discovery) ‘who ordered that?’

So what is dark energy?

Let me try to explain.

Astronomers had been wondering for decades whether the expansion of the Universe would eventually slow to the point where it would reverse and the Universe collapse into a “Big Crunch”. The Hubble Space Telescope was built specifically to answer this question but its answer, when it came, was baffling. The expansion wasn’t slowing at all. In fact, expansion had started to speed up around 4 billion years ago. This is as surprising as throwing a ball into the air and watching it disappear from sight instead of falling back to Earth.

It should be admitted that the theoretical possibility of an accelerating expansion was known. The mathematics of our Universe’s evolution was developed by Albert Einstein in 1919 but, because he thought the Universe was static, he put in a fudge—a mathematical fiddle factor that balanced out gravity. Then, in the 1920s, Edwin Hubble showed that the Universe is expanding and no such balance needed. Einstein described the fiddle as his biggest blunder and astronomers spent the next 60 years trying to forget it had ever happened. By the time the Hubble Space Telescope was in orbit, no-one expected it to show anything other than a Universe whose expansion rate was slowly dropping.

But everyone was wrong and Einsteinian fudge is needed again—fudge thick enough to do more than just gently balance gravity, we need fudge thick enough to complete overwhelm the biggest known force in the Universe. The data is clear; the accelerating expansion is real and our mathematics needs dark-energy in the Universe to give it a push.

So what is dark energy? I’ve no idea and neither has anyone else.

The problem is that dark, here, has the same sense as it does in ‘dark side of the Moon’, ‘being kept in the dark’ or that deplorable Victorian expression ‘darkest Africa’. It’s an expression of our ignorance much more than a literal lack of illumination. And, as Jim Al-Khalili explained, we also have dark matter to worry about as well as deeply dark questions on the nature of time and space. Our Universe hasn’t seemed so puzzling in more than a century.

And that’s where The World According to Physics comes in. What we learned from his talk was not that Professor Al Khalili is a new Einstein with answers but, instead, that his book has ideas about the experiments needed to shed light on these mysteries. I’m intrigued and will have to buy the book.

I guess the tease worked.

Words by Prof. Dave Waltham. Jim Al-Khalili’s talk premiered on Youtube on 11th May for Swindon Spring Festival.

Watch Jim’s talk on the Swindon Spring Festival’s YouTube channel

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