Professor Catherine Heymans talks to Writer at Large Neil Mackay about what came before the Big Bang, the Multiverse, alien life, time travel and her hunt for dark matter

CATHERINE Heymans can barely contain her excitement at the idea that humanity is just about to crack how to see the weather on Earth-like planets. She’s all but jumping up and down in her seat.

We’ll soon know if it’s raining sulphuric acid, liquid iron - or water - on worlds that could contain life far across the galaxy.

Heymans confounds every lazy stereotype about women and science. She’s just been appointed Scotland’s Astronomer Royal - the first woman to hold the title. There’s never been a woman Astronomer Royal anywhere in the UK. That makes her one of the most powerful women in science today.

She’s funny, a great conversationalist, and given to gales of laughter. Forget the tired old trope of the geeky science nerd. This is a global leader - based out of Edinburgh University, where she’s professor of observational cosmology. Her work has made her famous in the world of science. Yet here at home, we hardly talk about her. A depressing indication, perhaps, of where science sits in the public mind.

Fittingly, for a woman who studies space and time, she has barely a spare moment. When she’s not hunting dark matter - the undiscovered particle which will unlock the universe’s secrets - she’s negotiating multi-million pound research deals.

However, now the Herald has her undivided attention for an afternoon, let’s ask some big questions.


The Big Bang happened roughly 13.7 billion years ago. “The universe that was created,” says Heymans, “was incredibly hot and dense and inflated rapidly up to the big scale we see today.” It continues to expand as galaxies move away from us.

Due to the speed of light, we can look through the most advanced telescopes and see back to near the birth of the universe. We’ve mapped “this incredibly fiery hot period”, Heymans says, and charted the “cosmic microwave background” - the Big Bang’s afterglow. Heymans pines for the days when viewers switched on their TV and saw buzzing static snow on the screen - an echo of the Big Bang.

“One of the weird things is, you can look deep into the universe and the further away you look the farther back in time you’re looking. It’s very exciting - we can kind of time travel,” she says.

In terms of what came before the Big Bang, Heymans’ favourite theory was - and here she stresses the word ‘was’, as things are about to get weird - “a model of the universe which was sort of cyclic. So we know our universe is expanding - and there was this idea that eventually this expansion will stop and it’ll collapse in on itself, and in that hot fiery collapse, it’ll get so hot and dense that it’ll come back out again. I love all that - it’s very zen, the cycle of life.”

Effectively that means the universe has been expanding and contracting in Big Bangs and Big Crunches forever. “You don’t have to worry about how it started because it’s just always been there - no start, no end. Just cyclic.”

When Heymans, who’s now 43, was an astrophysics student at Edinburgh this cyclic model “really gelled with my sort of buddhist feelings at the time, the cycle of birth and rebirth.”

“Unfortunately,” she adds, “this model has been proved wrong.”

With the search for dark matter - “this weird new source of energy in our universe” - scientists uncovered that “our universe isn’t just expanding, the expansion is getting faster every day. So our universe is never going to collapse back on itself - it’s going to keep expanding forever”.

Is your mind-blown yet? Buckle up, it’s about to disintegrate.


So if the universe never ends, what the hell is going on? “Well, there’s one theory,” says Heymans “which looks at there not being just our universe but multiple universes. The idea is that when our universe was created, in order to stop our universe blowing up, it creates other universes. It’s called chaotic inflation. Now whether those universes are just lots of universes in different spaces and time, or whether they’re multiple realities - we can’t tell anything about that yet.”

Pause. Breathe.

What Heymans is saying is that the most current theory of the nature of reality poses that there’s either an infinity of vastly different universes out there which we can’t see - or potentially, an infinity of universes in which there are multiple versions of you and I: so a universe in which you read this article, and a universe in which you don’t. It’s impossible to listen to Heymans and not wonder ‘Am I the real me, then?’.

“I like this theory,” Heymans says. “It takes me back to that cyclic thing - there’s no start and end, just universes and more universes. You don’t have to ask what happened before the Big Bang because there’s no sort of start or end of time.”

Heymans makes clear that it’s not a question of ‘believing’ in the Multiverse - it’s simply a theory, just as the Big Crunch was a theory. “Scientists don’t have beliefs. We have theories.”


There’s another theory about what caused the Big Bang. We and our universe are made out of “matter”, says Heymans, “but we know that in particle physics experiments you can create anti-matter - and if you’ve anti-matter and matter coming together, it creates an awful lot of energy.

“So another theory is that somehow there was an odd and even amount of matter and anti-matter and it all collided and created lots of energy, and what was left was just the matter that we’re made out of and lots of energy - and that’s the Big Bang. Now you’ll ask me where did that anti-matter and matter come from - and I’ll say ‘I don’t know’.”

Current theories of the universe render humanity utterly insignificant on a cosmic scale - yet Heymans finds that reassuring. “It doesn’t matter if we mess up, but it also makes you realise how precious we are. We’re one planet out of eight in our solar system, and our star is one out of a hundred million in our Milky Way galaxy, and our Milky Way is essentially in an infinite body of galaxies and our universe might not be the only universe.

“So we’re tiny but think of all that we’ve done - we’ve sent probes to every planet in our solar system, we sent a probe outside our solar system with Voyager. Humans have gone out to our local moon. We understand how galaxies work and black holes. We’re phenomenal as a civilisation yet at the same time we’re completely trashing our planet.”


Just because you’re an atheist, like Heymans, it doesn’t mean the universe wasn’t ‘created’ - by some hugely intelligent but mortal being perhaps.

“Everything is governed by four fundamental forces,” says Heymans. There’s gravity, electromagnetism and the strong and weak forces which “make electrons and protons and quarks stick together”.

“Once you’ve got those, the universe just rolls,” she says. Humans often struggle to see how something so perfect couldn’t be purposefully designed. It’s the ‘watchmaker’ theory of creation. However, on the issue of a creator, Heymans says: “I defer to Stephen Hawking who said if there was an ethereal being who came up with these four fundamental forces do you think they’d be happy to just sit and watch what happens. Surely you’d dip in every now and again and go ‘actually, I don’t like that, I want to do this’.”


Astronomers are discovering exoplanets - Earth-like worlds - with astonishing regularity. “It’s highly unlikely we’re the only civilisation in the universe. The question is: do we exist in the same space and time as another civilisation. I think that’s highly unlikely.”

Humanity has been around 250,000 years - the universe is nearly 14 billion years old. “If these other civilisation out there are anything like us, they’ll have trashed their planet just as we’re trashing ours.”

Civilisations might be like lights twinkling off and on in terms of cosmic time. By the time ours goes out, another might come on - but we may never both be at the same stage of development which would allow us to contact each other. It’s an incredibly sad and tragic notion.

Even if we could travel at the speed of light - which we can’t if Einstein is correct, Heymans says - it would take four years to reach our nearest neighbouring star, Proxima Centauri. There we’d find the exoplanet Proxima B. As it’s stuck facing its sun, it’s roasting on one side and freezing on the other, but in the middle there’s a potentially habitable zone.

New technology means that “soon we’ll be able to look at the weather on these distant exoplanets”, says Heymans. Astronomers can already investigate the gases in a distant planet’s atmosphere to work out whether it’s Earth-like, but shortly we’ll be able to “zoom in to look at clouds moving around and what those clouds are made of - it’s awesome”.


“If you hold Einstein’s theory of general relativity as the truth, as gospel - which as scientists we don’t, because we don’t believe in anything - then time travel is impossible. As you approach the speed of light - which is what you have to do to time travel - you become infinitely massive and you slow to sort of zero time because time and space are connected.

“So then we ask is Einstein’s theory gospel? That’s part of my research. We know it works perfectly here on Earth - your SatNav wouldn’t work without it. But we also know Earth is a really special place. So might Einstein’s theory work differently somewhere else?”

When the universe was created and rapidly inflating, Heymans says, “the universe was essentially not behaving as Einstein would tell us”.

So the possibility of time travel exists. To explain these anomalies - and also the reason why our universe will expand forever - science has turned to dark matter and dark energy.


“We don’t know what the dark matter particle is, and we don’t know what dark energy is - yet” says Heymans. However, we know they “make up 95% of our universe”.

Scientists have been hunting dark matter for decades. It’s not really dark - we can’t see it, obviously. “We just call it dark because we’re all Star Wars fans, the Dark Side and all that,” Heymans says.

Heymans has charted a swathe of the night sky for dark matter - just under the constellation of Leo. It made her world famous within astronomy. She knows dark matter is there as it bends light. “When you’ve got a clump of dark matter, even though it’s invisible and you can’t touch it, it’ll curve space and time. It there’s a clump of dark matter between you and I in the same room, light would bend, it wouldn’t be in a straight line, and my nose would look very strange to you. So we can use this effect to map out where the dark matter is in distant galaxies.”

Living on Earth, with our atmosphere and light, makes an astronomer’s job extra difficult - that’s why Heymans dreams of building “a massive telescope on the dark side of the Moon”, and she wants to travel there to use it. On Earth, the biggest telescope will be the ‘Extremely Large Telescope’ - 30 metres across - in Chile. On the moon, Heymans envisions a telescope one kilometre across using liquid mercury for a “perfectly smooth surface” and the movement of the Moon acting as an observatory.

A Yorkshire mine has been rigged up with massive vats of Xenon - “like Dr Evil’s underground lair” - to catch dark matter. “I feel we’re really close,” Heymans says. “Can you imagine the headline: ‘Dark Matter caught in Yorkshire’.”


Heymans went to an all girls comprehensive in Hertfordshire so she didn’t experience any ‘boys are good at science, girls are good at arts’ stereotyping in her teens. It was different at Edinburgh university. In her astrophysics class, “there were six girls out of 100. I didn’t have a single female lecturer”. Today, a third of astrophysics undergrads are women and 10% of professors. “I was one in ten as an undergraduate and I’m still one in ten as a professor.”

As a working astronomer she’s experienced the kind of casual sexism that could have come straight from the sitcom The Big Bang Theory. When she published her first scientific paper - under the name ‘C.Heymans’ - she attended a conference with her co-author. “Somebody came up to them and said, ‘I saw that paper you wrote with Heymans. I’ve been looking for him’. My colleague said ‘she’s right here’.”

It wasn’t an attempt to hurt her, she says, it was “culturally embedded. None of my colleagues are intentionally sexist, they don’t go out of their way to make my life miserable because I’m female. The problem is unconscious. But there’s lots of teeny things that just knock you, and it takes time to pick yourself up.”

The roots of the problem lie in childhood, she believes. “Go into primary schools and every kid loves space. Then something happens between secondary - all of a sudden they become aware of their gender and cultural stereotypes.”

Only 20% of girls take physics at Higher. Heymans puts a lot of the responsibility on female role models and their own attitudes to subjects like maths - “the mums, grandmas and aunts saying to their daughters ‘don’t worry, I couldn’t do that either, it’s not important’.”. It clearly infuriates her - she mimics a whiny voice as she talks about women not encouraging their daughters in science. “It’s as important as reading and writing.”

Her worry extends beyond girls. Heymans is conscious of her “white privilege”. If it’s hard for a woman in science, it’s also hard for folk who aren’t white. Recently, she changed how she ran graduate recruitment for astronomy. She made the selection process blind - so nothing gave away candidates’ race or gender. “We typically recruit white, male students,” she says. After the blind selection there was near perfect gender/racial balance.

Heymans is a woman on a mission now - she takes her position as a role model very seriously indeed. The Astronomer Royal job is for life but she plans to hold the post for about five years. The time is ripe, she believes, to reset the scales for science after those infamous comments during Brexit by the likes of Michael Gove that Britain “had enough of experts”. Although it seems almost absurd for her to have to even say it, the pandemic, Heymans adds, has “taught us that science is important”. She thinks we’ve ‘reached peak Flat Earth’.

Heymans tries to get “stealth science” in wherever she can - even doing stand-up at the Edinburgh Festival in an attempt (which “petrified” her) to turn people on to physics through a few gags. She’s taken science on the road to music festivals too.

As a mum of three children, who homeschooled them through pandemic, she’s planning to use her clout as Astronomer Royal to get telescopes into every kids’ outdoor centre in Scotland in the hope of switching youngsters on to the big questions about life, the universe and everything.

Given she’s a gifted and charismatic communicator, might she one day fancy a stint on TV - as the new Brian Cox? “I’m not as handsome as Brian,” she says with a snigger. “And I think he had to give up his research. I’d be very sad to do that.”