Perhaps it is true of all small countries, but New Zealand loves finding the local angle on global news. Earthquake in a distant land – was a New Zealander caught up in the shaking? No? Don’t worry, let’s find a compatriot who visited earlier in the week.
How about two black holes colliding in a distant galaxy, a billion years before our little islands even emerged from the ocean? Well, since you ask, yes, there is a Kiwi connection.
The link is Roy Kerr, a 91 year old mathematician – who, in 1963, solved the equations that describe a spinning black hole. A couple of weeks ago a global collaboration of scientists announced observations that confirm that spinning black holes behave as Kerr predicted. This made news all over the world, and it meant that a local news site could run this headline:
A Kiwi scientist had a revolutionary theory. 60 years later it turns out he was right
To be pedantic about the headline: the revolutionary theory in question was Einstein’s General Relativity. And the “Kerr Solution” is a solution to Einstein’s equations whether or not Einstein’s theory is correct. But without Kerr’s solution it would be much harder to put Einstein’s theory to the test.
The observations announced last week were of ripples in space – gravitational waves, to use the technical term – generated by a merger of two black holes which produced a single, spinning black hole. Gravitational waves were originally predicted by Einstein in 1916 but it was a century before they were first detected in 2015. Since then, the technology has rapidly improved and in January 2025 we saw the formation of a spinning black hole for the first time.
Physics is a long game. Our students today grapple with ideas first formulated hundreds of years ago, a perspective famously summed up by Isaac Newton thus: “If I have seen further it is by standing on the shoulders of Giants”.
For me, this line conjures an image of a Roald Dahl-style Big Friendly Giant with a kid-sized scientist on his shoulder.
But it also carries a deeper sense that giants once walked the earth, and their sleeping forms are the hills and mountaintops of a landscape formed from the remains of our legendary predecessors. I’m not sure Newton had this version in mind, but it feels that way at times.
It’s also beyond argument that Newton was himself a metaphorical giant, conjuring yet another vivid picture of giants upon giants.
To get back to the spinning black holes: Einstein’s theory tells us that any black hole can be described by just three numbers – mass, electric charge, and spin. Everything has mass, but it turns out that very few astronomical bodies are electrically charged. However, all of them rotate – some slowly, some quickly. This means the Kerr solution (as we call it) describes every black hole in the universe, including the one identified last week.
Once an equation is solved, it is solved forever. Roy Kerr nailed this one, and as a reward his name will be spoken aloud for as long as humans talk about what we see in the sky.
A few years ago, I hosted a visiting big shot at Auckland for a hybrid seminar. As the audience filed in to the lecture theatre, names were also popping up on Zoom. One of the first was “Roy Kerr”, at which my esteemed guest turned to me and asked, “The Roy Kerr?” suddenly realising he might not be the biggest star in this room at the bottom of the world.
“Sure,” I replied. “Roy shows up to a lot of things round here.”
Giants do still walk among us, you just need to know what to look for.
HEADER IMAGE: Te Mata Peak; CC-BY 2.0 Flickr and, according to legend, the prostrate body of a great chief.
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