Stephen Hawking, who has died at 76, said he knew what he wanted on his gravestone.

The Cambridge professor made clear that he would like what is known as Hawking’s equation carved onto his grave.

The equation contains within it all of the most important parts of Professor Hawking’s most important discovery. It expresses neatly the idea that would come to define his work for the rest of his life: that black holes weren’t entirely black after all, and instead emitted a glow that would become known as Hawking radiation.

That breakthrough led us to new ways of understanding not only black holes but the ways that universe grows and changes over time. And much of it can be expressed in just a few letters:

The S that the equation serves to calculate is entropy: a complicated but significant part of black holes, that can be understood as a measure of how much disorder is present in the system. Sometimes the letter is written with a little “BH” next to it, standing for Professor Hawking and Jacob Bekenstein, the other scientist who did so much to help understand black holes.

The rest gives the important numbers required to calculate that entropy. The h is the Planck constant, so important in quantum mechanics; the G is Newton’s constant, used to understand gravity; the A refers to the area of the event horizon; the c is the speed of light, made so famous by Einstein’s great formula; and the k is Boltzmann’s constant, which is a way of understanding how energy relates to temperature.

All of which may appear to be a little complicated. But, as ever, Professor Hawking gave an incredibly simple explanation of how he arrived at the itself deceptively simple formula.

“In particular, I wondered, can one have atoms in which the nucleus is a tiny primordial black hole, formed in the early universe?” he wrote in 2002, during the celebrations of his 60th birthday. “To answer this, I studied how quantum fields would scatter off a black hole. I was expecting that part of an incident wave would be absorbed, and the remainder scattered.

Stephen Hawking: a life in pictures Show all 23 1 /23 Stephen Hawking: a life in pictures Stephen Hawking: a life in pictures Hawking at his Oxford graduation SWNS Stephen Hawking: a life in pictures The physicist at Cambridge University in 1988 Getty Stephen Hawking: a life in pictures Hawking navigates the narrow streets between his residence and university Alamy Stephen Hawking: a life in pictures Hawking as a young man Alamy Stephen Hawking: a life in pictures Stephen Hawking and Nobel Prize winner Dorothy Hodgkin with their portraits unveiled at the National Portrait Gallery in London, 1992 PA Stephen Hawking: a life in pictures Stephen Hawking and his new bride Elaine Mason pose for pictures after the blessing of their wedding in 1995 Reuters Stephen Hawking: a life in pictures Hawking arriving at the Chilean Antarctic base in 1997 Alamy Stephen Hawking: a life in pictures Bill Gates, accompanied by vice-chancellor Alec Broers, meets Hawking on a visit to Cambridge University in 1997 Reuters Stephen Hawking: a life in pictures Stephen Hawking celebrates his 60th birthday in 2002 at Cambridge University Brian Harris Stephen Hawking: a life in pictures Hawking holds a lecture for a symposium of cosmologists at Stockholm University in 2003 AP Stephen Hawking: a life in pictures The physicist floats in a weightless environment during a flight aboard a modified Boeing 727 in 2007 EPA Stephen Hawking: a life in pictures Stephen Hawking addresses a public meeting in Cape Town, 2008. Hawking was in South Africa for a short visit, accompanied by Nobel laureates David Gross and George Smoot Reuters Stephen Hawking: a life in pictures Nelson Mandela Hawking in Johannesburg, 2008 AFP/Getty Stephen Hawking: a life in pictures Barack Obama presents the Medal of Freedom to Hawking during a ceremony at the White House, 2009 Getty Stephen Hawking: a life in pictures The physicist enjoys the sun at the Stephen Hawking Garden for Motor Neurone Disease at the Chelsea Flower Show in 2010 Susannah Ireland Stephen Hawking: a life in pictures Hawking speaks via satellite during the Science Channel portion of the 2010 Television Critics Association Press Tour Getty Stephen Hawking: a life in pictures Hawking speaks during a press conference in London, 2014. Intel demonstrated with the professor a new communications platform to replace his decades-old system EPA Stephen Hawking: a life in pictures Actors Felicity Jones and Eddie Redmayne pose with Hawking at the UK premiere of the ‘The Theory of Everything’ in 2014 AFP/Getty Stephen Hawking: a life in pictures Hawking and Felicity Jones present the award for Special Visual Effects at the Baftas in 2015 Rex Stephen Hawking: a life in pictures Hawking takes part in a ‘Little Britain’ sketch for Red Nose Day 2015, with Catherine Tate and David Walliams Rex Stephen Hawking: a life in pictures Pope Francis meets with Hawking at the Vatican in 2016 AFP/Getty Stephen Hawking: a life in pictures Hawking receives his Freedom of the City of London scroll in 2017 AP Stephen Hawking: a life in pictures Participants listen to a recorded speech by Hawking on artificial intelligence at the Global Mobile Internet Conference in Beijing, 2017 AFP/Getty

“But to my great surprise, I found there seemed to be emission from the black hole. At first, I thought this must be a mistake in my calculation. But what persuaded me that it was real, was that the emission was exactly what was required to identify the area of the horizon with the entropy of a black hole.