A black hole lenses the light of the Milky Way in the background (Credit: Ute Kraus amd Axel Mellinger)

This weekend Stephen Hawking turns 70, an extraordinary physical accomplishment to add to an extraordinary list of physics accomplishments. Seeing this news reminded me of the the first time that I crossed paths with Hawking. I'd love to be able to say that it was in intellectual debate, an exchange of brilliant ideas, but in truth it was excruciatingly awkward - at least it was for me.

Twenty years ago I was a fledgling scientist, a graduate student in astronomy at the University of Cambridge. One of the few general expectations of us was that we would occasionally have to prepare lunch for the Wednesday seminar at the Institute of Astronomy (yes, I know, it sounds positively Dickensian). Not only did this involve having to set out tables laden with bread and cheese, pate, fruit and vegetables, but it also meant that someone had to be sent to Cambridge market to buy the ingredients. On this particularly chill autumn morning that lucky person was me.

As I locked up my bicycle by the market square in central Cambridge I realized that I had no money and needed to pay a visit to the ATM (cash machine for the natives). It was early enough that the city was extremely quiet, only a few bedraggled figures coming and going, the Sun just creeping above the rooftops to yellow the sandy bricks. In a fatigued and blinkered state I made a beeline for my bank. Out of the corner of my eye I noticed a figure with an enormous red pram also clearly heading for the lone ATM on the side of the building, and I indecorously sped up to beat them to it. Except the enormous pram wasn't a pram at all, and with a whirr it suddenly zipped past me to wedge itself in front of the bank, claiming the spot for the assistant trotting along after it.

Good grief, what a rude swine, I thought, and began making those English harrumphing, throat-clearing, tut-tutting noises that we use to express our complex and justified indignation. Of course that's when I realized that it was Stephen Hawking who had just muscled his way to the ATM ahead of me. As I stood rather deflated behind him and his assistant, I couldn't help but stare at this remarkable individual, whose Brief History of Time, a few years earlier had propelled him into the public eye.

Hawking's accomplishments go far deeper than popularizing science. His contributions include work on a number of so-called singularity theorems (exploring the very nature of regimes associated with phenomena such as black holes, where geodesic incompleteness is manifest), the black-hole "no hair" theorem (black holes are completely described by only 3 properties - mass, angular momentum, and electrical charge, and are otherwise hairless), the emission of thermal radiation from black holes (typically known as Hawking radiation, the idea that a black holes have temperature and entropy, and can actually evaporate), the no-boundary picture of the Big Bang (removing the singularity at the very beginning of the universe), and the idea of the "top-down" cosmology (an appallingly clever and disconcerting idea that the present state of the universe is what determines its past, thus side-stepping various issues of fine-tuning the cosmos for the physical laws that we observe today).

The list goes on, and also includes contributions to many other fundamental cosmological questions, such as the origin of the tiny perturbations in matter that eventually gave rise to all the structures that we see today, grown by gravity. More recently Hawking has commented a number of times on the possible nature of life elsewhere in the universe, and the reasons why we should perhaps think about this in very practical terms. To quote him "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans." (something that triggered one of my previous posts on "Bad Aliens").

Suffice to say, many years later when I found myself sitting a couple chairs away from Hawking at a cosmology conference in Chicago, peeking at him painstakingly assembling a response to a question on his computer screen (it took 5-10 minutes to create a two sentence reply), I could barely face my shame at having ever been churlish enough to try to deny him first place in the ATM queue in a cold street one autumn morning.

Happy birthday Stephen Hawking, CH, CBE!