Sixth Lesson: Probability, Time and the Heat of Black Holes.

stephen hawkins

The problem of heat was one that perplexed mid-nineteenth century physicists. One way of understanding it was to think of it as a kind of fluid, ‘caloric’ fluid. I guess that’s where we get the term calorific value. Food equals a certain amount of energy. But in the mid-nineteenth century there was thought to be two kinds of heat: hot and cold. Wrong, of course, but not for the reason we think. James Maxwell and the Austrian physicist Ludwig Boltzmann showed that heat moves in a gradient from hot to cold because atoms when heated oscillate more rapidly and are therefore more likely to collide with each other and create and lose energy. A cold teaspoon placed in a hot cup is therefore more likely to become hot. In quantum physics this is not fixed, but more highly probable than the alternatives, which are also in flux.

Heat changes the past and the future, but where does time go if it cannot flow? The answer is it does not go anywhere. It remains a position, a function, a variable, a location, a quantity. It is coterminous with space, having the same boundaries as space. Space equals time. But it also deictic. Sharing common but not the same boundaries, in the same way that Scotland and England share boundaries. And although you can heat up space, how can you heat up time?

See you next Thursday is dependent on context. Speak so I can hear you. Think of the Big Bang. Time and Space simultaneously radiating in the now. But what is now? A collection of forces interacting and pushing against each other in the Big Bounce and creating the probability of the Big Bang. Reductio ad absurdum. Einstein suggested that the distinction between the past present and future is nothing but a persistent, stubborn illusion.

Contrast with the more familiar idea of the German philosopher Martin Heidegger with the emphasis on ‘dwelling in time’. Physics becomes for some of his more extreme follower a discipline that is incapable of describing reality.

Let us look back and forward to the idea that heat is god. There is only a detectable difference between the past and future and different states when there is a flow of heat. Probability is king. But some of his subjects are subject to revolt.

Quantum gravity is a blurred vision of physics. But Stephen Hawkins has demonstrated that black holes are always ‘hot’. Hot space creates time in flux. The quanta of space, the vibrating ‘molecules’ that heat the surface of the black hole and are heated by the black hole generate change. Time in flux. Flux in time.   


Carlo Revelli (2015) Seven Brief Lessons on Physics, translated by Simon Carnell and Erica Segree.


First Lesson. The Most Beautiful of Theories.

I just nipped out at lunchtime to get a bigger brain, but they were all out, the only thing left –on special offer- was a Simon Cowell brain. I said to the lassie behind the counter, ‘Do I look that fuckin’ stupid?’

‘Or a two-for-one, David Cameron and… a black hole,’ she offered.

I didn’t hang about, I’ve got better things to do with my time. Of course I don’t need a bigger brain. After all, quite simply, The Most Beautiful of Theories is Einstein’s General Theory of Relativity. Kudos, a kind of mental judo, by owning this book, it makes me instantly brainer. It’s a general thing, some of you might not understand. Albert, like me, didn’t do that well at school. In second year of St Andrew’s school I sat my first exam in Physics. Question 2 had me going. Twenty-seven years later I was still sitting in the old gym hall, pondering.  Rovelli tells the reader Einstein ‘spent a year loafing aimlessly’ and he reminds us, ‘You don’t get anywhere by not wasting time’. I was off to a flier. Einstein didn’t sit any exams and neither did I – you can see where this is going?

I’m now going to explain gravity. And if it sounds like I’ve just made it up, it’s Einstein’s fault. Think back to Isaac Newton and the apple failing. That’s gravity at work, the force that draws all things together and keeps them apart, but on its day off it plays by different rules.  Newton imagined space to be ‘a great big empty container’. Farraday and Maxwell had filled the box with the pulses of an electromagnetic field and a gravitational field. Einstein’s genius was in seeing that the gravitational field is not diffused through space, something added, like a prosthetic nose. The gravitational field is space (and time and motion), the dancer and the dance, the singer and the notes of a song.

‘How can we describe the curvature of space?’ such as planets circling around the sun, asks Rovelli. I stuck my hand up here and shouted, ‘as a curve, sir?’ always a smart alec, although my name wasn’t alec. And, you know, I wasn’t far wrong. Bernhard Riemann had produced a doctoral thesis that was ‘completely useless’ and made no sense. Just the thing for the job. Riemann’s curvature (R) is equivalent to the energy of matter. I’ll not write out the full equation here because I’ve only got one lifetime to understand it, but I guess, you get the drift. Light stops moving in straight lines, space bends around a star and Mars bars become increasingly smaller the closer you come to buying one.

The whole of space can expand and contract, like the exhalation and inhalation of breath. Einstein’s equation predicted ‘The Big Bang’, or at least helped explain it in Homer Simpson bites as a young god slaving over an extremely small and extremely hot universe. Oops. Butter fingers.  Cosmic radiation flowing like waves from that small, fixed point in time and space were a glimpse of Einstein’s reality. I’m going to read a bit more of Riemann’s mathematics before I say more, but next up, Lesson 2, tomorrow, I’ll explain with the help of my old buddy Carlo Ravelli’s primer: Quanta.  Wow that should be big.