The Infinite Monkey Cage – How to Build a Universe. Robin Ince

near silence of the Lovell Telescope. Like some psychosomatic sense of feeling all those neutrinos passing through you, your imagination fabricates this same sensation of signals coming from beyond our galaxy.

      Back in the café, I ask Brian about gravitational waves. Here is another great day proving the frequent necessity of delayed gratification when it comes to physics. Sometimes a good idea needs to wait for the technology to be created to test it. This story starts with two black holes merging. As they merged, briefly there is a power output five hundred times greater than all the stars in the known universe. Lasers have detected the waves.

      Here is the gatherer of radio waves emitted by astronomical objects. This is where quasars were defined and pulsars observed.

      This is not psychogeography, this is psychoastronomy.

      Brian explained it like this.

      Brian: 1.3 billion years ago a storm in space and time was generated by the collision of two black holes. One of the black holes was 29 times the mass of our sun, the other 36 times more massive. The event lasted for less than two-tenths of a second, during which time the black holes accelerated from a closing speed of one-third of the speed of light to two-thirds of the speed of light before colliding and merging. Energy was lost to the system in the collision and the storm carried it away at the speed of light. For a tiny fraction of a second, the peak power output exceeded the power output of the entire observable Universe by a factor of fifty. 1.3 billion light years away on a small planet around a yellow star, salt water oceans were populated by single-celled organisms. As the spacetime storm approached, some of these single-celled creatures became organised into collaborative multi-cellular groups, colonised the land, learnt how to do science and built two giant laser facilities with 4km-long arms at right angles to each other at each end of a country called the United States. They switched on the lasers, which they called LIGO and had just upgraded, on 12 September 2015, and two days later at 5.51 a.m. Eastern Standard Time on 14 September 2015, the storm passed through the Earth, changing the effective length of the arms of the detectors by one-thousandth of the diameter of a proton. The signal, described in the box below, was exactly as predicted by Einstein’s Theory of General Relativity, first published a century before when nobody knew about black holes or lasers. Life can achieve a great deal in 1.3 billion years.

      Some thirty minutes later, Brian finished the story, or at least came to the point of the story where we were now at, because the story continues with each new discovery. He leaned back in his chair, reached for the hot pie that had been brought to him, bit into it, and let out a yelp.

      ‘Ow, it’s scorching.’

      He huffed, puffed and reached for his water, in obvious tongue-blistering discomfort. And I thought that there was something rather beautiful about that. Here is a human who can have a deep understanding of the nature of our universe, yet no understanding of the speed of the cooling of a pie.

      While touring, barely a week went by without Brian burning his mouth on some hot food. I would try to train him.

      ‘Chips, hot.’

      ‘Hot chips,’ he would smile, before singeing his lips again.

      ‘Remember what happened last time with the hot chips.’

      ‘Hot chips,’ he would smile again, then screech as his tongue swelled.

      Finally, I realised, there was nothing to be done. The small area of space where my brain had a series of connections to remind me that food sometimes needed to be cooled before it could be consumed had been used up by Brian to comprehend quantum entanglement. That was my tragedy. That was his tragedy. He would continue to burn himself on pie filling, but I would never truly understand how two photons could interact from a distance.

      The LIGO Hanford Observatory in Washington State.

      The LIGO Livingston Observatory in Louisiana.

      The LIGO Experiment

      The LIGO experiment consists of two devices known as laser interferometers. One is situated on the north-western seaboard of the US in Washington State, the other in the south east in Louisiana. Each arm consists of a 4-kilometre-long vacuum tube with heavy mirrors suspended at each end and a high-intensity laser beam bouncing between them. As a gravitational wave passes through the experiment, it changes the effective distance between the mirrors in a characteristic way predicted by Einstein’s Theory of General Relativity. Because the arms are at right angles, the prediction is that one arm will shrink as the other expands. Using a technique called laser interferometry, differences in the round-trip time of the photons as they bounce between the mirrors can be measured very accurately. The extreme precision, which is equivalent to measuring the distance to our nearest star to our solar system, Proxima Centauri, to less than the width of a human hair, is achieved by averaging the measurements over the very large number of photons in each high-intensity laser beam. Gravitational waves pass through the Earth at the speed of light, and because the two LIGO sites are separated by 3002 kilometres, an identical signal would be expected in both interferometers, with a time-delay equal to the light travel time between them, if the vibrations of the mirrors have an astrophysical origin.