What We Learned from Professor Brian Cox at Motorpoint Arena

What is our place in the universe? There are 200 billion stars in the Milky Way and there are 20 billion Earth-like planets. We can't see the structure of our galaxy from within but we can look at others, such as the Whirlpool galaxy, which is 22 million light years away and 100,000 light years across. We can see the Coma cluster, which contains 1,000 galaxies. The Sloan Digital Sky Survey maps the position of galaxies within the visible universe. It’s a veritable snowstorm of galaxies, but there is a structure to it; the cosmic web, it isn't random. There are 2 trillion galaxies in the visible universe. It is big, beautiful and complicated.

The Cassini mission has sent back some incredible images of Saturn. Its rings are only ten metres thick and are made of water ice. In the far, far distance, it's possible to see Earth, the pale blue dot. Astronauts often talk about the "overview" effect when looking down on our home planet and seeing its size in the universe. This is the perspective of knowledge and distance.

General Relativity was a theory of gravity but has become a theory of cosmology. Many roads lead to General Relativity, and nearly anything that you look at can lead to something interesting. The two main routes to it were thinking about motion and light. In his two equations dealing with electricity and magnetism, Maxwell showed just what light is. Later, these equations would be described as "nature revealed to a human being." Both of these equations feature c - the speed of light. Maxwell realised that light is a wave driving through space, and its speed is the ratio of the strength of these two forces. These waves propagate through space but what is that speed relative to? What is motion?

The Earth is moving around the Sun at eighteen miles per second, but we don't feel it. The only experience we have of this motion is the gentle passing of the seasons. You cannot tell if you’re moving or not and there is no experiment that you can do to show whether you are. Therefore, there is no such thing as absolute space. Einstein postulated a thought experiment about a clock that used light to keep time. As the clock moves, the path that light has to take gets longer. We already know that light moves at a constant speed, so it follows that time must pass more slowly for a moving clock. We can see this today in the Large Hadron Collider, where time passes 7,000 times slower for the particles that speed round at 99.99999% of the speed of light, compared with time for the observers. From this, Einstein concluded that there is also no such thing as absolute time.

From this came the idea of space-time; the fabric of the universe. Gravity is geometry; mass curves space-time. Matter tells space-time how to curve and space-time tells matter how to move. From this came General Relativity and Einstein's equations for gravity. The next step was to try and use these equations to model the whole galaxy. But, back in 1917, we didn't even realise that there were other galaxies beyond the Milky Way. This made it difficult to work out the matter distribution, which is one of the key inputs into the equations. Using a uniform matter distribution as a model, the solutions showed that the universe can't stay static. One of Einstein's peers, Lemaître reasoned that if the universe is expanding then we can track it back and there must have been "a day without a yesterday." Einstein wasn't totally comfortable with this idea, but for Lemaître it was proof of a creation event. This made him happy as he was a priest as well as a scientist and a creation event implies a creator.

So, from just looking at light and gravity came ideas about the very origin of the universe.

After a quick intermission, Robin Ince takes up the baton to talk Charles Darwin and how his nose almost prevented him from going on the Beagle. The ship's captain thought it was the nose of a lazy man. Darwin had to convince him that his nose "spoke falsely" before he could take his place on the voyage. He went on to describe the rainforests of Brazil: "the mind is a chaos of delight." Back at home, he started looking at earthworms. He discovered that they didn't react to a whistle so he played a bassoon at them. Still no reaction. Then, he tried shouting at them. Finally, he took some earthworms inside and played the piano at them. They still didn't react.

We have evolved so that we understand ourselves; we are atoms understanding atoms. Are places where such meaning exists common in the universe? What can life on Earth and its history tell us about the probability of life elsewhere? The Earth is 4.5 billion years old. For the first half a billion years it was a violent and volcanic place. Then, around 4 billion years ago, the oceans formed. Life formed 3.8 billion years ago and may have started even earlier; life formed as soon as it was able to. Every cell has the same chemistry of cascading protons. In the time it's taken you to read that sentence, more protons have cascaded through your body than there are stars in the observable universe.

Did bio-chemistry begin as geo-chemistry? The environments for such simple life to form aren't rare, not even in our own solar system. The moons of Saturn could be able to support life. Titan is a planetary sized moon. It is -180^oC on the surface with methane rivers and rain. However, there is liquid oxygen beneath the surface. Enceladus is about the size of Wales and we used to think that it would be geologically dead. However, Cassini has shown volcanos of water erupting from the surface, which then turns into ice. These jets may have hydrogen gas in them and there could be hydro-thermic vents under the ocean. These are the conditions that led to life on Earth. There are even similar conditions on Europa, a moon of Jupiter.

2.5 billion years ago, photosynthesis developed in single-celled bacteria on Earth. Even then, there was no evidence of multi-cellular life on our planet until 530 million years ago. The key to this is the eukaryotic cell, formed when two cells joined together, and this is the basis of all simple life. Around 450 million years ago, plants started to colonise the land and then 200,000 years ago, humans arrived. So, maybe simple life is common in the universe but complex life is rare? We've been incredibly lucky to find ourselves on a planet that has been stable for 5 billion years. The biology for complex life to develop is so complex that it may well turn out that we are the only civilisation in the Milky Way.

Black holes are collapsed stars that are made from the same stuff as us. We don't yet have the physics to understand what happens at the centre of a black hole, but they could be temporary structures that fade back into the universe as Hawking Radiation. We still don't know how the supermassive black holes at the centre of galaxies form.

There was a super volcanic eruption in Indonesia not long after humans emerged that nearly wiped us out. There are likely to be many beautiful planets out there, but there may only be one civilisation; we are the most interesting thing in the solar system.

The laws of nature seem beautifully set up for life. For example, if you turn down gravity just a little bit then stars and galaxies wouldn't form. How did these laws get to be how they are?

If you look at something far away, you are looking back in time. For example the Andromeda galaxy is 2 million light years away. This means the light that we can see coming from it has taken 2 million years to reach us, so we are seeing it as it was 2 million years ago. We can't see all the way back to the beginning of the universe 13.8 billion years ago because the very early universe was a soup of opaque, charged particles. However, we can look back to when the universe was just 377,000 years old. The Cosmic Microwave Background Radiation is a picture of this baby universe. There were no stars and no galaxies just an almost uniform, glowing hot dense universe.

Closer to the origin of the universe there was inflation and quantum fluctuations. Inflation is a relatively new theory, only really being talked about in the last thirty years. Starting with a patch of space the size of one billionth of a nucleus, it then doubles every 10^-37 seconds. Space is stretching very quickly and as it gets bigger it gets ripples in it. It gets to around the size of the Motorpoint Arena and then stops. The energy that was causing the expansion then creates all of the stuff that becomes the universe. This is a "hot Big Bang" and you can calculate how the ripples travel through it and into the Cosmic Microwave Background Radiation and through to today.

This has other implications, especially with the size of the observable universe versus the size of the total universe. There is more beyond what we can see but the light hasn't reached us yet. Why does inflation stop? It seems to stop in patches and then you get a Big Bang. This leads to a multiverse and could be going on right now. We have no idea how long it's been going on for but we do have a minimum time for our bubble: 13.8 billion years. The laws of nature may be different across the inflationary multiverse. We are pretty sure that inflation definitely happened, and this is now taught to undergraduates, but the idea of the multiverse is a little more theoretical.

Our time is limited. In 5 billion years, the sun will run out of fuel. Eventually, it will become a nebula and the atoms that were part of it will go back out into the universe. As the universe ages, star formation slows down. Consciousness is limited in an eternal universe.

And, with that, Brian and Robin head off stage and 6,000 science fans make their way out into the Nottingham evening. The idea that we may be the only intelligent life in the universe is both scary and humbling; we really need to start taking better care of each other…

Professor Brian Cox came to Motorpoint Arena Nottingham on Thursday 11 May 2017

Motorpoint Arena website