Human Universe (27 page)

And so we reach the end. Defining the Big Bang as the initial hot, dense phase of our observable universe that gave rise to the CMB 380,000 years later, we understand what happened before. There was a period of inflationary expansion, which could have been driven by a scalar field in accord with the known laws of physics. That inflationary expansion is probably still going on somewhere, spawning an incalculable number of universes as we speak, and it will continue doing this forever. We live in an eternal universe, in which everything that can happen does happen. And we are one of the things that can happen. Did the whole universe have a beginning, an essential, external cause in the spirit of Leibniz’s God? We still don’t know. Possibly there was a ‘mother of all Big Bangs’, and if so, we will certainly need a quantum theory of gravity to say anything more.

What does this mean? The wonderful thing for me is that nobody knows, because the philosophical and indeed theological consequences of eternal inflation have not been widely debated and discussed. My hope is that in trying to summarise the issues, regrettably briefly and necessarily superficially in the television series and in a little more depth here, these ideas will be accessible to a wider audience and stimulate discussion.

This is desirable and necessary, because ideas are the lifeblood of civilisation, and societies assimilate ideas and become comfortable with their implications through understanding and debate. If eternal inflation is the correct description of our universe, it will be the artists, philosophers, theologians, novelists and musicians, alongside the physicists, who explore its meaning. What does it mean if the existence of our universe is inevitable? What does it mean if we are not special in any way? What does it mean if our observable universe, with all its myriad galaxies and possibilities, is a vanishingly small leaf on an every-expanding fractal tree of universes? What does it mean if you are, because you have to be? I can’t tell you. I can only ask – what does it mean to you?

For small creatures such as we,
the vastness is bearable only through love.

Carl Sagan

I can hardly wait

To see you come of age

But I guess we’ll both just have to be patient

’Cause it’s a long way to go

A hard row to hoe

Yes it’s a long way to go

But in the meantime

Before you cross the street

Take my hand

Life is what happens to you

While you’re busy making other plans

John Lennon

They must have descended into the darkness for a reason. Their burning dry-grass torches would have filled the caverns with acrid smoke, sucking the oxygen from the wet air. They would have moved carefully, fearfully perhaps, enveloped in a dim, flickering sphere of red, fading into a profound silent dark, the like of which I don’t experience. A child held her hand against the rock, and blew a red-pigmented mixture across it with a straw. She smiled – ‘my hand’. Her companions reached into the pigment and, in careful movements, inked a line of dots beside the handprint. The precision of a young imagination. A retreat to the lightness of the cave mouth. ‘Perhaps we’ll come back someday,’ she thought.

Over 40,800 years later, I held my hand next to hers, because the experts on the Upper Paleolithic told me that the handprints are always those of children, and most likely always female. El Castillo in northern Spain contains some of the oldest cave-art in the world. It is not known precisely how old, because the pigments themselves cannot be dated. The art is covered in calcite, which dripped and crystalised across the handprints and dots as the whole of recorded history played out above. Calcite contains uranium-234 atoms, which decay with a half-life of 245,000 years into thorium-230, which in turn decays with a half-life of 75,000 years. Thorium is not soluble in water, so there was none when the limestone formed. By measuring the concentrations of the uranium isotopes 234 and 238, and the thorium-230, a precise date for the formation of the calcite can be measured. This gives a minimum date for the art, since of course it must have been created before it was covered. The limestone covering the red dots formed 40,800 years ago. The oldest handprint was covered 37,300 years ago.

These dates are significant, because before 41,000 years ago there is no evidence of modern humans in Europe.
Homo sapiens
arrived tantalisingly close to the minimum age of the art in the darkness of El Castillo, leading some anthropologists to suggest that the art is not human. Rather, it may have been created by our close cousins, the Neanderthals, who dominated Europe at the time. I find this possibility profoundly interesting, and moving. It is interesting because the creators of this art had all the attributes that we might lazily refer to as ‘uniquely human’. The retreat into the deep caves was undoubtedly a sophisticated response to the world. This is not mere decoration, because cave-art like this is not found near the cave entrances where these ‘people’ lived. Its creation is highly ritualised. The darkness is integral. One of the most beautiful pieces in El Castillo is a bison, half-carved out of a column of rock and shaded with pigments to emphasise the arch of its back. When illuminated by torchlight, the rock casts a flickering, animal shadow onto the cave wall. The interaction of light and dark was important to the rituals carried out here before history, perhaps before humans. The cave resonates with ideas, curiosities and fears. It represents a border; the transition from existence to living. If this is a human place, it is a record of the first stumbling steps towards humanity. But if it is Neanderthal, it is a record of an ending, an ascent cut short. ‘Perhaps we’ll come back someday,’ thought the little girl in my imagination. Not long afterwards, her species became extinct, out-competed by their incoming cousins. Perhaps. It is possible that the date coincides with the migration of
Homo sapiens
into Europe because the art is indeed human. Some anthropologists believe that the art may have been a response to the native Neanderthal population; a sort of prehistoric shock and awe, asserting cultural dominance and engendering a sense of community and superiority in the nascent human population. Things never change. If this is the case, the Neanderthals inadvertently played a role in our ascent. The roles may have been reversed, however. Perhaps our ancestors found a young, emerging and more sophisticated culture when they crossed the Mediterranean. A species distantly related to us whose desire to explore the darkness we assimilated. Perhaps our intellectual climb was, in part, a response to them. Intellectual superiority does not guarantee survival; witness the fall of classical civilisation.

This possibility is illustrative of a fact that we modern humans often subconsciously rest in the shadows. Things can end, for ever. Species become extinct, and that doesn’t only apply to animals with feathers and no feelings. The Neanderthals became extinct, and they may have begun to imagine a future before they lost it. The red handprints of El Castillo are overwhelming in this context. Go there. Hold your hand up to hers, hear the giggles, picture the smiles, imagine the beginnings of hope, and listen to the silence.

At least 40,800 years later, we can use our knowledge of nuclear physics to move backwards through time to piece together her story. Science is a time machine, and it goes both ways. We are able to predict our future with increasing certainty. Our ability to act in response to these predictions will ultimately determine our fate. Science and reason make the darkness visible. I worry that lack of investment in science and a retreat from reason may prevent us from seeing further, or delay our reaction to what we see, making a meaningful response impossible. There are no simple fixes. Our civilisation is complex, our global political system is inadequate, our internal differences of opinion are deep-seated. I’d bet you think you’re absolutely right about some things and virtually everyone else is an idiot. Climate Change? Europe? God? America? The Monarchy? Same-sex Marriage? Abortion? Big Business? Nationalism? The United Nations? The Bank Bailout? Tax Rates? Genetically Modified Crops? Eating Meat? Football? X Factor or Strictly? The way forward is to understand and accept that there are many opinions, but only one human civilisation, only one nature, and only one science. The collective goal of ensuring that there is never less than one human civilisation must surely override our personal prejudices. At least we have come far enough in 40,800 years to be able to state the obvious, and this is a necessary first step.

‘We’ve woken up at the wheel of the bus and
realised we don’t know how to drive it’

On 15 February 2013 at 9.13am a 12,000-tonne asteroid entered Earth’s upper atmosphere travelling at 60 times the speed of sound. It came from the direction of the Sun, so there was never any chance of seeing its approach. The rock broke up at an altitude of 29 kilometres, depositing over twenty times the energy of the Hiroshima bomb into the sky above the Russian town of Chelyabinsk. Thousands of buildings were damaged by the shockwave and 1500 people were injured, mainly by flying glass as windows smashed in multiple cities across the region. Sound waves from the explosion rattled around the globe twice, and were detected by a nuclear weapons monitoring station in the Antarctic. The Russian parliament’s foreign affairs committee chief Alexei Pushkov took to Twitter: ‘Instead of fighting on Earth, people should be creating a joint system of asteroid defence.’ Naïve idealism? Overreaction? Hollywood? Not really. Sixteen hours later, a 40,000-tonne asteroid named 367943 Duende streaked by at an altitude of 27,200 kilometres, well within the orbits of many of our satellites, although it missed them all. This one had a name, because it was discovered by astronomers in Spain in 2012. There is a 1 in 3000 chance that Duende will strike the Earth before 2069; if it does, it could destroy a city, which isn’t too bad.

Before Chelyabinsk, the last recorded large impact was the Tunguska event over Siberia in 1908. The shockwave created by the airburst flattened 2000km
²
of forest in an energy release close to that of the United States’ most powerful hydrogen bomb test at Bikini Atoll in March 1954. Events on this scale are thought to occur on average once every 300 years, and could easily wipe out a densely populated region. The best-known impact in popular culture was the Chicxulub event in Mexico’s Yucatan Peninsula 66,038,000 ± 11,000 years ago, which wiped out the non-avian dinosaurs. Precision is important when available. If they’d had a space programme, Carl Sagan once quipped, or perhaps lamented, the dinosaurs would still be around, although in that case we wouldn’t. The Chicxulub asteroid was probably around 9.5 kilometres in diameter, and the energy release of such an object exceeds that of the world’s combined nuclear arsenal by a factor of a thousand. Or, if you like scary statistics, that’s 8 billion Hiroshima bombs. Such events are estimated to occur on average every 100 million years, give or take, and are quite capable of destroying human civilisation and possibly causing our extinction. At the other end of the scale, rocks of around a millimetre in diameter hit the Earth at a rate of two a minute.

Alexei Pushkov was right. It is absolute idiocy not to pay attention to the danger of impacts from space, and fortunately our space agencies have begun to do so. NASA’s Near Earth Object Program created the Sentry system in 2002, which maintains an automated risk table continually updated by new observations from astronomers around the world. I am writing these words on 3 September 2014, and there are currently no high-risk objects in the table, although there are 13 asteroids with the potential to impact Earth that have been observed within the last 60 days. The risk posed by an asteroid is quantified on the Torino Scale.

Every known near-Earth asteroid is assigned a value on the Torino Scale between 1 and 10, calculated by combining the collision probability with the energy of the collision in megatons of TNT (see diagram for
here
1–10 of the Torino Scale). Asteroid 99942 Apophis reached level 4 on the Torino Scale in December 2004. Initial observations and calculations suggested this 350-metre-wide asteroid had a 1 in 37 chance of a potential collision with the Earth on 13 April 2029 and a further chance of hitting us seven years later if it missed first time around. This would not have been a civilisation-threatening event, but it could have laid waste to a small country. Subsequent observations have effectively ruled out the risk from 99942 Apophis, but statistically speaking such an impact is expected to occur every 80,000 years or so. Although the Sentry table is currently benign, there are at least two very good reasons why we shouldn’t relax and forget about impact risks. Firstly, we haven’t detected all of the threatening objects by any means, as the Chelyabinsk event so effectively reminded us. And secondly, we don’t currently know precisely what to do if we do observe an asteroid with our name on it, which could happen tomorrow. In 2015 a new early warning system called ATLAS (Asteroid Terrestrial Impact Last Alert Sytem) will come online.