Star systems, such as the solar and Castor systems, are grouped together into galaxies, with our home galaxy being the Milky Way. It contains at least 100 billion stars, and perhaps as many as 400 billion. Each star we can see twinkling in the night sky with our naked eyes is within our galaxy. It is possible to see our nearest galaxy with the naked eye on clear, moonless nights, but it is not possible to distinguish stars within it without a powerful telescope. There are estimated to be about 1 trillion galaxies in the observable universe, each separated by vast tracts of outer space. That is a lot of stars, and a lot of cosmic real estate that we can’t visit or communicate with. If there are intelligent aliens out there, they would have to be cosmically close by to know of our existence.
Guglielmo Marconi sent the first radio message – ‘Can you hear me?’ – about 125 years ago, in 1897. If an alien civilization was listening out for radio messages and heard this and was to immediately reply, ‘Yes, we can hear you,’ and we were to pick up their reply, they would have to be within 62.5 light years of Earth. Radio waves travel at the speed of light, so Marconi’s signal from Earth would have reached the most distant aliens who could have heard it sometime in 1959, and their response would be arriving back on Earth around now. There are about 15,000 stars within 62.5 light years of Earth, and we’ve heard nothing intelligent from any of these systems. Conversations with aliens on their home worlds will at their fastest take generations.
There is one radio signal astronomers have detected that may have originated from an extraterrestrial civilization. It is called the ‘Wow!’ signal, and it was recorded in 1977 by a radio telescope belonging to Ohio State University. The astronomer Jerry Ehman wrote ‘Wow!’ on the paper printout that contained the signal, and the name stuck. The signal sounds nothing like Marconi’s first radio message and instead is in the form of a type of wave nothing the like of which has been detected since. In 2012, humanity responded to the Wow! message by sending 10,000 tweets towards the constellation Sagittarius, the direction from which the signal came. If the signal was from aliens, let’s hope they don’t think we’re trolling them. Personally, I will remain doubtful that the Wow! signal is evidence of extraterrestrial life until we hear the same or a similar message again and can rule out other potential causes.
The reason I find the vast distances between star systems frustrating is I would dearly love to know how common life, and in particular intelligent life, is in our universe. The fact we have not encountered aliens does not mean they are not out there. Even if on average each galaxy contained only one planet that evolved intelligent life during its entire history, that would still equate to 1 trillion planets with civilizations in the observable universe, yet we would never know. It seems I am not destined to visit with aliens on other planets, but fortunately there is much to see on our own, and the history of our planet is amazing and has generated some breathtaking places to visit.
One of my favourite places on Earth is the Bungle Bungle mountain range of Western Australia. I became fixated on this corner of our planet as an undergraduate student. It was the late 1980s, and my friends and I were avid watchers of the Australian soap opera Neighbours. One character, Helen Daniels, announced occasional trips to the Bungle Bungles to paint, presumably whenever the actress who played her, Anne Haddy, needed a break. I didn’t believe there could possibly be a place called the Bungle Bungles so headed off to the library to learn more. After spending way more time than I had expected, and time I could ill afford, given my looming exams, I learned that the Bungle Bungles was an ancient mountain range consisting of beehive-shaped striped mounds and canyons carved by wind, water and sand over millions of years. The area had been first seen by Europeans in 1983 when a film crew flew over it, and four years later it was designated a National Park. The local Gija people had been visiting Purnululu, their name for the range and what it now should be referred to as, for over 20,000 years, and possibly much longer.
It took me thirty years to make the trek to Purnululu, with my wife Sonya, and my children Sophie, Georgia and Luke, visiting for my fiftieth birthday in 2018. To get there, we flew on progressively smaller planes from London to Singapore to Darwin to Kununurra before the final leg on an eight-seater propeller plane which deposited us on a sandy airstrip that is grandly named Purnululu airport, close to the range. Although it took me three decades to visit this UNESCO World Heritage-listed site, I was told by someone who had a dream job of working in the park that I had fallen for an Australian marketing campaign. Having gazetted the national park in 1987, the Australian Tourism Board wanted to attract visitors to it, and although I have been unable to independently verify this, embedding the Bungle Bungles into Helen Daniels’ lines was apparently part of the campaign.
The beehive-shaped mounds of Purnululu are striped orange and black, and they sit in front of mountains that today reach a height of only 575 metres above the surrounding plains. These mountains are criss-crossed by canyons carved over the course of millions of years. The history of the mountain range dates to a time when amphibians were the dominant animals, well before mammals had evolved. Between 350 and 375 million years ago, multiple layers of sediment were laid down in the bed of a river or lake before they were eventually compressed into layers of sandstone. Geological activity caused by the shifting of huge slabs of rock called tectonic plates that form the crust of our planet then pushed the sandstone upwards to form a towering mountain range. Over time, the range was eroded by rainfall, streams, wind and fluctuations in temperature, and Purnululu was formed. The orange and black stripes of the mounds have faced the brunt of winds blowing off what is now the Simpson Desert, and they are the most eroded part of the ancient range. The stripes are thought to be due to differences in the clay content of the sedimentary sandstone layers from which the range initially formed. The more clay that was in the sediment when it formed, the higher the water content of the rock, and these wetter layers are home to cyanobacteria, a species of photosynthesizing microorganism. The stripes are only a couple of millimetres thick because the cyanobacteria need light to survive and it does not penetrate far into the rock. The bacteria are also unable to survive in drier layers of the rock. The stripes are consequently indicators of fluctuations between wet and dry periods that took place over a 25-million-year period nearly 400 million years ago in the ancient lake where the sediment was laid down.
The Purnululu range is unique to Earth, and Earth itself is unique. In the topics we have covered so far in this book, we have not yet had to focus on local events. Gravity, electromagnetism and the weak and strong nuclear forces operate throughout the universe in the same way (or at least physicists assume they do because they emerged when the universe was very tiny and are thought not to have changed, and there is no evidence to suggest they vary from one galaxy to the next). Matter is not spread evenly throughout the universe due to quantum variation when the universe was very young, and that difference in its distribution resulted in gravity pulling together matter into stars and galaxies. The four fundamental forces are responsible for our planet and the solar system in which we reside, but to understand how our little corner of the universe came to be we must now think a little more locally. The details on how matter has been distributed in our neck of the woods become important as we consider how our solar system and planet formed. Was it inevitable that a star the size of our sun developed where it is today, or that it would have planets tracing the orbits we observe across our night sky? Each star is a little bit different, as is each solar system and galaxy. For you and me to exist, we needed the right combination of events to occur locally so that a planet formed where life could evolve and develop into an intelligent species. In this chapter, I largely focus on what we know about how our local conditions came about, and gravity is the force that takes centre stage. But before I get on to that, there is a gap to fill.