We live at a time when we know many of the secrets and history of the universe, and even where time and the universe are heading. Yet until only a few centuries ago, people looked into the night sky and — if they thought about it at all — had no real idea of what they were seeing, only myths and guesses.
The people of 1618 could look up and see the stars and planets (the latter looked like stars) but (the very few with the just-invented telescope aside) had no idea what they were, beyond being tiny dots of light in the blackness. They could see the moon, often even in daylight, but did not know what it was or what it did. During the day, they could see the sun and feel its heat, and while assuming it was a ball of fire, they did not know actually what it was, despite using it for agriculture, light and warmth.
Even a century ago — when, thanks to great developments in telescopes and science since 1618, we knew the Earth was a big globe that circled a star we called the Sun; that the Earth orbited the Sun and was one of a number of such orbiting planets, many of which had moons that circled them like our own moon; and that our Sun (a huge ball of plasma converting hydrogen into helium by nuclear fusion) was one of millions of stars in a galaxy we knew as the Milky Way — we believed our galaxy was the entire universe.
Today, we know the Milky Way contains billions of stars, many of them with their own orbiting planets, and that the universe contains billions of galaxies. Scientists have estimated the age of the universe at some 13.7 billion years and the age of the Earth as some 4.5 billion years, around the time our solar system formed from matter solidifying into lumps around our newly formed Sun.
We humans have walked upon this Earth for only 200,000 years. Civilisation — the groupings of people into villages, towns and cities and using written languages and rules governing how people interact — has existed for only some 5000 years of that speck of time, and in the beginning not everywhere on Earth, chiefly the Middle East, China, the Mediterranean and likely Zimbabwe and a few parts of what we now call Latin America.
Scientists today believe the universe started with a gigantic cataclysm we now call the Big Bang, a single moment in which time and space came into being. We can posit this—and the age of the universe—from the theories of geniuses like Albert Einstein and Stephen Hawking; by measuring the expansion of the visible galaxies into the void; and by such things as the background radiation believed to be from the Big Bang.
Current physics suggests that all the matter and energy in the entire universe was created in the instant of the Big Bang and was flung into space as plasma that settled, cooled and formed over billions of years into the galaxies, stars and planets, all of it shaped and held together and kept apart by gravity.
Gravity—still regarded as a semi-mysterious force—keeps us standing on the ground rather than floating into space; it keeps the moon orbiting the Earth (while creating the tides as the moon moves above us); the planets circling the sun; and all the stars in the Milky Way and all the other galaxies rotating in huge spirals in space. Spirals that probably have huge black holes in their centres, holes so dense and with gravity so strong that not even light can escape, so we cannot see them.
For some decades, up to the late 1990s, scientists believed the universe would continue expanding, though at a slowly decreasing rate, until gravity forced all the galaxies to fall back towards the centre where it all began, and then everything would collapse in a Big Crunch, leading to a new Big Bang that would start it all again.
But observation of the universe with our latest ocular and radio telescopes suggests the expansion of the universe is actually speeding up, not slowing. This acceleration has been hard to explain by Relativity Theory, so physicists have developed theories about “dark matter” adding to mass and “dark energy” driving the expansion — but so far, we can neither see nor find these strange matters and forces.
Stars have finite lives and though new ones are still being born, all will eventually die. Our sun will consume all its hydrogen in about five billion more years. If the universe keeps expanding to infinity, all the stars will eventually burn out, and nothing will remain — no light, no life, nothing. A dismal prospect.
And yet against all this wonder of the universe, we humans have become so conceited that many of us think we can wave a piece of paper and make the temperature of the Earth rise by exactly 1.5 °C, as if we were King Canute. Wise Canute, though, knew that he could not stop the tides, and proved it. Ironically, his home was Copenhagen.
- Image of the expanding universe courtesy NASA Jet Propulsion Laboratory