![]() However – and this is the key – during its first split second, the universe expanded enormously faster than light. For most of its history, it has expanded far more slowly than this. Consequently, the distance to the horizon would be 13.82 billion light years if the universe had expanded at the speed of light since its birth. Now, a light year is the distance light travels in a year (about 10 trillion kilometres). For all we know, there may be an infinite amount of the universe beyond the horizon. Outside the bubble are objects we cannot currently see because their light is still travelling across space to us. This amounts to about 100 billion galaxies. Inside the bubble – a region we call the “observable universe” – are all objects whose light has had time to reach us since the Big Bang. Think of it as like the surface of a soap bubble. For this reason, our universe is bounded by a “light horizon”. The fact that the universe was born 13.82 billion years ago means that we can see only those objects – galaxies and stars – whose light has taken less than 13.82 billion years to reach us. Myth 3: Since the universe is 13.82 billion years old, it is 13.82 billion light years to its edge This is why we live in a universe where clusters of galaxies continue to fly apart from each other, carried like driftwood in the cosmic flow, whereas smaller objects – individual galaxies, the Solar System, the Earth – are bound together by gravity and take no part in cosmic expansion. However, on the larger scales – masses bigger than a galaxy cluster – the expansion was irresistible. On the smaller scales – masses equivalent to stars and galaxies and even galaxy clusters – gravity was strong enough to overcome cosmic expansion. It caused clumps of debris to begin to shrink, becoming ever denser. The agent was gravity, a force of mutual attraction between all pieces of matter. What this tells us is that the expansion of the universe becomes ever more powerful and irresistible the larger the scale.īearing this in mind, this is what happened after the Big Bang: gradually, things began to congeal out of the expanding and cooling debris. In fact, two galaxies that are twice as far apart as two others will be receding twice as fast three times as far apart, three times as fast and so on. To understand why, you need to know something about the nature of the universe’s expansion.Īs the American astronomer Edwin Hubble discovered in 1929, the farther apart two galaxies are, the faster they are flying apart from each other. Neither is the Earth, nor our Solar System, nor our Milky Way, nor the Local Group of galaxies of which the Milky Way is a prominent member. The universe is certainly expanding but you yourself are not expanding. Myth 2: If the universe is expanding, the Solar System must be expanding too If you are finding all this hard to grasp, therefore, welcome to the club. Consequently, we can only ever catch glimpses – for instance, the one afforded by the image of the rising cake. And the universe is a 4D thing, extending in three dimensions of space and one of time, or, as Einstein realised, four dimensions of a curious blend known as “space-time”. The key thing to remember is that we, as three-dimensional beings, can never completely grasp a four-dimensional thing. It either goes on for ever or folds back on itself just like a higher-dimensional version of the surface of a football. ![]() The analogy with our universe is not, of course, perfect since a cake has an edge and the universe, as far as we know, does not. As the cake swells, every raisin recedes from every other raisin, and none is the centre of the expansion. It has become conventional to liken the expansion – which continues today with the galaxies like our own Milky Way flying apart from each other – to the rising of a cake studded with raisins. Every point of space exploded away from every other point in space. The Big Bang, however, did not occur at a particular location. Also, in a conventional explosion, stuff flies outwards from a single point in space. All space – not to mention matter, energy, and even time – burst into being and began expanding spontaneously. But, in the case of the Big Bang, there was no pre-existing space. In a conventional explosion, shrapnel flies outwards into a pre-existing space. In reality, the Big Bang was utterly different from any explosion we are familiar with. It stuck, despite the fact that it conveys a totally misleading image of an “explosion”. The term Big Bang was coined by the British astronomer Sir Fred Hoyle in a BBC radio broadcast in 1949. Myth 1: The Big Bang happened in a particular place You can find out more and subscribe here. This article is a preview from the Autumn 2014 edition of New Humanist.
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