Star Cluster NGC 2074 in the Large Magellanic Cloud | Credit: NASA, ESA, and M. Livio (STScI)
The universe began 13.5 billion years ago. We are fairly sure of this figure because of the way objects and particles move through the universe. Einestein taught us that nothing can travel faster than light. We know that light travels at a very definite speed (though the speed differs through different mediums).
In one second light can travel 7 times around the earth. It takes light 4 years to reach us from the nearest star Proxima Centauri in the Alpha Centauri system. We measure the universe in “light years”, the time it takes light to travel in a year. If we were to set off from the solar system to the nearest star it would take us 4.2 years traveling at the speed of light to reach it. Importantly, whenever we gaze up at that star now, we are seeing the light that left it 4.2 years ago. We are looking back into the past. We see it how it was then, not how it is now. If that star was suddenly to vanish, we will not know it until 4.2 years after the event.
We would have to go there, to see it how it is now. Unfortunately we have not yet mastered any advanced forms of propulsion, and in reality the journey would take us closer to 40 years for such a crossing, if not more. Nevertheless, speculating about such things should help us understand just how vast the scales of distance between stars really is.
Our galaxy is a massive conglomerate of stars, comprising as many as 200 – 400 billion, in a disc 200,000 light years across and 1,000 light years thick. Around the milky way drift smaller satellite galaxies, and nearby we are surrounded by a supercluster of galaxies, each containing hundreds of thousands of stars of its own.
Overlapping Galaxies | Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)
Our nearest neighbor, Andromeda, is 2.5 million light years away. Again we are not seeing Andromeda as it is now, but how it was 2.5 million light years ago. We have looked out into the universe and we can see for 13.5 billion years in every direction. Beyond this we can only see the microwave radiation left over from the birth of the universe. This tells us how long the light has been traveling for. This tells us the age of the universe (and there are many other methods of doing this).
We are a speck of dust in the great oceans of infinity. In all this time stars formed and began to shine, burned up hydrogen, and then as they used up their fuel, exploded in massive supernovae. These explosions scattered new materials into the universe. These heavy elements condensed down into stars and star systems, including ours, and provided the water, oxygen, carbon, and metals, indeed all the elements that are so essential for life. And life formed, on one world at least, from the dust of stars came life that was able to replicate, survive, thrive, and adapt.
Soon we (humans) came along, so that now the process is complete, we can use our telescope to look up at the boundless infinity of the universe and marvel at the inexhaustable vastness of it. We occupy such a tiny fraction of time and space. Our star formed 4.5 billion years ago, along with the earth; a third of all the time since the universe began. Human history occupies the latter 100,000 years of Earth's history, a meaningless fraction of the age of the Earth.
We must cast away the egocentric view of the universe as being designed especially for us, if we are to accept the harsh realities of our situation, and thrive in this universe. But far from being something to fear, it the universe about us is something to cherish, in all its marvelous beauty and wonder.
