Template:Galaxies Coalesce

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Quote of the Day

"For example, if the big bang had been one-part-in-a billion more powerful, it would have rushed out too fast for the galaxies to form and for life to begin." - Robert Lanza

"I do not claim any ability to read God's mind. I am sure of only one thing. When we look at the glory of stars and galaxies in the sky and the glory of forests and flowers in the living world around us, it is evident that God loves diversity. Perhaps the universe is constructed according to a principle of maximum diversity." - Freeman Dyson

Thoughts for the Day

Let us imagine

This week let's think about galaxies. Consider this image taken by Hubble. It is an image taken of the darkness between stars. In the darkness between stars Hubble found not just the odd galaxy but billions of galaxies:


The universe is made of vast amounts of empty space and then within that empty space is dotted billions of galaxies. Why is the universe filled with a hundred billion galaxies? Why would the universe need that many galaxies? What is the relevance of all that matter and space to us, as humans, here on Earth? Is it just to make us feel small and unimportant?

We live in one not-particularly-notable galaxy out of those hundred billion. From the point of view of creatures made of matter, such as us, galaxies are where it is happening. In fact, Robert Lanza is right; if galaxies hadn't formed, life might not have begun. The existence of life is indirectly powered by the gravitational potential energy released in the coalescence of our galaxy.

In actual fact, most of life is powered by the energy emitted by the Sun. And that energy comes from the nuclear potential energy inherent in hydrogen. But to fuse hydrogen the Sun had to be heated up and its own gravitational collapse and the gravitational potential energy released by that collapse is what heated it up. In order for something the size of the sun to collapse gravitationally from a cloud of gas and dust, the gas and dust must begin as a reasonably dense cloud to begin with. This was the role fulfilled by the galaxy. The collapse of galaxies, out of the more or less evenly distributed hydrogen gas of the early universe, created pockets of stable matter density within the expanding universe where stars will be able to continue to form for a trillion years.

So that explains why we need one galaxy. But why are there a hundred billion galaxies? The answer is opportunity. There are three reasons why opportunity is the answer. The first reason is that complex, intelligent life which can ask the question, 'Why a hundred billion?', is rare in this universe. How rare we don't know. But SETI has been looking for it for decades and has not found it yet. It may be that the universe needed to be this big in order to be home to at least one species that could ask the question. This is called the anthropic principle. Of course, the better way to state it is backwards, 'The question is meaningless because you couldn't ask it if you didn't exist and you wouldn't exist if there wasn't a significant probability of your coming to exist in this universe, and there wouldn't be a significant probability of your coming to exist if the universe didn't have a large number of chances to create you, given that you are so improbable.'

The second way in which opportunity is an answer is that an expanding universe allows the quantum state of the universe to change continuously forever without ever repeating. A universe of static size could reach the same quantum state as it occupied before and, therefore, enter an ever repeating loop. In such a universe there would be no opportunity to explore ever new states. The universe would become repetitive and boring.

The third way in which opportunity is an answer is that in a massive universe full of lifeless worlds there is plenty of opportunity for life to flower and spread and flower again and again.

Contemplation for the Day

Quietly contemplate the opportunities afforded to the universe, humanity, and Life in general by a hundred billion galaxies.

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