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Posts tagged existence

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Q: Why?

Mathematician: From time to time, people like asking us questions such as “Why?”, while steadfastly refusing to explain what the heck they are talking about. The best example of this was a naked guy who approached our “Ask a Mathematician / Ask a Physicist” booth at Burning Man. In an attempt to respect everyone’s right to not explain themselves, we’ll make a series of guesses about what those folks might be trying to get at, and briefly respond to each of these possible questions.


1. “Why do we exist?”

Mathematician: We exist because our ancestors were at least slightly better at passing down their genetic material than other people. If the environment of earth happened to be just a tad bit different, then other genes besides our own would have been favored, and we would not be here today. If the environment had been a little more different still, then not only would we not be here, but the human species would not even be here. Some other creatures (possibly of great intelligence) would now be romping around this planet. In conclusion, we exist because the process of evolution works, because our planet happened to have the right conditions for evolution to begin, and because conditions changed over time such that human genes (and more specifically, our ancestor’s genes) happened to be favored for survival. We all got very, very lucky.

Physicist: If the many-worlds hypothesis holds (it totally does), then everything that’s possible happens in some version of the universe.  If you can ask the question “Why do we exist?”, then you’ve already restricted your attention to the (possibly very small) set of universes where intelligent life exists.  This argument is called the “anthropic principle“.  So the reason we exist is because there is at least some vanishingly small chance that we could.

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Filed under physics mathematics universe anthropic principle existence aliens life nature

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Existence: Why is the universe just right for us?

25 July 2011 by Marcus Chown

IT HAS been called the Goldilocks paradox. If the strong nuclear force which glues atomic nuclei together were only a few per cent stronger than it is, stars like the sun would exhaust their hydrogen fuel in less than a second. Our sun would have exploded long ago and there would be no life on Earth. If the weak nuclear force were a few per cent weaker, the heavy elements that make up most of our world wouldn’t be here, and neither would you.

If gravity were a little weaker than it is, it would never have been able to crush the core of the sun sufficiently to ignite the nuclear reactions that create sunlight; a little stronger and, again, the sun would have burned all of its fuel billions of years ago. Once again, we could never have arisen.

Such instances of the fine-tuning of the laws of physics seem to abound. Many of the essential parameters of nature - the strengths of fundamental forces and the masses of fundamental particles - seem fixed at values that are “just right” for life to emerge. A whisker either way and we would not be here. It is as if the universe was made for us.

What are we to make of this? One possibility is that the universe was fine-tuned by a supreme being - God. Although many people like this explanation, scientists see no evidence that a supernatural entity is orchestrating the cosmos. The known laws of physics can explain the existence of the universe that we observe. To paraphrase astronomer Pierre-Simon Laplace when asked by Napoleon why his book Mécanique Céleste did not mention the creator: we have no need of that hypothesis.

Another possibility is that it simply couldn’t be any other way. We find ourselves in a universe ruled by laws compatible with life because, well, how could we not?

This could seem to imply that our existence is an incredible slice of luck - of all the universes that could have existed, we got one capable of supporting intelligent life. But most physicists don’t see it that way.

The most likely explanation for fine-tuning is possibly even more mind-expanding: that our universe is merely one of a vast ensemble of universes, each with different laws of physics. We find ourselves in one with laws suitable for life because, again, how could it be any other way?

The multiverse idea is not without theoretical backing. String theory, our best attempt yet at a theory of everything, predicts at least 10500 universes, each with different laws of physics. To put that number into perspective, there are an estimated 1025 grains of sand in the Sahara desert.

Fine-tuned fallacy

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Filed under universe multiverse cosmology existence string theory theoretical physics