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.
It's also been called the weak and strong "anthropic principle." To read the rest of the article, click here.