That is what it felt like to witness last month’s total solar eclipse from a ship off the east coast of Greenland. Sure, there was a bit of a slow fade as the moon moved into position over the course of an hour, but the transition from a little bit of sunlight to none at all was stark. What makes these astonishing cosmic shows possible is a coincidence that is perhaps even more astonishing: the sun is almost exactly 400 times bigger than the moon, and it is also almost exactly 400 times further away.
As we look into the sky, that translates to the two of them appearing just about the same size, which allows the moon to cover the disc of the sun, plunging the area under the shadow into sudden darkness. We may have finally solved cosmology’s chicken-or-the-egg problem It is another cosmic coincidence that we happen to be alive at just the right time to witness the wonder of a total solar eclipse. The moon is slowly receding from Earth.
It is moving less than 4 centimetres a year, but, over the aeons, that time adds up: in a little over 600 million years, eclipses will start to become more and more rare. By 1.2 billion years from now, Earth’s surface will have seen its last total solar eclipse. All this got me thinking about how extraordinary it is that we are here at all.
I don’t necessarily mean me in particular, or even humanity – the twin marvels of life arising from non-living matter and evolution are a bit outside my wheelhouse, and frankly too complicated for me to fully comprehend – but the conditions of the universe that make life, and planets, and suns, and even something as fundamental as matter possible. This is known as the fine-tuning problem in cosmology. There are dozens of fundamental constants – the strength of gravity, the masses and electric charges of fundamental particles like protons or quarks, and even the density of the universe – and all of them seem to have values that are exactly right for life to arise.
In A Brief History of Time, Stephen Hawking summarised this almost-unbelievable coincidence: “The remarkable fact is that the values of these numbers seem to have been very finely adjusted to make possible the development of life… It seems clear that there are relatively few ranges of values for the numbers that would allow for development of any form of intelligent life.” If the expansion rate of the universe were just a little bit higher, it would pull clouds of cosmic gas apart too fast for stars to form. If there were a little more mass in the universe, or if gravity were a tiny bit stronger, everything would have crunched in on itself long ago. If the strong nuclear force were just a little bit stronger, the universe wouldn’t have enough hydrogen, carbon or oxygen for life to arise.
I could go on and on, but you get the point: the cosmos is balanced on a razor’s edge where a tiny push in either direction would have rendered it uninhabitable by the likes of us. Naturally, scientists have been arguing over why this might be for ages. The fine-tuning problem has become one of the premier arguments for a multiverse in which infinite universes have infinite combinations of different fundamental constants, so the emergence of at least one with the right constants for life is inevitable.
Extract — continue reading at the source.
