02 Nov 2013 17:42:45
Wise words from Douglas Adams, but there are even more mind-boggling things in the universe than its distances (although I grant that its distances are truly brain-melting).
Black holes were first publicly postulated on 27 November, 1783, when a gifted scientist, John Michell, addressed the Royal Society and proposed the idea of a star so massive that "corpuscles" of light would not be able to escape its gravity. If that were the case, therefore, they would be invisible. It would also mean that if you were to fall into the gravity well of such a star, you would finally hit it at the speed of light. (However, due to relativistic effects later predicted by Einstein, an observer at a safe distance would instead see you hovering on the edge of the black hole's event horizon for ever. Got that?)
Black holes are generally depicted in science fiction as destructive monsters: there is a good Doctor Who episode in which the devil is kept imprisoned on a planet orbiting one (the science in it is seriously flaky, but never mind). Caleb Scharf is capable of semi-anthropomorphising them, too. At one point he invites us to imagine the black hole at the centre of our galaxy as "a great monster" that "made its home inside a castle that was deep inside a huge forest". But the point he is trying to make is that black holes are essential to the formation of life. Basically – and I don't think I'm spoiling the wonder of the book by giving away its conclusion – if the black hole at the centre of our galaxy were much bigger, or non-existent, or if we were significantly closer to it, or significantly further away, then the conditions for life might well not have arisen. Black holes may be huge and voracious beasts, and you wouldn't want to get anywhere near one, but we need them.
This is a book that is rich in the poetry of scientific language. Terms such as Schwarzschild radius, gravity wells, galaxy clusters and synchroton radiation stir me strangely; it is jargon that describes things that are immense, and extreme. To get the lay reader to appreciate these immensities, though, takes a special kind of skill, to string these terms and concepts together in such a way that we can respond to them. Scharf possesses this skill to a great degree: not only does he know more about the universe than you or I do, he knows how to transmit his knowledge by deft use of analogy.
Bumper cars, bicycles, rowing boats, and, as we've seen above, fairy stories are all employed to give us a grasp of the big picture. Which is big, indeed: a small black hole is about a million times heavier than our sun; the super-massive black hole that sits at the centre of a galaxy cluster may be a hundred times bigger than that, but its position within that cluster, from itself to the outer edges, is roughly the same in proportion as the size of the full stop at the end of this sentence to a distance about a third of the way to the moon.
One thing: the subtitle of this book had led me to hope that Scharf might speculate about what happens on the other side of the event horizon. There is plausible speculation that black holes can act as wormholes in space, or can be used for time travel. Scharf nods to these ideas, but doesn't discuss them. I was a little disappointed at first, but, really, there is enough to be getting on with here (it's a short book, and does not outstay its welcome in the slightest). I am reminded of another gag from Adams: "There is a theory which states that if ever anyone discovers exactly what the universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened."
