The Belgian cosmologist Hertog, a theoretical physicist at KU Leuven university, draws a vivid and philosophical picture of the evolution of beginning-times theorising in the latter half of the 20th century, including the changing opinions of Hawking himself. So On the Origin of Time is a gentle polemic, selling a particular theory, but no less rich and fascinating for that. Not mentioned in this book, however, is the idea promoted by the Albanian-American cosmologist Laura Mersini-Houghton that the birth of our universe from the multiverse might have left visible “scars” on the so-called “cosmic microwave background” – the fossil echo of the Big Bang that still permeates the sky. In his view, the idea shouldn’t even count as real science, on the grounds that it’s unfalsifiable: evidence of other universes completely inaccessible to our own would be impossible to come by. As Hawking noticed, the notion of an infinite number of universes seems to violate Occam’s Razor, which states that entities should not be needlessly multiplied just to prop up an explanation. The multiverse, he once remarked to his protégé and collaborator Thomas Hertog, was “outrageous”.

It’s an idea to which our very own celebrated black-hole-botherer Professor Stephen Hawking was very hostile. This idea, however, requires a multiverse – a higher sphere of many (perhaps infinitely many) universes, constantly being born from a seething quantum sea – a concept toyed with in the Oscar-winning, universe-hopping romp Everything Everywhere All at Once. This answer has not always satisfied scientists, some of whom prefer to think of our cosmos bubbling into existence from elsewhere and elsewhen. It’s the beginning of the idea of beginning. Similarly, once you’ve journeyed back in time to the Big Bang, there is no further left to travel. Once you are at the South Pole, you cannot walk any further south. In this sense, time is like a compass direction. According to the standard picture of modern cosmology, we are encouraged to think that the Big Bang, roughly 13.7 billion years ago, created time itself along with space, so that it is meaningless to talk of what came before it. “Who knows where the time goes?” asked Sandy Denny, though as good a question is where it came from in the first place.

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