It generally takes a child no more than three or four ingenuous questions to reach a humbling horizon beyond which no intellect, whether adult or child or Stephen Hawking, has passed: the question of how the universe began. Whatever we learn about the past, the answer to the next question–what came before that–rears up on the horizon, ever out of reach. I used to lie in bed as a child and imagine infinity until my head hurt.
We do know more than ever before, however, and some of that knowledge has arrived within my own lifetime. Books really do help, especially when written by a science writer par excellence like Simon Singh, who sets out to teach you the subject for real. Singh doesn’t water everything down to the point where it makes no sense. He trusts his readers’ intelligence and their natural childlike curiosity, and he has the writerly skill to make the real science into a fascinating story–a story which begins not with a bang but a person–Einstein.
Einstein’s theory of relativity predicts that matter causes the space of the universe to contract or expand–a dynamic notion of space that cannot be tested by everyday experience, but can be (and has been) tested by data collected from telescopes. Around 1920, Jewish-Russian mathematician Alexander Friedmann applied Einstein’s equations to cosmology in order to predict what was happening to the size of the whole universe; he predicted it was expanding. Georges Lemaître (a physicist who was also a Catholic priest, pictured next to Einstein in his white collar!) 
did the same and deduced that if the universe has expanded, it must once have been compact. The idea was not that the matter of the universe exploded like shrapnel from a bomb (one reason “Big Bang” is an imperfect name), but rather that the empty space of the universe itself was once compact and ever since has been stretching out like silly putty.
The general theory of relativity is evidently very difficult to translate into plain English, and I don’t understand it any further than physicist John Wheeler’s famous statement that “Matter tells space how to curve, and curved space tells matter how to move.” (It also tells light how to move. I’d like to see if it could get my kids to put their shoes on.) I do know this: whereas matter can’t move through space faster than light, space itself can change size faster than the speed of light. It’s often said that light from billions of light years away is showing us something billions of years in the past; light from afar is very old; that’s putatively because the light has been traveling for billions of years to get to us. I never understood how this could be, since I assumed that distant galaxies must have taken billions of light years to get so far away from our common Big Bang point of origin in the first place. Singh does not address this particular question, but other sources confirm that the universe seems to have expanded much faster than light in the beginning; I presume that’s how the infant universe could have blown out to a size billions of light-years across in less than billions of years, and how light from 14 billion light years away therefore could show us baby pictures of the universe. At any rate, Edwin Hubble’s observations of the skies, made on freezing nights through a giant telescope in Pasadena, and his analyses of observed Doppler shifts of spectra emitted by familiar elements like helium in distant stars, confirmed that the universe is indeed expanding, with the speed of expansion apparently increasing at farther distances out.
More support for the idea of the Big Bang came from particle physics. Russian refugee George Gamow concluded that the relative abundances of elements in the universe (90% hydrogen, 10% helium, trace amounts of heavier elements, as determined by spectroscopy on the heavens) could best be explained if the universe’s matter was once a condensed ball of plasma hotter and more pressurized than that inside stars–he called this universal primordium of subatomic particles ylem. Gamow’s young collaborator Ralph Alpher made mathematical models of the primordial universe; they showed that the early universe would have had the right conditions for the right length of time to support “nucleosynthesis” of 10% of the loose protons into helium. Then, with colleague Robert Hermann, Alpher theorized that the early universe should have cooled from plasma to gas 300,000 years after creation, an event called “recombination” (because it was now cool enough for electrons to “recombine” with atomic nuclei instead of flying all over the place? but were they ever combined before that?); they predicted that recombination should have allowed the early universe to radiate light instead of merely scattering it and the light should still be flying through space in every direction and that the expansion of the universe should by now have stretched the wavelength of the extant light of recombination to the point where it would be in the microwave part of the electromagnetic spectrum–the cosmic microwave background radiation (CMB radiation).
At this point the Nobel committee was paying serious attention to the Big Bang theory. In 1965 Arno Penzias and Robert Wilson, who worked for Bell Labs in New Jersey, confirmed the existence of the CMB radiation with a radio telescope and later won the Nobel prize. Finally, George Smoot got NASA to launch a satellite with a radiometer on it so that he could look for miniscule variations in the CMB radiation. These would reflect the existence of condensates of matter in the early universe–the precursors to today’s stars and galaxies; NASA launched it in 1989, the radiometer detected it, Smoot too won a Nobel prize for it. I am pretty sure that the variations in the CMB radiation do not explain why half my noodles are hot and half are cold when I reheat a bowl of pasta. Nonetheless, I blame the Big Bang. The end of the story of how we understand the beginning.
There are so many wonderfully human aspects to this history of an idea. The history of astronomy as Singh tells it is a history of passionate, suffering dreamers, of political refugees converging on England and America where they could think in peace. 20th century physics is also a history of the Jews, whose numbers in the Big Bang story far exceed those of helium in the stars (Einstein, Friedmann, Alpher, Hermann, and Penzias are among the Jewish free thinkers who built this progressive theory). The Big Bang is both an elucidation and a revelation of mysteries and cosmic order. Why then, does it hold such potential to make your head hurt and your soul ache with a sense of the empty, senseless, inhumanity of the universe? I feel this anxiety, yet I don’t trust it. See Part II.