A Brief History of Time | Study Guide

Stephen Hawking

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A Brief History of Time | Chapter 8 : The Origin and Fate of the Universe | Summary



The trajectory of the universe from an origin at the big bang to an ending at the big crunch is the topic Stephen Hawking approaches in this chapter. This consideration has traditionally been fraught with the dangers of trying to understand the very moment of creation as God's work (in which Pope John Paul II pointed out to Hawking and other scientists gathered at the Vatican in 1981 that it should not be the work of scientists). The paper Hawking presented at this conference was about the idea that space-time was not only finite but also without boundary, just as Earth itself is finite, but as a sphere Earth has no edge or "boundary" where it drops off and "isn't."

In order to trace the steps of this line of thought, Hawking returns to the Friedmann model, in which an expanding universe decreases in temperature. This observable decrease suggests that at earlier stages of its expansion, the universe had a much higher degree of temperature. And if the universe started out at zero size, then its temperature would have been infinitely hot. The story of what happened after the big bang is a whole lot easier to describe than the very instant of the event itself, but it accounts for the formations of observable types of stars and galaxy clusters of stars, which provide a starting point. However, for every question that is answered, a new group of questions arise.

Hawking explores several models for predicting initial states that could lead to a universe like what we observe. This includes versions of the anthropic principle, which Hawking paraphrases thus: "We see the universe the way it is because we exist." While the anthropic principle is useful for thinking about possible beginnings, it does not provide clear answers.

Hawking goes on to look at models that could explain the uniformity of the observable universe, including versions of the inflationary model, which proposes that symmetry between the four fundamental forces may have held for some period after the big bang. While these models seem to fit more closely with observations, still more questions are unanswered.

Next, Hawking proposes two properties he believes a quantum theory of gravity should contain. The first is Richard Feynman's sum over histories, and the second is Albert Einstein's model of curved space-time. From this, Hawking hypothesizes a finite universe that has no boundaries. The implication is that there need not be a singularity at the beginning or end of time, thus, the normal laws of science might hold at the big bang and/or the big crunch. If this is how the universe works, it is possible that the universe had no beginning and will have no end. This opens up theological questions, which Hawking leaves unanswered.


Stephen Hawking's meeting with Pope John Paul II is a reminder of the uneasy coexistence of science and faith, both of which attempt to explain existence. It was only in 1992 that the Church recognized that Galileo Galilei was right. Scientists themselves grapple with their own faiths in an attempt to reconcile it with observable facts. Hawking does not say what his beliefs are, but in A Brief History of Time, it appears he believes that God exists. Albert Einstein was Jewish, and Galileo was Catholic. Sir Isaac Newton was Protestant, and he was almost as adamant in politics opposing English rule by a Catholic king as he was in discrediting his fellow scientists.

The idea that space-time is both finite and without a boundary in a way that is comparable to the surface of Earth is somewhat reminiscent of the conditions of both natural fractals (observed in plants, trees, coastlines, etc.) and abstract fractals (the Mandelbrot "snowman") that are figures derived from a mathematical formula. Fractals are endlessly self-repeating patterns within a finite, enclosed contour.

Hawking briefly describes how such theories as multiple universes may explain the ways in which different laws are (or are not) applicable. However, he concludes that the range of such universes that would support such complex ordered systems as human beings would be very small. This is in keeping with the anthropic principle, which states that if our universe were any different than it is, human beings couldn't be around to observe it.

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