The Big Bang theory postulates that the universe came into being when what amounts to an infinitely large amount of energy suddenly appeared as an infinitesimally small speck (fittingly called a singularity). Where this energy came from—no one knows. How so much energy could occupy next to zero volume—no one knows. One theory postulates the existence of another universe, vastly bigger than the one we inhabit and hidden in additional space/time dimensions, and suggests that it could have created and fed the singularity. This background universe could be periodically “blowing bubbles” that inflate into universes. Our (relatively small, on this scale) universe could have originated within one of these bubbles. Superstring Theory (see Gödel’s Theorem, General Systems Theory, and The Conservation Laws) supports the existence of many universes (of which ours is one), each being formed from, and eventually returned to, empty space.
Regardless of what actually occurred to “begin our universe,” and what was needed before this event to cause it to happen, scientists can account for what is seen today simply by postulating that everything came from a single point in one Big Bang then applying some known laws of physics.
Rather than making guesses about what might have happened beyond and before our universe began (guesses that can never be substantiated—see What Started It All? of this chapter), let us start with what is generally accepted—a Big Bang/Inflationary origin to our universe. This theory is able to explain much that we observe, and it yields accurate predictions, hallmark properties of a good scientific theory. Assuming that the laws of physics as we know them today also applied almost immediately following the Bang, we can reconstruct the history of the universe. This has been carried out by various people over the past fifty years, with modifications and revisions being made each time someone was able to improve the fit between astronomical observations and theory. Today, scientists think that something very like the following occurred.
Immediately upon the original insertion of energy, time in this continuum began, and space was created by separating energy components. This was followed by an extremely rapid expansion. Starting about 10×10−37 of a second after the Bang, and lasting until about 10×10−34 of a second, this minute bubble of pure energy that was to become our universe inflated to 1050 times its previous size.
For the first one hundred seconds or so following the Bang, only energy (in various forms of radiation) could have existed. Continued expansion and further cooling of this hot dense ball of energy continued until, after about 300,000 years, the temperature was low enough (about 3,000°C) for atoms of hydrogen (and helium, the next lightest element) to remain intact. From this time onward the universe would contain matter.
These atoms of hydrogen and helium continued to move apart, and the temperature of the universe continued to drop. Gravitational forces pulled wisps of atoms closer together, forming tremendous, irregularly shaped clouds, and these eventually further condensed to form many giant gas balls. Condensation continued, with the gases at the centre of each ball forming first black holes, then supermassive black holes. Electrically charged gases (spiralling ever faster and faster around these holes before being swallowed) emitted intense electromagnetic radiation fields that pushed the surrounding gases away. Clouds of these gases then themselves condensed to form additional smaller balls. As gravity pulled the gases in each of these balls tighter together they began to heat up. Eventually the temperature within each became so high that thermonuclear reactions occurred, and the gas balls began to emit light. These high-temperature, hydrogen-gas balls, are called stars. The large collections of stars that rotate around supermassive black holes are called galaxies.
- Inflation theory suggests that the energy contained within the universe’s gravitational field exactly equals in amount, but opposes in type, the energy contained within all other constituents of the universe (photons and particles, etc.). Thus, since they balance out, the universe could have been created from nothing. This poses questions such as: “what existed to cause nothing to become something?” and, “are nothing and something one and the same thing, and if so, just what does that mean?”
- Theoretically, many inflation-causing bubbles could occur, each growing to contain a universe. Each universe would be discrete and unique, and each could perhaps be controlled by physical laws different from those that control events in our universe.
Current thoughts about the beginning of our universe (and the possibility that it could be only one of many) are presented by Martin Rees in “Exploring Our Universe and Others,” in the December 1999 issue of Scientific American, 78-83. (This article also provides a pictorial summary of the evolution of our universe from its beginning to its possible ending.)
See also Theories of Everything: The Quest for Ultimate Explanation by John D. Barrow (New York: Oxford University Press. 1990). This thought-provoking book explores the significance of the initial conditions, laws, constants, and other critical factors, in the development of our understanding of what makes the universe behave the way we observe it behaving. Barrow makes a somewhat difficult subject enjoyable to readers as he describes the thinking of philosophers, mathematicians and scientists, from the early days of science to the quantum theories of the present.
- Our “gigantic” universe is mostly space. It has been calculated that, if all the space separating galaxies, stars, electrons from nuclei in atoms, etc., were removed, then the whole of the universe’s matter would occupy a volume less than that enclosed by a sphere whose radius equalled the distance between our sun and Mars.
- This assumption may be incorrect. Recent measurements of the absorption spectra shown by light that passed less than a billion years after the Big Bang through gas clouds containing metallic atoms, suggest that the electronic charge at that time differed slightly from today’s value. This does not mean that the laws of physics have changed, but it does warn us to be careful about the assumptions we make: values thought to be constant, may not actually be so.
- 10-37 is shorthand for 1 divided by 1037, a very tiny fraction of anything.
- In other words about one thousandth of a second, a relatively short period of time for what transpired. This “inflationary” period immediately followed the energy insertion we call the Big Bang. (The whole episode might be compared to the rapid inflation of an automobile air-bag that follows the detonation of its initiating charge.)
- This inflationary behaviour explains the homogeneity of the cosmos by showing that it could have resulted from the universe’s initial uniformity being preserved by the rapidity of its expansion.
An excellent description of inflation is given in Michael White and John Gribbin’s book, Stephen Hawking: A Life in Science (London: Penguin Books, 1992).
- This is because, to produce the amount of matter we observe in our universe today, the initial radiation energy density—and thus its temperature—must have been so high that any matter forming would have been immediately broken apart by radiation bombardment.
- Neutrons, protons, and other particles of matter, would have formed from little packets of energy much earlier, but they would have been immediately broken apart by collisions with highly energetic radiation quanta.
- Smoot and Davidson summarize existing theories about events during various time periods, particularly the initial seconds following the Big Bang, in two colourful plates (between pages 182-183) of their book. See George Smoot and Keay Davidson, Wrinkles in Time: The Imprint of Creation (Little, Brown and Company (U.K.) Ltd., 1993).
- The extremely high early temperatures forced hydrogen nuclei to fuse together and form helium. This early fusion stopped after expansion sufficiently lowered the temperature, and the universe was left with the 23-24% helium content we now find throughout space. (Although fusion continues in the centre of stars, next to none of the helium produced by this means escapes into space.)
- There are many millions of black holes in our galaxy alone. They range in size from small, just a few times larger than our sun, to supermassive. Supermassive black holes can contain millions or billions of times more matter than our sun.
The Chandra X-ray satellite telescope has determined (by analyzing radiations from objects twelve billion light-years distant from the Earth) that twelve billion years ago the universe teemed with billions of active supermassive black holes sucking up gas, stars, and debris. This same telescope has recently confirmed that our galaxy, the Milky Way, rotates around a supermassive black hole (this one some two and a half million times more massive than our sun). A different detection method (red-shift spectrography) has found more than thirty supermassive black holes in our neighbourhood, including one in Andromeda. Many (if not all) galaxies rotate around supermassive black holes, most of which have engulfed much of the matter in their vicinity and thus become dormant.
- See “The First Stars in the Universe,” by Richard B. Larson and Volker Bromm, Scientific American, December 2001, 64-71, for an alternative, computer-generated, account of early star formation.