Fingerprints of the Creator

Observations of the cosmic microwave background rapidly im­proved, and it was soon found that the radiation had a spectrum almost perfectly consistent with one temperature, a type of radia­tion with what is called a thermal spectrum. This was additional support for its interpretation as relic radiation, because such a smooth spectrum only results from radiation that’s in equilib­rium with its surroundings. Since in this case the surroundings are the universe itself, thermal radiation is expected. Its temperature is 2.725 K and it is the most accurately measured temperature in nature.23

By the early 1970s, theorists had predicted that the microwave radiation should not be perfectly smooth. That’s because a slightly uneven distribution of matter causes very small variations in tem­perature, with denser regions hotter. The subtle variations in den­sity act as the seeds for later structure formation. Theories of gal­axy formation could not generate large lumps of matter without a little lumpiness with which to start. The initial variations are not really like “lumps” since they are physically extremely large and extremely shallow. In a purely metaphorical sense, the mighty oak trees that are present-day galaxies grew from the tiny acorns of anisotropy in the background radiation.

NASA’s Cosmic Background Explorer (COBE) was launched in 1989 to make more precise measurements of the microwave radia­tion than could be made from the ground or from high altitude bal­loons. COBE was cheap by modern standards, about $150 million, and extraordinarily successful. It confirmed the exquisite thermal nature of the spectrum, ruling out the last few remaining potential explanations other than a big bang. With only four years of data, the satellite was able to detect minute variations from smoothness; the radiation deviated from a constant temperature from one part of the sky to another by one part in a hundred thousand.24 These were the long-sought seeds of structure formation. Commentators and media pundits breathlessly embraced the story when project leader George Smoot talked about having discovered the “finger­prints of God.”25 Smoot and his colleague John Mather shared the 2006 Nobel Prize in Physics for their heroic work in advancing cosmology with the detection of these tiny fluctuations.

But there’s an extraordinary twist to this story. The smooth­ness of the microwaves and their perfectly thermal spectrum are difficult to explain in the standard big bang model because the universe was expanding so quickly early on. At the time the micro­waves were released, two points in space were receding at nearly sixty times the speed of light. Under these conditions, there’s no way disparate parts of the universe could come into equilibrium so adjacent patches of the sky shouldn’t be at exactly the same tem – perature.26 A related puzzle is the near-flatness of space. General relativity is based on curved space-time and it was expected that the vast mass of the universe would give an imprint of curvature. The cosmic background microwaves have traveled across the en­tire universe so should reveal if the space they’ve traveled through is curved. It’s not. To explain the smoothness of the radiation and the flatness of space, cosmologists have hypothesized a fantasti­cally early time, only 10-35 seconds after the big bang, when the en­tire universe expanded exponentially due to physics involved with the unification of three fundamental forces of nature. This event is called inflation.

Inflation modifies the big bang theory by positing that all we can see to the limit of vision of our telescopes—called the observ­able universe—is a small bubble of space-time that inflated to be­come large, smooth, and flat. The totality of space-t ime is very much larger, perhaps infinitely larger. Moreover, the variations in radiation that will grow to become galaxies are quantum fluctua­tions from a tiny fraction of a second after the big bang.27 It’s an extraordinary hypothesis.