In one of his essays in "Creation and Fall" written in 1933 Bonhoeffer breaks his own rule. In his concluding remarks regarding Genesis 1:14-19 he raises the "old rationalistic question" of how light could be created in day 1 and the sun not until day 4. Where did this "uncaused light" come from? Bonhoeffer discusses this apparent paradox and concludes by saying: "The light per se of the creation, the light which lay formless over the formless darkness, is bound to form, to law, to the fixed, to number; but it remains in God, it remains God's creation, and never itself becomes calculable number."
The "never itself becomes calculable number" part of his statement appears to be wrong. Bonhoeffer reasonably assumed that the specifics of the creation of the universe would be forever inaccessible to science. What he could not have anticipated was that fifteen years later, based on the principles of Einstein's general relativity, George Gamow would publish a model for the creation of the universe. This theory postulated:
- Light could not travel any appreciable distance in the initial years of the early universe because any emitted photons were immediately reabsorbed by the ionized matter around it.
- About 400,000 years after the Big Bang the universe had cooled enough for matter to "condense" into neutral atoms. This transition allowed light to freely travel throughout the universe. Because the universe was exceedingly uniform at that point (formless) this shift occurred concurrently throughout.
- Gamow calculated that these freed photons from this transition would still be continuously arriving at the earth, "cooled" by the subsequent expansion of the universe to an equivalent black body temperature of about 5 degrees above absolute zero.
In 1948 when Gamow made this 5 degree prediction the technology did not exist to prove or disprove it. However in 1964 two physicists testing their new microwave receiver pointed it at the sky. They expected to measure just the self-generated noise of their equipment. Instead they found that no matter where in the sky they pointed they measured more noise than they could explain. At first they attributed it to pigeon crap in their antenna. But eventually they established it was photons from the cosmos, arriving with an equivalent temperature of 3.5 degrees --the light from the Big Bang. Recent satellite based measurements have refined that temperature to 2.725 +- 0.02 degrees (really!)
The light of creation that illuminated the universe for almost ten billion years before our own sun ignited has been given a number.