In the 1930s Georges Lemaitre, a senior Jesuit priest and physicist, proposed that we live in an expanding universe which was at some point in the past in the form of a very small, hot, dense lump. This object then started to expand, developing into the universe we see around us today. He was the first to propose the universe is expanding, although in most modern publications Edwin Hubble seems to have stolen the credit.
The beginning of the expansion, an event now widely called the Big Bang, took place just under 14 billion years ago. The embryo universe was incredibly hot and dense, so much so that it was completely opaque to light, radio waves or any other kind of electromagnetic radiation. If we could have visited it and survived, we would have seen ourselves as being completely surrounded by a uniform, bright, utterly featureless glow. About 380,000 years after the Big Bang, the universe had expanded and cooled enough for atoms to form. At this point it became transparent, so that light and other electromagnetic waves could freely propagate. The radiation that was set free at that time is still present; we observe it as the “Cosmic Microwave Background” radiation (CMB), which was discovered in 1964 by Arno Penzias and Robert Wilson. That they had indeed discovered the CMB was confirmed in 1989 by the Cosmic Background Explorer (COBE) spacecraft. However, COBE also showed that some areas of the CMB are slightly warmer than others, which is evidence of the beginnings of structure, when the universe ceased being “without form and void”. This discovery led to the Wilkinson Microwave Anisotropy Probe (WMAP) which was launched in 2001, which yielded far better maps of these first stirrings of star and galaxy formation. Unfortunately, the observations were still not good enough to try out different ideas for what was going on. So in 2009 the Planck spacecraft was launched. This instrument is providing maps of the CMB with more detail and more sensitivity than ever before. Here are some of the results. The universe is 13.796 billion years old; 4.9% of the material in the universe is baryonic, that is, the stuff we’re made of. Dark matter accounts for 26.8% of the material and dark energy the remaining 68.3%. The maps also suggest that the birth of the first galaxies and stars was the result of ripples moving to and fro that were produced very soon after the Big Bang.
These new results are exciting. However, in a backhanded way one of the most exciting things is that these results are only very slightly different from those obtained earlier. It shows that we are indeed learning valid and scientifically valuable things about what must be the most fascinating period in the history of the universe. Obviously we’ll never understand everything that went on 13.796 billion years ago, but it is rather amazing what we have found out so far.
Once we thought we lived on the only world. Now we know there are countless other worlds. Once we thought we lived in the only galaxy, now we see countless galaxies. Do we live in the only universe?
Jupiter still dominates the western sky during the evening. Saturn rises around 9 p.m. The moon will reach first quarter on the April 18.
Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astro-physical Observatory in Penticton.