Over the last two weeks, we’ve noted how dramatically our understanding of the universe has changed over the last century. Cosmology is defined as the study of the origin and development of the universe. Yet only 100 years ago, the large majority of scientists didn’t even believe that the universe had an origin! They were convinced that the cosmos was eternal and unchanging.
Last week we focused on the tremendous impact of Edwin Hubble. Hubble showed that there is far more to our universe than just the Milky Way galaxy; he proved that there were many other galaxies.
But exactly how many galaxies are there? Modern astronomers have fittingly used the power of the Hubble Space Telescope in an attempt to answer this question. They’ve developed what are known as the Hubble Extreme Deep Field (XDF) images. These images are produced by fixing the telescope upon one tiny portion of the sky for an extended period of time in order to collect the light from extremely distant objects. Astronomers were stunned to learn that a single extreme deep field image captured thousands of galaxies. Scientists now estimate that our universe contains 100-200 billion galaxies!
Some of the galaxies in Hubble XDF images are among the most distant objects ever observed by mankind. The light from such galaxies has taken over 13 billion years to reach us, thereby allowing astronomers to peer back in time and observe the very first, “infant” galaxies which formed only about 300 million years after the Big Bang itself.
Edwin Hubble also revealed that galaxies were moving away from us, thus demonstrating that the universe was expanding. Hubble’s observations lent strong support to the idea of Georges Lamaitre, the Belgian priest and astronomer, who first advocated for what we now call the Big Bang theory. Lamaitre proposed that the universe had begun as a tiny “primeval atom” which then expanded at astonishingly high speeds.
As the result of Hubble’s efforts, the world of science had to wrestle with a completely new reality; the concept of an eternal, static universe had been knocked off its pedestal. Evidence now suggested a dynamic, expanding universe, which was very much smaller in the past. By rewinding the tape of cosmic history, eventually there must have been a moment when the universe sprang into existence – a moment of creation.
Many scientists strongly resisted the idea of the Big Bang, primarily because of the obvious the religious implications. The notion of the universe bursting into existence out of nothing was strongly consistent with the Christian idea of creation. Logic tells us that something can’t come from nothing. The Big Bang requires an agent who transcends the realm of nature. This supernatural being – possessing immense power and wisdom – must have freely chosen to call the universe into existence.
Sir Arthur Eddington was one such scientist who expressed distaste for a finite universe: “Philosophically, the notion of a beginning of the present order of nature is repugnant to me…I should like to find a genuine loophole.”
Georges Lamaitre’s theory predicted that at the moment of creation, every bit of matter and energy in our entire universe was compacted into an infinitesimally small volume with unfathomably high temperature and pressure. Then, as the universe expanded, the temperature cooled, and the pressure fell.
As theoretical physicists considered this new paradigm, they realized that the immense heat from the Big Bang should still be present. If you heat your oven and then open the door, the heat dissipates into the surrounding air. But the initial heat from the Big Bang has no place to go, for there is nowhere “outside” the universe where it can escape.
In 1948, George Gamow, Ralph Alpher and Robert Herman calculated that the Big Bang ought to result in residual radiation throughout the universe at a temperature of about 5 degrees Kelvin. (5 degrees Kelvin = 5 degrees above absolute zero, which is -460F. This is the coldest possible temperature, when all molecular motion ceases.)
It wasn’t until 1965 that this prediction was dramatically confirmed – completely by accident! Two radio astronomers, Arno Penzias and Robert Wilson, were working for Bell Labs in Holmdel, New Jersey, where they were using the world’s most sensitive radio receiving device. Penzias and Wilson were frustrated because no matter where they pointed their antenna, there was a very low level of microwave radiation corresponding to 3 degrees Kelvin. For months, the two scientists tried to eliminate this irksome radiation so that they could have greater confidence in their measurements. They even tried scraping the pigeon droppings off the antenna!
Eventually, word of this predicament reached nearby Princeton University, where another group of physicists were thinking about ways that they might detect the subtle radiation left over from the Big Bang. The Princeton group quickly realized that Penzias and Wilson had already found what they were looking for. Penzias and Wilson were shocked to learn that they had discovered a key piece of evidence in favor of the Big Bang. In 1978, they received the Nobel Prize in physics.
Arno Penzias would later state, “The easiest way to fit the observations…was one in which the universe was created out of nothing, in an instant, and continues to expand.” Robert Wilson added, “Certainly, if you are religious, I can’t think of a better theory of the origin of the universe to match with Genesis.”
The radiation found by Penzias and Wilson in 1965 is now referred to as cosmic microwave background (CMB) radiation. Cosmic denotes that the whole universe is the source. Microwaves are radio waves with wavelengths shorter than one meter. As the universe expanded, the intense heat was stretched out into the microwave portion of the spectrum. Background refers to the fact that this radiation can be measured everywhere.
The Big Bang theory predicts a very special kind of radiation: that of a perfectly efficient heat source called a blackbody radiator. The intensity of radiation coming from a blackbody source varies by wavelength in a very specific way called a blackbody curve. Scientists were exceedingly eager to determine if the cosmic microwave background radiation fit the blackbody curve, because this would provide overwhelming evidence that the Big Bang theory was correct. However, it wasn’t until some years later that the technology was available to provide measurements with the necessary precision.
In 1989, NASA launched the Cosmic Background Explorer (COBE) satellite. COBE was specifically designed to provide highly accurate measurements of the cosmic microwave background radiation. The instrument aboard the satellite soon began to gather data, which immediately showed that the CMB followed the blackbody curve. Richard Isaacman, one of the key COBE contributors, recalled this dramatic moment: “I felt like I was looking God in the face.”
The COBE team, led by physicist John Mather, was able to announce in 1990 that the background radiation matched the blackbody curve with a deviation of less than 1%. After an additional three years of data collection, the team narrowed the deviation to less than 0.03%. These findings indicated that the Big Bang accounts for at least 99.97% of the universe’s energy. The COBE scientists were delighted. Mather declared, “The Big Bang theory has passed the toughest test yet.”
However, the Big Bang theory did face one final, thorny problem. The fact that the CMB radiation was perfectly uniform in every direction was strong evidence in favor of the Big Bang. Yet ironically, this wonderfully smooth distribution also posed the most compelling challenge to the theory.
Although the overall distribution of matter in the universe is quite homogeneous, there must be some irregularity. Otherwise, it would be impossible for matter to clump together into galaxies & stars. Big Bang theorists predicted that there must be tiny fluctuations in the CMB radiation, on the order of only 1 part in 100,000.
Happily, another group of COBE scientists, led by astrophysicist George Smoot, were prepared to address this crucial issue. The satellite carried another instrument (a Differential Microwave Radiometer or DMR) specially designed to detect the theoretical ripples in the CMB radiation. Yet it wasn’t until April 24, 1992 – nearly 2 1/2 years after launch – that Smoot finally announced that the elusive irregularities had indeed been found. For their achievements, George Smoot and John Mather would receive the 2006 Nobel Prize in physics.
Once again, the Big Bang creation theory had been thoroughly vindicated. The electrifying news received widespread media coverage around the world.
Fermilab astrophysicist Michael Turner exulted: “The significance of this cannot be overstated. They have found the Holy Grail of cosmology.” Eminent theoretical physicist Stephen Hawking, a man not inclined to overstatement, proclaimed, “It is the discovery of the century, if not of all time.”
But perhaps George Smoot himself said it best: “What we have found is evidence for the birth of the universe. It’s like looking at God.”
