By Robert Hazen, Ph.D., George Mason University
Hubble’s remarkable discovery that all the distant galaxies are speeding away from us had incredible implications for the origin of the universe. It now appears that the universe began at an instant of time approximately 14 billion years ago. The three lines of evidence for the origin of this event are universal expansion, the cosmic microwave background, and the abundance of light elements.
Everything’s Moving Away
The first piece of evidence is Hubble’s observation of universal expansion. Hubble noticed that more distant galaxies are moving away from us faster. We find now that the most distant galaxies are more than ten billion light-years away, and they’re the ones that are moving fastest.
However, note that expansion alone doesn’t prove the Big Bang theory. It’s perfectly possible, for example, that the universe is in steady-state expansion—that is, new matter and new galaxies are constantly materializing, and as the galaxy moves apart, new galaxies and stars pop up to fill the spaces in between.
As cosmologists grappled with this strange consequence of expansion, they divided themselves into two camps, called the Bangers and the Anti-bangers. For example, Georges Lemaitre, the Catholic priest, naturally favored the Big Bang model; there was an origin. He said, “These considerations, beside providing a natural beginning, supply what can be called an inaccessible beginning.” In other words, Lemaitre was saying it opened the door for a divine act of creation at a point in time.
Anti-Banger Arthur Eddington, the atheist, saw the expanding universe as evidence that new matter—new stars and galaxies—was constantly being created as the universe expanded in a steady state. He wrote, “Philosophically, the notion of a beginning to the present order of nature is repugnant to me.”
Learn more about electromagnetism.
A Stroke of Luck
A second, compelling piece of information has really put the evidence towards the Big Bang theory, and that’s the universal cosmic microwave background radiation. Cosmic microwave background was discovered in the early 1960s by two researchers, Arno Penzias and Robert Wilson, who worked at the AT&T Bell Laboratories in New Jersey.
They were working on satellite communication with microwaves, and they were developing new high-sensitivity receivers. This was before cell phones, cable TV, and satellite TV. This was a fascinating, new area of research in the 1960s, and right from the start, they experienced a problem. They had a high level of static, of electronic noise, in their receivers. They tried everything to get rid of that noise.
Still, no matter what they tried, they could not get rid of this microwave background; this static kept coming into their receiver from anywhere they pointed the receiver.
By chance, there was a young astrophysicist, P.J.E. Peebles, working at Princeton University, and he heard of their problem. He realized that this settled a theoretical prediction that he had made: that there would be radiation left over from the Big Bang.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Radiation as Old as Origin of the Universe
At the moment of the Big Bang, the universe was flooded with highly energetic electromagnetic radiation. It permeated the whole universe, and it was very, very high-energy radiation.
That radiation is still with us, but as the universe expanded, the wavelengths of that radiation, that high-energy radiation, stretched out and stretched out and stretched out. At this point, the radiation is still with us, but it’s in the microwave region.
It also corresponds to a temperature of roughly three degrees Kelvin, which is the average temperature of the universe, after the universal expansion. So the microwave background radiation represents a remnant of that creation event; it’s evidence for the Big Bang.
Learn more about how do stars like the Sun die, and what is left behind.
Deuterium Is Subtle
The third line of evidence for the Big Bang is somewhat more subtle. Light elements condensed out of the Big Bang. While almost all this matter was hydrogen atoms, there was a small amount of helium, a small amount of lithium, and a small amount of deuterium, which is the real key.
The amount of deuterium in the universe today results from the specific interactions shortly after the Big Bang. It provides very compelling evidence for models of the Big Bang today.
Considering everything, astronomers now converge on the number of about 14 billion years for the universe’s age. It could be 12, it could be 16, but it’s something in that range, and each year we’re going to get more and more refinements on that number, so we now know about how old the universe is.
Common Questions about the Evidence for Origin of the Universe
When trying to explain the origin of the universe, astronomers were divided into two groups: the Bangers and the Anti-bangers. While the Bangers believed in the Big Bang model, Anti-bangers saw the expanding universe as evidence that new matter—new stars and galaxies—was constantly being created as the universe expanded in a steady state
The Big Bang theory suggests that at the moment of the Big Bang, the universe was flooded with highly energetic electromagnetic radiation. As the universe expanded, the wavelengths of that radiation stretched out. At this point, the radiation is still with us, but it’s in the microwave region.
Light elements condensed out of the Big Bang, and while almost all this matter was hydrogen atoms, there was a small amount of helium, a small amount of lithium, and a small amount of deuterium.