Do your eyes deceive you? No, this is indeed a science column. My goal here is simply to make complex yet relevant science available to readers of all levels of scientific understanding.
The Big Bang theory is the best model scientists have to explain the origin and development of the universe. It states that at one point, the universe was much more dense, but then it expanded outward rapidly and that this expansion is still occurring today.
But what is the evidence for this? We stand on Earth, and every night the stars look the same as the previous night. There are a few reasons why physicists believe the universe is expanding, but for simplicity’s sake, I will summarize only two of them: Olber’s Paradox and the idea of cosmic microwave background radiation.
Think for a moment that the universe is not expanding and that the universe is infinitely old. If the universe were infinitely old and infinite in space, it would have an infinite number of stars, and if this were the case, wherever in the night sky we looked, we would see a star. Every single possible direction our eyes could look, there would be a star at some distance, be it a few hundred light-years or a few billion light-years away. This would mean that the night sky would look as bright as a star, because from every possible point, a star would be sending its light. From experience, we know that this is not the case. We know that the night sky is mostly black and only speckled with stars. The fact that there is black space between stars in the night sky tells us that there is not an infinite number of stars in the universe and that the universe is not infinitely old.
One of the most central ideas supporting the Big Bang theory is the idea of cosmic microwave background radiation. These cosmic microwaves give an estimate for the time elapsed since the Big Bang, otherwise called the “age of the universe.” The explanation of this idea is extremely complex and involves subatomic particles and light scattering that would be difficult to explain in constrained space, so I will summarize. Basically, the farthest light in our universe that scientists have been able to detect is not visible light, which we are capable of seeing with our eyes, but microwaves. These microwaves have an extremely long wavelength, which means that they have been red-shifted. Red-shifted light comes from an extremely far distance and from something that is moving away from Earth. It is estimated that this light is coming from 13.7 billion light-years away, but not from stars. This light is instead originating from the remnants of a “mixture” of particles that is characteristic of what the Big Bang theory predicts would be present in the very aftermath of the initial explosion. And as it takes 13.7 billion years for light to travel 13.7 billion light-years, we are essentially looking 13.7 billion years back in time. We are peering into what the universe presumably looked like at its origination.
