Think Edwin Hubble
An American astronomer, who began to study galaxies observed in 1929 that they were speeding apart. Not just the close ones to the Milky Way but also to the ones that were very distant. His observation was so crucial to the understanding of the Universe that it forced Albert Einstein to modify his equations for General Relativity. Einstein introduced the “cosmological constant” meaning that the universe may have the appearance of expansion, but it could be explained by a constant that kept the universe in a stable format.
Two years before that, in 1927, the physicist George Lemaitre put forth a cosmological theory that became the Big Bang. However, it was Hubble that put forth astronomical evidence to support it.
His first finding was that the universe is continuously expanding. He traced the relationship of velocity to distance meaning that galaxies that are twice as far (from our own) speed away twice as fast. The second finding was that the universe was expanding in every direction.
Penzias and Wilson
Two other scientists were crucial to the understanding of the Big Bang because they actually found evidence for it.
Imagine an explosion taking place in a distant location. What are the events that follow the explosion? First, you see a bright light. Next, depending how far away you are, you may feel the force of the explosion, followed by the sound, and after a while the final remnants are driven your way that is the dust particles or matter that are floating in the atmosphere waiting to settle back down.
In 1964, at the Bell Labs, Arno Penzias and Robert Wilson were trying to detect microwaves from outer space. They uncovered some remnants like that explosion scenario. They built a radio receiver that was sensitive to microwave frequencies. Their initial observations were puzzling because while they could track the microwave frequency, but there was a slight buzz in the background that they could not shake, no matter where they pointed the receiver, and no matter what precautions they took to eliminate external noise.
In other words, they were detecting the final explosion outburst results, the “dust” so to speak that remained in the universal “atmosphere” from the big bang explosion. This became the cosmic microwave background radiation.
The COBE Affirmation
NASA launched the COBE satellite in 1989 with a mission to detect microwaves emanating from the outer reaches of the universe. The COBE satellite found that the microwaves, first detected by Penzias and Wilson, were remarkably uniform. This allowed cosmologists to conclude that the early stages of the universe had a homogenetic appearance and tendency. However, that was not all. The satellite discovered that this homogenetic feature did not last long because as the universe began to cool and while it was still expanding, small variations began to appear in the space structure due to temperature differences. This lay the foundation for galaxies to appear far into the future.
Shortly after the big bang, a period of inflation occurred. It lasted just a few microseconds. It started about 10-36 to 10-33 seconds after the big bang. However, the consequences were enormous. It changed the Hubble volume of the existing early universe by a factor of 1078. After that initial growth burst the expansion occurs but at a much slower rate.
The second most important part of the big bang was the creation of atoms, the first being of course, the creation of the universe.
The early universe had no structure; it was a plasma soup. It was so hot that it was not possible to form particles at the atomic level; they kept breaking apart. There was also an asymmetry of matter-antimatter with matter being dominant over anti-matter.
After 300,000 to 500,000 years, the temperature of the early universe cooled down enough, so atoms were able to form.
How Big is the Universe?
The big bang created a universe that shot up in volume in less than a microsecond, and it continues to expand. So how big is the Universe? That is, if it had a finite beginning in time 13.7 billion years ago, how big is it now?
Current astronomical observations put the observable region visible from Earth as a sphere with a radius of about 46 billion light years. This observation comes from the expansion of space noted from the most distant objects observed. Now, if you take the geometric formula for the circumference of a circle, 2 pi r, where pi = 3.1415 (rounded) and r = 46, then the circumference (or size) of the universe is 289 billion light-years.