Was the universe created at a specific time in the past, or has it always existed? That is the question that astronomers try to answer when they study the cosmos. If the universe came into existence at some time long ago, there should be evidence. If it has always existed, then there should be no evidence to the contrary. The discoveries that have been made about our universe point to one with a definite beginning at some time in the past. Astronomers refer to the beginning of the universe as the Big Bang.
Scientists don’t know much about what caused the Big Bang, although they have a theory about the conditions of the universe before it happened. They surmise that all of space was compacted into a very small point. The reason for this is that pressures had to be enormously high for the universe to be as vast as it is. If it is true that space was under that much pressure, the known laws of physics require that it was very hot, with temperatures in the millions. Scientists point to the relative scarcity of matter in the universe as evidence of the enormously high temperature of space in the past, arguing that matter cannot be formed at such temperatures.
There are three key points which suggest that the universe had a finite beginning:
1. There is a background radiation emanating from every point in the universe. This indicates cooling.
The Cosmic Microwave Background Radiation was first discovered in 1964 by radio astronomers Arno Penzias and Robert Wilson. Penzias and Wilson were testing a sensitive horn antenna when they noticed a slight hum that remained constant regardless of where they pointed the telescope. After rigorous testing and cleaning of the equipment, the pair determined that what they were detecting was a faint radiation. Measurements showed that the temperature of the radiation was between two and three degrees on the Kelvin scale. The lack of an apparent single source indicated that space had been this temperature for a long time. This suggests that space was once hotter than it currently is.
2. All galaxies in space have been detected moving away from one another. This suggests that at one time, all objects in space occupied the same location.
Astronomer Edwin Hubble discovered that all galaxies in the universe are traveling away from Earth at rates that increase according to their distances. Hubble’s Expanding Universe Theory has been modified since that time to state that galaxies are moving away from each other at rates that increase according to their distances. This increasing distance between galaxies is an indication that all objects were compacted into a single location at some point in the past.
3. The even distribution of light elements such as Hydrogen and Helium throughout space suggests that they were forced outward toward the edges of the universe at a finite point in the past.
Astronomers have discovered an abundance of the gases Hydrogen and Helium at every point in space. Not only are they the most abundant elements in stars, but they can be found at every single location in the cosmos. The even distribution of these gases indicates that something forced them outward in all directions. The fact that only the lightest of the elements received this jolt is also evidence that the universe was, at one time, very hot and only consisted of lightweight elements.
The Big Bang is the name that astronomers have given to the event at which the universe came into existence. Current estimates for the time at which the Big Bang occurred are 13.7 billion years.