Cosmology is the scientific study of the large-scale properties of the universe as a whole. It endeavors to use the scientific method to understand the origin, evolution, and ultimate fate of the entire universe. Like any field of science, cosmology involves the formation of theories or hypotheses about the universe which make specific predictions for phenomena that can be tested with observations.1
The Big Bang Theory
The Big Bang is the leading explanation about how the universe began. Simply put, it says the universe as we know it started with an infinitely hot and dense single point that inflated and stretched—first at unimaginable speeds, and then at a more measurable rate—over the next 13.8 billion years to the still-expanding cosmos that we know today.
Existing technology doesn't yet allow astronomers to literally peer back at the universe's birth, much of what we understand about the Big Bang comes from mathematical formulas and models. However, astronomers can see the "echo" of the expansion through a phenomenon known as the cosmic microwave background.
Dark Matter and Dark Energy
Observations have shown that the universe isn't just expanding, but its expansion is accelerating. This discovery led to the postulation of two mysterious components that dominate the universe:
- Dark Energy: This is a hypothetical form of energy that exerts a negative, repulsive pressure, behaving like the opposite of gravity. It is believed to be responsible for the accelerating expansion of the universe.
- Dark Matter: This is an unseen form of matter that does not emit or interact with electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum. Its existence is inferred from gravitational effects on visible matter, such as galaxies and stars.
Understanding these two enigmatic forces is one of the most significant challenges in modern cosmology, as they make up roughly 95% of the total mass-energy of the universe.