What Are the Theories of the Universe?

Humans have pondered the beginning of the universe since our species evolved. Generations of people have looked towards the sky as a source of amazement, religion, and wonder. Thankfully, over the last several centuries, scientists from around the world have begun to piece together empirical data to support a variety of hypotheses about how all of life as we know it began. Today, let’s take a closer look at an age-old question: what are the theories of the universe?

The Big Bang Theory

The most robust, well-supported theory as to the origins of the universe is the Big Bang Theory. A Belgian priest, Georges Lemaître, first suggested the idea of big bang theory in the 1920s. Since then, Einstein’s theory of relativity and modern science has lent credibility to this developing theory.

Big Bang Assumptions

Before we can get into specifics, let’s understand a few basic assumptions concerning the Big Bang Theory. Each of the following points is assumed to be true in the universe, and this notion is part of the foundation upon which the Big Bang rests. 

1. The universe is constant. This one is first for a reason; it’s important. Our modeling and understanding of the world hinge on the idea that physical properties are the same everywhere. For example, we assume gravity, electricity, magnetism, and light all behave the same way, even in far off places in the galaxy and universe. 
2. The universe is homogenous. Secondly, we assume that the universe is roughly the same in all directions. You can think of these like shovelfuls of dirt. Some scoops might have big rocks, some might have worms, and some may have more clay than others. But, in the long term, every 100 shovelfuls will be roughly the same in composition.
3. The universe is not centered around us. Physicists refer to this notion as the “privileged location.” This means that earth is somewhere in the universe, but we really have no idea where it is in relation to the “edge” (more on that later).
4. The universe has a beginning. All matter and energy that has ever been and that will ever be were created during the Big Bang. No new material or energy has been created since then.

Basics of the Big Bang

The Big Bang is the leading theory as to the origins of the universe as we know it. It describes the mechanism by which everything we know started as a small singularity that ballooned into the earth, solar system, galaxy, and universe. The easiest way to understand this theory is through a timeline, so let’s dig in.

1. 1 second. During the first second, the temperature around the big bang was about 5.5 billion degrees celsius (10 billion Fahrenheit). There would have been nothing to see at this point, though. According to NASA, “the free electrons would have caused light (photons) to scatter the way sunlight scatters from the water droplets in clouds.”
2. 3 seconds. The initial explosion contained all the necessary subatomic particles for atoms and molecules: neutrons, protons, and electrons. The first basic elements form at this point: hydrogen, helium, and lithium. 
3. 380,000 years. For the first time, light emerges into the universe. This radiation (light) is referred to as the cosmic microwave background. First predicted to exist in 1948 by Ralph Alpher, it is a signature mark of the Big Bang. This background of microwaves can still be observed today, and it used to estimate the age of the universe. 
4. 300 million years. We’re jumping forward a bit here. As the initial burst of atoms and gas expands, gravity starts to become a relevant factor. Pockets of different densities of gas give birth to stars and collections of stars start to form galaxies. 
5. ~9 billion years. Our sun forms. The universe is roughly 14 billion years old, and our sun is approximately 4.6 billion years old. 

Steady State Universe

The steady state universe hypothesis breaks one of the key Big Bang Theory assumptions. The steady state hypothesis states that matter and energy are being created continuously, steadily. First theorized in the 1920s by Sir James Jeans, the theory imagines a universe without a real beginning or end. 

In the steady state view, the universe has always been expanding and creating matter, and it will continue to do so. Although the theory has been revised and updated throughout the middle of the 20th century, an overwhelming amount of contradictory evidence supports the notion that the steady state hypothesis is largely false. 

Level II Multiverse

The multiverse concept is complicated. And, that may still be an understatement. One of the driving factors leading to the development of this theory is the seemingly perfect nature of physics in our universe. Light, gravity, physics… they all seem to work together perfectly to allow life to exist in our universe. This can be viewed as a major coincidence or an inevitability given a large number of trials. 

The multiverse concept postulates that multiple universes exist, simultaneously, and they each have different physical constants. For example, maybe a universe 2.0 (or 3.0 or 18.0 or 821.0) exists along with ours where light travels at a different speed. Changing this speed changes an exceptionally large number of other universal constants, and thus, everything we know about our universe.

Correct Hypothesis?

So, where does that leave us? What is the “correct” theory for the origin of the universe? By a large margin, the Big Bang is the most well-supported, evidence-based theory. That being said, new technology and new instruments allow us to gather different data every decade, so we will have to see what the future holds!

What other theories of the universe have you heard of? How do you think this all got here?

[Featured image by FelixMittermeier via Pixabay]

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