Alternatives to the Big Bang Theory

 Is there another theory for the origin of the universe?

The major hypothesis for how the universe began 13.8 billion years ago is the Big Bang Theory. Despite the fact that it is the most widely accepted explanation, several theorists have proposed alternate theories or extensions to the Big Bang Theory. In the infographic below, we go over some of these notions in depth.

To figure out how the cosmos came into being, we must first figure out what it is. According to NASA, the term "observable universe" refers to all that we can see.

Scientists can peek into an area of space that is 13.8 billion light-years away, meaning we can view 13.8 billion light-years in every direction, thanks to the relationship between distance and light speed. But it's not that easy. According to Forbes, new estimates set the diameter of the observable universe sphere at around 90 billion light-years due to the expansion of the universe.

BIG BANG THEORY ASSUMPTIONS

Based on theories and observations, scientists make three assumptions about the universe.

1. Physics' laws are timeless and unaffected by time or place.
2. In all directions, the cosmos is homogeneous, or about the same (though not necessarily all of the time).
3. Humans do not perceive the cosmos from a privileged vantage point such as the nucleus.

They imply that the universe has numerous qualities when applied to Einstein's equations:

1. The universe continues to grow.
2. At some infinite point in the past, the cosmos emerged from a hot, dense condition.
3. In the earliest moments of creation, the lightest elements, hydrogen and helium, were formed.
4. The universe is blanketed in a background of microwave radiation.

BIG BANG ALTERNATIVES

If any of these fundamental assumptions are incorrect, the Big Bang Theory will fail to explain all of the universe's features. As a result, some theorists wonder aloud, "Is it possible the Big Bang didn't happen?"

The Steady State universe is one alternate theory. According to NASA Cosmic Times, Steady State is an early contender to the Big Bang idea, positing the ongoing generation of matter throughout the cosmos to explain its apparent growth. There would be no beginning or end to this form of universe. However, a mass of evidence discovered since the mid-1960s contradicts this notion.

The Eternal Inflation idea is another option. The cosmos expanded fast after the Big Bang during a brief period known as inflation. According to the Eternal Inflation theory, inflation has never ended and will continue indefinitely. New universes are forming right now in a massive complex known as the multiverse. Different physical laws could exist in each of those universes.

In the Oscillating Universe concept, there were an infinite number of Big Bangs followed by Big Crunches that restarted the cycle indefinitely. Colliding "branes" are a part of the current cyclic model (a "membrane" within a higher-dimensional volume called the "bulk").

Quantum gravity and string theory implications tantalise, implying a universe that is nothing like it seems to human observers in reality. For example, it could be a flat hologram projected onto the surface of a sphere. It might also be a fully digital simulation that runs on a massive computer.

References:

Listen to ESA"s interview with astrophysicist Professor Joseph Silk on why we may never get to know whether the universe is finite or infinite.

Nicolai, Hermann. "Complexity and the Big Bang." Classical and Quantum Gravity 38.18 (2021): 187001.

Netchitailo, Vladimir S. "World-UniverseModel—Alternative to Big Bang Model." Journal of High Energy Physics, Gravitation and Cosmology 6.01 (2020): 133.

Wallace, David. The emergent multiverse: Quantum theory according to the Everett interpretation. Oxford University Press, 2012.