Big Bang


The Big Bang theory claims everything in our universe—from the sun to the very fabric of spacetime—has its origin in a single, explosive event that took place roughly 13.8 billion years ago.

The provocative theory has captured modernity's imagination as it continues to evolve and adapt to discoveries. 


For centuries, most scientists conceived of the cosmos as infinite and fixed, with no large-scale movement of celestial bodies other than observable orbits. 

Georges Lemaitre, a Belgian cosmologist and Roman Catholic priest, applied Einstein’s theory of relativity to cosmology in 1927 by proposing an expanding universe that originated from a so-called primeval atom. 

American astronomer Edwin Hubble independently confirmed Lemaitre’s claims two years later as he observed distant galaxies moving away from Earth at an accelerating pace proportional to their distance, a behavior later dubbed the Hubble-Lemaitre law.


What Hubble saw was an effect known as “redshift." Similar to the Doppler effect, an object redshifts, or appears redder, when lightwaves lengthen out, indicating the object is moving away from the viewer.

One of the most fascinating pieces of evidence for the Big Bang theory is the cosmic microwave background. The theory predicts the massive energy burst at the beginning of the universe would have left behind an “echo” of energy in the form of dispersed, lingering waves of energy.

Signs of this background radiation were first detected by astronomers in the 1960s, who famously believed a persistent hiss coming from their radio telescope was a defect caused by a buildup of pigeon waste in its antenna.

Observations of the relative age of stars and galaxies regularly confirm and refine current models of the age of the universe that are based on the Big Bang theory.

Universal Timeline

Scientists don't know what triggered the Big Bang, though some suggest a quantum fluctuation—or a random energy shift in a quantum vacuum—brought it into being. 

The immediate moments after the Big Bang saw the rise of subatomic particles and light elements like helium. As blazing hot temperatures cooled, the basic building blocks of larger matter formed and set in motion a billion-year formation of stars, solar systems, and galaxies, which continues today (watch 101). 

Mind-Bending Questions

Despite its explanatory power, the Big Bang theory prompts some fundamental questions whose answers are elusive. 

What came before the Big Bang? No one can be sure. Some scientists suggest our universe is just one within an infinite multiverse of parallel universes. Others believe a supernatural force caused it. The debate is one of the most enduring questions in human history.

What, if anything, are we expanding into? Theorists would argue the universe is, in fact, everything, so it only expands into itself. You can compare this to the surface of an inflated balloon, which expands while remaining itself. 

There are limits to the theory—dive into how it could progress further here

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One of Albert Einstein’s greatest accomplishments is his theory of general relativity, which relates mass, energy, and gravity. While revolutionizing physics, the equations introduced a conundrum—either the universe must be evolving, or an arbitrary constant must be added to account for a static universe. Einstein chose the latter path, only to later call his “cosmological constant” the biggest mistake of his career.

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One of the most counterintuitive aspects of quantum mechanics is that it describes the world as a set of probabilistic outcomes. Among other philosophical questions is whether the nature of quantum fluctuations may give rise to the science fiction-like possibility of multiple universes. Listen to physicist Neil deGrasse Tyson explore the concept of the multiverse in this ten-minute video.

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The James Webb Space Telescope was launched December 25, 2021, with tools allowing it to peer billions of years back in time. The successor space telescope to NASA's highly touted Hubble, the Webb's infrared imaging capability is 100 times superior to Hubble's, enabling it to capture more objects at a further distance. This visual explainer its unprecedented equipment and traces its peculiar solar orbit 1 million miles from Earth.

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The life of the universe is incomprehensibly long to the human mind. Scientists estimate the universe is 13.8 billion years old, the solar system 4.5 billion years old, modern humans have been around for about 200,000 years, and most of us live less than a century. This model built in the vastness of the Mojave Desert attempts to visually capture the age of the universe compared to our daily lives.

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Many major mysteries about the universe still confound scientists, from how the smallest building blocks behave to what makes up dark matter. A never-before-seen particle known as the axion may provide answers to the questions, but its existence to date is entirely hypothetical. Read about axions and how they may solve one of the biggest puzzles—why the universe is filled with matter, and not antimatter.

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It may sound like science fiction, but a number of theoretical physicists have argued our universe is shaped like a bubble, expanding into higher dimensional space. In an extra twist, surrounding our modest blob may be an infinite number of other universes, bubbling up in their own right. Untestable but fun to think about—what happens when and if these were to collide?

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