As far as theoretical physics go, the Big Bang theory is one of the more concrete concepts out there. Although we still don’t quite understand what caused the Big Bang itself, evidence of its occurrence is so strong that it’s developed from a theory into an established fact. Speaking of facts, here are eight interesting things you might not know about the birth of the universe.
Perhaps surprisingly, the first person to put the Big Bang theory into words was a Belgian Catholic priest. Well, a priest who was also an acclaimed mathematician and astronomer. Georges LeMaître came up with the idea in 1927 while studying at MIT. Observing that galaxies were moving away from each other, LeMaître supposed they must have been closer to each other in the past—so close that, at one point in time, they might have been compressed to the size of a “primeval atom,” the pressure of which generated an explosion of unimaginable proportions.
Although LeMaître came up with the theory of the Big Bang, he was not the one to coin its iconic name. That honor goes to Sir Fred Hoyle, an English astronomer belonging to an enclave of scholars who insisted that the universe was neither expanding nor contracting, but stational. He first used the term during a BBC radio broadcast in 1949, which he attended to refute the event’s existence.
If the existence of the Big Bang could be inferred from the growing distance between galaxies, so could the point in time that it happened. Using the redshift—the changing wavelength of cosmic light—LeMaître and astronomer Edwin Hubble, the namesake of the Hubble Space Telescope, could determine a galaxy’s velocity and speed. Hubble, using faulty calculations, estimated the universe to be only around 2 billion years old [PDF].
Future generations of scientists corrected the tiny mistakes in Hubble’s math, revealing that the universe was far older than previously believed, with the Big Bang happening at least 13.8 billion years ago. Even that number isn’t certain, though. In 2023, the discovery of “super-old” stars on the fringes of the cosmos led a researchers from the University of Ottawa to propose that the Big Bang could have happened as far back as 26.7 billion years ago.
Though based on solid observations, the Big Bang theory was dismissed for decades before it became commonly accepted. Among the disbelievers was Albert Einstein, who rejected the theory when it was pushed first by LeMaître and later by a Soviet physicist named Alexander Friedmann. Einstein’s theory of general relativity had been the most groundbreaking development since Isaac Newton, and while it explained many mysterious cosmic phenomena, the Big Bang was not one of them.
This is because, according to general relativity, the universe is supposed to be static, unmoving. If galaxies aren’t moving apart in the future, they weren’t closer together in the past, making the Big Bang inconceivable. This explains Einstein’s emphatic reaction to LeMaître: “Your calculations are correct, but your physics is abominable!” Even after the Big Bang became widely accepted, Einstein briefly revisited the theory of a static universe, according to a manuscript found after his death.
Debate over whether the universe was moving or not came to an end when, in 1965, lab physicists Arno Penzias and Robert Wilson discovered direct evidence of the Big Bang in the form of radio waves refurbishing throughout the cosmos. These waves, called the Cosmic Microwave Background, are the cooled-off remains of the light of the Big Bang itself.
Believe it or not, you’ve seen the Cosmic Microwave Background with your own eyes. And you’ve likely seen it more than once, because the CMB produces the static signal (a.k.a. “snow”) you see on analog TVs and hear on radios when you search between stations.
Contemporary scholarship doubts that the universe was once constricted to the single atom that LeMaître talked about. It has, however, been estimated to have covered an area smaller than the size of a pinhead. Although it’s almost obvious that the Big Bang was the most powerful explosion of all time, its approximate strength remains difficult to fully wrap your head around. According to Universe Magazine, the force released during the Big Bang equaled 1054 megatons of TNT. To put that into perspective, hydrogens bombs, the most destructive weapons humans can create, release around 50 megatons.
The Big Bang also happened fast. So fast that energy was thrown at the speed of light—300 million meters per second, a million times greater than hydrogen bombs. All this unfathomable speed and power produced an equally unfathomable amount of heat. It has been estimated that, in a fraction of a second past the detonation, temperatures could have risen to as high as 1000 trillion degrees Celsius.
The biggest challenge to the Big Bang theory in decades emerged shortly after the launch of the James Webb Space Telescope in 2021. The most powerful telescope in existence, it allows scientists to study parts of the universe that were previously unobservable. Searching the edge of the known universe, it discovered galaxies that were so large and so old, our current understanding of galactic formation and evolution fails to explain how they could have been created so shortly after the Big Bang.
The discovery presented two options: either the Big Bang theory was wrong, or the measurements taken from the James Webb Space Telescope were incorrect. The second one proved to be the case. Using more precise and reliable methods to determine the distance of the galaxies, NASA concluded that they were much smaller in size than they originally appeared—small enough for artificial intelligence to simulate their construction following the Big Bang.
If winding back the clock on cosmic expansion brings us to the beginning of the universe, winding the same clock forward could take us to its end. Several theories have been proposed for the death of the universe, many of which are mirror images to the Big Bang.
One of these theories is the Big Freeze, which supposes the universe will “die” when the distance between celestial objects has become so great that energy becomes evenly distributed and space approaches absolute zero temperature. Another possibility is the Big Crunch, which supposes the universe, stretched to its maximum, will one day cease to expand and start contracting, eventually recreating the conditions for another Big Bang. A third scenario called Eternal Inflation posits that expansion is a never-ending process that only stops in certain points of the universe, leading to the creation of self-contained pocket universes like the one we live in.
In his 2010 book Cycles of Time: An Extraordinary New View of the Universe, the Nobel prize-winning physicist Roger Penrose proposed that galactic formation was a cyclical (as opposed to linear) process, and that the Big Bang—far from marking the birth of everything in existence—is actually a transition between the end of an old universe and the start of a new one.
However, most efforts to imagine what happened before the Big Bang are poorly received in academic circles. As astrophysicist Ethan Siegel wrote for Big Think in 2023, there currently is no “evidence of a universe before the Big Bang.” If our universe arose from a previous one, through Eternal Inflation or otherwise, traces of that previous universe should show up in ours, in the structures of our galaxies and in the CMB. But they don’t, meaning that the Big Bang, as far as we can tell, was indeed the beginning of the beginning.