Starting With a Bang - How Did the Universe Begin?
- Brandon Holloman
- 30 minutes ago
- 5 min read
Updated: 1 minute ago
The universe encompasses everything we know to exist. Time itself only has meaning within the universe. It’s impossible to imagine that the universe may have once not existed at all, and yet, that’s the current consensus among cosmologists. The Big Bang is the most widely accepted theory for how the universe began.
In the early days of cosmology, it was assumed that the universe had always existed, and always would, in a steady state. There was no beginning of the universe, as it had simply always been there and there would be no end. In 1929, astronomer Edwin Hubble, for whom the Hubble Telescope was named, was studying the redshift of galaxies when discovered not only that other galaxies were moving away from each other, but that there was a correlation between how far they were and how fast they moved.
What Hubble had discovered was cosmic expansion. The universe itself was expanding like a balloon. If you were to draw multiple dots on a balloon, then blow it up, you would be able to see that every dot on the balloon moves away from every other dot, and the farther apart two dots were to begin with, the faster they would move apart because there’s more balloon surface expanding between them. This is exactly what Hubble discovered with galaxies. It’s not just galaxies moving away from each other, it’s the space between them expanding.
This correlation between distance and speed became known as Hubble’s Law, and it had some paradigm-shifting implications. If everything in the universe was moving apart, that meant there was a clear timeline to the universe’s growth. If one were to watch time in reverse, they would witness the universe shrinking. Go back far enough and there would be a moment when everything in the universe existed in a single point. A singularity of infinite density. The moment that the singularity began to expand is the moment that the universe was born. That was the Big Bang. Despite the name, the Big Bang was not an explosion in the traditional sense. It was not a shockwave racing out from a single point, but rather all of space expanding simultaneously.
Analysis of the expansion of the universe suggests that the Big Bang occurred 13.8 billion years ago. That’s three times the age of Earth and over a million times the age of human civilization. Within the first seconds of the Big Bang, the universe would have been a rapidly expanding cloud of ultra-heated plasma with the first atomic nuclei only barely beginning to form. During this time, the entirety of the universe was like one giant star. It would take 400,000 years for the universe to cool to the point where true atoms could form. The glow left over from this period is still visible today in the form of the Cosmic Microwave Background, one of the strongest pieces of physical evidence for the Big Bang theory. As it was light emitted from the entire universe, the Cosmic Microwave Background is visible in all directions. But even once matter as we know it began to form, it still took a hundred million years for the earliest stars to form. From that point on, the universe essentially became what we know it as today.
What about before the Big Bang? It’s impossible to say for sure. By definition, there may not be a “before.” If the universe started as a singularity of infinite density, then it also had infinite gravity. And, as you might have heard in relation to black holes, extreme gravity can actually slow down time. At the point of a singularity, time stops entirely, so if the entire universe were one singularity, there would be no time, and with no time, there is no “before.” Alternatively, our universe might just be the most recent in a cycle of universes that expand, then collapse, then expand again. Another theory is that our universe could have budded off from another universe’s black hole. After all, a black hole shares a lot in common with the singularity at the start of the Big Bang.
If the universe had a beginning, does that also mean it has an end? Many believe the answer is, unfortunately, yes. Scientists used to think that the expansion of the universe was either constant or slowing down, as would be expected of debris flung from a traditional explosion. But observational evidence suggests that is not the case. Not only is the universe expanding, it seems to be moving faster as time goes on. The only way for this to be possible is if there is some unseen force that works counter to gravity, which forces the universe to move apart. We call this unknown force dark energy.
Dark energy is one of the greatest mysteries in cosmology, and also one of the most important. The true nature of dark energy will dictate the ultimate fate of the universe. If dark energy continues to expand the universe, then there may come a day, trillions of years in the future, when the entirety of the universe could be ripped apart by the repulsive force of dark energy. Other possibilities are the eventual collapse of the universe into a new singularity, or the spreading of the energy of the universe so thin and far apart that everything freezes to absolute zero.
But those issues are nothing to worry about now. We’re far closer in time to the Big Bang than we are to the theoretical Big Rip, Big Crunch, or Big Freeze of the future. The universe is far less than a fraction of a fraction of a percent of the way through its life. There’s still plenty of life left in the universe.
One of the biggest questions of humanity is, “Where did we come from?” The ultimate answer to the question is found at the very beginning of the universe. The Big Bang was the formation of everything we know, and likely everything we ever will know. It set in motion the chain of events that would eventually lead to us. It is the ultimate beginning, to which everything else can be traced.