Whenever an astronomer tries to explain how the universe started, someone inevitably asks, “Yes, but what came before the Big Bang?”
Humans know the Big Bang as the beginning of it all. About 13.8 billion years ago, our universe began with every speck of its energy jammed into a very tiny point. And then, an initial, exponential growth spurt known as cosmic inflation created everything we know today.
But what happened before the Big Bang? What caused it? Did anything exist?
Well, if time itself began with the Big Bang, then there was simply no “before”. But hardly anyone finds that answer satisfying, and they are not to blame.
Physicists are most confident when discussing things they can see — and the oldest thing visible with our telescopes is the Cosmic Microwave Background. That’s like the “echo” of the Big Bang. An all-sky glow that we can measure and map with radio telescopes. This echo came into being 380,000 years after the Big Bang. Before that, we can’t see what the universe was like. Physicists think it was simply too full of matter for light to flow freely.
But if there are limits to what astronomers can see, there’s no limit to what theorists can imagine.
Some physicists believe that time didn’t start with the Big Bang. They suggest it emerged when the universe reached a certain level of complexity.
Others theorize that the universe runs in cycles, in a possibly endless series of expansions and contractions. If this “cyclic” model is right, the Big Bang wasn’t the beginning, but just a transition from an earlier era.
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The Big Bounce theory is not very different from the Big Bang theory. The Big Bounce suggests there were periods of expansion and contraction, and the current expansion of the universe is just one phase of this.
Another theory suggests that our universe is just one of countless “bubble universes” that pop up repeatedly in a “multiverse.”
It’s also possible that before the Big Bang, our universe was an infinite stretch of an ultrahot, dense material, persisting in a steady state until, for some reason, the Big Bang occurred. This extra-dense universe may have been governed by quantum mechanics, which deals with the tiniest scales.
For Stephen Hawking, the Big Bang was all that mattered: Before the Big Bang, he said, events are unmeasurable, and thus undefined. Hawking called this the no-boundary proposal: Time and space, he said, are finite, but they don’t have any boundaries or starting or ending points, the same way that the planet Earth is finite but has no edge.
Numerous ideas contradict each other, sometimes wildly, but they all pretty much agree that the Big Bang happened.
If we were to run the clock back as far as we could, all of the space that makes up our visible Universe today would be compressed down to a single point known as the singularity. The singularity was a point in space-time where all the matter and energy in the Universe was concentrated in.
However, if we compressed all the matter and energy present in today’s Universe into a tiny enough volume of space, the laws of physics would break down. But yet again, if you do the math, it appears that a singularity is inevitable.
So, things get too complicated when one asks questions like “what came before the Big Bang.” It almost doesn’t even make sense at all. It’s like asking “where am I” if space no longer exists.
There’s no doubt that physicists will continue to argue about which idea deserves to be taken seriously. Explaining our universe as the product of some earlier universe may sound appealing — but what caused that universe to exist?
If you have a cyclic cosmology — well, has it been cycling forever? And if so, how did the cycling start?
As you see, the question of “what caused it to exist” goes on forever and ever.
In science, there are things we can test, measure, predict, and confirm or refute. Everything else is nothing more than speculation.
The bottom line is that no one knows whether the Big Bang was the beginning of everything or rather a moment in time when the universe switched from a period of contraction to a period of expansion.
Scientists don’t yet have a way to peer back to even the instant of the Big Bang, much less what came before it.
Maybe, quantum physics will eventually give us the ultimate answer to this question. But humans have just started to scratch the surface in this field of physics, so there is a lot of work to do and a lot of stuff to learn.
At the moment accepting “I don’t know” as a valid answer is the only intellectually honest answer. Similarly, if we encounter a question like what is south of the south pole, we must accept the possibility that the question itself might be nonsensical.
After all, questions like this make the future exciting. We have so much to learn and no one knows if this learning process will ever end.