We understand that the universe is constantly expanding. That implies that the cosmos is expanding with each passing day. It also implies that our universe used to be smaller than it is now. If you go back far enough on that tape, science says that our universe was once a singularity—an endlessly small and dense point.
The majority of scientists believe that this point expanded during the Big Bang, but as all currently understood physics fails to work under the extreme circumstances that existed at the beginning of the universe, it is difficult to state with certainty what actually occurred at those early times.
Returning to the past
Identical celestial objects like those we see today were scattered throughout the universe over the majority of its history; they were merely closer together.
For instance, the universe’s volume was a million times less than it is now and its average temperature was roughly 10,000 kelvins when our universe was less than 380,000 years old. It was a plasma because it was extremely hot and dense, which causes atoms to shatter into protons, neutrons, and electrons. However, plasmas are a common occurrence in both space and on Earth, and as a result, we have a strong grasp of how they function.
However, the physics gets more intricate the further back we go. The protons, neutrons, and electrons that made up the universe when it was just 12 minutes old were still subject to the same laws of physics that control nuclear explosions and nuclear reactors.
But things become incredibly hazy if we go back any further.
We don’t have a physics theory that can account for the absurdly high pressures and temperatures the cosmos endured when it was less than a second old when we try to understand how the universe came to be. In certain circumstances, all of our physical theories fail to explain how particles, forces, and fields behave.
Birthing the singularity
Using Einstein’s general theory of relativity, which links the universe’s composition to its expansion history, physicists may map the universe’s expansion.
But there is a catastrophic error in Einstein’s idea. If general relativity is taken to its logical conclusion, our whole universe was once compressed into a single, impossibly dense point at a certain point in the past. The Big Bang singularity is what is meant by this.
It’s common to characterize the singularity as the “beginning” of the cosmos, although it’s really not.
The Big Bang singularity doesn’t mathematically indicate that the cosmos started there. Instead, it is informing us that general relativity has failed and has lost its capacity for explanation and prediction.
The limitations of general relativity have long been recognized by physicists. It is unable to account for quantum gravity, which is gravity at very tiny or strong scales. In other words, we need new physics to completely comprehend the very first moments of the universe.
It’s a question of all time
Sadly, such physics does not yet exist. String theory and loop quantum gravity are two hypotheses for quantum gravity, however, neither of these ideas has been completely developed or put to the test.
However, if any of those hypotheses are accurate, they can provide us with valuable information on the early universe.
A piece of space-time with a limited size stands in for the singularity in the context of loop quantum gravity. Meanwhile, according to string theory, our world is the result of a “landscape” of potential universes. It’s also conceivable that the world created by the Big Bang is merely one of an endless number of universes that exist in a multiverse. The haziness of these potential theories can only be clarified by further developments in theoretical physics.
Another issue is that we might never find out what triggered the Big Bang. Even our ideas of time and space collapse in the early stages. Normal, daily ideas like “beginning” and “before” would not even make sense at such enormous sizes.
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