According to the Big Bang theory, time came into being with the Big Bang. That is to say, there was no time before the Big Bang, or there was no such thing as "before the Big Bang", because without time, where did the "before" come from?
The Big Bang theory is the mainstream theory of modern cosmology on the origin of the universe, which holds that 13.8 billion years ago, a singularity with an infinitely small size and an infinitely high density temperature suddenly expanded, and then after a long evolution, we have our colorful world.
The moment of the Big Bang is the beginning of time.
More rigorously, our understanding of the universe began after the Big Bang had a Planck time, because Planck time is the smallest unit of time that makes sense, and any unit smaller than Planck time is meaningless.
Planck time is short, about 10 to the power of -43 seconds, so short that we can't imagine it.
The scope of modern human cosmology research began after the Big Bang occurred in the 10th to the 43rd power, that is, from time zero to 10 to the -43rd power of the very short time, we do not know what happened, this time is meaningless for us.
More importantly, there are more events in just three seconds after the Big Bang than in the universe three minutes later.
What do you mean?
In just three seconds, too many miracles have been staged in the universe, such as the emergence of the four basic forces, the emergence of elementary particles, the exponential and rapid expansion of the universe, and so on. These just three seconds determine the direction of the universe and the fate of the universe!
Three seconds later, everyone knows, as the universe slowly cools, elementary particles begin to combine to form nuclei, atoms and other particles, until the colorful world we see 13.8 billion years later.
But the Big Bang theory is not a perfect theory, and it has its flaws. For example, the birth of the singularity, time is born with the sudden expansion of the singularity, there is no time before the singularity, but how exactly is the singularity born?
According to the interpretation of the Big Bang theory, the singularity itself is a completely beyond our cognition, to put it bluntly, the singularity does not belong to our world at all, and it can be considered that it is something in spacetime.
However, everything can't always appear out of thin air, right? In our inherent thinking, everything always appears for a reason, and scientists also try to interpret the origin of the singularity and time.
Traditional classical physics is interpreted differently, because classical physics has the most fundamental laws: the law of conservation of energy and the law of causation. Energy is always conserved, and everything always appears for a reason.
But the singularity seems to completely break these two laws of classical physics. Because the singularity itself means infinite energy, it also seems to appear out of thin air.
Fortunately, the emergence of quantum mechanics has given people a different way of thinking about problems. Quantum mechanics itself is a highly disruptive theory, and we cannot think about the strange behavior of the quantum world with conventional thinking.
According to the interpretation of quantum mechanics, the singularity may come from quantum fluctuations in a vacuum.
Quantum fluctuations, also known as "quantum fluctuations". Various pairs of virtual particles are randomly derived from the vacuum. The virtual particle pair is randomly derived by borrowing the energy of the vacuum on credit, and then instantly annihilated to return the energy, as long as the whole process is short enough, nature does not care, this phenomenon can always appear, and does not violate the law of conservation of energy.
In fact, the essence of the quantum fluctuation phenomenon is the uncertainty principle in quantum mechanics, the uncertainty of time and energy has a certain relationship, and the product of the two must not be less than a constant.
That is, as long as the time is short enough, the energy can be infinite. And the energy of the infinity of the singularity is generated in this way.
This uncertainty in time and energy can also be embodied in the quantum tunneling effect, which has long been applied in our daily lives.
Some people may question: even if pairs of virtual particles are randomly derived, aren't they all annihilated in an instant?
Indeed, this is how it should be under normal circumstances. But the quantum world is so weird that it doesn't play cards according to routines. Some derived pairs of virtual particles will not disappear, but will remain, which is also a direct embodiment of the uncertainty principle. The uncertainty principle means that anything that can happen, and will happen, provided it is long enough.
Of course, this is just our interpretation of the singularity based on quantum mechanics. Human understanding of quantum mechanics is still only scratching the surface, we do not know the underlying logic hidden in quantum mechanics, we can only find the strange phenomena expressed in the quantum world, and do not know the essence of those phenomena.
Having said so much about quantum fluctuations, let's talk about time.
If the singularity really comes from quantum fluctuations in a vacuum, then there is no time before the singularity is born. Because quantum fluctuations in the vacuum are completely random behaviors, there are no laws to speak of, and even completely uncontrolled by the law of cause and effect, there is no concept of time.
A final digression. If the singularity itself is really produced by quantum fluctuations that have not been annihilated, and these quantum fluctuations should have been annihilated but not annihilated under random action, will annihilation occur again at some moment? Does it mean that our universe can disappear at any time and disappear in an instant?
This brain hole is too big for everyone to think and imagine!