The first one in a series of posts about the universe is the birth of universe in which this is about the Big Bang.
The universe is filled with mystery. Everything, even the universe itself is a mystery. It's formation, the celestial bodies, the probable ends, all are a mystery which we still can't figure out. But that doesn't mean that we can't let our imaginations run wild. Even the complex equations which astronomers talk about space and time is also based on our assumption.
A mind blowing fact - The universe was born at no place and no time! This is because time and space and time originated only after big bang. The universe started it's journey of 13.7 billion years (it is really a lot of time) ago, from a single point. This point contained infinite gravity and density and energy. Yes! a single point from which everything around us was created. Then, this extremely dense point exploded with unimaginable force, sent the matter into all possible directions. This is known as the big bang. But, there is no sound of bang during the big bang as sound can travel through a media and there was none - neither solid, liquid nor gas (the atomic particles had not been created yet to enable sound to pass). This is the widely accepted theory of the origins of big bang.
Our Universe is expanding even now. It was smaller when you started reading this post than now. It is expanding at the speed of anywhere from 68km to 74 km per second. Another interesting fact is that some scientists are beginning to unearth evidence that the reason our brains are hardwired to react to certain tonal configurations (minor chords, sound sad, etc.) has something to do with the overtones of the universe, formed by the inflation of the universe following the Big Bang.
There are some other alternatives to the big bang. The main rival to the big bang in the older times was the steady state universe, which states that the universe does not have a beginning, nor an end. Though the universe keeps on expanding, it's density remains the same. The galaxies, planets, and other forms of matter are always being created, and since the density is the same, the old ones are becoming unobservable with new creations. This theory was proposed by Sir James Jeans in 1920 and was re-established in 1948 by Hermann Bondi and Thomas Gold.
Another one is that our universe is formed beyond the event horizon of the black hole. But since we cannot cross the event horizon of the black hole, it cannot be proved. Some of the people, letting their imagination run real wild, proposed that our universe is a computer simulation. But scientists have got conclusive evidence that if our universe was a computer simulation, then that computer must control every small movement from an electrons to huge stars. Also, scientists have calculated that the record the information of a few electrons, all the atoms of the universe is not sufficient and that it's complexity increases with a every few electrons added.
What were the conditions of our universe, just after the big bang? Fortunately, we have a lot of predictions on this topic.
According to the Big Bang theory, the universe at the beginning was very hot and very small, and since then it has been expanding and cooling down since then and even now. Early universe was a very dense, dense enough to make a black hole. Remember that a black hole is formed when large amounts of matter is fused into a small space. That is the reason why a black hole is dense.
The Universe, 10^-43 seconds after it's creation, was extremely hot, about 10^32 degree Celsius. Here, the four fundamental forces were created as one namely -
1. Gravitational force - the weakest force. Has infinite range of action and all matter is affected by it throughout the universe. Due to the cooling of universe, it gets separated first.
2. Electromagnetic force - the second weakest force. It also has a range of infinite range of action and it keeps atoms and molecules together. Also responsible for the properties of matter. It was the last one to separate, during the the time when temperatures cooled enough to allow quarks ("building blocks" of subatomic particles "not subatomic particles".) and gradually, hadrons (subatomic particles) to form.
3. The weak nuclear force - Do not go by it's name as the weakest of the four. It is strong but it's force does not extend throughout the universe. Also, it is responsible for the fusion reactions and radioactive decay (process by which an unstable atomic nucleus loses energy by radiation).
4. The Strong nuclear force - It has the strongest force, but shortest range, keeping the nucleons (protons and neutrons) together. It gets separated after the gravitational force, when the universe starts to expand greater than the speed of light. During this time, temperatures dropped by a factor of 1,00,000.
Now, all of this, starting from the big bang, happened from 10^-43 seconds to 10^-6 seconds (the time when quarks were formed) By the time the universe was 1 second old, it had expanded to a size about a thousand times the size of our solar system, and the temperature dropped to about ten thousand million degrees. During this time, first quarks, then hadrons, then leptons (particles not affected by strong force) dominated the universe as the most common type of matter.
This kept on changing because antimatter of quarks, hadrons, leptons kept annihilating each other. Now, something extraordinary happened, which changed the entire destiny of the universe and also, made the universe, in the way we know now.
The above images are taken from Google.
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