Causes and Consequences of the Big Bang
Before talking about the Big Bang, it's convenient to shed some light on what caused this primordial explosion. What provoked it, and why this mysterious causing agent made arise, from an apparent emptiness, a Universe prone to the appearance of life and to all the known phenomena and physical dimensions? Two exemplifying answers to this problem, both assuming that our Universe is closed (which nowadays doesn't seem to be true) may be emphasized:
Universe with no borders by Stephen Hawking (MoonRunner Design UK)
The Anthropic Principle
Then, why is our Universe prone to the appearance of life? After all, won't the laws of physics need to be submitted to a very strict range of parameters so that the life and the known configurations are able to arise?
The Intensity of the Fundamental Forces
If, as an example, the electromagnetic force was slightly more intense when compared to the strong nuclear force, neither the helium nor any other heavy element would have ever been formed from the hydrogen, because inside the atomic nucleus the electromagnetic force would be strong enough to counteract the strong nuclear force, which drives the fusion of this element. The Universe would be totally made of hydrogen, so the appearance of life (which is based on heavier elements) would be made impossible. If the electromagnetic force was slightly less intense when compared with the strong nuclear force, the emergence of diprotons (nuclei made by two single protons) would become possible, because the attractive energy between the protons could then overcome the repulsive energy resulting from the electromagnetic force exerted by the interaction between two positively charged objects. On the other hand, the totality of the existing hydrogen would be fused into heavier nuclei, making impossible the formation of water molecules (made by 2 atoms of hydrogen and 1 atom of oxygen), which are essential to terrestrial-like life forms. Anyway, for sure that the evolution of the Universe would be radically different from the one that shaped the Universe that we know today.
Another example would be the eventuality of a stronger gravitational force: in that case, the contraction of the stars would be so strong that very likely these would be forced to compensate it with a much higher rhythm of nuclear fusion, which would imply the quicker extinction of the fuel that feeds the stars... life (assuming that it exclusively develops in places that are close to such energy sources) could have no chance to arise in such a short time span. The Universe itself would much more easily and quickly contract again under the action of gravity, which would reduce the chance of life to arise. In case the gravitational force would be weaker than it is, the stars would be bigger and would have larger life spans than if they were in our Universe. The Universe would expand more quickly and if that expansion was quick enough the aggregation of matter in galaxies that are home to life forms could be very endangered.
Finally, the intensity of the weak nuclear force is also relevant for the chances of life to arise, because it determines in which degree the neutrinos interact with the barions. In a supernova, a shock wave expands and faces the resistance of the outer layers of the star. At the same time, a wave of neutrinos is produced inside the violently contracting nucleus, traveling toward the exterior at velocities close to the light speed. If the weak nuclear force was less intense, the neutrinos wouldn't interact with barions existing in the resistance zone and couldn't give away any impulse to the prosecution of the expansion of the shock wave. The supernova would end up being to feeble for the elements fused in its interior to be scattered into the interstellar space and re-used by the life emerging in future planetary systems. If the weak nuclear force was more intense, then the neutrinos would end up interacting with the barions located at the deep heart of the exploding star, never reaching the slowing down region and, therefore, they wouldn't give any contribution for the push of the outer layers of the star.
Even if the physical laws and parameters were the ideal for the emergence of life, we still face the problem of, given this condition, the Universe be able to assume much more chaotic configurations that the ones that are observed. Could life be born in such a Universe?
The Strong Principle and the Weak Principle
Why does our Universe favour so much our existence? Many may argue that this happens because God created a Universe to serve Humanity... In our days scientists propose two not very theories to explain these facts:
On the other hand, it shall be emphasized that it's impossible that the real laws of physics vary inside a single Universe because that way, according to Stephen Hawking, it would not be possible to travel from one region to another.
Strong anthropic principle: among a big variety of universes, only one (the one containing the small sphere) holds parameters compatible with life (MoonRunner Design UK)