The sun is a giant nuclear reactor that constantly transforms atoms of hydrogen into helium and produces heat in the process. What is crucial to this process however is the incredible precision with which these reactions are balanced within the sun. The slightest change in any of the forces governing these reactions would result in their failure or in a catastrophic runaway explosion.

The conversion of helium into carbon is the alchemy of red giants. In smaller stars like our sun, a simpler sort of alchemy takes place. The sun converts hydrogen into helium and this reaction is the source of its energy.

This reaction is no less essential for us to exist than are the reactions in the red giants. Moreover, the sun's nuclear reaction is also a designed process, just like the one in red giants.

Hydrogen, the input element for this reaction, is the simplest element in the universe for its nucleus consists of a single proton. In a helium nucleus, there are two protons and two neutrons. The process taking place in the sun is the fusion of four hydrogen atoms into one helium atom.

An enormous amount of energy is released during this process. Nearly all the thermal and light energy reaching Earth is the result of this solar nuclear reaction.

Single-proton hydrogen nuclei 

Helium nucleus with two protons and two nueutrons


1) Above: Four hydrogen atoms in the sun join together to form a single helium atom.
2) Below1: This is a two-step process. First two hydrogen atoms fuse forming a deuteron. This transformation is a slow one and is what keeps the sun burning constantly.

3) Below2: If the strong nuclear force were just a little bit stronger, a di-proton would be formed instead of a deuteron. Such a reaction however cannot be sustained for any length of time: a runaway catastrophic explosion would occur in just a few seconds.

Single-proton hydrogen nuclei

Deutron nucleus with one proton and one neutron

Single-proton hydrogen nuclei

Di-proton nucleus with two proton

Like the reactions taking place in red giants, this solar nuclear reaction turns out to involve a number of unexpected aspects without which it could not take place. You can't simply jam four hydrogen atoms together and turn them into helium. To make this happen, a two-step process is required, paralleling the one taking place in red giants. In the first step, two hydrogen atoms combine to form an intermediary nucleus called deuteron consisting of one proton and one neutron.

What force could be great enough to produce a deuteron by jamming two nuclei together? This force is the "strong nuclear force", one of the four fundamental forces of the universe. This is the most powerful physical force in the universe and is billions of billions of billions of billions times stronger than the gravitational force. Nothing but this force could unite two nuclei like this.
Now the really curious thing about all this is that research shows that, strong as it is, the strong nuclear force is just barely strong enough to do what it does. If it were even slightly weaker than it is, it would not be able to unite the two nuclei. Instead, two protons nearing each other would repel each other immediately and the reaction in the sun fizzle out before it ever began. In other words, the sun would not exist as an energy-radiating star. Concerning this, George Greenstein says: "Had the strong force had been only slightly less strong, the light of the world would have never been lit." George Greenstein, The Symbiotic Universe, p. 100 

What, on the other hand, if the strong nuclear force were stronger? To answer that, we first have to look at the process of converting two hydrogen atoms into a deuteron in a little more detail. First, one of the protons is stripped of its electrical charge and becomes a neutron. This neutron forms a deuteron by uniting with a proton. The force causing this unification is the "strong nuclear force"; the force that converts a proton into a neutron on the other hand is a different one and is called the "weak nuclear force". It is weak only by comparison however and it takes about ten minutes to make the conversion. At the atomic level, this is an immensely long time and it has the effect of slowing down the rate at which the reaction in the sun takes place.

Let us now return to our question: What would happen if the strong nuclear force were stronger? The answer is that the reaction in the sun would be changed dramatically because the weak nuclear force would be eliminated from the reaction.

If the strong nuclear force were any stronger than it is, it would be able to fuse two protons to one another immediately and without having to wait ten minutes for a proton to be converted into a neutron. As a result of this reaction, there would be one nucleus with two protons instead of a deuteron. Scientists call such a nucleus a "di-proton". It is a theoretical particle however insofar as it has never been observed to occur naturally. But if the strong nuclear force were much stronger than it is, then there would be real di-protons in the sun. So what? Well by getting rid of the proton-to-neutron conversion, we would be eliminating the "throttle" that keeps the sun's "engine" running as slowly as it does. George Greenstein explains what the result of that would be:
The Sun would change because the first stage in the formation of helium would no longer be the formation of the deuteron. It would be the formation of the di-proton. And this reaction would not involve the transformation of a proton into a neutron at all. The role of the weak force would be eliminated, and only the strong force would be involved…and as a result the Sun's fuel would suddenly become very good indeed. It would become so powerful, so ferociously reactive, that the Sun and every other star like it would instantaneously explode. George Greenstein, The Symbiotic Universe, p. 100 

The explosion of the sun would cause the world and everything on it to burst into flames, burning our blue planet to a crisp in a few seconds. Because the strong nuclear force is precisely fine-tuned to be neither too strong nor too weak, the sun's nuclear reaction is slowed down and the star has been able to radiate light and energy for billions of years. This precise tuning is what makes it possible for mankind to live. If there were even the slightest deviation in this arrangement, the stars (including our sun) would not exist or if they did, they would explode in a short time.

In other words the structure of the sun is neither accidental nor unintentional. Quite the contrary: Allah has created the sun for people to live, as expressed in the verse:

The sun and the moon follow courses (exactly) computed. (Surat ar-Rahman: 5)