Why did the iron element that we are so familiar with on Earth become the last material in the universe?

How was the universe born? Where will it go? Among the many theories about the end of the universe, there is one particularly convincing theory: The universe may become a giant block of iron. Why did the iron element that we are so familiar with on Earth become the last material in the universe?

When exploring the ultimate fate of the universe, we must refer to thermodynamics, the second law of thermodynamics, and the principle of increasing entropy, which are key to our understanding of the evolution of universe. Entropy, simply put, is a measure of the disorder of a system. On a cosmic scale, this means that the total entropy of the universe is increasing over time.

As one of the most important thermodynamic systems in the universe, stars play an important role in the expansion phase of the universe. The birth and death of stars are not only key to the circulation of matter in the universe. Their fate also sheds light on the evolution of elements in the universe, especially the special fate of iron.

Stars convert light elements such as hydrogen and helium into heavier elements through nucleosynthesis. During this process, the temperature and pressure inside the stars continue to increase until they can create iron. However, once the amount of iron in the star's core accumulates to a certain level, the nucleosynthesis process will stop. Since iron has the highest nuclear binding energy , it does not release energy to support further stellar fusion. The end of this process has different results for stars of different masses.

Iron has the highest nuclear binding energy.

For smaller stars, such as our Sun, it will eventually become a white dwarf, a dense object supported by electron degeneracy pressure. These white dwarfs will gradually cool, eventually turning into cool stars made of iron and other heavy elements. For more massive stars, their end can be a supernova, one of the most spectacular events in the universe.

In a supernova explosion, the star's core collapses into an extremely dense object, either a neutron star or a black hole. During this collapse process, a large number of iron cores will be synthesized. These iron cores were ejected in the shock wave of the supernova explosion and spread to every corner of the universe.

As the universe evolved, the iron core gradually spread throughout the universe . Because iron is a relatively stable element, it gradually clumps together to form iron blocks of different sizes. These iron clumps attract each other in space, gradually forming larger iron clumps, which can eventually evolve into iron stars or iron planets. Over time, new stars will not be formed any slower than the rate at which other stars are dying. Eventually, the light in the universe will gradually disappear and the galaxies will dim until they go out completely.

As the universe evolved, the iron core gradually spread throughout the universe.

Current observations show that the expansion of the universe is accelerating. As the universe expands, matter will become farther apart, causing the average temperature of the universe to decrease. According to Hawking radiation theory, the black hole will slowly evaporate through quantum effects and release radiation.

On extremely long time scales, even supermassive black holes will eventually disappear , leaving behind a uniform field of low-energy radiation. When all matter in the universe reaches uniform energy distribution, the universe will enter a static state, which is heat death. If the role of dark energy continues to grow, it could cause the expansion of the universe to accelerate enough to tear apart everything from galaxies and stars to planets and atoms, even both the fabric of time and space. In the process, the universe will undergo irreversible decay until even the most fundamental particles are torn apart.

The sun will contract and become a white dwarf, but it won't turn into iron either.

However, the complexity of the universe goes beyond these simple predictions. Under stably controlled conditions, if the fusion reaction could continue to undergo changes for countless years, it could actually convert to iron. However, the reality is not that simple. For example, our Sun, according to scientists' calculations, when the Sun runs out of hydrogen in its core, it will burn a helium flame and expand into a red giant star. However, this is just one chapter in its life story.

Over time, the Sun will contract and become a white dwarf, even at this stage the Sun will not turn into iron. In fact, white dwarfs will continue to collapse and evolve into black dwarfs wandering around the universe. Additionally, many stars in the universe will not eventually convert to iron. Most stars will evolve into white dwarfs, black dwarfs, neutron stars, or black holes.

So in the end the universe won't have only the element iron left. When the fusion fuel is exhausted, the material cannot resist the strong gravitational force and will directly skip the stage of iron element formation, directly affecting electrons and protons. Neutron stars are celestial bodies formed after electrons are compressed into protons by strong gravity.

In addition, the fission of heavy elements also produces a similar effect. It is worth mentioning that humans have not yet discovered a celestial body made entirely of heavy elements. This means that in the universe there may not be objects made of heavy elements because before forming, they could have collapsed into other types of objects due to gravity. 

We can conclude that the final destination of the universe is definitely not iron!

Although iron plays an important role in the universe, according to current scientific observations and calculations, no celestial body composed entirely of iron has been found . Instead, our space telescopes have observed many other types of objects, such as white dwarfs, black dwarfs, neutron stars, and black holes. According to scientists' calculations, our universe is about 13.8 billion years old. That's a long time, and if in the end the universe was left with only iron, there would be some signs of that by now. However, we have not observed any celestial bodies that can explain this phenomenon. So we can conclude that the final destination of the universe is definitely not iron!

While the 'iron universe' offers an interesting perspective on the end of the universe, it is just one of many theories. The ultimate outcome of the universe may be something we cannot imagine, but iron, as one of the most stable elements in the universe, could turn out to be the most important part of this outcome .