Anthropic Principle

It might sound rather medieval and retrograde, but did you know that it is theoretically accepted that the universe and, more specifically, our Solar System, are structured as we know them because the existence of planet Earth is allowed?

A concept that, at first sight, would indicate the centrality of the human being, whose importance would obscure all the remaining realities existing in the cosmos. Indeed, this deduction is swept away by the Copernican principle, which unquestionably promulgates the heliocentric structure of the Solar System and the confinement of the Earth to a secondary object but which, not for this reason, cannot coexist with the anthropic principle.

1. Representation of the proto-Earth.

The Universe, and with it all the stars, the planets, the nebulae, the galaxies and the clusters of galaxies that compose it, is constantly expanding and its behavior is regulated by a series of ordered and mathematically perfect physical laws; these indisputable laws fit into a perfectly proven mechanism that allowed living organisms to originate. Therefore it makes sense to say that the Earth is a special place, as it presents a physically and chemically perfect setting that gives way to life to generate and endure over time. Nevertheless, it is incorrect to support the uniqueness of the Earth, given that every year astronomers discover a considerable amount of planets that, just like ours, orbit around stars similar to the Sun, at a technically ideal distance to allow carbon to form organic substances that could form the anchors of living organisms.

During the celebrations of the 500th anniversary of the birth of Nicolò Copernico in 1973, the Australian physicist Brandon Carter coined the term anthropic principle, centralizing with it the attention towards the privileged position of the Earth inside the cosmos, and unquestionably affirming that the laws of the cosmos itself are compatible with life, as we know it.

2. image Nasa/Esa, Herschel Space Observatory. Infrared image of the center of the Milky Way.

What Carter was trying to say is the hypothesis that if there were not a considerable number of extraordinary coincidences in the values of the constants of the physical laws, not only would biology not exist, but the existence of common astronomical objects and ordinary matter would not be possible either.

For example: the force of gravity exerted by the solar mass is powerful enough to compress the hydrogen atoms of the Sun, excite them to such an extent as to fuse them through thermonuclear reactions, generating helium atoms, and allowing our star to shine in space; if the force of gravity exerted by the solar mass were minimally lower or higher this would not be possible and, as a result, planet Earth would not receive that heat so perfectly balanced that allows us to perform our vital functions (this concept applies not only to our Solar System, but to each star, to which corresponds a solar system of its own, unique and different from any other in the universe).

Consequently, carbon, the chemical element on which every Earth’s life cycle is based, is also formed within stars and, more concretely, is generated by the fusion of helium with beryllium 8 (the latter a highly unstable element that dissolves in a fraction of a second): if beryllium 8 was minimally, imperceptibly more elusive, we could never find carbon in our periodic table and carbon-based life would have no way of existing.

3. diagram of the Earth’s magnetic field that protects us from the solar wind.

Another crucial example: with 5,515 kg/m³ Earth is the planet of the Solar System that has the highest average density, despite being only a small rocky planet. This fundamental characteristic is due to the fact that when our Sun was in its embryonic protostar phase, some heavy elements orbiting it, such as iron, nickel, iridium and lead compacted in great quantity and began to manufacture what would become the present earth’s core: a huge iron sphere at very high temperature that constitutes 32% of the total mass of our planet, even more massive than the entire planet Mars. The great properties of iron, heated up to 6,700 C, allowed the existence of a magnetic field whose range extends well beyond our atmosphere, and acts as a shield in defense against the deadly attacks of ultraviolet rays carried by the solar wind. If we had slightly lower values in the mass of the Earth’s core, the magnetic field produced would not have been strong enough to fight against the solar wind, and the Earth’s atmosphere would have been literally blown away, and the surface would have been slowly burned, just like it happened on Mars!

4. Milky Way

Among the hundreds examples that can be cited, we release one last, more difficult to understand, but which allows us to understand that, not our Solar System, but our entire universe, is a mechanism tested specifically to encourage the proliferation of life, once again tending the hand to the anthropic principle: the dark energy.

Not directly detectable, it homogeneously permeates the entire universe, constituting 68% of its overall composition and identifiable as the energy corresponding to the physical vacuum.Its infinitesimally small density, 0.0000000000000000000000167 kg/m³, is enough to overcome the force of gravity, thus causing the acceleration of the expansion of the universe outwards.At the same time it is low enough to allow galaxies, stars, planets, atoms, DNA to remain united. The anthropic principle aims to conclude that if life in our universe was not possible, evidently the reason would be to search for hypothetical different physical constants that would have developed a cosmic dimension completely different from the known one, definitely not suitable for life based on carbon and, therefore, with different physical constants the universe itself would not have been the same.

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