In this blog post, we will look at why the universe has the conditions that make human existence possible, and explore the principles of humanity and their scientific implications in depth.
The conditions for intelligent life to occur on a planet like ours are very demanding. This planet must be located in a narrow region where water can exist as a liquid, and water must be rich in organic matter. This is because water is not only the basic building block of life, but also acts as a medium that enables the metabolism of living things. It must also maintain the temperature conditions necessary for chemical reactions to occur smoothly, and for this, the energy emitted by the star must be at the appropriate level.
In addition, it must have the right amount of gravity to hold the atmosphere in place, and the atmosphere must contain oxygen to form the ozone layer that blocks ultraviolet rays. In addition, planets like Earth need a magnetic field to block strong stellar winds. To do this, the planet’s core must be made of liquid metal, and it must also have the right rotation speed to maintain the fluidity of the core. This is because without a magnetic field, harmful particles emitted by the sun or other stars can directly affect life forms.
Even if all these conditions are met, humans can only appear after being lucky enough to avoid external threats (interplanetary collisions, orbital ejections, etc.) that would damage the planet for 4.5 billion years. Earth is truly a miraculous planet.
However, if we change the order of our thinking, the situation changes. Since the fact that humanity exists is clear, we can conclude that there must be a planet that meets all the conditions for humanity to exist, and that it is no surprise that we live on it. The “Weak Anthropic Principle” is the extension of this logic to the entire universe beyond Earth. The core of this logic is that the universe we observe is a place where intelligent life forms such as humans can be created, so it is not surprising that the universe exists in its current form.
Applying this principle, the probability that a planet will have the conditions for life to form is very low, but the fact that the home planet of intelligent life is a rare planet is not surprising. For example, just as life can be found in the middle of a vast desert, even though it is rare, it can be interpreted that the probability of humanity being born in the infinite space of the universe is slim, but not impossible. This principle is not a logical leap and can be used in various experiments and theories. For example, when designing an experiment to measure a constant that you know nothing about, you can design an experiment more efficiently by applying the weak anthropic principle to predict the possible values of the constant and then designing the experiment accordingly.
On the other hand, the “strong anthropic principle” is based on the logic that the universe, which can be observed by humanity, inevitably formed the current structure because it requires intelligent life. The important thing in this logic is the fact that any physical phenomenon becomes natural and inevitable through the existence of humanity. The Weak Human Principle cannot answer the question, “Why is the mass of a proton 1,836 times that of an electron?” However, we can only say that the chemical reactions necessary for the process of the formation of humanity are possible when the mass of a proton is 1,836 times that of an electron, so it is not surprising that this value has been observed. On the other hand, the strong anthropic principle can be answered by saying that if the mass of the proton were different from what it is now, humanity would not have existed, so the mass of the proton should be 1836 times that of the electron.
This principle seems attractive at first glance, but it uses dangerous logic that ignores the basic law of causality. The probability that a planet has the conditions for the emergence of humanity is very low, but since there are many planets in the universe, it would not be strange if a few of them had such conditions. And on one of those planets, humanity could have really emerged. It is not correct to argue that the planet on which humanity lives is special because of this fact. To follow the strong anthropic principle, we must accept the logical fallacy that the Earth was shaped into an environment suitable for human life from the time it was first formed 4.5 billion years ago.
Physics always struggles with the question “Why?” Any theory always involves assumptions, and “Why?” is a question that attacks those assumptions, which is a problem that cannot be answered by contemporary science. For example, the speed of light is determined by the dielectric constant and permeability of a vacuum, and since these values are constants that are not related to the state of motion, we can deduce that the speed of light is always constant regardless of the state of motion. However, we still don’t know why the speed is 300,000 km per second. Until we get to deeper physics, we can only accept the value measured by experiments. This problem applies equally to the important assumptions that form the basic framework of physics. The Lorenz symmetry is the assumption that the laws of physics are always constant regardless of the position or state of motion of the experimenter, but the reason why the Lorenz symmetry is established cannot be answered with current science.
Physicists had hoped that as physics developed, the number of assumptions would decrease, but a deeper understanding of nature did not mean that fewer assumptions were needed. In classical electromagnetism, it was possible to create a theory by accepting only four Maxwell equations, the speed of light, and the permittivity of a vacuum, but in modern standard models, 25 constants are needed. Baez, J. (2011) This uncomfortable situation was exacerbated by the need for fine-tuning of the constants. Fine-tuning is the act of adjusting the value of a constant to a very small “unnatural” value within the range of the constant that allows a theory to work properly. A typical example is the cosmological constant. This constant is a value that determines the extent to which the universe expands or contracts, and is known to be about 10^-122. The fact that the suitability of a theory is greatly affected by the fine-tuning of the constant indicates that the theory is not perfect, and some physicists, uncomfortable with the fact that humanity’s deepest understanding of nature is very incomplete, have tried to resolve this situation through the strong anthropic principle.
Physicists who accept the principle of humanity always give the same answer to the question, “Why?” The reason why the cosmological constant has become such a small value is because humanity exists in the universe, and the values of the 25 constants in the standard model were also determined in such a way that humanity could live in the universe. There are more than 10^500 types of universes predicted by string theory, but Douglas, M. R. (2003) argues that there is nothing to worry about because there is only one universe in which humanity could have been born.
This claim is intended to explain a difficult-to-accept assumption, and it can be seen as stemming from the fear of the unknown. No matter how much science advances, there will always be questions about assumptions, and even if another theory comes along to solve those questions, it will contain other assumptions that cannot be explained. The principle of humanity that can break this chain of ignorance may have seemed like a sufficiently attractive weapon to them.
Meanwhile, the principle of humanity places equal importance on observability and the laws of physics, as the universe in which intelligent life cannot be observed cannot exist. This kind of thinking does not help the development of science. This is because it is forbidden to question. If we accept that all observable physical phenomena are the natural result of human existence, what should we study? Since we can already answer all the questions, we cannot question and create new theories.
Another problem with the Principle of Humanity is that it cannot be disproved or verified. To disprove the principle of humanity, we would have to observe a universe in which humanity cannot occur, which is a contradictory situation. Verification is impossible at all because the nature of the claim that the laws of physics are tailored to make humanity possible. Such a claim cannot be called proper science.
Science is imperfect. As mentioned above, even if a more advanced theory emerges, there will always be assumptions that cannot be explained in the end. However, the goal of science is not to create a perfect theory that solves all questions. If we understand that the purpose of science is to endlessly pursue a deeper understanding and explanation than the current theory, and that the purpose of science is to gradually increase the breadth and depth of our understanding of nature through this process, then the Principle of Humanity will lose its place and disappear.
