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It's a universe full of wonders. The greatest miracle of these is that it gives birth to life and produces intelligent life that can observe and think about the universe. To get to this point, many prerequisites are needed, such as the large-scale structure of the universe, the existence of galaxies, stars, planets, chemical reactions, the origin of life, and so on. These are incredibly small coincidences.

The essence of the universe is physics (this statement is in doubt), and its operation is governed by the laws of physics. Among the many laws of physics are a large number of physical constants, the values of which determine the final form of our universe. It can be said that all the coincidences and miracles in the universe are due to the fact that the values of these constants fall within some very small range. If the values of these constants change slightly, our universe will be unrecognizable, not only will it not be able to support life, but galaxies and stars will not appear.

For this reason, people often refer to such universes as fine-tuned universes or universes on the knife-edge.

Let's take a look at how outrageously demanding the range of precision of the physical constants is required to reach the present state of the universe.

1. The gravitational constant appears in many physical laws, from Newton's law of universal gravitation to general relativity, and is crucial to the macrostructure of the universe. The value of this constant should be familiar to everyone: 6.67 x 10^-11.

If the gravitational constant were 10^-36 less than the current value, the star would not be able to exist stably. Its own gravitational pull cannot compete with the radiation pressure from the fusion of the core, and will collapse in an instant.

If the gravitational constant is 10^-40 greater than the current value, the universe will be full of black holes and there will be no more stars under the action of too strong gravity.

10^-36 is a number so small that the human brain cannot comprehend. Here's an example that might help you understand it. If you connect 10^36 grains of sand with a diameter of 0.1 mm, it will be 114 times longer than the diameter of the observable universe (93 billion light years). At such an unimaginable length, if you take out a grain of sand, the whole universe collapses.

In addition, there are other parameters that play an important role in the present state of the universe. Some of them are physical constants, and some are the result of the combined action of multiple constants.

2. The efficiency of stellar fusion is 0.007, which means that when hydrogen fuses into helium, 0.7% of the mass is converted into energy. This parameter is determined by a number of other physical constants, including the magnitude of the strong interaction force. If the value of this parameter is 0.006, then complex chemical elements cannot exist, and complex chemical reactions on which life activities depend cannot occur. If the value of this parameter is 0.008, then all hydrogen will be quickly depleted after the Big Bang. However, not all physicists agree with this view, and they believe that hydrogen can be stable for a long time as long as the strong interaction force does not increase by more than 50%.

3. The density parameter of the universe is the ratio of the density of matter in the universe to the critical density, which is approximately equal to 1. If the density of matter in the universe is too great for dark energy to push the universe to expand, then the universe will shrink rapidly before the Big Bang. Conversely, if the density of matter in the universe is too small, it cannot provide enough gravitational pull to form stars.

4. The cosmological constant describes the ratio of the dark energy density to the key energy density of the universe. The order of magnitude of this constant is 10^-122. This tiny value dictates that it can only function on the scale of 1 billion light-years. If it weren't so small, neither stars nor galaxies would have been able to form.

5. The third low-energy state of the carbon-12 atom is 7.656 MeV. If this value is below 7.596 MeV or above 7.716 MeV, the carbon produced by the star will not be enough to support carbon-based life. Similarly, to produce oxygen for life on Earth, we require 0.5% of the magnitude of the strong interaction force and 4% of the magnitude of the electromagnetic force. Of course, if you believe that other elements, such as silicon, can also support life, you can ignore this.

There are many more such examples, such as fine structure constants, the dimensions of the universe, etc., so I will not repeat them here. However, it cannot be overlooked that the ultimate state of the universe today is the result of all these factors. They must both fall within the specified range. So, the probability that we get the universe today is the product of all the small probabilities. You can probably imagine what kind of jackpot we won.

From both a scientific and philosophical point of view, a precisely regulated universe is an unavoidable problem. Why, then, do we get such a universe that seems to have been designed specifically for us?

First of all, we must take into account that physics has not advanced to the point of answering all the questions in the universe. The physical constants that currently appear to be independent of each other may be interrelated on a deeper level. In the future, we may find that the probability of the current state of the universe is much greater than the above calculations.

Let's take a look at the various attempts to explain the precisely regulated universe.

1. Intelligent design

An easy answer to think of is: the universe was designed by more advanced intelligent beings, whether gods or aliens that we can't understand. The purpose of designing such a universe is to give birth to life in it, or to be an experiment to see how long it takes for the sprouts of life to spread throughout the universe. If we extend this idea further, we can even assume that our universe is just a virtual world of computer systems.

Opponents of this view argue that it would be too inefficient to create a universe of this magnitude and history just to feed a few creatures on a small inconspicuous blue star (after all, we have not found reliable evidence of extraterrestrial life). This is not an effective way to overturn the idea of intelligent design, because the first bacterium in a petri dish may ask the same question.

The extent to which this answer solves your problem, though, depends on how devotion you are to your faith. If you think that a God who is omnipotent is the ultimate answer to all questions, and that the existence and origin of this God itself cannot be questioned, then you need not think any further. If, on the other hand, you want to continue to apply the methods of scientific research to thinking about the existence of intelligent designers themselves, you will find yourself falling into an infinite loop: intelligent beings who can design the universe are certainly more incomprehensible than the universe itself.

2. The principle of anthropy

Proponents of the anthropic principle argue that "if the universe had not been precisely adjusted to its present state, human beings would not have existed, nor would they have observed and contemplated the universe".

There are many versions of the anthropic principle, among which the anthropic principle holds that the possible values of parameters in physics and cosmology are not exactly the same, and that the universe favors those that allow carbon-based life to evolve.

The strong-choice principle goes a step further by arguing that the universe must have a nature that allows life to develop at certain stages. Ultimately, the Anthropic Principle holds that the process of processing information containing wisdom must appear in the universe, and once it appears, it will not perish. Opponents of the anthropic principle argue that this idea is neither experimental nor falsifyable, and that it reverses cause and effect. Humans evolved to fit the universe, not the universe to adapt to humans. Hawking also argues that our universe is not as special as the anthropic principle describes.

3. Multiverse TheoryAmong the many explanations, the multiverse theory is probably the one most closely related to physics. According to this view, all values of physical constants are possible and must exist. It's just that they exist in different universes. The universe we live in happens to have the existing constant values, so we finally got the current state of the universe, and intelligent life has emerged that can observe and think about the universe. Other universes get different constants, so they may collapse quickly after the Big Bang and return to the singularity without forming galaxies and stars; In some universes, stars may be destroyed the moment they ignite, and life cannot evolve.

There are many different versions of the multiverse hypothesis in current physics. The only hypothesis that can be used to explain the precisely regulated universe is probably based on string theory or M-theory. For details, please refer to What is the relationship between string theory and parallel universes? However, neither string theory nor multi-universe theory is currently unprovable. In the same way, a precisely regulated universe is an unanswered question.

(Author: Zhihu Mandelbrot)

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