Why does the Big Bang Theory explain the origin of the universe, yet it is controversial due to controversial concepts such as dark matter, energy, and the density of the universe?

The Big Bang theory plays an important role in explaining the origin of the universe, but it is still criticized and questioned due to controversial concepts such as dark matter, energy, and the density of the universe.

 

We live on Earth. We are part of the solar system, the solar system is part of our galaxy, and our galaxy is part of the vast universe. So where did our universe come from? Scientists have come up with many theories to find the beginning and end of the universe. Ever since Hubble observed the expansion of the universe, the leading theory to explain its origin has been George Gamow’s Big Bang theory. According to this theory, the universe started from a single point and expanded rapidly, resulting in its current shape.
When scientists first encountered the theory, they thought it was absurd, and the name “BIG BANG” was meant to mock George Gamow’s idea. The most prominent of the opposing views was Fred Hoyle’s normal cosmology. This theory claims that the universe is always in the same state regardless of space and time, that it has no beginning or end, and that new matter comes from somewhere and forms a new universe. However, the discovery of the 2.7K cosmic background radiation as strong evidence for the Big Bang theory led to the abandonment of normal cosmology. Cosmic background radiation is the microwave radiation generated when protons and electrons combine in the early universe, and the absolute temperature of these microwaves decreases over time. Microwaves of the same temperature are found in all directions of the universe, providing strong evidence for the Big Bang theory. Since then, theories have been published that further strengthen the Big Bang theory. With the introduction of the concept of the Planck epoch, it was explained how the four fundamental forces of nature were separated after the birth of the universe, and the existence of the Higgs boson proved how fundamental particles such as quarks and leptons acquired mass. With the advent of these auxiliary theories, humanity has gotten closer and closer to understanding the origin of the universe. In that sense, the Big Bang theory is considered the most successful explanation of the universe.
However, as the Big Bang theory has expanded, there have been areas where the evidence is unclear or not easily understood. A prime example is dark energy and dark matter. In the Big Bang theory, scientists calculated the mass and volume of the universe to explain its density. However, a contradiction was found in these calculations. When the theoretical mass of the universe was calculated to be 100, the sum of the masses of all the matter we can observe was only 4. So scientists hypothesized that there is invisible matter in the universe and named it dark matter. The problem with this theory is that, compared to previous hypotheses, there is no evidence for it and no possibility of finding it. Although the Big Bang theory explains most of the observed phenomena of the universe, it is open to criticism for theories with uncertain foundations, such as dark matter. In this article, we’ll take a look at some of the key concepts of the Big Bang Theory, and address some of its possible criticisms.
First, there’s the aforementioned dark matter and dark energy. The main problem with these two concepts is that they only exist in theory. Dark matter is a hypothetical substance to solve the problem of the density of the universe, and dark energy is a hypothetical energy postulated to solve the problem of the force created by dark matter. This problem goes to the heart of the Big Bang theory. Dark matter has mass, so it exchanges gravity with other matter. However, if you take them all into account and calculate the gravitational force of the entire universe, you get a value that would cause the universe to contract. In other words, dark matter contradicts the expansion of the universe, a key concept in the Big Bang theory, so scientists have added dark energy, which exerts a force on the universe to keep it expanding. However, there is still no evidence to support either concept. Currently, cold dark matter, such as excons, is predicted to be dark matter, but it’s only a prediction. In other words, dark matter and dark energy are tools to explain what has already been observed, and the biggest problem with these tools is that they are unobservable. The word “dark” itself refers to their unobservability. We need to be cautious about accepting dark matter and energy as the mainstays of the Big Bang cosmology, because in the process of explaining the core of the theory, they introduce concepts that are hard to find evidence for.
Then there’s the matter of the density of the universe. Our universe is isotropic, meaning it has the same density at every point. This is called the cosmological density. In the Big Bang theory, there are three possible models of the universe: the Big Freeze, in which the universe grows uncontrollably and eventually cools down to a temperature close to absolute zero; the Flat Universe, in which the universe continues to expand and grow in size; and the Big Crunch, in which gravity becomes too strong at some point and the universe begins to contract, leading to a cataclysmic collapse. Which state any given universe falls into is determined by its density. If the density of the universe is greater than the critical density, it will experience a Big Crunch, if it is less than the critical density, it will experience a Big Freeze, and if it is equal to the critical density, it will be a flat universe. Interestingly, the density of our universe is exactly the same as the critical density. If it deviated from this value, the universe would not be what it is today, and it would have died out relatively soon. However, our universe is exactly at the same value as this critical density, and it has maintained its current shape. The problem is, the probability of any universe being at the critical density is extremely low. Is this just a coincidence, or is there a scientific explanation?
One popular answer is the “anthropic principle”. To understand the anthropic principle, we need to understand the concept of multiverse theory. According to multiverse theory, our universe is not the only universe, but new universes are constantly being created, just like air bubbles rising in water, and this process repeats infinitely, creating an infinite number of universes. These universes have different densities, and since there are infinitely many densities, there must eventually be a universe with a critical density. The anthropic principle states that an observer in such a universe must be living in a universe with a critical density.
Since the cosmological density problem deals with the most fundamental question of all, “Why does it have that value?”, it is difficult to come up with a logical answer except for the anthropic principle. However, the anthropic principle itself has two inherent problems. First, the multiverse theory used by the anthropic principle is, like dark matter, unproven. Moreover, unlike dark matter, it is difficult to find evidence for it because the natural laws of the universe are different between universes. The multiverse is more of a philosophical concept, as it is an argument based solely on imagination. The anthropic principle is also hardly a scientific proposition. According to Popper’s theory of science, science is evidence-based and must be disprovable. However, the anthropic principle, or the proposition that observers cannot exist in a universe that is not close to critical density, and therefore our universe, with its observers, is at critical density, is itself a logical fallacy. However, these theories are widely accepted because the Big Bang theory successfully explains the universe, and there is no scientific theory that can replace it.
We need to recognize the value of the Big Bang theory for its contribution to humanity’s view of the universe. But at the same time, we shouldn’t forget to be critical of its limitations and the hypotheses that have been built to support it. Science starts with endless questions and ends with proofs, which are always being verified and disproven along the way. So while we should understand the Big Bang theory, we should also be ready to ask new questions when we discover areas it doesn’t cover. This is how science will progress.