Problems such as dark matter, the nature of time, aliens and the formation of supermassive black holes have puzzled astronomers for decades.
In the last decade we have learned a lot about the Universe and how it works: we have photographed black holes, studied the inside of atoms and seen the birth of the Universe… Yet there are still gaps in our understanding of the Universe and the laws that govern it. These gaps are the puzzles that physicists and astronomers are expected to solve in the years to come.
1-Why is there more matter than antimatter?
Everyday matter is made up of protons, neutrons or electrons. These particles have counterparts with the same mass but opposite electric charge, known as antiparticles, such as antiprotons, antineutrons and positrons, respectively. The known universe is composed of everyday matter.
The mystery is why the universe is not made up of equal parts of antimatter, since the Big Bang, which is thought to have created the universe 13.7 billion years ago, produced equal parts of both. Matter and antimatter appear to be mirror images of each other in all respects except for their electric charge. In this case, matter and antimatter annihilate when they encounter each other.
But if this were to happen, both would have to be completely annihilated. Protons should cancel each other out with antiprotons, electrons with anti-electrons (positrons), neutrons with antineutrons and so on. But we know that this does not happen. After all, this is how we exist. There is no accepted explanation for this. It remains one of the mysteries of the universe.
2- Why is there a big black hole at the center of every galaxy?
As far as we know, there are about two trillion galaxies in our Universe. At the center of almost every one of them is a supermassive black hole. The question of how these black holes reach the center is one of the great problems of cosmology waiting to be solved. Massive (very massive, massive) stars undergo supernova explosions at the end of their lives. As a result of the death of these stars, that is, their collapse under their own gravity, stellar black holes are formed.
3- What is Dark Matter?
Dark matter is matter that does not interact with any electromagnetic radiation. In other words, it does not emit light or energy. Physicists believe that a staggering 27 percent of the mass and energy in the known universe is made up of something called “dark matter”. This means that the matter that makes up the vast majority of the universe is something very different from what we have thought for centuries. This mysterious matter is more than five times more than normal matter as we know it. Perhaps one of the 20th century’s most important lessons for humanity was the realization that known matter only makes up about 4% of the universe.
The existence of this unobservable matter can be determined by its gravitational effect on other matter. With this effect, dark matter helps galaxies to maintain their integrity and stars to stay together. For example, if it were not for the gravitational effect of dark matter, the Milky Way would not have had enough matter to form stars in the 13.82 billion years since the Big Bang. Therefore, we can say that dark matter has a role in accelerating the birth of stars in our galaxy.
4- Does Time Exist?
We are wrong about most of the things we think we know about time. For example, we say that time flows. However, for something to flow, it must flow relative to something else, like a river flows relative to its banks. So, relative to what does time flow? Can we say that there is a second time? Most likely, the flow of time is an illusion created by our brain to organize the information we receive. We perceive time in three different ways: past, present and future. However, the idea of a common real time is a concept that does not correspond to reality. Because with relativity, time has lost its absoluteness. So exactly how someone else’s time is sliced depends on how fast they are moving relative to you or the strength of gravity they are experiencing.
This difference in time is too small to be noticed in our daily lives. This is because these effects are only noticeable at relative speeds close to the speed of light or in ultra-strong gravity. Nevertheless, thanks to relativity, we know that the space and time span of one person is not the same as that of another person. With the theory of relativity, space and time cease to be two separate concepts, but are inextricably intertwined. In our Universe, all events – from the Big Bang to the death of the Universe – are organized in a pre-existing four-dimensional spacetime. So, nothing actually “progresses” through time.
If we imagine rewinding the expansion of the Universe in the same way we rewind a movie, we could arrive at a moment when space and time were torn apart. Based on this moment, physicists suspect that time may have emerged from something more fundamental at the beginning of the Universe. However, no one knows what that something is.
5- What is Dark Energy?
Dark energy is an invisible energy with a repulsive gravitational force that drives galaxies apart and the Universe to expand. Astrophysicists discovered “dark energy” in 1998. Observable evidence for its existence came from measurements of Type 1A supernovae.
At the time, scientists thought that the only force affecting the large-scale Universe was gravity, which acts like an invisible web between galaxies, stopping cosmic expansion. The dark energy that drives the expansion of the Universe accounts for about two-thirds of the Universe’s mass energy. This was a result that surprised cosmologists. Because dark energy suppressed the gravitational pull affecting the entire Universe and took control of the Universe about five billion years ago.
6- Why don’t we see any signs of aliens?
In 1950, Enrico Fermi, the man who built the first nuclear reactor, was having lunch in the canteen of the Los Alamos bomb lab in New Mexico. Suddenly he said: “Where is everybody?” Everyone at the table understood exactly what he meant. Years later, Fermi’s question was independently analyzed by American physicists Michael Hart and Frank Tipler. Hart thought that aliens were spreading out and colonizing the Milky Way. Tipler hypothesized that alien colonists would be helped by self-generating robots. Hart and Tipler hypothesized that every star in the galaxy would be visited, even at low speeds. They came to this conclusion by comparing the age of the Milky Way with travel times. So, as Fermi pointed out, aliens must be here on Earth. But it doesn’t look like they are here. This phenomenon has been called the “Fermi paradox”.
There are hundreds of explanations for aliens to solve the paradox. For example, one of these ideas was that we were the first intelligence to appear in the galaxy. These explanations also included the idea that we were completely alone in the galaxy and excluded from advanced civilizations that could have negatively affected our development. A more likely hypothesis that could resolve the paradox is that there is no paradox. Any traces of a visit by aliens in the distant past could be erased by wind, rain and geological processes. Thus the paradox disappears.
We have been searching for extraterrestrial life with telescopes for more than half a century. Yet we have yet to find any trace of aliens in our galaxy, but only in a very small part of it. At this point, we can recall the words of Douglas Adams in The Hitchhiker’s Guide to the Galaxy. “The dimensions of space are mind-bogglingly vast. You cannot believe how vast the vacuum of space is. Imagine a long road leading to a pharmacy far, far away. From a distance, that building looks as small as a pea, and everything in space is like a pea in that vast void.”
7- The Problem of the Basic Building Blocks of Nature
By combining Lego pieces in different combinations, we can build thousands of different models. If we think of the matter in the Universe like these models, we see that they all have the same basic building blocks: quarks and leptons. Now let’s assume that Lego pieces hundreds and thousands of times larger are made and put on the market. This is exactly what nature does for the basic building blocks.
Normal matter consists of only two types of quarks and two types of leptons. Let’s call them the first generation. However, there is a second ‘generation’ of quarks and leptons with the same properties as the first, as well as all particles being hundreds of times heavier. There is also a third generation with the same properties as the first generation, but thousands of times heavier.
Creating heavier generations requires more energy. That’s why we see fewer of them today. But quarks and leptons heavier than the first generation are likely to have played a critical role in the Big Bang. Here a new mystery arises. Why does each generation have quite different particle masses?
Why are there 3 different generations of particles?
American physicist and Nobel laureate Dr. Steven Weinberg has an interesting explanation. The fundamental building blocks of matter gain mass by interacting with the Higgs field. The Higgs field is an energy field that is thought to exist in every region of the universe. In this field, a fundamental particle called the Higgs boson exists and interacts with other particles.
The formation and amount of mass depends on how the particle interacts with the field. For example, photons are massless particles because they do not interact with the Higgs field. Weinberg suggested that particles that interact directly with the Higgs could only be particles of the third generation. Maybe the second generation gets its mass by interacting with an undiscovered particle that interacts directly with the Higgs. And maybe the first-generation particles also gain mass by interacting with a second, as yet undiscovered particle in the same way.
We can liken mass gain over generations to a game of word of mouth. As the game progresses, a different sentence starts to emerge from the initial sentence. We can look at mass gain in a similar way. Perhaps each sub-generation interacts less with the Higgs field. Therefore, the mass-forming effect of the field is less effective in the lower generations. Weinberg does not know how such a mechanism would work in detail. But physicists emphasize that Weinberg may have given a clue to the problem of “nature’s building blocks in three different forms”.
