Various probable patterns of the universe. The real, accelerating version is shown on the right. It will take enough time, and the acceleration isolates all connected galactic or supergalactic structures of the Universe, and all the rest irrevocably move away from them.One of the greatest dangers in science is making hasty decisions based on the limited data we have in our hands. We can never observe everything with arbitrary precision, so we are always forced to extrapolate on the basis of what we see. But what if we just lack the critical information that can lead us to the correct conclusion? This situation will arise in billions of years with the Big Bang. This frightening conclusion led to a beautiful question that is asked by our reader:
If intelligent life reappears in our solar system after several billion years, by that time only a few points of light will remain in the sky. What theory of the universe can these beings invent? It will almost certainly be wrong. Why do we think that what we see can lead us to the “correct” theory, if a few billion years before us everything could have looked completely different?
Let's talk about what someone will see in the distant future, say, in tens of billions of years.
Galaxy Centaurus A has a dust disk, but it is dominated by an elliptical shape and a halo from satellites: evidence of a long-developing galaxy that has experienced many mergers in the pastHundreds of billions of stars will still be visible in the sky, and no matter how intelligent a life form arises, she will be able to see them using the same telescopes that we have today. But some details will be different:
- there will be less dust and neutral gas
- in proportion to older, red stars of small mass will be more,
- sites of active star formation will be much less
- stars will be distributed in a large elliptical halo, and not in a plane like the Milky Way.
The main reason for this is that in 4-7 billion years the Milky Way,
Andromeda , and as a result, all the
galaxies of the local group will merge into one.
A frame-by-frame image of the merging of the Milky Way with Andromeda, and how the appearance of the sky from Earth will change. This merger will occur in about 4 billion years, with a huge burst of star formation, which will lead to the appearance of an elliptical galaxy filled with red and dead stars, and not having free gas: Milkdromedy.When such large mergers occur, a huge number of new stars appear that capture most of the gas and dust present in the galaxy. When a small region of very active star formation appears, we call this phenomenon a starburst. When this region covers the entire galaxy, we call it a
starburst galaxy . In such cases, the neutral atoms very quickly come together and form new stars everywhere, but the most massive of them live very little. After just a few hundred million years, the most massive stars disappear, leaving only sun-like and less massive stars to burn. After tens of billions of years pass, only the coldest and most red stars will remain. They may not be as bright, but the amount of dust that could block their light will be much smaller.
The starburst galaxy Henize 2-10 , located 30 million light years from us. When stars appear throughout the galaxy, a starburst occurs. But after this outburst there is very little unused material for subsequent generations of stars.But all this is true only for the stars of our Galaxy (and the local group): for the future giant elliptical galaxy Milkdromeda. If a civilization of a distant future looks beyond the limits of our future Galaxy, it will see only emptiness. With the continuation of the development of the Universe, all galaxies that do not belong to a local group will move away from us due to the presence of dark energy. Now, the nearest galaxies are about 10 million light-years away, but the universe is accelerating. When the universe is twice as old, these galaxies will be twice as far; when she is three times more, they will be four times farther; after quadrupling of age, they will be eight times farther, and so on. By the time the universe turns 100 billion years old, the galaxy nearest us will be located a billion light years away. Accelerated expansion of the universe will lead to what we feel as if we are alone in the entire universe.
After merging, large spiral galaxies will merge into one giant elliptical galaxy. Over time, the stars inside it will be redder, because the blue dies the fastest. The gas and dust blocking the light will eventually either be used to create new generations of stars, or will completely disappear after a starburst outbreak.Also, there will be no signs of relic radiation. Today, there are hundreds of residual photons per cubic centimeter, with temperatures a couple of degrees above absolute zero, falling into the microwave part of the spectrum. With the expansion of the Universe, both the density and the energy of these photons will fall. After 100 billion years, less than one photon per cubic centimeter will remain, and the background radiation will no longer be in the microwave range, but only in the far part of the radio range. If someone does not realize the existence of ultra-distant galaxies and these weak radio signals, then the civilizations of the distant future may not open the Big Bang.
With the expansion of the fabric of the universe, the wavelength of distant light sources increases. As for the residual luminescence of the Big Bang, it could be observed in the visible part of the spectrum at the time it was emitted, then it shifted to the infrared and then to the microwave part, and eventually the part of the spectrum would go to the radio with the extension continued. Its power and intensity, as well as the density of photons, will continue to fall over time.Instead, they would conclude that their galaxy represents the entire Universe. That there is nothing more around them, and only they are. Without some clues about the existence of something else, there will be no desire to search for something at large, unexplored distances, to try to find ultradar galaxies that are today closest to us. There will be no motive to assume the existence of the afterglow of the Big Bang, since no one will notice the expansion of the Universe. All that we will have is our Galaxy, Milkdromeda, stretching for a couple of hundred thousand light years. They may find dark matter in their own galaxy, but that's all. Unless they stumble upon ultra-far-off ultra-dull traces of distant parts of the Universe, they may even be able to believe in the
hypothesis of a stationary Universe .
Our local supercluster , the Laniakey , contains the Milky Way, our local galaxy group, the Virgo cluster, and many smaller groups and clusters in the back yard. However, each group and cluster is gravitationally connected only with itself, and the dark energy expanding the Universe will separate them from each other. After 100 billion years, even the nearest galaxy outside of our local group will be about a billion light years about us, and there will be many thousands, or even millions of times (considering the change of generations of stars inside it) dimmer than today's ones galaxies. Today we can see them in modern telescopes, but will we understand that we should look for them, and will we be lucky to look in the right direction?They will ask questions like where did their galaxy come from? Why is she only one? Where did matter come from to form long-lived stars? Why are there so few young blue stars? Without evidence of the expansion of the Universe, the Big Bang or distant objects outside the Milky Way, they will definitely make the wrong conclusions of the century, if not eternity. After countless generations of searches for the deepest chasms of the Universe, having found nothing, they will be forced to conclude that they are alone. There is only their galaxy, only their stars, only they. Alone in the endless abyss of dark loneliness.
The isolated galaxy MCG + 01-02-015, alone for more than 100,000,000 light years in all directions, is now considered the longest galaxy in the Universe [ Void galaxy is one of the galaxies found in cosmic voids / approx. transl.] In the distant future, Milkdromeda will be even more alone.We have the privilege to reach in our research to the state in which we are, both evolutionarily and technologically, while the Universe is still so young. Today we live in a time when the nearest galaxies showed us an expanding Universe, hinting to us the need to search for signs of the times when the Universe was smaller, denser and hotter. And we have found very reliable signs of those times, both close and distant, and we know what to look for at huge space distances due to what is near us. But if we did not see anything? If we thought that our galaxy is all that exists? There would be no further motivation to search further. In the distant future, civilizations will have to look at distances hundreds or even thousands of times large to see the nearest objects outside the galaxy.
Our conclusions about the current state of our Universe and its history depend on when we appeared.
Universe with dark energy: our Universe. We can discover this dark energy only because we live today; if we appeared 11 billion years ago, we would not have noticed it. Maybe we are missing something because we live today and not sooner or later?Does this make you think, as our reader thought, are there important components or properties of the Universe that have already been lost? We assume that the Universe consists of normal matter, radiation, dark matter, neutrinos, black holes and dark energy — that’s practically all. But if you look back, we know that neutrinos and radiation were then much more important than they are now, and that dark energy did not manifest itself at a detectable level until the Universe knocked several billion years. Can there be other types of energy in the Universe that have disappeared before radiation, the existence of which is unknown to us due to the fact that there is no evidence of their presence?
The various components and contributions to the energy density of the universe, and the times when they dominate. If cosmic strings or domain walls existed in some tangible quantity, they would make a significant contribution to the expansion of the Universe. There may be other components, such that we can no longer see, and those that have not yet appeared!All that we can do now is to set limits on these components from the evidence we have. Realistically speaking, these restrictions are not very good. We can see a sufficient part of the Universe so that we can confidently assert the correctness of the Big Bang hypothesis, and that the Universe should have had an inflationary origin that prepared and created the Big Bang. But apart from this, the Universe may have other components that actually played an important role in the remote past, and their signs no longer exist. Scientists very rarely concentrate on this possibility, since our theories reproduce well what we are seeing. But in the distant future the situation will be exactly the same - the assumption of a stationary Universe that existed without changes for tens of billions of years will work very well.
This is a sobering reminder that no matter how well our scientific theories work, they can always be reconsidered and that we should never stop searching for gaps in them. It is on the border of the measurable and the observable that we find new ways of moving forward. Without probing ever more distant horizons, from subatomic to cosmic, we will never reveal the deepest truths of the universe. We have already learned a lot, but, like many scientists, I have a feeling that we still have a lot to go through. And to get there, you will need modesty, and, perhaps, searches in unlikely places.
Ethan Siegel - astrophysicist, popularizer of science, blog Starts With A Bang! He wrote the books Beyond The Galaxy , and Treknologiya: Star Trek Science [ Treknology ].