13.8 billion years ago in a hot Big Bang our universe was born. Since then it has expanded and cooled down, up to the present day. From our point of view, we can look at 46 billion light years in all directions, thanks to the speed of light and expansion of space. And although this is a huge distance, it is not infinite. Because we do not see further. What lies beyond the horizon of these 46 billion light years, and may the universe be infinite?
First of all, it is worth noting that we don’t know the universe is finite or infinite. But we know that beyond what we can see, there are a lot of things, said the physicist Ethan Siegel in his article on Medium.com.
The farther away the objects that we observe in the Universe, the farther back in time we go, until the time when atoms did not exist until the Big Bang
Looking as far as possible, we are also moving back in time. The nearest galaxy, located 2.5 million light-years from us, appears to us, as it was 2.5 million years ago, because the world needs so much time to reach our eyes from where it was emitted. Many galaxies we see as they were tens of millions, hundreds of millions or even billions of years ago. Looking farther into space, we see the light as it was in the early days of the Universe. Why would we not look to the beginning, to see how everything was 13.8 billion years ago? We not only looked, but also found something: the cosmic microwave background, the afterglow of the Big Bang.
It turned out that at that time the universe was almost perfectly uniform, but some areas were more or less dense than average, and 1 part of 30 000. This is enough to form stars, galaxies, galactic clusters and cosmic voids that we observe today. But in those early imperfections that we see from this satellite image, contains an incredible amount of information about the Universe. For example, a striking fact: the curvature of space, as far as we know, totally flat. If the space was arched, as if we lived on the surface of a four dimensional sphere, far rays of light merged. If the space was concave, as the four-dimensional surface of a saddle, the far radiated. But no, far rays of light move in a preset direction, and the fluctuations reflect almost perfect plane.
Values of hot and cold spots, as well as their magnitude indicate the curvature of the Universe. We came to the conclusion that it is perfectly flat
Of the limitations associated with the cosmic microwave background and large scale structure of the Universe together, one can conclude that if the universe is finite and closed on itself, it must be at least 250 times more than the part that we see. Since we live in three dimensions, 250 times the radius means (250)3 volume, and this is 15 million times more space. And yet, no matter how large this number may seem, it is not infinite. The lower boundary of the Universe is at least 11 trillion light years in all directions, and it’s a lot but still of course.
And of course, we have reason to believe that the universe is much more than that. The big Bang could mark the beginning of the observable Universe, to which we are accustomed, but it will not necessarily mark the birth of space-time. Before the Big Bang, the universe experienced a period of cosmic inflation. Instead be filled with matter and radiation in a hot state, the universe was different:
- filled with energy inherent in the space;
- expanded at a constant exponential rate;
- created new space so quickly that the smallest physical length, the Planck length, you can stretch to the size of the currently observed Universe in just 10-32 seconds.
Inflation leads to the fact that space is expanding exponentially, which can very quickly lead to the fact that any previously curved space would be flat.
In our region of the Universe inflation ended, it’s true. But there are three questions that we don’t know the answer. They are extremely important for determining how big the universe really infinite or not.
How big was the Universe after inflation, which was born the Big Bang?
Looking at our Universe today, the uniform afterglow of the Big Bang, to the plane of the Universe and fluctuations that stretched through the Universe on all scales, we can extract some information. We can define an upper limit on the energy scales at which inflation proceeded; we can see how much the Universe had to pass through inflation; we can learn a lower limit on how long one had to continue inflation.
But the pocket of the inflationary Universe which spawned us, could be much more than this lower limit! It can be in hundreds, millions, or googol times bigger than we see, or truly endless. And yet, not being able to observe most of the Universe, we do not have enough information for decision-making.
True if the idea of “eternal inflation”?
If we assume that inflation is expected to be a quantum field at any given point at this stage of exponential expansion is likely that inflation will end, which will lead to the Big Bang, and the likelihood of further inflation by creating more space. Our calculations lead us to the inevitable conclusion: for the inflation made the Universe that we observe, it must always create more space in which inflation will continue, compared to areas in which inflation ended with a Big Bang.
Although our observable universe could appear as a result of the end of inflation in our region of space 13.8 billion years ago, there were still areas in which inflation continues, creating more and more space, even today. This idea is known as eternal inflation and in General accepted by the community of theoretical physicists. But how great then must be the entire unobservable universe?
How long did inflation, yet not over the Big Bang?
We can only see the observable Universe generated by the end of inflation and Big Bang. We know that inflation had to occur at least within 10-32 seconds or so, but surely she could proceed longer. But how much longer? Seconds? Years? Billions of years? Eternity? Is it always the universe was in a state of inflation? Did inflation start? Whether it is from the previous state, which was eternal? Or all of time and space emerged out of nothing some time ago? All can be, and all of these options are not final and check the answer.
As far as we know, the universe is much more than the part that we see. Beyond the observable, we should expect a lot more of the Universe, similar to ours, with the same physical laws, same constants, space structures and chances of the emergence of complex life. There must be other “bubble” where inflation has ended, lots of bubbles, prisoners in an even greater space-time, subject to endless inflation. And yet, no matter how big this universe — or multiverse — may be, it may not be infinite. Most likely, the universe has its end, its length, though most speculative.
The only problem is that we don’t have enough information to definitively answer this question. We only know how to access information available within our observable Universe: 46 billion light years in all directions. The answer to the pressing question can be encoded in the Universe itself, but we just can’t reach it. Yet.
What if the Universe has no end?
Ilya Hel