Observable universe, how big is the universe? In Cosmology, the observable universe is a space region enclosed by a sphere centered on the observer, which contains everything he can observe.
Obviously, with the observable universe is meant the portion of the universe that is indisputable to man, so with the sphere centered on Earth, but in fact, every position in space possesses its observable universe.
The universe. Is already! It soon comes to say the universe. But what is meant by the universe?
The house of all Galaxies? Of the star clusters, the super clutter? The house of all visible and invisible matter?
What is meant by visible? And how do you measure the universe?
Is the universe endless or infinite? What are its boundaries? So let’s start from what we know. We know that the universe was born from a singularity. From a point with pressure and temperature to say the least unimaginable. Then an outbreak. And after a very short time, in the midst of billions of billions of billionths of a second, the universe went from the size of an atom to that of an orange. The universe was thus super-accelerated, an expansion that left the light behind. Physicists call it “Inflation“.
What does it mean? Because inflation was at a speed higher than that of light, the light radiation could not keep up with it. There was thus a gap between the portion of universe reached by light and the cosmos in its entirety. And with the next expansion, which is still ongoing, the gap has been maintained. No instrument is able to see what is beyond the portion reached by light, but it is estimated that there are still billions of light-years beyond the boundary of the ‘unobservable’ universe. It means there is a part of the universe beyond the visible that continues to expand at a speed higher than that of light. In other words, there is a part of the universe that we will never see or know how great it is because we only see that part of the universe reached by light. This leads us to exclude from our calculations this part of the universe that we will never know. From these considerations emerges, then, that we can only look to a certain distance. The universe, that is, has a horizon. And the horizon is for a very simple reason: the light that travels at a finite speed has had only a finite time to propagate, that is, that spent by the Big Bang today.
For this reason, we can feel that around us there is a sphere of space that has a very special limit that surrounds it. In other words, we can only see what’s in this sphere. The observable universe. At this point, it is enough to ask what is the radius of this sphere and our problem about the measure of the observable universe is solved by the normally regular and solid geometry of the circle and the sphere. All we have to do is get this cosmic ray out of here somewhere. In rescue, we consider that the observable universe consists of all the matter that can be seen from Earth at this time. Well, the scientists tell us that the Big Bang originated 13.7 billion light years ago. So the light that went off 13.7 billion years ago, should be the first picture of the Universe.
Then can we conclude that the “edge” of the horizon, the distant region we can observe, is 13.7 billion light-years? Is this the ray of the observable universe? The reasoning would have been right if the Universe stayed firm, but space spread from the beginning. What we see goes back to 13.7 billion light-years, but in the meantime, the universe has continued to expand and even faster. The universe has “dilated” with all the galaxies and their stars. At this precise moment, whatever is on this “edge” of the horizon that sends us its light, we have to wait 13.7 billion years and more billions of years due to the expansion of the universe to see it come. Here things get complicated when we think we have found our cosmic ray. The problem would seem unsurpassed. But, as the Universe has expanded, some scientists have calculated (I save the considerations) that the farthest things we see should have been dragged to a distance almost three times greater than 13.7 billion light-years, that is, to 46.5 billion light-years. This statement would seem contradictory to the age of the universe (about 14 billion light-years) as if there were older objects. It is not that there are older objects in the Big Bang (this is impossible), but objects that, because of their distance and space expansion, have not yet succeeded (and most likely will never succeed) to bring their light (which Travel at finite speed) to us. Problem solved?
Not even for idea.
Because we unintentionally placed Earth at the center of the universe.
Since we have assumed the ‘isotropic’ universe (that is, in all its parts), the observable universe would have the shape of a sphere centered on the Earth (observation point) whose radius is equal to the distance of the farthest object whose light has been able to reach the Earth. The real universe, on the other hand, could have any form we can not know. To this, we should add the gravitational force of Dark Matter that deforms the space and the presence of dark energy that could further “deform” the universe.
It follows that every point in the universe has its own observable universe. Sometimes these universes may have common parts, but they may also be completely separate. So at this point, we have to conclude that the dimensions of the Universe, according to current Knowledge, are not known, and good news at all.
But … it is thought that the size of the universe is hundreds or thousands of times larger than the size of the observable universe (indeed of every observable universe because they vary from place to place)
From Einstein‘s General Relativity, space is created in the presence of a mass.
The curvature is much larger than the mass of the body causing the curvature of its volume, that is, the greater the density. In other words, the “curvature” of the universe depends on its average expansion velocity and the average density of matter contained in it. If the average density of matter (distributed equally throughout the universe, according to the cosmological principle) is greater than a certain critical value, determined by the expansion velocity, space converges to a point close to itself. The trajectories traveled from the bodies (from particles to galaxies) and even the path of the rays of light incur and speak in this case of the closed universe with a finite extension (universe finite). If the density is less than the critical value, the universe is curled to the contrary, outwardly, and is said to be open. In this case, space is infinite (infinite universe). Finally, if the density coincides (equal) with the critical value, it is the limit case of a flat universe (even in this infinite case).
Here, now the uncertainty of the universe dimension is total.
Observable universe, how big is the universe?
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