Thought Experiment to the Border of Universe
Author: Leshan, C. Kiev University
The question about borders of universe worried the scientists of all the times beginning with the philosophers of ancient Greece. But not only they were interested in this question. Every curious man wants to understand where in that world he or she lives. That's how expressions like "at the ends of the world" or "in the ninth sky" appeared. Expressions that define the place where the universe as known by them ends and the magic world of gods begins. In antiquity, the idea of the stars fixed on the crystal canopy of the sky was accepted by everyone. And nothing, but the gods, was supposed to exist behind it. And now let's analyze this problem from the point of view of modern physics.
Albert Einstein was sure that the universe is curved and has a limited volume, not being able to have an infinite one because its existence is limited. After the Big Bang, the initial explosion that gave birth to the universe, occurred in a limited time would occupy a limited volume. Now if it has a limited volume it should have a border too, even if it consists only in some points. Then, what can be behind/outside this border?
Some authors assert that "there is nothing outside the universe, neither galaxies, not substance; there is absolutely nothing - neither space, no time" in generally.1 In other words outside the universe there could be a "pointform space" where the distance between two points is always equal to zero and as a matter of fact we could name it "zero-space" or "hole."
The idea of the existence of a "border" of the universe was rejected by the scientists of the ancient world. This argument was based on the existence of a limit that would suppose the existence of a "wall" in space that can't be passed. Let's examine the idea. What will happen if we send a spaceship to the universe's border? Taking into account that the displacing galaxies are flying away at a high velocity, the spaceship must approach to the speed of light in a vacuum. However we are studying the geometrical peculiarities of the universe, that is why we say that in our imaginary experiment, the expansion velocity of universe is low, otherwise this spaceship never reaches this border.
Let's now imagine the universe having the shape of a sphere suspended in a zero-space. The distance between every two points from the external surface of this sphere would be equal to zero. Because in zero-space length doesn't exist, the external area of this sphere would be also equal to zero. Then if there exists a border of the universe, the distance between the borders would be equal to zero. It means that our spaceship would pass this border without realizing it while still being in the same universe. After a limited time, the spaceship would come to the launch point from the opposite side of "sky" (universe), after having made a trip around the universe. The universe is thereby "curved" due to the existence of these "zero-points" or holes. Not taking into account that borders exist in our spaceship, we can travel to the infinite without meeting the "wall" of the universe.
If the expansion velocity of universe were smaller, there could exist a "mirror sky" effect. The ray emitted in one direction must arrive from the opposite side of the sky. Every star must have its mirror reflection on the opposite side of the sky. However we don't observe it because the size of the universe and its expansion velocity is too great for the ray to reach this imaginary board. Probably the expansion velocity of the universe is equal or surpasses the speed of light. Perhaps matter that is encountered completely absorbs the light.
This "mirror sky" effect may have a cosmological significance. One can safely say that, the "Mirror sky" effect could be observed in a contracting universe if one had the capability to do so. Moreover this border can not exist in a single place as it would violate the cosmological principle. This is the principle by which holds that within the universe there can't be places or points which are privileged towards other places or points of the universe. As things stand, the border of the universe must pass through every point of space. These virtual holes in space and time must therefore exist in every point of the universe. This physical object is so-called "vacuum with holes" or "hole vacuum."2
J. Bruno wrote: "The centre of the universe is everywhere, as well as its border but does not exist anywhere."3 But now we can affirm that the universe has a centre that exists everywhere and also has borders that exist everywhere. This statement does not violate any physical or philosophical rules. The universe is and will stay infinite and isotropic.
1. Novicov I.D. 1990. Evolution of Universe. Moscow: Science.
2. Conference Proceeding of ICPS'94, S. Petersburg, 15-21 August 1994.
3. Bruno, Giordano (1548-1600); Barashencov B.S.- Suchestvuwt li granici nauki. M.:Misli,1982," [Do exist the border of science. Moscow, Misli, 1982.]
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