2 Answers

  1. It is known that the visible part of the universe is a flat (non-curved) open three-dimensional space. �This space has no boundary.�

    When we say that the universe is expanding, we mean that the distance between any two arbitrary galaxies increases with time. Space is stretched.

    If you put an observer in any galaxy in our universe, he will see the same picture: he will see himself as if in the center and all the surrounding galaxies will move away from him. All points in our universe are equal.

    Hypothetically, we can imagine that there is a fourth spatial dimension where the universe is expanding. But all the experimental data show that the number of spatial dimensions is three. General relativity is consistent and can explain the expansion of the universe by increasing the distance (dilation of the metric) between arbitrary two points without involving additional dimensions of space.

  2. The edge of the universe is a complex concept. Let's start from afar. There is a concept of the Hubble sphere, a region of the expanding universe surrounding the observer, outside of which objects are moving away from the observer at a speed greater than the speed of light. That is, we will never see or reach objects farther away, since we cannot exceed the speed of light. However, the universe is much larger than the Hubble sphere. The second point is that to reach any object in the universe, you need to overcome the force of gravity. To enter near-Earth orbit, you need to reach the first cosmic speed – �7.9 km/s. To reach the moon, you need to dial the second cosmic speed – �11.2 km/s. To fly into the interstellar space of our galaxy, you need to gain the third cosmic speed-about 42 km/s. Go beyond the Milky Way galaxy-you need a speed of at least�250-300 km/s. And to go beyond the Hubble sphere, you need a speed higher than the speed of light.

    If we consider the entire Universe as if from the outside, then it is a single space-time continuum, let's imagine it as an inflating balloon, inside which our universe is, outside-we don't know what. In principle, we understand the laws of physics that apply inside the ball, outside is… fuck knows what's in there, maybe there's nothing there. Suppose that we are on a spaceship approaching from the inside to the wall of the ball. To do this, we need to overcome the gravity of the entire universe! If this is possible, it is likely that we will asymptotically approach it for an infinite time.

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