Until 1929, American astronomer Edwin Hubble found that all galaxies were moving away from each other, and they were not static. Only by combining observation with relevant research can people realize that the universe is not eternal, and like everything on earth, the universe has a beginning and an end.
To explore the boundary of the universe, we should start with the observable universe. Because light plays the role of messenger in the universe, the speed of light is constant, so the distance between the earth and celestial bodies can be calculated by the time when light reaches the earth. For example, the distance between the earth and the moon is measured by laser.
For those exostars and galaxies, the astronomical community adopts spectral ranging, because the color of light on the surface of stars is not static, but will change with time.
Astronomers can calculate how much energy the stars have emitted since their birth according to their colors, and calculate their approximate distance from the earth by comparing the true brightness of the stars with the brightness difference from the earth.
The speed of light of 300,000 kilometers per second is not enough to transmit information to every corner of Hubble volume, so human beings will never see the whole picture of the universe. In addition, due to the superluminal expansion of space-time in the universe, the return speed of galaxies 65.438+0.45 billion light years away officially exceeds the speed of light, so galaxies beyond this distance are equivalent to losing contact with humans.
Today, 654.38+03.82 billion years after the birth of the universe, only 3% of the galaxies in the Hubble volume can be reached and touched by human civilization, and this proportion will continue to decline with the accelerated expansion of space in the future.
The Hubble volume with a diameter of 93 billion light-years is just the universe we can see at present, not the edge of the real universe. The universe is still expanding in a dark place that we can't see, and the expansion speed far exceeds the speed of light, so the universe has no boundaries, at least in the sense of observation.
Zooming in from the Hubble volume step by step, we will see this scene:
On the scale of billions to billions of light years, supercluster will become the node of the Great Wall of the Universe, and the network structure composed of billions of light years of the Great Wall of the Universe will be divided by nearly 70% of dark energy.
When the field of vision is reduced by 10 times, the distance is 65.438+0 billion light years, and the galaxies with dense centers begin to become clear. The Milky Way is located in the virgo supercluster in the Ranyakaya supercluster.
On the scale of 6.5438+0.8 million light years, local galaxy clusters and local galaxy clusters began to appear, and the basic outline of the Milky Way with a diameter of 6.5438+0.8 million light years can also be vaguely recognized.
On the scale of 1 million light years to 100,000 light years, the Milky Way will become the main body of vision, and our solar system is located on the spiral arm of Orion. On the scale of 10 light-year to 1 light-year, the sun will be in local bubbles with the surrounding stars, and the earth will be as small as dust further down on this scale.
The final shape of our universe is likely to be similar to that of the earth, belonging to a bounded sphere, specifically a closed four-dimensional hypersphere. So, just like a ship can't leave the earth, it can only keep returning to the origin. In the future, human beings will fly in one direction, and eventually they will return to the starting point with great probability, because human beings and spacecraft are three-dimensional objects.
Just like leaving the earth, you must use rockets to force in the other direction. In the future, if human beings want to jump out of the present three-dimensional universe and see the whole picture or boundary of the universe with their own eyes, they must first enter the four-dimensional space.
If the great unification theory studied by Einstein in his later years is successful, and if the four basic forces are really integrated into a framework and the inherent similarity of the universe is found, then perhaps human beings can really break through the constraints of dimensions and enter a high-dimensional space, and then see the real boundary shape of the universe.
It's a pity that Einstein didn't finish his theory until his death. What's more, until today, there has never been a physicist like Einstein in physics.