The universe gives back all things

Does the universe have a center?

Bit by bit, astronomy has turned our blue planet from the center of the cosmos to an insignificant speck of dust in the infinite expanse of space. In the ancient world view, the sun, moon, planets and stars initially circled the earth. In the heliocentric worldview, the sun then moved into the cosmic center. But today we know that the sun is only one of several hundred billion stars in the Milky Way that orbit the galactic center - and the Milky Way in turn is just one of countless galaxies in the universe.

Classic representation of the geocentric worldview

In the twenties of the last century, astronomers came across the strange finding that almost all galaxies seem to be moving away from us. And the greater the distance a galaxy is from us, the higher the "escape speed" with which the star system strives away from us.

So are we in a special place after all, in the center of the cosmos? Not at all! Every observer in the universe, no matter where he is, is presented with the same picture of the galaxy escape. Because the galaxies do not really move away from us - or from another observer - but it is the space itself that is expanding and thus increasing all the distances between the galaxies. Think raisins in a big raisin cake. As the cake rises, from every raisin's point of view all the other raisins seem to be disappearing.

Where did the big bang take place?

If one calculates the expansion of the universe back into the past, the universe must have started in an extremely dense state. According to current knowledge, this “Big Bang” took place 13.7 billion years ago. For laypeople, this often raises the question of where in the universe this big bang took place. But this question is based on the misconception of the Big Bang as an explosion in space in which matter flew away in all directions from one point. But with the Big Bang, not only matter was created, but also space and time. The matter does not expand into an already existing space, but rather together with the space. Strictly speaking, the Big Bang therefore took place in every place in today's cosmos.

Classic representation of the heliocentric worldview

So does the universe even have a center? Popular science depictions often use the example of an inflating balloon to demonstrate that our universe has no center. Flat inhabitants of the balloon surface would make observations very similar to ours: Their cosmos is expanding, but there is no excellent place on the balloon surface from which this expansion originates. Because the center of the balloon surface is inside the balloon, i.e. outside of the two-dimensional cosmos that can be observed by the surface dwellers.

So is our three-dimensional universe also curved into another dimension and is the center therefore also outside the cosmos that we can experience? So far, there have been no observations that support this idea: All measurements show that the universe is “flat”, meaning that it has no curvature. So the model of the balloon surface would not apply and there would be no four-dimensional center of the cosmos.

And beyond the horizon?

But we can probably only survey and measure a small part of the cosmos. If the universe was formed 13.7 billion years ago, the maximum light that can reach us is 13.7 billion light years ago. The parts of the cosmos from which the path of light to us is greater than the age of the world multiplied by the speed of light lie behind the cosmological horizon, unobservable for us. But if the universe is considerably larger than this area that we can observe - and there are many indications of this - then we cannot make any definitive statements about the physical state and topology of the universe as a whole - and thus also no definitive answer to the question after getting a center point of the universe. To stay with the balloon image: The balloon is so huge that we cannot see the curvature in the tiny area that we can overlook.