# How would the universe sound like if

## Astrophysicist Nicolai on the beginning of the universe : "We are so unimaginably insignificant"

Mr. Nicolai, I would like to speak to you about the birth of the universe. What does physics know about it?

In fact, we still do not know what happened at the moment of the birth. However, we can determine the date relatively precisely. The universe is around 13.7 billion years old and was probably created in a kind of big bang. Whereby you shouldn't imagine it like a normal explosion, because it wasn't something in an existing space that exploded, but space and time themselves were created in the process.

How do you come up with such an idea?

The astronomer Edwin Hubble discovered 90 years ago that the stars move away from us and the faster the further away they are. Since then, Hubble’s law has been confirmed more and more precisely. And if something drifts apart, then you can calculate the movement of the fractions back to the beginning.

What do you need for that?

A lot of math, anyway. But the continuously improved measurement methods are just as important. Observing the sky was at the beginning of astronomy. Of course, Galileo only saw what we can see with our eyes with his telescope. Visible light corresponds to only a very small part of the spectrum of electromagnetic waves. Today we have instruments with which we can “see” the very short waves - that is, ultraviolet light, X-rays, gamma rays - and also the long ones, that is, infrared. With this we can look up to the horizon of the universe, i.e. the most distant point from which light has come to us up to now. We can only speculate about what lies behind it. Or we wait a billion years, then we can look a little further.

How do you know if something is moving away?

By the so-called redshift, a kind of Doppler effect. Everyone knows who has heard an ambulance drive by. If the car comes towards you, the siren sounds higher because the sound waves compress and thus become shorter. If the car drives away from you, the siren tone is lower because the sound waves spread apart. It's similar with light. When an object moves away from me, the waves are pulled apart and the light appears redder. A galaxy approaching us would appear bluer than it is.

If you can see that everything is moving away and also know since when, shouldn't you be able to calculate the location of the Big Bang, i.e. the center of the universe?

A basic assumption of cosmology is the so-called cosmological principle, which was introduced by Einstein. According to this, the universe looks the same from every point and in all directions. There is no center there.

To get a clear idea of ​​it, we have to reduce the picture by one dimension: If we imagine our four-dimensional universe, which extends not only into space but also into time, as a balloon in three-dimensional space, then we are sitting we are not in the center of the balloon and the stars on the surface, but we are all together two-dimensionally on the surface - like ants crawling around there, and each of whom can imagine that they are in the center of this balloon universe.

So nothing with humanity as the crown and center of creation?

We are as unimaginably insignificant as the universe is unimaginably large. The Voyager probe, which was launched in 1977, flies through space at 17,000 meters per second and is now just at the edge of the solar system after 40 years. The closest star to us is Alpha Centauri, four light years away, a stone's throw away on a cosmic scale. With every realistically conceivable technology it would take at least 30,000 years. And here on earth we also have completely wrong ideas about which matter dominates in space. 74 percent of the visible matter in the cosmos - let's leave the dark aside - is hydrogen and 24 percent helium. The heavier elements that we mostly find here on earth and of which we are made come from the remaining two percent. But all of this is overwhelmed by dark matter, which is five times as much as there is visible matter.

What did the cosmos look like at the time of the Big Bang?

Extremely dense and unimaginably hot, it has been cooling down ever since.

And how big was he?

Extremely tiny, much smaller than a proton. Even so, we understand a lot about what happened right after the Big Bang. Like the primordial soup of elementary particles, protons and neutrons, the atoms were created, then the elements. And thanks to the neutron star collision demonstrated a few weeks ago with gravitational waves, we now also know how the heavy elements beyond iron, such as gold and platinum, are formed. For example, the amount of gold created in this collision is equivalent to a lump the size of the planet Jupiter.

Oh, that would drive the price down a lot.

Investors don't need to worry about that. No human or robot would survive gold mining near a neutron star.