How is the observable universe represented

Podcast How big is the universe really?

About 100 years ago we thought our Milky Way, our galaxy was the universe. We can now observe billions of galaxies. Only in the past few decades has the development progressed so far that the question of the size of the universe is answered with measurements.

The edge of our universe is currently defined at a distance of 13.819 billion light years. That is how far the best telescopes go. A light year is about 10 trillion kilometers. So people can see almost 140 trillion kilometers into space. According to the current model of our universe, this edge is equally far away in every direction. This also makes it clear which optical field of vision is available to us from the universe, says astrophysicist Hendrik Hildebrandt, professor at Ruhr University Bochum.

The observable universe is a sphere - a sphere with a radius of 13.8 billion light years.

Professor at Ruhr University BochumHendrik Hildebrandt

Measuring in the universe is an adventure

But not only the human range of vision has a limit, but also the point of view - i.e. how we see the universe. Because of the slowness of the light we see what happens in distant galaxies only with a great time delay. "So we see galaxies that are a billion light-years away as they were a billion years ago," says Hildebrand, describing the fascination and also the tragedy of cosmology:

That means I can't look at the universe as a whole.

Hendrik Hildebrandt astrophysicist

Can only look into the past

The cosmologists would only ever see excerpts from the past. That also means: where the edge is for us today, at a distance of 13.8 billion light years, there was once the edge, over 13 billion years ago. So the real universe would have to be much bigger. Because when we look out into space, we know from our modern measurements that it is flying apart at unbelievable speed.

"And this expansion is added to the age of the universe, so to speak," says Professor Hendrik Hildebrandt. The radius of the universe is not only 13.8 billion light years. But you can figure out where this edge should currently be. "If we could put a tape measure on the universe, we would now measure a radius of 46 billion light years." And if you have been careful with geometry, you know that the universe is over 90 billion light years from one end to the other - nowadays.