The Quantum Universe

Quantum fluctuations played a crucial role in the formation of the structure of our universe.

  • Viatcheslav F. Mukhanov
  • 09 / 2015 Seite: 41

On March 21, 2013 something very remarkable happened. The Planck science team released a highly precise photograph of our universe when it was only few hundred thousand years old. This photograph is so detailed that it shows some major features that the universe acquired only 10–35 seconds after creation. Most strikingly, the observed nontrivial features in the portrait of such a young universe came in exact agreement with what had been predicted by the theorists more than thirty years ago, long before the experiment was carried out. Without any exaggeration one can say that by now it is experimentally proven that quantum physics, which is normally considered to be relevant in atomic and smaller scales, also played the crucial role in determining the structure of the whole universe, including the galaxies, stars and planets.

Of course scientists and philosophers have always been interested in the origin of our universe. However, cosmology only became a natural science less than a hundred years ago. It was not until 1923 that the American astronomer Edwin Hubble was able to resolve individual stars in the Andromeda Nebula and to conclude that for sure it is located outside of our own galaxy. This was the beginning of extragalactic astronomy. Today it is well established that there are about a hundred billion galaxies in our universe. Thus, the stars form galaxies with a size of about a hundred thousand light years. Moreover, the distance between neighboring galaxies is a few million light years. Observing the spectral lines of the galaxies, Hubble discovered that they are slightly redshifted. He interpreted this as a Doppler shift due to the relative motion of the other galaxies, which try to escape from us. Hubble also found that the spectral lines of galaxies further away show higher redshift. This means that they are escaping with higher velocities, proportional to the distance (v  = H r) and thus the universe expands. This discovery was the beginning of scientific cosmology. 

With Hubble’s discovery it became clear that our universe is evolving as a whole. This did not come as a big surprise! In 1922 the Russian physicist Alexander Fried­man had found that the generic solutions of the Einstein’s equations describe either an expanding or a contracting Universe. Assuming that the total mass of the universe is about a hundred billion times larger than the mass of our galaxy, Friedman was even able to conclude that the universe must be about 10 billion years old. Thus, Hubble’s discovery can be considered as a brilliant confirmation of the theoretical prediction by Friedman. The most important conclusion from Hubble’s discovery was that the universe was created about several billions years ago. This extremely important discovery remained for many years the single experimentally established fact in cosmology. Only after more than thirty years the other piece of the puzzle was discovered. ...

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