What does the universe mean flat

The universe is flat and full of "dark energy"

In the late 1990s, astronomers found that the expansion of the universe was accelerating. For some reason a mysterious force seems to be driving the cosmos apart faster and faster against gravity, which was supposed to slow down the expansion of the universe. The scientists called this force "dark energy" so that the child would at least have a name.

Even if cosmologists still lack a deeper understanding of this "dark energy", it should actually exist, as has been shown by various measurements in the past. Now, independently of previous investigations, two French scientists have provided another indication of the existence of this force. The researchers took a closer look at pairs of distant galaxies and determined the effects of cosmological parameters on the appearance of these galaxies.

Redshift in the expanding universe

In order to determine the exact position of a galaxy in space, a lot of effort is necessary, because there are no clear "landmarks" to orientate oneself. Astronomers determine the extent of the so-called redshift of the radiation emitted by the respective object. The redshift in turn results from the expansion of the cosmos. It follows from this: The further away a galaxy is from Earth, the more the spectrum of its radiation is shifted in the direction of red.

The reconstruction of the galaxy's whereabouts is ultimately based on some assumptions about the nature of the space in between. The curvature of the space plays a role because it has a significant influence on the rules of geometry: in a positively curved cosmos (like a spherical surface) the sum of the interior angles of a hypothetical triangle in space is over 180 degrees, in a negatively curved space it is less than 180 degrees. The rules of classical geometry only apply in a "flat" universe.

Uncurved space

Now the two French cosmologists Christian Marinoni and Adeline Buzzi from the Center de Physique Théorique at the Université de Provence in Marseille, while investigating the redshift and the orientation of galaxy pairs, have found that the universe must firstly be flat and secondly the "dark energy" unites has significant influence in the universe. The basic assumption of the two researchers was that the orientation of two galaxies is purely random and has no preferred direction. So that this randomness in the orientation can also be brought into line with their actual observations, the cosmologists calculated that the universe cannot exhibit any curvature as it is in the specialist journal Nature expound.

Einstein's donkey

Furthermore, the assumption of randomly distributed alignment only fits if "dark energy" makes up about three quarters of the total mass-energy content of the universe. The results of the two scientists indicate that the energy density of the universe is around the value at which space-time neither bends in itself nor unfolds outward. Incidentally, the results of the investigations coincide with Albert Einstein's cosmological constant, which the physicist said was his greatest donkey - maybe it was a stroke of genius after all ... (red)