Cosmic background radiation (CMB) provides passport photo of early universe
Is there a fifth fundamental force? What role did "dark energy" at the Big Bang? The cosmological models can be tested with the help of the measurement results of the WMAP satellite (anisotropy of the background radiation). New calculations suggest that dark energy may have contributed very little to the evolution of the early universe.
Since 1998 cosmologists have a problem: Instead of slowing down its expansion under the influence of its own gravity, the universe has been growing faster and faster for several billion years – this was suggested by observations of very distant supernovae. In addition to the known four basic forces gravitation, electromagnetism, weak nuclear force, strong nuclear force, therefore a fifth, abstracting force (the quintessence) is postulated, which is supposed to counteract gravitation – a possibility, which already Einstein called the "cosmological constant" in his theory of the expanding universe. The field energy of the fifth force is the so-called "dark energy" (cf. The universe is full of dark energy).
Three phases in the formation of the cosmos: the primordial soup just after the Big Bang, the decoupling of background radiation from matter, the present Images: NASA
The royal road to statements about the first seconds and minutes after the Big Bang is the determination of the abundances of the very first atomic nuclei, which were formed during the cooling of the billion degree hot, super dense early universe, in the Big Bang Nucleosynthesis (BBN)
The initially free baryons (protons and neutrons) of the primordial soup combined primarily to form helium-4 (nucleus with 2 protons, 2 neutrons) but also helium-3 (2P, 1N), deuterium (1P, 1N) and lithium (3P, 3N). However, the largest part of the matter was hydrogen (1P). The astrophysicists have unfortunately the "curse of late birth"They are dependent on determining the elemental abundances today and must hope to find matter that has not changed since the big bang or to be able to. to reconstruct the changes and to calculate them out. In spite of this limitation the model of the BBN is consistent and well confirmed (76% hydrogen, 24% helium-4, the other elements or isotopes in traces). isotopes in traces).
One of many ways of nucleosynthesis: deuterium is turned into helium-4 in two steps
Since February 2003 a new access opens: the Meng of the anisotropy of the cosmic background radiation (CMB) by the WMAP probe of the NASA. The CMB is a black body radiation (today at T = 2.73 Kelvin) and gives direct information about density, temperature and homogeneity of the universe 380.000 years after the big bang, when atomic nuclei and electrons combined to form neutral atoms. WMAP found smallest variations of the radiation temperature with an accuracy of 1 millionth Kelvin. The circumstances in the first minutes, the time of the BBN, can be derived from this. The predictions of elemental abundance obtained in this way are consistent with earlier observations and are much more accurate.
This is how WMAP sees the background radiation: the small irregularities are the highlight
At the University of Illinois, astrophysicist Brian D. Fields drew the consequences for the dark energy:
As much as it may dominate today, dark energy can have represented only a very small fraction of the total energy of the cosmos during the first seconds and minutes.
The estimation results from the fact that the presence of dark energy influenced the BBN and led to the formation of more light elements. Cosmologists who want to save dark energy will have to find a way to eliminate this influence "off" – or maybe to change the quintessence theory?