How do we recognize dark energy radiation

Quintessence and Dark Energy

In addition to the 4 elements of the ancient Greeks, fire, water, earth and air, there should have been a "fifth essence" that ruled the moon and stars. Today we are looking for dark energy as the modern quintessence ...

Supernovae of the type SN Ia are used by astronomers as so-called standard candles for determining distances. These star explosions always begin with almost the same absolute brightness at the outbreak. Once you have determined the exact distance to such a (relatively close) event using other methods, you can easily deduce distant objects. Because the brightness can be measured very precisely and you can get exact distance information. Another way to determine the distance of a glowing object is to use the redshift caused by the expansion of the universe z of light. The redshift of a certain spectral line from e.g. z = 1.0 corresponds to a shift of 100% to the red end of the spectrum.

In 1997, the Hubble telescope detected the most distant supernova of the type SN Ia. It showed a redshift of z = 1.7 which corresponds to a distance of 10 billion light years. However, their measured brightness was far too low. That could only mean that it is further away than it should actually be due to the redshift! In the right picture you can see the supernova as a digital difference of temporally separated recordings.

Courtesy Adam Riess (STScI) et al., NASA

These differences in the distance determinations meant a bitter pill for the cosmologists, as they only allowed one conclusion: the expansion of the universe is accelerating! Distant objects escape faster than previous models have predicted. There are now dozens of Type Ia supernovae at redshifts of z> 1.0 can measure and always got the same result. They were always fainter!

So there has to be some force that is accelerating the expansion of the universe. The ancient Greeks introduced a fifth to the four elements they knew, fire, water, earth and air, which held the moon and stars together and named it Quintessence (∼ the fifth essence). Today it is used to describe this mysterious, anti-gravitational force. Because it can neither be seen nor proven in any way, it is analogous to dark matter too Dark energy called. This could even be identical to the energy of the vacuum and / or the Einsteinian Cosmological constant (with the label ).

Certainly some objections to the observations of the distant supernovae are justified: The light of these objects could be weakened by intergalactic dust. It would also be conceivable that the explosions in distant supernovae proceed differently than in the nearby ones. However, this is contradicted by the fact that white dwarfs, the triggers of the supernovae of the type SN Ia, can only exist in a very narrow mass range. This means that only a certain amount of material can flow over onto them from a companion until a core explosion occurs on their surface. Therefore to have Supernovae SN Ia always have the same brightness and we can clearly identify them based on their light curves. For this reason, most cosmologists today are convinced of the correctness of the observations and thus of the accelerated expanding cosmos. You are now faced with the truly not easy task of delivering a physical explanation of the quintessence.

Here you can see more supernovae from 1998 that initiated the turnaround in modern cosmology. Despite some skeptics, it is now of the opinion that our universe not only contains large amounts of dark matter, but is actually flooded by the mysterious dark energy. The proportion of visible matter in the form of stars and gas clouds is just 4%, dark matter already makes up 23% of the universe, while dark energy makes up the lion's share of 73%!

Courtesy of High-Z Supernova Search Team, HST, NASA

When Einstein turned to cosmology in 1917, he recognized from his field equations that the universe should actually contract in the long term due to the gravity of the matter it contains. At that time, however, people were firmly convinced of a static, unchangeable universe, and so he added the famous one to his equations Cosmological constant added. It represented a vacuum force with an antigravity effect (see also negative energy), which prevented the gravitational collapse of the universe. In 1930 Edwin Hubble discovered the galaxy escape and that we live in an expanding cosmos. Now the cosmological constant was superfluous, Einstein removed it from his equations and referred to it himself as "the biggest donkey of my life". Nevertheless, Einstein's constant is on everyone's lips again today, perhaps to find an explanation for the accelerated expansion in it.

Paul Steinhardt, who predicted an accelerated expanding universe as early as 1995 (!), Thinks that the problem of the cosmological constant is that it is a constant. Their size is therefore unchangeable. The quintessence, on the other hand, encompasses an abundance of possibilities. It is dynamic, develops over time and represents a form of energy with negative pressure that accelerates the expansion more and more. It is imagined as a quantum field with kinetic and potential energy. The quintessence arose with the big bang, but it was just the beginning switched onwhen, after 380,000 years, the radiation-dominated cosmos changed into a matter-dominated universe. The accelerating power of dark energy did not develop noticeably, however, only after 10 billion years.

But what is this quintessence, what is dark energy made of? Nobody knows. All known manifestations of energy, radiation, normal or even dark matter, exert a positive pressure and thus have a gravitationally attractive effect. So there has to be something out there that is putting negative pressure on our space. According to Steinhardt's view, the quintessence could interact with matter and develop further the longer it is in contact with it. It could also be that at some point, when the density of matter in the cosmos is only low due to the expansion, it will disintegrate into completely new forms of hot matter or radiation and thus lose its negative pressure. We would then no longer be condemned to live in an eternally expanding universe, the cosmic expansion would one day come to a standstill. According to recent considerations, the dark energy could even come off Gravitational waves exist that arose in the early cosmos. If that were to be the case, the scientists' unsatisfactory need for explanations would come to an end. Various experiments are running (or are still being developed) around the world to prove the previously only theoretical gravitational waves.

Astronomers and cosmologists are fascinated by this new quintessential phenomenon. We cannot take them in our hands and examine them, we are not even able to produce them in the laboratory and we have no idea what is behind their veil. However, the scientists take this phenomenon very seriously and want to try to find out more details about dark energy through long-term observations. Such is a project called SNAP, S.greatNova A.cceleration Project, planned to go into space before 2020. Here a satellite with a 2 m telescope is specially set up to detect and examine more than 2000 supernovae that are far away every year.

Meanwhile, various missions were in action, in addition to WMAP, Wilkinson Microwave Anisotropy Probe as a descendant of the Compton satellites WMAP was able to recognize the finest ripples in the cosmic microwave background. This background is a holdover from the universe when it became transparent at 380,000 years of age. The Planck mission carried out from 2009 to 2013 then carried out further refined measurements of the background radiation. With these instruments we have been able to answer many questions so far, e.g. that we live in an open universe with Euclidean geometry and that the proportion of dark energy is 72% of the total content of our universe. But we don't yet know what the quintessence is, whether it exists or just one cosmic error is. The graphic shows a comparison of the results of the missions mentioned above.

What looks like a crazy pattern here is the cosmic background of the microwave radiation. The finest ripples in the temperature, which are amplified and shown as differences in color, are now also convincing those skeptics who have so far lacked the evidence. Our universe is stranger than ever thought, filled with dark matter and dark energy. We are seeing the oldest objects in the universe here, just when it was 380,000 years old.

Courtesy of Very Small Array Collaboration, Tenerife