The mystery of dark energy

Currently dark energy is an overwhelming component in the universe (70% versus 25% dark matter and 5% ordinary matter), dark energy is making the universe expand with acceleration.

But what is the dark energy nature? There is currently no single answer. Here is an article on this issue by two authors Adam G.Riess (Johns Hopkins University - Nobel Prize for Physics in 2011 for discovering the rapid expansion of the universe) and Mario Livio (Hubble Space Telescope - operative The famous book Brilliant Blunders: From Darwin to Einstein: Colossal Mistakes by Great Scientists) published in Scientific American magazine, March 3/2016.

Why does the universe expand with acceleration? After two decades, that question remains a mystery even though some things have been further elucidated. According to physicists, the universe is expanding because of dark energy. But what is dark energy? Why is dark energy so small compared to the theories about it? How does dark energy affect the future of the universe? And in the end, are the dark energy characteristics of our universe random? If those characteristics are random, does that mean that our universe is just one of many other universes with many different dark energy features? The following are three key hypotheses to answer the above questions.

How does dark energy affect the future of the universe?

Three hypotheses about dark energy

1. The first hypothesis

The first hypothesis is associated with the vacuum of space . In vacuum, virtual pairs of particles give birth and cancel each other continuously in a snap. The vacuum contains the same energy and energy as the gravitational mass, but different from the mass, dark energy can cause repulsion or attraction depending on the pressure being negative or positive. In theory, the pressure of dark energy must be negative and that is the origin of the accelerated expansion of the universe. The idea in this hypothesis is equivalent to the idea of "m - cosmological cosmological constant. Einstein's constant λ " . In that idea, the density of dark energy is constant (space) in space and time.

Figure 1. The cosmological constant hypothesis.

Now when it is estimated that the total dark energy according to the quantum states of the vacuum of the universal universe, a value greater than the observed value of 120 steps is obtained. If introduced into supersymmetry, the theoretical value is still higher than the observation value by 10 steps. So if you explain dark energy with vacuum energy, why is dark energy observed so small?

According to this hypothesis, the universe will expand forever, making the galaxies move further away and become more and more difficult to observe. And even the CMB (Cosmic Microwave Background) will also spread so the wavelengths will gradually become larger than the size of the observed area and therefore they become difficult to measure. We are lucky at the time when we recorded CMB.

Dark energy has a small observation value. Physicists have come up with the idea that this observation value is random among many values ​​that belong to the other universes of a multiverse. Steven Weinberg thinks we exist because we are in a universe with a small amount of dark energy. This idea was further developed by Alexander Vilenkin (Tuft University), Martin Rees (Cambridge University), Mario Livio and called anthropic principle.

Vilenkin and Andrei Linde (Stanford University) argue that cosmic inflation once happened, continues forever and creates many separate bubbles with different characteristics and properties. The multiverse hypothesis is also a consequence of string theory (LTD).

Raphael Rousso and Joseph Polchinski in M ​​theory (extension of LTD) suggest that there are 10500 universes with different characteristics and even with different dimensions. The authors of this article (Riess & Livio) also claim that CMB may contain many wrinkles resulting from the collision of our universe with other universes.

2. The second hypothesis

The second hypothesis is associated with a "quintessence" that permeates the universe and creates a repulsive force. Physicists are used to the concept of this form - similar to in electrodynamics or in gravitation - it is a field. If dark energy is a field, that field changes in space and time. In this case dark energy may be stronger or weaker than it is today and may affect different universes at different times. Thus dark energy can affect the future universe in many different directions.

In this hypothesis theorists assume that the minimum potential energy relative to dark energy is so low that only a small fraction of dark energy spills out into space, but they also assume that this field is very interactive. less with everything else (except attractive propulsion).

Figure 2. The dark energy hypothesis is a field.

Two possible options for the distant future of the universe: Big Crunch, Big Crunch (Big Crunch). In this hypothesis, the future of the universe depends on the variable the paradise of this hypothetical field: the universe can advance to a Big Tears - everything in the universe apart from each other as if torn apart - or stop expanding and reach a Department Big Crunch is a big point about the point of Big Bang. In the first possibility the universe is called falling into a cold death.

3. The third hypothesis

In the third hypothesis there is no energy at all. Accelerated expansion may suggest that Einstein's theory is inadequate for large areas of the universe. But there is currently no theory that corrects Einstein's theory at large dimensions in the universe.

Figure 3. No energy at all.Need to correct Einstein theory.Find the answer.

The best path to the answer is to measure the ratio w = pressure ratio on density - which is a characteristic of the so-called equation of state parameter . If dark energy is vacuum (cosmological constant) then w = constant = -1.

If dark energy is associated with a time-varying field, then w ≠ - 1 and progress according to the history of the universe.

If it is the case that Einstein's theory should be changed at large dimensions, we will see inconsistency in the value of w in different dimensions of the universe.

By studying the formation and growth of galaxy clusters, physicists can imagine how dark energy has changed at times of cosmic history. Using gravitational lensing we can know the mass of galaxy clusters and when studying that effect at many distances we can imagine the growth of galactic clusters in many time.

We can also study the expansion rate of the universe over time thanks to the redshift effect of light from galaxies.

Figure 4. Dark energy density over time.

Currently most of the observed data for the value w = - 1 with an error of about 10% and so it seems that hypothesis 1 on the cosmological constant seems to be true in the present. Riess with the Hubble space telescope has studied dark energy in the past about 10 billion years (using supernovae) and found that there is no special variation of w. However, recently a combination of CMB measurements (from Planck satellites) with gravitational lens results shows that the negative w is more than - 1. Many other results also show that w has change. But later results need to be re-verified.

Many projects have begun, such as DES (Dark Energy Survey), LSST (Large Synoptic Survey Telescope), WFIRST-AFTA (NASA's Wide Field Infrared Survey Telescope-Astrophysics Focused Telescope Assets), which is aimed at finding more accuracy of treatment. number w.

In addition, many experiments have now been conducted in the hope of finding differences with Einstein's theory (in large sizes).

Therefore, the following years will be hinged years for dark energy research and it is hoped that it will bring many answers to the mystery of dark energy and from that visualize the future of the universe.