A strange form of viscous dark matter, which accounts for most of the matter in the Universe, could have an amazing effect on early evolution — and to make sure that the ripples from the Big Bang would be detected. It is known that dark matter is a mysterious substance which makes up 80% of matter in our world, but it interacts with ordinary matter only gravitationally. At the moment the most popular candidate for the dark matter consider wimpy (WIMP), weakly interacting massive particles, but decades of this particle searches in what have not resulted. WIMP also predict specific things which we do not see in the Universe, like a swarm of mini-galaxies around the milky Way.
There are other candidates for dark matter. For example, Paul Shapiro from the University of Texas at Austin and his colleagues previously examined one alternative form of dark matter which consists of particles called bosons, which — unlike winow and ordinary matter — can be in one quantum state. This property may also allow them to stick together in a strange, viscous state of matter — condensate Bose — Einstein (BEC), in which the population of particles behaves as a single quantum object.
Now Shapiro and his graduate student Lee Buch studying how this form of dark matter could affect the early Universe.
Growth spurt
Cosmologists used to believe that in the first moments of its existence, the universe experienced an exponential growth spurt. This is the extension that was leaking chips in the first seconds after the Big Bang, called inflation, should send ripples through relativistic space-time — primary (or primitive, call it what you want) gravitational waves.
Physicists thought that they see evidence of these waves, when I was working with the BICEP2 telescope in 2013, but it turned out that it is not. But at the beginning of this year, the LIGO experiment saw gravitational waves colliding black holes than proved that such waves do exist.
In the standard picture of these primary gravitational waves must be so small that LIGO will never see them. “Our model is something completely different,” says Shapiro. — Dark matter changes its behavior, if we go back in time”.
Although viscous dark matter behaves exactly the same as wimpy in our time, the calculations of scientists show that in the early stages of her behavior changed: she acted not as a substance, like radiation. Moving even further back in time, dark matter was denser and behaved like a liquid, resisting the compression.
“Trying to break her, we need to keep in mind the pressure,” says Shapiro. — When you collect it in a pile, she wants to swell back. We fill the Universe like a fluid.
Scientists didn’t expect to find such.
This elasticity means that this strange viscous dark matter could slow the pace of expansion of the Universe in those days. Starting with the end of inflation the universe would have expanded much more slowly from dark matter than without it.
But the primary gravitational wave were to sweep the young Universe with the same speed as before. And because they are more imprinted on the background, they may be easier to detect.
Primary wave
In the report of the meeting of the American physical society in salt lake city, Utah, last month, a pair of scientists said that dark matter could suppress the expansion is sufficiently below the primary gravity waves could be detected by LIGO.
“In the standard history, without dark matter, they will be far below the limit where the gravitational wave detectors, modern or future, will be able to find them. But our model shows that hope is still there”.
Tanya Redinbo from the LIGO team indicates that since we do not know much about what the early universe was, to speak with certainty about this possibility is impossible. In her opinion, there is no guarantee that these waves exist or that they will be able to see our future detectors. But this work is interesting in that provides this capability.
Viscous dark matter would slow the expansion of the Universe
Ilya Hel