The only thing I know is that I know nothing, called it in the Socrates paradox. It is not really true. For example, we know a lot about the matter. You own and everything you see around you, your phone or the magazine you are reading now, and even all the universe of stars and planets, are all made up of atoms. And atoms, we know quite well.
But the matter of the atoms is only a very small part of the universe: less than five per cent. The other 95% we know nothing about.
the dark matter. It represents almost 27 percent of the universe. Thus, there are more than five times as much dark as regular matter. And it is everywhere: in us, on us and inside us. The entire Milky way is enveloped by an orb of dark matter.
But the dark matter is not visible, and we don’t know what it is. We only know that it must be, among other things, because the galaxies are much heavier than they appear to be. Anything solid that does not send out light keeps them together.
The dark matter must be composed of something entirely different than the particles we consist of. The hottest candidate called wimps, weak interacting massive particles, or heavy elementary particles which only know by very weak forces.
– There are particles that weigh about the same as the nucleus of an atom, and that can fly straight through everything, ” says Sebastian Baum, phd student in theoretical physics at Stockholm university.
several different methods to find particles of dark matter. At the large hadron COLLIDER at Cern in Geneva tries to physicists produce wimps or other dark matter particles. Space telescopes searching for the light that is created when wimps collide with each other and are destroyed. In underground tanks filled with liquid xenon (a noble gas) or other substances, scientists hope to be able to see traces of wimps that pass.
– You have a ton of liquid xenon, under a great mountain or far down in the soil, and look carefully at it for a year or so to hope to see a wimp colliding with a nucleus in real time. But so far no one has seen anything. We have tried this in almost 30 years, and the only way to improve the detectors is to build bigger and bigger tanks. Now we are up a ton, and there is a limit to how big the tanks can be, and an experiment can only hold on more than a few years, ” says Sebastian Baum.
in Stockholm, sweden, and Poland suggest he is now a completely different place to look for dark matter: in the old stones down in the bedrock.
– Our idea is to use something that has been keeping an eye out for a very, very long time, billions of years. The earth is only 4 billion years, so the oldest minerals is around 1 billion years old.
the Atoms in a mineral sits arranged in a pattern with fixed distance between each other. If a wimp collides with the nucleus of an atom can atom get a boost so that the father away a bit by kristallmönstret and unravels a trail of damage behind them. Even if it happened for a very long time ago is the track left behind as a memory, a fossil or a recording of the dark matter-particle, which once went by the stone. Such marks are possible to detect, says Sebastian Baum.
– And we don’t need tons of stone. It is enough with a bit of stone from the deep hole. Such cores are already available, from the studies made by geologists and oil companies, ” he says.
In an article in the journal Physical Review D describes Sebastian Baum and his colleagues Andrzej Drukier, Katherine Freese, Maciej Górski and Patrick Stengel how the ancient stones could be used as detectors for dark matter. Before the end of the year, they hope that it is possible to make the first small-scale experiments to show that the technology works. To find traces of wimps will take longer, and even longer before we have enough evidence that they are the elusive dark matter.
– There is something extraordinary, and requires extraordinary evidence. But we believe that it is possible to see dark matter in the bedrock, ” says Sebastian Baum.
Hobby-Eberly telescope in west Texas is one of the world’s largest optical telescope. Photo: Ethan Tweedie
a component to, in addition to matter and dark matter, we got to know only at the end of the 1990s. Two groups of astronomers discovered independently of each other that space expanded faster and faster, contrary to what everyone thought.
The driver of the expansion, and which constitutes 68% of the universe we call dark energy.
– But it may not be dark, and it may not be energy. It is just a name we have invented to describe our ignorance, ” says Karl Gebhardt, professor of astrophysics at the University of Texas in Austin.
He runs the experiment, Hetdex, Hobby-Eberly Telescope Dark Energy Experiment. The Hobby-Eberly telescope in west Texas, one of the world’s largest optical telescopes, Karl Gebhardt’s research group uses it to investigate how the expansion looked like when the universe was very young.
” We want to examine at least a million galaxies between nine and eleven billion light-years away. Since we’re in Texas, I must say that it is the biggest survey that has ever been made, ” he says.
the expansion has been during different eras in the universe’s history.
– We must know how fast the universe expanded for two billion years ago, five billion years ago, and so on and so forth to be able to identify the whole story, ” says Karl Gebhardt.
It is impossible to examine the entire night sky. Instead, the target Hetdex on a piece that is about as big as the big dipper, and studying galaxies at different distances.
the Area is also located at the big dipper. So I usually say that we finally get to know what it contains.
Different theories of dark energy makes different assumptions about how the expansionshastigheten has varied. Karl Gebhardt hopes to be able to exclude some of them and give support to others.
According to the current theory we should not find so much if we look so far back in time. But we want to check. Let us examine a new era and see if we can find an unexpected effect. I think it is so you learn the most, ” he says.
Perhaps, the explanation is anything other than dark energy.
– Our theories of gravationen have changed in the past. First came the Newton, and described it. Then came Einstein with a better theory, and showed that Newton was wrong. And now we know that Einstein’s theory does not, nor is it complete. In order to understand the universe, we may need to change the gravity again, ” says Karl Gebhardt.
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