And what, if dark matter - it's not the particles?
All we have ever observed in the universe, from matter to radiation, can be expanded to the smallest components. Everything in this world is made of atoms, which consist of electrons and nucleons and nucleons are divided into quark and gluons. Light also consists of particles: photons. Even gravitational waves, in theory, consist of gravitons: particles that we will one day, if we're lucky, we can find and fix. But that dark matter? Indirect proof of its existence can not be denied. But whether it should also be made of particles?
We used to assume that dark matter consists of particles, and desperately trying to find them. But what if we're not looking for something and not there?
If dark energy can be interpreted as the energy inherent in the fabric of space, could it be that the "dark matter" is also an internal function of the space itself - closely or distantly related to dark energy? And that instead of dark matter gravitational effects, which could explain our observations, there are more due to "dark mass"?
Well, for you a physicist Ethan Siegel sort through our theoretical approaches and possible scenarios.
One of the most interesting features of the universe is in a ratio of one-to-one relationship between the fact that there are in the universe, and how the expansion rate changes over time. Thanks to many careful measurements of many disparate sources - stars, galaxies, supernovas, the cosmic microwave background and the large-scale structures of the universe - we were able to measure both, defining what makes up the universe. In principle, there are many different ideas about which of our universe, and they all have different effects on the cosmic expansion may consist. Due to the information received, we now know that the universe is made of the following:
- 68% dark energy, which remains at a constant energy density even during the expansion space;
- 27% of dark matter, which shows the gravitational force, blurred with increasing volume and does not itself measured using any other known power;
- 4, 9% of ordinary matter, which exhibits all the forces blurred with increasing volume straying into lumps and consists of particles;
- 0, 1% neutrinos which exhibit gravitational and electroweak interaction consist of particles and stray together, only when slowing down enough to behave like matter, not radiation;
- 0, 01% of the photons that exhibit gravitational and electromagnetic effects, behave as radiation and eroded both by increasing the volume and tensile wavelengths.
With time, these various components are relatively more or less important, and this percentage is from what today is the universe.
Dark energy, according to the best of our measurements, has the same properties in every point in space, space in all directions and in all the episodes of our cosmic history. In other words, the dark energy is simultaneously homogeneous and isotropic: it is everywhere and always the same. As far as we can tell, dark energy does not need particles; it can easily be a property inherent in the fabric of space.
But dark matter is fundamentally different.
to form a structure that we see in the universe, especially in large cosmic scales, dark matter must not only exist, but also to gather together. She may not be the same density throughout the space; rather, it should be concentrated in high-density regions and should have a lower density, or absent, in the low-density regions. We can actually say how many agents are in different regions of space, guided by the observations. Here are the three most important ones: The power spectrum of matter. Map the matter in the universe, look at the extent to which it meets the galaxies - that is, how likely you will find another galaxy at a distance from one galaxy with which you start - and learn the result. If the universe consisted of a uniform material structure would be lubricated. If the universe was dark matter, which has not met early enough structure on a small scale it would be destroyed. Spectrum Power energy tells us that about 85% of matter in the universe represented by dark matter, which is very different from protons, neutrons, and electrons, and this dark matter is born cold, or else its kinetic energy is comparable to the rest mass.
The gravitational lensing. Take a look at the massive object. Suppose quasar galaxies or clusters of galaxies. See how the background light is distorted by the presence of the object. Because we understand the laws of gravity, which is regulated by Einstein's general theory of relativity, the way light bends, it allows us to determine how much mass there is in each object. By other means, we can determine the amount of weight that is present in ordinary matter:. Stars, gas, dust, black holes, plasma, etc. And we find again that 85% of the matter is represented by dark matter. Moreover, it has distributed more diffusely cloudy than ordinary matter. This is confirmed by the weak and strong lensing.
Cosmic microwave background. If you look at the rest of the glow of the Big Bang radiation, you will find that it is approximately even 2, 725 KBO all directions. But if you look closely, you may find that there are defects in the tiny scales of tens to hundreds of microkelvin. They tell us a few important things, including energy density of ordinary matter, dark matter and dark energy, but most importantly - they tell us how the universe was homogeneous, when she was only 0 and 003% of its current age. The answer is that the densest region was only 0, 01% denser than less dense region. In other words, beginning with dark matter and homogeneous state as time lost its flow into lumps.
Combining all of this, we conclude that dark matter should behave like a fluid that fills the universe. This liquid has negligible pressure and viscosity, is responsive to radiation pressure, it does not interfere with photons or ordinary matter, was born and cold nonrelativistic and bunch up under the action of gravity over time. It determines the formation of structures in the universe on the largest scales. It is highly heterogeneous, and the value of its heterogeneity increases with time.
Here's what we can say about it on a large scale, as they relate to observations. On a small scale, we can only speculate, without being fully sure what dark matter consists of particles with properties that cause it to behave in this way on a large scale. The reason that we assume is that the universe as we know, consists of particles in a profound way, and that's all. If you stuff if you have mass, the quantum analogue, you will inevitably have to be composed of particles at a certain level. But as long as we did not find this particle, we can not rule out other possibilities: for example, it is a kind of fluid field, which is not composed of particles, but the effect on space-time, as were the particles.
That is why it is important to attempt to direct detection of dark matter. To confirm or deny a fundamental component of the dark matter in theory it is impossible, but in practice, corroborating observations. Apparently, the dark matter has nothing to do with dark energy.
Whether it consists of particles? Until we find them, we can only guess. The universe behaves as quantum in nature, when it comes to any other form of matter, it is reasonable to assume that dark matter is the same.