Dark Matter and Dark Energy
Matter, as we know it: atoms, stars, galaxies, planets, trees, rocks, and us. The known matter accounts for about 5% of the universe. About 25% is dark matter, and about 70% is dark energy. Both of them are invisible. This is totally strange because it suggests that everything we experience is only a tiny fraction of reality. But it gets worse. We have no clue what dark matter and energy really are. We don’t even know how they work. We are pretty sure they exist, though. So, what do we know?
Dark matter is the stuff that makes it possible for galaxies to exist. When we calculated why the universe is structured the way it is, it became clear that there’s just not enough normal matter. The gravity of the visible matter is not strong enough to form galaxies and complex structures. The stars would more likely be scattered around aimlessly. So, we know that there is something around and inside them. Something that doesn’t emit or reflect light. Something… dark. But, besides being able to calculate the existence of dark matter, we can kind of see it by observing how energy travels. Places with a high concentration of dark matter bend the light passing by. So, we know something is there, interacting with gravity. Right now, we have more ideas about what dark matter is not than what it is.
We know that dark matter cannot be normal clouds of matter without stars, because it would emit particles we could detect. Dark matter is not anti-matter because anti-matter produces unique gamma rays when it reacts with normal matter. Dark matter is not made up of black holes because black holes are matter gathered around one vortex. Dark matter is just scattered around. Basically, we only know three things for sure:
Something is out there.
It interacts with gravity.
There is a lot of it.
Dark matter is probably made up of a complicated exotic particle that doesn’t interact with light and matter in the way we would expect. But right now, we just don’t know.
Dark energy is even more mysterious than dark matter. We can’t detect it, measure it, or even taste it. But we do see its effects very clearly. In 1929, Edward Hubble examined the wavelength of light emitted by distant galaxies. He found that fainter, more distant galaxies showed a large degree of red shift. Closer galaxies? Not so much.
Hubble determined that this was because the universe itself is expanding. The red shift occurs because the wavelengths of light are stretched as the universe expands. More recent discoveries show that the expansion is accelerating. Before, it was thought that the pull of gravity would cause the expansion to slow down, or even make the universe collapse upon itself (glad that didn’t happen). Space doesn’t change its properties as it expands; there’s just more of it. New space is constantly created everywhere. Galaxies are tight-bound clusters of stars that are held together by gravity, so we do not experience this in daily life. But, wherever there is empty space in the universe, more is forming every second. So, dark energy seems to be some kind of energy that is intrinsic to empty space. Energy that is stronger than anything else we know, and keeps getting stronger. Empty space is stronger than the rest of the universe combined.
We have multiple ideas about what dark energy might be. One idea is that dark energy is not a thing, but a property of space. Empty space is not nothing; it has its own energy. It can generate more energy and is quite active. So, as the universe expands, it could just be that more space appears to fill the gaps, and this leads to a faster-expanding universe. This idea is similar to an idea Einstein had back in 1917, about a concept of a cosmological constant: a force that counteracted gravity. The only problem is, when we tried to calculate the amount of energy, the result was so wrong and weird that it only added to the confusion.
Another idea is that empty space is actually full of temporary, virtual particles that continually form from nothing, and then disappear into nothing again. The energy from those particles could be dark energy. Or maybe dark energy is an unknown kind of dynamic energy fluid or field which permeates the entire universe, but has the opposite effect than normal energy. But if it exists, we do not know how or where to detect it. So, there are still a lot of questions to answer. Our theories about dark energy and matter are just… theories. On one hand, this is frustrating while on the other, it is exciting.
No matter how much we feel that we’re on top of things, we are just some complex beings on a fragile island, looking up at the sky and wondering how our universe works.