The Dark Matter and Dark Energy

    Matter as we know it, atoms, stars, the galaxies, planets & trees, rocks and us, this matter accounts for less than 5% of the known universe, about 25% is dark matter and 70% dark energy, both of which are invisible. This is kind of strange because it suggests that everything we experience is really only tiny fraction of reality. We really have no clue that what dark matter and energy are or 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 calculate, what the universe is structured the way it is, it quickly became clear that it'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 all over the place and not form galaxies. So we know that there is something else inside and around them, something that doesn't emit or reflects light, something dark. But besides being able to calculate the existence of dark matter we can see it kind of. Places with a high concentration of dark matter bend light passing nearby. So, we know that something there that interacts with gravity. Right now we have more ideas about what dark energy is not, than what it is? We know dark matter is not just clouds of normal 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 they react with normal matter. Dark matter is also not made up of the black holes, very compact objects that violently affect their surrounding while dark matter seems to be scattered all over the place, basically we know we only know three things for sure:-

(1) Something is out there. 

(2) It interacts with gravity 

(3) There is a lot of it... 

    Dark matter is probably made up of a complicated exotic particle that doesn’t interact with light & matter in a way we expect, but right now, we just don't know. Dark energy is even more strange & mysterious. We can’t detect it, we can’t measure it & we can’t taste it. But we do see, it affects, very clearly. In 1929, Edvin Hubble examined how the wavelength of light emitted by distant galaxies shifts to more thread end of the electromagnetic spectrum as it travels through space. He found it later that more distant galaxies showed a large degree of red-shifts, 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 have shown that the expansion of the universe is accelerating. Before that, it was thought the pull of gravity would cause the expansion to either slow down or even retract and collapse in itself at some point. 

    Space does not change its properties as it expands, there is just more of it. Galaxies are tight bound clusters of stuff held together by gravity so we don't experience this expansion around us in our daily life but we see it everywhere around us. Wherever there is empty space in the universe,  more is forming every second. So, dark energy seems to be some kind of energy intrinsic to empty space, energy that is stronger than anything else we know and it keeps getting stronger as time passes by. Empty space has more energy than everything else in the universe combined. 

    We have multiple ideas about what dark energy might be. One idea is that the dark energy is not a thing but just a property of space. Empty space is not nothing, it has its own energy. It can generate more space and is quiet active. So as the universe expands, it could be that just more and more space appears through the gaps and this leads to a faster expanding universe. This idea is close to an idea that Einstein had back in 1917 over concept of a cosmological constant, the only problem is that when we try to calculate the amount of this energy, the result was so long and it only added to the confusion. Another idea is that empty space is actually full of temporary virtual particles that spontaneously and continuously form from nothing and then disappear into nothing. The energy from these particles could be dark energy, or maybe dark energy is an unknown kind of dynamic energy, fluid or field which permits the entire universe but somehow has the opposite effect on universe than the normal energy or matter. So, there are still a lot of questions but if it exists, we don't know how, where or how we could detect it to answer. Our theory is about dark matter and dark energy are still just theories. On one hand, this is kind of frustrating, on the other hand this exciting.

    Our presence in universe is just like we are on a tiny fragile island in space looking into the sky, wondering how our universe works.

    There is so much left to learn and that is awesome.