Dark matter and dark energy explained.
Dark matter and dark energy make up the vast majority of our universe, and yet we can’t really perceive them.
However, we have ways to perceive their influence, and it’s as wide-reaching as dark matter and energy are.
All matter as we know it, from muons, electrons and atoms all the way up to planets, stars and galactic clusters, makes up less than a meager 5% of everything in the universe.
As far we we know so far, roughly 25% is dark matter and 70% is dark energy. But the thing about those two massive chunks of everything are invisible. Basically, all that we perceive is only a very small part of reality.
To top it all off, we don’t REALLY understand what dark matter and dark energy are.
So where do we even get the idea of those two massive bits of craziness from?
When astrophysicists did the math to figure out how the universe was structured, it didn’t hold up. There just wasn’t enough visible matter in the universe to make it work. Taking all of the gravity generated by the matter we can see together is not enough to form the massive and complex forms we see throughout the universe: Without SOMETHING else to hold it all together, it looked like stars should just be scatter willy-nilly instead of ever clustering together to make galaxies.
That something has to be woven all around the visible matter. But it can’t be seen, never emitting or reflecting light…a.k.a. dark matter.
However, we can tell dark matter is there even if we can’t actually see it with telescopes. It does have a gravitational effect on spacetime. Light passing around these dark matter mega-clumps is actually bent.
At the same time, though, dark matter cannot be normal matter, because we WOULD be able to detect some kind of emissions if that were the case. It also doesn’t even react with normal matter. Antimatter makes gamma rays when it reacts with normal matter. Dark matter apparently does nothing.
But it’s THERE.
The most accepted possibility now is that dark matter is some kind of exotic particle that we simply don’t know anything about. Some possibilities for these particles could be GIMPs (gravitationally-interacting massive particles) and WIMPs (weakly-interacting massive particles). Perhaps it might be created in a particle accelerator experiment at some point, though we may not recognize it for what it is.
And then we have dark energy, which is, believe it or not, even stranger.
Just as with dark matter, we can’t truly detect or examine it, but we can see how dark energy effects the universe around it. This started with Edward Hubble in 1929 when he saw the redshifting of light wavelengths as he looked deeper and deeper into space: Distant (and therefore faint) galaxies showed a lot of redshift, while galaxies that were more visible and closer redshifted much less. This led to our understanding that the universe has always been expanding, which would stretch the wavelength of light as everything moved farther and farther apart.
Since then, research has demonstrated that this expansion has been accelerating. This throws out the ideas that we will see an eventual retraction leading to a “big crunch”. Currently, the belief is that space will just continue expanding until matter is basically stretched so thin that everything comes to a total standstill, even atomic movement — the “heat death of the universe” theory. Don’t let that get you down, though. We’re talking billions of years into the future.
So, as expansion goes on, the universe and all of space is essentially gaining in volume. Because we’re held together in a nice tidy bundle of stars called the Milky Way galaxy, the expansion doesn’t affect us directly, but we see other galaxies redshifting away from us just as we’re redshifting away from wherever the center of the universe is.
Whatever is propelling this expansion is what we call dark energy. It represents more energy than everything else taken together: all the stars, black holes, gas giants, quasars and everything else combined doesn’t come close to the sheer power dark energy represents.
As to what dark energy is, again, we can’t be certain. It may be some intrinsic property of space. As the universe expands, more space is created, thus pushing expansion further and further with ever-increasing acceleration.
Einstein’s “cosmological constant” concept from 1917 was similar. He proposed it as a force that countered gravity, but the mathematics didn’t produce any viable results and just confused things further. This is also known as “vacuum energy”, as in empty space is a vacuum.
Another possibility is that dark matter is made of spontaneously-forming particles that continuously pop up and disappear as new space forms, which in turn generates the dark energy. This continues on in a never-ending loop which keeps the expansion going.
Ultimately, dark matter and dark energy are key components of the universe’s make-up that are currently beyond our technological ability to understand. However, unlike the mystery of what came before our universe’s creation, dark matter and energy actually exist in the here and now, and as we advance in our scientific understanding there is a great chance that we will some day grasp their full origins and purpose.
For now, just keep looking up into the night sky and know that there are so many wonders still out there for us to find and comprehend. As long as we dream of the stars, we will discover more about them.
Thank you for reading and sharing!
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