Dark Matter, Dark Energy and Normal Matter

Dark matter fascinates me and fascinates scientists, even we can't really prove it exists. 

Why do we think there is such a thing? Galaxies don’t rotate by the same physics that we know and understand. Scientists noticed that stars at a galaxy’s edge rotate faster than expected. 

How can we explain that? There must be matter that is invisible to us that is there. In 1998, the Hubble Space Telescope observations of a very distant supernova showed that a long time ago the universe was actually expanding more slowly than it is today. We once believed that gravity was causing the slowing expansion of the universe, but now that wasn't a certainty. 

 
Credit: NASA/STSci/Ann Feild[

The diagram above shows the rate of expansion since the universe's birth 15 billion years ago. The curve changes noticeably about 7.5 billion years ago, when objects in the universe began flying apart at a faster rate. Astronomers theorize that the faster expansion rate is due to a mysterious, dark force that is pulling galaxies apart. 

Astronomers know more about what dark matter is not than what it actually is. Roughly 68% of the universe is dark energy, and dark matter makes up about 27%. The rest is everything on Earth. This "normal matter" is less than 5% of the universe. Actually, that hardly makes it qualify as the"norm."

Most of the universe is made up of dark energy, and that mysterious force drives the accelerating expansion of the universe. The next largest ingredient is dark matter. 

At one time, the theory was that MACHOs (Massive Compact Halo Objects) were the cause.  A MACHO, such as a brown dwarf star, would be so massive that it would bend light around them. We know they exist, and we know they are out there, even though they are too dark for us to see. But this theory fell out of favor because there are not enough of them to make the galaxy-rotation math work.

Astrophysicists next came up with the WIMP (Weakly Interacting Massive Particles - the scientists do have a sense of humor). Maybe the universe is full of very small things we can’t see.

And maybe dark matter is made up of a different object we have never observed. One candidate is the neutralino.

We keep looking. The Large Hadron Collider, one of the most expensive science experiments ever built, is looking, but hasn't found them. But we do know that the universe is "heavier" than what we can see.

"There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy," says Hamlet and that continues to be true. 

This month a TV series titled Dark Matter, based on the novel of the same name by Blake Crouch hits streaming service Apple+.

Dark matter and the expanding universe don't keep me up at night, but it did bother Alvy in the film Annie Hall.