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.

Mapping the Universe

From the first lunar atlas -1647

A lot of us think of mapping the universe as starting with people like Galileo and the invention of the telescope, but obviously we have ben looking to the heavens and, perhaps in crude ways, trying to put it down and record what we saw for a much longer time. This cataloging of the the heavens and making visible both what we see and later what we imagined was there or beyond is still going on, and I imagine it will continue well past all our lifetimes..

We know a lot now. This week NASAs' Juno spacecraft went into its orbit around Jupiter and we'll know even more. And yet we still have much to learn and discover.

Several articles on the www.brainpickings.org website ponted me to books about the ways we have imagined the shape and design of the uinverse. One of those is Mapping the Heavens: The Radical Scientific Ideas That Reveal the Cosmos by Yale theoretical astrophysicist Priyamvada Natarajan. Her premise is that the advent of modern cosmology and astrophysics is what has shaped our understanding of the universe and our place in it.

The book gets into the mapping of the invisible, such as black holes and dark matter, the accelerating expansion of the universe, the echo of the big bang, the discovery of exoplanets, and the possibility of other universes.

We are far beyond the earliest maps of the Sun and Moon and the attempt to describe why they - or was it the Earth? - was changing positions in the heavens.

The book and this kind of inquiry also reminds us that science will always be changing and incomplete, and that is a thing wonderful in the old full-of-wonder manner.

Astrophysics, say Natarajan, is using powerful tools to answer the same questions that our ancestors tried to answer through mythology:

Cosmology, perhaps more essentially than any other scientific discipline, has transformed not only our conception of the universe but also our place in it. This need to locate ourselves and explain natural phenomena seems primordial. Ancient creation myths shared striking similarities across cultures and helped humans deal with the uncertainty of violent natural phenomena. These supernatural explanations evoke a belief in an invisible and yet more powerful reality, and besides, they rely deeply on channeling our sense of wonder at the natural world. The complex human imagination enabled ancient civilizations to envision entities that were not immediately present but still felt real. Take for instance Enki, the Sumerian god of water whose wrath unleashed floods, or the Hindu god of rain and thunderstorms, Indra, whose bow was the rainbow stretched across the sky with a lightning bolt as his arrow. The most powerful myths are the ones that force us to take huge leaps of imagination but, at the same time, help us to remain rooted.

The Juno spacecraft entered orbit around Jupiter on the 4th of July this year (NASA/JPL-Caltech)