This is republished from my Science Column in ConNotations Newszine, where I am a staff writer. I also write book and movie reviews and other non-fiction for the magazine. My science column is directed at convention fanboys and fangirls that were not self-punishing enough to get three science degrees like myself, but want to be able to understand complicated topics, like dark matter, string theory, teleportation, where the universe came from, astro-physics, the God Particle, and other issues. My attempt with each short column is to explain a concept in layman’s terms. This is on Dark Matter. The photos were added for this web edition.
Is Space Empty or Full?
by Michael Bradley
Most have heard the term “dark matter” but what does it mean? We look up at the night sky and we notice the stars, constellations, galaxies and heavenly bodies. Unconsciously, we might also notice everything else – the black portion. It is human nature to assume that the black portion represents nothingness, and emptiness broken up in its expanse only by those objects we can see. For the known history of mankind, everyone would have accepted that as truth, until less than one hundred years ago.
As humans, we know and experience our reality through senses; smell, touch, sight, hearing, temperature, etc. If we cannot sense something, it is often overlooked or missed by our minds. In physics and astronomy the same is true. We “see” the sky at night through two major lenses, one is the light emitted by heavenly bodies, and the second is the radiation and radio wave emissions from the sky. We can observe the lights and the radiations and draw theories to understand them.
Based on the movement of the lights, we learned through observation that the planets rotate, that the Earth moves around the Sun, that we are in a galaxy called the Milky Way, that their are other galaxies, and many helpful facts. The universe appears to be expanding, which also leads to the Big Bang Theory, calculations of time and so forth.
In the 1880s, Christian Doppler discovered the Doppler Effect, in which sound and light waves are compressed to different frequencies by the motion of mass. For instance, a rushing locomotive sounds different as its mass moves toward and away from the listener. This also creates the Blue/Red shift in light from celestial bodies. As a galaxy spins, the section moving toward us turns bluer, while the section moving away turns redder on the light frequency spectrum.
Using the blue/red shift and physics, scientists were able to calculate the relative mass of galaxies and other objects which spin and cast off light. Fritz Zwicky noticed in 1934 that the math did not add up, and came up with an explanation now known commonly as “dark matter.” His theory is that either the majority of the mass of these objects does not give off light, or, the theory of gravitational pull is flawed in its calculations of mass. To explain this missing mass, he theorized that there must be matter which neither reflects nor gives off light or radiation emissions measurable on Earth, but which has mass. By only making calculations of spin based on visible matter, we are missing the dark matter.
If the dark matter theory is true, then 83% of the matter in the universe and 23% of the mass energy could be from dark matter. It could be that our ability to perceive what space is composed of is much like a blind-folded man with ear muffs and a cold trying to describe his surroundings. Or, consider a dark field and across from you are 1,000 people holding flashlights, but only 230 have them on. So you think there are only 230 people.
Could there actually be so much out there that we can not see through light or through radiation?
Theorists have explored the possibilities for the last eighty years and have mainly created more theories than answers. Some say the gravitational theory is wrong and that instead of trying to “fix” the math by the creation of a theoretical dark matter you should start there. Some have broken up dark matter into deeper theoretical categories, such as Machos and Wimps. You can’t make this stuff up.
Machos are Massive Astrophysical Compact Halo Objects more commonly referred to as brown dwarfs and black holes, or referred to as baryonic, or more normal matter, that happens to be dark. Wimps are Weakly Interacting Massive Particles which would be non-baryonic in nature. Wimps are thought to pass through normal matter though they have mass, without interacting with it. There are also theories of the dark matter in which they break them into mixed dark matter, cold dark matter, warm dark matter and hot dark matter. Who says physicists don’t have a sense of humor?
In any case, the next time you look up at the night sky, just realize that mathematically, either all we know about gravity is wrong, or you are seeing only a tiny portion of what is there. It is 2012, and we often think we have it all figured out, and yet in the very night sky above our heads we understand and perceive very little.