So apparently, everything we can see in the whole universe is just the tip of the proverbial iceberg. Like the back jelly beans in this picture (which I’ve stolen from the Chandra Blog), most of the universe is completely invisible and undetectable to us. Regular matter makes up about 4% (0.4% stars and 3.6% intergalactic gas) while 23% is dark matter, and a whopping 73% is the mysterious dark energy.
Frankly, I’m not buying it.
The trouble with both of these concepts is that they rest on some pretty hefty suppositions. Are we to believe that we can see all the baryonic matter in the universe? If so, are we to believe that we actually know what it is we’re looking at? As an astrochemist, I can say quite readily that we do not. Phenomena such as the (often overlooked) Diffuse Interstellar Bands, for instance tell us that almost everywhere we look, we see things that cannot be explained. Technically, the diffuse bands come from what could be called “dark matter”. We know it’s there, but we don’t know what it is. How can anyone realistically say how much of the universe is made up of these mysterious chemicals? You might notice that the percentages I gave in the first paragraph make no reference to interstellar gas. Or dust. While it may certainly be true that out of the solar system’s known mass, the Sun accounts for around 99.86% of it. This however, cannot account for objects like the Oort cloud, or other regions of the Solar system that aren’t fully understood.
The actual concept of Dark Matter, I fully agree with. We can’t see everything, pure and simple. It seems logical that a substantial part of the universe is composed of things that we might not even know how to look for yet, but — are people really looking for it in the right way. Lots of people talk about Weakly Interacting Massive Particles (WIMPs) as a possible contender for dark matter. So far, no one’s actually found any, but some people seem to speak about them as if they were fact. We know there are hypothetical cousins of our familiar matter with quixotic names like “Strange Matter” and “Charmed Matter”, but no one’s really seen them in the cosmos either. Should astronomers really keep looking for things that they can’t see, or should they start to reconsider whether or not they fully understand what they can see?
So that’s dark matter, but what about this dark energy stuff? Personally, I don’t believe in dark energy. I’m sorry, I just don’t. Observations were made that implied it’s existence. Implied. Not proved. Too many people seem to take the existence of dark energy to be a given. Many alternative hypotheses exist, from a failure of general relativity over the largest scales, to a simple optical illusion created by the propagation of radiation over comological scales. I don’t think there’s any way to be sure of the apparent acceleration of the universe’s expansion until we understand what it’s made of – in other words, until we get what dark matter is, perhaps we shouldn’t be considering dark energy, if indeed it does exist.
Occam’s Razor is a principle traditionally used in formulating scientific theories. It states that “the explanation of any phenomenon should make as few assumptions as possible, eliminating those that make no difference in the observable predictions of the explanatory hypothesis or theory”. In other words, of two competing theories, if they are the same in all other respects, the one that makes the fewest assumtions and makes the fewest references to things that may or may not exist is the better one. To that end, perhaps Modified Newtonian Dynamics (MOND) is a better explanation than dark matter.
Then again, perhaps this is all resting on the assumption that we understand the fabric of reality and how spacetime works at a fundamental level. In my humble opinion, I don’t believe that to be true. Perhaps we will one day. For the meantime, we shall have to wait and see!