Science and Exploration

[dreadgeek]

So, I said I'd do this a few days ago. I apologize for the delay:

Science advances not when someone exclaims "Eureka!" but when someone cocks their head and says, "well now, that's unexpected". There are a number of issues that caused astronomers, astrophysicists and cosmologists to say "well, I wasn't expecting that". I'll only take two because they are the easiest to explain and require no math to get to an understanding.

The first is the concept of gravity lensing. Gravity lensing is caused when the light of a very distant object is warped around an intervening mass like, say, a galaxy. As everyone knows, light moves from point A to point B and, as everyone is aware of from the idea of black holes, light can be affected by gravity. When this happens at astronomical distances what happens is that the object either appears as either a ring (known as an Einstein ring) or it'll appear slightly offset from where the object actually is. Now, if we know the approximate mass of a galaxy (which can be estimated from its size and density of stars) then we can know about how much refraction there should be. The problem then is that astronomers see more lensing than can strictly speaking inferred from the masses in between them and some distant light source. This begs the question of *why* this is happening.

The second concept is the spin of a galaxy. This is a bit more complicated. Think of a spiral galaxy like a solar system writ large. In the center of the galaxy is a hugely massive orbit (a supermassive black hole) and most of the mass of the galaxy is in that bulge in the center. Then there's the spiral arms. Calculating the rotational speed of a galaxy of a given size *should* be a pretty straightforward application of Newton's and Kepler's laws that work very well when applied to solar systems. The basic idea here is that the closer to the gravitational center an object is, the faster it rotates and the farther out it is, the slower it rotates. Except that's *not* what we see. Instead we see a near uniform rotational speed even at the outer extremities of the galaxy--for instance where our solar system is in relation to the rest of the Milky Way. Again, this begs the question of *why*.

Now, the proposed answer is that there is some 'missing' matter that we can't directly observe. This missing matter is called 'dark matter'. Why dark? Because it does not interact strongly with the electromagnetic force (light in all its form and splendor). Ordinary matter (the kind of stuff we and everything we can see) will interact with the electromagnetic force. For instance, someone walking into the room where you currently sit reading this can see you because all of the matter that makes you you is reflecting electromagnetism in the visible portion of the spectrum. Dark matter doesn't do that. Instead if it interacts with light at all it does so very weakly and all evidence, so far, is that it does not interact with it at all.

If this were all that there was to dark matter it would be almost impossible to find but fortunately this isn't the case. Dark matter *does* interact with itself and when it does it splits off into exotic particles that were predicted by physicists who started working on the problem. The experiment aboard the ISS (International Space Station) detected the kinds of particles that the theory predicted which is usually a sign that we're on the right track.

Dark matter and dark energy are *not* the same thing and shouldn't be confused with one another.

Cheers
Aj