Why do the distant mountains look blue?
Faraway objects shrink with distance, and on the horizon a range of lofty mountains may look like a row of small molehills. On the Earth, distant objects also lose their colors or at any rate often change their colors. Those distant mountains may look gray or bluish gray, and as we approach we find that their true colors are brown or green. This color change is caused by the Earth’s atmosphere. The air around us is a mixture of gases, and gases are made from separate atoms and molecules. There are countless trillions of these particles in a room, but there are not enough of them to change our view of the walls. However, gazing out across miles of open country, the number of air particles between us and the horizon is past the imagination. Also present in the air are fragments of soot and grime, dust and dirt. The air and this floating debris tend to change the colors of the distant mountains.
My research is in theoretical cosmology: the structure and evolution of the universe. Cosmologists seek to answer questions such as: What is the universe made of? What happened at the very beginning of the universe? How did the universe evolve from the very beginning to today? I am continually amazed by how much we know about the universe, and, at the same time, by how much we don’t know and still have to learn. Using physics and mathematics, we are able to extract remarkable knowledge about the vast universe just from data we can take here on Earth and with satellites near the Earth. We now have a strong theory about the make-up of the universe, how it evolved, and possibly even what happened at the big bang: the “standard cosmological model”. The theory is impressively consistent with everything we know, including many different kinds of precise data based on different physical assumptions. However, there are some important things we don’t understand yet (such as what really is “dark
