A Cosmic Mystery Story: Beginnings
This is an excellent chapter as it really emphasizes the difference between reality and our perceptions. A long time ago, a man was imprisoned for life because he claimed something that wasn’t obvious. Now, that man is known to be right and the group that condemned him finally (400 years later) admitted that the whole affair was handled badly.
Likewise, now, certain groups think things should be obvious and ignore the massive amounts of evidence that say, in a nutshell, “common sense doesn’t cut it in the real world”.
But we’re talking about the universe. You may have heard of this guy mentioned briefly in chapter 1. A man named Albert Einstein. Well, he, over a decade or so, developed this hypothesis of how the universe (especially gravity) ought to work. When he applied his hypothesis to a problem that had vexed astronomers for a long time, his hypothesis was able to do what no one else had been able to. Predict the motion of the planet Mercury.
This is what scientists do when they make claims. They go out and make predictions based on those claims, then examine the real world to see if they work. So this, and many other experiments in the future, confirmed that Einstein’s hypothesis, now called a theory. So, what happened when Einstein applied his theory to the universe as a whole?
Well, he got a very unexpected result. The universe was expanding. It was such a crazy idea that Einstein rewrote his theory with a “cosmological constant” whose sole purpose was to ‘fix’ the equations to make the universe static.
Later, Edwin Hubble, using the work of Henrietta Swan Leavitt, was able to show that certain stars called Cepheids were far outside of our galaxy. Almost overnight, the size of our universe increased from one small galaxy, to one small galaxy among hundreds of billions of galaxies.
But the next discovery was to shock the world and, especially, poor Albert. You see, stars emit light. We should all know that when you run sunlight through a prism you get a rainbow. We science types call that rainbow a ‘spectrum’. If you are able to examine that spectrum very, very carefully, you will see something called “absorption bands” in it.
After some serious analysis and experimentation, scientists know that these black bands in the spectrum are caused by certain atoms absorbing certain (very specific) frequencies of light.
Another astronomer was observing the spectra of these new-fangled galaxy things and Hubble compared those from galaxies that we knew the distance to (because of the Cepheid stars). What he found was that the location of the absorption bands changed places. Like so:
Notice that this is the exact same absorption bands in the bottom image, but they are moved over a little bit. If you are familiar with sound, you know that the sounds from an object coming toward are higher in pitch than sounds from an object moving away from you. This is called the Doppler Effect.
This same principle applies to light, except that the frequency shifts. Something moving away from you appears more red and something moving toward you appears more blue. Now, this only applies at very, very high velocities (i.e. significant fractions of the speed of light). But what Hubble found was that almost all the galaxies were moving away from us. He also found that the farther away they are, the faster they are moving. Only the very closest galaxies to Earth are blue-shifted. (And yes, that means what you think. In a few million years, the closest neighbors to the Milky Way will slam into it.)
The really neat part, and I’m not going to spend a lot of time on it, you either get it or you don’t. This change appears the same, no matter where you are in the universe. If you are in a galaxy far, far away from us, then it will appear that all the other galaxies are moving away from you. In other words, it doesn’t matter where you stand. Anywhere you stand in the universe, it looks as those everything is expanding away from you.
There are some fine stories in the book, which you ought to read. Krauss is a good writer and I won’t belabor the entire thing here.
Now, once we realize that the universe is expanding, then we must realize that, at some point, it came from something really, really small. Scientists have traced the timeline of the universe backwards (as well as forwards) to that point and the explosion we call, The Big Bang.
Now, what’s really interesting is that we understand particle physics and thermodynamics quite well (well, some people do) and can look at the conditions around the time of the Big Bang and use that to predict what the state of the universe should be if certain things happened. Then we observe the universe around us and compare that to the predictions from the math.
What we discover (and Krauss goes some length into this) is that
Only a hot Big Bang can produce the observed abundance of light elements and maintain consistency with the current observed expansion of the universe.
Krauss goes into some detail about how supernova affect the distribution of elements and the age of the universe.
So far, the Big Bang theory is in good shape.