But if the universe is expanding, then what was it like before? A million years ago it would have been smaller than it is now, and two million years ago even smaller, and so on, until, at one time, it was no bigger than the period at the end of this sentence. And before that even smaller.
This was too hard to take, for some. Astronomer Fred Hoyle, and others, promulgated the steady state theory. On the large--very large--scale, the universe seems to be homogeneous, the same here as there. Suppose we take this symmetry further, and assume the universe is the same now as it always was, on average. How can this be if the universe is expanding? The answer is that matter is being creating continuously. Since the universe is so big, do not worry about going into your basement one morning and seeing a new pile of matter (unless you forgot to let the pooch out). In order to account for the universe as we now see it, you would have to wait centuries and centuries just to see a new electron, which you probably would not notice anyway.
And so it came to pass that there were two camps, the expanding universe groupies and the steady state cosmology fans. How do good scientists convince everybody they are right? Cast the other view in the pejorative. And so it came to pass that the steady state advocates made fun of the other side, smirking that the universe began from a big bang. And so it came to pass this tactic backfired and subsequent measurements prove we live in an expanding universe. And so it came to pass we had the big bang, and the name was good. Cosmology was settled and that is that. Or, that was that. Like theoreticians like me who never stop theorizing, observers never stop observing. In 1998 a paper was published that rocked the world. It is the subject of this chapter and according to some, represents today’s biggest problem. What in the world happened? I would like to quote, almost verbatim, from the 1998 paper. Let me explain first that SN Ia are supernova, stars that explode when they can no longer undergo fusion. These are the brightest things in the universe, which is why we can see them even though they are incredibly far away.
So, the cosmological constant is not dead after all? Let me explain all this, but remember, when you look into the heavens you are looking into the past. The light from the sun you see right now left eight minutes ago. If you look at nearby stars, the light you see left years ago, and if you look at Andromeda the light left hundreds of millions of years ago. The Hubble telescope is able to see billions of years into the past.
What the astronomers really observed is this. Distant supernova are redshifted. The amount of redshift is proportional to the distance (Hubble’s law). The recent observations I quote above show that very distant objects are not redshifted as much as we expected. In other words, billions of years ago the rate of expansion was less than it is today. In other words, the rate of the expansion of the universe is bigger today than it was in the past. In other words, the expansion of the universe is accelerating.
This is so profound it is worth repeating, the expansion rate of the universe is accelerating. Everybody always thought the rate of expansion should be decreasing. Why? I put it to you.
QUESTION: Why did everybody expect the rate of expansion to be decreasing.
1. The universe, like geezers, gets tired and slows down.
2. The intergalactic ozone acts like a sort of cosmic muck, gumming up the works.
3. It is due to gravity, which is an attractive force.
4. Nothing goes on forever.
Last week I took a jog. As I was gasping for air, a geezer zipped past me, so 1 is not the answer. Two is my ozone trap answer. Later I will try and think of a question where ozone is the answer, but intergalactic ozone is as sparse as the hair on my head. I am not sure what 4 means, which leaves 3 as the right answer. By the way, I lifted some of these questions from my astronomy course, so you can keep track and give yourself a grade at the end. Suppose are you standing on the moon and throw a rock up in the vacuum. What happens? It slows down, and eventually falls back to the surface. If you could toss it fast enough, it would still slow down on its way up, but it may never return. It slows down because the moon’s gravity pulls it back (we went to the moon to do this experiment so we would not have to worry about the atmosphere). If the rock started to speed up on its way up, you would have to scratch your helmet, thinking it is a magic rock. Same thing for the universe, which is made of billions of galaxies. They are flying apart because that is how the big bang started things, but they tug on each other, so they should be slowing down. Instead, it is like the magic rock we threw, speeding up on its upward trajectory. Something, it seems, is pushing everything away, but the only forms of matter we know about do just the opposite. Let me put it to you again.
QUESTION. What causes the expansion rate of the universe to be increasing.
1. It is not really increasing, the observations are wrong.
2. It is the cosmological constant, Einstein’s big blunder.
3. The universe is filled with a mysterious form of matter or energy that we have never seen, and this mystery goo is pushing the universe apart faster and faster.
4. The general theory of relativity is wrong.
5. Light gets tired.
6. The redshifts that lead to this conclusion are caused by something else.
7. None of the above.
ANSWER: It could be any of the above. This is today’s zany state of affairs, and no one understands why!