The Fate of the Universe

Birth and Death of our Universe

Our universe is expanding! That is, groups of galaxies are moving away from each other according to Hubble's Law. This law states that the further a galaxy is from us, the faster it is moving away from us. Any model used to explain the birth of the universe must take this into account.

Prior to the 1960's, there were two competing ideas about the origin of the universe. One called the Steady State Theory and the other called the Big Bang. The Steady State Theory claimed that the universe had no beginning ... will not have an end ... is infinite ... will expand forever ... and never change. To keep the universe from changing ... new matter had to be created in the void left by expansion. If you have a PC running Windows, you may have seen the "flying windows" or "moving stars" screen saver. This is very much like the Steady State Theory.

The Expanding Universe in a Steady State (animation)

The Big Bang (animatiopn)

The Big Bang Model simply traces the expansion back to a time when all matter was together. It proposes that the universe had an instant of creation and it is still expanding as a result of this "explosion". But which model is correct?

In the 1960's, a prediction was made that if the universe was created in a Big Bang, there should be residual radiation from it and it should permeate all of space. In 1964, Arno Penzias and Bob Wilson, working for the Bell Laboratories, discovered this "cosmic background radiation". It confirmed that Big Bang Model ... now all we have to do is work out the details.

The Big Bang is not like any explosion you've ever witnessed. It is literally an explosion of reality ... the creation of matter, energy, space and time. It is pointless to ask what happened before the Big Bang ... there was nothing. Or to ask what caused it! It is an excellent boundary between science and religion simply because no scientist can investigate it, explain it, or predict its occurrence.

Today, astronomers believe the universe was created somewhere around ~14 billion years ago. The exact time depends on the rate of expansion ... and that is a problem since it is difficult to know exactly how far away some very distant objects actually are.

Here are a couple of interesting breakthroughs. When accurate maps of the cosmic background radiation were made, it was found that it is very, very smooth and uniform (but not totally). Yet the universe that we know is very lumpy. How did this radiation start out so uniform? One idea assumes the universe underwent a very rapid period of expansion in its initial stages. This is known as inflation. In this model, the universe went from the size of an atom to the size of a walnut in almost no time at all (much, much faster than the current rate of expansion). If this was the case, it would help explain why we had such a uniform universe in the past (the details are beyond the scope of this class).

Standard Big Bang Model (animation) Inflationary Universe (animation)

What is the future of the universe?

Just about everyone contemplates questions like this. There are several possibilities. An open universe is one that continues to expand forever. A closed universe is one where gravity eventually wins out and the universe halts its expansion. Then the universe falls back into a "big crunch". Each fate can be accomplished an infinite number of ways. For example, if you throw a ball straight up, it will eventually come back down. Think of that as one possibility for a closed universe. But there are many, many different speeds you can throw the ball up, and it still comes back down to your hand. Now let us assume you have superhuman abilities and are able to throw the ball so fast that it achieves escape velocity and never comes down. This is what an open universe is like. But this, too, may occur many different ways. What if the superhuman throws the ball even faster? Wouldn't that be another possible open universe? Why do we bother to bring this up? Because the universe appears to be right on the edge between an open universe and a closed universe. It is too close to call! Astronomers call this a flat universe.

Technically, a flat universe will expand forever (sometimes called marginally open). That is, it appears to have density just below the "critical density" which means it would expand forever (which is also a prediction of inflation).

Breaking News:

What amazed astronomers in (1998) is that instead of seeing a universe that is expanding and slowing down with time ... it is possible that it is expanding and speeding up with time?!?! This "accelerating universe" was detected by two independent studies. It is as if you were throwing a ball upward in the air and (to your amazement), it started speeding up as it left your hand!!!

Does the universe do this? Notice the acceleration toward the end. (animation)

In order for the universe to accelerate as it expands ... there has to be some kind of "anti gravity" force pushing things apart. This mysterious force has been labeled dark energy. If these results continue to be confirmed, scientists will have to concede that the universe is indeed open, but they will have bigger challenges trying to explain the nature of this new force.

Click here for an article.

So here we are ... the very end of the class! And what can we say about the universe we live in? We don't know what 90 % of the universe is made of, and we have no way of explaining why it is moving the way it appears to be moving! Isn't science great?

Links

A super web page explaining the details of the early universe