The State of the Universe

by Panini

January 5, 1999

Copyright (c) panini. All Rights Reserved

Every year, the President of the United States is required by the Constitution to give a State of the Union Address to the citizens of America. I wish someone would give an annual State of the Universe Address too. After all, the Universe is bigger than America. Someone of the stature of the recently departed Carl Sagan, could stand up and tell us where we stand in our knowledge of the universe and how that knowledge has changed over the past year, summarizing the key results and discoveries.

If such a thing had existed, the 1999 State of the Universe Address would be full of turmoil! Not that the universe is in trouble; it’s doing just fine, thank you. It’s that our understanding of the universe is about to undergo some radical changes. And we don’t yet know what those changes are going to be. But we do know they will change some of our basic assumptions about the universe we live in.

Now, you might think the scientists working on these problems would be very distressed and upset about this situation. Not so. It is precisely times like these that are the most exciting for researchers in the field. These are the chances to solve tough problems, invent brilliant new theories, get into the history books. You see, science is not hurt by challenges to current theories; rather, it thrives on them. Far from being weakened when a scientific theory proves false, it absorbs the new data and produces an even better theory, making it stronger still. Science is a "self-correcting system of inquiry," as science writer Timothy Ferris says, "in which errors -- of which of course there are plenty -- are sooner or later detected by experiment or by more careful analysis."

In order to fully appreciate the gravity (pun intended!) of the current situation, it will be necessary to delve into some background so that you can see what led up to this point. So please bear with me through this background material. In return, I promise not to give any mathematical equations. And your reward will be a deeper understand of the universe we live in.

Until this century, the universe was thought to be more or less static. Sure, individual stars might get created or destroyed and even galaxies could move around and change, but on a large scale the universe as a whole remained the same. It was infinite in extent, had existed infinitely far back in the past, and would continue infinitely far into the future. This is a very simple model of the universe, and one which is emotionally reassuring to most people because of the absolute stability implied. Unfortunately, the Universe does not necessarily feel any obligation to be emotionally reassuring to human beings.

In the 1920’s Einstein discovered a serious problem with this static model. He found that his own Theory of Relativity implied that through mutual gravitational attraction, all the galaxies would cause the entire universe to contract until there was a Big Crunch. So much for stability! So Einstein added an ugly "patch" to his theory called the Cosmological Constant. This term would represent a mysterious repulsive force that was just strong enough to cancel out the mutual gravitational attraction of the galaxies and prevent them from colliding into each other. Einstein hated doing this, and later abandoned the idea calling it his "biggest blunder."

In 1929, the year the stock market dropped faster than a prom dress, Edwin Hubble, often called the "greatest astronomer of the century," made a monumental discovery. (If his name sounds familiar, it’s because he’s the guy who the Hubble Space Telescope is named after). He found that pretty much everything is moving away from us, no matter which direction he looked. And the farther away the object was, the faster it was moving away. There are only two theories that can explain this: either the universe is expanding, or we Earthlings have really, really bad B.O. Scientists went with the first explanation, which became known as the Big Bang model. In this model, the entire universe -- including all the stars, galaxies, etc. that we see today -- was once compressed into a space smaller than the size of a proton. And you thought the malls are crowded.

Hence, the Big Bang theory became the dominant one as it simply explained the key observational fact of the expansion of the universe. However, as advances continued to be made in particle physics and as telescopic observations became more accurate, chinks began to appear in the armor of the Big Bang Theory. First, there was the problem of magnetic monopoles. If you pick up any magnet or magnetic object, it will exhibit polarity. Namely, it will have both a North and South pole. But you will never find a "naked" pole -- a North pole without a corresponding South pole, or vice versa. Why not? The Big Bang Theory predicted that scads of monopoles should have been created in the initial Bang. The fact that one has never been observed despite years of trying was at odds with the theory.

Second, there was the horizon problem. The universe is clearly homogenous on a large scale. No matter which direction you look, you will find about the same number of galaxies, stars, nebula, etc., and they seem to be uniformly distributed. The problem is that during the early phases of the Big Bang, the universe expanded very fast -- faster even than the speed of light! This means that there still has not been enough time yet for light, heat, radiation, etc. from one part of the universe to reach all the other parts of the universe. And this means that it could not have been influenced in any way by those other parts of the universe, so that it is impossible to explain the homogeneity (other than sheer coincidence, which is considered too unlikely to be worth entertaining).

Finally, there is the flatness problem. There are three possible geometries for the universe: open, closed, or flat. Which one it is depends entirely on the total amount of mass in the universe. There is a critical mass amount which makes the universe exactly flat -- a little more and it becomes closed; a little less and it becomes open. So far, so good. When astronomers add up all the mass that we can see, it comes to 1% of the critical mass, which would result in an open universe. But wait, this is just the mass we can see. From observations and analysis of galaxy cluster motion, and galaxy rotation curves, we know there is a lot more mass than we can see -- in fact, ten times more! There is some controversy over the exact nature of this unseen mass. Possible candidates include giant dust clouds, brown dwarves (no relation to Snow White), MACHOs (Massive Compact Halo Objects), and Disposable Diapers. Whatever it is, we know its there. This brings the total mass to 10% of critical, which still results in an open universe. Now here’s the problem: cosmologists think that is FAR too close to being flat to be a coincidence. Now you might be thinking those cosmologists must be crazy if they think 10% is close! But remember that the Big Bang tends to amplify things geometrically. If the universe started out being slightly open, then by now it would have been tremendously open. Similarly, if it started out slightly closed, it would by now have been tremendously closed. In order to be even within a factor of 10 of critical mass today, it had to have been at least 99.9999999999999999999999999999999999(add several more "9"s)% of critical at the start. Now you can see why theorists think this is too close to be a coincidence; the odds would be greater than winning a lottery where every atom in the universe is a lottery ticket and you have only one ticket. This is what they mean when cosmologists say "for strong theoretical reasons, we believe the universe is flat."

These three major problems with the Big Bang theory were neatly solved in the early 1980’s by Alan Guth, Andre Linde, and others, who developed an elegant theory called "inflation". No, this is not the inflation that happens when the government prints too much money. It is not a replacement for the Big Bang theory, but an addition. In covers what happens in the first fraction of a second after the birth of the universe, after which the standard Big Bang theory takes over. Inflation theory invented a new type of quantum field called an "inflaton field" which imparts a strong antigravity force on space itself, causing the universe to expand very rapidly -- even more rapidly that the standard Big Bang theory predicts. In fact, during the inflationary period, the universe expanded even faster than the speed of light! The universe went from the size of a proton to the size of a grapefruit in less than 0.00000000000000000000000000000000000000001 seconds! Inflationary theory brilliantly solved the major problems in the Big Bang theory. Inflation predicts a flat universe, explains the horizon problem, and accounts for the lack of magnetic monopoles.

With this new Inflationary Big Bang theory, our knowledge of the universe seemed pretty secure. However as astronomical observations became more and more accurate, especially since the Hubble Space Telescope, they suggested a troubling trend. Although inflation predicted a flat universe, evidence continued to mount that the universe may not actually be flat. There doesn’t seem to be enough mass to make it flat. In this past year we made an important discovery -- that neutrinos have mass. This adds a significant amount of mass to the universe, but it is still not enough to make it flat. There was also the age problem -- determining the age of the universe. There are several different methods for estimating the age of the universe; all of them gave different results.

A calculation based the initial measurements of the Hubble constant (the rate of expansion of the universe) yielded an age of 2 billion years or less for the universe. This is clearly absurd, since I have socks older than that. Estimates based on observations of globular clusters yielded an age of 15 billion or more. Clearly, this is a problem. More recent observations have brought these two numbers to 10 and 13 billion years, respectively. This is much closer, but there is still a discrepancy. Finally, here is the kicker: a study of Type 1A Supernovae showed that far from the expansion of the universe slowing down, it actually seems to be accelerating! These results have yet to be positively confirmed, but if true it means our current theory is definitely wrong.

So, what do we do about this? There are three possibilities. First is to say that inflation is completely wrong and abandon it in favor of a totally new theory. But then all the problems that had been solved by inflation would reappear and would have to be solved in a different way by any new theory. Currently there is no candidate for any alternate theory (except for a few crackpot theories like the one espoused by Richard C. Hoagland).

Second, we could reintroduce the cosmological constant that Einstein had added, and then discarded in disgust. This cosmological constant would correspond to the vacuum of empty space having a measurable amount of energy, and would have an anti-gravity effect causing the universe to expand faster and faster. Actually the Casimir Effect, which can be easily demonstrated in the lab, shows that even seemingly empty space is teeming with a host of virtual particles. Take two highly polished blocks of metal and put them against each other. It will become tremendously hard to pull them apart again. This is the Casimir Effect at work.

Third, we can make a slight modification to inflation so that flatness is no longer implied. This modified inflation theory called Open Inflation would have the early universe falling into a "false vacuum" state which is metastable. If something triggers it, it can collapse to a true vacuum state, but not all parts of the universe would collapse at the same time. Some may still not have collapsed. This would lead to a "Bubble Universe" model where there are several bubble universes, and everything we see is inside one of the bubbles. Someone outside our bubble could enter, but once inside he could never leave because that would require travelling faster than the speed of light. Hey, that’s exactly what happens for a Black Hole too! Hmmm... Two bubbles could in theory collide, causing a universe-sized explosion. Interestingly, Stephen Hawking had also proposed a Bubble Universe model for slightly different reasons (see my Hawking article).

Of the three possibilities, the third is my personal favorite theory for resolving the current paradoxes. With Open Inflation, the theory again agrees with all observations without need of a cosmological constant. These questions should be resolved within a decade or so when we get more accurate data. Especially from space missions like the NASA Microwave Anisotrophy Probe, the European Planck Probe, and others. When that happens, it will be possible to give a State of the Universe Address saying, "We think we understand the universe again!" -- at least until the next set of paradoxes comes along.

References and Recommendations for Further Reading

1. Hogan, Craig, et al, "Surveying Space-time with Supernovae", Scientific American, January 1999
2. Bucher, Martin, and Spergel, David "Inflation in a Low-Density Universe", Scientific American, January 1999
3. Krauss, Lawrence, "The End of The Age Problem ...", Astrophysical Journal, July 10, 1998, URL: http://xxx.lanl.gov/abs/astro-ph/9706128
4. Ferris, Timothy, The Whole Shebang: A State-Of-The-Universe(s) Report, Simon & Schuster, 1998
5. Guth, Alan, The Inflationary Universe: The Quest for a New Theory of Cosmic Origins, Addison-Wesley, 1997
6. Hawking, Stephen, Black Holes and Baby Universes and Other Essays, Addison-Wesley, 1997
7. Lemonick, Michael, The Light at the Edge of the Universe, Villard Books, 1993
8. Gribbin, John, and Rees, Martin, Cosmic Coincidences, Bantam Books, 1989