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Feb.11, 2009

Vol. 109, No. 8


The cosmic apocalypse

Princeton cosmologists are working to discern the ultimate fate of the universe

By Mark Alpert ’82
Published in the February11, 2009, issue

Physics professor Paul Steinhardt with equations describing what happened just before the Big Bang if his theory of a “cyclic” universe is correct.
Beverly Schaefer
Physics professor Paul Steinhardt with equations describing what happened just before the Big Bang if his theory of a “cyclic” universe is correct.

“Some say the world will end in fire, some say in ice.”— Robert Frost.

It’s perhaps the scariest question one can contemplate. Will the universe die? Will all the planets, stars and galaxies in the cosmos, and all the myriad forms of life that they sustain, eventually cease to exist? Astronomers long have known that the earth is doomed; in about 5 billion years the sun will run out of hydrogen fuel and swell to gigantic size, vaporizing our planet. But will there always be new stars born from the ashes of their predecessors, and new planets for life to colonize?

Most cosmologists — the scientists who study the shape, structure, and history of the universe — are not very hopeful on this point. The universe has been expanding ever since the Big Bang started nearly 14 billion years ago. In the late 1990s researchers were shocked to discover that the cosmic expansion isn’t slowing down as they had expected. Instead, it’s speeding up. The implications are dire: If the universal acceleration continues, the multitude of galaxies that now pepper the night sky will recede from view. Our local group of galaxies — the Milky Way, Andromeda, and a few dozen lesser lights — will be surrounded by darkness, like a lone campfire in a vast black desert. In about 100 trillion years our aging galaxy no longer will have enough hydrogen to produce new stars, and the embers of our diminished universe will slowly cool and decay. After 10 years — an unimaginably long but not infinite stretch of time — nothing will be left except an extremely diffuse scattering of particles. (Imagine one electron surrounded by billions of light-years of empty space.) This is the icy apocalypse that Robert Frost envisioned in his poem “Fire and Ice.” Or as T.S. Eliot put it in “The Hollow Men”: “This is the way the world ends, not with a bang but a whimper.”

In the past few years, though, some theorists have held out the promise of a fiery rebirth. Princeton University cosmologist Paul Steinhardt is one of the architects of the cyclic model, a hypothesis that challenges the conventional view of our universe’s beginning and makes very different predictions about its end. If the cyclic model is correct, the universe would stop expanding about a trillion years from now, then slowly contract for another 10 billion years. The contraction would be so gradual that the future inhabitants of our galaxy wouldn’t notice anything amiss except for a shift in the values of certain physical constants. “They would see that something strange was happening with the laws of physics,” Steinhardt says. “And then the universe would be blitzed with huge amounts of energy.” The result would be another Big Bang, injecting new matter and radiation into the cosmos and triggering a new round of expansion. All traces of civilization would be annihilated, but perhaps life could arise again in the next cosmic cycle.

Neither the fiery nor icy future seems particularly pleasant, but it would be nice to know which one we’re facing. Luckily, the clues to our ultimate fate may be all around us, hidden in plain sight. At the start of the Big Bang the universe was a hot, seething soup of protons, electrons, and photons (particles of light), but after 380,000 years the soup cooled enough to allow protons and electrons to form hydrogen atoms. The universe suddenly became transparent, and the primordial photons have been streaming across the cosmos ever since, appearing in present-day telescopes as a sea of radiation called the cosmic microwave background (CMB). Cosmologists now are using ever more precise instruments to examine this radiation because it offers a snapshot of the universe in its infancy, with intricate fluctuations that may reveal exactly how it was born and how it might die.

Princeton has a special connection to the CMB. In 1964, a group of researchers in the University’s physics department — including Robert Dicke ’39, Jim Peebles, David Wilkinson, and Peter Roll — was preparing to build an instrument that could detect the primordial radiation. They were gathered for a lunchtime meeting when Dicke got a phone call from Arno Penzias, a Bell Labs scientist who was trying to find the source of some odd static he’d picked up with his laboratory’s radio antenna in nearby Holmdel, N.J. Dicke quickly realized that Penzias had discovered the CMB. After he hung up the phone, he turned to his colleagues and said, “Well, boys, we’ve been scooped.” (Penzias and his Bell Labs co-worker Robert Wilson later received the Nobel Prize.)

The Atacama Cosmology Telescope in Chile.
Alumni Journeys
The Atacama Cosmology Telescope in Chile.
Professors David Spergel ’82, left, and Lyman Page at the ACT site.
Courtesy Lou Tucciarone ’79
Professors David Spergel ’82, left, and Lyman Page at the ACT site.

In the following decades, however, Princeton researchers made up for the scoop by participating in several studies that investigated the properties of the CMB. The first measurements of the radiation indicated that it was isotropic — that is, all the photons shared a temperature of 2.7 kelvins (2.7 degrees Celsius above absolute zero), no matter which direction they were coming from. This finding suggested that the primordial soup of the infant universe was almost perfectly smooth. But in the early 1990s a NASA satellite called the Cosmic Background Explorer found slight variations in the CMB’s temperature: The photons coming from some spots in the sky were a few ten-thousandths of a degree hotter or colder than the photons coming from other spots. In 2001 NASA launched the Wilkinson Microwave Anisotropy Probe, which made even more detailed observations of the CMB from a parking spot in deep space known as the L2 Sun-Earth Lagrangian point, nearly a million miles from our planet. The probe was named in honor of David Wilkinson, the Princeton cosmologist who died in 2002. The mission’s science team includes Lyman Page and Norman Jarosik of Princeton’s physics department and David Spergel ’82, now the chairman of the astrophysics department.

Although the Wilkinson probe still is collecting data, its results already have revolutionized cosmology. The observed CMB temperature fluctuations closely match the pattern predicted by the theory of inflation, which was developed in the 1980s to address the paradox of the universe’s smoothness. At that time, scientists couldn’t understand why widely separated parts of the universe look so much alike; because there is no mechanism that could mix such a vast cosmic soup, researchers had expected it to be a lot lumpier. Cosmologists tried to solve the problem by proposing that in the first moments of the Big Bang, something called the inflaton field triggered an ultrafast expansion of the universe that swiftly stretched microscopic volumes into smooth, flat expanses of space. The theory predicted, however, that the early universe wouldn’t be perfectly smooth. The brief epoch of inflation would leave a distinctive pattern of high- and low-density patches in the primordial soup — which correspond to the hot and cold spots in the CMB — and the high-density patches later would evolve into the galaxies and galaxy clusters that we see today.

The CMB observations support this hypothesis, but not all cosmologists are convinced that inflation jump-started the universe. The theory has a few holes in it. First, scientists don’t know what the inflaton field is, much less why it appeared when it did or what existed before it came on the scene. Second, one of the consequences of the theory is that inflation must be an ongoing, never-ending process — the inflaton field generates an infinite number of universes, each emerging like a bubble from a glass of champagne. As a result, the theory can’t explain many of the properties of our own universe, except to say that they arose by chance.

In an effort to give inflation a firmer footing, some researchers have tried to derive the hypothesis from string theory, the proposed “theory of everything” that attempts to unify all the forces of nature. Professors and graduate students from Princeton and other universities wrestled with this problem at a conference titled “The Big Bang and Beyond” that was held at Jadwin Hall last October. As the cosmologists scribbled equations on the blackboard of the colloquium room and continued the abstruse discussions in the faculty lounge while slurping tea and gobbling cookies, it became clear that merging inflation with string theory would be a formidable task. Moreover, the inflationary models don’t explain why our universe is now expanding at an accelerating pace. Cosmologists use the term “dark energy” to describe the unknown agent that is causing the acceleration, but the phenomenon remains just as mysterious as the origins of the Big Bang.

Post Comments
13 Responses to The cosmic apocalypse

Bill Barber '62 Says:

2009-02-09 10:23:15

Have believed this or earlier scenario for demise (asteroid) for most of my 68 yrs & want to see Inevitable used to put end to conflicts of all sorts on our poor planet!

Spencer Wolling '45 Says:

2009-02-09 10:24:51

Interesting news, but seems very impractical to spend lots of money on something so distant in time. I wonder if we won't destroy this earth long before that happens, or some other forces of nature cause the population to become extinct even if the earth survives.

Jay Master '52 Says:

2009-02-09 10:29:16

A lucid article on a complicated subject. This, obviously, is going to be an exciting field of research for a long time. Keep us updated! One question: Can you get a few clerics to weigh in?

Jack Moffly Woodrow Wilson '49 Says:

2009-02-09 10:32:11

What is so fascinating about this article is the fact that cosmologists have actually find a away to measure such infinitesamally tiny points of energy and matter that no one can see. Will we ever know for sure how the universe began and how it will end? Perhaps we will, but I wonder if we won't be disappointed. We need to have frontiers of the unknown to challenge us.

Richard Roberts '58 Says:

2009-02-16 15:09:25

Congratulations to all involved - for grit. What fun!

Wm. Gillham '64 Says:

2009-02-16 15:26:41

If we discover what was going on before the "Big Bang," we will then wonder what was going on before that second "Big Bang." If we discover something outside our "Universe," we will wonder what's beyond that "universe." The Infinite seems destined to remain an unending mystery to finite minds. "Before time" and "outside space" seem unthinkable nonsense. The heuristic utility of mathematical abstractions in physical cosmology, like "multiple infinites," do not address metaphysical questions satisfactorily, even when resorting to metaphors like "curved space." It is nonsense to affirm that "it is true that there is no truth." There will always be truth about the past that no finite mind grasps. In Charles Hartshorne's words [cf. Plato], there must be some sort of Home of All Truth, beyond the sum of all finite memories. "Immortal, invisible, God only wise."

Mark DeBellis *88 Says:

2009-02-16 15:30:26

Interesting article. I think where it says "10100 years" the 100 is supposed to be a superscript or exponent (it doesn't appear as such in my browser).

Louis T. Klauder Jr. '58 Says:

2009-02-17 09:58:31

My 1958 sr. thesis in physics advised by John Wheeler was on the correlation between the well known isotropic homogeneous solutions of Einstein's equation for general relativity and the then observed contents and rate of expansion of the universe. Since then the persuasiveness of the 'big bang' (which was neither big nor a bang) picture has been increased by 1) its explanation of the abundances of H, He, and LI in spatial regions not yet enriched with heavier nuclei produced in stars and by stellar explosions and 2) by modeling that shows the nice correlation (mentioned in the article) between the anisotropy in the cosmic microwave background and the statistics of the large-scale distribution of mass in space. However, the basic picture was pretty well set in stone by Edwin Hubble's observations showing the uniform expansion of the then visible galaxies back around 1929. One commendable alternative picture based on ongoing creation of matter in space was eventually ruled out by subsequent observations. I am intrigued by comments above by Jay Master and Wm. Gillham. Ever since the so-called Enlightenment there has been a school of thought I will refer to as rationalism holding that the reality measured and described by physicists is the fundamental reality underlying any and all other realities. I would say in contrast that the concept of physics implies that physics is not all that there is and that reality is fundamentally miraculous. I do not mean miraculous in the sense of what the Gospel of John calls 'signs', but miraculous in an every-day way. What I take to imply miracle is our shared belief in the ability of the human mind to discover truth. Rationalists believe in that ability but appear to me to stop short of its implication. Namely, if physics is all that there really is, then people are machines, and machines behave mechanically so that their actions, while in some respects chaotic, are nevertheless predetermined and cannot include episodes of discovering truth. This line of thinking is not considered a proof of anything, but it does tell me that rationalism is an incoherent posture, and that belief in the miraculous is much more consistent with what we all believe in practice. For someone who shares such a view the concept of a reason for the universe is thinkable and the long term fate of the universe may be less of a concern. However, trying to discern its patterns and details continues to be a wonderful challenge.

Robert B. Dodd '49 Says:

2009-02-17 10:03:52

I'm 81 years old and I don't expect the end of the universe before my own, so I can't lose any sleep over it. I am willing to let those that come after me to determine their own end.

John Garth '56 Says:

2009-04-20 11:14:43

There are few subjects more fascinating than the age of the universe. I majored in engineering physics at Princeton and obtained my PhD in physics at the Univ. of Illinois. I spent my research career with the Air Force in the field of charged particle transport. I gladly admit that my knowledge of cosmology is quite limited. That said, I am supremely grateful that, through God's kindness, I had a "born-again Christian" experience. My conversion happened while reading and, at last, understanding the meaning of the Gospel as is well expounded in the New Testament book of Romans. As anyone can learn by reading Psalms 19 and 119, God expects us to take His Word very seriously and as literally true. Thus the Genesis creation account (chapters 1-2) cannot be too easily dismissed. I find it noteworthy that "buried" in the middle of the all-important "Ten Commandments" is Exodus 20:11, which states, "For in six days the Lord made the heavens and the earth...". If Professor Steinhardt and many other cosmologists like him really believe that the age of the universe to be 14 billion years, I suspect there will be a brutal "awakening" when they finally meet their Creator (who really knows!). Let me ask a basic question: If there really was a "Big Bang", how did the universe suddenly come into being out of nothing? The Bible addresses this topic in numerous ways. I fear that most physicists, with their "superior knowledge" (and their academic reputations and jobs at stake!), dare not allow themselves to believe the plain truths of the Bible! I'm sorry, guys, but I admire and respect you too much not to point this out to you. For an in-depth discussion, I commend to you the book "Dismantling the Big Bang" by Alex Williams and John Hartnett. (By the way, I thought I was a bit daring to write all this, but reading the above comments by Gilliam, Klauder and Dodd, I see that I am not alone!)

Thomas Zaslavsky *65 Says:

2011-05-02 09:29:02

I was surprised at the preponderance of comments that are philosophical or religious rather than scientific. I'll redress the balance by saying that cosmology is utterly fascinating and in recent decades its excitement has grown even faster than the field's own expansion. This is an exceptionally good article; no doubt that working at Scientific American is good training for a science writer.

Jerry Feheley Says:

2011-05-02 18:54:15

The Universe itself is God and humans are the Universe understanding itself.

Jerry Feheley Says:

2011-05-09 09:25:57

Everything is cyclic, even the universe itself. No entity can last forever. A cyclic universe that creates life can be forever. Life that reproduces itself in cycles within the universe is the design the universe uses to have life be immortal. Each individual life is part of that immortality. Forever? If the universe has had a trillion to the trillionth power of cycles, then the answer to its creation is forever lost to the majestic mystery of the universe's existence.
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CURRENT ISSUE: Feb.11, 2009
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  • The cosmic apocalypse
    Princeton cosmologists are working to discern the ultimate fate of the universe