The Cosmos


In the Beginning

Did the universe have a beginning? What, if anything, came before the Big Bang?

Today, we see galaxies rushing away from us in every direction, suggesting that, if you could press the rewind button on the entire universe, the whole thing would screech to a halt at a moment about 13.7 billion years in the past, when the entire cosmos was apparently compressed into a singularity—an infinitely small, dense point.

“How does the universe begin from such a state?” asks Alexander Vilenkin, a theoretical physicist at Tufts University. Indeed, the laws of physics as we know them break down around singularities, so physicists have devised a number of ways to sidestep the singularity problem.

One possibility is that the universe is cyclic: Every Big Bang expansion is followed by a contraction, ending in a “Big Crunch” from which a new Big Bang emerges, and so on and so on in an infinite series that extends eternally into the past and future. The idea was first proposed centuries ago, but received a fresh take from the physicists Paul Steinhardt and Neil Turok in 2002. There is a problem with this elegant idea, though: the second law of thermodynamics, which states that the total amount of disorder or entropy in a system increases over time—the party-pooper law that prevents the existence of perpetual motion machines. A universe that experienced repeated cycles of expansion and contraction would have get more and more disordered over time until it began completely disordered, something we do not see in our universe. One way to avoid such increasing entropy would be for the volume of the cosmos to increase with each cycle. However, if one ran this scenario backward in time, one would still be forced to conclude the universe began with a singularity.

If our Big Bang wasn’t preceded by a Big Crunch, perhaps our universe instead existed as kind of dormant seed—“like a cosmic egg,” says Vilenkin—before suddenly breaking open in the Big Bang. But here, too, there is a problem: In the uncertain world of quantum physics, the “egg” couldn’t stay stable forever. It would have expanded and contracted and could have even collapsed into nothingness. “This means it couldn’t have existed forever in the past,” Vilenkin said, findings he and his student Audrey Mithani detailed in the January issue of the Journal of Cosmology and Astroparticle Physics.

But the same quantum fluctuations that could have cracked the cosmic egg could be birthing new universes as you read this, says Vilenkin. This idea, called eternal inflation, suggests that our universe is just one bubble within a larger multiverse which is perpetually popping out new bubble universes. Although inflation may have stopped in bubbles such as ours, new instances of inflation occur in the multiverse forever into the future, keeping the idea of eternal inflation true to its name. But what about the past? If one assumes that the multiverse is expanding and not contracting, then it had to have expanded from a certain point in time, Vilenkin explains. Even eternal inflation must have a beginning.

Even if the universe did have a beginning, it likely occurred so very far in the past that the cosmos might as well appear as if began an eternity ago, says theoretical physicist Leonard Susskind at Stanford University in California.”We’re talking about the beginning potentially occurring at time scales vastly, vastly larger than the age of our universe, longer than any time that you can name,” Susskind explains. “Statistically, given this extremely long amount of time, we probably occurred very, very late in history, making us very far from the beginning, so most of the information about the beginning would be lost to us. I think we’re really in the dark about what it would’ve been like.”

Still, Vilenkin is hopeful that it might be possible to observe evidence of the beginning. In some versions of the eternal inflation model, bubbles occasionally collide, which we might detect as distortions in the cosmic microwave background radiation that pervades all of space. If there are a number of collisions between bubbles that are clumped together in one direction more than another, “that might be linked with the beginning of the universe,” he said.

Vilenkin has no problem with the universe having a beginning. “I think it’s possible for the universe to spontaneously appear from nothing in a natural way,” he said. The key there lies again in quantum physics—even nothingness fluctuates, a fact seen with so-called virtual particles that scientists have seen pop in and out of existence, and the birth of the universe may have occurred in a similar manner.

“Of course, maybe someone will come up with another model of an eternal universe, and we’ll have to start thinking about it all over again,” Vilenkin said.

Go Deeper
Editor’s picks for further reading

arXiv: Eternal Inflation and Its Implications
Alan Guth, the physicist who originated the inflation hypothesis, summarizes the arguments for eternal inflation.

Edge: The Cyclic Universe
Neil Turok on the past and present of the cyclic universe model.

FQXi: Did the Universe Have a Beginning?
In this podcast, Alexander Vilenkin asks whether the universe could have existed forever into the past.

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Charles Choi

    Charles Q. Choi has written for Scientific American, The New York Times, Wired, Science and Nature, among others. In his spare time, he has traveled to all seven continents, including scaling the side of an iceberg in Antarctica, investigating mummies from Siberia, snorkeling in the Galapagos, climbing Mt. Kilimanjaro, camping in the Outback, avoiding thieves near Shaolin Temple and hunting for mammoth DNA in Yukon.

    • Alan Scotch

      Here’s your model: Every movement we see in our visible universe creates another fork of a universe. Each fork has a probability of existing equal to the probability of that movement occurring. (The probability of me writing this post is smaller than that of me not writing. I have just launched another universe where this post exists whilst the previous universe now continues without this post. ). The “space” ( the dimension in ) which all these new universes spawn could be manifesting what we see as dark matter / energy ?

      • Wwolfe

        This is Hugh Everett’s “many worlds” interpretation of quantum mechanics.

    • Anonymous

      What does the math say? Math, as the language of the universe that we discover and not create, should technically be able to give us the definitive answer. If an idea violates mathematical laws, then it should be rejected. Or is the math of such questions so inherently complex that it shows many different possibilities? Or does the math show that all these possibilities truly exist?

      What assumptions do we make with our math that our math break down at singularities? One hurdle is that math, by definitition, describes systems, that is, the relationships between multiple things. The simplest system is of two things. How do you then achieve a math of one thing? Would it be sufficient for a math to be based on one thing described at two different times? Or perhaps we must learn to be satisfied with never being able to open Einstein’s clock and simply define singularities in terms of their observable effects as we do with other quantum phenomena.

      So back to the Big Bang…under what conditions does a singularity explode? Does this require we propose anti-gravitons? If there is a relationship between gravity and the three other elemental forces and if gravitons exist, then is it possible that black holes first convert all matter into gravitons and then, at a critical mass, gravitons convert to anti-gravitons which causes an explosion? Does the gravity of a black hole increase proportionally to the amount of mass entering it or does the gravity increase more than we would expect for a given amount of mass? What happens then if there is no more mass entering the black hole? Do the anti-gravitons gain the upperhand and cause the singularity to explode or evaporate? What is space? Is it sufficient to describe it as “that which isn’t particles?” If so, how does space expand? Is space “that by which we can observe that one thing is separate from another thing, i.e., that particles are in fact particles?”

      In the end, we are doomed to cyclically describe one form of energy in terms of another as “to be” is described in dictionaries as “to exist” and vice~versa.
      Perhaps the state of things before the big bang can be described as a state of nothing and not-nothing being unified as one “thing”… ah, the dilemma of language. (We are going to start sounding like Taoists now). Even so, perhaps future directions lie not with math but with transcending the conceptual limitations of our current languages – languages which matured within Newtonian macro-world experience. What kind of concepts and language would we have if we had been raised in a quantum world?

    • Pilgrim

      Those scientists who say that to take any discipline, or any subject of learning to its farthermost point is to have all of them eventually meet, and come to the same conclusions, are (in my opinion) correct.

      To speak of time extending backward into eternity, and forward into eternity, sounds like religion to me. To speak of everything beginning from a single, small,dense point before a “big bang” occurs sounds fine, but where did the dense point come from? How did it get there (wherever that is). Where did the empty space come from that is always ready and waiting for the expansions to occur?

      To say that “It aways was, and always will be” sounds as plausible, or as silly (make your own choice) as it is to say that “God always was and always will be.

    • Codysponaugle


    • Vinko Ivo Milić Díaz

      We know all about it. NOVA is the best science source in public television. Thank you WGBH and PBS for this and more.

    • Endless time! Fascinating as ever.