The Universe As Inquiry:
At some time or other, just
about everyone has looked up at the night sky and marveled
at the moon, planets, and stars, wondering how this strange
universe came into being.
Scientists today posit that the “Big Bang,” the
theoretical “birth” of the universe, happened
some 15 to 20 billion years ago—our small Earth is
a relative newcomer, appearing on the cosmic landscape about
4.5 billion years ago and located in a galaxy that is but
one of billions. Although much has been learned about the
cosmos through observation and theory, many important questions
An impressive number of answers—or at least
tantalizing possibilities—have been advanced by noted
physics professor Alexander Vilenkin, the director of the
Tufts Institute of Cosmology.
Since arriving at Tufts more than a quarter century ago,
Vilenkin has helped shape the field of cosmology, informing
our conception of the universe on the most fundamental levels.
He has had critical insights about the origins of the universe:
the “inflationary” process that enlarged the
universe in an explosive burst, filling it with matter and
energy; the existence of multiple regions within our universe;
and the role of primordial remnants called “cosmic
strings” that stretch across space. His ideas have
established his international reputation and his colleagues
are among the most respected cosmologists at work today.
Andrei Linde of Stanford University, for one, is quick to
praise Vilenkin as “a deep and original thinker who
hasmade profound contributions to our notions about the creation
of the universe.”
Vilenkin, 55, wears that praise lightly at Tufts, where he
spins theoretical models from a modest, book-cluttered third-floor
office in Robinson Hall. A faculty member in the Department
of Physics and Astronomy and director of the Institute of
Cosmology, he is as unassuming as he is soft-spoken. He takes
a moment to reflect when asked why he has devoted his life
to working out elegant and sometimes mind-boggling mathematical
models that have helped us understand the structure and history
of the universe.
“Cosmology is an interesting field to have a conversation
about,” he says, “but what got me fascinated
is that not only can we talk about it, we can learn something
about it. There is no question now that there was a ‘Big
Bang’—we see the afterglow of the Big Bang in
radiation coming to us from the remotest parts of the universe.
So our theories have been confirmed. Still, there are some
puzzling questions I’d very much like to understand.
It’s a pleasure to think about them, and there’s
always the hope that I might come up with an idea that provides
some answers. It’s a great time to be in this field.”
There is not enough space in this magazine to offer a complete
Vilenkin “primer” on cosmology. Still, here are
three “big” ideas that offer a glimpse into his
theories and how they have led to new understanding about
that mystery called the universe.
1. The Beginning
The idea of inflation emerged in 1981 — an idea to
which Vilenkin has made vital contributions. In essence,
inflation is a violent, yet incredibly brief period of exponential
growth during the first fraction of a second of its existence.
Inflation ignited the “bang” behind the Big Bang,
setting the universe on its current expansionary course.
By combining inflation with quantum cosmology, Vilenkin showed
how to produce a universe much like the one we see today.
How, asked Vilenkin, could matter, energy, space, and time
have arisen spontaneously from nothing? In quantum mechanics,
the reigning theory of physics on a small scale, particles
spring into existence out of nowhere for a brief moment,
then vanish just as suddenly. If particles could do that,
Vilenkin surmised, why not an entire universe? He worked
through the equations and showed how a universe might emerge
literally from nothing. “It seemed like a totally crazy
idea,” he admits, “but this is what the calculations
were suggesting.” Vilenkin’s breakthrough provided
the first mathematical descriptions of the creation of the
universe. “At that time, the question of how the universe
came into being was not discussed at all,” recalls
Vilenkin. “The idea was that physics discusses how
you got from ‘state A’ to ‘state B’ but
it doesn’t answer the question: ‘Why was ‘state
A’ there to begin with?’ It was kind of a taboo
question. When I gave a seminar at Harvard, one guy came
up to me and said, ‘It’s amazing to give a talk
like that and survive!’ What used to be philosophy
was becoming physics. Now it is a very active subject.”
As a follow-up, he made the astonishing suggestion that almost
all inflation models are “eternal,” meaning that
once the process starts, it never ends. Inflation, he said,
is like a chain reaction, stopping in one region of space
only to start in another, ultimately spawning an infinite
number of separate regions, isolated from each other by distance
and time, yet still part of a single, unfathomably vast entity.
Vilenkin’s insights not only changed our conception
of the inflationary process, they transformed our picture
of the universe on a large scale, pointing to a complex,
never-ending structure that continues to create worlds entirely
beyond our view.
2. Ever-curious Cosmic Strings
The universe went through phase transitions in its earliest
moments, transitions similar to the freezing of water.
As a result, defects of various forms were produced, including
linear strands that extend clear across the cosmos, thus
known as “cosmic strings.” In the pantheon
of weird objects in the universe, these hypothetical entities
stand beside black holes as two of the most bizarre phenomena.
Either infinitely long or closed loops, they are incredibly
dense and yet thinner than a subatomic particle.
Vilenkin began thinking about cosmic strings in 1980 and
since then has established himself as “the world leader” in
developing the concept, according to MIT physicist Alan Guth.
In 1982, Vilenkin proposed that cosmic strings may have provided
the seeds for galaxy formation—drawing matter together
through unusual gravitational effects that warp the geometry
of space. Since the 1990s, however, astronomical observations
have made this scenario increasingly implausible. The theory
that strings provided the glue that enabled galaxies and
galaxy clusters to congeal wasn’t intrinsically flawed,
Vilenkin explains. “It just described the wrong universe.”
That doesn’t mean we should write off the whole notion
of cosmic strings, says Princeton cosmologist James Peebles. “The
physics is as persuasive today as ever. I expect we’ll
be hearing more about cosmic strings and, when we do, we’ll
be returning to Alex’s fundamental papers.”
Cosmic strings might still exist, Vilenkin agrees. “The
early universe went through several transitions, and it would
be surprising if there are no defects.” He’s
now investigating the “observational signatures” left
behind by such defects, which could provide “a unique
window on the high-energy physics of the early universe.”
Lately, superstring theorists, who dominate theoretical physics
today, have also become enamored of cosmic strings, which
seem to be a common byproduct of their cosmological models.
This interest has led to a spate of papers and a “cosmic
string revival” that vindicates Vilenkin’s pioneering
work, according to MIT physicist Max Tegmark. “Alex
Vilenkin does not hop on the bandwagon. But after a while,
the bandwagon follows him.”
3. Déjà Vu
All Over Again
Vilenkin’s idea of eternal inflation, if correct, led
him to another startling observation about the universe.
Based on the inflation model, there are, he said, a limitless
number of regions (the same size as our observable region)
within the universe, though separated by insurmountable stretches
of space. In other words, an infinite number of regions exist
beyond the visible world.
Pondering the implications of these multiple regions in a
recent paper, Vilenkin and former postdoctoral fellow Jaume
Garriga (now at the University of Barcelona) arrived at a
jarring conclusion: the number of “histories”—or
things that could possibly happen within these realms—is
finite. “That means, if you have an infinite number
of regions and a finite number of histories, it’s clear
that these histories must repeat,” he says. “If
you have dice, and you throw the dice, you have only a finite
number of possible outcomes. Now imagine an infinite number
of people throwing those dice. I can predict an infinite
number of people who will get the same result that I get
Vilenkin sees this as an extension of the Copernican revolution,
which placed the sun, rather than the Earth, at the center
of the universe. “We now see that we’re not the
center of the universe, and we’re not special either,” he
says. “Our history is typical among possible histories.”
So somewhere, in another universe, for example, will long-suffering
Red Sox fans have to wait 86 years for the “Curse of
the Bambino” to be lifted?
Yes, says Vilenkin, and he’s not particularly happy
about it—on a cosmic scale. “I don’t like
this conclusion,” he says. “I did not like to
admit that we’re not special – good or bad, but
at least I had hoped we might be unique!”