Big Bang to Little Swoosh
By MAX TEGMARK, APRIL 11, 2014, NYT.
CAMBRIDGE, Mass. — The shock waves are still reverberating from the bombshell
announcement of the discovery of cosmology’s holy grail: telltale signature of ripples in the
very fabric of space generated as it “inflated” during our cosmic origins.
I think that if this discovery holds up, it will go down as one of the greatest in the history of
science. It teaches us humans that we need to think big, because we are the masters of
underestimation. Again and again we have underestimated not only the size of our cosmos,
discovering that everything we thought existed was merely a small part of a much grander
structure (a planet, a solar system, a galaxy, a universe, and maybe even a multiverse), but we
have also repeatedly underestimated the power of our human minds to understand our
cosmos.
By discovering hidden mathematical patterns and regularities in nature that we call equations
of physics, we have gotten progressively better at predicting things — from tomorrow’s
weather to tomorrow’s technology. The planet Neptune, the radio wave and the Higgs boson
were all predicted mathematically before they were observed. Our most audacious prediction
ever is the theory of cosmological inflation, which extrapolates known physics to energies a
trillion times higher than those of the Large Hadron Collider.
Inflation predicts that our baby universe grew very much the way you yourself did right after
conception: Each of your cells doubled roughly daily, causing your total number of cells to
increase day by day as 1, 2, 4, 8, 16, etc. Repeated doubling is a powerful process, so your
mom would have been in trouble if you had kept doubling your weight every day until you
were born. After nine months (about 274 doublings), you’d have weighed more than all the
matter in our observable universe!
Crazy as it sounds, this is exactly what inflation does: It takes a speck of matter with less mass
than an apple, smaller than a billionth the size of a proton, and repeatedly doubles its size until
it is more massive than our entire observable universe, because of an instability in Einstein’s
theory of general relativity. And whereas you doubled in size once per day, our universe
doubled once every hundredth of a trillionth of a trillionth of a trillionth of a second.
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Then, just as you eventually stopped your regular doubling and began growing at a more
leisurely pace, so did our baby universe, once it had exploded to the size of a grapefruit. But
at this point it was flying apart so rapidly that its expansion continued for another 13.8 billion
years, during which it cooled and clustered to form ever more interesting objects: quarks,
nuclei, atoms, stars, planets and, ultimately, us.
Extraordinary claims require extraordinary evidence, and the claim that physics needs less
than an apple’s worth of mass to create the billions of galaxies that adorn our current cosmos
is certainly extraordinary. Fortunately, this theory makes a long list of predictions, and we
cosmologists have become awestruck as they’ve proven correct at an ever-accelerating pace,
with a recent crescendo culminating with the startling discovery of ancient ripples in space.
Predictions confirmed so far include that our universe is expanding (1929), that it was once as
hot as the surface of the Sun and left behind an afterglow (1965) that can be photographed to
provide baby pictures from when it was 400,000 years old (1992), and that the spots in these
baby pictures have the predicted sizes (1999-2000) and a large number of other predicted
properties to exquisite precision (past decade).
Then there was the mother of all predictions: that the repeated early doubling of space was
violent enough to cause ripples in the fabric of space known as gravitational waves, and that
these would be so intense and huge (close to a billion light years long) that no other process
could have made them.
Making such strong gravitational waves requires extreme violence, and one can prove that
any physical process other than inflation would make predominantly shorter ones. For
example, a cataclysmic collision of two black holes squeezing more than the Sun’s mass into
a volume smaller than a city can create gravitational waves that the American-based LIGO
experiment hopes to detect — but these waves are only about as big as the pair of objects
creating them.
That is why my colleagues and I felt so amazed when it was announced that enormous
gravitational waves had been discovered. Gravitational waves distort light, and after spending
three years zooming in on about 1 percent of the sky from the Bicep2 telescope near the South
Pole and taking an even sharper baby photo of our universe, including its polarization,
scientists discovered that it was distorted in precisely the way inflation had predicted.
Now what? First of all, we will look forward to seeing whether other experiments can confirm
the Bicep2 findings. Because gravitational waves from inflation have long been the holy grail
of cosmology, the search for them has been intensely competitive, so if the gravitational
waves are as long and strong as claimed, then many other experiments will soon detect them
and measure them even more precisely.
Second, this discovery has triggered big spring cleaning in theoretical physics. If the results
stand the test of time, they rule out not only all compelling competitors to inflation (including
the cyclic-ekpyrotic universe models), but also the vast majority of popular inflation models.
For both the Higgs boson and inflation, the original models were extremely simple, and then
creative theorists added bells and whistles to concoct countless complicated models during the
decades that followed. In both cases, however, the experimental results brought us “back to
basics,” agreeing beautifully with the simplest models and chalking up striking victories for
Occam’s razor.
If inflation really happened, it fundamentally transforms our understanding of our origins. We
need to stop saying that inflation happened shortly after our Big Bang, because it happened
before it, creating it. It is inappropriate to define our Hot Big Bang as the beginning of time,
because we don’t know whether time actually had a beginning, and because the early stages
of inflation were neither strikingly hot nor big nor much of a bang.
Inflation is better thought of as a Cold Little Swoosh, because at that time our universe was
not that hot (getting a thousand times hotter once inflation ended), not that big (less massive
than an apple and less than a billionth of the size of a proton) and not much of a bang
(expanding a trillion trillion times slower than after inflation).
In sum, Bicep2 has revealed that our Hot Big Bang was created by a Cold Little Swoosh, and
that although we humans may be small, the power of our minds to figure things out has
superseded our ancestors’ wildest dreams.
Max Tegmark is a physics professor at M.I.T. and the author of “Our Mathematical
Universe.”