What's behind the Big Bang controversy?

Story highlights

  • Meg Urry: A controversy about the origin of the universe came to light this week
  • Urry: The idea that there was rapid "inflation" in the early universe is being questioned
  • She says controversy may be messy but that's how we make progress in science
  • Urry: Most scientists don't care about the "win" -- we care about getting nature right

Everyone wants to be right. Most of us sure hate being wrong.

But scientists know that new discoveries often change or even invalidate earlier ideas. Being wrong can mean we have learned something new.

This week, a controversy about the Big Bang and the origin of the universe came to light at the American Astronomical Society conference in Boston. In an invited lecture sponsored by the Kavli Foundation, Princeton astrophysicist David Spergel offered a different idea about a discovery made last March, where the BICEP2 Antarctic cosmology experiment reported evidence of a period of rapid "inflation" in the very early universe. Specifically, researchers detected the special pattern of polarization that would be caused by gravitational waves stretching and squeezing space itself during inflation.

Meg Urry

Last week, three theorists -- Alan Guth, Andrei Linde and Alexei Starobinsky -- were awarded the prestigious Kavli Prize for astrophysics for their work developing the theory of cosmic inflation. (This prize and the AAS lecture were sponsored by the same foundation but were otherwise completely independent.) Their award may well have been prompted by the BICEP2 discovery, which generated a lot of excitement about early universe cosmology.

But at the American Astronomical Society conference, Spergel argued that the BICEP2 results reported in March could instead be explained by a more pedestrian effect, namely, light scattering off dust between the stars in our Milky Way galaxy. If he is correct, the widely heralded BICEP2 announcement was premature at best and wrong at worst.

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This kind of controversy is completely normal in science. It's the way science progresses. You put an idea out there and your colleagues -- many of them good friends and scientific collaborators -- try to shoot it down.

A scientist's first reaction to a new idea is often: "That's wrong because...." To which the proponent replies, "No, you are wrong because..." And so the debate begins.

No matter how much a scientist might hope to be right, nature holds the answer. One theory may be more beautiful than another, or more complicated, or more elegant, but nature doesn't know or care. The job of a scientist is to find out what the real answer is, not to advocate for any one point of view.

We do that by making careful measurements and assessing the accuracy of the result. BICEP2 detected certain polarization patterns in light from the cosmic microwave background, which they believe were created during inflation. David Spergel is instead suggesting the light was polarized by passing through galactic dust near the end of its journey to our telescopes -- indeed, he argued, this dust is expected to create the kind of polarization signal BICEP2 saw.

To support his contention, Spergel cited data from a space experiment called Planck, which like BICEP2 measures polarized light from the cosmic microwave background. Planck's ability to measure light at more wavelengths than BICEP2 gives it an advantage in diagnosing the effects of dust.

If the BICEP2 team is correct, they detected the first signs of gravitational wave distortions of space in the first one hundred millionth of a trillionth of a trillionth of a second of an early, extreme inflation of space -- an extremely important discovery.

If Spergel is correct, a significant signal from primordial gravitational waves has not yet detected and we need to keep looking for this critical probe of our universe.

New measurements from the Planck team are expected next fall. Maybe they will settle the controversy. Either way, an array of increasingly sensitive experiments will make still better measurements of the cosmic microwave background.

This is an important goal. Since the early universe is far hotter than any laboratory on Earth -- or, for that matter, in the most energetic regions around black holes or in the most massive clusters of galaxies -- it offers a very important experimental laboratory for testing fundamental physics theories.

That's one reason the debates will continue until one side convinces the other. But most scientists really don't care about the "win" -- we care about understanding nature.

Even Spergel, at the beginning of his address to the American Astronomical Society audience, called the BICEP2 results "heroic science" -- a very difficult measurement that pushes the limits of current technology.

Controversy and debate may be messy but that's how we make progress in science.

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