The BICEP telescope located at the south pole. Image Credit: CfA / Harvard

Landmark Discovery: New Results Provide Direct Evidence for Cosmic Inflation

Article Updated: 26 Apr , 2016


Astronomers have announced Nobel Prize-worthy evidence of primordial gravitational waves — ripples in the fabric of spacetime — providing the first direct evidence the universe underwent a brief but stupendously accelerated expansion immediately following the big bang.

“The implications for this detection stagger the mind,” said co-leader Jamie Bock from Caltech. “We are measuring a signal that comes from the dawn of time.”

BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) scans the sky from the south pole, looking for a subtle effect in the cosmic microwave background (CMB) — the radiation released 380,000 years after the Big Bang when the universe cooled enough to allow photons to travel freely across the cosmos.

The CMB fills every cubic centimeter of the observable universe with approximately 400 microwave photons. The so-called afterglow of the big bang is nearly uniform in all directions, but small residual variations (on the level of one in 100,000) in temperature show a specific pattern. These irregularities match what would be expected if minute quantum fluctuations had ballooned to the size of the observable universe today.

So astronomers dreamed up the theory of inflation — the epoch immediately following the big bang (10-34 seconds later) when the universe expanded exponentially (by at least a factor of 1025) — causing quantum fluctuations to magnify to cosmic size. Not only does inflation help explain why the universe is so smooth on such massive scales, but also why it’s flat when there’s an infinite number of other possible curvatures.

While inflation is a pillar of big bang cosmology, it has remained purely a theoretical framework. Many astronomers don’t buy it as we can’t explain what physical mechanism would have driven such a massive expansion, let alone stop it. The results announced today provide a strong case in support of inflation.

In Depth: We’ve Discovered Inflation! Now What?

The trick is in looking at the CMB where inflation’s signature is imprinted as incredibly faint patterns of polarized light — some of the light waves have a preferred plane of vibration. If a gravitational wave passes through the fabric of spacetime it will squeeze spacetime in one direction (making it hotter) and stretch it in another (making it cooler). Inflation will then amplify these quantum fluctuations into a detectable signal: the hotter and therefore more energetic photons will be visible in the CMB, leaving a slight polarization imprint.

E-modes (left side)

E-modes (left side) look the same when reflected in a mirror. B-modes (right side) do not. Image Credit: Nathan Miller

This effect will create two distinct patterns: E-modes and B-modes, which are differentiated based on whether or not they have even or odd parity. In simpler terms: E-mode patterns will look the same when reflected in a mirror, whereas B-mode patterns will not.

E-modes have already been extensively detected and studied. While both are the result of primordial gravitational waves, E-modes can be produced through multiple mechanisms whereas B-modes can only be produced via primordial gravitational waves. Detecting the latter is a clean diagnostic — or as astronomers are putting it: “smoking gun evidence” — of inflation, which amplified gravitational waves in the early Universe.

“The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky,” said co-leader Chao-Lin Kuo from Stanford University, designer of the BICEP2 detector.

Polarization patterns imprinted in the CMB. Image Credit: CfA

Shown here are the actual B-mode polarization patterns provided by the BICEP2 Telescope. Image Credit: Harvard-Smithsonian Center for Astrophysics

The team analyzed sections of the sky spanning one to five degrees (two to 10 times the size of the full moon) for more than three years. They created a unique array of 512 detectors, which collectively operate at a frosty 0.25 Kelvin. This new technology enabled them to make detections at a speed 10 times faster than before.

The results are surprisingly robust, with a 5.9 sigma detection. For comparison, when particle physicists announced the discovery of the Higgs Boson in July, 2012 they had to reach at least a 5 sigma result, or a confidence level of 99.9999 percent.  At this level, the chance that the result is erroneous due to random statistical fluctuations is only one in a million. Those are pretty good odds.

While the team was careful to rule out any errors, it will be crucial for another team to verify these results. The Planck spacecraft, which has been producing exquisite measurements of the CMB, will be reporting its own findings later this year. At least a dozen other teams have also been searching for this signature.

“This work offers new insights into some of our most basic questions: Why do we exist? How did the universe begin?” commented Harvard theorist Avi Loeb. “These results are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was.”

Not only does inflation succeed in explaining the origin of cosmic structure — how the cosmic web formed from the smooth aftermath of the big bang — but it makes wilder predictions as well. The model seems to produce not just one universe, but rather an ensemble of universes, otherwise known as a multiverse. This collection of universes has no end and no beginning, continuing to pop up eternally.

Today’s results provide a stronger case for “eternal inflation,” which gives a new perspective on our desolate place within the cosmos. Not only do we live on a small planet orbiting one star out of hundreds of billions, in one galaxy out of hundreds of billions, but our entire universe may just be one bubble out of a vast cosmic ocean of others.

The detailed paper may be found here.
The full set of papers are here.
An FAQ summarizing the data is here.

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10 Responses

  1. Hematite says:

    “Today’s results provide a stronger case for “eternal inflation,” which gives a new perspective on our desolate place within the cosmos. Not only do we live on a small planet orbiting one star out of hundreds of billions, in one galaxy out of hundreds of billions, but our entire universe may just be one bubble out of a vast cosmic ocean of others.”

    If this is true (and the “eternal” in this hypothesis is a philosophical not a scientific statement), then our place in the universe is no more “desolate” than any other place: desolate compared to what? Typical silly self pitying materialism! Human worth doesn’t consist in where we are, but who we are, which is strongly related to how we act.

    • EmmanuelBA says:

      Worth is a relative notion. Talking about human worth implies that some people are worth more than others. This kind of thinking is directly induced by the market economy we live in. There is no such thing as an “act”. brain activity is deterministic, there is no free will, there are no acts, but we like to think of it that way primarily to justify the existence of our counterproductive judicial system, instead of trying to actually solve social issues by looking at the root causes of behavior. If a meaningful life is a life with direction, there is no need to look for a meaning, it’s already there: we have a body with emotions and desires. They are the drivers. We just need to extrapolate what we know from human behavior and from human psychology to know what society we want to build and live in. this society is the direction.
      Check out the Zeitgeist movement

  2. jc hanford says:

    A preprint of “BICEP 2 I: Detection of B-mode Polarization at Degree Angular Scales” is available here:

    (the site appears to be overwhelmed at the moment!)

  3. metalman_5150 says:

    “n fact, LIGO, in its several years of operation, has never registered a single gravitational wave even when theory predicted it should. So of course plans are proposed to build a more sensitive Advanced LIGO that will be 10x more sensitive than the original LIGO. In such an instrument, theoreticians predict gravitational waves will be detected daily by the time it’s operational in 2014.

    The dogged adherence to gravitational waves and neutron stars in the face of falsifying data has reached a point where one could agree to fund such a device if the failure in detecting gravitational waves in 2014 would cause the astrophysical community to consider a Universe that includes the obvious presence of electrical currents in space.”
    credit –

    • mewo says:

      Oh wonderful. More “electric universe” mumbo-jumbo.

    • No, it was God…. and his Unicorn Yeti, wielding the Hammer of Time! But seriously, I laugh when very rigorous evidence comes out that supports a widely held theory in opposition to some crack-pot hyjinx, so the ONLY way they can argue against the hard data is to conjure a grand conspiracy of disparate people around the world… “It MUST be falsified if it runs counter to my irrefutable-though-non-confirmed nonsense”.

  4. Aqua4U says:

    Next up… further defining that ‘blob’ in the CMB…

  5. I can’t read that headline without inserting a certain present participle verb between “Landmark” and “Discovery” that I will refrain from mentioning here… This is truly Epic!

  6. “Not only do we live on a small planet orbiting one star out of hundreds of billions, in one galaxy out of hundreds of billions, but our entire universe may just be one bubble out of a vast cosmic ocean of others.”

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