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Evidence of Inflation: B-mode Polarization

With the detection of B-mode polarization, we were one step closer to making sure that inflation is indeed true.
Last time we talked about the four problems that the Big Bang theory cannot explain, but inflation theory can solve all these four problems. But, however, inflation theory is still a theory, it’s not proven yet. There’s no observational proof yet. So how do we prove this inflation theory? That’s what we’re gonna talk about today. And then, uh, so, inflation is at the beginning of the history of the universe. Then if we find evidence of the inflation, that sure, I believe is a Nobel Prize. Um, here, to detect inflation we’re gonna talk about this Hawking radiation. So Hawking, we talked about Hawking radiation creates gravitational wave as well. So this pair creation in the early universe, it also includes graviton and antigraviton.
So, inflation, um, also creates a gravitational wave background when one of the graviton goes outside of the event horizon then the other one is going to fly to us. So inflations protects gravitational wave background. How do we detect this gravitational wave background? Then we’re gonna talk about CMB polarization. When CMB photon encounters electron, its experience Thomson’s scattering and then light is polarized. For example, if the photon comes this way, and then meet(s) electron and scatters then light is polarized this way, right?
And when two photons come from different direction(s), for example cold photon from this way, hot photon from this way, and it gets polarized, but in this case cold photon is stronger than hot photon, so cold photon is polarized this way and then light is polarized in this way, because hot photon is weaker. So, this CMB polarization happens because there are a lot of electrons in the other universe when the Big Bang, when the universe was hot plasma. And here, primordial gravitational wave is quadruple from Einstein’s equation, its quadruple. Quadruple means, this is this kind of oscillation, and this, this kind of oscillation, 45 degrees.
So here, plus this way and this way, but also 45 degrees this way and this way. So, quadruple oscillation, and quadruple oscillation and in quadruple oscillation only can produce polarization pattern that is B-mode this is curl, this you know, rotating curl modes. This polarization patter can be only created by the quadruple, which is gravitational wave. CMB temperature fluctuation, CMB also has temperature fluctuation from the same Hawking radiation, right? But, these temperature fluctuations can only produce E-mode, these kind of, you know, gradients mode. So, if we can detect this B-mode polarization, then, that is a proof of the inflation theory, that is from the gravitational wave, predicted by the inflation theory.
So that’s why people are trying to detect this B-mode polarization. One of the telescope(s) is this BICEP2 telescope at the South Pole, they are trying to detect uh, CMB polarization at the South Pole.
And in, in 2014 they, uh, published the observational results of B-mode polarization in a map, on the sky it looks like this, so these are directions and strengths of the B-mode polarization. And there are some patterns. If you take a look at the power spectrum of that data, it looks like this. So this is a power, in this Fourier space, and this is a power as a function of scale. So this is Fourier space so this is large scale, and large number it’s small scale. And their data, BICEP2, is these black points.
Their sensitivity is much better than other telescopes, the, the sensitivity is much better, and then this winding curve, this one is a theoretical prediction from primordial gravitational wave. Does it match(es) with the data? It seems here it matches right?
So, they did a, um, announcement, uh, they detected, they thought they detected a primordial gravitational wave which is a, which is a proof of the inflation theory, and then congratulated, um, Andrei Linde, one of the founders of the inflation theory in Stanford. However, um, next year 2015, Planck’s satellites collaboration, uh, published new polarization data from the dust, and then in this plot in their plot. So this is the, their detection of the B-mode polarization from BICEP2, and then this blue area is the region, uh, consistent to be the dust emission polarization from the dust in the Milky Way, by the Planck satellite.
So unfortunately this curve, and then this blue region perfectly matches, so the detection by the BICEP2 team can be explained with the dust emission from the Milky Way galaxy, unfortunately. However, our journey continues. So, BICEP2 teams are making new telescope, BICEP3, and started observation. This is much more sensitive than BICEP2 observation. And they are taking data even now, and then we’re getting one more sensitive, and I don’t know where’s the signal, but once they reach the signal, uh, they should be able to detect it, maybe in the next several years and then once they detect it, it’s proof of inflation theory, and it’s worth Nobel Prize, so the exciting moments are coming in few years I believe.
So, we live in a very exciting era.

Even if we were able to predict inflation, it will not be helpful for us if we cannot show that it is indeed real.

In this video, Prof. Goto will discuss how can we prove that inflation is real by detecting what we call B-mode polarization. He will also mention one instance of this detection using the BICEP2 telescope located at South Pole.

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