Monday, 22 September 2014

Quantum Fluctuations and Cosmic Inflation

By Maharshi Chakravortee

Let me ask you a question. Has it ever struck your curious mind as to how all these incredibly beautiful structures - these planets, stars, galaxies - came from a mere singularity, or in simple words the ‘Big Bang’? Since the Big Bang was hypothesised, all theoretical, experimental and astronomical physicists went bonkers to find out exactly how ‘inflation’ (I will come to that) can be proved to cement the Big Bang Theory, or if the Big Bang Theory is just a crazy idea to satisfy our minds temporarily about the origins of the universe. Are we all in a state of oblivion, or does science actually play God in this?

Look at this image for starters:


This is a baby photo of our universe, from when the universe was about 380 thousand years old. Now if you’re thinking that 380 thousand years doesn’t sound that young and asking yourself why we can’t get an image of the universe before that, this is because at that time the universe was so hot, that all matter, including protons and electrons, were in a state of plasma, a sort of jumbled mess. Any light that passed through it would be scattered or absorbed. This made the universe opaque, until 380 thousand years ago when the universe was cool enough to make these protons and electrons, allowing the formation of Hydrogen atoms and allowing light, or photons rather, to spread out. So from the 380 thousandth year to the present day, roughly 13 billion years, these photons would travel through the space-time continuum until it hit our detectors, which made us this image.

Now if you think about it, these photons travelled as the universe expanded. So what might have started as ultraviolet or blue light, ended up as microwaves by the time they got to us. The wavelength of the light expanded as our universe expanded. That is why we can’t see this radiation but we can detect them using microwave telescopes.

The discovery of the microwave background image started off as a funny incident. Two radio astronomers, A.A. Penzias and R.W. Wilson, were observing certain radio images at the sky, but they always got this annoying background noise while taking results. So maybe they thought a cable was loose, or maybe it was bird poop on their telescopes. Triple checking everything, all they got was one uniform image, wherever they pointed their telescopes. So the real early baby photo actually looked like this:

That was the early state of the universe, where all of it was completely uniform, and variations only occurred in about one part of a hundred thousand. To observe these variations, we built better telescopes and sent them to space to get a better-refined image, and what we got was this:

Thanks to the curious human brain, we liked that image so much that we built better telescopes and got this further refined image with incredible details of the variations, which looked like this:

This is the perfect baby image with variations of dark red-hot spots and orange-yellow cold spots, showing the higher density regions and lower density regions respectively. Now this lumpiness and non-uniformity (variations) are very important as these show that the parts, which are red or denser, have a stronger gravitational pull, pulling mass around it, forming clusters of stars or galaxies. So basically without these variations, we wouldn’t even exist.

Now, where did those lumps come from? The idea seems to come from quantum fluctuations, the basic idea that every matter is made up of quantum fields, and it is impossible to keep those quantum fields at a state of uniformity, there will be particles popping in and out every instant, the very idea of Heisenberg’s Uncertainty Principle. This actually gives us the fact that we exist due to this: quantum fluctuations is the mother of our existence.

Now coming back to the problem of the true baby photo, the uniformity. How can the universe be of the exact same temperature after the Big Bang? Isn’t that weird? That is when physicists proposed ‘inflation’, the idea that this uniform image is actually an expanded version of the real image. Consider this for an example.

This is a picture of a dog. I know, cute right? Now what would happen if I expand or ‘inflate’ this image a million times? You’ll end up with something like this.

This looks rather more uniform, kind of like the early baby photo. So what scientists presumed was that the uniform image was an inflated version of the true photo, a photo that we cannot take. But this is kind of a crazy idea created to deal with the problem with that picture. I mean is it really true, did inflation really happen? Or is it just a convenient fiction to try to explain the uniform baby photo? I mean how can we get an answer to this hypothesis, when we can’t get detect any light older than 380 thousand years?

This is where an incredibly interesting term of gravitational waves comes in. Gravitational waves are nothing but the fluctuations or the rippling in the space-time continuum that are caused due movement of bodies. According to calculations, the gravitational waves that accompanied inflation should have been strong enough to have left an imprint on the cosmic microwave background, an imprint in the form of polarisation of light, a kind of a ‘swirl’, around the hot and cold spots. This means scientists were studying the Cosmic Microwave Background to see if it contains polarised patterns, which would have been made by gravitational waves much earlier.

Arriving to the drumroll of this article, scientists obtained a polarised pattern while studying the CMB in the South Pole. And how did the pattern match with the predicted pattern? EXACTLY HOW IT SHOULD HAVE!

This is one of the HUGEST discoveries in a lifetime. Of course this result has a lot of debate to face, but this certainly cements the idea of the Big Bang, the Origin of the Universe and inflation. It really is an exciting era of science to live in!


1.Wikipedia- Cosmic Background Radiation
2.Wikipedia- Gravitational Waves
3.Wikipedia- Inflation


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