Tuesday, March 18, 2014

How to describe today's discovery to your grandma!

BICEP2 telescope in South Pole
Figure.1: BICEP2 telescope at South Pole
Today, a major discovery in astrophysics has been announced by a research collaboration named BICEP2 which raised lots of interest, attention, and discussions in the science community as well as in public. Paolo already wrote a great note on this at The Gravity Room but here I would like to add another note to show you how I summarize the whole story to my grandma (or whoever else not in the field):
1. Question: What they have discovered?
Answer: A strong evidence for the existence of gravitational waves (GWs) coming all the way from the very early stages of the universe i.e. just after Big Bang explosion!
More details: Using a modern telescope located at south pole, they have found another strong evidence for existence of GWs by studying the polarization of CMB (Cosmic Microwave Background) data. This is another indirect detection of GWs but not the first one. The first (indirect) detection was made by Hulse and Taylor (Nobel Prize winners of 1993) from a binary pulsar source while this recent experiment has detected the signature of GWs from the very early stages of the universe i.e. just after the Big Bang. Compared to the Hulse-Tayor's Binary Pulsar, in this case GWs are coming from completely different sources! Remember, we have not detected GW directly yet. This is what LIGO/VIRGO and other interferometric GW detectors are supposed to do in the next few years: the first direct detection of GWs...

Figure.2: Look grandma! This diagram is the heart of the story which compares the previous results (red) to BICEP2 results (blue) on measuring two parameters of CMBpolarization (vertical and horizontal axises). In another word, the red and blue areas show the allowed values of CMB polarization parameters based on the old and new experiments. New results (blue) clearly exclude the possibility of parameter "r" to be zero! This means a smoking gun for GWs coming all the way from Big Bang!
2. Question: Why is it important?
Answer: This is the first time that we have observed the signature of GWs from the Big Bang! It's quite exciting, isn't it? It also supports our early scenarios of the early universe and quantum gravity specially the Big Bang and Cosmic Inflation... In addition, if the results get confirmed by future experiments and the result holds up, it gives us an unprecedented view of the earliest moments in the history of the universe.
3. Question: Should we celebrate now?
Answer: Yes, but not too much! Because (1) Looking at the same thing (polarization of CMB in B-modes), soon, several similar experiments will come out with new data/results. So it's better to wait a bit and see the confirmations/disconfirmations... This is how science works! (2) A much bigger party is on the way: LIGO! In which we will be able to directly detect GWs from compact binary systems for the first time. LIGO will not only directly detect GWs but also will open a completely new branch of astronomy i.e. GW Astronomy; in which we can measure the physical parameters of the astronomical objects like sky-position, mass, spin, etc that for some cases we might not even be able to measure by other instruments such as optical-, radio-, x-ray-, and gamma-ray-telescopes.

Figure.3: The frequency spectrum of Gravitational Waves and the sensitive range of different detectors. So, grandma! Focus on the "red" lines/notes. Looking at this figure, this is all they are talking about: using "Cosmic CMB polarization" as a detector to detect those GWs emitted from "quantum fluctuations in early universe" in the low frequency band of the spectrum. Notice that the primordial GWs coming from the early universe can be seen in a broad range of frequencies but CMB polarization experiments can only detect a small range of lower frequencies. Now you may ask "what do you need LIGO for while BICEP2 has already detected GWs!" Grandma! Look! Now focus on purple lines/notes and notice that the GWs that LIGO (one among other Terrestrial Interferometers) is supposed to detect is in the other side of the frequency spectrum for higher frequencies and for different sources including quantum fluctuations of early universe at much higher frequencies plus others sources such as compact binary systems and supernova explosions.
Grandma! You should fight against gravity and stay tuned until the first detection announcement of LIGO in the next few years... Then we can totally celebrate testing the last untested piece of Einstein's General Theory of Relativity: Gravitational Waves!

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