A week or so ago, physicists and astronomers alike got really exited by some published research out of Harvard. Astronomers claimed to have detected gravitational waves for the first time! Sounds cool, but hold the phone – these scientists are leaving us at the mercy of some complicated physics.
Here are the questions I hope to address in this post:
1. What is a gravitational wave?
2. How is this plot showing us the presence of gravitational waves?
3. Why is this at all important?
This plot demonstrates the polarization of the magnetic field. Polarization shows how light has been twisted due to the presence of gravitational waves.
1. What is a gravitational wave?
The first important point to understand is that a gravitational wave is not the same as a gravity wave.
A gravity wave is a wave that occurs as the result of gravity – you can see these in the ocean or in the atmosphere. They look like this:
Gravity waves in the atmosphere as the result of density differences in the air.
In contrast, a gravitational wave is a prediction of Einstein’s theory of general relativity. Gravitational waves are a theoretical way in which energy is radiated outward due to a disturbance in the curvature of space time.
What? In Einstein’s theory of relativity massive objects create a dimple of sorts in the very fabric of space time. So for instance, if there is a star orbiting around a black hole, this star will distort the dimple as it orbits, and as a result of this acceleration, energy will be radiated away in the form of gravitational waves.
Massive objects create dimples in the fabric of space time. When a massive object orbits another, it distorts the distortion of the other; this creates gravitational waves.
2. How is this plot showing us the presence of gravitational waves?
As gravitational waves propagate through space, they create a disturbance that looks like this:
This is a linearly polarized gravitational wave because it’s stretching the very nature of light, creating a linear polarization signal in the light detected.
But now it gets more complicated. This linear polarization is only from a specific kind of gravitational wave source. The gravitational waves theoretically predicted from inflation in the early universe are thought to have a circular “swirly” polarization in the magnetic field of the Comic Microwave Background. This is evident in observations and was detected to be much stronger than expected.
The Cosmic Microwave Background is from a very early period in our universe, and is basically equivalent to looking back at the infancy of the universe. This period of time occurred 1/10^35 of a second after the Big Bang. This is 1/(10+35 zeros). This is a an opportunity for physicists to observe energy beyond their wildest imagination, leading us right into point 3:
3. Why is this at all important?
For decades now, scientists have been attempting to pin down how our universe is behaving now and how its beginnings may explain this behavior. This discovery answers some important questions about inflation.
What is inflation?
Through observations, astronomers have been able to show that more or less, the present day universe is not homogeneous. This means it’s not the same in all directions. We see large clumps of galaxies called galaxy groups and superclusters. HOWEVER, from the observations of the Cosmic Microwave Background (earlier observations than this most recent study), we see that in microwave light, the CMB is more or less homogeneous. So how does an early homogeneous universe become the not homogeneous universe we live in today?
We also know that the universe is expanding – galaxies are moving away from us. And this expansion is accelerating. The theory of inflation states that the universe must have expanded extremely extremely rapidly in the first few nanoseconds to preserve our non-homogenous present day universe. This is a bit difficult to wrap your mind around so think about it like this:
Since matter is expanding faster than the speed of light during expansion, it cannot communicate with other patches of matter. Small quantum perturbations in a clump of matter may eventually lead to large scale structure, such as galaxy webs.
A galaxy web created through simulations of the behavior of cold dark matter – this matches our observations of galaxy web structure.
The new observations of the strength of the gravitational waves present in the CMB tell us that inflation was occurring and was much stronger than previously thought. This discovery will spur particle physicists and cosmologists alike to rethink their ideas of the strange physics of the extremely early universe.
Not only does this study tell us about the past, but it helps predict how the universe will develop from its present day structure. This sort of observational evidence from the BICEP-2 team at the south pole pushes the forefront of physics research both in terms of new powerful technology (which we usually find an application for in more practical pursuits) and by providing theoreticians with some fodder to continue their exploration of the physics that we don’t quite understand.
Good work at the south pole, guys!
It may be cold, but the air is thin and dry – great for astronomy!
unravelingthesky 