How It's Made: Gravitational Waves

Surprise! Who would have guessed it; Einstein gets it right again. Thanks to the amazing scientists and engineers at the Laser Interferometer Gravitational-Wave Observatory (LIGO), this past September we were able to make the first ever direct-detection of gravitational waves. The existence of these waves is something that has been expected since Einstein's theory of general relativity became a commonly accepted idea. In fact it was the only remaining item yet to be confirmed from his famous theory. However this discovery holds significance beyond just the confirmation of his ideas. In time, we may soon be able to see the universe in a completely new way.

 For this post, I will be discussing the origins of these waves as well as some of their properties that makes this discovery so significant. However, to truly understand the nature of gravitational waves, you must first have a complete understanding of what gravity is.

Ripples on a Pond

I'm sure you have all heard the story before; Isaac Newton sits in his garden under his favorite apple tree, pondering the behaviors of the universe, when suddenly it hits him (the apple, that is). "There must be a force of attraction between all objects with mass, otherwise this apple would have no reason to fall downwards!" Now obviously the validity of the story is questionable, but the significance remains the same.  Isaac Newton's discovery on the forces of gravity was monumental in the world of physics. However there was one question that Newton was never able to find the answer to: Where does this force originate from?

2-D representation of gravity

Enter Albert Einstein, roughly 300 years later, with the answer to one of the world's most puzzling questions. Einstein proposed that gravity was not just some mystical force of attraction between two objects, but the reaction of mass to the warp of space-time. This concept intimidates many, but visualizing is the key to understanding in this case. Take the Earth and the Moon for example. The Earth, being a massive object, will create a distortion in space-time. Because of this distortion, or curvature as some people refer to it, the moon has a tendency to fall towards the earth and doesn't travel forever in one direction. This can be said the same for why the Earth revolves around the sun, or why the sun revolves around the center of the galaxy. As the late John Wheeler once described it, "'Matter tells space how to curve. Space tells matter how to move."

A simulation of the two neutron stars revolving around one another

So where do these gravitational waves come into play you ask? Well it's important to realize that gravity and gravitational waves are not one and the same. While gravitational waves are a consequence of gravity, they are two completely different phenomenon. Gravitational waves are made when you take massive objects that are warping space-time, and you begin to accelerate them. In the case of the September 15th discovery at the LIGO observatory, scientists detected a pair of stars rapidly revolving around each other until combining together. Because of the extremely high density and speed of rotation for these stars, intense gravitational waves were created and emanated towards Earth. As of right now only highly energetic events like these are able to be detected, but as the equipment advances, more and more cosmic events will be able to be observed.

A Light in the Dark

Nearly all the information we have gained of other celestial bodies, up until now, has been through observing its electromagnetic radiation (light). If it gave off an intense enough electromagnetic wave, then it can be analyzed to further understand its properties. In many ways, gravitational waves share the same tendencies as electromagnetic radiation. Both carry some amount of energy. Both travel at the speed of light. Both carry information about the source of their existence. How the two differ is what makes gravitational waves so important though.

As electromagnetic radiation travels through space-time, the intensity of the radiation decreases at a pretty significant rate. Also, obstacles that may block our view limit the amount of light that can be analyzed. For example during different seasons we would not be able to look at the stars blocked by our sun. Gravitational waves travel through space-time with a constant intensity, and are able to pass through matter completely unchanged. This combination of characteristics means that at any point in time, no matter the position of Earth's rotation or the distance between the source and the Earth, we will be able to receive it's message. Metaphorically speaking, astrophysicists have always used their eyes when looking for information, but now they are finally learning how to use their "ears".

Sources:

Redd, Nola Taylor. "Einstein's Theory of General Relativity." Space.com. N.p., 11 Feb. 2016. Web. 21 Apr. 2016. <http://www.space.com/17661-theory-general-relativity.html>. 

Cho, Adrian. "Gravitational Waves, Einstein's Ripples in Spacetime, Spotted for First Time." Science. N.p., 10 Feb. 2016. Web. 21 Apr. 2016. <http://www.sciencemag.org/news/2016/02/gravitational-waves-einsteins-ripples-spacetime-spotted-first-time>.

"Gravitational Waves Detected 100 Years After Einstein's Prediction." LIGO Lab. N.p., 11 Feb. 2016. Web. 21 Apr. 2016. <https://www.ligo.caltech.edu/news/ligo20160211>. 

Warped grid Earth and moon. Digital image. Science Blogs. N.p., n.d. Web. 21 Apr. 2016. <http://scienceblogs.com/startswithabang/files/2013/01/Warped_grid-earth-moon1-590x442.jpg>.