Looking into the Past

Abstract

LOOKING INTO THE PAST BY MOONSUK JANG USING GRAVITATIONAL WAVES TO STUDY THE WPRIMORDIAL UNIVERSE F ebruary 11, 2016. LIGO scientists offi- cially announced the direct detection of gravitational waves. It instantly became one of the hottest topics of the day, and people expressed their excitement. Some because they understood the significance of the discovery, and some because they wanted to blend in. To better understand about the excitement, it is important to know what gravitational wave is, and why it is a remarkable achievement to detect them. WHAT IS GRAVITATIONAL WAVE Gravitational waves are, of course, waves, but where did they get “gravitational” part from? To know why these waves are spe- cifically called “gravitational” waves, we need to first take a look at some features of gravity. According to Einstein, gravity can be explained as curved space. “Gravitation- al waves are ripples in the fabric of space- time.” 1 Just like heavy objects can bend space around them, propagation of grav- itational waves creates ripples, or distor- tion, in the spacetime fabric. Gravitational waves can be generated by any accelerating object with mass, which means objects we can see everywhere such as cars, can gen- erate gravitational waves. However, to gen- erate strong enough gravitational waves to be detected, we need much more energy than that. The gravitational waves scientists detected at LIGO was caused by two black holes, each with mass of 29 and 36 suns, colliding with each other 1.3 billion years ago. 3 suns’ worth of mass turned into pure energy which was radiated as gravitational waves. Kip Thorne, a physicist at the Cal- ifornia Institute of Technology, said, “It is by far the most powerful explosion humans have ever detected except for the Big Bang.” 2 Another distinctive feature that gravita- tional waves have is that it can travel free- ly. Most waves like sound waves or ocean waves require medium to propagate. That means, without proper medium, there can- not be waves. Electromagnetic waves, on the other hand, do not require any medium, and that is why this is about the only tool we can use to study about the universe. Just by using electromagnetic waves, scientists could unravel many mysteries about the universe, but it has its limit. We know from our daily experience that light can easily be blocked. Also, light can be bent, distorted, or even trapped by strong gravity. Some of the most interesting objects, such as black holes cannot be studied using electro- magnetic waves. Since light cannot escape from inside black holes, it is impossible to study what is going on inside black holes using electromagnetic waves. Gravitational waves, however, barely interact with mat- ters, which means that they do not lose as much information as they travel across the universe. Gravitational waves can still be absorbed by enough masses with dissipa- tive forces, but it is practically impossible. 3 HISTORY OF SEARCH FOR GRAVITATION- AL WAVES Ever since their existence was predicted by FALL 2016 | Berkeley Scientific Journal