It seems that in the coming days we will talk a lot about gravitational waves. But why sometimes they are mistakenly called “waves of aggression”? In this world of social media, where brevity is most often valued primarily, it may seem that reducing the phrase “gravitational waves” to “waves of a wave” is not such a big deal. Moreover, it allows you to save a few extra characters for fans of Twitter!
And most likely you will see a lot of headlines in the news, foreshadowing “gravitational waves of science”, replaced by the word “brawling”, but don't fall into this trap. While both words have weight, in essence, gravitational waves and waves of aggression are completely different “creatures”. Read on to find out how they differ, and even be able to show off your gravitational knowledge the next time in front of friends in a pub.
Gravitational waves are, in the most general sense, some kind of ripples in space and time. Einstein’s theory of general relativity predicted their existence more than a hundred years ago, and they were formed on the acceleration (or actually slowing down) of massive objects in space. If a star explodes as a supernova, then gravitational waves carry energy away from detonation at the speed of light. If two black holes collide, they will cause a ripple in space and time, resembling a ripple in a pond where a stone was thrown. If two neutron stars rotate with each other very closely, their energy, which is carried away from the system - you guessed it - is called gravitational waves. If we could detect and observe these waves, which the new era of astronomy of gravitational waves may possibly allow, we will learn to recognize gravitational waves and work with the phenomena that reproduced them. For example, a sudden impulse of gravitational waves may indicate that they were received from an explosion from a supernova, while a continuous oscillating signal may indicate a close orbit of two black holes before they merge. Until now, gravitational waves are theoretical, despite the existence of strong indirect evidence. Interestingly, since gravitational waves propagate through space, they will physically deform the “fabric” of space, that is, very weakly reduce or expand the space between two objects. The effect is negligible, but using a laser interferometer, such as a gravitational-wave observatory laser interferometer or LIGO, which measures the smallest waves in lasers reflected through 2.5-kilometer L-shaped vacuum tunnels, gravitational waves can be detected across our planet. In the case of LIGO, there are 2 stations located on opposite sides of the USA, divided by almost 2000 miles. If the gravitational wave signal is real, its signature will be observed in both places; if this is a false signal (that is, a truck just drove past), then only one station will detect the signal. Although LIGO began its activities in 2002, it has yet to detect gravitational waves. But in September 2015, the system was upgraded to Advanced LIGO and it is hoped that physicists will finally provide us with good news on Thursday.
Bonus: Primary gravity waves. You may remember the turmoil with the “discovery” of BICEP2 (and then with non-detection) of gravitational waves in the faint initial “luminescence” of the Big Bang known as the cosmic microwave background (CMF). Although the “discovery” of BICEP2 turned out to be hopeless, it is believed that tiny gravitational waves around the time of the Big Bang can leave their “imprint” in this ancient radiation as a special kind of polarized light. If the imprint of the primary gravitational waves (those produced by the Big Bang) is observed, then some models of cosmic inflation and quantum gravity can be confirmed. However, these are not the gravitational waves that LIGO is hunting. LIGO (and the observatory similar to it) is looking for gravitational waves, which are generated by energy events taking place now in our modern Universe. Hunting for primary gravitational waves is a semblance of an archaeological excavation of the past of our Universe.
Waves are physical disturbances, controlled by restoring gravity in a planetary environment. In other words, the waves are characteristic only for planetary atmospheres and water bodies. In the case of atmospheres, the air blows through the ocean, and then, encountering an island, for example, is forced to rise. On the leeward side, the air will be forced to stay at a lower height under the action of gravity, but its buoyancy will work against gravity, causing it to rise again. As a result, often an area of oscillating air in the atmosphere can produce clouds in the crests of the waves. Examples of waves are wind waves, tides and tsunamis.
Thus, it turns out that gravity drives gravity waves and waves of gravity, but they have very different properties that should not be confused.
