GTR-General Theory of Relativity
LIGO-Laser Interferometer Gravitational-Wave Observatory
General Theory of Relativity
In order to understand gravitational waves, we first need to have a basic knowledge of Einstein’s General Theory of Relativity, one of the greatest theories in the history of theoretical sciences. It is a belief that Einstein had remarkable imagining power. One of his thought experiments lead him to believe that there was a fourth dimension in the universe, the space-time. This concept totally changed how humans understood gravity. In his GTR, Einstein proposed that objects with comparatively higher masses cause a ‘dent’ in the space-time dimension. This becomes the cause of attraction between any two objects in the universe. This was Einstein’s way of explaining gravitational force. In case of our own solar system, the comparatively higher mass in the local region of milky way galaxy would be the SUN, which becomes the reason of planets orbiting the sun in a specific way.
This theory can be explained by a very simple physical experiment. A small clip of this very experiment has been attached with the blog post.
AN INSIGHT ABOUT THE EXPERIMENT
Conducting the experiment is actually really fun and simple. We take a trampoline like object, and we put a very heavy bowling ball on it. The bowling ball automatically causes a stretch right in the middle of the trampoline, pulling the material with the maximum amount of force, and hence causing an expansion in a very specific region of the material. Next, we take smaller pebbles, with a much smaller mass in comparison to the bowling ball. We observe that if we release the pebbles with some external force, the pebbles start to form a certain path around the bowling ball, and they continue to revolve in that particular path for a limited amount of time, before they lose all of the angular velocity and fall into the dent created by the bowling ball. If we compare this experiment to our solar system, there aren’t many differences. The bowling ball is the parallel for sun in our solar system, the pebbles are the parallel of the planets, and if you haven’t guessed already, the trampoline is the parallel for the fourth-dimension space-time. This concludes the GTR party for the blog. We could go on and on about a topic such as GTR, but for this particular post, this much is enough to understand our main topic. NOTE- in the video attached, a heavy magnet is used instead of the Bowling ball.
What did Einstein have to say about Gravitational Waves?
Einstein’s GTR was first published in 1915. It was after a decade of hard work that Einstein was finally able to publish the GTR. But Einstein did not stop there. In the year 1916, Einstein predicted about Gravitational waves. Though he was not the first scientist to speak about gravitational waves, he was the first one to be able to explain it in a proper manner and understand the concept himself. His perception of gravitational waves was built on the concept of his own theory GTR.
He stated that if there were to be a sudden change in the gravitational field of a celestial body due to an explosion or collision of astronomical objects, it would lead into the formation of gravitational waves. He added that these waves would travel with the speed of light, throughout the universe, causing an expansion and a subsequent contraction in the whole universe.
I know all of this seems crazy, but it will make sense soon enough. If we consider the space-time dimension as a surface, then all of this becomes much more understandable.
In order to simplify the concept, let’s go back one step. What exactly causes Ripples in space-time, or GW? It is actually really hard to imagine a phenomenon such as GW, and that is why it is practically impossible for humans to mathematically solve such a complex cosmological happening. Now GW are formed when two black holes, pull each other with an imperceivable magnitude of gravitational force, they spiral around each other and eventually collide. This is considered to be one of the biggest cosmological events. When such an event takes place in the universe, it forms ripples in space-time. Merging of black holes is considered to be the main source of GW or ripples in space-time.
WHAT ARE GRAVITATIONAL WAVES?
You might have heard that GW are nothing but ripples in space-time. As we talked about GW in the last para, whenever ripples in space-time occur, they cause a contraction and a subsequent expansion in the universe. In the observable universe, a “wave” is formed, not too much different from the waves that we are familiar with.
Let us consider one more experiment to simplify this concept. Imagine there is a 50-meter sheet, and two people hold it from two distinct points, making sure that the sheet is completely stretched. Now, what will happen if one of the two people creates a disturbance in the sheet? The answer is quite obvious. A wave will be formed in the sheet itself, and within a time period of a few seconds, there will be a very negligible expansion, and contraction in the sheet, which will be very easily visible to both the volunteers. But, because both the expansion and contraction occur subsequently, there is no observable net change in the length of the sheet. It was 50 meters long initially and it will remain 50 meters long after the wave is stopped.
Now, let’s go back to the moment when one of the people holding the sheet caused a disturbance in it. Initially, the sheet was at rest, i.e., the net force acting on the body was zero, but the moment there was disturbance, some amount of work was done on the sheet, which means there was some energy stored in the sheet for a fraction of second. When the sheet tries to release this energy, it causes ripples/ waves in the sheet. Somewhat of a similar phenomenon occurs in space, the only difference is that the disturbance is caused by cosmological events happening in the universe. Now where is our planet in this whole experiment? Let’s say the experiment was being conducted in the open, and a small particle of dirt came flying and fell on the sheet, when the wave was caused. This particle obviously has a very small mass and radius. Consider its radius to be 0.3 nanometer. Now, let us say there is a microorganism on the particle. Will the microorganism feel any disturbance? Quite obviously, the answer is no. Well, the dirt particle was the Earth itself, and the microorganism is the parallel of humans.
This whole experiment was just to make you realize the scale of our planet when compared to the Earth, which naturally makes it really difficult for humans to detect GW.In fact, it takes a Laser Interferometer Gravitational-Wave Observatory in order to even detect GW. LIGO is one of the most complex machines ever created by humans.
HOW DO WE KNOW THAT GRAVITATIONAL WAVES DO EXIST?
All of the matter that you have read until now might seem very predictive with almost no solid proof that confirms the claims about GW. Well, not until 14 September 2015, there wasn’t. On this particular date, gravitational waves were detected for the first time in the history of mankind. The first direct observation of gravitational waves was made on 14 September 2015 and was announced by the LIGO and Virgo collaborations on 11 February 2016.
In my opinion, detection of gravitational waves does not only confirm Einstein’s theory about space-time, but it also remarks mankind’s success in space exploration. It gives motive for us to spend more time and money into research about the fourth dimension and GW. Now that GW have been detected multiple times, a lot more scientists and Space research organization have started to study more and more about GW.
Einstein predicted this phenomenon exactly 100 years ago. This leaves me with now words for him. I get the chills whenever I study or read about GW and Einstein’s GTR. He was an absolute genius. He is an inspiration to me and millions of other people.
SOURCES OF VIDEO EXPLANATIONS-