If you follow science, you would have heard about the discovery of gravitational waves which are present in the universe. Gravitational waves were first discovered in 2016 in a high-precision experiment at the LIGO (Laser Interferometer Gravitational-Wave Observatory). This was reconfirmed in June 2023 by the observations made at the NANOGrav (North American Nanohertz Observatory for Gravitational Waves). Interestingly, in 1916, Einstein predicted the presence of gravitational waves in his Theory of General Relativity. These observations and experiments confirmed it. It is definitely great progress for science.
Yes, gravitational waves have been observed in different experiments. The problem is that there is limited understanding of what exactly they are. There are many unanswered questions. Do gravitational waves really move across space? Also, the fact that science still does not have a complete understanding of how gravity really works. So, is the terminology “gravitational waves” really accurate? To answer these questions, we will provide a fresh perspective on gravitational waves. In this essay, we will cover the following topics:
- Gravitational Waves—Perspective according to Science
- Unanswered Questions about Gravitational Waves
- Untold Story of Gravitational Waves
1. Gravitational Waves—Perspective according to Science
A simple definition of gravitational waves is that they are invisible waves which travel in space at the speed of light. A technical understanding of gravitational waves would be that they are due to the spacetime fabric. Spacetime is a word coined by Einstein to indicate that there is a fabric in space which is made up of three dimensions of space and a fourth dimension of time. This spacetime fabric causes gravitational waves. These are not your typical understanding of waves, like sound waves. Sound waves propagate through space. Gravitational waves are different. They have a direct effect on space. They compress and expand space. To give a visual description of this concept, it is like the tree in front of you (or any other object) coming closer to you and moving away. The tree’s position moves forward and backward. Space is being compressed and expanded like a wave. The example of the tree coming closer and moving away is extreme, but that is what is really happening on a nano scale. We will never notice these minute changes, but they are really happening. Gravitational waves expand and compress space.
The spacetime fabric can be compared to a rubber sheet. If you place a heavy ball on this rubber sheet, the rubber sheet will curve around it. While this curvature forms, there will be vibrations or ripples all over the rubber sheet. These ripples are like gravitational waves. Another example is that you throw a stone in a pond; waves are formed in the pond. The bigger the stone, the larger the waves in the pond. The waves travel outward in the pond. The spacetime fabric behaves similarly. Any object placed on the spacetime fabric will cause ripples in the fabric. The larger the object, the bigger the ripples or waves. Small objects will not cause much of a ripple as compared to larger objects.
The only addition in the spacetime fabric is that ripples cause space to shrink or compress. Yes, this does happen—space shrinks. This was predicted based on Einstein’s Theory of Relativity. These ripples of space are the gravitational waves discovered by scientists. So, what causes these ripples of space? Small objects will not make much of a dent, only massive objects will. The most massive objects known in the universe are black holes. Science believes that when two black holes combine somewhere in space, they cause ripples in space, which can be noticed or observed. In that regard, there is no shortage of black holes in space. In our own galaxy—the Milky Way—it is estimated that there are about 10 million black holes. There are over one billion galaxies in this universe. Also, each of the billion galaxies has a supermassive black hole in its center. All the stars and solar systems rotate around this black hole. So, we can see there is no shortage of black holes in the universe. The supermassive black holes are very dense and heavy in mass. Some of the biggest black holes have a mass of about 40 billion times the mass of our sun. So, when a large black hole finds a way to combine with another black hole, it has a tremendous impact on the spacetime fabric. A ripple is created in the spacetime fabric, and it moves all over the universe at the speed of light. The greater the mass of the black holes combining, the greater the impact on space, the longer the ripple will travel all over the universe.
The goal of the scientist is to track these ripples in the spacetime fabric and try and measure them, try and understand these ripples. The science of gravitational waves was born to understand and measure these gravitational waves. To date, two experiments have been conducted. Let us discuss these briefly.
LIGO (Laser Interferometer Gravitational-Wave Observatory): LIGO’s design is simple, but the construction must be extremely precise and accurate. Two arms in an L shape are constructed. The length of each arm must be the same at 4 km. This measurement must be exact without any error. At the end of each tunnel is a reflecting mirror. At the source, a laser beam is divided and sent through the two arms. Each beam travels through an arm and is reflected by the mirror at the other end. On their return journey, the two beams meet and combine at the starting point. The distance traveled by the two beams is the same. If the initial two beams were 90 degrees out of phase, when they combine the two beams will cancel each other and no light will be detected at the end-point detector. This is the working principle of the LIGO system.
The objects that create gravitational waves are far away. Most of the time, these events only cause weak gravitational waves. The waves are very weak by the time they reach Earth. This makes gravitational waves hard to detect.
However, there was success in September 2015. When a gravitational wave passed through the LIGO system, one of the arms was compressed by a very small amount. This meant that the distance traveled by the light beams in the two arms would not be the same. So, after reflecting from the mirrors, the light beams were out of phase. Since the beams were out of phase, the two beams did not cancel each other out; instead, the detector received a signal from the LIGO system. The signal was because of the gravitational wave. On investigation, they found that the gravitational wave in this case was due to two black holes merging about 1.3 billion light-years from Earth.
It is amazing how sensitive the LIGO system is. LIGO is able to detect a change in distance between its mirrors of up to 1/10,000th the width of a proton! The width of a proton is 10-15 meters. What an engineering feat is the construction of the LIGO system! This is equivalent to measuring the distance to the nearest star (some 4.2 light-years away) to an accuracy smaller than the width of a human hair.
To remove any bias or avoid any false alarms, a few LIGO systems have been built around the world. When a gravitational wave passes through, it must be read by all the LIGO systems. This way any false alarms are avoided.
It is amazing to know that the wavelengths generated by gravitational waves can be up to four light-years long, or 20 million million miles. Wow! It is so hard to imagine a wave with a wavelength this long! In that way, the LIGO system is limited. The LIGO system can catch gravitational waves up to roughly 2000 miles. Obviously, the LIGO system is not designed to discover gravitational waves which have these long wavelengths. To catch these long gravitational waves, a different approach was needed. The NANOGrav group was formed to undertake this task.
NANOGrav (North American Nanohertz Observatory for Gravitational Waves): NANOGrav is a team of 100 members from dozens of countries including the US, Canada, India, and China. Basically, the approach is very different from the LIGO system.
Here the pulsar stars which are available in the universe are used to detect gravitational waves. Pulsars are super-dense, spinning cores of dead stars. Each pulsar is small, about the size of a city, but it spins hundreds of times a second, sending out beams of radio emissions. On every rotation of a pulsar star, the radio pulse is picked up by a radio telescope on Earth. The rotation speed of the pulsar is very steady, so the timing of the pulse received is also accurate. It is always on time. However, when a gravitational wave passes through the pulsar, the rotation of the pulsar is disturbed. This means that the timing of the pulses received on Earth is disturbed. This change in pulse timing has allowed scientists to study gravitational waves. There are so many pulsar stars in the universe. Different members or groups who are part of NANOGrav are currently studying around 60 different pulsars for gravitational waves. The data collected confirms the presence of gravitational waves. As more data is collected, scientists’ understanding of the gravitational waves will only improve.
2. Unanswered Questions about Gravitational Waves
We have just read about the understanding of gravitational waves according to science. There are many unanswered questions about gravitational waves. We will try and raise some of these questions.
a. It is quite clear that any wave must have a propagation medium. There must be some medium through which the wave must travel. We know air is the propagation medium for sound waves. Air is compressed and expands so that sound can travel. For water waves, the medium is water. So, logically, gravitational waves or even the full spectrum of electromagnetic waves must have a propagation medium. Earlier it was thought that there was an ether in space through which light waves or gravitational waves traveled. Scientists have tried to track this ether. They designed different experiments to discover this ether. After all this effort, they concluded that there was no ether in space. Einstein mentioned the presence of the spacetime fabric. Maybe this fabric was the propagation medium. Once again, there is no fabric in space. Science has not discovered this fabric. If you think about it, spacetime fabric is an imaginary idea which is required to explain the functioning of space. It gives an idea of how gravity works. But, in reality, there is no fabric in space. So where is the spacetime fabric which Einstein proposed? So how do the gravitational waves propagate? Unfortunately, there is no answer. It is a mystery. There must be an answer to this question. We will give a fresh perspective to this problem in the next section.
b. The name “gravitational waves” is indeed quite intriguing. It is quite a fancy name. What does it really mean? We are all taught about the gravitational force—an attraction force between two objects. According to science, it is one of the four forces in nature. Science has a pretty good understanding of three forces—electromagnetic, strong nuclear, and weak nuclear forces. The only force which remains a mystery is gravitational force. Scientists believe there is a particle called graviton which provides the gravitational force. But this graviton particle is still unknown, still undiscovered. With this lack of understanding about gravity, it is quite intriguing why the waves in the above experiments are called gravitational waves. Are gravitational waves the correct name to understand this concept?
3. Untold Story of Gravitational Waves
While defining gravitational waves, we saw earlier that they are connected to the spacetime fabric. Einstein coined the term “spacetime” to describe the fabric of the universe. This term causes confusion. There are now two terms—there is space and there is spacetime. What is the difference? Space is what we see when we look out, and everything in space is measured in distances. The tree is 200 feet away; the plane is flying at 30,000 feet. Space is visible and operates in three dimensions.
Spacetime looks at the same objects in terms of time. This term is confusing and not accurate because there is no space in spacetime; there is only time. In spacetime, the measurement is in units of time alone; no distances are measured. For example, light takes eight minutes to reach us from the sun; the distant star is 500 million light-years away. Everything in spacetime is measured only in time. There are NO distances, only time.
Einstein indicated that there is a fabric to this universe and this fabric is made up of spacetime. Of what is spacetime fabric made? You guessed it: this fabric is made up of time alone. Not easy to grasp, but you can try to imagine a fabric made of time. Time is the only variable of the fabric. Since this term “spacetime fabric” does cause confusion, it is therefore more appropriate to call the spacetime fabric “the time fabric.” Time fabric is more accurate and conveys the meaning that time alone is the variable in spacetime. Henceforth, we will refer to spacetime fabric as time fabric.
Spacetime Fabric = Time Fabric
Science wrongly conveys the impression that the time fabric operates in space. This is wrong because time operates on a different plane. As Einstein stated, spacetime has four dimensions. Space has three dimensions and time is the fourth dimension. One thing is clear: the fourth dimension cannot function in the three dimensions, otherwise we would have to say that space has four dimensions. Time and the time fabric, the fourth dimension—it cannot function in space. Then, where does time function; where does the time fabric operate? If it is not space—then where? If you think and analyze, the only other logical place where time and the time fabric function is the mind. The fourth dimension is within the mind. Strange but true. Please read my essay “Understanding Time,” which is available on my website, where we have analyzed and shown that time is a function of the mind. Time operates only within the mind. Vedanta has been very clear about this—kaala (time) is a function of the mind alone.
Since time and the time fabric function in the mind, it is only logical that all the objects which are placed on the time fabric also function in the mind. The sun is placed eight minutes away on the fabric. The moon is placed three seconds away on the fabric. The plane flying at 30,000 feet is placed three milliseconds away on the fabric. All possible objects are placed on the fabric in this way. The objects on the time fabric are not gross objects, which you see in space, but subtle objects. As Vedanta teaches us, the subtle objects in the mind are made up of vrittis or waveforms. You must read my essay “Life Is a Living Wave,” where I have given a detailed analysis to show that there is a fully functioning universe made up of waveforms. There is a cosmic waveform which is the total of all the possible object waveforms. This cosmic waveform operates in the cosmic mind. Hiranyagarbha (golden egg/womb) is the technical word used in Vedanta to represent this idea. Everything happens first in the cosmic mind, and then a part of this or a subset is projected out by the individual minds. If you think about it, quantum physics does support this concept. The foundation of quantum physics is that every object in this universe has a particle property and a wave property. Yes, everything right from the smallest to the largest objects in the universe has a wave version and a particle version. This is so like the teaching of Vedanta with subtle objects and gross objects. If quantum physics focuses on better understanding the wave version of objects, scientists will also reach the same conclusion that there is a fully functional subtle universe made up of waveforms.
If you fully understand and are convinced that there is a fully functioning universe made up of vrittis or waveforms, we are then ready to tackle the question of gravitational waves. As mentioned earlier, the origin of the gravitational waves is when two large black holes spin around each other and finally merge. The subtle version (waveform version) of the black holes is spinning around on the time fabric. This process makes a deeper curvature on the time fabric. When this happens, the time fabric gets stretched around the merged black hole and the entire time fabric is pulled inward. The inward pull compresses the time fabric. This inward compression causes ripples in the time fabric. These ripples start from the merged black hole and move outward on the time fabric. All this is happening in the cosmic mind. So, the gravitational waves are nothing but the compression of the time fabric. When the time fabric gets compressed, time slows down. This is logical because, upon compression, the interval between the time unit on the fabric is smaller. When the time unit is smaller, time must slow down. Therefore, the ripple of the time fabric causes time to slow down as the ripple moves outward.
The ripple in the time fabric and the time slowing down happens in the cosmic mind. So, what happens in space? Einstein’s Theory of Relativity does connect time and space. If time slows down, then even space gets more compressed. As we have seen discussed in many different essays, space is created by the stretching of time. One second of time fabric becomes 186,000 miles of space. If time is compressed in the fabric, space will also be compressed. This is the direct connection between time and space. When space is compressed, the objects in that space are also affected.
Gravitational waves are a product of the subtle universe, causing time to slow down. This translates into space getting compressed in the gross universe, thereby affecting objects in their path.
This is the untold story of gravitational waves.