Gravitational waves can be defined as the vibration of space-time. Sky is an ocean in which the waves are stationary.

When you throw a rock into the water, when a taut rope is plucked, when a spring is compressed and then released, or when our larynx vibrates, what forms is a wave. In each case, the medium where the wave forms is different: water, air, etc. Interestingly, light waves do not need a medium to travel.  A common feature of all kinds of waves is that they have wavelengths, frequencies and amplitudes. Another important feature they have is that there needs to be a source that triggers the wave. A spring, for example, needs to be compressed to produce the wave.

Gravitational waves, on the other hand, can be defined as the vibration of space-time. These waves were predicted by Einstein in 1916 in relation to the general theory of relativity. Let us consider that all interstellar and intergalactic space is filled up with a substance similar to water. Then when, say, two black holes collide, space itself ripples like water. In fact, discussions have long continued over the existence of ether, a substance that forms the texture and essence of matter. If there are waves in space, then it is highly likely that there is ether that fills up space as well.

In a very interesting narration, the Prophet Muhammad, peace be upon him, is reported to have suggested that heavens are not a vacuum: “The sky is a wave held back” (Tirmidhi, Tafsir surah, 57/1). Bediuzzaman Said Nursi, in his interpretation of this hadith, says, “[Sky] is an ocean in which the waves are stationary” (The Gleams, Twelfth Gleam); in other words, heavens are a sea whose waves have settled, calmed and become still. The Qur’anic verse 36:40 reads “It is not for the sun to overtake the moon, nor does the night outstrip the day. All (the celestial bodies and systems) float (swim) in an orbit (determined for each).” We can infer from this verse that space is likened to a sea because floating or swimming can occur in a substance but not in a vacuum.

The discovery of gravitational waves

Gravitational waves were discovered by a team of experimental physicists on February 11, 2016, that is, exactly one hundred years after they were predicted by Einstein in 1916, and the discovery earned three physicists, Rainer Weiss, Barry C. Barish, Kip S. Thorne, the Nobel Prize in 2017. The LIGO observatory (www.ligo.caltech.edu/page/what-are-gw) used an extremely sensitive interferometer to detect the gravitational waves produced by the collision of two black holes, one having 29 times the mass of the sun and the other 36, 1.3 billion years ago. The researchers used such a precise mechanism that it (the interferometer) could measure the distance to the nearest star to an accuracy smaller than the width of a human hair.

The LIGO observatory used an extremely sensitive interferometer to detect the gravitational waves produced by the collision of two black holes, one having 29 times the mass of the sun and the other 36, 1.3 billion years ago.

The working principle of an interferometer is based on the idea of splitting a laser beam from a single source into two components and then recombining them. The split beams get to the target at the same time after diverging at a right angle and being reflected back from two mirrors. Scientifically speaking, there is not any phase difference between the two. However, if the beams are subject to an effect like gravitational waves, the waves cannot get to the target at the same time, or in scientific terms, an interference pattern is formed on the screen because of the phase difference. In the same way, the waves generated by the collision of two black holes had an impact on the movements of the perpendicular laser beams as they ran past the area that housed the interferometer built by the LIGO team and caused a time difference in their arrival at the detector. In this experiment, the effect of the gravitational waves was measured by directing laser lights through L-shaped vacuum tunnels four kilometers long. The length of the tunnels was so precisely adjusted as to measure a difference, if any, as small as a proton.

The reason why the laser interferometer was so finely tuned is that the waves generated by two colliding black holes are so infinitesimally weak that only such an experimental mechanism could capture them. In other words, the experiment had to be precise beyond the atomic scale because the gravitational waves that reached the solar system could change the distance between the sun and the earth by just the size of an atom. To reiterate, the mechanism was designed so precisely that it can detect differences between laser beams as short as ten-thousandths the size of a proton. It should be remembered that a proton is a very, very small particle in the nucleus of an atom with a diameter of 10^-15 (one-million millionth) of a millimeter.

Furthermore, the gravitational waves were discovered simultaneously by two separate interferometers, which were located at a distance of 3220 km from each other. The reason for the dual measurement tools was to ensure that the waves were indeed gravitational waves.

What has excited scientists most about the discovery of gravitational waves, besides their confirmation of Einstein’s theory, is the fact that we will be able to exploit gravitational waves in addition to light and radio waves in order to explore space. It can be foreseen that telescopes working with gravitational waves can be developed or advanced laser interferometers can be built in space and discover other gravitational waves.

Gravitational waves are generated in space all the time. Large-scale phenomena such as the collision of two black holes or the explosion of supernovae cause ripples in the sea of space. It is highly likely that systems that can detect these waves will provide us with new information about the fabric of space and thus lead to new discoveries.

The fact that gravitational waves were discovered using technological tools is an excellent example of how technology can nurture science. Moreover, this study proves that some discoveries can only be made by big teams like those in the CERN experiments.

It is postulated that the universe rippled violently during the first creation as a result of the tremendous expansion, the effects of which might still exist and should warrant new studies. It is only a matter of time that a super-sensitive mechanism could confirm the Big Bang theory. It is believed that the gravitational waves generated at the very beginning of this expansion are still present and experimental designs such as that in the LIGO are likely to discover them. The Qur’anic verse 51: 47 is considered to be referring to this expansion: “And the heaven, We have constructed it mightily; and it is surely We Who have vast power, and keep expanding it.”

It is almost certain that technological progress will lead to new discoveries that will provide us with deeper insights into the incredible composition of the universe. Bediuzzaman describes the universe as “a rosebud, wrapped in thousands a variety of veils of unity” (The Rays, Second Ray, Third Station). Every new discovery is going to show us the magnificent secrets of this rosebud.

Original Article: Kim, D-H et al., Science 333, 838 (2011).

We often see patients in hospitals with many cables attached to their bodies. Now there is hope to replace these mobility-limiting settings with something very portable. Engineers have developed an ultrathin, stretchy, and flexible synthetic skin that consists of electronic components such as sensors, antennae, and light-emitting diodes (LEDs). Embedded solar cells or wireless power transfer can be employed to power the patch. The device is thin enough to stick to skin using only the short-range van der Waals forces without the addition of any adhesives, and it can be applied and removed like a temporary tattoo. As a result, electronic skin is much more comfortable than traditional electrodes and gives the user complete freedom of movement. These devices have many potential applications in medical diagnostics, including EEG and EMG sensors to monitor nerve and muscle activity. Gathering patient data during normal activity is especially beneficial for continuous monitoring of health and wellness. During the tests, the patches collected data accurately for up to six hours, and showed no signs of degradation or irritation to the arm, neck, forehead, cheek, or chin after 24 hours. In addition, the researchers used electronic skin to control a video game by collecting electrical activity of muscles from the user’s throat, demonstrating the potential for human-computer interfacing. In the near future, patients with muscular or neurological disorders could use this technology to communicate with computers. There is one major obstacle for long-term use. The patch falls off after a few days due to the continual shedding of skin cells. Researchers are looking for ways around this so they can be worn for months at a time.

2- Searching memory engines

Original Article: Sparrow, B. et al., Science 333, 776 (2011).

What is the capital of Liberia? Which year did Edison invent the light bulb? Are your fingers itching to “Google” the answers? Evidently, the answer is yes. Researchers led by Betsy Sparrow of Columbia University cleverly designed four experiments to investigate how we process information in our memory. In one experiment, participants were presented with trivia-like statements, e.g. “An ostrich’s eye is bigger than its brain,” to which they immediately thought about computers or accessing the Internet. In another experiment, participants were asked to type answers to trivia questions. The computer would either save or erase their answers. When participants thought their answers were saved, they remembered information less as opposed to the erased-from-the-computer-condition. In the other experiments, participants were given statements along with the names of the folders where one can reach that information (e.g. DATA, INFO, ITEMS). They remembered where to find the information (i.e. folders) more accurately than the information itself. To sum up, this research showed that we come to utilize computers or Google as external or transactive memory. In the 1980s, Daniel Wegner of Harvard University first coined the term “transactive memory.” Dr. Wegner, co-author of this article, suggested that people relied on others such as spouses or friends to remember various things. However, it seems like the duty is all on Google now.

3- Lasers come to life

Original Article: Gather, M.C. & Yun, S.H., Nature Photonics 5, 406 (2011).

Since its invention in 1960, the laser became an invaluable device that found uses in numerous applications in many segments of today’s world, including science, medicine, industry, electronics, and entertainment. Laser, an acryonym for Light Amplification by Stimulated Emission of Radiation, works through a process where light amplifies by bouncing back and forth between two mirrors. Sandwiched between these mirrors, lasers utilize a gain medium made of non-biological materials such as dyes or crystal. Two physicists at Harvard Medical School, Seok Hyun Yun and Malte Gather, were able to replace gain medium with a living cell. The cells used in this study produce green fluorescent protein (GFP) the material that makes jellyfish fluoresce. When illuminated with relatively weak blue light, GFP amplified the light and the cell produced a visible green laser. Even though their biolaser is currently in the development stage, the researchers predict that it will be very useful in science and medicine in the future. For example, they suggest that biolasing may be used for unraveling the structure of living cells. Yun and Gather are now trying to integrate a nanoscale cavity inside the cell rather than using external mirrors. Such self-lasing cells may allow medical applications where cells can be specifically targeted for disease treatment.

4- The smallest farmers of the world

Original Articles: Brock, D. A. et al., Nature 469, 393 (2011).

A social amoeba, Dictyostellum discoideum, lives independently and feeds on bacteria, but when the food becomes scarce, many amoebas bond and form a slug-like organism that can move around to find more resources to feed on. It was thought the amoeba exhausts all its resources by eating all nearby bacteria before forming the slug structure. Surprisingly, scientists from Rice University found that these single-cell organisms use a very simple form of agriculture in the form of bacterial husbandry. Agriculture in the general sense includes the scattering of food seeds, farming of crops, and harvesting. Humans have used agriculture for thousand of years and it was one of the transforming forces behind our switch from nomadic to settled lifestyles. Researchers showed that a group of amoeba, called farmers, eat less and engulf bacteria into their migratory systems instead of consuming all food they encounter. The slugs of the farmer amoeba travel slowly because of packed food, and one-third of Dicty found in nature turns out to be farmers. Apparently, being a farmer is a genetic trait but it comes with a cost: farmers produce less spores during feasts, but more during famine, which explains why there are both farmers and non-farmers still present. There are still many mysteries, yet this article shows the principles of frugality even in the single-cell realm.

In this path of loving, how can it possibly be That we see the world through You, and yet we don’t see You?
Rumi

What is the universe? The search for the answer to this fundamental question has been the starting point of philosophy and science. However, believers, mostly turn to religion for an ultimate answer. Most Muslim thinkers have considered the Divine Names as the primary things to be comprehended through which we can gain knowledge of the cosmos. And growing numbers of people have suggested that the universe is a hologram which makes us images of a higher reality. The first question that comes to mind is this: Can God’s manifestation, as explained in Sufi texts, promote to a holographic universe? The article, however, does not aim to answer this question, but rather to show that holographic model of the universe can feed our imaginations to perceive self-disclosure (tajalli) of God in everything. For this purpose, we will first concentrate on the main characteristics of a hologram, explore what is meant by a holographic universe, and then use these as metaphors to understand the cosmos in terms of God’s names.

What is a Hologram?

Holography is an imaging technique much like photography. However, in the case of holography, the image of the object is three-dimensional. The main instrument behind this dimensionality is the laser light. Let’s see how we can obtain a hologram, for example, of a flower. To achieve this, a beam of laser light is separated into two by a beam-splitter. One beam falls directly onto light-sensitive film. The other beam is reflected from the flower and then shines onto the same film. When these two beams overlap, they form an interference pattern on the film which is called a “hologram.” The pattern, which looks like the ripples formed by rain drops on a pond, can be seen once the film is developed. A three-dimensional image of the flower is produced as soon as the hologram is illuminated by another laser light. That is because the whole message of all the visual aspects of the flower is enfolded on the two-dimensional surface of the film. Actually, what happens is the revelation of the flower information, as recorded in the interference pattern. The startling feature is that if we cut the hologram in half and then illuminate one piece by a laser, we will still be able to produce the entire image. Even, if we keep cutting the film into smaller and smaller pieces, every single piece will still possess the whole information of the flower. Furthermore, we can see the different sides of the flower when we look at its image from different angles, giving us a convincing illusion of seeing a three-dimensional object.

The Holographic Universe

The idea that universe can be a hologram is brought forward by the fact that not only light waves, but also matter waves, can display the behavior of interference. A deeper level of interpretation for a holographic universe arose through the theoretical models that try to explain the coordinated action of the four fundamental forces in nature. These theories suggest 11 dimensions of space-time which actually appear four-dimensional on a human scale. This would, in a way, imply that the information of reality in eleven dimensions is projected onto the four-dimensional space-time substrate that we live in. However, it is with Gerard’t Hooft’s “Holographic Principle” that the holographic nature of all physical systems became apparent, for it explains how a three-dimensional physical system can be described by a theory based on a system’s two-dimensional surface area. Thus, the idea of a “holographic universe” was on stage once this principle had been applied to universe, the biggest physical system we know of. With the holographic model of universe comes the realization that each point in the universe contains the whole universe in itself: every grain of sand is connected to every planet in the cosmos, just as every subatomic particle comprises a web of interconnections by which it becomes intertwined with the human cell. David Bohm is one of the 20th century scientists known for recognizing this wholeness in nature. Bohm’s interpretation of the universe as a hologram came as an explanation to a 1982 experiment, performed by Alain Aspect and his team, which revealed how fast sub-atomic particles communicate with each other. Actually, the communication is found to be so fast, even faster than speed of light, as if particles “knew each others’ fates.” Bohm suggested that particles do not need any signal to communicate with each other simply because the separation between them is an illusion. The explicit separateness is a projection from a higher level of reality, that he calls Implicate Order, where everything is connected. The particle acts as if it knows the other particle’s fate because it has the other particle’s information within itself. Another scientist who saw the holography in action is neurophysiologist Karl Pribram. He was trying to find which specific locations in the brain are assigned to store our memories. His experiments revealed there is no such localization. Pribram claims that the pattern formed by the interference of electrical signals from each nerve cell in the brain is where, in fact, the memories are “stored.”

God’s Manifestation

Many Muslim thinkers, from Ghazzali to Ibn al Arabi, have presented God as Light, and all entities in the cosmos as the dim reflections of that Light. The Qur’an affirms this approach with its many verses, one of the best known being that “God is the light (nur) of the heavens and the earth” (24:35). However, since God has neither resemblance nor similarity to any of His creatures, this kind of description should not be considered as a likeness to the light we know of, but as a metaphor. The symbolism of light is used mainly to explain the relationship between God and creation. But first, one should know about Divine Names to understand this relationship.

In point of fact, in the Qur’an, the verses generally end with a mention of some of the Divine Names-The Life Giver, The Slayer, The Forgiver, The All-Provider, The All-Knowing, The Creator, etc. Actually, we name Him “Creator” after witnessing the effect of this name on creation. For example, we witness mercy on creation and so we call Him “The Merciful.” Everything from physical beings to the sciences manifests God’s names in some mode or another. All types of hearing originate from Him being “The All-Hearing.” “The All-Just” shines in the way the planets are placed in their orbits, while “The All-Provider” can be seen in how each and every animal is taken care of. Medicine reflects “The All-Healing,” while geometry reflects “The All-Shaping.” To explain God’s manifestation (zohur), Said Nursi once gave the example of the sun and its light in his Sixteenth Word: We can think the light from the sun as God’s light and its attributes as God’s attributes. For example, the heat of the white light can be thought as God’s Power, and brightness as God’s Knowledge. The moment the sun reflects, let’s say on a mirror, its heat and brightness are also there in addition to its image. In a similar manner, God manifests Himself in all beings with all His attributes. However there is ranking in this manifestation which depends upon the being’s abilities and quality. We can use the analogy of light to see how different qualities give rise to different manifestations. A flat mirror has the ability to produce the image of the object with its original size and shape, while mirrors in fun houses can cause distortions depending on the curvature. Actually, in Sufism, the fact that the Names are various and are being manifested to varying degrees is given as the reason for variety in the universe as well as in human beings. And thus, human beings, created with the most complex abilities, have the highest place in the ranking, while the heart, the subtlest faculty of a man is considered as the center of manifestation.

Taking the analogy of light further, and using the allegory of a hologram, we can better visualize the relationship between the creation and God and the idea of ranking in His manifestation. In our analogy, laser light represents God’s attributes, the hologram (film) represents four-dimensional space-time, and the interference pattern corresponds to interfering with God’s names. Therefore, everything in the cosmos can be viewed as a pattern of Divine Names enfolded throughout space and time. As a result, one can conclude that the

Divine Names are not so much ontological entities but simply the effect of such interference, like two lights overlapping. God’s attributes give birth to all existent things just as laser light interference gives birth to a hologram. This analogy is consistent with the Sufi texts that draw the distinction between God’s Names (asma) and Attributes (sifat). Imam Rabbani, a well known Islamic scholar, emphasizes this distinction in his Letters. Divine attributes (such as Existence, Having No Beginning, Eternal Permanence, Being Unlike the Created, Self-Subsistence, Life, Knowledge, Power, Speech, Will, Hearing, Seeing, and Creating) are the features that cannot be separated from God Himself (Dhat). But once God discloses Himself, the effects of the Attributes are manifested and we call these effects Divine Names. In a nutshell, this means, the Attributes are the sources of Names, just as the light is the source of interference.

Furthermore, with the analogy of space-time as a hologram, if we cut the space-time into an infinite number of pieces, the whole universe is present at every location. Mahmud Shabstari expresses perfectly such an interconnection and unity in all creation in his Gulshan-i Raz (The Mystic Rose Garden):

Know the world is a mirror from head to foot,

In every atom a hundred blazing suns.

If you cleave the heart of one drop of water,

A hundred pure oceans emerge from it.

If you examine closely each grain of sand,

A thousand Adams may be seen in it.

In its members a gnat is like an elephant;

In its qualities a drop of rain is like the Nile.

The heart of a barley-corn equals a hundred harvests,

A world dwells in the heart of a millet seed.

In the wing of a gnat is the ocean of the life,

In the pupil of the eye a heaven;

What though the grain of the heart be small,

It is a station for the Lord of both worlds to dwell therein. (Translated by E. H. Whinfield)

This way of looking at everything may lead a believer to embrace the doctrine of wahdat-al wujud, the interpretation of oneness of existence. This results in the denial of the existence of the universe and because of the belief that the only thing that exists is God. One remark necessary at this point is that this might sound a lot like pantheism. However, a critical distinction is that in pantheism, what is denied is God, not the universe. Actually, many people, in trying to integrate the perspective of holographic universe with Sufism, adopt the Sufi belief “hama ost,” meaning “All is He,” another name for wahdat-al wujud. But the holographic metaphor, as presented above, may better serve in our attempt to understand God’s Unity (tawhid) without denying the universe. Thinking all beings as an interference of God’s names is consistent with the faith that every entity is a Divine location. However, note that we drew the distinction between Divine Names and Divine Attributes. Every being is kept in existence through God’s names. Things exist not because God abides in them with his infinite Being. In other words, and most importantly, it is not that God Himself is everywhere in the cosmos, but rather that His Names are present at every point. He does not dwell in cosmos, but is, instead, the source of cosmos. He is eternal-while cosmos ceases to exist once its connection to Him is cut. This standpoint is referred in Sufism as “hama az ost,” meaning “All is from Him.” In this view, the existence of universe is not denied but its level of existence can be questioned. If the true existence is defined as God’s Absolute existence, the universe does not have a true existence but is still in a mode of existence which is temporal and contingent. This existential challenge is explained by Islamic thinkers through the example of a shadow. The relationship of creation to the Creator is like that between a shadow and the actual shape. Thus, the likeness witnessed in a shadow and a hologram is such that we can conceptualize God’s manifestation-but He is not limited by these dimensions.

In fact, the similitude of hologram can also help us to conceive the spiritual unveiling. Interference patterns originating from different objects can be recorded on the same film by projecting the laser beams at different and varying angles. In such a case, depending on the direction and frequency of the beam that you send through the film, a different three-dimensional image will appear. Two points to emphasize are that the use of laser light is necessary to see the higher dimensionality, and that one can see different realities. In a similar fashion, in a spiritual journey, a traveler needs to have radiance from God’s light to be able to witness further dimensions. With the light of God, spiritual unveiling occurs and a Sufi may see different instances of a reality depending upon His station, which Divine name He is reflecting on or reciting, etc. Thus, the complex information that every element in the universe can reveal about every other entity depends on the fact that God’s names denote each other. We can further use the notion of interference to delineate the concept of ranking in God’s manifestation. In an interference pattern, not all points have the same brightness. The degree of brightness depends on the location and the way the two lights overlap. There are even points where no light can be observed. This, however, does not mean there is no light there; it simply cannot be seen due to destructive interference. Extrapolating this into God’s manifestation, every entity is a Divine location, even if it cannot manifest Him.

To end this train of thought, we should find an answer to a mysterious question. If everything in four-dimensional space-time comes into existence once a higher reality is projected on the void of darkness by God’s Light, what, then, is that higher multidimensional reality? It is a reality which can only be witnessed by those who see behind the appearance of things-by those who free themselves from the material world and carnal desires. It is, perhaps, the Preserved Tablet (Lawh al-Mahfuz) mentioned in chapter, The Constellations (Buruj). Ultimately, this is a question that can only be answered by those who have purified their hearts and can see beyond.

Defining the target

Gravitational waves are generated only by the equivalent of a rotating or oscillating system — that is, two or more masses accelerating toward or away from each other and exhibiting a quadrupole moment of inertia.

Only such quadrupole and higher multipole sources can generate gravitational waves because, whereas there are negative electric charges, there are no negative masses. A negative electric charge oscillating back and forth is the equivalent of a positive charge moving in the opposite direction, and this equivalence enhances the generation of electromagnetic waves. Since there is just one gravitational polarity, however, a mass can oscillate only with respect to a counterweight. This counterweight reacts to the oscillation and generates a gravitational disturbance that almost, but not quite, cancels the disturbance of the body.

As explained by physicist Paul Davies of Australia’s University of Adelaide, the gravitational disturbances would completely cancel out but for the time required for them to travel between the masses. It is this out-of-phase imbalance in the disturbance’s cancellation that propagates a gravitational wave. For this reason, such waves are not generated by quiescent stars, those rotating on their axis symmetrically or even exploding symmetrically, because there is no quadrupole moment. However, that situation changes if they explode asymmetrically or change their shape.

On the other hand, a typical binary star system has a quadrupole moment and should produce a slow periodic gravitational wave. A near-enough binary star system would cause a measurable distortion a little in excess of one part in 1021 on Earth.

For the wave to lie in the gravitational-wave detector’s frequency range (typically 1000 +/-1 Hz.), though, the two stars of the binary must be in the final stage of coalescing, a rare situation. For comparison, a supernova is expected to produce damped exponential impulse waveforms, each of which lasts for 1 millisecond. A collision or collapse of a binary system between two neutron stars, or between a neutron star and a black hole, would produce gravitational waves with a sliding frequency in the 1 to 1000 Hz range, as one star spirals in on its partner.

Why are we searching?

A long time ago, in the Large Magellanic Cloud-one of our Milky Way’s two companion galaxies, a star exploded. In 1987, 160,000 years later, radiation from that event finally reached Earth. The first to see the brightening star were astronomers in the southern hemisphere.

Scarcely 24 hours earlier, in other parts of the world, other types of detectors had “seen” something. At the University of Rome (Italy) and the University of Maryland at College Park (the U.S.), gravitational-wave detectors registered 12 fairly large and about 100 small pulses over a period of 2 hours. Around the same time, the Mont Blanc Neutrino Observatory (France) registered five pulses of neutrinos over a 7-second interval. Similar recordings were made by neutrino detectors in Kamioka, Japan, and Frejus, France.

Astrophysicists are still debating the significance of those observations recorded on Feb. 23 and 24. But others claim the pulses registered in Rome and Maryland may have been due to actual gravitational radiation from an identifiable source — the supernova of 1987.

Physicists find this ambiguity unsatisfactory. They want to detect the gravitational waves themselves, directly and unequivocally. Indeed, the detection of waves has been called “the most important of all tests” of Einstein’s general theory of relativity by theoretician Kip S. Thorne of the California Institute of Technology (CalTech) in Pasadena. The sensing or reception of gravitational waves also may deepen astronomers’ understanding of the dynamics of such violent events as supernovas, exploding black holes, and the interactions between black holes and neutron stars. As a bonus, whatever is learned about detecting ultra-weak signals might help engineers measuring extraordinarily small displacements or strains.

The understanding, according to Einstein’s general theory of relativity, is that all objects exist in four-dimensional space-time (that is, in a continuum having three dimensions of space and one of time). The mass of every object curves space-time, a curvature that manifests itself as the gravitational field of the mass. The greater the mass, the greater the curvature of space-time, and the greater the gravitational field.

According to the same theory, massive objects that rotate or explode asymmetrically, or oscillate, give off gravitational waves or ripples that propagate through space-time, like ripples or waves on the surface of the ocean.

Gravitational waves conform to an inverse square law relationship, just like electromagnetic waves. The force of both types of energy declines in proportion to the square of their distance from their source. But gravitational waves are so much weaker than the Coulomb electric force, which renders the detection of such weak waves a monumental challenge to instrumentation.

The evidence that gravitational waves exist is compelling, albeit indirect. The firmest evidence relies on observations made over 7 years by astronomers Joseph Taylor, of Princeton University in New Jersey, and Russell Hulse, then at the University of Massachusetts at Amherst but now also at Princeton. Their measurements of radio waves from a binary pulsar designated PSR1913+16 show that the pulsar’s 8-hour orbit around the neutron star is gradually contracting; the faster the pulsar revolves around the neutron star, the smaller its orbit gets. As the rate of decrease agrees to within 0.5 percent with predictions derived from the general theory of relativity, the finding is excellent circumstantial evidence for orbital decay being a result of energy lost by gravitational radiation. Even though the gravitational radiation itself was not detected, Taylor and Hulse shared the 1993 Nobel Prize in Physics for this work.

But what would it take to observe the weak gravitational radiation directly? Gravitational waves are generally believed to travel at the speed of light and to deform or distort an object geometrically as they pass through it. For plane-polarized gravitational waves, the two directions are at 45 degrees to each other, not perpendicular as they are for light. In other words, a passing gravitational wave distorts an object first in one direction, then (in the next half-cycle) in another, rotated at a 45-degree angle to the initial direction. It takes another half gravitational wave cycle for the wave to distort at the 90-degree angle characteristic of electro-magnetic waves in the first half-cycle.

Resonant bar detector

In principle, it should be possible to sense this distortion and its after-effects with the aid of strain detectors attached to a suitable “antenna” — a space-time seismometer, if you will. But such an antenna resembles nothing familiar to electrical engineers. In its simplest manifestation, the antenna is a large solid cylindrical bar.

The pioneering resonant-bar detector was designed in the late 1950s and built in the early 1960s by Joseph Weber, professor of physics at the University of Maryland. Weber’s design called for a mechanically isolated cylinder of solid aluminum weighing several metric tons. Piezoelectric strain transducers attached at intervals around its circumference converted the vibrations induced by any passing gravitational wave into an electric signal. Weber’s bar resonated mechanically around 1 kHz, so that it would “ring” after being distorted by an incoming damped-exponential wave, the shape expected of a gravitational wave from a supernova. Subsequently, other bar detectors were built at many institutions around the world.

The main problem with resonant-bar antennas is their insensitivity. Even the latest of them yield dimensionless strain sensitivities of about one part in 1018 (that is, only 10-18 meter distortion per meter of length), too little to detect gravitational waves from any but the nearest and most violent events.

The laser alternative

The laser interferometer owes its sensitivity in detecting gravitational waves to an arrangement of mirrors suspended on vibration-isolated pendulums. Two pairs of mirrors create two light paths perpendicular to one another. A laser beam is split and the halves sent down each path, rebounding back and forth along the leg between the mirrors hundreds of times before being recombined. The multiple passes create the very long light path required to amplify the gravitational-wave input to detectable amplitude.

In brief, if a gravitational wave passes by, the pendulums holding the mirrors are expected to move a little apart in one leg and a little together in the other leg, in each case by the same tiny fraction of the laser light wavelength. Their movement would shift the relative phase of the two halves of the laser beam, momentarily upsetting the interference patterns that would otherwise be cancelled out. At that instant, the interference pattern would brighten by an amount proportional to the strength of the gravitational wave. The job of monitoring the interference pattern for brightening is handled by electro-optic detectors, which indicate when a passing gravitational wave is detected and which recover its variation over time.

Not only are laser-interferometer detectors potentially more sensitive than resonant-bar antennas, they are also better at detecting a variety of sources because they are inherently broadband. They respond to gravitational waves having a frequency from 10 Hz to 10 kHz, versus the resonant-bar antennas’ 1-Hz bandwidth at 1 kHz.

Input from space

A third and truly exotic method of detecting gravitational waves has been proposed: monitoring the Doppler shift of the carrier frequency (or rather, the retransmission of the tracking station’s frequency) from two or more interplanetary spacecraft simultaneously. This project is known as LISA (The Laser Interferometry Space Antenna).

The technique is analogous to laser interferometry. The idea is to detect the Doppler shift in a spacecraft’s microwave frequency as the craft is jostled by a passing gravitational wave — that is, as space-time is warped in its vicinity.

Inevitably, there are obstacles to overcome. Since the effects of a passing gravitational wave are so small, the reference oscillator must be extremely stable to detect any Doppler shift. Observers must also consider variations in the pressure of the solar wind (which differs from time to time and with the changing distance of the spacecraft from Earth), in forces from the attitude control thrusters (used to occasionally correct the space-craft’s orientation), and in the refraction of Earth’s atmosphere (through which the signal must travel). Subtracting all of these variations, the interplanetary detector is expected to have a theoretical sensitivity of about one part in 1016 — corresponding to a displacement of about 0.065 mm over the shortest distance from Earth to Jupiter, and one-eighth of that over the shortest distance from Earth to Mars.

The noise problem

Noise degrades the sensitivity of any gravitational-wave receiver. The interference is mostly due to seismic activity in the earth, acoustic interference (also known as microphonics) from inhabited surroundings, and heat (thermal noise). Especially troublesome are the non-Gaussian tails of noise distribution, which produce a significant number of false detections.

When a gravitational wave passes through the cylinder and distorts its shape, the moving input coil produces minute changes in the magnetic flux. That magnetic flux change then creates a relatively large variation in the voltage across the SQUID** junctions. In turn, these variations are passed along as voltage signals to succeeding stages of amplification — generally room-temperature FET amplifiers with optimal filtering for the anticipated signals. If tuned mechanical transformers or resonators are installed between the antenna and the transducer, transfer of the gravitational wave’s pulse is maximized and amplifier noise coupling is minimized.

Conclusion

Much is being done to achieve a breakthrough in the detection of gravitational waves. A recent High Frequency Gravitational Wave conference held at MITRE Corporation featured proposals and experiment descriptions that could lead to an apparatus that uses gravitational waves for communications. Several large laser interferometer gravitational wave observatories are online and taking data while making sensitivity improvements. The reader is urged to delve further (see references below) to see why there is so much excitement about this new window on the universe.

References

– Gibbs, W. W. “Ripples in Spacetime.” Scientific American, April 2002.

– Lewis, M. “Gravitational Waves versus Electromagnetic Wave Antennas.” IEEE Antennas and Propagation Magazine 37, no. 3, June 1995. Also see http://solo3.abac.com/gwinstitute/.

– Blair, D. The Detection of Gravitational Waves. Cambridge Univ.: 1991.

– Boughn, Stephen. “Detecting Gravitational Waves,” American Scientist, no. 68. March-April 1980, 174-83. (An overview of the early work in the search for gravitational waves.)

– Will, Clifford M. Was Einstein Right? New York: Basic Books, 1986. (A readable account of the binary pulsar PSR1913+16 and its role in providing evidence for gravitational waves.)

– Blair, David G., ed. The Detection of Gravitational Radiation. England and New York: Cambridge Univ. Press, 1991. (Sums up the state of the art in gravitational-wave receivers.)

– Misner, Charles, Kip S. Thorne, and John Wheeler. Gravitation. W. H. Freeman: 1973. (Still the most used book by students and practitioners in gravitational-wave research.)

– Thorne, Kip S. Black Holes and Time Warps: Einstein’s Outrageous Legacy. New York: W. W. Norton, 1994. See chapter 10: “The Ripples of Curvature,” which summarizes plans for the Laser Interferometry Gravitational-Wave Observatory (LIGO).

– E. Amaldi et al. “Coincidences among the Maryland and Rome Gravitational Wave Detector Data and the Mont Blanc and Kamioka Neutrino Detector in the Period of SN1987A.” Annals of the New York Academy of Sciences, vol. 571, 1990, 561-76. (Proceedings of the l4th Texas Symposium of Relativistic Astrophysics). (Discusses whether or not gravitational waves were detected along with the first sightings of the 1987 supernova).

– Grishchuk, Leonid. “Update on Gravitational Wave Research. Online at Los Alamos’ website on preprints gr-qc/0305051, 13 May 2003. (Provides a more technical treatment.)

** A superconducting quantum interference device (SQUID) is a mechanism used to measure extremely weak signals, such as subtle changes in the human body’s electromagnetic energy field.

A brief history of lasers

During the nineteenth and twentieth centuries, scientists made many improvements to our life. One of the most important was a more accurate understanding of light, currently defined as traveling electromagnetic waves. Like the ocean’s waves, light also has an amplitude (which determines its power) and a frequency (which determines its color and energy). The better we understand light, the more uses we find for it in our life. For example, today we are faced with many technological devices based on light, such as printers, CD writers and readers, and fiber optic devices for telecommunications.

Many scientists are very interested in photons, for they can be used in communication, computation, and many other fields. Also, many researchers think that the technology of the future will be built on optoelectronics”photons and electrons.

The invention of lasers is a very important step in the science of optics. While lasers started out as a major component of science fiction stories, science fiction is rapidly becoming scientific reality due to continual improvements and discoveries.

Lasers defined

By definition, a laser is amplified light. However, its amplification is very different from a normal amplification, for this amplification makes the photons coherent by causing them to have the same energy and same direction. Such coherence enables a laser light to travel over long distances without diverging. If the laser beam is kept in a dispersionless media, theoretically it can keep the same waist size forever. However, the only media that currently can serve as a dispersionless media is a vacuum.

In a laser system, many atoms have to have electrons in the same high energy levels. If this is the case, any effect that stimulates the atoms’ system will emit coherent light. For the emission to continue, the system should be constructed so that there are always some electrons changing their energy level.

Observing several laser systems will give us a clearer understanding of lasers.

Ruby lasers

The first lasing structure was the ruby crystal (see Figure 1), devised by Dr. T. H. Maiman in 1960. This was a surprising development, for researchers thought that gases would be the first lasers. The ruby crystal is Al2O3 (called sapphire), and has an impurity level of 0.05% Cr+3 ions.

The ruby laser consists of a ruby crystal surrounded by a flash tube enclosed within an aluminum cylindrical cavity that is cooled by forced air. The laser cavity is pumped by a flash light. When the light’s power exceeds a certain limit, it begins to re-excite some ions inside the ruby crystal to higher state. The cavity ends are coated with evaporated silver. However, one side has a lower reflection ability so that some light can pass through it.

Gas lasers

Most elements and many molecules can be made to lase in a gaseous state. The first example of a gas laser is the HeNe (helium neon) laser, as depicted in Figure 2. In a high voltage tube, colliding helium and neon atoms transfer energy to neon atoms, which then assume a meta-stable state. After this, spontaneous emission occurs when neon atoms transit from a higher energy level to lower energy level. Like other lasers, the HeNe laser also needs to have a population inversion. The high population for neon’s meta-stable state is achieved by applying a high voltage to the tube. Although the stimulated emission decreases the number of atoms in the meta-stable state, the high voltage pumps the system back into the population inversion condition.

Having many different wavelengths (colors), HeNe laser are useful for all sorts of applications, from semiconductor technology to construction leveling.

Improvements in semiconductor technology have made many contributions to laser technology. Data storage on CDs, computer, printers, and telecommunication tools are just a few examples of the places where semiconductor lasers are used.

Semiconductor lasers

Three different materials have the properties necessary to serve as electron (carrier) conductors: metals, insulators, and semiconductors. Metals are good conductors for carriers, whereas insulators do not conduct electricity. In a solid state material, electrons stay in the bands determined by the attraction between positive and negative charges (electrons and nucleus). The further band for an electron is called the conduction band. In metals, the conduction band is partially filled, while in insulators the conduction band is totally empty. There is also a very large energy difference between the conduction band the valence band (the band just before conduction band). Thus, a large amount of energy has to be supplied in order to produce some carriers in the conduction band.

Conduction occurs when electrons are present in a conduction band, for they are somehow free in that band. They are not so free that they can escape it, but they are free enough to walk around in it. Research is revealing many other surprises or gifts that the All-Wise Creator has put in front of us.Our discovery of certain materials’ ability to serve as insulators and/or conductors has made our life much easier.

A very important step in the field of semiconductors is the use of optics during experiments. The electron in the conduction band can loose energy by radiating light, and one can use this energy to build lasers. The laser’s wavelength mainly depends on the energy gap between the conduction and the valence bands. If this energy gap is known, researchers can grow appropriate semiconductor structures to lase.

As growth techniques for semiconductors improve, the quality and variety of semiconductor lasers increase. Early semiconductor lasers were built from bulk structures. But after the 1980s, scientists discovered that layering different semiconductors could increase optical efficiency. The commercial state-of-art now is semiconductor quantum well lasers. In these structures, the electron’s mobility is restricted on a plane, giving carriers a two-dimensional freedom. Lasers using quantum dots (quasi-zero dimensional structures with superior optical properties) also have appeared during the last 5 years.

Conclusion

To see how our life will change via improvements in optics, just look at how fast communication has become, thanks to telecommunication lasers. Old thick and slow copper wires are being replaced by fast thin fibers. A computer and a camera gives one access to visual telecommunication via the Internet. All of this used to belong to science fiction. Not any more!

I believe that one we will develop a technology to transport material instantly, as stated in Qur’an: One who had knowledge of the Book said: I will bring it to you within the twinkling of an eye! When (Solomon) saw it placed firmly before him, he said: This is by the Grace of my Lord! – to test me whether I am grateful or ungrateful! If anyone is grateful, truly his gratitude is (a gain) for his own soul. But if any is ungrateful, truly my Lord is free of all needs, supreme in honor! (27:40).

In conclusion, we have to learn how to read the Book of the Universe and to understand it so that we can make even more beneficial discoveries.

References

• Arakawa, Y. and H. Sakaki. Multidimensional Quantum Well Laser and Temperature Dependence of Its Threshold Current. Appl. Phys. Lett. 40, no. 11 (June 1982): 939-41.
• Davis, Christopher C. Lasers and Electro-Optics: Fundamentals and Engineering. Cambridge Univ. Press: 1996.
• Hecht, Eugene. Optics. 4th ed. Addison-Wesley: 2001.
• Hitz, Breck et al. Introduction to Laser Technology. 3d ed. IEEE: 2001.
• http://home.achilles.net/~jtalbot/
• Kirstdter, N. et al. Low Threshold, Large T Injection Laser Emission from (InGa) as Quantum Dots. Electron. Lett. 30, no. 17 (Aug. 1994): 1416-17.
• Ledentsov, N. N. et al. Quantum-dot Heterostructure Lasers. IEEE J. Select. Topics Quantum Electron. 6 (May-June 2000): 439-51.
• Maiman, Theodore. The Laser Odyssey. Laser Press: 2000.
• Svelto, Orazio (ed.). Principles of Lasers. Translated by David C. Hanna. 4th ed. Plenum Publishing Corp.: 1998.