It is widely accepted in modern culture that people should eat three meals: breakfast, lunch, and dinner. Nutritionists generally recommend adding two snacks (one in the morning and the other in the afternoon) to help control appetite.

Interestingly, the practice of eating three meals a day is a recent phenomenon. Ancient Romans had only one meal, which they usually had at about four in the afternoon, and they believed it was unhealthy to eat more than once a day. What the Romans ate in the morning and at noon was very light and fast [1]. Later, rules in monasteries affected people’s behavior around food and drink.

During the industrial revolution, breakfast gained importance; workers needed food before work. And dinner didn’t become popular – at least in its current form – until the prevalence of artificial lighting made it possible to eat before dawn and after dusk [2]. The understanding that eating three meals a day is a healthy choice stems from a combination of belief, culture, and early epidemiological studies [3].

There are studies suggesting that having a regular eating habit positively impacts health, regardless of frequency of meals. On the other hand, in a recent and comprehensive study by Kahleova et al., which studied 50,660 adult members of churches in the USA and Canada, it was found that eating one or two meals a day caused lower weight than eating three meals, and also a relatively lower body-mass index (BMI) which got even lower as overnight fasts got longer [4]. The authors state that the positive effects of such a diet are caused by a combination of timing, meal frequency, and overnight fasting, as well as having less frequent meals coupled with precise timing. These results indicate that eating one or two meals is better than eating three or more.

The Prophet’s example

The Prophet Muhammad’s, peace be upon him, recommendations and behaviors lend support to modern medical studies in the area of nutrition, as in many others. He would eat no more than two meals and ensure that one of the meals should consist of light food (such as dates). The Prophet recommended that dinner be eaten, even if it was only a small meal. “Do not leave dinner, even if it is only a handful of dates, because abandoning it makes one weak” (Sunan Ibn Majah).

He defined dinner as the second and last meal of the day, and that it should be eaten after dusk or immediately after the evening prayer.

The Prophet set so many examples about nutrition. He highlighted the dangers of obesity, stating that “What I fear most about my community are developing a belly, oversleeping and idling.” This was centuries ago; nowadays, obesity is an epidemic raging across the world, and its prevalence has almost doubled in more than 70 countries since 1980. In 2015, a total of 107.7 million children and 603.7 million adults were obese [5]. Seventy-five percent of the world’s population is overweight. Obesity, along with dyslipidemia and hypertension, is one of the major factors in cardiovascular diseases. Studies have shown that exercise, as well as meal timing and frequency, are quite effective in weight control [6].

As for table manners, the Prophet said, “The human does not fill any container that is worse than his stomach,” and, “It is sufficient for the son of Adam to eat what will support his back.” Throughout his 63-year-long life, the Prophet never left the table on a full stomach or ate before getting hungry; he recommended that food should not be swallowed without chewing, a practice he maintained. By refusing to sit at tables where there were several types of food, our Prophet was occasionally unable to find anything to eat. There is also no information that our Prophet ever had lunch.

The Prophet’s insistence on fewer meals looks very wise. Not only does eating fewer meals lead to lower incidences of obesity; if it includes a reduction in carbohydrate intake, it can also lead to decreases in total and LDL (bad) cholesterol levels [7]. Considering meal frequency and timing, it is crucial which meals are maintained. In general, breakfast-eaters tend to run a lower risk of weight gain than non-breakfast-eaters – and a significantly lower risk of heart disease [4].

Current studies indicate that food content has as much impact on blood lipids and insulin as meal frequency. Although we cannot fully explain the effects of a single factor on physical health, we are pretty much sure that meal frequencies are closely related to meal timing and which kind of foods are eaten.

The Prophet’s main requirement of food was that it should be lawful and clean, as well as beneficial for the body. His two meals consisted of breakfast and dinner, as is recommended by modern medicine. In a nutshell, the amount of intake and eating etiquette recommended by our Prophet is allocating “one third of the stomach for food, one-third for drink, and one-third for air” (Tirmidhi, Zuhd, 47) and completing meals without getting full. Increasingly, science suggests this may have been good advice!

References

1. Flandrin, J.-L.; Montanari, M. Storia dell’alimentazione; Laterza: Bari, Italy, 2003. 2.Affinita, A.; Catalani, L.; Cecchetto, G.; De Lorenzo, G.; Dilillo, D.; Donegani, G.; Fransos, L.; Lucidi, F.; Mameli, C.; Manna, E.; et al. Breakfast: A multidisciplinary approach. Ital. J. Pediatr. 2013, 39, 44.
2. Potter, C.; Griggs, R.L.; Brunstrom, J.M.; Rogers, P.J. Breaking the fast: Meal patterns and beliefs about healthy eating style are associated with adherence to intermittent fasting diets. Appetite 2018, 133, 32–39.
3. Kahleova, H.; Lloren, J.I.; Mashchak, A.; Hill, M.; Fraser, G.E. Meal frequency and timing are associated with changes in body mass index in adventist health study 2. J. Nutr. 2017, 147, 1722–1728
4. Collaborators, G.B.D.O.; Afshin, A.; Forouzanfar, M.H.; Reitsma, M.B.; Sur, P.; Estep, K.; Lee, A.; Marczak, L.; Mokdad, A.H.; Moradi-Lakeh, M.; et al. Health effects of overweight and obesity in 195 countries over 25 years. N. Engl. J. Med. 2017, 377, 13–27.
5. Paoli, A.; Moro, T.; Marcolin, G.; Neri, M.; Bianco, A.; Palma, A.; Grimaldi, K. High-intensity interval resistance training (hirt) influences resting energy expenditure and respiratory ratio in non-dieting individuals. J. Transl. Med. 2012, 10, 237.
6. McGrath, S.A.; Gibney, M.J. The effects of altered frequency of eating on plasma lipids in free-living healthy males on normal self-selected diets. Eur. J. Clin. Nutr. 1994, 48, 402–407.

Every human being asks the question “why,” though at different levels, to explain the unexplained. It follows a pattern of questions, like “Why did the financial crisis in the U.S. happen in August 2008?” “Why did the space shuttle Challenger explode?” “Why did the terrorists commit the September 11 attacks?” In statistical terms, such unexpected events are named “outliers,” however, they are part of the system and among the components constituting the overall system’s complex behavior. Thus, they need to be part of the explanation in order for the explanation to be complete. We are naturally tempted to come up with universal explanations of the complexity behind these major events so that we can be ready when a similar thing happens again. Though simple mathematical equations or relationships relate to us better and provide a universal explanation, they are typically practical only when the outliers are excluded from the system behavior. Statistics help us greatly in quantifying and characterizing the outliers, especially in the form of probabilistic expressions, such as “there is a 30% chance of a hurricane next week.”

Understanding the complexity around us involves the development of a model that is simple enough for us to comprehend but yet universal enough to capture most of the dynamics of the complexity. The simpler and the more universal the model, the more powerful it is. The universality of a model, however, is hindered by the potential inability to capture something unexpected. The tradeoff between simplicity and universality exists in all modeling efforts; and the models finding the delicate balance in this tradeoff are the most effective ones. A simple mathematical relationship known as “the power law” has been used extensively to characterize and model various natural and social phenomena.

What is the Power Law?

The “power law” does not refer to a misconception that “whoever has power will rule,” but rather it refers to a particular way of characterizing dependency between two quantities. When the number or frequency of an object or event varies as a power of some attribute of that object (e.g., its size), the number or frequency is said to follow a power law. In more general terms, there exists a power law relationship between x and y if y is growing or reducing polynomially when x is growing linearly (y _͌ x^–α). Mathematically speaking, this means that the relationship between y and x is mainly characterized by the exponent -a. An exponent is simply shorthand for multiplying that number of identical factors. So, 4³ is the same as 4x4x4; that is three identical factors of 4. As shown in Figure 1, a quantity with an exponent has three components: the base, the exponent, and the coefficient. So, for 4³, the base is 4, the exponent is 3, and the coefficient is an implicit 1.

Figure 1: Description of an exponent in a power law relationship.

Figure 2: Sample power law relationships between x and y, where y = x^–α.

The power law relationships are traditionally expressed with a negative exponent, which simply means the inverse of the quantity. That is, y _͌ x^–α is equivalent to y _͌ 1/x^α. For example, when a is 2, y will reduce from 1/4 (i.e. 0.25) to 1/9 (i.e. ~0.11) if x grows from 2 to 3. Likewise, when a is 0.5, y will reduce from 1/2 (i.e. 0.5) to 1/3 (i.e. 0.33) if x grows from 4 to 9. For those who enjoy graphs, Figure 2 illustrates these mathematical relationships in linear and logarithmic scales.

Power law on different scales: Atoms to planets

To start with, gravitation, acoustics, electrostatics, and light and electromagnetic radiation, all exhibit a form of power law in that physical quantity or strength that is inversely proportional to the square of the distance, which corresponds to a power exponent of 2. [1] Gravitational force between two particles, the electrostatic force of attraction between two electrically charged particles, the intensity of sound signals coming from a source, and finally the intensity of light or electromagnetic field coming from a source all follow a power law with respect to the distance.

What makes the power law relationships more interesting is their independence from scale or size of the measures being related to each other. This is why we sometimes call power law relationships as “scale-free” relationships or “scale-invariance.” For example, the gravitational force between two spherical particles decays with a power exponent of 2 regardless of the sizes of the particles though the actual force is certainly dependent on the particle sizes. So, the particles can be at nano scales (e.g. a group of atoms) or macro scales (e.g. a planet), but the relationship stays the same!

Power law in frequency: Wealth, terror, and earthquakes

A common usage of power law relationships has been to model and understand frequency of a varying measure. A power law typically very well represents the distribution of wealth in a society. [2] According to a recent study, the distribution of wealth in China during the years 2003–2005 follows a power law with an exponent ranging from 1.758 to 2.285. If we consider an average exponent of 2 for Chinese wealth distribution, this means that if there are 1 million Chinese people who owned $1000 there were 1000 that owned $1M. Thus, the power law essentially expresses how skewed the distribution of a frequency is (see Figure 2). The larger the power exponent, the more skewed the distribution. In this case, a larger power exponent means a more imbalanced wealth distribution while a power exponent of 1 refers to an evenly distributed wealth.

Many other social patterns exhibit power law. A recent study showed that it exists even in terror events! The number of casualties per insurgent event and the number of insurgent events per day follow a power law. [3] Historical data for the last two centuries show further that the number of casualties per war or a terror attack follows a power law distribution. What is even more interesting is that the number of casualties and the number of attacks within an insurgent conflict both follow power law. That is, when only a particular conflict between two countries or ethnic groups is considered, the number of casualties per insurgent event and the number of insurgent events per day follow the power law. This suggests a “self-similar” pattern. Likewise, traffic measurements for many systems show power law distributions of size. For instance, if one observes the data traffic on an Internet connection and counts the number of bytes being transmitted per hour over that connection, a power law distribution of the count of bytes will emerge. Further, if this counting is done per minute instead of per hour, a similar distribution will still emerge – again showing a self-similar pattern. [4]

The power law has been observed in several natural phenomena as well. The frequency of earthquake magnitudes follows a power law. [5] This refers to the intuitive notion that the number of earthquakes with small magnitudes (which humans do not even feel) is much larger than the number of earthquakes with large magnitudes, (which can kill many humans). Small earthquakes are the norm while large ones the outliers. However, without the outliers, there is no power law distribution! Thus, the power law distribution of a quantity comes with an interesting observation: If a quantity is indeed following a power law distribution, then the likelihood of an outlier event increases as the time goes by without an outlier event. This is why geoscientists would make comments like “The region X is due for a major earthquake!” indicating that the region X has not been receiving a major earthquake (i.e. an outlier) for several years. The issue, though, is determining the threshold for an outlier is typically ambiguous and may require many years of measurements and data, which may be impractical.

Power law in growth: Rich get richer

Growth of systems also exhibit power law in various ways. Social growth follows power law due to the well-known “rich get richer” rule, which refers to the intuition that “important” people in the society attract more of the attention of newcomers. This dynamic situation is observed, for example, in the growth of the Internet. Several studies [6] showed that the connections between Internet Service Providers (ISPs) (e.g., AOL, Yahoo!, AT&T, Sprint) follow a power law distribution in that the number of connections per ISP (which shows how well an ISP is connected to the rest of the world) is represented by power law. In other words, there are few ISPs with many connections to other ISPs while most ISPs have a few connections to the others. This is believed to be due to the “rich get richer” rule since an existing ISP with many connections is more likely to gain the business of a new ISP who is joining to the Internet. So, it is somewhat an economic pattern too.

If economics (or the money) is taken out of the picture, social growth still exhibits power law. Online social networks such as Facebook, LinkedIn, and Flickr are clearly following a power law distribution. It is found that the power exponents are in the range of 2.5 to 3.7, indicating a highly imbalanced social growth pattern where few people are at the “center” of the social network with hundreds or thousands of friends, and many people have only one or two friends. [7] Again, the typical explanation for this growth pattern has been the “rich get richer” rule, but “richness” refers to the number of existing friends in this context rather than money.

Physical growth shows power law too in many ways. For instance, roughness of a growing surface as time goes by follows a power law distribution with an exponent ranging between 0 and 1 where an exponent of 0 refers to a smooth growth and 1 refers to a stiff growth. The surface roughness is measured by the variance of heights of surface locations. [8]

Does it really exist? Why does it exist?

Verifying existence of a power law distribution is not easy and requires enough number of samples to show the “tail” of the distribution. The tail of the distribution refers to the samples with large (or rare) values. For example, for the power law distributions in Figure 2, the portion of the distribution when x is greater than 10 (i.e. x>10) roughly corresponds to the “tail.” The tail corresponds to the rare samples. Though statistical theory calls those rare samples “outliers,” the distribution will not be a power law distribution without them. They are strictly parts of pieces that constitute a power law relationship, and observing them typically requires long periods or large numbers of measurements. Due to this difficulty, the existence of the power law is questioned for many real systems. Most of the time, claims of the existence of the power law typically come with an error factor indicating the confidence of the claim. The bottom-line is to observe trends in the samples and thus establish sufficient confidence (e.g., more than 95%) that the power law distribution does exist in the samples.

For those systems with clear exhibition of power law, the root causes of it have been of high interest. The “rich get richer” rule is intuitively one of the root causes, and it is intuitively a natural dynamic to get attracted by a rich member rather than a poor one. Growth certainly naturally follows the “rich get richer” rule, but we have system components slowing their growth, flattening, and then deteriorating. So, not everything is growing, and actually, we have as many things deteriorating as growing. For instance, participants join or leave the Internet or the social networks, and likewise, people join (i.e. birth) or leave (i.e. death) society. How does the power law stay in such systems then?

Due to the “rich get richer” intuition, the power law is considered to be the signature of “self-organization.” The fact that so many natural or synthetic systems are exhibiting this signature deserves the question: “Is it really self-organization?” Maintaining a global power law distribution for a system requires either (i) every member joining or leaving the system according to the “rich get richer” rule and having global knowledge of the whole system or (ii) somebody who knows everything about the system and gives explicit direct orders to each member when they are joining or leaving. Which one is more likely?

Murat Yuksel is an Assistant Professor at the CSE Department of The University of Nevada – Reno (UNR), Reno, NV.

References

[1] Wikipedia, “Inverse-square law,” http://en.wikipedia.org/wiki/Inverse-square_law

[2] M. A. Santos, R. Coelho, G. Hegyi, Z. Néda, and J. Ramasco. 2007. “Wealth distribution in modern and medieval societies,” The European Physical Journal, Volume 143, Number 1, pages 81-85.

[3] J. C. Bohorquez, S. Gourley, A. R. Dixon, M. Spagat, and N. F. Johnson. 2009. “Common ecology quantifies human insurgency,” Nature, Volume 462, December, pages 911-914.

[4] T. Karagiannis, M. Molle, and M. Faloutsos. 2004. “Long-Range Dependence: Ten Years of Internet Traffic Modeling,” IEEE Internet Computing, September/October, pages 57-64.

[5] T. Lay and T. Wallace. 1995. Modern Global Seismology, Academic Press, San Diego, CA.

[6] M. Faloutsos, P. Faloutsos, and C. Faloutsos. 1999. “On power-law relationships of the Internet topology,” ACM Computer Communication Review, Volume 29, Issue 4.

[7] R. Kumar, J. Novak, and A. Tomkins. 2006. “Structure and evolution of online social networks,” Proceedings of ACM SIGKDD, pages 611-617.

[8] A. L. Barabasi and H. E. Stanley. 1995. Fractal Concepts in Surface Growth, Cambridge University Press, Cambridge, England.

In this work we study a verse from the Qur’an, the 47th verse of the Sura al-Dhariyat (The Winds that Scatter), under the light of new discoveries in the field of astrophysics. We note that recent evidence about the accelerating expansion of the universe is also strongly consistent with this verse, although this has shocked the scientific community. In the last part of the article, we discuss possible relations of “metaphysical dimensions” and the concept of “the seven layers” with the word “sama” (translated in to English as “heaven”) as mentioned in the verse.

The existence of the universe is perhaps one of the greatest mysteries in science and philosophy. No convincing argument has been ever put forward that has enabled us to understand this amazing event, not since the beginning of modern science. Religions like Islam, Christianity, and Judaism, on the other hand, explain that the Creator built our robust universe directly out of physical nothingness, independent of any cause. Therefore, the initial creation of such universe would be impossible to explain physically (M. F. Gulen, from his conference on “Evolution and reality”).

In his translation of the relevant verse, S. Yildirim has noted that God keeps the universe expanding and He will continue to do so. Yildirim attributes two meanings to the word musiun in the verse; the first is the owner of great power, strength and wealth; the second is one who expands. Thus, it should not be a surprise to learn that this verse is indeed describing a continually-expanding universe. This might further lead Muslims to think that the Creator has not left the universe unattended after the Big Bang, but rather it is He who has kept creating and expanding it.

In the 1920’s a discovery was made that completely changed our perception of space. It was discovered that distant stars depart from the solar system and leave us even more and more alone in dark space. Then, Fr. Georges-Henri Lemaître, a Belgian astrophysicist, mathematician, and Catholic priest, proposed the idea of the expanding universe. Despite its finite size, it was believed that the universe was expanding.

We can explain this fact simply by an analogy. Think of a toy balloon with spots on it. Mark one of those spots and inflate the balloon. As we inflate it, we observe that all other spots on the surface of the balloon move away from the marked one. So, if we replace the balloon with our universe, the spots will be the stars and planets. If the universe is expanding indeed, then we expect them to be moving away from each other. In other words, the distances between heavenly bodies must be increasing.

Unfortunately, we don’t have a gigantic ruler to measure such immense distances. However, there are other means, such as measuring wave frequencies. Consider the following analogy: Someone throws one ball every second toward a target. Assume that balls travel with constant velocity. If the thrower is stationary, the target will receive one ball every second. However, if the thrower is moving towards the target, it will receive balls more frequently because the balls will be less spaced out. The converse is true if the thrower is moving away from the target. So it is actually the wavelength which is affected; as a consequence, the perceived frequency is also affected. That is, the distances between the waves emitted by objects moving away from us (wavelength) must be increasing, so the frequency decreasing. Likewise, think of an ambulance siren coming towards you and going away from you. It is a good example showing that while an acoustic source that is approaching us emits a higher frequency, the same source radiates lower frequency when going away from us. In physics this is known as the Doppler effect.

Red shift

This phenomenon does not only occur with sound waves, but also with electromagnetic waves. When we think of the spectrum of light, violet at one end has the shortest wavelength and red at the other end has the longest wavelength of visible light. So, any wave of light shifting toward red means the source is moving away from us. It has been determined that the frequency of light emitted by the elements within distant stars shift to a lower frequency, which is called a red shift.

It is this shift that makes astrophysicists think that the universe is expanding. One mustn’t be confused by red shift. This terminology is just used to explain in what direction the frequency is actually shifting on the spectrum. Those signals captured from distant stars have a much smaller frequency (much higher wavelength) than that of red light and they are indeed in the microwave regime and shifting to even much smaller frequency radio waves.

In 2002, an article presenting new evidence of the accelerating expansion of the universe was published by the Royal Astronomical Society. It was not so long ago, only five years, that general opinion concurred with a decelerating expansion. However, the first evidence found by two astronomers in that year led us into a universe that expands in an accelerating fashion, contrary to previous views. This result was absolutely unexpected, because many scientists believed that expansion would slow down due to gravity. Another interesting fact is that if space were to cease expanding, this would be in contradiction to the above verse. God, however, by never allowing this to happen, shows how futile the actions of those who deny His verses are and how extensive His power is, as well as how purposefully He creates.

Dark energy

The groups who worked in the above study figured out, from the brightness of supernovas in distant galaxies, that the universe must expand more and more in the future due to a peculiar dark energy within it. The concept of dark energy was first postulated by Einstein, who named it the “cosmological constant.” However, since this did not fit in well with his theory of general relativity, he withdrew it and said that it was a scientific blunder. Since then, dark energy has had a rather controversial history.

A team of 27 astronomers, directed by Professor Efstathiou of Cambridge University, proposed strong evidence supporting the existence of dark matter, based on completely novel techniques. Their results, which were consistent with previous supernovas, showed that the universe is indeed full of dark matter. Professor Efstathiou thinks that the explanation of dark energy might include additional dimensions like creation (Big Bang) as well. Fr. Lemaître also proposed the expanding universe theory at an opportune time since Edwin Hubble would soon release his red shift observations that strongly supported an expanding universe and, consequently, the Big Bang theory. Here, the Big Bang is seen as the beginning of a continuous expansion.

The verse seems to tell us miraculously that the expansion of the universe will not cease, despite our limited knowledge of the physical reason for its acceleration.

The Hubble Telescope

Another article, published in Nature, presents us the first and deepest picture of space taken by the Hubble Space Telescope. This caused the astronomers to compete in solving the mysteries of the arts of God. The picture, also known as the Hubble Ultra Deep Field, was broadcasted and published in various programs and journals. It has not only shown us the farthest stars of the universe, but the youngest as well. It was very difficult to detect such weak light with the former technology. This picture reveals the embryonic universe, with an age of only 500 million years old. Estimated age of the universe is 13-14 billion years. Three physicists from American Natural History Museum in New York started a competition to publish an article on the Ultra Deep Field picture after the data was disclosed. They hope to answer many questions about the past and future universe. A group at the Stony Brook University, New York, directed by Kenneth Lanzetta, analysed the embryonic samples in the picture to try to discover when various galaxies had been born and how they had evolved. Two other groups are studying the motions of stars and galaxies, as the picture is a result of data collected over a month.

Having looked at the expansion of universe under the light of recent discoveries, now we turn our attention to two other arguments that could be relevant to expansion. Namely, ether (a substance which it is believed fills up the vast universe and which is the ultimate building block of the space), and the seven-layer-universe.

Despite the Michelson-Morley experiment, which argued against theory of luminiferous ether, the propagation of electric, light, or heat in space shows the existence of a substance through which they flow. The Michelson-Morley experiment is nothing more than just a test of the non-existence of certain qualities of ether. For example, in order to show the existence of photons, of which light is made up, we cannot go beyond showing the features of photons. In other words, depending on how we have defined its qualities, we can observe different aspects in the photon, ether, or anything else. In fact, even today, we don’t really know what a photon really is, although we observe its affects every day. In short, it is not possible to show the non-existence of phenomena that cannot be absolutely defined. Instead, we can only test the existence of the properties that we have defined and attributed to them, and thus we better understand their nature of existence in the context of those pre-defined qualities. Hence, the existence of ether is still controversial and needs more thorough research.

Seven layers

Regarding the seven-layer-universe, on the other hand, how is it possible for ether to manifest itself in seven heavens? It may be that these seven layers are not all posed above our heads, but rather that they may be found one with another. The universe is composed of many systems and networks that are the building blocks of their counterparts on larger scales. Each system is governed by laws, which differ slightly from one another. Inside the atom there exists a proton with its unique organization and in a proton we find quarks. For example, communication between protons and electrons is mediated by the electromagnetic force, while the quarks inside the protons communicate via the strong force. These interleaved circles show us that the universe is indeed composed of numerous layers.

We may use these layers for the metaphysical world as well. The human being is not only composed of matter, but also has a mind, a soul, and intelligence. Although these components are accepted as existing by all, their exact nature has not yet been explained by positive sciences.

It seems that the universe is composed of at least two different worlds: The material world (physical) and the immaterial (metaphysical) world. Are these two worlds completely separate, or do they have some features in common? In fact, the existence of humanity might prove to be this common set. But, it may also be true for the universe itself. Nursi states that the distant galaxies, stars and planets are not empty, but home to many spirits and angels who have their own consciences. Thus, one can say that despite the boundaries which separate these two worlds, such as different numbers of temporal and spatial dimensions, they constitute a whole, the Universe. The interaction between them will never fail as long as the universe exists.

The existence of two separate worlds is not that difficult to believe, but there is more:

It is He Who (prepared the earth for your life before He gave you life, and) created all that is in the world for you (in order to create you – the human species – and make the earth suitable for your life); then He directed (His Knowledge, Will, Power, and Favor) to the heaven, and formed it into seven heavens. He has full knowledge of everything. (Baqara 2:29)

The Qur’an calls the heaven where the sun, moon and stars are the lowest heaven or the heaven of the world (Mulk 67:5). The other six heavens may be the heavens of the worlds of the Hereafter.1 We are not sure whether this seven-layer heavens can only be attributed to the physical universe. It might be able to apply to the universe as a whole, with its all seen and unseen layers as well. Even the worlds of angels and spirits may be expanding in accordance with the laws therein, to show how the power and the wealth of God are comprehended in those worlds as well. Although our Earth is finite, the expansion may not be restricted to our finite world, but it may continue in infinite worlds as well.

It is possible that the space being filled with ether has an important role in paving the orbits of planets or stars, as well as other heavenly bodies. We believe that future studies on dark matter, ether, and string theory will help us to better understand the expansion process of the universe.

Note

1. What the Qur’an means by seven heavens has been interpreted in different ways. For further information see Unal, 2006, p. 19.

References

• Ünal, Ali, The Qur’an with Annotated Interpretation in Modern English, The Light, Inc., New Jersey: 2006.
• Monthly Notices of the Royal Astronomical Society, 330, 21 (2002).
• Nursi, S., The Words, The Light, Inc., Istanbul: 2005.

In 1896, Marconi was successful in sending signals through a wireless telegraph to a distance of a few kilometers away. However, how would it be possible to provide intercontinental communication via radiotelegraphy and radiotelephone? In 1901, together with his assistants, G.S. Kemp and P.W. Paget, Marconi successfully transmitted and received transatlantic signals between Poldhu, Cornwall and New Foundland, Canada, using a kite aerial at Signal Hill in Cornwall, England. It was Edward Appleton who first discovered that radio waves were broadcast around the world after they are reflected back from the ionosphere, one of the highest electrified layers of the atmosphere that contains large concentrations of charged particles (ions) and free electrons. Electromagnetic waves that are sent from radio transmitters to outer space are reflected back to every corner of the Earth after hitting this gas and plasma layer that is composed of charged particles. Thus, radio and radiotelephone communication is made possible for the benefit of human beings. After that time, being able to use a law that had been ordained by the Supreme Creator, human beings were able to reach a level that enabled them to conduct transatlantic communications via radiotelegraphy. But what makes radio waves so special?

Radio waves

The frequency spectrum of electromagnetic waves begins from the “sub-sound frequency region” (1Hz) stretching up until cosmic rays (Figure 1). Radio communication is made using the electromagnetic waves that form part of this frequency spectrum. Radio communication systems can be classified into four groups relating to their frequency regions:

– LF/MF (Low Frequency/Medium Frequency)

– HF (High Frequency)

– VHF/UHF (Very /Ultra High Frequency)

– SHF (Super High Frequency)

Specifications of radio waves are taken into account in this classification. The main element that makes radio waves similar or different from each other is the frequency band that determines their wave length. Radio waves move at the speed of light (300 thousand km per second), much faster than sound itself, so to find the wave length of a radio wave, we divide its velocity by its frequency.

Frequencies used within the radio frequency spectrum measure between 20 KHz and 30 GHz. Theoretically, the high frequency band is between 3 and 30 MHz, while in practice it is between 1.6 and 30 MHz. The interval between 4 and 18 MHz is the most-widely used region in the spectrum.

The atmosphere

Our Lord, Who incessantly prepares the Earth in a beautiful manner, also protects all of life with a perfect shield called the “atmosphere.” Scientists have divided the atmosphere into seven layers in order to reveal the unknown facts about it. These seven layers are different from each other in terms of temperature, pressure and humidity levels, and the natural events that occur in them. If we ascend from the Earth toward the sky, we pass through the layers of the troposphere, stratosphere, ozonosphere, mesosphere, thermosphere, ionosphere and the exosphere. All these layers cover a distance of about 3,000 km. Each of the atmospheric layers serves a vital cause. Every layer has many functions, ranging from the formation of rain clouds to the prevention of harmful beams reaching the Earth, from reflecting radio waves to inactivating meteors. One duty of the ionosphere that we are aware of today is to act as a reflector and distributor for radio waves.

The ionosphere and distribution of radio waves

Good transatlantic radio communication depends upon many factors. Depending on the frequency of the radio waves, the season of the year, the position of the Sun, the location of the broadcasting area and the time of day, the communication area may vary from 100 km to 10,000 km.

Radio waves are propagated around the Earth in two forms, either as ground waves or as sky waves (Figure 2). In high-frequency radio communication, it is important to choose the best frequency for the time and means of propagation.

Starting from 50 km above the Earth and stretching 440 km, the ionosphere is filled with a high concentration of free electrons and gases. Why is the ionosphere important for transatlantic radio communication? The electrified ions that fill the whole of the ionospheric layer that completely surrounds the Earth reflect radio waves from all directions to every part of the world. According to their frequencies and ionization, radio waves are completely absorbed in the ionosphere and they are either partly refracted and distributed to the outer space or are reflected and returned to the world. The electromagnetic waves within a range of 30 MHz can return to Earth after being reflected by the ionosphere.

It is accepted that the ionosphere is formed at different ionizing levels in different layers, known as D, E, F1, and F2 (Figure 3). The ionization level in the outer layers of the ionosphere is higher than that of the inner layers. The D layer, the innermost layer of the ionosphere, is 76-93 km above the Earth and is characterized by low ion densities and low collision frequencies of electrons and ions with neutral particles. Serving to absorb most energy below 7 MHz, this layer is ionized during the daylight hours, completely disappearing at night. It reaches full ionization level just after sunrise and is at its peak at noon time, immediately losing energy after sun-set.

The E layer is the region of the ionosphere that was discovered first. In this layer, molecular ion production is at its peak at about 110-115 km above the Earth. There are plenty of molecular gases at this height. This layer is a suitable platform from which radio operators can reflect signals to distant stations. Reaching a maximum at noon, the ionization in the E layer decreases towards the end of the day, disappearing completely at midnight. Moreover, at unpredictable intervals, ionized gas clouds accumulate in certain regions of this layer. This can be detected by the variable dense clouds of ionization that occur in the E layer due to the spatial and temporal structure in the ionizing particle precipitation. The plasma density of the E layer can be greatly changed because of these occasional formations. These formations, which are called “sporadic E layers,” are used by radio amateurs for long distance VHF (Very High Frequency) operation. Since the plasma density in layers D and E is highest at noon and present during the other hours of daylight, these layers are used in the daytime.

The next layer of ionosphere exists at about 160 and 400 km above the Earth and consists of layers that have a higher density of free electrons caused by the ionizing effect of solar radiation. Since the density of gas molecules at this height is low, ion and electron collisions occur very slowly in this layer. When solar radiation is high (during the day) this layer can be divided into two independent regions, F1 and F2. The F1 layer is present at 152 and 203 km above the surface of the Earth. During the night, the F1 layer merges with the F2 layer. The F2 layer exists at 250 and 400 km above the surface of the Earth. The majority of HF (shortwave) transmissions are propagated by the F2 layer, which is the main reflecting layer for HF communications both at day and at night. Reaching its maximum level of ionization just after midday, the layer is at its minimum just before sunrise. The F2 layer can be used for 10-20 MHz during the day and 3-8 MHz during the night. Since the F layer exists at a very high altitude, it is exposed to sunlight for longer periods of the day and it dissipates very slowly at night. In this case, the only layer of the ionosphere that can be used during the night is the F layer, which I is composed of the F1 and F2 layers.

Solar radiation, and consequently ionization, alters periodically. For instance, as the days are long during the summer months, ionization is also high at this period. During this time, radio waves are absorbed or attenuated more in layers E and D, and propagation covers only a small area. However, since the days are shorter during the autumn and winter, less solar energy reaches these ionospheric layers. Hence, low frequencies can easily pass through the weakly ionized D and E layers and reach the stronger F layer from where they can be propagated over long distances.

Another long term factor in ionization is the regular 11-year activity cycle of sun spots. Sun spots are believed to be caused by violent eruptions on the Sun and they are characterized by unusually strong magnetic fields. During periods of maximum sun spot activity, the density of ionization increases in all the layers of the ionosphere. During these periods, the D layer absorbs more and the critical frequencies of layers E, F1 and F2 are higher, therefore, for long distance communication higher operating frequencies over 30 MHz should be used. During terms of minimum sun spot activity, the E and F layers have weak ionization, so they cannot reflect the radio waves back onto the Earth. In this period, frequencies over 20 MHz are not used much. Along with this regular variation, “sudden ionospheric disturbances (SID)” also negatively affect the propagation of radio waves. SID are thought to be caused by severe solar eruptions, but the real cause of this phenomena is still not clearly known. (Figure 4)

Sudden ionospheric disturbances can disturb radio communication for hours or even days. Strong solar eruptions cause a sudden abnormal increase in the ionization density in the D layer, hence even the high frequency radio waves coming from the side of the Earth that is facing the Sun are completely absorbed by this layer and frequencies above 2 MHz are unable to penetrate it. When SID occurs, long distance propagation of HF radio waves may be completely blocked.

Ionospheric storms are another disturbing factor for radio communication. When a solar eruption occurs, it takes between 20 and 40 hours for the magnetic storm to reach the Earth. The ionospheric storms cause the F2 layer to virtually lose its ion density. At this time, when the range of frequencies used for communication is much smaller than normal, communication is only possible at lower frequencies.

Frequency and propagation routes in radio communications

The definition of the frequency to be used for radio communication is an important parameter for ensuring healthy propagation. For this, the Maximum Usable Frequency (MUF), and the Lowest Usable Frequency (LUF) are determined. Frequencies over MUF penetrate the ionosphere, shooting right through the ionosphere and going out into space, whereas frequencies below MUF are reflected. LUF is the lowest frequency that is completely absorbed in the D layer. To conduct good communication, a frequency, calculated as MUF×0.85, should be used. This frequency may be lower at night and higher during the day.

Apart from the propagation frequency, the path that is chosen to transmit the radio waves from one point to the other also must be calculated accurately. The angle at which the radio waves enter the atmosphere (angle of incidence) defines the path that will be covered by the waves on their way to Earth. The angle of incidence should be small enough for the waves to be reflected back to Earth and large enough so that the waves will not penetrate the ionospheric layer. Smaller critical angles should be used for smaller frequencies and larger critical angles should be used for larger frequencies so that they will not penetrate through the ionospheric layer and be lost in space.

Consequently, apart from periods when solar eruptions are strong, radio waves that are over 30 MHz frequency are not reflected and can penetrate the atmosphere and reach outer space, hence making the communication between outer space and the Earth possible.

For transatlantic communications conducted via communication satellites, radio waves over 30 MHz are used. Artificial satellites imitate the ionospheric layer, their original source of inspiration, and act as a reflector for these waves (Figure 5). Waves coming from the Earth are reflected by these satellites if they are within their coverage area. However, these manmade satellites have very limited coverage areas. Although they are produced with the highest technology available, their cost is very high and they last only for about 25 years. Nevertheless, for radio waves lower than 30 MHz, the ionosphere, that covers the whole of our planet, acts as a natural satellite. Because of this characteristic of the ionosphere, we do not have to focus at any certain point. Moreover, there is no need for maintenance, nor any energy supplement, and the ionosphere is permanent. The atmosphere has been granted for our service for as long as Earth survives. Through searching and exploring new facts about the universe and all beings, we realize more and more that neither meaningless nor useless matter exists in the material world of creation. Therefore, we are better able to understand that the universe is packed with wonderful favors and blessings that are addressed directly to humanity.

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.

In today’s cellular communication systems, cellular phones operate in several frequency bands. European systems use the Global System for Mobile Communications (GSM) at around 900 MHz and 1800 MHz; American systems use 850 MHz and 1900 MHz, frequencies that fall between the operating frequency ranges of televisions and microwaves. This frequency range is called non-ionizing, for the wave’s energy does not release electrons from atoms in living tissue. For instance, an X-ray is an ionizing wave that, to a degree, damages exposed biological material. Therefore, most concerns deal with RF energy’s heating effect rather than with ionization.

Technical Motivation

The electromagnetic spectrum extends from DC (direct current) to ionizing radiation. Scientists divide this spectrum into subregions. Cellular phones fall into the ultra-high frequency (UHF) regime, specifically from 300 MHz to 3000 MHz. By itself, a continuous UHF wave carries no information and does not enhance communication. It only becomes useful when modulation, defined as means carrying the information on a high frequency carrier, like UHF, is applied. The most common modulation techniques are amplitude modulation (AM) and frequency modulation (FM).

The capacity of the spectrum’s given section to carry information is limited by the Shannon Theorem. According to this theorem, channel capacity can be increased by increasing the system’s signal-to-noise ratio. In wired communications, channel capacity can be increased by adding more parallel optical fibers. Channel capacity in wireless communications can be increased by transmitting weak signals that attenuate rapidly near the transmitter and thus provide a given portion of the electromagnetic spectrum to be utilized many times. How a given spectrum is allocated among users affects the channel capacity. Therefore, there are several coding techniques, the most common of which are Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA).

Neglecting some small details, an electromagnetic (EM) wave’s energy is expressed in terms of power density (W/m2) across a surface. Power density measures an incident EM wave’s strength. Easily measured, it is a very preferable metric to UHF fields. For uncontrolled environments, the American National Standards Institute and the Institute of Electrical and Electronics Engineers (ANSI/IEEE C95.1) recommend a 2 to 20 W/m2 for an average external exposure to UHF. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) has similar power density recommendations for limiting the general public’s exposure to RF energy so that people will not be overheated by RF energy. As a comparison, for example, summer sunshine peaks around 1000 W/m2.

However, as power density is not a good indicator inside a living organism, scientists have defined a Specific Absorption Rate: SAR (in W/kg). For uncontrolled environments, ANSI/IEEE limits the spatial-average SAR to 0.08 W/kg whole body and to 1.6 W/kg averaged over any 1 gram of tissue. Also, 1998 ICNIRP restrictions are similar to ANSI/IEEE’s. The SAR can be estimated in three ways.

– Micro-antenna: Small antennas can determine a tissue’s electric field as well as its SAR. But it is difficult to place the antenna, and the tissue’s properties may not be known.

– Miniature thermal probes: Since RF energy heats the tissue, this technique detects the heat and the SAR in the neighborhood of the temperature cell, which then can be computed accordingly. However, this method also seems very difficult technologically.

– Numerical modeling: The numerical modeling of macroscopic bodies enables a numerical simulation, known as the Finite Difference Time Domain (FDTD), that can estimate the SAR. However, this process can be time-consuming and expensive.

Possible Health Issues

An EM wave can effect a biological change in living tissue in two ways: Depositing enough energy while passing through the biological material to alter some structures, or depositing packets of energy larger than the bond energy. Yet neither way seems to be possible, for the photon energy within the UHF zone is far less than the bond energy or the energy required to alter a living tissue’s structures. Therefore, many scientists now argue that UHF radiation at subthermal power levels can cause some biological damage.

Due to relatively low exposure levels, relatively small populations, and a lack of reliable dose estimates, proving or disproving the existence of RF exposure’s biological hazards remains an issue for epidemiology (e.g., statistical analysis of health records and animal studies).

Epidemiological Studies

Epidemiological studies were conducted among people who worked in a high frequency environment, such as radar stations. Search criteria were not limited to cellular and personnel communication system (PCS) frequencies. Due to the nature of radar and other military equipment, broader frequency ranges were covered. The epidemiology of cancer and RF radiation includes studies of cancer mortality rates among those exposed to RF energy.

Throughout these studies, people’s records were searched to determine if their cancer was due to RF exposure. These studies were made in various institutions, including the Radar Laboratory of the Massachusetts Institute of Technology, the U.S. Navy and Air Force, and the Polish military. There was no conclusive evidence that RF exposure increases the risk of cancer. Also, due to the lack of comparisons with total cancer, it was suggested that RF exposure does not have a strong effect on cancer.

Since brain cancer takes a long time to develop and epidemiological studies tell nothing about future risks, these studies have not proved or disproved that RF exposure increases the risk of cancer.

Animal Studies

Animals are the other source of information that potentially may answer people’s concerns. Experiments have studied rats exposed to certain power levels of RF energy. However, these studies found no link between cell phones and cancer.

In 1999, a Motorola-funded research program concluded that exposing rats to pulse-modulated 837 MHz RF energy, very close to that radiated by a digital cell phone, does not cause or develop brain cancer. A study in April 2000 reported that this conclusion is valid for continuous-wave RF (analog cell phones). But a 1995 study at the University of Washington (Seattle) reported that exposing rats to RF radiation at an average whole-body exposure of 1 W/kg of body weight caused breaks in their brain cells’ DNA, which is an indication of cancer. No other study has confirmed this finding.

Other studies have focused on different aspects of RF radiation rather than brain cancer. They searched animals for certain diseases and noticed an increase in disease rate. However, despite such research findings, animal studies seem to be far removed from human health.

Conclusion

Epidemiological findings and animal studies have neither proved nor disproved the health hazards of mobile phones. A February 2000 essay by the U.S. Food and Drug Administration (FDA) stated that: There is currently insufficient scientific basis for concluding either that wireless communication technologies are safe or that they pose a health risk to millions of users. Research activity continues. For example, France’s International Agency for Research on Cancer has received a research project of 8 million euros from the European Commission for a 3-year, wide epidemiological study. Also, the FDA and the Cellular Telephone Industry Association have undertaken a $1 million research project to clarify the health risks of mobile phones.

Meanwhile, some researchers are trying to find the head’s SAR by using electromagnetic simulations (FDTD). So far, they have discovered that it is strongly affected by the cell phone’s position as well as the head’s shape and properties. Therefore phone-makers are trying to design handset designs to reduce the SAR. However, it seems that the debate will remain until scientific proof is confirmed and made available.

• References
• http://www.fda.gov/cdrh/ocd/mobilphone.html.
• IEEE Spectrum. Are Mobile Phones Safe? (August 2000): 23-28.
• Moulder et. al. Cell Phones and Cancer: What is the Evidence for a Connection? Radiation Research Society, 151 (1999): 513-31.