14SCIENCE REPORTER, FEBRUARY 2015

comfortable with the unknown, then it’s diffi cult to be a scientist… I don’t need an answer. I don’t need answers to everything. I want to have answers to fi nd.”

It is not easy to take this disposition; after all in schools and colleges we ‘mug-up’ the ‘right answers’ marked out in the text book or guide books. We answer questions in the examination, obtain good scores and feel ‘smart’. But the whole point of science is not about what we know, but what we still don’t know.

When it is unknown, then everyone, you me or Einstein are ignorant. As Schwartz observes, “Focusing on important questions puts us in the awkward position of being ignorant.” But then “one of the beautiful things about science is that it allows us to bumble along, getting it wrong time after time, and feel perfectly fi ne as long as we learn something each time.”

Schwartz further says “no doubt, this can be diffi cult for students who are accustomed to getting the answers right” and argues that science education can do well if we do not exclusively harp on “learning what other people once discovered to making your own discoveries”. Schwartz goes on to

CO

VER

CO

VER

STO

RYST

ORY

SCIENCE REPORTER FEBRUAUARYRY 2015

‘THE importance of stupidity in scientifi c research’, is indeed an eye-catching title. Published in the Journal of Cell Sciences (121, 1771; 2008), the author Martin A. Schwartz, a microbiologist at the University of Virginia, provokingly says: “Science makes me feel stupid …. in fact, that I actively seek out new opportunities to feel stupid. I wouldn’t know what to do without that feeling.”

Stupidity and science? Think of Aristotle, Aryabhatta, Galileo, Newton, Einstein, NASA or our own ISRO; what comes to our mind is a glowing bulb and a big fat brain. It is words like ‘genius’, ‘smart’, ‘brainy’, ‘shrewd’ that we would associate with them, not ‘stupid’.

Schwartz says, “[when you] do a research project, it is a whole different thing...” and “What makes it diffi cult is that research is immersion in the unknown. We just don’t know what we’re doing. We can’t be sure whether we’re asking the right question or doing the right experiment until we get the answer or the result.” No one knows the right answer, until someone discovers it; and there is no formula for discovering it.

Endorsing the sentiment, physicist Brian Cox says: “I’m comfortable with the unknown—that’s the point of science. There are places out there, billions of places out there, that we know nothing about. And the fact that we know nothing about them excites me, and I want to go out and fi nd out about them. And that’s what science is. So I think if you’re not

There are millions of questions out there for which we have no answers today. But this need not be a cause for discouragement; our ignorance forces us to muddle through, illuminating our way through the uncharted terrain.

celebrate being constructively stupid, “The more comfortable we become with being stupid, the deeper we will wade into the unknown and the more likely we are to make big discoveries.”

The crucial point is that what we don’t know is not merely vast, but for all practical purposes, infi nite. This is not a cause for discouragement, but actually is liberating. Since our ignorance is infi nite, the only way forward is to muddle through as best we can, with reason to illuminate our way through the uncharted terrain.

There are millions of questions out there for which we have no answers today. Be it mundane, ‘How does a bicycle work’; or profound, ‘What is time’. But there are questions galore all around us. There is a wide wonderful world out there to be discovered and made sense of. With this selection of ten enticing questions we invite you to the world of the curious.

A Question of BirthImagine a brick lying on an open ground. Suddenly the brick animates and makes copies of itself – two, four, eight, and so on. The growing numbers of bricks then start to form structures; initially the fl oor, then the four walls, then windows

T.V. VENKATESWARAN

15 SCIENCE REPORTER, FEBRUARY 2015

COVERCOVER STORY

nearby have to collectively differentiate. Obviously we do not want fi ngers to grow from the middle of the palms instead of the tips; eyes to be formed in toes or gut rather than the head. Lastly, when the fi ngers and other organs have grown to the right size further cell multiplication has to stop.

How does it happen? How does a cell know how to make a human (or any other mammal)? Bricks on the fi eld cannot by themselves build the whole edifi ce without a mason and a plan. But unlike the bricks, cells have DNA which have codes for the preparation of amino acids and production of proteins, the building blocks of the organism. However, each cell has the same genome and the eye cell differs from skin cell not because they have different genomes, but because different sets of genes are expressed.

On the other hand, in contrast to a building site, with a mason to direct where each brick should go, there is no commanding offi cer to direct the troops; each of the millions of cells in the embryo

has to make its own decisions, according to its own copy of the genetic instructions and take its own particular location and decide its stage of growth. The puzzle of developmental biology is: how does a set of cells differentiate, organise and grow? How does a single cell at conception multiply and ultimately give rise to an adorable petite chubby child?

A Question of DeathCertain species of tortoise live for 300 years, while certain varieties of Mayfl ies are alive for just a few minutes. Why do animals live as long as they do? What determines their natural life span?

We know from the second law of thermodynamics, decay is natural. Red blood cells decay and are replaced once in every 120 days; the stomach wall is replenished every three days. The lungs are at the best six weeks old. The DNA, in every single cell, is damaged by free radicals and cap’s on chromosomes, the Telomeres, shorten with every cell division. When the length of the Telomeres becomes shorter than a certain length, after a certain number of cell divisions, apoptosis, or cell death occurs.

But what determines the natural life span of every species? One theory says that larger the species, the slower its energy-delivery systems, the lower the metabolic rate, the longer the life. If one plots the metabolic rate against the longevity the resultant graph is almost a straight line.

This has resulted in what is popularly called the ‘one billion heart-beats’ theory. Although not to be taken literally, it says, every organism has a life span of one billion heart beats. The rat with high heart beat rate of 420 per minutes has an

and door opening and at last the roof. One after another the apartments are made stacked on the sides and above. Eventually a skyscraper with hundreds of fl oors and thousands of apartments stands on the fi eld. Sounds plausible?

But that is what happens when the single fertilised cell grows in to a bubbly baby. Initially, at the time of conception, there is just a single fertilised cell in the human womb (or in the womb of any animal). Then the cell multiplies and proliferates. At some point of the embryo growth, the front and back are de-marketed in the blob of cells. The head develops in the front, and the legs come out from the back. The entire human child is shaped slowly like the magical brick replicating and producing a hundred-storey skyscraper.

In the course of the development multiplying cells have to differentiate. Some cells have to become bone cells, some tissue cells, some nerve cells and so on. Further, these differentiations have to be ordered. That is, a group of cells

Tortoise – long life span Mayfl y – Alive for just a few minutes

But that is what happens when the single fertilised cell grows into a bubbly baby.

16SCIENCE REPORTER, FEBRUARY 2015

approximate life span of about four years while a blue whale with just six times a minute lives around 80-90 years to have the ‘one billion heart beats’. Similarly, the horse with 38 bpm (beats per minute) lives around 60 years, whereas a rabbit with 205 bpm has a life span of about 9 years.

Animals can live fast or burn slow. As animals get bigger, from the tiny mice to the huge blue whale, their pulse rates slow down and life spans stretch out longer, conspiring so that the number of heartbeats during an average stay on Earth tends to be roughly the same, around a billion.

If heart beats are indicative of metabolic rate then it is easy to understand why faster the heart beat shorter the life span. Higher metabolic rate implies that the organism will wear-out faster. A mouse is living faster, faster heartbeats, faster burning of calories, so it lives a shorter life. Thus, the life span of organisms is perhaps predetermined by the basic energetics of the living cells. The observed inverse relation between life span and heart rate possibly indicates that the heart rate is a proxy for the metabolic rate.

Further, despite a difference of many millions in body weight, heart weight, stroke volume, and total blood pumped per lifetime, the total oxygen consumption and ATP usage per unit mass and lifetime are almost identical together with the total number of the heart beats per lifetime.

Thus, it appears that all living creatures have about the same amount of energetic life, with one particular exception. Humans and our evolutionary cousins primates are outliers in an otherwise almost neat graph. For the rate of heart beats that we have, we seem to be living longer than we should be.

Firstly, why at all there is an invariant is unclear; secondly if the relationship between heartbeats and life span is indeed real and not apparent, then why primates, and in particular humans, are different is an enigma.

Are Junk DNA Treasure or Trash?A typical human cell contains more than 6 feet of tightly packed DNA. But only about an inch of that carries the codes needed to make proteins. Is there any relevance for the remaining 71 inches of DNA in each and every cell of our body?

Way back in the 1970s, Nobel laureate Sydney Brenner fl ippantly called these non-coding parts as ‘junk DNA’ and the name stuck. Are these so-called junk DNA really just trash or an invaluble treasure? Earlier, some scientists thought that these vast terrain of dark DNA consisted of genetic parasites that copy segments of DNA and paste themselves repeatedly in the genome, like computer viruses. While others claimed that perhaps these are fossils of once useful genes that have now been switched off.

If noncoding DNA were mere historical appendages, then they should be rapidly undergoing mutation. As they are useless any arrangement in the junk part should not matter. However, surprisingly for millions of years they have remained basically the same. Hence, they should mean something.

Perhaps, junk DNA are protective buffers against genetic damage and harmful mutations. For example, at the time of chromosomal crossover event, the buffer of junk DNA may protect the functional DNA from being destroyed. Thus, the species may become more tolerant to the mechanism of genetic recombination. On the other hand, an experimental study on mouse shows that

COVER STORY

even artifi cially removing 1% of the junk did not result in any detectable phenotype changes. Thus, it is possible that junk DNA may indeed be trash.

However, a recent theory gives the so-called junk DNA a crucial role in cell assembly. It is claimed that while the genes create proteins, it is the junk DNA that assemble them. You may have machines and lathes that produce nuts, bolts and carious components, but only the assembly line puts them into a car.

How exactly the non-coding section of the genome plays a part is still an enigma.

Why are Humans Bipedal?We walk upright on our two legs. Perhaps when we were two- or three-month old babies we crawled, but then we learnt to stand upright, take baby steps and literally ran amok keeping our mother on her toes. Humans, along with our evolutionary cousins the great apes, are the only animals that have the ability to stand upright and walk on two legs – known as bipedalism.

Modern human beings evolved from hominids, which include the “great apes”, living and extinct. For millions of years, all the hominids were short, had tiny brains compared with modern humans, and could not speak or make a tool. But one thing distinguished them from the rest – bipedalism – the ability to stand upright and walk on two legs. This was a crucial transformation for our ancestors, which led to all that we today see as unique features of humans – large brain, opposable thumb and so on.

How did we become upright? One of the standard answers hitherto given was that as our ancestors moved out of the forest and onto the savannas, they had to look over tall grass or get to isolated stands of trees, bipedalism had an evolutionary advantage. The hypothesis

Heartbeat per Lifetime (Log Scale)

Hear

t Rat

e (b.

p.m

, Log

Sca

le)

Life Expectancy (Years)

Life

Exp

ecta

ncy (

Year

s, Lo

g Sc

ale) Animals can live fast or

burn slow. As animals get bigger, from the tiny mice to the huge blue whale, their pulse rates slow down and life spans stretch out longer.

17 SCIENCE REPORTER, FEBRUARY 2015

COVER STORY

looks interesting, even plausible. But it is just a speculation.

That the hominids, coming down cautiously from the safety of the tree, stood on two legs to wade their way through the tall grass of the savannas has a nice ring to it. But it is just a story. Fossil evidence shows that the hominids may not have lived in the savannas until 2 million to 2.5 million years ago, whereas the earliest fossil with bipedalism is at least 5-6 million years old. The earliest hominids are found not in savannas at all but a variety of lightly to densely wooded landscapes. Therefore, savanna grassland could not have triggered the bipedialism.

Adam may have fallen from grace for he plucked a forbidden fruit from the Garden of Eden, but in another tantalizing speculation emergence of bipedalism is linked to the task of plucking fruits from the overarching branches. The living apes, like chimpanzees have been observed in the wild to stand upright on the branches of trees to pluck fruits hanging overhead, or stand on the ground to pull down branches. Yet this too is a speculation needing robust evidence. We have known from the history of science that all that sounds good need not be sound.

We know a lot about the implication of the emergence of bipedalism – larger brain, lesser energy used to cool the body, thereby energy available for other functions, including growing brain and so on. Widely prevalent back pain and spondylitis are some of the negative impacts of bipedalism. How bipedalism evolved, what evolutionary pressures led the hominids to stand on two legs is still an open question in paleoanthropology.

Why do we Sleep?We all need a good sleep. We spend almost one third of our life in sleep; even a night’s sleep deprivation makes us sluggish, hungry, emotional and unable to concentrate. Sleeplessness makes us forgetful, slows the reactions and affects decision making and at times vision.

Studies have shown that lack of sleep can weaken the immune system making us susceptible to colds and other infections, and can even increase your blood pressure. So, sleep has a restorative function.

Most adults require about 7–8 hours of sleep to feel rested and refreshed upon waking. For infants, the requirement is much higher – about 16 hours a day, and teenagers need on an average about 9

hours of sleep. As people age, they tend to sleep more lightly and for shorter times, although often needing about the same amount of sleep as in early adulthood.

Not just humans but most species sleep. Giraffes require very little sleep; they enjoy only about 30 minutes a day of deep sleep split into several separate sessions. On the other hand, brown bats average close to 20 hours a day. We are not sure if the fi sh and amphibians actually sleep or just exhibit behaviours that suggest a resting state. Insects, on the other hand, do set aside time for slumber. However, it must be noted that there are signifi cant differences between the sleeping patterns of different types of animals. Although sleep or at least a physiological period of quiescence occurs

In the wild, a sleeping animal is like a sitting duck – an easy target for the prey. Evolution should have eliminated ‘sleep’ which is a hurdle in survival. Nevertheless, most animals sleep.

Most adults require about 7–8 hours of sleep to feel rested and refreshed upon waking. For infants, the requirement is much higher.Walking chimpanzees

18SCIENCE REPORTER, FEBRUARY 2015

COVER STORY

up of billions of stars. As the galaxies rotate, the stars at the edge should be rotating slower, like Neptune, as compared to the inner stars, like Mercury. While this Keplerian motion is what we expect, observations show that the stars at the edge of the galaxies are rotating faster than what they should be.

Unless we assume that laws of gravity are different in other galaxies, we are left with no option but to conclude that there is some kind of mysterious ‘dark matter’ engulfi ng the galaxies. Totally invisible to telescopes and the human eye, dark matter neither emits nor absorbs visible light (or any form of electromagnetic radiation).

The anomalies in the rotation of galaxies were fi rst discovered in 1933 by an astronomer Zwicky. He coined the term dunkle Materie, or dark matter to explain the anomaly. Through his studies on the motions of galactic clusters he realized that some additional unseen matter must be exerting a gravitational infl uence on them. Astronomer Vera Rubin in the late 1960s furthered the research and computed rotation curves of many galaxies and showed that the stars in the outer region do not follow Keplerian motion.

At that time, mainstream astronomers scoffed at the idea and Vera was shunned for many years. Ultimately, with improved instrumentation, when rotation curves of many more galaxies and galactic clusters were precisely measured, the anomalous rotation curve

in animals ranging from fruit fl ies to humans we do not know why we sleep.

We know what happens when we sleep. Sleep is the time when our bodies repair tissues and perform other maintenance activities. It is well established that it is during sleep time that the brain glycogen is replenished, which is consumed during the waking hours.

While it is the lymphatic system that fl ushes out the waste produced by cells from the rest of the body, the brain is disconnected from this system. The brain has its own cleaner, cerebrospinal fl uid, which collects the waste products and toxins from the brain fl ushing them down to the liver for excretion. During sleep it is found that the neurons in the brain shrink, permitting the cerebral fl uid to move faster. In a recent study done on mice it has been found that cerebral spinal fl uid fl ows around the brain 10 times faster when they are asleep. This fl ushes out toxins more effi ciently.

But then a signifi cant part of sleep time is given to REM sleep, when the brain is anything but idle. REM stands for rapid eye movement. During this time there is incessant rapid eye movement and the brain is hyper active. Usually vivid dreams occur during this time. Researchers say that it is at this time that the brain assesses all the inputs received during the day and selects those memories that have to be etched removing unnecessary details. On the other hand, it has been found that although anti-depressants suppress REM sleep, patients taking them suffer no memory impairment.

The restorative nature of sleep appears to be the result of the maintenance activities, such as cleaning toxins and

consolidating memories. But why sleep emerged in the fi rst place is still a mystery.

In the wild, a sleeping animal is like a sitting duck – an easy target for the prey. Evolution should have eliminated ‘sleep’ which is a hurdle in survival. Nevertheless, most animals sleep, which implies there must be some evolutionary advantages that outweigh this considerable disadvantage. Researchers point out that it is only those animals that can hide well, that have the luxury of deep slumber. Other organisms have to remain alert at all times. Therefore, some animals sleep with one part of the brain alert while the other half is in sleep mode. After some time the other part slips into sleep, while the fi rst part wakes up. This explains ‘how’ sleep is managed, but not when and why sleep evolved.

Dark Matter and Dark EnergyYou, this magazine, your table, the food in your house, the tree outside, the dog loitering in the street, the Sun, Stars, the billions and billions of galaxies, the interstellar gas clouds, the fundamental particles and atoms spread over the deep space – all account for a mere 4 percent of what is actually out there. The rest, astronomers for want of a better word, say is made up of mysterious dark matter (23%) and even more perplexing dark energy (73%). Atoms, particles and all that we know are just these 4%, the rest 96% of the universe is unknown!

In our solar system, planets orbit around the Sun according to Kepler’s law. Mercury which is closest to the Sun has an orbital velocity of about 48 kilometers a second, whereas Neptune which is far away has an orbital velocity of just 5 kilometers a second. Galaxies are made

13.7 Billion Years Ago(Universe 380,000 years old)

TodayOrdinary matter (Atoms)

4.6%

Dark matter 23%

Dark energy 72% Dark matter

63%

Neutrinos 10%

Photons 15%

Ordinary matter

(Atoms) 12%

Dark Matter & Dark Energy

While dark matter makes up an estimated 80% of all mass, dark energy is a hypothetical form of energy believed to make up around 70% of all content in the Universe.

19 SCIENCE REPORTER, FEBRUARY 2015

COVERCOVER STORY

became evident. Vera Rubin’s ideas are now accepted and an intense search has been mounted to discover the dark matter.

Many scientists believe dark matter is comprised of weakly interacting massive particles (WIMPs), which could be up to 100 times more massive than a proton, but don’t readily interact with the baryonic matter our instruments were designed to detect.

Of all the great mysteries of science today, dark energy might be the most enigmatic of all. While dark matter makes up an estimated 80% of all mass, dark energy is a hypothetical form of energy believed to make up around 70% of all content in the Universe.

About fi fteen years ago, astronomers held that the universe was expanding impelled by the Big-Bang. Since the big-bang for the past fourteen billion years, galaxies and clusters were moving apart; however, astronomers thought that it should be slowing down ever since dragged by the gravitational pull of untold billions of galaxies. The laws of physics should be keeping the galloping cosmos in check; while the universe was expanding by the initial impulse, the force of gravity should be slowing down the rate of expansion.

The neat picture was shattered when supernovae were observed at anomalous distances. In 1997, astronomers Schmidt and Riess observed a supernova that appeared to be further away than where it should have been. This implied that the

cosmos was lot bigger, and had expanded beyond what it should have. That means the gravitational pulling power of the universe was somehow being overwhelmed. Some energy was pushing the universe against gravity and making the expansion of the universe to speed up.

An independent team, led by Saul Perlmutter arrived at the same result. In 2011, Schmidt, Riess and Perlmutter shared the Nobel Prize in Physics for groundbreaking measurements revealing that the expansion of the universe was accelerating.

Cosmologist Michael Turner coined the name “dark energy” to designate the unknown force or fi eld that is pushing space apart, causing the expansion of the universe to speed up. Dark energy is one of the most intriguing mysteries in cosmology today.

Mysterious Solar Corona We are aware of the story of Birbal cooking khichadi, keeping the pot way high over the fi re. Obviously, the khichadi did not cook and perhaps Akbar could learn his lesson on conduction and convection of heat. But imagine, even when the pot was far above the fi re, if the khichadi had boiled nice and hot? That would really be perplexing, isn’t it?

The Sun’s core is really hot. Due to thermonuclear fusion taking place at the core, the temperatures are estimated to be about 15 million kelvin. As this energy slowly percolates above due to convection and convention, the surface of the Sun is heated up and shines at about 6000

kelvin. Beyond the surface enveloping the Sun is a very low density ‘atmosphere’, called solar corona. Inexplicably, the temperature of the corona is computed to be around a whopping one million kelvin! It is as if hot steam comes out of an ice cube. Puzzling, baffl ing and mystifying.

On a normal day, solar corona is not visible to the naked eye. The brilliance of the sun hides it from our view. However, during the totality of the total solar eclipse for a brief few moments, the visually enthralling solar corona can be seen. Way back in 1939, two astronomers Grotrian and Edlen studied the solar corona during a solar eclipse with a spectroscope. They found that the spectral lines of elements such as iron (Fe), calcium (Ca), and nickel (Ni) in the corona were in very high stages of ionization. This implied that the coronal temperatures should be around one million kelvin.

This was known since then as the coronal heating mystery. If Birbal’s khichadi had cooked, we would have wondered, how the energy from the fi re was transported to the pot far away. In like manner, we know that there is enough energy in the Sun to heat up the low density corona. However, the question is what is the energy transportation mechanism?

In earlier times, acoustic waves were considered as a serious contender to explain the solar coronal heating. However, studies in the past have eliminated that possibility. Today two dominant theories exist to explain this mystery. One attributes the heating to the loops of the magnetic fi eld, which stretch across the solar surface and can snap and release energy. Another ascribes the heating to waves emanating from below the solar surface, which carry magnetic energy and deposit it in the corona. Observations show both these processes continually occur on the Sun. Until now, scientists have been unable to determine whether either one of these mechanisms releases suffi cient energy to heat the corona to such high temperatures.

Recently, two scientists, Hahn and Savin, using the data from the Extreme

Some energy is pushing the universe against gravity and making the expansion of the universe to speed up.

20SCIENCE REPORTER, FEBRUARY 2015

Ultraviolet Imaging Spectrometer aboard the Japanese satellite Hinode have observed the polar coronal hole transporting energy to the corona. Although this is not the last word in the 70-year-old solar physics conundrum about the unexplained extreme temperature of the Sun’s corona, scientists believe it is a major step forward. The mystery is yet to be completely unravelled. Perhaps India’s forthcoming Adithya space mission may provide the much needed data on Sun to explain the mystery.

Goldbach ConjectureGoldbach conjecture is one of the tantalising unsolved problems of mathematics. The problem is simple. Take any even number greater than 4; the conjecture says it can be written as a sum of two primes. For example, 4 = 2 + 2; 6 = 3 + 3, 8 = 3 + 5, 10 = 3 + 7 = 5 + 5. That is, it can be written as a sum of two primes in two ways. And 100 = 3 + 97 = 11 + 89 = 17 + 83 = 29 + 71 = 41 + 59 = 47 + 53; hundred can be written in six ways.

The crucial point of the conjecture is, ‘ALL EVEN NUMBERS’ can be written as a sum of two primes. As even numbers are infi nite, we cannot check every one of them to conclude whether the conjecture is true or false. Thus in a nutshell, the verifi cation of a conjecture means proving mathematically the conjecture holds good for every even number, or fi nd a counter-example, an even number that cannot be written as sum of two primes.

The conjecture was originally proposed by Christian Goldbach, an amateur mathematician and an offi cial of the Russian Court in his letter to the mathematician Leonhard Euler on June 7, 1742. The letter stated that “at least it seems that every number that is greater than 2 is the sum of three primes”.

Initially when this letter was received, Euler thought that there was nothing interesting in this and treated it with some disdain. However, as days went by, the suggestion provoked curiosity and Euler wrote a reply on June 30, 1742 to Goldbach. In his reply Euler re-expressed an equivalent form of this conjecture, called the “strong” or “binary” Goldbach conjecture, which asserts that all positive even integers greater than or equal to 4 can be expressed as the sum of two primes. Note that at that time,

mathematicians considered the number 1 to be a prime, a convention that is no longer followed.

The conjecture looks simple and has also been computationally tested for very large numbers, yet proof eludes. Faber and Faber even announced a reward of 100000 US $ for anyone who could solve the conjecture between March 20, 2000 and March 20, 2002, but the prize went unclaimed and the conjecture remains open.

Trying to prove this conjecture, a Soviet mathematician, Schnirelmann during the 1930s proved that there is a number N such that every number from that point onwards can be written as the sum of two primes. Another Soviet mathematician Vinogradov proved that every odd number from some point onwards can be written as the sum of 3 primes. Chen Jingrun, a Chinese mathematician, in 1966 proved that every suffi ciently large even integer is the sum of a prime and an “almost prime” (a number with at most 2 prime factors).

Schnirelmann is credited to have physically computed and verifi ed the conjecture for numbers upto 300000. In modern times computers have been used to check the conjecture and Oliveira de Silva verifi ed the same for numbers upto 10 powers of 18 in 2012. No counter examples have been found, and the problem is still unsolved.

Which Freezes Faster – Hot or Cold Water? Mpemba was an unassuming but observant Tanzanian student. Mpemba was on his way to a cooking class; that day he and his friends had to make ice cream. Unfortunately the water with which Mpemba had to prepare the mixture was

warmer than his friend’s. As there was no option, both of them made the mixture and put them inside the refrigerator to freeze. After sometime, when they opened the refrigerator, to their utter surprise they found that Mpemba’s warmer mixture had turned into ice much faster than his friend’s.

Although Aristotle too mentions this puzzling phenomenon in his work, scientists were not willing to accept what seems to fl y in the face of known physics. Historians of science soon found that not just Aristotle, but Francis Bacon and René Descartes had too observed it. Impelled by claims, the experiment was conducted in laboratory conditions. Lo and behold, indeed warmer water froze faster!

Possible explanations have been proposed. One idea is that warm containers make better thermal contact with a refrigerator and so conduct heat more effi ciently; hence the faster freezing. Another is that warm water evaporates rapidly and since this is an endothermic process, it cools the water making it freeze more quickly. However, when computed, none of these explanations could be entirely convincing.

Recently, Xi Zhang and his colleagues from the Nanyang Technological University in Singapore have come up with a more interesting explanation. They claim that the Mpemba paradox is the result of the unique properties of the different bonds that hold water together.

Water is H2O – the two atoms of hydrogen and oxygen form a standard covalent bond. As the three atoms make an angle of about 104.5 degrees, the H-O-H appear like Mickey Mouse with two protruding ears. In fact, in this arrangement, the two ears of the Mickey Mouse, that is hydrogen atoms, and the

Cold Water

Warm Water

Short hydrogen bonds

Longhydrogen bonds

Long O-H covalent bonds

Short O-H covalent bonds

... After sometime, when they opened the refrigerator, to their utter surprise they found that Mpemba’s warmer mixture had turned into ice much faster than his friend’s.

COVERCOVER STORY

21 SCIENCE REPORTER, FEBRUARY 2015

chin that is oxygen atom, are respectively positively and negatively charged. As both the positively charged H atoms in the molecule are sticking out like two hands, they attach to another molecule’s negatively charged oxygen atom. This bond is weak and is called the hydrogen bond. It is due to this additional bonding that the boiling point of water is higher than the liquids of similar molecules.

Xi says that hydrogen bonds bring water molecules into close contact and when this happens the natural repulsion between the molecules causes the covalent O-H bonds to stretch and store energy. But as the liquid warms up, water molecules move further away and it is the hydrogen bond that stretches. As the molecules sit further apart in a warmer liquid, inter-molecular repulsion would be a little less than room temperature water. Therefore, unlike molecules at room temperature, the warm water molecule’s covalent bonds can shrink again and give up their energy. The important point is that this process in which the covalent bonds give up energy is equivalent to cooling.

Xi and his team have also computed that this effect would be additional to the conventional process of cooling. In fact they have also computed the magnitude of the additional cooling effect and show that it exactly accounts for the observed differences in experiments that measure the different cooling rates of hot and cold water.

Yet this theory is not accepted by physicists as complete. Physicists expect that they need to use this theory to predict a novel measurable property that would arise out of shortened covalent bond, which would otherwise be not present. Until then, for physicists, it is just a good hypothesis.

Perhaps Xi is correct; but we are not sure, as of now. Nevertheless, the Mpemba effect is a great example of how a seemingly simple phenomenon is actually harder to explain once you delve into it.

Leftist Universe?If you go deeper you will fi nd that all of us are left-handed. Yes, at least the bits that make up our amino acids and proteins are exclusively left-handed. But the sugars that make up the helical backbone of DNA and RNA are all right-handed. The dominance of left-handed molecules in the biological process is one of the big chemical conundrums in biology.

Handedness, or as it is technically called, “chirality,” occurs in certain molecules that come in two varieties that are mirror images of each other. Just like right- and left-handed gloves have the same number and kind of fi ngers yet their arrangements make them unique, chiral molecues have the same number and kind of atoms, but one is a mirror image of the other. Lactic acid (2-hydroxypropanoic acid) is a fairly common and simple example of a molecule having such a chirality.

Just as you cannot superimpose right hand on the left hand, even while both chiral molecules have the same molecular and structural formulae, one cannot be superimposed on the other. No matter how hard you try the molecule on the left will not turn into the molecule on the right. In biochemistry, chiral molecules are called L when “left-handed” and D when “right-handed” (these labels come from “levorotatory” and “dextrorotatory”). While the usual chemical isomers will have distinctly different chemical and physical properties, L and D type molecules will have the same chemical properties.

No one is certain why, but it turns out that all the amino acids produced in our body are L-type and sugars are D-type. This implies, all the larger molecules that are made from these L amino acids are also L-type. As sugars form the frame or the base of DNA, it is twisted in clockwise direction. That is, almost all the molecules in our body have the same “handedness” or chirality, so they are called “homochiral.”

However, the puzzle is, when we synthesise these molecules in the laboratory we always get a 50:50 mix of left- and right-handed molecules. On the other hand, when it is produced biologically, in say our bodies, often it is only one type, mostly L-type. While the lactic acid formed in the muscle is ‘L’ type left-handed, that found in sour milk

contains a mixture of both left and right. In like manner vitamin C tablets contain both the D and L type ascorbic acid. On the other hand our body produces and absorbs exclusively left-handed vitamin C.

Usually the right- and left-handed molecules have only a slight difference in impact. Right-handed ascorbic acid would be just washed away through the urine. In case of the molecule carvone, the right-handed version smells like caraway seeds, but the left-handed one has a peppermint odour. This hardly matters, but in the case of the drug thalidomide, the left-handed form helps relieve morning sickness, while the right-handed form induces birth defects. The drug industry has to strive hard to ensure only the left-handed drug is produced and dispensed as drug.

Why the biochemistry of life prefers one direction to another is a big question. Some postulate that if the body produced both handed molecules then it would need to have two types of enzymes to digest them. Some postulate, just accidental in the early stages of evolution, left-handed were a wee bit more and hence came to dominate over time.

What is even more surprising is that the universe itself appears to be lefty. When data of more than one lakh spiral galaxies were pooled and examined they seem to prefer to spin counter-clockwise as seen from Earth. In the subatomic world, interactions involving the weak force, the force of nature responsible for radioactivity, all electrons have a leftist spin and researchers found that every neutrino had a left-handed spin, while every anti-neutrino was right-handed.

Dr T.V. Venkateswaran is a scientist in Vigyan Prasar. Address: A-50, Institutional Area, Sector 62, NOIDA, Pin 201309 UP

When data of more than one lakh spiral galaxies were pooled and examined they seem to prefer to spin counter-clockwise as seen from Earth.

COVERCOVER STORY