Category Archives: Astro-Physics

100 years of General Relativity Part 5: Black Holes


This is the fifth part of the VERITAS series on General Relativity. Just to remind our readers: We are doing this series on Einstein’s Theory of Relativity to celebrate the 100th Anniversary of General Theory of Relativity. If you have missed any of the first four parts, you can read them here:

In the previous parts we discussed the fundamental idea behind General Relativity- The Equivalence Principle and its consequences. We used the equivalence principle to show that light is bent by gravity. And then we reasoned that gravity bends space-time and that objects moving along this distorted space-time seem to be moving under the influence of a force. We also saw that gravity slows down time. If you have not read the previous parts, I suggest you read them before reading this one.

Continue reading 100 years of General Relativity Part 5: Black Holes

Types of Black Holes


We have all heard or read about black holes in popular science books/articles. The general idea is that a black hole is a region from which nothing, not even light can escape. And many of us know that black holes are formed when large stars reach the end of their lives.

The physics of Black Holes is very complex and vast. To understand black holes we require the knowledge of Einstein’s General Relativity. In this VERITAS I will just tell you about the various kinds of black holes and how these black holes are formed. But before I mention the kinds of black holes it is important to realize that anything can become a black hole if it is compressed to a high density. Every object in the universe has what is known as Schwarzschild radius  and if you compress the mass of that object into a sphere of that radius you will get a black hole. For Earth the Schwarzschild radius is about 9mm( the size of a peanut). So if you want to make a black hole using Earth you will have to compress the whole mass of Earth into the size of a peanut! The Schwarzschild radius for the sun is about 3 Km.

There are three kinds of black holes:

  •  Stellar black holes: When most us talk about black holes, this is the kind we are referring to. These are formed when large stars collapse under the influence of gravity. The mass of these black holes ranges from 3 solar masses( ie 3 times the mass of our sun) to several tens of solar masses. To understand how these are formed we will have to first understand how a star is formed. A star starts its life with the gravitational collapse of a clould of interstellar gas consisting mostly of hydrogen. Compressional heating raises the core temperature to such a high level that thermonuclear reactions are ignited- hydrogen is fused to form helium and this process releases energy. Lots of it! The star reaches a steady state in which the energy lost to radiation is balanced by the energy produced by thermonuclear reactions. At this time our Sun is in a steady state. But after billions of years the star may run out of hydrogen to burn. And then gravitational collapse starts again. Smaller stars end up as white dwarfs or neutron stars. But if the original star was larger than about 3 times the mass of our sun, the gravitational collapse continues forever and what we get is a black hole. Nothing, not even light can escape its pull. How are such black holes detected? By their effect on nearby stars, gravitational lensing and Hawking radiation. These effects are very interesting but I cannot talk about them in this short article. There are many objects which scientists suspect are black holes. The nearest one to Earth is known as A0620-00 and is about 3000 light years away and has a mass of about 12 times that of our sun.
  • Supermassive black holes: A supermassive black hole, as the name suggests is huge! Much bigger than stellar black holes. The mass of a supermassive black hole ranges from millions to billions of solar masses. These black holes are typically found in the centres of galaxies. Scientists believe that our own galaxy, the milky way  also has a supermassive black hole in its center. These black holes are formed when the centre of a galaxy collapses under extreme gravity. However, this is not the only way: Sometimes gravitational collapse occurs when galaxies collide or merge and sometimes a galaxy forms around an preexisting supermassive black hole. The nearest supermassive blackhole to Earth is the one at the center of our galaxy. It is about 26000 light years away and has the mass of about 4 million suns!
  • Primordial Black Holes:  Primordial black holes are very different from stellar and supermassive black holes. Whereas stellar and supermassive black holes can form at any time due to the collapse of stars or centres of galaxies, primordial black holes could only have been formed during the early stages of the universe.  Immediately after the Big Bang the universe became a place with enormous temperature and pressure. Today we know( from the study of cosmic background radiation) that the universe at that time was very smooth but had some tiny fluctuations in the density- in other words, the matter density all over the universe was the same but there were some places where the density was different. Some of these places with density fluctuations may have undergone a gravitational collapse to create small black holes. The mass of these black holes could be as small as 10^-8 kg ( The mass of a flea’s egg)! Of course, they could also be bigger. No primordial black hole has yet been detected but some scientists think that primordial black holes may be the prime candidate for dark matter in our universe.

Now lets compare these three kind of black holes using the Hawking radiation coming out from them. In 1974 Stephen Hawking applied quantum mechanics to the study of black holes and found that they must radiate and the radiation is inversely proportional to their mass. Hawking also showed that black holes decrease in mass due to this radiation. For stellar and supermassive black holes the radiation is very small and does not cause much mass loss. In fact, for stellar and supermassive black holes the mass gain due to absorption of nearby matter completely overwhelms any mass loss to Hawking radiation. But even if the black hole did not absorb anything the rate of mass loss due to Hawking radiation for a stellar or supermassive black hole is very small over the age of the universe. But for a primordial black hole this is very different. Since the mass is very small the Hawking radiation is much more.

As a primordial black hole radiates, it decreases in mass and therefore radiates more. This results in runaway evaporation resulting in a massive explosion just before the black hole completely vanishes. Many small primordial black holes would have already exploded because of Hawking radiation. Scientists have calculated that primordial black holes of the mass of about 10^11 Kg( the mass of a mountain on earth) would be exploding now. So to detect primordial black holes, scientists are looking for explosions which are caused by Hawking radiation. These explosions would be coming from a very small area- the Schwarzschild radius for a black hole of this mass is less than a nanometer! If a primordial black hole is detected we will have very strong evidence of Big Bang, Einstein’s general relativity, the theory of how the universe evolved after Big Bang and also Hawking radiation.

The physics of black holes is very interesting.  Einstein’s General theory of Relativity can tell us how black holes are formed and some of their properties but there is a lot of stuff that we still do not know. And the biggest mystery is at the centre of a black hole- a place known as the singularity. At this place the known laws of physics completely break down. This is the place of infinite gravity and curvature. This is the place where both quantum mechanics and general relativity completely fail! But we absolutely do want to understand singularities! This is because the universe at the time of the Big Bang was a singularity. So to understand the beginning of our universe we must understand singularities.

But the most interesting thing( and also the most frustrating thing!) about a singularity is that it may never ever be observed. And this is because of something known as the Cosmic Censorship Hypothesis. Basically what it says is this: all singularities are covered by black holes. So there is no “naked” singularity. In other words: An observer can NEVER observe a singularity. What happens inside a black hole stays within the black hole!

So black holes and their singularities are the ultimate mysteries of Physics. Nothing else even comes close.



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Go wondrous creature, mount where science guides

go measure earth, weigh air, state the tides,

instruct the planets in what orbs to run

correct old time, regulate the sun

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Modern Version of Galileo’s Leaning Tower of Pisa Experiment


Galileo’s leaning tower of Pisa experiment is one of the most famous and important experiments in the history of science. In today’s VERITAS article we will examine the status of that experiment today.

The question that you may ask is: that experiment was done. Why do we need to examine its modern status? The answer is that in scientific method there is no final answer to anything. So experiments need to be repeated again and again. And new experiments should be an improvement over previous ones. For a history of the scientific method read my book: Pilgrims of Episteme: Story of the Scientific Method.

Before we start, lets recall Galileo’s experiment and understand its significance. Aristotle believed that if two objects, one heavier and the other lighter were dropped together, the heavier one will fall faster and therefore reach the ground first. The problem with Aristotle was that he was a great philosopher but he did not like to experiment. So he just imagined that the heavier object would fall faster and formulated his “theory” of gravity. The problem with the world was that they just followed what Aristotle said- and they believed that he had to be right- for nearly 2000 years! But Galileo was different. He wanted to test this and so in 1589 he went up to the top of leaning tower of Pisa and dropped a wooden and a lead ball. The balls landed at the same time much to the astonishment of Aristotelian teachers.  This experiment is extremely important because it formed the basis of Newton’s theory of gravity and also the equivalence principle which formed the basis of Einstein’s general relativity.

Now some historians doubt whether this experiment actually took place. But Galileo had done several other experiments and shown that gravity causes the same acceleration in all falling bodies. Galileo had also created a thought experiment to show that a heavier body and a lighter body will fall at the same rate. Here is how it goes: if we say that a heavier body falls faster than a lighter one then what would happen if the heavier and the lighter body are tied together using a string? Would the light body not slow down the fall of the heavier body? But this cannot be right because the combined weight of the two bodies is a sum of their individual weights. So it should fall at a speed greater than either of them. So this is a paradox because we get different answers depending on how we approach the problem and we have logical inconsistency.  The only way to solve the paradox is to reject the assumption that the heavier body would fall at a faster rate. Therefore all bodies fall at the same rate irrespective of their weights.

This is a nice thought experiment but the ultimate test of all science is experiment. In this VERITAS I want to tell you the status of this experiment today. When we say that all bodies fall at the same rate, this is a scientific theory. An experiment can NEVER say something like that. An experiment can only state the limits or accuracy to which this theory( or any other theory) has been verified.  So the aim of experimental scientists is to keep creating better experiments to test a theory to a greater limit or accuracy than previous experiments.

The modern version of Galileo’s experiment does not measure the rate of fall of two balls. It measures the rate of fall of Earth and Moon towards the sun! So the experiment is done on a massive scale. And this experiment has been going on for over three decades and will continue to give us new data for many years to come. The name of the experiment is Lunar Ranging Experiment. And this is how it was done: Apollo 11, 14 and 15 missions to the moon from 1969 to 1971 left hundreds of corner-cube retroreflectors  on the surface of the moon.  A corner cube retroreflector is a device that has the property that it reflects any incident light back in the direction from where it came, no matter what its incident angle was.

For more than 30 years laser pulses have been sent from earth to the moon. Each pulse lasts 200 pico seconds and such laser pulses are sent 10 times each second. These laser pulses strike the retroreflectors and return back to earth where they are detected. From this  we can calculate the distance between Earth and Moon to the precision of a few mm!

By observing the return times of the pulses, scientists have confirmed that the moon and Earth fall or accelerate towards the sun at the same rate – to the precision of 1.5 X 10 ^ -13.  If the rate of fall of the earth and moon was different, it would have shown in the results of this experiment as deviations in trajectory and therefore distance between Earth and the moon.

So we know that the theory that all masses accelerate equally under the influence of a gravitational field is true to the accuracy of the 13th place of decimal. This is one of the most accurate experiments done in the history of science. But we still keep doing more experiments and keep improving the accuracy of the Lunar Ranging experiment because even if we find that this principle is not valid to a place of decimal after the 13th, we will reject the theory, and consequently reject Einstein’s general relativity and look for a better theory of gravity.

In this article I had made reference to the equivalence principle which forms the basis of Einstein’s general relativity which is the currently accepted theory of gravity. Let me briefly describe this very interesting principle. Einstein noted that if a person falls in a gravitational field and only observes objects around him, he would think that he is weightless ie does not experience any gravitational field. To illustrate the principle, lets take a person and a few objects( say a cup, a ball and paper) and put them in a closed box. Now lets drop this box from a great height on Earth( or any planet). While the box is falling, the man, the objects inside the box and the box itself are all falling at the same rate( as shown by Galileo’s experiment and its modern version- the Lunar Ranging experiment). Since the man, the box, the ball, the paper and the cup are falling at the same rate, the man would not think that he or any other object is moving at all- the relative velocity of these objects with respect to each other is 0. Now lets place the same box( with the same objects) in outer space, far away from any gravitational field. Since there is no gravitational field, the man, the box and the other objects are at rest with respect to each other. So the man feels weightless. Einstein said that no experiment can distinguish between these two scenarios- the box freely falling on Earth and the box floating about in outer space are equivalent to each other for all objects inside the box. This principle is one of the central assumptions of Einstein’s general relativity- and we have see that this too is based on Galileo’s experiment and its modern version – the Lunar Ranging experiment.


============= ============ =================== ============== ========= =====

Go wondrous creature, mount where science guides

go measure earth, weigh air, state the tides,

instruct the planets in what orbs to run

correct old time, regulate the sun

====== ======= =========== ============================== =============

The Earth has a Trojan


                The world is a beautiful place full of remarkable things. But when I use the word “world”, I did not just mean the earth. We all know that the earth is beautiful, but remember that it is just a little speck of dust in an infinite universe. To give you an idea of the size of the universe, there are more than 10 stars for every grain of sand on earth( including every beach, every desert and anything else that you can think of). And our sun is just one of these stars.

                So we should not restrict our search for beauty to the earth alone. The power of science is that it lets you find laws which are not just applicable to our earth, but to the entire universe. Today I will tell you about a beautiful/interesting phenomenon, which probably occurs all over the universe. Today I will  tell you about Trojans. And the exciting breaking news is that The Earth also has a Trojan!

                When we imagine a planet, we image a massive sphere revolving at an enormous speed around a star- through the void of space.  That is how I imagined a planet to move. But a few years back I learnt that in certain cases this picture may become even more interesting. There can be another body in the same orbit, always a certain distance ahead or behind the planet. So a planet may not be alone in its orbit, there may be other bodies ahead or behind it, revolving in such a way that a collision never happens. Such objects are known as Trojans.

                Now let’s understand how this configuration can be stable.  The great French physicist and mathematician Joseph Louis Lagrange studied the three body problem( how three bodies move under the gravitational field of each other) and he found that there are 5 configurations of three bodies( one of them much smaller than the other two) which can be perfectly stable under each other’s gravity. In other words, if a planet is revolving around a star, there are 5 points at which a third much smaller body can be put so as to be gravitationally stable with respect to the other two larger bodies. These 5 points are known as Lagrangian points. Out of these 5 points, there are 3 points which lie on the orbit of the planet. A Trojan is a small body at any one of these three points.

                So, if earth is revolving around the sun, there are three points on the earth’s orbit on which a much smaller body can exist and remain stable. The first one is the simplest to understand. The object can be diametrically opposite the planet. So if earth is on one side of the sun, this point is on the opposite side, and the three bodies( The Trojan, the Sun and The earth) form a straight line. In terms of angles, we say that the Trojan is placed at 180 degrees with respect to the planet(earth).  This point has been the subject of many science fiction and mythological stories and is typically known as anti-earth.


                Now, lets look at the other two points at which Trojans can exist. One point is 60 degrees ahead of the planet and the other is 60 degrees behind. So the line connecting these Trojans to the sun would make an angle of 60 degrees with a line connecting the planet to the sun.  See the attached image from Wikipedia. The 5 lagrangian points are shown. The planet is shown in blue, the sun as yellow and the 5 Lagrangian points are numbered from 1 to 5. The Lagrangian point at 180 degrees is typically called L3. The points at 60 degree ahead and behind are known as L4 and L5 respectively. So a Trojan at L4 is always revolving the star in front of the planet. The Trojan at L5 is always behind the planet. But they never collide.

                Trojans are pretty common in our solar system. Jupiter, Neptune and Mars have many Trojans. The first discovery of Trojans happened in the case of Jupiter. Astronomers follow a very interesting  naming convention for naming Jupiter’s Trojans. I am sure you all know about the Trojan war- the Greeks fought the state of Troy sometime between 1260 and 1240 BC. This war involved Helen( of Troy) and the Trojan horse. I am sure many of you would have seen the movie “Troy”. Anyway, so if a Trojan is found at point L4 of Jupiter( 60 degree ahead of Jupiter) it is named after a character on the Greek side( example Achilles or Agamemnon). If a Trojan is found at L5 of Jupiter ( 60 degrees behind Jupiter) it is named after someone on the Trojan camp( like Paris or Laocoon). Two Trojans have been placed on the wrong side. One is Hektor which is named after the character on the Trojan camp but it orbits at L4. There are more than a million Trojans in L4 and L5 of Jupiter.

                Interestingly Saturn does not have a Trojan. However the moons of Saturn have a lot of Trojans. These are called the Trojan moons of Saturn. A Trojan moon and a “normal” moon share the same orbit around the planet. So a Trojan Moon is found at the lagrangian points of a “normal” moon in its orbit around the planet.

                Also, interestingly, there are no known L3( 180 degrees opposite) Trojans in our solar system.  The reason is that L3 is relatively unstable and a small nudge will displace the Trojan from its orbit permanently. When I said that objects at Lagrangian points are stable, I said stable with respect to the sun and the planet. However if there is another gravitational influence, apart from the planet and the star then L3 is the most unstable so no Trojans are found there.

                Typically Trojans are small objects, many less than a km across. The biggest Trojan in our solar system is Jupiter’s Trojan Hektor which is 370 Km across. So most Trojans are asteroids. However, theoretically it is possible for a small planet to be the Trojan of a much larger planet. These are called Trojan Planets. However no such planet has been found.

                And now for the breaking news, in 2010, astronomers found the first Earth Trojan. It has been named 2010 TK7( a rather uninteresting name). It orbits at Lagrangian point L4( so it is 60 degrees ahead of earth). It is a small body( about 300 m in diameter).

                Maybe there are more Trojans in the solar system. Maybe Earth has more Trojans at L4 or L5. Who knows. But what I do know is that the universe is a very interesting place and we still have a lot to learn.

                And before we close, a short poem by Sterling Bunch:

In starry skies, long years ago,

I found my Science. Heart aglow

I watched each night unfold a maze

Of mystic suns and worlds ablaze,

That spoke: “Know us and wiser grow.”


And with each season’s ebb and flow,

My soul with faltering steps and slow,

Still wanders up far-glimmering ways,

In starry skies.


Nor do I heed Life’s gaudy show,

But onward, upward I shall go,

Until new star-lands meet my gaze,

And where, perhaps in after days,

I’ll learn the things I long to know

In starry skies.






Go wondrous creature, mount where science guides

go measure earth, weigh air, state the tides,

instruct the planets in what orbs to run

correct old time, regulate the sun



Nemesis and Tyche – The myth and the hypothesis


                In Greek mythology, Nemesis and Tyche were two sisters and the daughters of Zeus or Oceanus. Nemesis was the goddess of divine retribution. So if you displayed hubris i.e considered yourself better than the gods, Nemesis would teach you a lesson. So Nemesis personified the revenge of fate against arrogance. Her sister Tyche was responsible for the fate of cities.  Tyche was responsible for the sudden outburst of a disease or an earthquake or a flood.

                But why am I telling you all this? But I do have the habit of telling people what they don’t want to know or don’t need to know. J Anyway, read on and I will tell you something more interesting.

                We all know that a massive extinction event wiped out the dinosaurs and gave rise to the mammalian domination of earth. Actually there was not just one extinction event in the history of earth. There have been several and scientists have found that extinction events are regular and periodic. Scientists estimate that there is an extinction event every 26 to 30 million years.

                Now, how do we explain these periodic extinction events?

                In a VERITAS posted in 2004( VERITAS: The Belt and the Cloud see, I had told you about the places where comets originate from. Short range comets ( with orbits less than 200 years) come from a place known as the Kuiper belt which is a belt of icy bodies just outside Neptune’s orbit. Long range comets( orbits sometimes in thousands of years) originate in a huge spherical cloud of bodies which lies about 1 light year from the sun. The Oort cloud surrounds the solar system. Isn’t it amazing that the Sun does not just hold planets till Neptune/Pluto. Sun’s gravity goes far beyond that. To give you an idea of the distance- Astronomical distances are measured in light years and in Astronomical units. A light year is the distance  covered by light in one year. Astronomical unit is the distance between Earth and Sun. It is written as AU. Light takes 8 minutes to travel from Sun to Earth. So 1 AU = 8 light minutes. Pluto is at a distance of 50 AU from the sun. That is about 6 light hours from the sun.  Now imagine this: The Oort cloud is 50,000 times the distance from Earth to the Sun. This is 50,000 Astronomical Units or AU. Yes, the solar system does not end with Neptune or Pluto- there are things in the solar system far beyond the 9 planets( 8 now!) that we studied in school.

                So the Oort cloud is a spherical ball of icy bodies with a radius of 1 light year with the sun at the center! Some people even estimate that the outer edge of the Oort cloud is about 100,000 AU to 200,000 AU. That is nearly 3 light years! So we have parts of the solar system nearly 3 light years away from the sun! And the interesting thing is that the nearest star to the Sun is Alpha Centauri and that is 4 light years away.

                The proposal to explain the periodic ( 26 million year) extinction cycle on Earth is that every 26 million years, something perturbs some objects in the Oort cloud and hurls them towards the earth at a HUGE speed. These objects, which may become  long range comets later change the seasons when they pass the earth and cause widespread extinction of the lifeforms that exist on earth at that time. Some may even hit the earth causing widespread damage. By the way, lots of comets have originated in the Oort cloud. Halley’s comet was once a Oort cloud object but now has an elliptical orbit with a period of 76 years.

                Okay, so to come back to the theory: once every 26 million years something disturbs a Oort cloud object hurling it towards the earth causing extinction events. But what? There are many hypothesis. In this VERITAS we will talk about two of them: Nemesis and Tyche.

                Scientists have postulated that there is a brown dwarf star just beyond the Oort cloud and revolves around the sun in a highly elliptical orbit. Its orbital period around the sun is 26 million years or so. When it comes near the Oort cloud, after every 26 million years, it disturbs the Oort cloud bodies and sends them hurling through space towards the sun. Some of these bodies hit the earth causing a huge amount of dust in the air, climate change and therefore mass extinctions. We know that dinosaur extinctions have been caused by such a body falling on the earth. The name of this hypothetical star is Nemesis. A brown dwarf star is a star that is not large enough to sustain nuclear fusion. So it does not shine. It is therefore practically invisible. If this is true than the Sun and Nemesis form a binary star pair- Binary stars are pretty common in the universe.

                Some other scientists found that all mass extinctions have been caused by objects that have come from the same point in the sky- and that point lies in the orbital plane of the planets. Let me explain. All planets and the sun lie on a single plane. So if I were to take a huge sheet of paper and pass it through the sun and mercury, that sheet of paper will pass through all the other planets also. There are no planets “above” or “below” the planetary orbital plane( Pluto was an exception but now it has been plutoed. See VERITAS: Pluto has been plutoed, 20 January 2010

                So if scientists find that the objects causing mass extinctions come from a point in the orbital plane of planets far away in the Oort cloud, what could that imply? Yes, scientists believe that there may be a planet revolving around the sun with an orbit so huge that it crosses the Oort cloud! And this planet dislodges objects in the Oort cloud and they hit the earth at high speeds causing mass extinctions every 26 million years or so. The name that scientists have given this hypothetical planet is Tyche.

                So Nemesis and Tyche are the names of hypothetical objects( one star and one planet) which explain the periodic mass extinctions on earth. Scientists are trying real hard to confirm or deny their existence. This may take several years.

                Our earth is a tiny spec of nothingness and our lives are even more tiny and insignificant. Yet, we go about our lives with the seriousness that is almost ridiculous and laughable! The only useful thing we can do in our lives is to use this short insignificant period of consciousness to admire the infinite beauty and mystery that surrounds us.

                Here is a nice little poem by Jane Draper:


 Stars have ways that I do not know,

   Enormity that checks my thought,

   Yet on the loom of their fine glow

   The fabric of my dreams is wrought.


   I look into the stars, and one

  After one, convictions die,

   While more than I have lost is spun

   Delicately across the sky.


    I look into the stars, and all

    The fuming purposes life gives

    Pass, like mists of evening fall,

    And all life never has been, lives.






Go wondrous creature, mount where science guides

go measure earth, weigh air, state the tides,

instruct the planets in what orbs to run

correct old time, regulate the sun



Strange Stars




        We have seen in earlier VERITAS articles that neutron stars are stars that consist only of neutrons of atoms. So the atoms are not there.

The electrons and protons that form normal atoms have been stripped off in neutron stars. So a neutron star is a pure huge collection of neutrons. A neutron star is VERY dense. A teaspoon of a neutron star can weigh a million tonnes!

        What is denser than a neutron star? A black hole! It is so massive that it does not even let light escape it.

  Till a few years back two stars designated RXJ185635-3754 and 3C58 were thought to be neutron stars. But a more detailed analysis using the laws of Physics showed that they were much more dense than what they would have been if they were neutron stars. But they are not black holes either. So their density is between a neutron star and a black hole!

      But what kind of matter can be so dense?? We know that neutrons, electrons and protons are made up of quarks. If a neutron star gets too dense then the individual neutrons break and the quarks come out and fuse together. This kind of matter- formed by a collection of quarks is called “strange matter” or “quark matter”. And a star formed from this type of matter is called a “strange star”. So a strange star is not composed of neutrons but is composed of quarks. There are three kinds of quarks that form strange stars: up quark, down quark and strange quark.

        So we have a weird new form of matter: composed of quarks only.

Note that all matter is ultimately composed of quarks. But normal matter consists of quarks bound together as electrons, protons and neutrons and these bound in a atomic structure and those further bound as molecules. Strange matter is just a sea of quarks connected to each other without any other detailed structure. Theories suggest that strange matter may be stable and thus exist under normal conditions. Our universe could be full of strange stars of various sizes or small groups of quarks bound together. A small group of quarks bound together is called a strangelet. A strangelet may be microscopically small. Our universe may be full of strangelets.

 When ordinary matter comes in contact with a strangelet, the massive gravitational pull of the strangelet pulls the quarks out of the ordinary matter. So the quarks of the ordinary matter fuse with the strangelet to increase its size. So ordinary matter is “eaten” by the strangelet.

       We know that a huge amount of mass in our Universe is unaccounted for. Theories of Physics predict a much larger mass of the universe than what we see around us. This unaccounted mass has been named “dark matter”.

Scientists are desperately searching for it. Some Physicists suggest that strange matter may be able to explain this unaccounted mass. Dark matter may just be strange matter!


                “Call it then, what thou wilt-

                 Call it bliss! Heart! Love! God!

                 I have no name to give it!

                 Feeling is all in all:

                 The Name is sound and smoke

                 Obscuring Heaven’s clear glow.” – Goethe ( Faust )








  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                 

  Instruct the planets in what orbs to run,                          

  Correct old time and regulate the Sun;                             


The Horizon Problem and Inflation

Friends, today we will talk about a problem that plagued the big bang theory of the universe for decades and the strange solution that physicists proposed to solve it.


        In an earlier VERITAS we had studied about the cosmic background radiation. This is the radiation left by the big bang itself. It is the cosmic radiation “smoke” that tells us that a loooong time back an explosion ( the big bang ) happened. So if you point sensitive equipment to any part of the sky you will “hear” a dim background noise. Its source is something 14 billion light years away from us. IF you calculate the temperature at which matter would radiate like this you would find that it is about 4 Kelvin( 4 degrees above absolute Zero). And remember that when you look farther into the Universe you are looking backwards in time. Since light takes 14 billion years to come from the cosmic background radiation spot to us that means that we are looking 14 billion years back in time!!!

        Look towards the east. You will find 4K cosmic bacground radiation 14 billion light years away. Look towards the west. You will find 4K cosmic background radiation 14 billion light years away. The cosmic background radiation(CBR)  looks exactly the same whether you look towards the east or towards the west. They seem to be in an thermal equilibrium with each other. How much is the distance between the two horizons? It is 28 billion light years! So the east and west horizon have not met for atleast 28 billion years. And what is the age of the Universe? 14 billion years! Isnt that weird?????!!!! If the CBR at the east and west horizon came from the same big bang then they have been separated by 28 billion light years. But our universe is only 14 billion years old. SInce nothing can travel faster than light this means that these two parts of the CBR have never interacted!!! We say that the CBR in the east lies outside the light horizon of the CBR in the west.

Similarly the CBR in the north lies outside the light horizon of the CBR in the south. Since all these parts of the CBRs have never interacted how come they are soo similar? How come they are at thermal equilibrium with each other? This is the Horizon problem.

Physicists hace come up with a very strange theory to explain this. They propose that within a minute of the big bang there was a HUGE expansion in the universe. We know that the universe is expanding at a particular rate.

But this expansion was not this normal expansion. It was A MUCH MUCH BIGGER expansion. It expanded much faster than light! It just blew up. It blew up by a factor of 10^50 ( 10 followed by 50

zeros) in a very very short time ( .000000000000000000000000000000000001  i.e 10^-32 second). So in a small fraction of a second the Universe just blew up in a huge way! This would not violate Special Relativity which says that nothing can move faster than light because space and time themselves were expanding. If inflation happened then the east and west CBRs are within the light horizon of each other. So they have interacted in the past( within the lifetime of the Universe) to reach the same temperature.

        But if inflation is true then there is a stranger consequence: the observable universe ( the 28 billion light year diameter) is a very small portion of the complete universe. There is a huge amount of stuff outside this. It is outside our light horizon so we will never  be able to interact with it!

      Not all Physicists believe in the inflation theory. SOme think that maybe the speed of light was much greater just after big bang than it is now and that would explain how these CBRs interacted within the lifetime of the universe.

      But how do we verify these theories? We cannot experiment with the universe! Are we to just philosophise fruitlessly?


        Friends, we exist for such a short time. And there is so much to learn. Would our lives finish without this thirst for knowledge quenched? And how does one quench this thirst for knowledge when we know how limited our tiny brains are???!!! I sometimes wish that there were a God. Then at least I would be able to ask him about the Universe. The human endeavour to search for truth, our Science, is too painful. How little we achieve through Science in our tiny lives!!!!!! If only we could ask God the questions. Without God life seems to be so useless and incomplete- a drop of water that will never reach the ocean.


      Why cannot I be the one who sits in front of Krishna and Krishna says as he said to Arjuna: “I shall now declare unto you in full this knowledge, both phenomenal and numinous. This being known, nothing further shall remain for you to know.”


Why should I struggle endlessly with false knowledge, false books and a limited time on earth:



        Study is like the heaven’s glorious sun

        That will not be deep-search’d with saucy looks:

        Small have continual plodders ever won

        Save base authority from other’s books

        These earthly godfathers of heaven’s lights

        That give a name to every fixed star

        Have no more profit of their shining lights

        Than those that walk and wot not what they are.

        Too much to know is to know nought but fame;

        And every godfather can give a name.








  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                 

  Instruct the planets in what orbs to run,                          

  Correct old time and regulate the Sun;                             


In what orbs to run



        In yesterday’s math forum meeting some interesting questions regarding orbits of planets were raised. Since these would interest everyone in the VERITAS group I thought I should post the answers as a VERITAS article:

1) How do we know that earth orbits the sun and not the other way?

   This is actually a very valid question. We take it for granted that earth orbits the sun. But why? The Sun is not God! Why should earth orbit the Sun? When we look at the Earth-Sun system we realize that these are 2 bodies moving under the gravity of each other. Sun pulls Earth. Earth pulls Sun. SUch a system is called a two body system. In a two body system the bodies move around their centre of mass. So earth does not orbit the Sun. And the Sun does not orbit the earth. They both orbit their common centre of mass. But the sun is SOOOOOOOOOO massive compared to the earth. The centre of mass of the earth-sun system lies within the body of the Sun. See that! So the earth orbits the Centre of mass which is within Sun. It cannot be the other way round. No need to even observe. All this can be shown mathematically. The solution of the two body problem is well known and is textbook material.

   I would also like to mention that the three body problem is still unsolved in Physics. Physicists dont have an equation to describe how three bodies move under mutual attraction!!!! They have to do this approximately and numerically! Physicists talk about the universe but they cannot solve a 3-body problem. What to talk of the 10 body solar system!


      Remember Einstein’s words:

“Whoever undertakes to set himself up as judge in the field of truth and knowledge is shipwrecked by the laughter of the Gods.”


2) Why are the orbits of Planets elliptical and not round?

    I have struggled with this question a lot in my younger days.

It made me feel so miserable. Only after reading Herbert Goldstein’s “Classical Mechanics” did I felt better.

      Why do we have a desire for round orbits? Lets first look deeper at this question? This desire comes from our stupid educational system that gives us analogies to help our learning but does not warn us when we go too far with these analogies. In our school days we were told that earth orbits sun much like a stone tied to a thread can be rotated in a circular motion! And electrons also orbit the nucleus the same way! Nice for learning but these kind of analogies hamper any deeper reflections on these subjects.

   Lets understand the stone tied to a string rotation in detail. A stone tied to a string is rotated. It moves in a circular fashion. The stone’s “desire to move outward”(centrifugal force) is exactly balanced by the pull of the thread. Now rotate the stone faster. The stone’s velocity increases. Its centrifugal force increases. But it is exactly balanced by the increased tension in the string. Now increase the velocity further. More tension! …. it keeps going round and round till the string breaks and the stone goes far away!


   Now lets look at the earth sun example. first thing: there is no string. So there is no balance! It is something like this: The earth moves towards the sun… in this motion it gains a lot of velocity( think of it like falling toward the sun). When it comes near the sun the velocity is so huge that it whizzes past the sun. Now it is moving away from the sun.

In this motion it keeps getting slower( its direction is opposite to sun’s pull). It reaches a point where its “desire to move away” is exactly balanced by the sun’s attraction. Its velocity in a direction away from the sun becomes zero. And it falls again.

 Here are the major differences between the earth-sun orbit and the stone -string analogy:

a) In the earth sun system the balance between centrifugal force and pull happens only at the end points. In a stone with string thing every point is balanced.

b)If the velocity of the earth is increased it will make a bigger orbit around the sun. But if the velocity of the stone tied to a string is increased the orbit stays circular. This is because the thread can take more tension. And you have not let the stone move to a larger orbital.

You have taken a unstretcheble string. You have not allowed the stone to move away!

c)The pull of sun on earth decreases as earth moves away. The pull of the thread on the stone always adjusts to exactly match the pull of the stone.

So the analogy on which we base our desire to give a circular orbit to earth is not a valid one. A better analogy would be to imagine a stone tied to a flexible elastic. The elastic allows the stone to move away.

However even this analogy is not perfect.

    There is a point around the sun where if earth is placed with a particular velocity a perfect balance between opposing forces will be achieved. And a circular motion will follow! But the natural motion of planets around a star is not circular. It can be elliptical(least velocity of planet), parabolic( more velocity) or hyperbolic( highest velocity! The planet will not come back!)


            And, if each system in gradation roll

            Alike essential to th’ amazing whole,

            The least confusion but in one, not all

            That system only, but the whole must fall.

            Let earth unbalanc’d from her orbit fly,

            Planets and suns run lawless through the sky;

            Let ruling angels from their spheres be hurl’d,

            Being on being wreck’d, and world on world;

            Heav’n’s whole foundations to their centre nod,

            And nature trembles to the throne of God.


                              ( Alexander Pope)








  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                 

  Instruct the planets in what orbs to run,                          

  Correct old time and regulate the Sun;                             


The Mysterious Flashes


      In the late 1960s the US military satellites started looking for gamma radiation suspecting secret Soviet nuclear tests. But instead of finding gamma radiation from Russia they found flashes of gamma radiation from outer space. These flashes were very intense and lasted a very short duration. Scientists named these flashes Gamma Ray Bursts.

      At first scientists thought that Gamma Ray Bursts(GRBs) orignate from our own galaxy( Milky Way). But when more GRBs were detected they seemed to come from all possible directions. So the theory that they orignate from the Milky way was rejected. They come from all possible directions in the Universe.


      The radiation from GRBs is VERY VERY intense. It can be hundreds of times the light produced from a typical supernova( blast at the end of a star’s existance). A typical GRB can be a million trillion times brighter than the Sun. This makes a GRB the brightest source of gamma ray photons as long as it lasts.

      GRBs are very common. Since 1991 more than 2500 GRBs have been detected.

      In 1997 scientists got some data about the location of a GRB. But they were shocked to discover that the particular GRB was more than 12 billion light years away!!! So it had occurred 12 billion years back and light has reached us now. That means that whatever event caused that GRB occurred when our earth was just born.

      If a GRB occurs in our Galaxy it would most likely kill us by the intense radiation. It will turn night into a day of intense and blinding light!

      GRBs are classified into two types: short duration( lasting less than 2 seconds) and long duration( lasting more than 2 seconds). The radiation of these two is very different and scientists suspect that they may be caused by different kinds of events.

      One theory is that long duration GRBs are caused by hypernovae: the huge explosion caused when a special type of star( Wolf-Raylet) star dies. A Wolf-Raylet star is a very heavy, very hot star that sometimes produces fits of material ejection. When such a star collapses the collapsing core sends a blast wave through the star at speeds close to the speed of light. This blast wave hits material inside the star and produces huge amount of light and gamma rays. These come to us as Gamma Ray Bursts. A hypernova explosion can be hundreds of times more violent then a supernova.

      Another theory that tries to explain short duration GRBs proposes that such GRBs are produced when neutron stars collide and annihilate each other. Neutron stars and very dense stars that have atoms stripped of everything except their nucleus.

      But no one knows for sure. What I can say for sure is that the earth may be a violent place but the violence on earth is NOTHING compared to the violence in the Universe. And when we look at the Universe we realize our smallness and the trivilality of our concerns.


      “When men are calling names

       and making faces

       And all the world is ajangle and ajar

       I meditate on inter-stellar space

       And smoke a mild cigar”

                        -Bert Taylor






  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                  

  Instruct the planets in what orbs to run,                          

  Correct old time and regulate the Sun;                             



The Belt and the Cloud


      Most of us think that the Solar system ends at Pluto. In fact most astronomers thought that this was the case. But then somebody asked the question: where from do the comets come from??? We will try to answer this question in this VERITAS and we will learn about worlds beyond Pluto.

      In 1950 a Dutch astronomer Jan Oort suggested that comets come from a vast reservoir of icy bodies at the distance of 50,000 AU( AU means Astronomical Unit. 1 AU is the distance from Earth to the Sun). About a year later Gerard Kuiper suggested that 50,000 AU is too far away for comets and that comets are placed just beyond the orbit of Neptune ( Neptune is placed at about 30 AU).

      Today we know that both these theories are true. There is a belt of icy bodies just beyond the orbit of Neptune. We call it the Kuiper belt. We know of atleast 70,000 objects in this belt each with a diameter of atleast 100 kilometres. Astronomers are sure that there are more.

And there are zillions of more objects with diametres between 10 and 50 Kms in this belt. The Kuiper belt extends from 30 to 50 AU. Many astronomers  are of the opinion that Pluto should not be called a planet but a Kuiper Belt Object(KBO). This is because of its small size and its funny rotation ( it does not rotate on a North-South axis but on a East-west axis i.e it rotates on its side).

        Most of the short period comets come from the Kuiper belt.

Helley’s comet is a short period comet( just 76 years) and it comes from the Kuiper belt.

The long period comets come from the OOrt Cloud. There are comets humans have seen just once. These comets might have the priod of thousands of years. When Jan OOrt observed these long period comets he realized that thay come from somewhere very far away. He also noticed another strange things: these comets come from any direction in space. These facts made him hyphothesize that these comets come from a spherical cloud about 50,000 Au from us. Note that all the planets and the Kuiper belt lie on one plane and this is the plane in which the equator of the Sun is at the centre. This is because the Sun’s gravity is strongest here. But at the distance of 50,000 AU the sun is just a small spec of light and thus the oort cloud is not located in a plane. It is spherical.

So we are surrounded by a spherical cloud of small icy worlds.

They are held in that spherical cloud by the gravity of Sun.

See how far Sun’s Gravity can be felt. The diameter of the Oort cloud is about 2 light years!!!! The sun’s gravity has trapped things even to a distance of 1 light year!!!!!!!!

      But wait a minute! How far is the nearest star? It is just 4 light years away. This OOrt cloud is affected by that star too. So every once in a while this star(Alpha centauri) perturbs an object of the OOrt cloud. Remember that the OOrt Cloud objects are very loosely bound to Sun’s gravity. So a small push by a passing star is enough to move them. When perturbed this object falls “down”.But where? It falls towards the sun. It is this object that comes hurling towards the sun that we call a comet. What a traveller. What a sight from Earth.   

      Short period comets are formed when a Kuiper Belt object is perturbed by one of the outer large planets.

      OOrt cloud and Kuiper belt are remains of the formation of the solar system. The giant planets Jupiter, Saturn, uranus and Neptune created a lot of left overs when they were being formed. Some of this debry was set into orbit and formed the Kuiper Belt. The rest of the debry way kicked out of the solar system. It however could not escape the gravity of sun altogether and went to form the OOrt Cloud.

      See the attached illustration of the Kuiper belt and the OOrt cloud. See how little the Sun is. And what a small portion of this entire thing is the solar system till pluto. Also see the spherical OOrt cloud surrounding the sun and planets.


      Friends, The earth is a small place in this grand scheme of things. It is no doubt our home but lets not restrict our thinking to just our little home. Lets explore beyond the farthest reaches of space and time. The human brain constantlyt searches for infinity.

Lets not deny it its pleasure:


            THE BRAIN is wider than the sky,

              For, put them side by side,

            The one the other will include

              With ease, and you beside.


            The brain is deeper than the sea,       

              For, hold them, blue to blue,

            The one the other will absorb,

              As sponges, buckets do.


            The brain is just the weight of God,

              For, lift them, pound for pound,       

            And they will differ, if they do,

              As syllable from sound.


                              ( – Emily Dickenson)







  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                 

  Instruct the planets in what orbs to run,                          

  Correct old time and regulate the Sun;