Dark Mysteries of Our Mysterious Universe

In response to tahmed, I want to mention that I had described quantum loop gravity in my earlier papers, e.g. , Three Hard Questions and Quest for Their Solutions, and Quandary in Quantum Mechanics which were published on Chowk. I am giving an extract from Three Hard Questions... in the following for reference.

I (Lee Smolin) personally have little doubt that in the end loop quantum gravity and string theory will be seen as two parts of a single theory. Whether it will take a Newton to find this theory, or whether it is something we mortals can do, is something that only time will tell”, (Three Roads to Quantum Gravity, 2001, p. 193).

In spite of these recent advances, it is not yet clear when the efforts of unifying all the forces completely will bear fruit. I will close this paper with a perceptive quote from Phil Gibbs: “According to conventional wisdom among physicists, the process of unification will continue until all physics is unified into one neat and tidy theory. There is no a priori reason to be so sure of this. It is quite possible that physicists will always be discovering new forces, or finding new layers of structure in particles, without ever arriving at a final theory. It is quite simply the nature of laws of physics as we currently know them that inspires the belief that we are getting closer to the end”, (http://adela.mff.cuni.cz/~motl/Gibbs/qugrav.htm).

What has a better chance of unifying all the forces, I would like to leave it for the specialists in this field.

Regarding Naqshbandi`s comments, I had a Pakistani friend in Nigeria who had two M.Sc`s in agricultural science; one from the Agricultural University of Lyallpur and another from the US. He believed that the spacewalk by the astronauts and space exploration per se were American hoaxes and the USSR was part and parcel of the American conspiracy (Why? He did not explain). The pictures of the space-walk were simply studio pictures, he had claimed. I didn`t argue with him. What`s the point?

Mohammad Gill

Its only conjecture folks. They just make up things! subhan Allah! Is there doubt? Is there doubt in Allah?! Real knowledge is knowledge of the Real, that is knowledge of Allah! This is their great civilisation. Syphillisation!

firaq/freethinker/macgupta: actually, any discussion on the frontiers of physics that discusses string theory must also discuss the theory of quantum loop gravity. it is at least as fascinating as string theory: both are the same insofar as they take as a starting point the ground covered by theory of relativity vs. quantum mechanics. but quantum loop gravity focuses on the ``fabric`` of space itself, and comes up with remarkable parallels with string theory: quantum loop considers space and time to be themselves made up of discrete units (rather than being continuous) - with the smallest unit of space (the space equivalent of an atom) being calculated at 10 to the power -99 centimeters. This is incredibly tiny: in a SINGLE cubic centimter of space there are more of these ``space atoms`` then the total number of cubic centimeters in the known universe!! In string theory, strings are equally tiny - if an atom was the size of the solar system, a string would be the size of a tree.

They even have plans to test this theory as they have for string theory (which we discussed earlier): the US has a satellite due for launch in 2006 that is geared to test a key implication of the quantum loop gravity theory (that gamma rays emitted by objects on the edges of the known horizon would have travelled to earth at varying speeds depending on their energy content).

Perhaps the known universe is thus indeed a mere projection of knowledge from outside our four dimensions (as the hologram theory states): and everything we perceive is no more real than the flickering images on a computer screen - with the pixels being replaced by tiny strings, tiny units of space, and tiny units of time. And all this is fairly firm ground on the frontiers of science!!

=== Interact Filtered ===
view this users filtered interacts

To round off the discussion, I thought it might be appropriate to give thumbnail biographical profiles of some of the earlier epoch making cosmologists. Most of the readers are familiar with Einstein, so I’ll skip him after mentioning that he was the founder of the modern theoretical physics of cosmology. I’ll discuss only a few of these pioneers. Let me first begin with Friedmann.

Alexander Alexanderovich Friedmann was born in St. Petersburg (later Leningrad) on June 17, 1888. His father with the same name was a ballet dancer and composer. After his master’s degree, Friedmann became interested in Meteorology

At the outbreak of the First World War, Friedmann entered the army and was on the Austrian front. In 1915, he wrote in a letter with a touch of stoicism, “My life is fairly quiet apart from such happenings as a shrapnel exploding at a distance of half a step, when I got off nearly scot-free, and a fall on my face and head resulting in nicking my upper lip and suffering some headaches.”

After the war, he worked at Kiev’s Central Aeronautical Station. After the end of the civil war, he went back to St. Petersburg and worked on hydrodynamics and other theoretical areas of mathematics at the Main Geophysical Observatory.

In the summer of 1925, he went on a daring balloon flight to study the upper atmosphere, reaching the Soviet record altitude of 7400 m. Two months later he died of probably typhus of the stomach. He was then only 37 years old.

According to Kragh (Helge Kragh, Cosmology and Controversy, Princeton University Press, Princeton, 1996), “In his paper of 1933 Friedmann offered a complete analysis of the solutions of Einstein’s cosmological field equations that wen beyond the earlier solutions of Einstein and de Sitter as it also included non-static solutions.” According to the prevailing wisdom, the universe was considered closed and static, i.e., neither contracting nor expanding. This belief was so strong that even Einstein fixed his solution somewhat arbitrarily using the cosmological constant. Faith in the static universe was as strong as faith in the centrality and immobility of the earth, after Aristotle. Friedmann was certainly not a Galileo but he did draw the attention to the possibility of expanding universe.

Willem de Sitter was another cosmologist whose work was prominently noted in the 1920’s. He was a Dutch astronomer who was also well versed in mathematics. He was a professor of astronomy at the University of Leiden.

According to Kragh, “In his (de Sitter’s) third report to the Royal Astronomical Society (de Sitter was a foreign member) of 1917, he drew attention to what subsequently became known de Sitter solution….De Sitter’s model was an empty universe (zero density)…., spatially closed in spite of its lack of matter…De Sitter showed that his universe had a peculiar property; if a particle was introduced at a distance r from the origin of a system of coordinates, it would appear moving away from the observer.”

His was the second general relativistic model of the universe; the first one being Einstein’s.

Another cosmologist who dominated the last two decades of the first half of the twentieth century was Lemaitre. Georges Edouard Lemaitre was a Belgian catholic priest and a cosmologist. He did not let his science get affected by his religion. He was born in 1894 in Charleroi. He had studied astrophysics at MIT and had the opportunity of working with Eddington at Cambridge, England.

In 1933, Einstein and Lemaitre went to California on a series of seminars. In one of the seminars, Lemaitre introduced Einstein’s theory. His introduction was so good that Einstein said, “This is the beautiful and satisfactory explanation of creation to which I have ever listened.”

According to Kragh, “Lemaitre’s cosmology rested on the assumption of a non-vanishing cosmological constant. Like his former teacher, Eddington, but for different reasons, he strongly believed in the necessity of this assumption,….. Far from being a blunder or a superfluous constant, he believed that it was a natural, indeed an indispensable, part of relativistic cosmology.”

Of course then there was Eddington. Arthur Eddington’s parents were Quaker. He was born in 1882. He had a stellar educational career right from the beginning. He won numerous awards in his life.

In 1914, Eddington was appointed director of the Cambridge Observatory and thus had effectively taken over the responsibility for both experimental and theoretical astronomy at Cambridge.

In 1919, he led the eclipse expedition to Principe Island in West Africa. His measurements verified Einstein’s theoretical predictions of bending of light rays in the vicinity of the Sun. He wrote a rubaiyii in the spirit of Omar Khayyam describing this principle, which is as follows:

Oh leave the wise our measures to collate
One thing at least is certain, light has weight
One thing is certain and the rest debate
Light rays, when near the Sun, do not go straight

His obituary in The Times summed up his achievements as follows: He was a gifted astronomer whose original theories and powers of mathematical analysis took his science a long way forward; he was a brilliant expositor of physics and of astronomy, able to communicate the most difficult conceptions in the simplest and most fascinating language (He did not believe in the ‘singularity explosion’ inception of the universe and said sneeringly “.. I do not believe that the universe began with a bang.” This inspired the nomenclature of big bang, {Gill’s comment}); and he was able interpreter to philosophers of the significance of the latest scientific theories.”

He was so self-assured that he could dismiss other scientists’ hard-worked theories if they did not conform with his ideas, instantaneously without giving a second thoughts. Chandrasekhar who was his student planned to present his paper on black holes in one of the conferences which was presided by Eddington. Chandrasekhar had shown his paper to his teacher before the presentation. Eddington thought Chandrasekhar`’ formulation of black holes was preposterous. He shredded Chandrasekhar’s theory in his introduction without giving his student a chance to make his presentation. Nonetheless, Chandrasekhar presented his work which proved monumental in due time and won him the Nobel Prize.

And lastly, George (or Georgii) Antonovich Gamow. Gamow was a nuclear physicist who brought quantum mechanics and cosmology within the same fold. He is accredited with the formulation of the big bang theory although numerous other scientists had also worked in the development of the concept. The big bang theory did not abruptly emerge on the world horizon, it evolved gradually. Without going into too much detail, let me reproduce from Kragh:

Gamow was the Russian-born nuclear physicist whose theory of alpha decay had served as the foundation for the first application of quantum mechanics to stellar element synthesis. Gamow was born in Odessa in southern Ukraine on 4 March 1904. As a young boy he came to question the truth of the Christian dogmas he was taught in school. Could the wine and bread served during Communion really turn into the blood and flesh of Jesus Christ? George decided to check the dogma scientifically, and examined the supposedly transubstantiated wine and bread under his small microscope. He could find no sign of transubstantiation. “I think this was the experiment which made me a scientist,” he recalled.

And an excellent and superb scientist he became in his life.

He was a student of Friedmann.

I have to draw a line now. This feedback has already exceeded reasonable space limits. I should sign off now. It is 10-00 p.m. now; the new year is only two hours away. Readers, I wish all of you a happy new year.

Mohammad Gill

One more difference between the balloon and the grenade : In the grenade explosion, there is a center of explosion, and an observer at rest at this center is the one who sees shrapnel receding from him uniformly in all directions, with the faster particles further away and so on. An observer riding on one of the particles does not see this uniformity in all directions.

In the inflation of the surface of the balloon, an observer at any point of the balloon sees the same kind of expansion in all directions.

Since it is very unlikely that we are in a privileged observation spot in the universe, the balloon analogy is closer to the isotropy (same in all directions) and homogeneity (same at all locations) of the universe that is theoretically preferred and that is so far broadly supported by observations.

Re:22 by freethinker

Indeed, I was talking about the vacuum energy, which gives the cosmological constant by the formula you gave, i.e. Vacuum energy = Lambda/(8 Pi G).

The number I was giving around (10^19 GeV)^4 was what one should theoretically expect, from our current understanding of quantum field theory and gravity. This is because in any quantum field theory (for e.g. the weak interactions), the vacuum energy is of the order of the scale of the interactions raised to the 4th power. By scale, I mean the energy scale above which we believe there will be some new physics (for e.g. new particles etc) which we can ignore, as long as we consider processes below that scale. For the weak interactions, this is about (200 GeV) so the vacuum energy for weak interactions should be (200 GeV)^4 which is approximately 10^47 erg/cm^3. This is the theoretical prediction for the vacuum energy from weak interactions. In a theory of gravity, the plank scale is the relevant scale, which is around (10^18) or (10^19) Gev. So the vacuum energy coming from gravitational interactions should be about (10^18 GeV)^4 which is around 10^110 erg/cm^3. This is again a theoretical prediction. The experimentally observed value is, (10^(-12) GeV)^4 which is around 10^(-10) erg/cm^3. This is about 10^(120) orders of magnitude smaller than the theoretically predicted value. So clearly, there is something very fundamental which we are missing in the theory. This is the cosmological constant problem...which is to explain, theoretically, why the observed value of the cosmological constant (or vacuum energy) is so small. Supersymmetry makes the problem slightly better. We expect, (for other reasons which I dont want to go into right now), that the scale of supersymmetry breaking is of the order of 1TeV. That would lead to a prediction for the cosmological constant, which is still about 10^58 orders of magnitude more than the observed value.

This discrepancy, between the theoretically predicted value and the experimentally observed value for the cosmological constant is perhaps the most important problem currently in theoretical physics. A solution to this problem is expected to profoundly change our understading of fundamental physics.

Re: # 19 ...tahamed32

It is indeed true that string theory predicts the existence of extra dimensions (a total of 1 time and 9 space dimensions in string theory, or 1 time and 10 space dimensions in M-theory, which is the theory which contains all string theories in special limits). This, however, does not make the theory untestable. The basic idea is that all these extra space dimensions (6 or 7 in string or M-theory) are curled up into a very small ball. An analogy (which you might already be familiar with) will help here...consider a garden hose. This is a tube with a two dimensional surface. An ant crawling on the surface can move in two dimensions...along the length of the tube, in addition to moving along the circular direction. So the ant perceives two spatial dimensions (and of course, one time). Now consider a huge creature, of size much bigger than the radius of the hose. To this creature, the hose will appear as a one dimensional object, i.e. it can only perceive the dimension along the tube but not the circular direction. The fact that this creature cannot perceive the circular direction does not mean that it does not exist. In fact, if this creature has a powerful enough microscope, it will conclude that space indeed has an extra dimension, its just that it is too small for it to easily see. This is exactly what string theorist believe our reality is like. And by doing experiments (in particle accelerators which are the analogues of microscopes), in principle it is possible to perceive these extra directions. Right now, we are somewhat far away from to see these, but that is a limitation of experiments. String theory does make specific predictions. It is definitely a scientific theory.

About the graviton and LHC...

Indeed, there is a huge hadron collider being built in CERN (Geneva). This is called the large hadron collider (or LHC). However, there is no hope of seeing the graviton there. What it will see is hopefully the Higgs particle (responsible for the electroweak symmetry breaking in the Salam-Weinberg model of weak interactions) and more promisingly, it will see the supersymmetric partners of the various particles, like the electron, quarks etc. That will indirectly support string theory, because string theory predicts supersymmetry (but not the other way round, in the sense that we can write down many supersymemtric theories which are not string theories).

To see evidence for the graviton, we need to see gravitational waves. There are expected from some cosmological events, like supernovae. There are some experiments which hope to see these waves in the near future.

Some interesting implications of an expanding universe are:

(a) many of the distant objects we see today are already way beyond our visual horizon of 12 billion light years.

(b) since distant objects move faster than closer ones (as initially confirmed by hubble through actual observations using I assume the candles, or the cepheid stars and supernovae, macGupta refers to), there must be an upper limit to this speed (the speed of light). So what happens when to objects when they have speeded up to the speed of light (somewhere beyond our visual horizon)? Even google is no help here. damn. maybe someone on chowk knows.

(c) Toss in the implications of string theory (in its current generally accepted form as put forward by Ed Witten in 1995) and we have an 11 dimensional universe (which our brains are not wired to comprehend anymoe than a dog`s brain is wired to comprehend the newtonian physics of everyday life), but whose existence we can infer logically and even test in practice by verifying the existence of graviton and watching it ``disappear`` to other dimensions (as the fermilab scientists are busy trying to do even now, and for which purpose the europeans are investing billions in a atom smasher 6 times more powerful than fermilab). Surely the expansion of the universe as we understand it would be better understood in this broader context of the full 11 dimensions - it would be odd if only our three dimensional space was expanding while the other dimensions had no bearing on this expansion
(d) Communicating with other dimensions: If the graviton is indeed observed to coolly transport itself in and out of our known world of three dimensional space plus time - couldnt it be used to communicate with intelligence residing in the remaining 7 dimensions? As someone said, even more exciting than finding life in our known universe would be the finding of evidence of multidimensional universe (via gravitons, sparticles and so on). So, stand by for the next exciting episode from fermilab or from the cern lab being built on the french-belgian border - it could very well happen within the lifetimes of those among us who have trouble believing that man actually made it to the moon three decades ago.

=== Interact Filtered ===
view this users filtered interacts

=== Interact Filtered ===
view this users filtered interacts

Thanks Mohammad ! This is a very interesting topic that you`ve been writing on :)

The initial measurements of the rate of expansion of the universe were of no greater precision than to verify a roughly linear law of expansion - the velocity of recession of a galaxy was proportional to its distance. The proportionality constant is called Hubble`s constant. Hubble`s measurements gave a value of around 500 km/s per megaparsec, I believe. By the early 90s, the measurements were consistent with a value of 50-100 km/s per megaparsec, still a factor of two uncertainity! ( Physicists loved to joke about the astronomers` lack of precision :))

With the new generation of large telescopes like Keck, and space-based telescopes, like Hubble, greater precision has become possible. I`m not sure how much ground-based telescopes have contributed; but most certainly the telescopes in orbit have been crucial.

I broke off my last post, because I had managed to confuse myself. After some thought, here is how I think one can understand the results. I`m using some made-up numbers in the following, for illustrative purposes only. Say Hubble`s constant is 60 km/s per Megaparsec. This value is a kind of average derived from galaxies that are 2 Megaparsecs away, and 10 megaparsecs away and 20 megaparsecs away, and so on. A galaxy 10 megaparsecs away would have a red-shift corresponding to a recessional velocity of 600 km/s.

Now, suppose we found that the galaxy with a recessional velocity of 600 km/s is not at 10 megaparsecs, but is at 12 megaparsecs (giving us an effective Hubble constant, derived from this galaxy alone, of 50 km/s per megaparsec. That would mean that way back when light left that galaxy, the universe was expanding much more slowly. In more recent times, the universe has been expanding at a faster rate (or if you like, has a higher effective Hubble`s constant now).

Using the specific supernovas as a ``standard candle`` indeed, this is what is found. Supernovas in distant galaxies are dimmer than expected assuming a constant rate of expansion. That is, for a given red-shift, the galaxies are further away than expected for that red-shift, assuming a constant rate of expansion (like my example above). This is the basis for the claim that the expansion of the universe is accelerating.

ironman, when a grenade explodes, it is exploding into space. The expansion of the universe is somewhat different. There are at least two analogies that are used to try to explain it outside of mathematics. The first is, imagine that space is two-dimensional and is the surface of a balloon. When you blow into the balloon, its surface expands and any two points you`ve marked on the balloon become further apart. If you drew a line of one centimeter length and another of two centimeter length, and then inflated the balloon till the line lengths double, then the two points that were one centimeter apart moved apart by an additional one centimeter, and the two points that were two centimeters apart moved apart by twice that amount, two additional centimeters. So the speed of recession of points increases with distance, and the expansion is not like a grenade explosion!

What is misleading in the first analogy is that the balloon is expanding in three dimensional space. But, we do not need to postulate any such embedding for the universe as such. So, let us imagine that we have a meter stick that is not going to go wierd on us and going to expand or contract, and let us imagine we have marked positions in space (say, by putting galaxies at those positions :)). Suppose we make a measurement at one time, measuring the distances between every pair of points, and then later, we repeat the measurements and find that all the measurements have doubled - this is like the expansion of the universe. Of course, we have no way of making the measurements between every pair of objects in our universe at a given time; what we can do is measure the distance of various galaxies from us at various times. Note that galaxies themselves, and even clusters of galaxies, that are gravitationally bound systems, do not themselves participate in the expansion (that is, the component parts of such a system do not grow further and further apart).

In a grenade explosion, everything started from the same place and things are imparted different velocities in the initial explosion. In the balloon example, nothing is imparted a velocity, every point remains in the same relative position to its neighboring points, and is locally at rest. This is a property of the expansion of the universe as well.

I like to acknowledge and appreciate firaq`s interest in the paper and I thank him for his useful comments. In fact one of the objectives of the paper was to stimulate the knowledgable people and interest them to provide appropriate information in lay man`s non-technical lingo. His comments regardibg the string theory and supersymmetry (SUSY) are also welcome.

However one small observation on the vacuum energy and the cosmological constant. From the units of Gev (energy units) that he has given, it appears he was talking about the vacuum energy density and not the cosmological constant. Also he was talking about an infinitessimal value of the constant while the value he gave was extremely high. It was probably an oversight.

The dimension of the cosmological constant is the inverse square of length. A typical value given for the `tightest bound` of the cosmological constant by S.E. Rugh and H. Zinkernagel is:

Lambda = 10^-56 /cm squared

where Lambda= cosmological constant.

Cosmological constant and the vaccum energy density are interrelated through a simple formula, as firaq surely knows, which is as follows.

Vacuum Energy Density = Lambda/ (8.pi.G)

in which G= gravitational constant.

I appreciate silly`s interest in the paper and am pleased to know that it was helpful to him.

Mohammad Gill

mcgupta`s comments are informative and apprpriate to the subject matter of the paper. If he wants to make additional topical comments, he is most welcome.

Mohammad Gill

macgupta, tahmed and others,

I would like to repeat/rephrase the question I asked in post #1.

When we look at deep space from earth, we see a picture painted in `Time`. The nearer galaxies are closer in time (we see them as they were a few million years ago)...to the furthest galaxies (as they were 12 billion years ago).

Now in a typical explosion..say that of a grenade...the shards attain their maximum velocity a few milliseconds after the explosion...and thereafter their speed decreases in time.

So if I take a picture 0.1 seconds after the explosion and then another...3 seconds after the explosion...I would find the first picture a blur of high velocity objects while the second would show much slower clearer objects.

This is exactly what we see in the sky.
Objects (galaxies) farther away are older pictures (closer to big-bang explosion) while objects nearer are later in time (more time after explosion).

Obviously, we should expect the older (farther) pictures to show faster objects. So farthest galaxies having higher speeds than closer ones...should not come as a surprise.


Rephrased Question:
How can we look at a picture 12 billion years old and say that the `current` universe is expanding at so-and-so rate? Accelerating or Decelerating.

Imagine having an object of a definite and fixed brightness in every galaxy. Then, by measuring the apparent brightness of this object, we would be able to compute how far away the galaxy is. Of course, this object would have to be bright enough for us to spot in our telescopes.

Nature, of course, does not oblige with us with such a ``standard candle``. However, a certain type of supernova is pretty close to one such (by the standards of astronomy) - that is, the actual brightness of the supernova can be inferred pretty accurately. Moreover, these supernova are very bright and visible.

Now, by measuring the red-shift of a galaxy one is measuring how fast it was receding from us at the time when the light left the galaxy, and by measuring the apparent brightness of the appropriate type of supernova in that galaxy, one is able to infer how far away the galaxy was. Yes, the further away the galaxy, the more remote is it in time, we are seeing what was, further and further into the past.

Now, if the universe is expanding (and is roughly the same everywhere), then the further away the galaxy the more it has receded from us - and us from it. So, greater the distance, greater the redshift. To a first approximation (and to within the precision of measurements that were possible a decade ago), there is a uniform rate of expansion. The recession of a galaxy is approx 65 kilometers/sec for each megaparsec ( approx 3 million light years) that it is distant from us.

The next question is - is the recession slowing down, or speeding up? Since gravity is attractive in nature, people expected the recession to be slowing down. However, the supernova data indicate the opposite. More on this later.