Favourites - The Feynman Lectures on Physics

Rereading some of my favourite sections and thought i'd share what lessons I think professor Feynman was trying to convey. Enjoy.

Each piece, or part, of the whole nature is always an approximation to the complete truth, or the complete truth so far as we know it. In fact, everything we know is only some kind of approximation, because we know that we do not know all the laws as yet. Therefore, things must be learned only to be unlearned again or, more likely, to be corrected.......The test of all knowledge is experiment. Experiment is the sole judge of scientific “truth”.
~Volume I, 1-1, Introduction

A poet once said, "The whole universe is in a glass of wine." We will probably never know in what sense he meant that, for poets do not write to be understood. But it is true that if we look at a glass of wine closely enough we see the entire universe. There are the things of physics: the twisting liquid which evaporates depending on the wind and weather, the reflections in the glass, and our imagination adds the atoms. The glass is a distillation of the Earth's rocks, and in its composition we see the secrets of the universe's age, and the evolution of stars. What strange arrays of chemicals are in the wine? How did they come to be? There are the ferments, the enzymes, the substrates, and the products. There in wine is found the great generalization: all life is fermentation. Nobody can discover the chemistry of wine without discovering, as did Louis Pasteur, the cause of much disease. How vivid is the claret, pressing its existence into the consciousness that watches it! If our small minds, for some convenience, divide this glass of wine, this universe, into parts — physics, biology, geology, astronomy, psychology, and so on — remember that Nature does not know it! So let us put it all back together, not forgetting ultimately what it is for. Let it give us one more final pleasure: drink it and forget it all!
~Volume I, 3-10, The relation of Physics to other sciences

It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount.
~Volume I, 4-1

We can't define anything precisely. If we attempt to, we get into that paralysis of thought that comes to philosophers… one saying to the other: "you don't know what you are talking about!". The second one says: "what do you mean by talking? What do you mean by you? What do you mean by know?"
~Volume I, 8-2

From a long view of the history of mankind — seen from, say, ten thousand years from now, there can be little doubt that the most significant event of the 19th century will be judged as Maxwell's discovery of the laws of electrodynamics. The American Civil War will pale into provincial insignificance in comparison with this important scientific event of the same decade.
~Volume II, 1-6 end

In fact, the science of thermodynamics began with an analysis, by the great engineer Sadi Carnot, of the problem of how to build the best and most efficient engine, and this constitutes one of the few famous cases in which engineering has contributed to fundamental physical theory. Another example that comes to mind is the more recent analysis of information theory by Claude Shannon. These two analyses, incidentally, turn out to be closely related.
~"The Laws of Thermodynamics"

If, in some cataclysm, all scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or atomic fact, or whatever you wish to call it) that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence you will see an enormous amount of information about the world, if just a little imagination and thinking are applied.

Poets say science takes away from the beauty of the stars — mere globs of gas atoms. Nothing is "mere". I too can see the stars on a desert night, and feel them. But do I see less or more? The vastness of the heavens stretches my imagination — stuck on this carousel my little eye can catch one-million-year-old light. A vast pattern — of which I am a part... What is the pattern or the meaning or the why? It does not do harm to the mystery to know a little more about it. For far more marvelous is the truth than any artists of the past imagined it. Why do the poets of the present not speak of it? What men are poets who can speak of Jupiter if he were a man, but if he is an immense spinning sphere of methane and ammonia must be silent?
~Footnote

So, ultimately, in order to understand nature it may be necessary to have a deeper understanding of mathematical relationships. But the real reason is that the subject is enjoyable, and although we humans cut nature up in different ways, and we have different courses in different departments, such compartmentalization is really artificial, and we should take our intellectual pleasures where we find them.

...the "paradox" is only a conflict between reality and your feeling of what reality "ought to be."
~Volume III, p. 18-9

...and you will find someday that, after all, it isn’t as horrible as it looks.
~Volume III, Epilogue

~"Physics is like sex. Sure, it may give some practical results, but that's not why we do it."

Hawking on God again - "The Grand Design"

I woke up this morning to the news that, according to Stephen Hawking, God did not create the Universe but it was instead an “inevitable consequence of the Law of Physics”. By sheer coincidence this daft pronouncement has come out at the same time as the publication of Professor Hawking’s new book, an extract of which appears in todays Times.

Before I express my viewpoints, I'd like to establish that I do not believe in God, and yes, that means i'm an atheist. Therefore, my remarks might seem biased, but that's what keeps the debate on religion vs science going. I'm sure I will have several more posts on this topic in the future.

Stephen Hawking is undoubtedly a very brilliant theoretical physicist, though I wouldn't rank him in my top 20 all time physicists. However, something I’ve noticed about theoretical physicists over the years is that if you get them talking on subjects outside physics they are generally likely to say things just as daft as some drunk bloke down the pub. I’m afraid this is a case in point. And it's quite saddening to think that numerous fans follow every one of his remarks - no matter how religulous they may be.

God and physics are in my view pretty much orthogonal. To put it another way, if I were religious, there’s nothing in theoretical physics that would change make me want to change my mind. However, I’ll leave it to those many physicists who are learned in matters of theology to take up the (metaphorical) cudgels with Professor Hawking.

Though I haven't read the book yet, i'm sure it will be the usual nonsense some people put just to get media attention for a while to fund their studies. No offense to Professor Hawking, whom I respect very much.

Everything is Emergent ... Really?

It’s funny how when one thing is going good, it’s going great. And no one portrays that better than Erik Verlinde, who has made a claim that the reason why physicists do not understand the fundamentals of gravity is due to the fact that gravity is an emergent phenomenon, or an “entropic force”. As usual, the media gets all hyped, and so his claim ends up in the New York Times.

Now, if there is one model in physics that I am truly not very fond of, it would be the Standard Model. However, Verlinde has took his claim one step further with the help of Peter Freund, to claim that the Standard Model is also an emergent phenomenon. In fact, Freund has a new paper out on the arXiv entitled “Emergent Gauge Fields” with the following abstract:

Erik Verlinde’s proposal of the emergence of the gravitational force as an entropic force is extended to abelian and non-abelian gauge fields and to matter fields. This suggests a picture with no fundamental forces or forms of matter whatsoever.

And the appreciation:

I wish to thank Erik Verlinde for very helpful correspondence from which it is clear that he independently has also arrived at the conclusion that not only gravity, but all gauge fields should be emergent.

Geoffrey Chew's failed "bootstrap program" of the sixties - much the same reminiscing theoretical idea:

It is as if assuming certain forces and forms of matter to be fundamental is tantamount (in the sense of an effective theory) to assuming that there are no fundamental forces or forms of matter whatsoever, and everything is emergent. This latter picture in which nothing is fundamental is reminiscent of Chew’s bootstrap approach, the original breeding ground of string theory. Could it be that after all its mathematically and physically exquisite developments, string theory has returned to its birthplace?

It is still puzzling to me as to why this is a good thing. During David Gross' (a former student of Chew's) Nobel prize lecture, he explains:

I can remember the precise moment at which I was disillusioned with the bootstrap program. This was at the 1966 Rochester meeting, held at Berkeley. Francis Low, in the session following his talk, remarked that the bootstrap was less of a theory than a tautology…

From Strings to Ekpyrosis

I have been recently reading Neil Turok & Paul Steinhardt's new book "The Endless Universe - Beyond the Big Bang" which I bought at the Quantum to Cosmos festival held at Waterloo a few months ago. This book provides a fascinating glimpse into the process of cosmological and theoretical physics research. Both authors recount their personal history, their introduction to cosmology, and how they became involved in research related to the Big Bang theory. Overall, a great read for those anxious of physics related advancements since the 2000s. Here is a snippet of one of my favourite chapters.

Let’s talk physics history. An ever-so exciting tale of young physicists that changed the mindset of physics for decades to come since the late 1960s.

“Make everything as simple as possible but not simpler.” – Albert Einstein.

Nowhere was the optimism of particle physicists in the early 1980s more evident than at the annual Workshop on Grand Unification, known by the acronym WOGU (pronounced “whoa-goo”). Each spring the leading physicists, their postdoctoral fellows, and their students would gather at a different site to discuss the latest experimental breakthroughs and theoretical advances. Every year, the exciting presentations at WOGU seemed to engender new confidence that quantum field theory and grand unification were on track … until the fourth WOGU, when a soft spoken young theorist politely suggested that a sharp turn in the current thinking might be needed.

The meeting took place in April 1983 at the University of Pennsylvania, in Philadelphia, about fifty miles from Princeton, New Jersey, the home of Edward Witten. Only thirty-two years old at the time, he was already recognized as a theoretical physicist of great vision. For years, he had been a much admired pioneer in exploring the theoretical underpinnings of grand unification.

When Witten was invited by one of WOGU’s organizers to give a presentation, surprisingly, Witten was reluctant to accept. He explained that he was working on something new and was not sure the topic would be appropriate for a meeting on grand unified theories. That only made the prospect more intriguing, and so with persistence, Witten finally agreed to speak.

When the time came for Witten to talk, the last of the meeting, the auditorium was packed to standing room only. In his characteristic calm and gentle voice, Witten began by noting ways in which the current attempts at grand unification were failing. The most dramatic prediction, the instability of protons, had been tested, but no decays had been seen. The predictions of the masses of matter particles had also turned out wrong. Physicists could adjust the models to evade these problems, but only at the cost of adding ugly complications that made the whole framework implausible.

Witten then suggested that it might be time to consider a totally new approach. He proposed three guiding principles. First, the new approach should include gravity from the outset. Particle physicists were used to ignoring gravity because the gravitational attraction between elementary particles is normally negligible. However, when particles were smashed together at high energies, their collective mass rises in accordance with Einstein’s famous equations E = mc², and the effects of gravity become stronger and stronger. At the very high energies where the strong and electroweak forces seem to merge into a single unified force, gravity is nearly as strong. For this reason, Witten argues, gravity has to be included in any theory of unification.

Dealing with gravity would be no easy task. Einstein had developed his theory of gravity in the early part of the twentieth century, at the same time that quantum theory was emerging. Despite all attempts, the two strands of physics had never been successfully joined. Einstein’s theory works tremendously well on large scales for describing gravity on the Earth, the solar system, and in the universe. But just like electromagnetism and light, gravity must be formulated in a way that is consistent with the laws of quantum physics in order to make sense on microscopic scales. For the other three forces, the quantum field approach had been spectacularly successful. But for gravity, every attempt to quantize Einstein’s theory had failed, leading to infinities, negative probabilities, or, at best, an infinite number of indeterminate parameters. A totally new approach was needed, one that would give a sensible answer.

Everyone in the audience knew about these difficulties in building a quantum theory of gravity. So all in attendance were naturally anxious to learn what Witten had in mind. Witten emphasized that he did not deserve credit for the idea he was going to suggest. Hard work had been done by a small, intrepid group of theorists working largely unnoticed and unappreciated. But Witten was now advocating, as his second principle, considering their daring proposal: a conceptual framework known as string theory.

Many in the auditorium had heard of string theory before, but most knew little about its history because it had had little impact on mainstream particle physics or cosmology up to that point. String theory had been developed in a rather roundabout way.

In 1968, Gabriele Veneziano at the European Organization for Nuclear Research (CERN) had proposed a formula for describing the scattering of nuclear particles interacting via the strong nuclear force. In 1970, Yoichiro Nambu at the University of Chicago, Holger Nielsen at the Niels Bohr Institute in Copenhagen, and Leonard Susskind, then at Belfer Graduate College in Israel and now at Stanford University, showed that Veneziano’s formula could be interpreted as a model of vibrating one-dimensional strings. Unfortunately, it was soon discovered that the model had various pathologies, such as a tachyon, a physically impossible particle that moves faster than light. But this problem was cured as people realized that string theory was much more than a theory of nuclear particles. First, Joel Scherk at the Ecole Normale Superieure in Paris and John Schwarz at the California Institute of Technology showed that string theory included a particle behaving like a graviton, the troublesome quantum of Einstein’s theory of gravity. Then, by incorporating matter particles using a powerful new quantum symmetry called super-symmetry, Scherk with David Olive and other physicists managed to construct a completely consistent model with no tachyon.

In this way, the theory originally designed to describe the strong nuclear force was suddenly transformed into a unified theory with the potential to describe all the forces and particles in nature, including quantized gravity. But these developments went largely unnoticed. The 1970s were the heyday of quantum field theory, and string theory was seen as a speculative backwater. A few lonely theorists continued to struggle to develop the theory and iron out its remaining mathematical difficulties. This was a daunting and slow process, since few people were willing to risk working on the subject.

Witten’s talk went on to describe the advantages of reinterpreting elementary particles as tiny spinning bits of string. Just as Einstein pictures three-dimensional space as an elastic substance that can be stretched and distorted, you can think of string as a geometrical curve with no width that can bend and turn in all possible ways, like an infinitely thin strand of rubber. The string is perfectly elastic, so it can shrink to a point or be stretched out to an arbitrary length. If you stretch a piece of string out in a straight line, the free ends pull together with a fixed force called the string tension.

Some of the properties of string are actually very similar to those of cosmic strings. But whereas cosmic strings are really twisted-up configurations of fields with a minuscule but finite width, fundamental strings are ideal one-dimensional mathematical curves.

The string picture is beautiful in that one basic entity – string – can potentially account for the myriad of elementary particles observed in nature. Bits of string vibrate and spin, in certain specific quantized motions. Each new quantized state has a set of physical attributes: mass, charge, and spin. The little pieces of string describing photons, electrons, or gravitons are far too tiny to be seen, much less than a trillionth the diameter of a proton. To us, they appear like pointlike particles. But if string theory is correct, the masses, charges, ad spins of these little bits of string should precisely match the physical properties of all of the particles ever discovered.

Witten was especially attracted to this picture because it included gravitons as a hidden bonus, as Scherk and Schwarz had first shown. Bits of string with two free ends could account for all known types of matter particles. But the mathematics of string also allows for closed loops, like tiny elastic bands. When vibrating and spinning in just the right way, these loops have the same properties as gravitons, the quanta of the gravitational field. Even better, while calculations assuming pointlike particles and gravitons give nonsensical, infinite answers, calculations for stringy particles and loopy gravitons produce sensible, finite results. Although not designed for the purpose, string theory appears to automatically incorporate a theory of quantum gravity without infinities.

The reason string theory works where the particle description of quantum field theory fails can be explained by simple geometry. If two pointlike particles collide, their energy is concentrated at a point. Such pileups of energy cause a large gravitational field, curving space and drawing even more energy into the region. A runaway process ensues in which space curls up irretrievably into a tinier and tinier knot: a singularity. This catastrophe leads to mathematical infinities signaling a breakdown of the theory. On the other hand, if particles are tiny vibrating strings, their energy is spread out. If a collision causes a momentary pileup of energy, the string rapidly wriggles away and spreads out the energy, preventing the gravitational distortion from concentrating in one spot. Calculations of what happens when two bits of string collide, join, and break apart again give sensible, finite results. There are no singularities, and no infinities.

Witten’s third guiding principle dealt with the major hitch theorists had previously discovered about string theory. The equations describing the quantized vibrations of strings give sensible answers only if the number of spatial dimensions is nine. Nine!? To most physicists, this seemed absurd. Why study a theory that predicts six extra dimensions of space that have never been seen?

Witten addressed the problem of extra dimensions head-on: Learn to live with them, he said. Just accept the six extra dimensions of string theory; they are an essential aspect of the geometry of the universe. He reminded the audience that back in the 1920s the Swedish physicist Oskar Klein, building on the work of the German physicist Theodor Kaluza, had dreamed up a way of linking Maxwell’s electromagnetic theory with Einstein’s theory of gravity, in a model of the universe where one extra dimension of space was hidden from view.

To see how this works, consider the surface of a long soda straw. From a long distance away, it appears to be one-dimensional because you cannot detect its thickness. But up close, you can see the surface of the straw. To prove to yourself that the surface is two dimensional, slit the straw along its length and flatten it out. You will get a rectangle, a shape that is obviously two dimensional because it has both length and width.

Klein supposed that in addition to the three familiar dimensions of height, width, and length, there is a fourth dimension of space that is curled up in a circle so tiny that it cannot normally be seen. Kaluza and Klein’s remarkable discovery was that Einstein’s theory of gravity in four space dimensions, with one of the dimensions curled up as described, contained both Einstein’s theory of gravity in the remaining three extended dimensions and Maxwell’s theory of electromagnetism. Electric and magnetic fields arise, in this picture, from a “twisting” of the small extra dimension as you move along one of the large everyday dimensions.

According to Witten, theorists simply had to adapt Klein’s idea to the six extra spatial dimensions in string theory. There is no problem having strings wiggle in nine spatial dimensions, so long as six of the spatial dimensions are too small to be seen.

The extra dimensions would exist at every point in three-dimensional space. As an analogy, I’m going to use a rather famous one - consider a pile carpet made of woolen loops. To us, looking from above, it appears as a two-dimensional surface. But to an ant it seems like a huge forest of loops. At any point, the ant can choose to run along the direction of the floor, that is, along one of the two extended dimensions, or around one of the woolen loops that describe the curled-up dimension. In the same way, the extra dimensions in Kaluza and Klein’s approach are invisible, because their tiny size is too small to be seen. But in principle, with a very powerful microscope using very short wave-length radiation, one would be able, like the ants on the pile carpet, to see the convoluted structure of the extra dimensions on tiny length scales.

Witten framed his lecture carefully and peppered it with qualifications, but his message was clear. In a mere forty minutes, he made a compelling case that theories of grand unification were incomplete and that gravity, strings, and extra dimensions ought to be considered. Research on the fundamental laws of physics could be headed toward a revolution, he quietly suggested. You could have heard a pin drop in the auditorium as many physicists described. The audience was stunned, unsure how seriously to take Witten’s remarks.

Through the remainder of 1983, there were few signs that anything was going to change. During the Aspen summer workshop that year, for example, the talk was almost all about grand unification and field theory. But, sure enough, Witten’s lecture was the harbinger of a revolution that would soon sweep the world. The “first string revolution,” as it has been called, was ignited a year later at the 1984 Aspen workshop when Michael Green, then at Queen Mary College, London (now at Cambridge), and John Schwarz overcame a key mathematical roadblock in the construction of realistic string theories.

Until that point, there were many versions of string theory with different ways of folding the extra dimensions, but they all seemed to be fatally flawed. Witten had recently shown that many versions of string theory are unacceptable because they violate the conservation of energy through a quantum effect known as an anomaly. Green and Schwarz’s breakthrough was the identification of a special version of string theory that had realistic matter particles and no anomalies. Now, for the first time, one could point to a quantum theory that incorporated gravity and other forces and gave finite, sensible answers.

Working at Princeton, David Gross, one of the leading pioneers of unified quantum field theories (now director of the Kavli Institute for Theoretical Physics in Santa Barbara), along with Jeffrey Harvey and Emil Martinec (both now at the University of Chicago) and Ryan Rohm (now at Boston University) produced a compelling example known as heterotic string theory. The word heterotic, meaning hybrid, was added because it combined different versions of string theory to obtain one that has more of the ingredients needed to make a realistic theory of elementary particle physics. (A later, further improved form, heterotic M theory, was the stimulus for the Cyclic model of the universe.) These successes, and others that followed in rapid succession, captivated the international community of theoretical physicists. Almost overnight, it seemed, the focus of research shifted from particles to strings. And the merger of fundamental physics and cosmology that had seemed imminent in 1983 was put on hold.

On an unrelated note, i'm going to be posting less often as exam season is approaching. Oh the suspense ... Hooray for new banner & layout!

Back to the future

Groing up, I have always pondered on what the future holds. What will the future bring? If the inflationary model is correct, all of us live on a planet that is lost in the multiverse. Almost nowhere, are the physical conditions like those we observe. And our rare pocket of the universe is running out of time. Dark energy has already overtaken all other forms of matter and radiation, and has taken command of the expansion of the universe.

In a trillion years, our home will be well on its way toward a vacuous oblivion. Virtually all the galaxies we see today will still exist, but the stars will be gradually burning out. There will in all likelihood still be stars, planets, and life. But the accelerated expansion due to dark energy will have spread out the galaxies so much that nothing beyond the Andromeda Galaxy be visible to us.

The surviving civilizations in the Milky Way will know from the historical record that the universe was once filled with billions of galaxies, which emerged from tiny fluctuations in a hot plasma uniformly spread over space. But all the observational clues available today will be long gone by then. It is hard to imagine that a newly emerging civilization could piece together cosmic history on its own. In the inflationary model, therefore, the present is a unique epoch in the evolution of the universe where we can see both substantial amounts of the matter and radiation that dominated our past and the dark energy that will dominate our future. At other epochs, only one or the other would be detectable.

The same trillion-year prospectus applies if the Cyclic model is correct, but it holds nearly everywhere in space, not just in isolated pockets. After a trillion years, however, the story changes dramatically. The branes begin to approach each other, the dark energy decreases, and expansion slowly grinds to a halt. There will be no galaxies or other distant sources that future observers can use to detect the expansion rate, unless the future civilizations send regular test probes beyond the Milky Way. Yet there will be some novel physical effects to indicate that the end of the cycle is near. First, many fundamental physical constants of nature, like the strength of gravity and the strong, weak, and electromagnetic forces, will begin to change noticeably because their values depend on the separation between the branes. They don’t change during earlier stages, like today, because the brane separation is frozen. That is why they are interpreted as constants of nature. However, once the branes start to rush toward each other, all the physical constants will start to change in concert. A number of sensitive experiments exist today that monitor these constants and search for time variation. So far, no conclusive evidence for change has been found. According to the cyclic model, physicists performing those same experiments during the last 10 billion years before the next brane collision would detect a large variation of the constants, whose rate would increase as the branes speed up. In the final moments before the crunch, the rapid changes would become dramatic: particles would lose their mass and the laws of nature would be restored to a much simpler and more symmetrical form.

In reality, what is happening is that something enormous is approaching fast along a dimension we cannot see. The realization will come in a flash when, suddenly, everywhere in space lights up with new matter and radiation from the collision. The temperature soars to 10^15 times the surface temperature of the sun, evaporating any remnant structures from the previous cycle. The quarks and gluons of which we all are made join the flood of new quarks and gluons created at the bang, and the cycle of the cosmos is renewed.

One Hundred Years

The cosmological debate between the inflationary and the cyclic models is only just beginning to simmer in the scientific community. Many cosmologists have not yet given the issue much consideration because they see no reason for thinking about an alternative until some observation or experiment contradicts the inflationary picture. Others are reluctant to consider a model so deeply rooted in concepts like extra dimensions or branes because they regard these ideas as too far-fetched, even though string theorists are finding these concepts to be essential for unifying our understanding of the fundamental forces. In fact, contemporary versions of the inflationary model are now using the same stringy building blocks.

The reluctance of some to introduce so many new elements into cosmology is understandable. Science usually advances through small variations on an established idea. Radically new directions are not considered unless the scientific case is compelling. For that to happen, the problems with the conventional picture (which might be swept under the rug if there were no competing idea) have to become recognized, and the novel components underlying the new approach have to become familiar. Historically, this conservative approach has served science well, enabling it to make steady progress without getting diverted. In cosmology, for example, the main elements of the current inflationary model – the big bang picture, inflationary expansion, dark matter, and dark energy – were all subject to the same resistance when they were first introduced, and it took many years for them to be accepted.

The cyclic model, if it is worthy, will require similar patience. As discussions and investigations of the cyclic picture continue over the next few years and some of the weaknesses of the inflationary model become more exposed, interest will grow. The fact that two such dissimilar models can predict such similar results is too intriguing to ignore. Creative experiments will feel compelled to mount the decisive test between the two views of cosmic history because the issues at stake are too captivating to be ignored.

In settling the debate, cosmologists will have come to grips with the most fundamental questions about space and our place in the cosmos; about time and our moment in cosmic history; and about nature and our ultimate ability to figure out its laws. The answers will be our legacy to future generations. One hundred years from now, they will be taught to every schoolchild. They will permeate human discourse and inform our philosophical and religious views. And they will motivate many of the scientific advances of the twenty-second century.

Every elementary science textbook will include the WMAP snapshot or some improved image of the cosmic background radiation across the sky. The authors of the textbook will point to it as one of the great achievements of the twenty-first century. What will they claim about its significance?

If the inflationary model is proven correct, they will write that the image shows primordial wrinkles created at the end of inflation, about 10^-35 seconds after the big bang, when the temperature of the universe was about 10^27 degrees. The universe had a beginning of some sort, perhaps the big bang, but the period of rapid expansion diluted all information about what happened before inflation. Because human-made particle accelerators cannot possibly reach the energies needed to probe conditions before inflation, there is a limit to how much we can learn through observations or experiments about the fundamental laws of the universe. If the inflationary landscape picture survives, it may be impossible to discover the secrets of the universe because everything we see, no matter how far we look, has little in common with the rest of the cosmos, which consists of a combination of inflating regions and pocket universes with different physical properties. As for our own island, the likely outcome is that we are approaching a vacuous, uninhabitable state that will last forever. Perhaps we live in a misanthropic universe.

If the cyclic model proves to be correct, the textbook authors will write that the image shows the splatter of matter and radiation created at the big bang itself. The big bang was not the beginning but the moment separating our current period of expansion and cooling from a previous one. They will explain that the universe has an extra dimension, that the extra dimension is bounded by branes, and that the branes collided with each other to create the bang. They will show how the image can be used to determine the collision speed of the branes and to check that all the matter and radiation we see was created by the collision.

They will write that the WMAP image is also a window on the previous cycle. The small wrinkles in distribution of matter and energy were created billions of years before by random quantum waves that spontaneously appeared on the surfaces of the branes. A similar effect is beginning now that will eventually give birth to new galaxies and new stars in the next cycle. Because conditions everywhere in the universe are similar to what we observe here and because we can collect observable and measureable traces from an entire cycle, the whole cosmos can be comprehended from our single vantage point.

In 2010, it is too early to say which, if any, of these models will appear in the textbooks of the next century. But all of us can watch as a new theory blossoms into maturity and a mature theory is reinvigorated by the challenge. We can have the fun of debating the two visions of the universe and weighing in with our personal convictions while the matter remains in doubt. And we can do all this secure in the knowledge that the debate will not be endless.

Top 10 Beautiful Physics Experiments

This is why I prefer theoretical physics ...



Source

1. Double-slit electron diffraction

The French physicist Louis de Broglie proposed in 1924 that electrons and other discrete bits of matter, which until then had been conceived only as material particles, also have wave properties such as wavelength and frequency. Later (1927) the wave nature of electrons was experimentally established by C.J. Davisson and L.H. Germer in New York and by G.P. Thomson in Aberdeen, Scot.

To explain the idea, to others and themselves, physicists often used a thought experiment, in which Young's double-slit demonstration is repeated with a beam of electrons instead of light. Obeying the laws of quantum mechanics, the stream of particles would split in two, and the smaller streams would interfere with each other, leaving the same kind of light- and dark-striped pattern as was cast by light. Particles would act like waves. According to an accompanying article in Physics World, by the magazine's editor, Peter Rodgers, it wasn't until 1961 that someone (Claus Jönsson of Tübingen) carried out the experiment in the real world.



2. Galileo's experiment on falling objects

In the late 1500's, everyone knew that heavy objects fall faster than lighter ones. After all, Aristotle had said so. That an ancient Greek scholar still held such sway was a sign of how far science had declined during the dark ages.

Galileo Galilei, who held a chair in mathematics at the University of Pisa, was impudent enough to question the common knowledge. The story has become part of the folklore of science: he is reputed to have dropped two different weights from the town's Leaning Tower showing that they landed at the same time. His challenges to Aristotle may have cost Galileo his job, but he had demonstrated the importance of taking nature, not human authority, as the final arbiter in matters of science.



3. Millikan's oil-drop experiment

Oil-drop experiment was the first direct and compelling measurement of the electric charge of a single electron (1.602176487×10^−19 C). It was performed originally in 1909 by the American physicist Robert A. Millikan. Using a perfume atomizer, he sprayed tiny drops of oil into a transparent chamber. At the top and bottom were metal plates hooked to a battery, making one positive (red in animation) and the other negative (blue in animation). Since each droplet picked up a slight charge of static electricity as it traveled through the air, the speed of its motion could be controlled by altering the voltage on the plates. When the space between the metal plates is ionized by radiation (e.g., X rays), electrons from the air attach themselves to oil droplets, causing them to acquire a negative charge. Millikan observed one drop after another, varying the voltage and noting the effect. After many repetitions he concluded that charge could only assume certain fixed values. The smallest of these portions was none other than the charge of a single electron.



4. Newton's decomposition of sunlight with a prism

Isaac Newton was born the year Galileo died. He graduated from Trinity College, Cambridge, in 1665, then holed up at home for a couple of years waiting out the plague. He had no trouble keeping himself occupied.

The common wisdom held that white light is the purest form (Aristotle again) and that colored light must therefore have been altered somehow. To test this hypothesis, Newton shined a beam of sunlight through a glass prism and showed that it decomposed into a spectrum cast on the wall. People already knew about rainbows, of course, but they were considered to be little more than pretty aberrations. Actually, Newton concluded, it was these colors — red, orange, yellow, green, blue, indigo, violet and the gradations in between — that were fundamental. What seemed simple on the surface, a beam of white light, was, if one looked deeper, beautifully complex.



5. Young's light-interference experiment

Newton wasn't always right. Through various arguments, he had moved the scientific mainstream toward the conviction that light consists exclusively of particles rather than waves. In 1803, Thomas Young, an English physician and physicist, put the idea to a test. He cut a hole in a window shutter, covered it with a thick piece of paper punctured with a tiny pinhole and used a mirror to divert the thin beam that came shining through. Then he took "a slip of a card, about one-thirtieth of an inch in breadth" and held it edgewise in the path of the beam, dividing it in two. The result was a shadow of alternating light and dark bands — a phenomenon that could be explained if the two beams were interacting like waves. Bright bands appeared where two crests overlapped, reinforcing each other; dark bands marked where a crest lined up with a trough, neutralizing each other.

The demonstration was often repeated over the years using a card with two holes to divide the beam. These so-called double-slit experiments became the standard for determining wavelike motion — a fact that was to become especially important a century later when quantum theory began.



6. Cavendish's torsion-bar experiment

The experiment was performed in 1797–98 by the English scientist Henry Cavendish. He followed a method prescribed and used apparatus built by his countryman, the geologist John Michell, who had died in 1793. The apparatus employed was a torsion balance, essentially a stretched wire supporting spherical weights. Attraction between pairs of weights caused the wire to twist slightly, which thus allowed the first calculation of the value of the gravitational constant G. The experiment was popularly known as weighing the Earth because determination of G permitted calculation of the Earth's mass.



7. Eratosthenes' measurement of the Earth's circumference

At Syene (now Aswan), some 800 km (500 miles) southeast of Alexandria in Egypt, the Sun's rays fall vertically at noon at the summer solstice. Eratosthenes, who was born in c. 276 BC, noted that at Alexandria, at the same date and time, sunlight fell at an angle of about 7° from the vertical. He correctly assumed the Sun's distance to be very great; its rays therefore are practically parallel when they reach the Earth. Given estimates of the distance between the two cities, he was able to calculate the circumference of the Earth. The exact length of the units (stadia) he used is doubtful, and the accuracy of his result is therefore uncertain; it may have varied by 0.5 to 17 percent from the value accepted by modern astronomers.



8. Galileo's experiments with rolling balls down inclined planes

Galileo continued to refine his ideas about objects in motion. He took a board 12 cubits long and half a cubit wide (about 20 feet by 10 inches) and cut a groove, as straight and smooth as possible, down the center. He inclined the plane and rolled brass balls down it, timing their descent with a water clock — a large vessel that emptied through a thin tube into a glass. After each run he would weigh the water that had flowed out — his measurement of elapsed time — and compare it with the distance the ball had traveled.

Aristotle would have predicted that the velocity of a rolling ball was constant: double its time in transit and you would double the distance it traversed. Galileo was able to show that the distance is actually proportional to the square of the time: Double it and the ball would go four times as far. The reason is that it is being constantly accelerated by gravity.



9. Rutherford's discovery of the nucleus

When Ernest Rutherford was experimenting with radioactivity at the University of Manchester in 1911, atoms were generally believed to consist of large mushy blobs of positive electrical charge with electrons embedded inside — the "plum pudding" model. But when he and his assistants fired tiny positively charged projectiles, called alpha particles, at a thin foil of gold, they were surprised that a tiny percentage of them came bouncing back. It was as though bullets had ricocheted off Jell-O. Rutherford calculated that actually atoms were not so mushy after all. Most of the mass must be concentrated in a tiny core, now called the nucleus, with the electrons hovering around it. With amendments from quantum theory, this image of the atom persists today.





10. Foucault's pendulum

Last year when scientists mounted a pendulum above the South Pole and watched it swing, they were replicating a celebrated demonstration performed in Paris in 1851. Using a steel wire 220 feet long, the French scientist Jean-Bernard-Léon Foucault suspended a 62-pound iron ball from the dome of the Panthéon and set it in motion, rocking back and forth. To mark its progress he attached a stylus to the ball and placed a ring of damp sand on the floor below.

The audience watched in awe as the pendulum inexplicably appeared to rotate, leaving a slightly different trace with each swing. Actually it was the floor of the Panthéon that was slowly moving, and Foucault had shown, more convincingly than ever, that the earth revolves on its axis. At the latitude of Paris, the pendulum's path would complete a full clockwise rotation every 30 hours; on the Southern Hemisphere it would rotate counterclockwise, and on the Equator it wouldn't revolve at all. At the South Pole, as the modern-day scientists confirmed, the period of rotation is 24 hours.





On an unrelated note, my friend Yara has just started his own blog - "The Inquiring Mind". I have conveniently added a non-edible link to his blog on my "Blogroll" tab. Check it out!

Also, congratulations to my friends Brian & Cyril for making the official & unofficial teams of Canada for this years IOI, held in University of Waterloo. Sadly, Cyril missed the official team by one point. Check out their blogs too!

~ Happy Mothers Day! Words cannot express my love & appreciation for my mother.

Quantum Philosophy

Quantum Mechanics
Let us consider briefly the two aspects of this problem. As always, one is the philosophical implication for physics, and the other is the extrapolation of philosophical matters to other fields. When philosophical ideas associated with science in general, are dragged into another field, they are usually completely distorted. Therefore we shall confine our remarks as much as possible to physics itself.

First of all, the most interesting aspect is the idea of the uncertainty principle; making an observation affects a phenomenon. It has always been known that making observations affects a phenomenon, but the point is that the effect cannot be disregarded or minimized or decreased arbitrarily by rearranging the apparatus. When we look for a certain phenomenon we cannot help but disturb it in a certain minimum way, and the disturbance is necessary for the consistency of the viewpoint. The observer was sometimes important in prequantum physics, but only in a trivial sense. However, there is no doubt that a problem has been raised: if a tree falls in forest and there is nobody there to hear it, does it make a noise? A real tree falling in a real forest makes a sound, of course, even if nobody is there. Even if nobody is present to hear it, there are other traces left. The sound will shake some leaves, and if we were careful enough we might find somewhere that some thorn had rubbed against a leaf and made a tiny scratch that could not be explained unless we assumed the leaf were vibrating. So in a certain sense I guess, we would have to admit that there is a sound made. We might ask some question like: was there a sensation of sound? No, sensations have to do, presumably, with consciousness. And whether ants are conscious and whether there were ants in the forest, or whether the tree was conscious, we do not know. Let us just leave that problem in that form.

Another thing that people have emphasized since quantum mechanics was developed is the idea that we should not speak about those things which we cannot measure. Unless a thing can be defined by measurement, it has no place in a theory - simple as that. And since an accurate value of the momentum of a localized particle cannot be defined by measurement, it therefore has no place in the theory. The idea that what was the matter with classical theory is a false position. It is careless analysis of the situation. Just because we cannot measure position and momentum precisely does not a priori mean that we cannot talk about them. It only means that we need not to talk about them. The situation in the sciences is this: A concept or an idea which cannot be measured or cannot be referred directly to experiment may or may not be useful. It need not exist in theory. In other words, suppose we compare the classical theory of the world with the quantum theory of the world, and suppose that it is true experimentally that we can measure position and momentum only imprecisely. The question is whether the ideas of the exact position of a particle and the exact momentum of a particle are valid or not. The classical theory admits the idea, and hence, the quantum theory does not. This does not mean that classical physics is wrong. When the new quantum mechanics was discovered, the classical people - which by the way included everyone except Heisenberg, Schrödinger, and Born - said something like, "Look, your theory is not any good because you cannot answer certain questions like: what is the exact position of a particle? Which slit does it go through?" etc … and Heisenberg's answer would've been something like, "I do not need to answer such questions because you cannot ask such a question experimentally" It is that we do not have to. Consider two theories a and b. a contains an idea that cannot be checked directly but which is used in the analysis, and the other, b, does not contain the idea. If they disagree in their preconditions, one could not claim that b is false because it cannot explain this idea that is in a because that idea is one of the things that cannot be checked directly. It is always good to know (in my opinion) which ideas cannot be checked directly, but it is not necessary to remove them all. It is not true that we can pursue science completely by using only those concepts which are directly subject to experiment.

In quantum mechanics itself there is a probability amplitude, there is a potential, and there are many constructs that we cannot measure directly. The basis of science is its ability to predict. To predict means to tell what will happen in an experiment that has never been done. How can we do that? By assuming that we know what is there, independent of the experiment. We must extrapolate the experiments to a region where they have not yet been checked. If we do not do that, we have no prediction. So it was perfectly sensible for the classical physicists to go happily along and suppose that the position - which lets say obviously meant something for a baseball - meant something for an electron. It was a sensible procedure. Today we say that the law of relativity is supposed to be true at all energies, but someday somebody may come along and say how stupid we were. We do not know where we are "stupid" until we "stick our neck out" and so the whole idea is to put our neck out. And the only way to find out that we are wrong is to find out what our predictions are. It is absolutely necessary to make constructs.

We have already made a few remarks about the indeterminacy of quantum mechanics. That is, that we are unable now to predict what will happen in physics in a given physical circumstance which is arranged as carefully as possible. If we have an atom that is in an excited state and so is going to emit a photon, we cannot say when it will emit the photon. It has a certain amplitude to emit the photon at any time, and we can predict only a probability for emission: we cannot predict the future exactly. This is given rise to all kinds of nonsense and questions on the meaning of freedom of will, and of the idea that the world is uncertain.

Of course we must emphasize that classical physics is also indeterminate, in a sense. It’s usually thought that this indeterminacy, that we cannot predict the future, is an important quantum mechanical thing, and this is said to explain the behavior of the mind, feelings of free will etc ... But if the world were classical - if the laws of mechanics were classical - it is not quite obvious that the mind would not feel more or less the same. It is true classically that if we knew the position and the velocity of every particle in the world, or in a box of gas, we could predict exactly what would happen. Therefore the classical world is deterministic. Suppose, however, that we have a finite accuracy and do not know exactly where just one atom is, say to one part in a billion. Then as it goes along it hits another atom, and because we did not know the position better then to one part in a billion, we find an even larger error in the position after the collision. If we start with only a tiny error it rapidly magnifies to a very great uncertainty. For me to give an example, lets say, if water falls over a dam, it splashes obviously. If we stand nearby, every now and then a drop will land on our nose. This appears to be completely random, yet such a behavior would be predicted by purely classical laws! The exact position of all drops depends upon the precise wigglings of the water before it goes over the dam. Maybe you’re asking yourself now, how? Well, the tinniest irregularities are magnified in falling, so that we get complete randomness. Obviously, we cannot really predict the position of the drops unless we know the motion of the water absolutely, exactly.

Given an arbitrary accuracy, no matter how precise, one can find a time long enough that we cannot make predictions valid for that long a time. Now the point is that this length of time is not very large. It is not that the time is millions of years if the accuracy is one part in a billion. The time goes, in fact, only logarithmically with the error, and it turns out that in only a very, very tiny time we lose all our information. If the accuracy is taken to be one part in billions and billions - no matter how many billions we wish, provided we do stop somewhere - then we can find a time less than the time it took to state the accuracy - after which we can no longer predict what is going to happen! It is therefore not fair to say that from the apparent freedom and indeterminacy of the human mind, we should have realized that classical "deterministic" physics could not ever hope to understand it, and to welcome quantum mechanics as a release from a completely mechanistic universe. For already in classical mechanics there was indeterminability from a practical point of view.

~ Food for thought