Singular World

Some interesting discussions about String Theory

sujan — Fri, 13 Nov 2009 03:57:02 +0000

For last 20 years or so, we are hearing about this theory of physics. Even today we haven’t found out any evidences for this theory, still many physicists are excited about this theory. I was just going through the Elegant Universe website, there I found interviews of many physicists, most of them are string theorists, but here I’ll quote some part of ‘Sheldon Glashow’s interview. He is a particle physicist and he won the Nobel Prize in 1969 along with Steven Weinberg and Abdus Salam.

The question was ‘is there any danger in this for physics in general?’ ” There is today a disconnect in the world of physics. There are physicists, and there are string theorists. Of course the string theorists are physicists, but the string theorists in general will not attend lectures on experimental physics. They will not be terribly concerned about the results of experiments. They will talk to one another.

At Harvard today there’s a very strong group of string theorists upstairs on the fourth floor of the Jefferson Laboratory. Each week there are visitors from around the world giving lectures. I’ve occasionally attempted to attend these lectures. I can’t understand the titles, and I can’t understand the lectures, and it’s not just me. I think most theoretical physicists who are not themselves string theorists could not possibly follow these lectures. In other words, we don’t listen to them, and they don’t listen to us. We can’t understand them, and what we do is not of any direct interest to them.

It is a new discipline. Unfortunately, many of us have nothing in common with them, and many of them have nothing in common with us, except intellectually. Just as there’s a biology department that I respect and understand a little bit, there’s a philosophy department that I respect and understand a little bit, so there’s a string theory structure. That’s a problem, I think, in physics. “

In last 3 months @ Grad-school, I have attended many talks related to String theory and Supersymmetry in YITP. And it is really difficult for a 1st year grad students to understand what they are saying. So most of us come out of those seminars without understanding much. But suddenly you will see, somebody talking about ADS/CFT correspondence or some moduli space or something about differential geometry. Just try to ask someone what is N=4 super yang mills theory? or what is a moduli space? I am sure that you will not find any confident grad student there answering your questions, even 2nd year or 3rd year student. If you have some mathematical background, then you will have fun with them. People who have troubles in understanding Landau’s Mechanics or Sakurai’s QM or Jackson, talk about black hole entropy and superstrings. After reading Glashow’s comment, I am thinking what kind of physicists string theorists are… They don’t talk something that other physicists can understand and definitely they don’t have sufficient background to talk about mathematics. But this doesn’t stop here, it is misleading many young students around the world because many undergraduates or engineering students ask for books on String Theory. How can one understand it without any understanding of QFT or GR.. I don’t know. I just tell them popular string texts and wish them good luck.

I am not criticizing string theory or string theorists, it is indeed very interesting theory with a beautiful mathematical structure and one should make some extra efforts in learning it properly, but I am just imagining what will be the situation after 25 years. There will be a Physics tower, then there will be a Math tower, then there will be a simons center and new String theory tower in Stony Brook???

Before I end this topic, I should write something in support of string theory, let me add Ed Witten’s comment here. ” Back in the early ’70s, the Italian physicist, Daniele Amati reportedly said that string theory was part of 21st-century physics that fell by chance into the 20th century. I think it was a very wise remark. How wise it was is so clear from the fact that 30 years later we’re still trying to understand what string theory really is. What Amati meant was that usually the physical theory isn’t developed until there are more or less the concepts and ideas in hand for making sense out of it. By the time Einstein developed general relativity, he actually knew what he was doing.

But string theory wasn’t like that. The first traces appeared in 1968 with the Venetziano model. Nobody at the time had the conception that could have led to string theory in a clear way or understood what it was. It was something incredibly beautiful, a trail that people followed without understanding what it was. We’ve come through 30 years of remarkable discoveries, and we can see a lot of puzzles still ahead.

I guess it’s possible that string theory could be wrong. But if it is in fact wrong, it’s amazing that it’s been so rich and has survived so many brushes with catastrophe and has linked up with the established physical theories in so many ways, providing so many new insights about them. I wouldn’t have thought that a wrong theory should lead us to understand better the ordinary quantum field theories or to have new insights about the quantum states of black holes.”

Scientist: Four golden lessons

sujan — Sat, 15 Nov 2008 06:40:44 +0000

Prof. M K Harbola gave us grades which we didnt deserve. That was the only course in IITK in which I got the feeling of misjudged by the instructor. But I know after 10 years I might forget about that course and even its instructor. The thing that I ll never forget is this article which Prof Harbola gave me to read after the course. This is the talk which Steven Weinberg delivered at McGill University.—

“When I received my undergraduate degree — about a hundred years ago — the physics literature seemed to me a vast, unexplored ocean, every part of which I had to chart before beginning any research of my own. How could I do anything without knowing everything that had already been done? Fortunately, in my first year of graduate school, I had the good luck to fall into the hands of senior physicists who insisted, over my anxious objections, that I must start doing research, and pick up what I needed to know as I went along. It was sink or swim. To my surprise, I found that this works. I managed to get a quick PhD — though when I got it I knew almost nothing about physics. But I did learn one big thing: that no one knows everything, and you don’t have to.

Another lesson to be learned, to continue using my oceanographic metaphor, is that while you are swimming and not sinking you should aim for rough water. When I was teaching at the Massachusetts Institute of Technology in the late 1960s, a student told me that he wanted to go into general relativity rather than the area I was working on, elementary particle physics, because the principles of the former were well known, while the latter seemed like a mess to him. It struck me that he had just given a perfectly good reason for doing the opposite. Particle physics was an area where creative work could still be done. It really was a mess in the 1960s, but since that time the work of many theoretical and experimental physicists has been able to sort it out, and put everything (well, almost everything) together in a beautiful theory known as the standard model. My advice is to go for the messes — that’s where the action is.

My third piece of advice is probably the hardest to take. It is to forgive yourself for wasting time. Students are only asked to solve problems that their professors (unless unusually cruel) know to be solvable. In addition, it doesn’t matter if the problems are scientifically important — they have to be solved to pass the course. But in the real world, it’s very hard to know which problems are important, and you never know whether at a given moment in history a problem is solvable. At the beginning of the twentieth century, several leading physicists, including Lorentz and Abraham, were trying to work out a theory of the electron. This was partly in order to understand why all attempts to detect effects of Earth’s motion through the ether had failed. We now know that they were working on the wrong problem. At that time, no one could have developed a successful theory of the electron, because quantum mechanics had not yet been discovered. It took the genius of Albert Einstein in 1905 to realize that the right problem on which to work was the effect of motion on measurements of space and time. This led him to the special theory of relativity. As you will never be sure which are the right problems to work on, most of the time that you spend in the laboratory or at your desk will be wasted. If you want to be creative, then you will have to get used to spending most of your time not being creative, to being becalmed on the ocean of scientific knowledge.

Finally, learn something about the history of science, or at a minimum the history of your own branch of science. The least important reason for this is that the history may actually be of some use to you in your own scientific work. For instance, now and then scientists are hampered by believing one of the over-simplified models of science that have been proposed by philosophers from Francis Bacon to Thomas Kuhn and Karl Popper. The best antidote to the philosophy of science is a knowledge of the history of science.

More importantly, the history of science can make your work seem more worthwhile to you. As a scientist, you’re probably not going to get rich. Your friends and relatives probably won’t understand what you’re doing. And if you work in a field like elementary particle physics, you won’t even have the satisfaction of doing something that is immediately useful. But you can get great satisfaction by recognizing that your work in science is a part of history.

Look back 100 years, to 1903. How important is it now who was Prime Minister of Great Britain in 1903, or President of the United States? What stands out as really important is that at McGill University, Ernest Rutherford and Frederick Soddy were working out the nature of radioactivity. This work (of course!) had practical applications, but much more important were its cultural implications. The understanding of radioactivity allowed physicists to explain how the Sun and Earth’s cores could still be hot after millions of years. In this way, it removed the last scientific objection to what many geologists and paleontologists thought was the great age of the Earth and the Sun. After this, Christians and Jews either had to give up belief in the literal truth of the Bible or resign themselves to intellectual irrelevance. This was just one step in a sequence of steps from Galileo through Newton and Darwin to the present that, time after time, has weakened the hold of religious dogmatism. Reading any newspaper nowadays is enough to show you that this work is not yet complete. But it is civilizing work, of which scientists are able to feel proud.”

Einstein’s views about Mathematics

sujan — Sun, 18 Jun 2006 06:24:12 +0000

One reason why mathematics enjoys special esteem,above all other sciences,is that its propositions are absolutely certain and indisputable,while those of all other sciences are to some extent debatable and in constant danger of being overthrown by newly discovered facts. In spite of this, the investigator in another department of science would not need to envy the mathematician if the propositions of mathematics refered to objects of our mere imagination, and not to objects of reality.
There is another reason for the high repute of mathematics, in that it is mathematics which affords the exact natural sciences a certain measure of certainty,to which without mathematics they could not attain.