The Center for 

Cooperative Phenomena


About Us




Nonlinear Science

Science Education

Science and Religion


Giving and Partnerships

November, 2006

What attracted you to physics?  

I was always obsessed about asking why things happened.  I loved tinkering with construction kits and especially electrical circuits, and had many, many questions for my parents!  As I grew older and more passionate about really trying to understand the "bigger" questions, it was very exciting to see that some of these big questions could be answered, and to do this you used physics.

In high school I took physics and loved it, and told my physics teacher that I wanted to major in it in college.  His (well-intentioned) reply was that they had figured out all of the interesting stuff and there was really nothing left to do, and so I should study engineering instead - there were always new products that could be invented using these laws of physics!  So I spent my first year in college as an electrical engineering student, but absolutely hated it.  It was fine if one's interest in science was a 9-to-5 job where you were primarily concerned with getting a (profitable) product out the door, but it wasn't concerned with constantly trying to answer "why does that happen?".  The summer after that first year I had a research job at NASA where I was around professional and student physicists for the first time, and it was immediately clear this was where I belonged.  The first day back at college as a Sophomore I changed majors to physics (and additionally math) and I've been happy ever since.

Of course many of these questions are very philosophical - "Where did we come from?", "What is the universe made of?" and so forth.  Humans have been asking these questions since the dawn of time, but physics lets you actually answer them in a definite way.  It may not seem like much when you just start to study physics and you are working on simple things like pendulums and inclined planes, but the amazing thing is that after only a few years you can indeed start to ask (and answer!) some of these deep questions.  Nature is actually very willing to answer these questions, but the language she speaks is mathematics.  And after you do it a while you get very addicted to the process of really wanting substantial, mathematical answers to these questions, without philosophical ambiguities.  This is why physicists' attitude towards philosophy is like the general public's attitude towards sex: we all think of ourselves as accomplished amateurs, but we have little regard for professionals!  Obviously physics will never be able to answer purely philosophical questions like how to lead a happy life, though eminent physicist Frank Wilczek actually has developed a formula for determining who to marry! 

One thing that I think something that doesn't always come across to the general public is how personal science is.  When one first encounters a lot of equations or theories it may give the impression that they have just always existed or it was just anonymous people in white lab coats that simply wrote them down correctly the first time they started thinking about it.  In actuality there are many different people working on problems from different perspectives, and who need to be inspired to research something.  And we take a lot of wrong turns before we figure out the right answer!  It can be very frustrating at times but its wonderful when it works out.  

You arrived at Columbia University in 1999 just as Brian Greene was on the verge of becoming famous. What was that like? 

I did my undergraduate work at Duke University in North Carolina, and had never even heard of strings until my Junior year, when I did a research project with an outstanding string physicist, Ronen Plesser.  Though I knew nothing about strings Ronen was super-inspirational and I figured if someone as brilliant as he is was this excited about strings, it might be worth thinking about.  When it came time to apply to graduate school I told him that I thought I might consider doing strings and he encouraged me to go to Columbia to work with a colleague of his named Brian Greene.  This was a few months before Brian's book came out, so I had only vaguely heard of him because he had done a video math course with Duke.  But it sounded good and so I arrived at Columbia later that summer after the book came out, and it was a bit strange to see him on The Colbert Report or movies like Frequency.  Not too many students get emails from their advisor discussing a technical paper we were collaborating on, and then a postscript at the end, "I'm going to be on Letterman tonight if you happen to catch it"!

I am a bit amazed how his fame has entered mainstream culture - his name (and also that of Ed Witten, a major contributor to string theory) has been mentioned in an episode of the Buffy the Vampire Slayer spinoff show Angel.  And once I was browsing some online personals, and a woman had mentioned that if she could be anywhere at the moment, "It would be looking over Brian Greene's shoulder as he performed his string theory calculations."  I replied to the ad with "We should talk..."  

What aspect of string cosmology are you working on at this time? 

My research interests have focused on applying superstring theory to cosmology.  Since string theory provides the first known quantum mechanical formulation of gravity, such a complete theory should also be capable of answering the basic questions of cosmology: how the universe began, is evolving, and its eventual fate.  Both cosmology and particle physics will soon be facing a deluge of new high-precision data, ushering in a golden age of model-building.  My interest is in bridging this gap between the cosmologists and the particle theorists, using ideas in one to gain insight in the other.  Lately this has focused a lot on cosmic strings.

Cosmic strings are long filaments of energy which might be stretched across the sky, predicted by many models to exist after the early universe has undergone a phase transition.  While recent cosmic microwave background data has proven that cosmic strings cannot be the major source of structure formation in the universe, there is nothing to suggest they could not be present in minute quantities.  Although these are not a priori related to the strings studied in superstring theory, there is an obvious similarity, and it was Witten in 1985 who postulated the idea of “cosmic superstrings”.  He found these were unfeasible for a variety of reasons, and the idea was promptly dismissed.  In the past several years technical advances have overcome each of these obstacles, and cosmic superstrings have emerged as a viable by-product of cosmological phase transitions.  These theoretical advances have been matched by a very promising chance that cosmic strings will be detected in the near future by gravitational lensing or through the LIGO, VIRGO and proposed LISA gravitational wave detectors.

My contribution to this emerging field has been to develop ways in which cosmic superstrings could be distinguished from the traditional cosmic strings.  The primary method is by noting that string reconnection happens for the latter type with virtual certainty, whereas for cosmic superstrings this happens only with some probability P which is typically much less than unity.  In my work with N. Jones and J. Polchinski we calculated P for a variety of models and found it depends sensitively on parameters in the theory.  If even a single cosmic string is detected, our results will provide the framework by which detailed information of the string theory can be extracted.  I then extended this result to general backgrounds, developing a systematic way to calculate the effect that extra dimensions and background fields would have on P.  Additionally, I have studied how  (p,q)-junction properties of cosmic string networks believed to be unique to superstrings might possibly be emulated by traditional cosmic strings.  Though the minimal-energy model I studied cannot match the (p,q) spectrum exactly, it might be possible for higher-energy solutions to closely approximate it.  Finally, I have been developing methods to calculate individual cosmic superstring amplitudes for a variety of interaction processes, rather than just total cross-sections for intercommutation.  This will allow one to estimate loop corrections to the previous intercommutation results, as well as calculate the amplitude for radiation of gravitons or small closed loops, and also compute differences from the classical cosmic string results.

Since this is a very new topic in superstring theory and cosmology, there are still many major unanswered questions which I hope to explore.  These include a complete understanding of the difference between the two types of cosmic strings, a study of precisely which observable properties of cosmic strings would yield the most information about the underlying physics, and whether cosmic strings may have played any significant role in the early development of the universe.  

I am later hoping to get more involved in some of the major unsolved problems in cosmology and try to apply string theory as an answer.  For example, it is now very well-documented that most of the universe is "dark", in that we can't see it but know it is there from its gravitational effects.  Perhaps string theory can predict what this exotic matter is made of.  

One occasionally hears comments to the effect that Nature is becoming more resistant to our efforts. Is it your sense that the pace of discovery in fundamental physics is slowing down? 

If you look at the history of physics, it has primarily been experiment-driven.  People knew what the orbits of the planets were, they just needed a good theory to explain why.  People knew that there was electricity and magnetism, they just needed a good theory to explain why.  And in the past hundred years, there was a tremendous amount of experiments that could be performed to study the fundamental particles, determine their properties, and then come up with a theory to explain them.  Some of these experiments could be done in a single room, and some have required giant accelerators like Fermilab or CERN, but they were within the scope of human achievement.  The trouble is that there is a limit to how complex an experiment humans can create, since the cost and bureaucracy will increase faster than the scientific information gained.

This is a problem for string theory, or any other "Theory of Everything", because the predictions it makes are so subtle that particle accelerators would have to be prohibitively large in order to measure any difference.  In the future I think we are going to have to be more creative about how we measure things.  For example, recently we have been exploiting cosmology to test theories.  We can now measure the cosmic microwave background very precisely and use it test different theories of how the universe began (this was the basis for the recently awarded 2006 Nobel Prize in Physics).  And cosmic strings, which I've previously described, could potentially yield a tremendous amount of information about fundamental physics.  But first we have to find one!  

Last January Time magazine had a cover story captioned “IS AMERICA FLUNKING SCIENCE? Our superiority was once the envy of the world. But we are slacking off just as other countries are getting stronger.” It seems that science in the U.S.  is going the way of grape picking, that is it is increasingly being left to people who weren’t born in this country. What are your thoughts in this regard? 

America is very pragmatic - we do not tend to spend a lot of money on something unless we see its tangible benefit, meaning commercially or militaristically.  World War II and the Cold War created an extreme example of this: Hitler drove the intellectual community of Europe straight into America's hands, and the American government was willing to spend huge resources on developing scientific superiority due to the arms race.

Nowadays there is tremendous progress being made in sciences like biochemistry and genetics, because there are so many companies willing to invest heavily in finding cures for illnesses.  In physics, it is tougher to explain why we need to research a grand unified theory of everything!  Of course, discussing strings, extra dimensions and black holes can make it sound sexy, but that is not the same as getting people to fund you.  The experiments we need tend to cost a lot of money,  which would likely have to be paid for by the government.  It would be hard for scientists to justify this expense unless it is for national defense.  It would be best if someone discovered a commercial application of superstring theory, so that we could get companies to hire physicists!  For example, if we discovered a way to manipulate these extra dimensions and made a Star Trek-like teleporter which found shortcuts for people or cargo to travel through, that would have obvious commercial value!  But I'm afraid that is a ways off.

45% of Americans believe that “God created man pretty much in his present form at one time within the last 10,000 years,”  84% of Americans believe in miracles, and 40% of Americans believe the world will come to an end within their lifetime. At the very least these figures seem to imply a profound disconnect between science and religion. In your opinion,  is this partly responsible for the fact that fewer students are serious about pursuing careers in science?

Our country has very puritanical, religious roots that hold views which sometimes don't agree with scientific discoveries, especially those that answer the big questions that I discussed.  Different people deal with this in different ways.  I personally know many people who come from religious backgrounds, and while they value this cultural perspective they do not take it as any basis for explaining how the world really works!  But for others, reconciling their religious upbringing and scientific evidence is more of an obstacle.  Some reject the scientific evidence outright, as though the data and instruments we use to observe the world were part of a vast conspiracy!  Others try to come with beliefs that incorporate modern science into some religious framework.

For example, lately there has been a lot of discussion about "Intelligent Design", which purports to be a "scientific" explanation of divine creation.  It essentially advocates the viewpoint, "The world is the way it is because an intelligent creator designed it that way."  I think this is silly, since for all we know there is a comet headed straight for Earth which will end all life - not very intelligent of the creator to set it up that way!  Whenever I hear people try to tell me that Intelligent Design is a legitimate scientific theory, I think of a time in college when I ordered a pizza, and after about two hours it still hadn't arrived.  I called the company and asked them, "Where's the pizza that I ordered?"  The woman's response was, "Its on it's way."  To which I replied, "How do you know it's on its way if I didn't tell you my name?"  She asked, "What's your name?", and when I told her, she said "Yeah, its on its way."  Now clearly she was trained to give the same response no matter what the question was, and so there was no information contained in her answer!  Similarly for Intelligent Design, this isn't even science - there is no information that could ever be extracted from such a theory if the answer is always "...the intelligent designer wanted it that way." You're just trying to make yourself feel good that you've explained something without really explaining it.

In good physical theories, there are answers based on mathematical self-consistency, not someone's opinion of what makes an "intelligent" theory.  For example, there are a lot of different mathematical objects called "symmetry groups", which in physics would give rise to different forces.  The ones we measure just happen to be those that we call SU(3) x SU(2) x U(1), but we have no idea why nature would choose that particular combination of symmetry groups - for all we know, it could have been something completely different, like SU(17) x SU(7) x E(6) x U(1).  A proponent of Intelligent Design would claim, "Ah, but an Intelligent Creator made it SU(3) x SU(2) x U(1) because that was what was necessary for life to exist", which doesn't even appear to be true.  But it turns out that in string theory, the mathematical self-consistency of the theory actually demands that nature choose something very similar to what is observed in nature, called E8 x E8 (you'll have to trust me that this is indeed similar to nature, even though it doesn't look like it).  So it is conceivable that one day we will find that what appeared to be a rather random collection of physical laws which only an "intelligent designer" could have come up with, was actually just some solution to an equation demanded by mathematical self-consistency by string theory or whatever.  It would be like asking, "Why does pi have the value 3.14159...?  It just does, because that's the only way math makes sense, it just wouldn't work any other way.