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MARK G. JACKSON
INTERVIEW
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.
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