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Top > Vol.12 -Jokob Hansen
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 Name: Jakob Hansen Ph.D |
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Nationality: Denmark |
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| Affiliated research center/ school in Waseda |
Faculty of Science and Engineering |
| Affiliated research institution at home country |
The Niels Bohr Institute, University of Copenhagen |
| Period of stay at Waseda |
From November 2007 to November 2009
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Subject of research
Numerical simulation of black holes and wormholes
About My background
 Picture of lake in my hometown of Copenhagen
The Niels Bohr Institute at the University of Copenhagen from where I received my Ph.D. |
Ever since I was a little boy I have had a great interest in science, in
particular in physics and astronomy. I used to spend half my day doing
physics experiments and the other half dreaming of being an astronaut traveling
through the cosmos in my own spaceship, unraveling the mysteries of the
Universe.
Although I soon realized that my chances of becoming an astronaut were quite slim. my interest in science continued throughout my upbringing. Hence, when the time came for choosing a career path, I decided to study physics and astronomy at the University of Copenhagen, Copenhagen, Denmark.
After obtaining my B. Sc. degree, it was time for me to specialize. I had
always been very fascinated by the concept of "black holes",
objects with a gravity so powerful that they bend space and time and from
which not even light can escape from them. As it happened, one of the world
specialists in Einstein's general theory of relativity (the physical theory
that describes gravity and black holes) was a professor at the University
of Copenhagen, so I decided to go and have a talk with him. His name was
Igor Novikov and he became the supervisor for my subsequent studies.
Computerized black holes
The research topic for my M. Sc. and Ph. D. degrees was to become "numerical
relativity". That is the technique (some say "art") of using
computers to find solutions to Einstein's general theory of relativity.
This theory can be written as an extremely complicated set of equations
whose solutions describe the physics of gravity and physics of astrophysical
objects governed by gravity, e.g. black holes. In principle, all that is
needed in order to learn about gravitational physics is to solve this set
of equations. Unfortunately, in practice this is very difficult, because
the equations of general relativity are so complicated that finding analytic
solutions is impossible in the general case. However, there is another
way, namely to solve the equations by using powerful computer programs,
this approach is known as numerical relativity.
The next four years I studied the complex equations of the general theory
of relativity and developed my skills as computer programmer, learning
to make computer simulations of black holes. Finally, in June 2005, I obtained
my Ph. D. degree and was ready for an international life as a researcher
so soon after I ventured onto a job as a research associate at the University
of Chicago, Chicago, USA.
After living for two years in Chicago I was faced with the decision of
what to do next; should I go back to Denmark, should I apply for a new
postdoctoral position somewhere else or should I do something third? I
wished to continue my research, in particular I was interested in pursuing
some ideas which my Ph. D. supervisor had suggested to me. I considered
if it would be possible to carry out my research in Japan as I had always
been fascinated by Japan (had even taken a few Japanese language classes).
Furthermore, coming from Denmark and after living two years in the far
west of America, somehow it seemed appropriate to live two years in the
far east.
During my studies in Denmark, I had made friends with a Japanese physicist,
Professor Takao Koikawa of the Otsuma Women's University in Tokyo, who
had been spending a sabbatical year at the Niels Bohr Institute in Copenhagen.
I presented my considerations to him and he recommended that I applied
for a JSPS postdoctoral fellowship. Not only that, he also introduced me
to Professor Kei-ichi Maeda of the Department of Physics at Waseda University,
who were to become my host professor here at Waseda. I initiated communication
with Professor Maeda and we soon agreed that we shared similar research
interests and that Waseda would be a good place for me to carry out my
research. Hence, I applied for a JSPS postdoctoral fellowship and next
thing I knew, I was living and working in Japan. .
Collaboration with international colleageus in Copenhagen
Summer camp in Izu with members of my laboratory at Waseda
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Example of computer simulation of a wormhole |
Research at Waseda
My research topic here at Waseda is an extension my Ph. D. studies. The
first task has been to develop a computer program which can be used to
solve the complex equations of general relativity for the physical scenarios
that I want to investigate. This is now done and currently I have entered
the second stage of my research project where I am using my computer program
to study the physics of gravitational objects. The first usage of the program
has been to make simulations of objects known as "wormholes".
Wormholes are theoretical objects which connects different parts of the
Universe through a short path. These are very fascinating objects because,
if they exist, in principle they could be used to travel from one part
of our Universe to another very fast. Even more fascinating, they could
theoretically be used to construct a time machine.
Wormholes have not yet been discovered in our Universe, but as far as
we know, there are no known physical laws or principles which disallow
their existence in principle. On the contrary, they can be described as
solutions to Einstein's equations which mean that in principle these objects
may exist. It also means that they can be simulated by my computer program
which allows us to study their properties.
I am especially interested in studying the physical stability of wormholes;
The main question is whether or not wormholes are inherently unstable,
that is, if we imagine they were somehow created, would they be stable
enough to exist on extended timescales or would they rapidly self destruct?
Subsequently, if they are stable, would it be possible for a physical object
to travel through them or would such an action trigger some instability
causing them to self destruct? These and similar question are some of which
I try to answer with my research. Other aspects of my research involve
using my computer program to make similar studies of other objects, such
as study the physics of black holes or the evolution of the Universe.
The Future
What my future plans will be is yet uncertain. I hope that I can continue
my research in numerical relativity, but where in the world I will do so
is yet to be decided. However, what is certain is that I will have some
very valuable and precious memories from my time here at Waseda.
It was my childhood dream to have my own spaceship, flying through the Universe and unraveling its mysteries. I don't really have my own spaceship, but in a way I do, because using my computer simulations, every day I can "travel" to fascinating and exotic objects such as black holes and wormholes. My childhood dream has finally come true.
 
With Prof.Maeda Here I am with friends after climbing to the
top of Mt.Kintoki
Major Publications
- J. Hansen, "The Evolution Problem of General Relativity", Master's
thesis, University of Copenhagen (2001).
- N. Jansen, P. Diener, J. Hansen, A. M. Khokhlov I. D. Novikov, ``Local
and global properties of conformal initial data for black hole collisions'',
Class. Quantum Grav. 20 (2003) 51-73.
- J. Hansen, A. M. Khokhlov, I. D. Novikov, ``Properties of four numerical
schemes applied to a nonlinear scalar wave equation with a GR-type nonlinearity.'',
Modern Physics D, Vol. 13, Number 5, (2004).
- J. Hansen, A. M. Khokhlov, I. D. Novikov, ``Physics of the interior of a spherical, charged black hole with a scalar field'',Phys. Rev. D71 (2005) 064013.
- J. Hansen, "Evolution Problems of General Relativity", Doctorate
thesis, University of Copenhagen, (2005).
- V. Paschalidis, J. Hansen and A. Khokhlow, ``Numerical performance of
the Parabolized ADM formulation compared to that of the ADM adn KST systems'',
(2007) gr-qc//0712.1258 (submitted to Phys Rev. D).
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