Prosle godine imao sam priliku razgovarati sa Dr. Leonard Susskindom, profesorom
na Stanford University. Dr. Susskind je jedan od vodecih teoretskih fizicara
danasnjice, sa poduzim popisom vaznih doprinosa teoretskoj fizici
Understanding Melodies of Cosmic Strings
In the last century,
physicists discovered that everything around us, including our body and
the whole Universe, consists of tiny elementary particles and four forces
– nuclear, weak, electromagnetic, and gravitational – that run their
interactions. These particles form larger structures, which in turn form
even larger structures, like atoms and molecules, with the Universe as the
largest known to us.
However, physicists believe that behind all this, there is even smaller
substructure, currently undetectable to us, which would unify all forces
and all particles into one big "theory of everything". This
theory would also be able to explain how the Universe was created and why
it consists of exactly these particles.
We had the
opportunity to speak with Dr.
Leonard Susskind from Stanford University, a
pioneer of this remarkable theory. In more than 30 years of his work,
he has developed many milestones in the theoretical physics of elementary
particles and forces that influence them. In the last decade, he extended
his theories to black holes with again impressive results.
The ultimate goal of theoretical physicists is to create the theory of
everything, the theory that would incorporate the whole Universe and
explain it to the most basic elementary level. In your opinion, how close
are we to that goal and what are the biggest obstacles?
It is very hard to say how close we are to the theory of everything.
It could happen any day, or it could take a hundred years. Over the
last 20 years or so, we have made a lot of progress in combining
the Einstein’s theory of gravity and with quantum mechanics. There
were enormous puzzles about how they fit together, and those puzzle
revolved largely around the quantum mechanical properties of black
holes. We have made a good deal of progress in understanding the
connection between quantum mechanics, gravity, and black holes within
string theory. What we do not understand are the details,
such as the detailed properties of elementary particles. We have a
variety of different theories, which produce various kinds of pictures
how the particles ought to behave, but there is no exact, precise one.
The other thing that we have not made a great deal of progress is
understanding the connections between the very fundamental ideas of
string theory, quantum mechanics, and gravity on the one hand, and
cosmology, Big Bang, the evolution of the Universe, the future of
the Universe on the other hand. Those things are still not yet part
of our standard understanding of physics.
In the recent years, a lot of
hopes have been put in the superstring theory. What are the basic ideas of
The basic idea of superstring theory started
out more than 30 years ago with the idea that elementary particles are
little bits of one-dimensional strings, free to vibrate, to oscillate.
That theory originally was born in trying to understand protons,
neutrons, and other particles that constitute the nucleus. Later, that
same theory took on a new, different life. It became clear that it gives
a very good explanation why there is gravity in the world. The string
theory combines the quantum mechanics and gravitation and offers some
idea how space and time and matter fit together in the way that Einstein
hoped for in a unified theory. At the moment, we know an enormous amount
about the mathematics of the string theory, but we have not yet put it
together into a precise understanding of nature as we know it. I would
also add that the only framework that we have for asking questions about
quantum mechanics, gravity, cosmology, and so forth, is the string
theory. Every other attempt to think about it has failed. String theory
has produced an enormous amount of mathematical knowledge, enormous
amount of consistent theoretical pictures of how these things work, but
the details have to be filled in. It is famous saying that the devil is
in the details. It may get a long time until we get the details solved.
Black holes played an important
role in your professional life. How did that start and where did that lead
About 25 years ago, Steven Hawking dropped a
bomb on the theoretical physics community. He suggested that black holes
were going to violate all standard rules of quantum mechanics that we
knew about. The reason was because information gets sucked into the
interior of a black hole and can not get out, and that simply conflicts
with everything that we know about the quantum mechanics. In quantum
mechanics, information can not get lost. It can get scrambled, but it
can not get lost. Black holes where things which seemed to violate that
and that was very, very troublesome. My own view was that Steven was
wrong. I shared that view with Gerard ‘t Hooft, a recent Noble Prize
winner, and just everybody else shared the Steven’s view. We were very
troubled about how the future of physics was going to develop if Steven
was right. Ultimately, it turned out that Steven was wrong, but the
questions he asked were extremely good ones. By a lot of thinking, a lot
of use of string theory, a lot of guessing, we have come to a totally
new way of thinking about space and time, that is called the holographic
principle. By thinking thought experiments about black holes, and what
happens to things that go down a black hole, has led to a totally now
paradigm about the way space and time and matter fit together.
You often emphasize the importance
of something called the holographic principle. What is this principle
about and why is it so important?
It is a whole new way of thinking about the
world, quantum mechanics, gravitation. It came from thinking about black
holes and information that apparently gets lost down into the infinity,
so called singularity, of a black hole. Some of us had the idea that the
information that falls onto a black hole is stored on its surface, on
the so called horizon. This was something very new. Whole civilizations
could fall into a giant black hole, but all things inside the black hole
would have to be represented in a some way on the surface of the black
hole. The surface would behave like a hologram representing everything
that was inside of it. For example, in this room ordinarily you would
think that if you want to understand things inside it you would have to
give information about each little space within the room, each little
block or piece of space. According to the holographic idea, that is not
true, that is too much information and the only thing you really have to
know is what is going on on the walls of the room. But you have to know
with a very high precision. And that is enough. The walls of the room
are a kind of holographic film, which store all of the information about
what is going on inside of the room. All you have to do is to figure out
how to read the hologram. That is very hard.
Do we actually know what happens
inside of a black hole?
We qualitatively know that if you freely fell
into a black hole not very much would happen to you until you approach
the singularity. If it were very large black hole than nothing much
would happen to you as you fell through the event horizon. The
singularity is where you would feel the bad effects of a highly
condensed, singular distribution of matter, and would be squashed,
squeezed, stretched, destroyed completely. On the other hand, if
somebody were watching all of this from outside of the black hole, they
would see something entirely different. They would see you fall onto the
surface of the horizon of the black hole, get heated, destroyed, turned
into photons and radiated back out. That is the curious feature of what
we now understand about black holes. That idea is called "black
I believe that for non-scientists
is very hard to imagine the life of a theoretical physicist. Often they
are imagined as eccentric people with a preference to the Einstein-type of
hairstyle. So, what does the life of theoretical physicists look like?
By in large their lives are like anybody
else’s. They do have this passion, though, to understand how nature
works. Most of their working time, when not doing things that ordinary
people do, they are obsessed and preoccupied passionately with trying to
understand how nature works, or how gravity or electricity or magnetism
work. They spend a good deal of time interacting with each other,
exchanging ideas, trying ideas on each other, working at a blackboard,
writing equations, trying to figure out how all this works. I do not
think we are terribly different from anybody else who has a passion. My
father was a plumber and had a passion for plumbing. He loved to talk
about plumbing with his other plumber friends. I would sit around as a
little kid listening to them talk about how water flows through pipes.
In a way, we are not very different.
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