Interview with Marcelo Gleiser - The Dartmouth Undergraduate

Interview
Marcelo Gleiser
Dartmouth Professor of Physics and Astronomy
Andrew Zureick ‘13
What are some of the big
mysteries surrounding the
origins of the cell, life, and
chirality?
Image retrieved from http://www.dartmouth.edu/~mgleiser/graphics/gleiser.jpg
(Accessed 8 May 2011).
Professor Marcelo Gleiser.
T
he DUJS talked to Marcelo
Gleiser, Dartmouth professor
of physics and astronomy who
has been a part of the Dartmouth College faculty since 1991. He currently
teaches Physics 1, Understanding
the Universe; Physics 16, Introductory Physics II (Honors); and Physics 92, Physics of the Early Universe.
As a physicist, I’m very interested
in fundamental questions about nature.
In particular, the origins questions. I
have spent a long time of my life thinking about the origin of the universe, and
the origin of matter in the universe. A
few years back I asked: how does matter organize into living matter? How do
you go from atoms and molecules to
living atoms and molecules? This transition from non-living to living is one
of the most fascinating and completely
open questions in science. Where does
life come from, or how does the self-organization of biochemical reaction networks actually become a living thing?
All living systems have proteins,
and all of these proteins are made of
amino acids. If you synthesize all of the
amino acids, like alanine, in the laboratory, you will get a mixture of 50%
that are “left-handed” and 50% that are
“right-handed,” which says something
about the spatial structure of those
molecules. They come in two possible
conformations. They can be either in
the “left-handed” form or “right-handed” form, like your two hands. Hands
are not superimposable on each other,
so you cannot put a right hand on a left
hand or shake a person’s left hand with
your right hand. These molecules are
like that too. It turns out that these two
forms are non-superimposable mirror
images of each other. So, you would
expect life to have both left-handed
and right-handed amino acids. But
when you look at the proteins of living
things, from bacteria to people, they
are all left-handed. Why did life choose
a specific kind of chirality—chiral from
“hand” in Greek—to work? Nobody
knows! I am always very interested in
these kinds of asymmetries, because I
think asymmetries are the key to understanding the origin of complexity
in nature, or the complex structures we
see in nature, from DNA structures to
hurricanes. They have to do with some
kind of asymmetry. The origin of life
seems to be much related to this question of chirality. It is an open question.
If you talk to people, some will say you
need chirality to get life, while others
believe you need life and then you can
get chirality. I am part of the team that
believes you need chirality to get life.
If you look at the structures within
a cell like the nucleic acids that make
up DNA and RNA, they also have chirality. In their case, it has to do with the
sugars that form the backbone of these
What was your path to
becoming a professor at
Dartmouth?
I did my PhD in theoretical physics
at the University of London, King’s College. In my area, you have to do some
post-doctoral fellowships before you
can apply for professorship. I did two
post-doctoral fellowships, where you
are paid to do research in a group. One
was at Fermilab, a high-energy physics lab close to Chicago. The other was
at the University of California at Santa
Barbara [at the Institute for Theoretical Physics]. I came here as an assistant professor a long time ago [1991].
SPRING 2011
Image retrieved from http://en.wikipedia.org/wiki/File:L-alanine-3D-balls.png (Accessed 8 May 2011). Adjustments by Chen Huang ‘12.
L- and D-Alanine are non-superimposable mirror images of each other.
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molecules; they’re always right-handed.
So, you have left-handed proteins and
right-handed DNA. These two seem to
be connected with a key and lock mechanism to make the biochemistry of life
possible. To me, it is interesting, coming from physics, not from biochemistry, that there are actually some things
we can say about what’s going on. These
are the questions that are fascinating.
However, since I am a cosmologist by
training and interested in the origin
of the universe, I always look back at
the beginning of things. I think about
traveling through time back four billion
years in the history of the earth to when
there was no life. What was here? Was
it real mass? It was hot, and the oceans,
if they formed, would have evaporated
really quickly. In Darwin’s “warm little
pond,” chemical reactions began to take
place in higher rates without being so
disturbed by the environment, but still
being influenced by it. Eventually, this
first living thing—and by living, I mean
self-supporting, self-organizing chemical reaction network capable of metabolism and duplication—came about.
That is the most essential definition of
life; nobody really agrees on what life
even is. An operational definition of life
is a “self-supporting chemical network
capable of metabolism and duplication
that is absorbing energy from the environment and putting energy out.” Of
course, you can have living things that
don’t multiply; there are some problems
with these definitions. At what level of
chemical complexity can something
that is non-living become living? Can
you draw some sort of transition there?
I’ve read about the
endosymbiotic theory as
it pertains to the origin of
eukaryotic cells—are there
any other widely accepted
theories?
You start with these chemical reactions, but they need to be protected
from the environment in order to work
well. The external environment can
be too messy. That’s where the cell or
“protocell” comes in—you will be creating some sort of veil that will isolate interesting catalytic, metabolic reactions
from possible interference from the
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Image retrieved from http://commons.wikimedia.org/wiki/File:Gravitationell-lins-4.jpg (Accessed 8 May 2011).
A Hubble Space Telescope image of gravitational lensing caused by the Abell 1689 cluster. Dark
matter accounts for most of the mass contained within the cluster.
outside. You need not only the self-interactions on these networks, but also
the protection. How does that happen?
Why would it happen in the first place?
There are many people who have been
looking at that, and David Deamer of
University of California at Santa Cruz
talks about little lipid drops that could
serve as the environment where cells
are born. Alexander Oparin was a Russian scientist from the early 20’s and
30’s who dreamed up this whole way
of thinking about how life could have
appeared on earth. Initially, there are
chemical reactions that are isolated in
little bubbles, and these bubbles can
collide with each other. If they split and
have enough chemicals in them they can
become protocells themselves. Whoever
has the most efficient metabolic system
would win. He starts thinking about
these things and people begin modeling them. Along with the handedness
of chemicals and the self-organization
of these autocatalytic chemicals, which
can make more of themselves, you
need these protective environments.
I have a paper with my PhD student, Sara Walker. She’s currently a
NASA astrobiology fellow studying
the origin of life. You can start with a
reaction network of simple chemical
reactions that self-organize into little
bubbles. The chemicals like to be inside
little bubbles, and the chemicals inside
the bubble are chiral. So, you have little
chiral networks of reactions inside little
bubbles, and we call these things protocells. All we did was start with simple
(perhaps, not so simple) non-linear
reactions that people use to describe
polymerization, and we obtain these
very interesting asymmetric solutions.
What exactly are dark energy
and dark matter?
If you study the recipe of the universe, and what the universe is made
up of today, the stuff we’re made up
of—atoms, molecules, protons, and
Dartmouth Undergraduate Journal of Science
electrons—make up only 4%! The
rest, 96%, is other stuff. Of this other
stuff, 23% is what we call dark matter, which is made of particles (little
pieces of matter like protons) that do
not interact with electric charges and
do not interact with forces that keep a
nucleus together. All we know is that
they have mass and they interact by
gravity; we don’t know what they are
at all. We don’t even know if they exist, but these models fit well with what
people see in galaxies. They’re called
dark because they don’t produce visible
light, as opposed to stars. They produce
invisible light like infrared radiation.
How do you know dark matter is
there? One way is to look at galaxies
and see how galaxies rotate, and you
find that to explain the speed at which
the stars are rotating in a galaxy, especially the outer stars. You need to have
the galaxy also having a protective layer, an all-enveloping layer made of dark
matter particles. You can think of the
galaxy as what you see, with this invisible cloak of surrounding dark matter
particles that make up six to ten times
more mass than the stars themselves.
Then you have dark energy, the remaining 73%, which is even more mysterious than dark matter. We have only
known of dark energy since 1998, so it
is very recent. How did we know about
it? People look at very far away galaxies, like five billion light years across
from us, about half the way across the
universe. What they find there is that
they have stars that can explode like
supernova, stars that make a big bang
each time they die. People are able to
see these, even though they are very
far away, because supernovae are very
bright. They look for Type 1A Supernovae, and they realize they are lodged
in galaxies that are moving away from
us much faster than we would expect. We knew, since 1929, that the
universe was expanding, but we did
not know it was expanding this fast.
What could be making the universe expand so fast? There’s some sort
of force pushing matter apart. It is the
geometry of space that stretches. When
you think of cosmology, you think of
space as a rubber sheet, and this rubber
sheet has been stretched out faster than
expected. What is going on, why is that
happening, and what could be causing
it? We have a few candidates; the most
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plausible one is that this stuff that is
pushing the universe apart comes from
the fluctuations of energy of space itself.
In physics, especially quantum physics,
nothing stands still. Everything is always oscillating. There is some kind of
residual energy there. Possibly, if you
add up all this residual energy of stuff
across the whole volume of the universe,
you get this effect that may be pushing
the universe apart. This thing is called
dark energy. Ask me again in 10 years,
and maybe we will have a better idea.
Image courtesy of Marcelo Gleiser.
Could you tell me about your
book, A Tear at the Edge of
Creation?
This is my third book published in
English, published last year. It is several things: for one, it is a critique of
our idea that we can find a theory that
can explain all there is, the so-called
“Theory of Everything.” People like
Stephen Hawking and Brian Greene
write about this theory a lot. There is
this notion that science can come up
with a single, all-encompassing explanation of the why the world is the way it
is. For physics in particular, this theory
explains why the particles of matter interact the way they do. What I’m saying is that there is no reason whatsoever to believe that such theories exist, or
make sense. I go on to show that, cul-
turally, this idea that everything comes
from a single source can be traced back
to monotheistic notions, such as “all
is one because all comes from God.”
I think that is just a prejudice that we
have. When we look at nature, we don’t
see any evidence that it is true. We see
simplification; that’s what science is
about, trying to simplify complicated
things, but not to the level of finding
a single explanation that is behind everything. The book is a critique of that.
In fact, it shows that, instead of looking
for this all encompassing super-theory
and super-symmetry, we should really
be looking at asymmetry and broken
symmetries as the driving engine behind all that is interesting in nature.
The book has several parts. One is
called the asymmetry of time, in which
I talk about cosmology and why time is
going forward. I talk about dark energy
and dark matter, and the asymmetry of
matter. There is something called antimatter in nature. We only see matter;
we do not see anti-matter unless we
make it in a lab. I also talk about the
asymmetry of life, that is, the chirality
and the origin of life on earth, and why
chirality is so important. I talk about
what this all means to us on this planet, that is, the more we study life, the
more we realize that complex life, like
multicellular organized life, is probably very rare because it depends on a
series of conditions which are difficult
to satisfy in the universe. It’s not just
that the planet has to have water, carbon, nitrogen, hydrogen, and oxygen. It
requires much more than that to have
a long-living, complex multicellular
organisms. That brings us back to the
center of things. Obviously we are not
at the center of the universe, but we are
incredibly important in the big scheme
of things because we are self-conscious,
very sophisticated living things. Hence,
I try to bring human life back to its
place where we are important, and our
role is to preserve life. The book ends
with an ecological manifesto in which
people become the guardians of life.
We have a mission. The book also talks
about aliens and the possibility of alien
life. I find it very hard to believe. There
may be other intelligences out there,
but if there are, they are so far away
that we will never know. We are here
alone, and because of that, we have
some things we have to take care of.
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