Translator: Queenie Lee
Reviewer: Rhonda Jacobs Has anyone here
used your quantum devices today? Anyone? Yes, a few of you. Here is one of my favorites,
my cell phone. It's literally my entire world here, right there. But maybe some of you
have used your TV, or a laptop, or perhaps you have used
your iPad, camera. And maybe some of you are clumsy like me, and you've dropped
one of your fancy devices, and it broke. And then you had this powerful urge
to take it apart and look what's inside. And then when you did that,
you saw there's a bunch of electronics made up of billions and billions
of tiny transistors - the fundamental building blocks
of these devices. And in order to make
those transistors work, we need to figure out
the science of semiconductors. And to control semiconductors
and build a multi-billion dollar industry, we need to understand structure
and interactions at the atomic level. And that's quantum physics - the study of the laws
that govern microscopic objects like atoms and electrons; and even photons,
which are particles of light. You may have heard
of another little invention called the laser. Quantum device. So this amazing scientific theory
called quantum mechanics has transformed our lives today. But my fascination in quantum physics
actually started in the stars. So, this image here
may look familiar to you. It's what we call a solar spectrum. It's what you see when you
pass sunlight through a prism and it breaks up
into all of its constituent colors. This has been taken
by a powerful telescope, so it's a very high-resolution image. And what you may notice
is a bunch of dark lines. And that's not dirt
or scratches or anything, that's real. Those are places where the light
is actually missing. And before quantum mechanics,
we didn't really understand why is it that there are these specific
colors that are missing from sunlight. Well, the reason they are missing
is because that light has been absorbed by gases surrounding
the sun, cooler gases. And the specific colors that are absorbed
depends on what that gas is made of. Is it hydrogen? Is it helium? Calcium? And in fact, using quantum mechanics, we can understand the structure
of different types of atoms - hydrogen vs. calcium vs.
any other element in the periodic table. So then, we know
which of those particular atoms will absorb which colors of light. So each of these missing spots
is like a unique bar code which tells us what the atom is. So by studying the bar code, we can figure out what is the gas
surrounding the sun. So for me, this was amazing! Here is a secret message
encoded in sunlight, about the composition of the sun, and we can decode it with quantum physics. But in fact, that secret message is even bigger, it's an incredible message
about the entire universe, and the person who decoded it was a young woman
named Cecilia Payne, in 1925. So Cecilia Payne was
a Ph.D. student at Harvard. Actually back then in the 20s, you couldn't actually take classes
at Harvard if you were a woman, so she was enrolled in Radcliffe College, but she did all of her observations
and her studies at Harvard Observatory. And she was studying different spectra
just like the one I showed you, not just for the sun
but also for other stars. And all these different spectra -
they look different, so those bar codes
are at different places. And she was trying to understand
what that difference was. So she used equations from quantum physics
and figured out something amazing. All those differences in the bar code was because all these different stars
had different temperatures. But in fact, by far the most common
element in all those stars was hydrogen and helium. There's a hundred billion stars
in our galaxy alone, and there's a hundred billion
galaxies out there. And using these equations
from quantum theory, this young woman
was able to figure out something, a universal property of all these stars. And that is like figuring out
the chemical composition of the universe. This was actually quite surprising
because back in that time, people thought that the composition
of the sun and stars was very much like the earth. So in fact, Cecelia Payne
didn't even believe her own results, but very soon after her work,
others confirmed this. And in fact, indeed today we know that the universe is basically made
of hydrogen and helium, with everything else
just in very, very small amounts, including all of the elements
we know here on earth. So, this was really an incredible thing. Cecelia Payne, she presented this
as part of her Ph.D. thesis. In fact, it was the first Ph.D.
awarded to any student, male or female, at Harvard Observatory. And what a way to start. She chose to stay on at Harvard
and continued to do amazing research, and she taught courses, but they didn't quite know what to do
with this new Ph.D. who is a female. They weren't really sure what to do, so they actually could not even
give her an official title for the next decade or so. And the courses she taught
were not even listed on the books. Finally, in 1938, they gave her the title of Astronomer, and then eventually, in 1956,
she became a Professor at Harvard, and very soon afterwards, she became
the chair of the astronomy department. In fact, the first female chair
of any department at Harvard. That's Cecelia Payne-Gaposchkin. She's not a household name. She should be!
But that's a different talk. But I was lucky. I, in fact, did learn
about her story and her work when I was a graduate
student myself, starting out. And it was of course
very inspiring to me - both her science and her experiences
as a woman scientist. Her work brilliantly illustrated
the power of this incredible theory called quantum physics, but also I learned something else. I learned that, in fact, the fundamental laws of nature
are accessible to everybody: male or female, young or old,
known or unknown. And that was a really
important message for me, back then when I was starting out. So, I followed my passion, and eventually, I earned
my own Ph.D. in physics, not a first at Harvard
or anything like that, but the first woman
in my family to do that. And of course, I chose to focus my research area
in quantum physics. But instead of studying
the largest objects like stars, I decided that I want to investigate
the smallest scales - the worlds of individual atoms. So we cannot actually
directly see an atom; it's far too small. But we can set up experiments where we can shine a laser beam
at a cloud of atoms. And the atoms will interact
with the laser light, and they will leave a shadow
of that interaction in the light, and we can collect that light
and analyze it and extract that shadow, and from that, we can actually
construct a picture to see this atom. Here's such a picture from data taken in the lab of my colleague
Poul Jessen, at the University of Arizona. So, as you can see,
the picture shows the world of the atom, which is represented by a sphere. And the laws that govern
this kind of world is the laws of quantum physics. And that's actually
a very strange set of laws. For example, there's something called
"the uncertainty principle," which says that we cannot know exactly
where the atom is located on this surface. So what you're seeing here
is actually an image of likelihood. Red shows where the atom
is most likely to be, and blue where it's least likely to be. The other thing that we can do is we can actually engineer
the surface of this sphere, so actually create a world for the atom. And, for example, how do we do that? Well, we use lasers and magnetic fields
to control this world. And one of the things we can do is we can insert barriers
and change the shapes of islands on the surface of this world. So this white line shows a barrier
that's constructed, so a barrier is essentially like a wall
that you and I could not actually cross. And then, what we can do is we can take many such pictures
of the atom over time, and we can put them together
and make a movie, so, the first such movies
of this kind ever made. Here's such a movie. Watch what happens. The atom is moving back and forth. It doesn't seem to be seeing
this so-called "barrier," and it's not actually climbing
over the barrier, it's passing straight through. It's an incredible quantum effect
called "quantum tunneling." What you are actually seeing here is literally an atom walking
through a wall. And that was, of course,
an amazing scientific discovery for me, and I was very excited, but I did see another one
of those secret encoded messages sent to us by the universe. The universe is showing us
that barriers are meant to be crossed. And furthermore, quantum tunneling connects
directly back to the stars. If you look deep
in the heart of stars - the core - it's actually a powerful
nuclear fusion reactor. That's where all of the sunlight
and energy is produced, and some of that comes to us
as sunlight from our star. And, of course, we know that it's critical
for life on earth. But how does that nuclear reactor work? Well, thanks to gravity,
the hydrogen nuclei in the core combine, they fuse together to create helium, and that releases
enormous amounts of energy. But here's the problem: Hydrogen nuclei, they have
positive protons, positive charges. And as you know,
like charges repel each other. So as you try to bring
these hydrogen nuclei close together, they push against each other. There is a barrier, an energy barrier, and the hydrogen atoms
cannot cross that barrier. But yet, they can. And the reason they cross it
is exactly because of quantum tunneling. They tunnel through the barrier and are able to complete
the fusion process from which we get light and energy. So sunlight on earth,
and a reason that we have life on earth, is because quantum particles
can walk through walls. And, now that we understand
the physics of quantum tunneling, we can control it
and build amazing devices like scanning tunneling microscopes,
and tunneling diodes. And these are amazing devices
and cutting edge technologies, but we're just scratching the surface. Tunneling is just one of many
incredible quantum effects that we are exploring now, to try to build
future quantum technologies. For example, quantum particles
can get connected together in a powerful connection
that we call entanglement. So if you make a change
to one of the quantum particles, it instantly affects
all the other particles, no matter how far away
they are in the universe. And again, we find that in order
to understand quantum theory and what it's saying about entanglement, we have to question
our very fundamental ideas about the nature of reality
and space and time itself. And that's amazing,
but there is a nice side effect. By exploring entanglement,
we have found that like tunneling, it's a resource that we can use
to build technologies. So, it's the fuel that we must have in order to build future
cutting technologies like quantum computers, or teleportation, or maybe some technology
that we have not even dreamed of as yet. So quantum physics has led us on an amazing journey
of discovery over the last century. We have been able to look
into the hearts of stars; it has to lead us to understand the structure,
the composition of the universe; it has shown us new ways
to think about barriers and connections through space and time. And, it has shown us that by studying fundamental
scientific laws of nature, we get really nice side effects, like cool technologies
and awesome devices. But for me, my fascination
remains those secret messages, those encoded mysteries out there in the universe. The universe very generously
has left us clues all around us, and we humans,
we get to be nature's detectives. We are constrained to this planet, we have limited resources
and limited knowledge. And yet, thanks to physics
and developing our theories, we can expand our understanding
to the entire universe. What will be that next secret message
that we will decode, that will lead to breakthroughs
in science as well as society? I don't know. And that is the most exciting part. Thank you. (Applause)
