Describe your latest project.
Helen: The puzzle is this: how come the universe has lots of matter — well, some anyway; it makes up everything we can see — but very little antimatter? To discuss this takes us on a journey across the history of the Universe and through the laws of physics — because it is in the interplay of these two things that the puzzle must have an answer. We don't yet know for sure what the answer is, so our book, The Mystery of the Missing Antimatter, explores the options.

Yossi: The mystery of the missing antimatter started as the question of why there is no antimatter in the universe. In time, we understood that, but now the question is, why has matter not disappeared too? Andhow is there so much of it that survived? The story of matter and antimatter in the universe has occupied the minds of physicists for more than seventy years, and is still an open problem that combines cosmology and particle physics. At the same time that we tell the story of science, we use it to tell the story of scientists: how do physicists think? How do they work? What makes them happy?

What inspires you to sit down and write?
Helen: I can't help it — I guess this book has given me the writing bug. My head is full of things that I think are worth explaining for those who are interested. I write too much. However, the real crunch comes when there's a deadline to be met — then I have to stop playing around and start editing and reworking 'til it is short and clear enough to be interesting and readable.

Yossi: In my case, this is the wrong question. I do not need inspiration to write. Instead, writing inspires my thinking. Somehow, when I write, my thinking becomes more creative, sharper, and more critical.

Describe your favorite childhood teacher and how that teacher influenced you.
Helen: My high school math teacher, Miss Cunningham. She wore her whispy, graying hair tied back in a severe bun, and tilted her head to read our work through her bifocals. She really knew mathematics and could teach it well. She told me, "Helen, you couldn't be a mathematician, because you are so lazy; you'll never do a problem just by working through it, you always have to find an easier way." She understood my ideas and gave me new ones to think about. No doubt today she would be a mathematician herself, but in her time professional women were teachers or nurses. She was probably the first person who seriously suggested to me that I could be anything other than a wife and mother, the "career" my parents aspired to for me even while they encouraged my studies.

Yossi: Mario Livio, currently an astrophysicist in the Hubble Space Telescope Science Center, was my physics teacher at high school. He was enthusiastic, full of charm, and happy to play basketball with the students during the break. I often think that I chose to study physics not because I knew what it would be like to do physics, but because Mario was the most charismatic teacher. But whether I chose physics for the wrong or the right reasons, I never had any regrets about this choice.

Have you ever taken the Geek Test? How did you rate?
Helen: I have not — and wouldn't want to. Probably in some ways I'm a geek, but I'm lots of other things too.

Chess or video games?
Helen: Neither — as a kid I liked checkers (which we called draughts) and a card game called canasta. Nowadays I don't find time for games —I'd sooner read, work in my garden, or make something —the things range from benches for my deck to a coat I designed myself for my daughter. To relax, I like to take a walk in the woods.

Yossi: Neither. I do not have the patience for chess. And I was born too early to appreciate video games.

What do you do for relaxation?
Yossi: Read every evening, play soccer once a week, and hike in nature every month.

What's your favorite Blog right now?
Helen: I've tried reading blogs, but I'd sooner read a good novel.

Douglas Adams or Scott Adams?
Helen: Douglas, of course. Dilbert is amusing, but I think Hitchhiking the Universe is much more interesting. I love a good cup of strong tea, so the line "they gave him a brown liquid that was almost, but not quite, completely unlike tea" is my favorite. It's such a perfect description of what you get when you ask for tea almost anywhere in the US.

What was your favorite book as a kid?
Helen: Depends when. Dr Dolittle maybe, I loved the idea of the push-me-pull-you with heads at both ends. I read Bambi many times, weeping every time. Books no one in the US knows — the Billabong series, Anderson's Jo — stories of kids growing up in the Australian land.

What new technology do you think may actually have the potential for making people's lives better?
Helen: Which people? In the villages of Guatemala lots of people still cook over open fires — a simple stove with a flue can save lots of trees and save their lungs too. For them that's new technology, and it would make their lives better, and reduce carbon dioxide production too. In general, technologies for efficient and clean energy production, storage, and use will be important if we want to reverse the alarming global climate trends.

If you could be reincarnated for one day to live the life of any scientist or writer, who would you choose and why?
Helen: I'd choose to be me — boring as that may seem. I've no desire to be anyone else.

Yossi: I believe that the most amazing scientist of them all was Isaac Newton. I am intrigued to grasp how his mind worked. But I have no wish to live his life. I have a feeling that he was not happy, not even for one day of his life.

What was your best subject in high school? Your worst?
Helen: My worst is easy — it was art. Whatever I tried just turned out ugly. I convinced myself at an early age that I could not draw or paint, and so I could not. Later I let go of that judgement, and now I like to draw. Best — math and English.

Yossi: My Ph.D. advisor in the university once told me that someone that was good in all subjects at school is unlikely to become a good physicist. Since then, I hesitate to admit the truth: I was very good in all subjects.

By the end of your life, where do you think humankind will be in terms of new science and technological advancement?
Helen: I'd estimate I've got about 30 years — I think we'll understand a lot more about the brain and how it works, and have figured out how to use genetic information to individually tailor drug the most effective treatments of many diseases. Basic science — who can guess, that's the beauty of frontiers. We'll know more about the universe and about the way the laws of physics work in it than we do today.

Which country do you believe currently leads the world in science and technology? In ten years?
Helen: For the past three years congress has been saying the future of the US economy depends on maintaining our leadership in science and promising new money for research and science education. Then in the final budget crunch it all goes away and science is flat-funded. With that pattern the US is losing the leadership it had only a few years ago. Overall Europe and the US are now quite comparable, so if I can count (western) Europe as a single economy I'd say it's a dead heat. In ten years I'd bet on Europe. China, India and even Brazil are making big strides. They have a huge burden of infrastructure problems that will interfere with moving to world leadership on a ten-year time scale — but they will be players. Perhaps we'll even get past this idea of a single leader and instead recognize that we live all in one world and that good ideas can come from many places.

Yossi: Let me focus on my own field in science, that is, particle physics. For many years, the leadership was shared by Europe and the US. But in the last few years, the US is cutting drastically its experimental program, giving up on leadership. A question such as What is the dark matter made of? may find an answer in ten years or so but, if it happens, it will happen in Europe.

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Helen R. Quinn is professor of physics at the Stanford Linear Accelerator Center at Stanford University. A member of the National Academy of Sciences, she is the coauthor of The Charm of Strange Quarks: Mysteries and Revolutions of Particle Physics.

Yossi Nir is professor of physics at the Weizmann Institute of Science in Israel.