Dan Goldman (Ph.D. Physics '02), a physicist at Georgia Tech, is exploring how animals move on tricky surfaces like sand, bark, leaves and grass. The New York Times produced two videos on his research, which revealed how sidewinder snakes climb up sand dunes and how the sandfish lizard "swims" through sand. Tomorrow, he's delivering a talk to undergraduates at UT Austin titled "Robophysics: Physics Meets Robotics." We recently chatted about his work.
You study all these different animals, like snakes, lizards and crabs, moving in complex environments. Where did the interest in that come from?
My love as a kid was herpetology—lizards and snakes and all of these weird animals. At some point, I read a popular physics book on relativity and I thought this is what I should be doing. I went to graduate school at UT Austin to do research with professor Harry Swinney on the non-linear dynamics of granular materials like sand. Then I did a postdoc at U.C. Berkeley under Bob Full, who was using non-linear dynamics to understand how small animals like roaches and geckos move. There I learned about a world of biology that few physical scientists were working in and it really dovetailed with my interest in organisms as a kid. I realized there are lots of animals people don't know much about that live in sandy environments and I had worked on sand in graduate school, so I thought it would be interesting to marry the two. Sure enough, it has turned into a rich and fruitful research program and we have learned all about how animals move in and on top of sand.
How did that work lead you to robots?
As a post doc in Bob Full's lab, I was put on a DARPA [Defense Advanced Research Projects Agency] project aimed at building a robot that could climb vertical surfaces. Bob and others realized that robots could be physical models of living things. You could vary different parameters to try to explain how the organism moves. You could make predictions and then test them in the real system. And that's what I've been doing for the past 10 years.
Is the goal to understand how these animals move, or is it to build better robots, or is it both?
The goal is both. The goal is to learn about the richness of the phenomena we find in the world. The robots help you discover new phenomena that you wouldn't have otherwise learned about if you just watched balls colliding with a wall, for example. So it's multi-pronged. There is the more practical aspect—we can better understand robots and organisms. There is also a beauty in the understanding of these systems. And finally, there is the unexpected phenomena that we had no clue about until we studied these systems.
What kinds of things have you learned from this research?
We work with dyed-in-the-wool robotics folks who want to build robots for search and rescue. They said 'we can't get around cluttered environments well,' and we thought about this from the animal perspective. So, for example, we learned how sidewinder snakes get over sand dunes. It had to do with how the snakes send waves down their bodies. We could program a robotic snake to do the same thing and it worked. My colleague had tried to make a robot go into a cave in Egypt and he couldn't do it. And now we can. We also learned about some interesting physics associated with the sand, which we hadn't known about, about how the sand flows on a dune when you shove on it.
What are the big challenges?
One is working with animals. They're animals, so they do what they want to do. It turns out we got lucky. The animals we ended up studying are the sort of animals that do what we wanted them to do. The sidewinder, you'd think they'd curl up and want to strike at you, but they just side wind away. The turtles run for their lives. Sometimes it's more challenging. Also, building the robots is complicated and expensive.
What do you enjoy most about the work?
I think the primary things that drive me are the creative aspects and thinking about potentially beautiful concepts that we get to uncover in the natural world and in the artificial world. It's also interesting to work with engineers who build robots that have to go into nasty environments to help people trapped in rubble and things like that.
We also spend time on an animal dear to our hearts, especially in Texas and for us in Georgia, and that is the fire ant. They make complex nests under the ground, and if you fall into one it hurts like hell because you get stung. They're big pests, but enormously cool animals to study, because now you have lots of animals trying to create structures in confined environments. We try to see how they excavate and not clog themselves up in the nest. In essence, it is the physics and engineering of an ant nest.
What was your experience like as a grad student at UT?
Texas was transformative for me. I worked with Harry Swinney, in this wonderful place called the Center for Nonlinear Dynamics. It was this incredibly vibrant place where people were vibrating granular materials to see how patterns form, rotating tanks of fluids to try to understand Jupiter's atmosphere or watching liquids bounce. It was just an incredible wonderland of problems, which some people might not have even considered physics, but he turned them into physics. He gave me license to think more broadly about what physics could be.
You're speaking to undergraduate students this week at UT Austin. What do you hope to convey?
The wonderful thing about physics is that the whole universe is your playground. So robotics can be physics. In that sense, there is an arrogance in physics in that we say, "I'll go and try it," and a naiveté and a joy. And that's what I want to communicate in my undergraduate lecture. Sometimes people work on problems they are told are fundable, and I want to show them that there is a whole world of problems if you just open your eyes and try things.