🔬 An Oscar, Two Asteroids, and the Algorithm in Your sklearn: John Platt on AI for Science

How often do you get to talk to a guest who has both an Academy Award and who invented textbook machine learning algorithms? John Platt has an Oscar, two textbook algorithms, two named asteroids, and an Erdos-Bacon number of 6. This was easily the most fun bio of all the guests we’ve read to date. And the result was an epic and fun chat covering Google’s Empirical Research Assistance (ERA), how AI can help battle climate change, and tons of great stories about the co-evolution of science and AI.

John’s colleague Dave Bacon likes to tease John that his career has been defined by being twenty years early to the next big thing. This may be convolutional neural networks (some credit him with coining the term), fusion research, quantum computing. John and Google have been working on solving some of humanity’s hardest problems with AI and computation for well over a decade now. Recently John and his team set their sights on using AI to solve any scientific problem that can be written down as a score.

Google’s Empirical Research Assistance (ERA)

John’s team has taken on many hard scientific problems over the years. In solving these, they noticed a pattern, many scientific problems can be reduced to what John calls a “scoreable task”. Once you have the score function, the goal is to find some code that maximizes the score. The hard part is in formulating the score, but once you have the score finding the maximizer can still be quite a lot of effort.

John’s team set out to automate solutions to this general problem. This came out of the idea of an “auto-Kaggle” AI, which can solve any Kaggle problem you can throw at it. Kaggle is owned by Google, so all the data was ready and easily available to them!

The result is Google’s Empirical Research Assistance or ERA (paper, github, blog). ERA is surprisingly simple conceptually. Gemini (or your LLM of choice) keeps a running tree of past experiments (notebooks) and where they’re going. It’s a close cousin of Monte Carlo Tree Search: at each iteration the Upper Confidence Bound rule picks which notebooks are most promising to mutate. This is optimistic, not greedy, so sometimes even the fifth-best notebook gets chosen. Gemini then proposes mutations for each one, about ten at a time. The history of each branch is shared, so different leaves can learn from each other.

“It’s almost like having a hyper-eager grad student who doesn’t sleep.”

Evolutionary algorithms have been around since the 70s, but this works because Gemini actually knows where to look! What’s even more interesting is that there was a step change between Gemini 2.0 and 2.5, and this went from just not working to working great.

ERA is so powerful that John and his team solved many outstanding problems with it, resulting in at least ten papers. Some of these were climate change related, which we talk about in the next section.

So, we had to ask: if you have an optimization god how do you avoid fooling yourself? John’s answer is that ERA provides predictive models. It’s up to the scientist to make sure they’re truly descriptive. Some of this just involves good old-fashioned careful machine learning science. “It’s a power tool. It can slice your fingers off.” This led to some fun discussion about Kaggle competitions, and the fun ways people can overfit to datasets without meaningfully solving the problem you actually care about: Google’s contrail-detection competition was won by entrants who noticed a half-pixel error in the labels (is the origin at the corner of the pixel or the center?) and this turned out to be a part of the winning special sauce. Great for winning $15,000, not so helpful if you actually want to solve contrails.

“People themselves will act like these LLMs and try to reward hack. It goes back to Goodhart’s law: any metric that becomes a target is no longer good as a metric.”

His advice for where to start instead?

“Always just fit linear regression. Just do it. Just do it. Just do it. Or SVM.”

Tackling Climate Change with AI

John and his team have worked extensively to mitigate the effects of climate change. We talked about several of their initiatives.

Perhaps the most interesting result we talked about was reducing the effects of condensation trails (contrails) from airplanes. Those little streaks you see running behind planes somehow account for 1% of all human-induced global warming?!? Some of these trails of ice crystals can hang out for days. These crystals are black in the infrared, acting like a thermal blanket that traps heat day and night.

It’s easy to understand what’s happening here, a region of atmosphere becomes “ice supersaturated”, and a tiny bit of exhaust seeds water vapor that instantly crystallizes. The scale here is astounding, with a single gram of exhaust resulting in ten kilograms of ice crystals.

The solution to all of this is quite simple, in principle! We know what parts of the atmosphere are most likely for the trails to form. Just have the planes drop a flight level or two. Problem solved, right? Well, the hard part is accounting for how much warming was prevented. This is a counterfactual problem, parts of which stumped John’s team for over two years. They had a working model for the heat-trapping half, but not for the reflected sunlight. ERA was able to find a simple model with some confounders they hadn’t considered. Cracked it!

Modeling climate generally is a hard problem. Climate is best thought of an attractor of many different possible weather outcomes. This makes it much harder to model.

“Weather is where you are on the attractor, and climate is the statistics of the attractor. The problem with climate is that we’re altering it. The attractor itself is changing, it’s moving.”

John and his team have worked on treating both the symptoms and the disease of climate change, with several other works in the area. Another fun example we briefly cover is FireSat, a way of using a constellation of satellites to rapidly identify fires before they grow too big to put out. For anyone living in California, you understand the problem. In dry years a small fire can result in hundreds of thousands of acres. If you could find this fire when it’s the size of a r