Games may be life with all the hard bits removed, but they provide a way to study why people make the choices they make. Traditional games are usually played against a static background: the rewards per outcome are constant. That limits their relevance to behavior because, in real life, the rewards and consequences of strategic choices are ever-changing. Now, researchers have used a mathematical model to study a series of games that include evolving strategies and randomly varying returns.

A bit of history

Perhaps the most famous game-theory contest is the prisoner’s dilemma. In the prisoner’s dilemma, a pair of thieves have been captured and are being separately interrogated by the police. If both clam up, they will be punished for a lesser crime. If one prisoner makes a deal (defects) then that prisoner gets to go free and the other gets a heavier sentence. If both make a deal, they both get an in-between punishment.

The person running the game can start it with different rewards for cooperating and defecting to explore how the optimum strategy varies with reward and risk, which the players can figure out by varying the strategies across multiple rounds. Depending on the balance between the reward for staying silent (cooperating) and betrayal, the game stabilizes with everyone betraying everyone. In this simple situation, everyone loses.

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A photon is a single particle of light, and under normal circumstances, it can't be divided. But a photon is also not a particle, in the sense that it does not have a specific location. Instead, it is an extended object.

So if a photon is only partway through the process of reflecting from a perfect mirror and you yank the mirror away, what happens? The answer, from a trio of Norwegian physicists, turns out (arxiv.org link) to be more complex than I expected.

A photon divided?

Let’s first talk briefly about dividing and combining photons. If this were a common experience in our lives, then shining a single color of light through a piece of glass or reflecting it from a surface might cause photons to divide or combine. This would lead to an amazing array of colors: Our universe would be the most fantastic and legal LSD trip you could imagine. But this doesn't generally happen, hence LSD.

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Gold is weird. It's one of the few metals that doesn’t really oxidize. Even silver and copper—from the same column of the periodic table—form weak oxides. Naively, you might expect that gold would tarnish just like silver. Gold also sits right next to platinum, but it has none of that metal’s catalytic properties.

Then came gold nanoparticles that acted like catalysts, and we were confused by their apparent willingness to take part in chemical reactions.

Now, a pair of scientists has explained that gold’s inertness isn’t inherent to the atom but rather to the surfaces that gold crystals form. Before we get to the results, let’s first take a look at the traditional explanation for gold’s inertness and why an inert material that has no catalytic activity suddenly acts as a catalyst when in its nanoparticle form.

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