You can only save one— who do you choose? - Doug MacKay

You are the captain of the Mallory 7, an interstellar cargo transport. On your way to the New Lindley spaceport, you receive a distress call. There’s been an explosion on the Telic 12, and its passengers are running out of oxygen. As you set a course to intercept, you check the Telic 12′s manifest. It’s currently transporting 30 middle-aged individuals from some of Earth’s poorest districts to the labor center on New Lindley, where they'll be assigned jobs on the spaceport.

But as you approach the Telic 12, you receive a second distress call. A luxury space cruiser called the Pareto has lost a thruster, sending them careening towards an asteroid belt. Without your help, the 20 college students headed for vacation aboard the Pareto are all doomed. So, with only enough time to save one ship, which one should you choose?

This dilemma is an example of a broader class of problems where a life-saving resource—such as a donated organ or vaccine—is scarce. There are many schools of thought on how to approach these problems, and one of the most influential is utilitarianism, an ethical view first systematically developed by Jeremy Bentham and John Stuart Mill. In this view, you should choose the action which promises the greatest sum of happiness.

Though how to define and measure happiness is a difficult question. For example, hedonists would suggest a happy life contains the most pleasure and the least pain. Others might say it’s the life where your desires are most fulfilled. However, happiness is defined, most would agree that saving 30 lives has the potential to generate more happiness than saving 20. But is it enough to consider how many lives would be saved? Or should you also consider how many life years would be?

Assuming a life expectancy of 80, saving the lives of the students, with an average age of 20, saves 1,200 life years, while saving the workers, with an average age of 45, saves 1,050. All things being equal, a longer life should promise a greater sum of happiness than a shorter one. So perhaps saving the smaller ship actually has the potential to generate the most happiness.

If all these calculations feel a bit cold, you may want to consider a different approach. The philosopher Derek Parfit argues we should give priority to the worse off since benefits to those groups matter more than equivalent benefits to the well-off. In this view, it’s more urgent to help those whose basic needs aren’t met even if they’re harder to help than those who are flourishing.

But often, determining which group is truly worse off can get complicated fast. In our case, Earth is still beset by drastic inequalities in wealth and opportunity. And those able to afford a vacation on New Lindley and transport on a luxury cruiser are no doubt among the most well-off people on the planet.

The workers, by contrast, are among the most disadvantaged, traveling away from home for months at a time to perform service work. With fewer resources and opportunities, it’s likely they’ve experienced more hardship in their lives than the vacationers, so maybe they’re more deserving of rescue? On the other hand, the students have experienced less life overall—so perhaps they’re worse off? Or maybe none of these variables should influence our decision.

The philosopher John Taurek famously argued that in these types of cases, the numbers don’t count. Each person is deserving of equal concern and respect, so the best way to decide which passengers to save is to flip a coin. While this might seem arbitrary at first, this approach treats all parties equally, giving each individual an equal chance of being rescued.

Could any passenger argue that they're being treated unfairly by a coin flip? It’s tough to say. But how they—and you—feel about the result may be another dilemma altogether.