There are many reasons to be skeptical of the idea that you can change someone’s mind on a hot-button political issue simply by talking to them. We hold many of our political beliefs close, and our brains are built in a way to filter out and discount evidence that challenges them. That’s part of the reason a new study in Science is so surprising: It suggests that gay canvassers were able to significantly influence voters’ beliefs about same-sex marriage with just a 20-minute conversation, that this effect lasted at least nine months after those conversation ended, and that it spread to other members of the household in question.

For the study, Michael LaCour of UCLA and Donald Green of Columbia surveyed a bunch of registered voters in Southern California to get their views on gay marriage (and a bunch of other issues, to hide the true purpose of the study), and offered them financial incentives to get friends and family members to participate as well.

Then, trained canvassers were dispatched to the homes of the people who had taken the survey, where they delivered a script about either gay marriage or recycling (to create a placebo group) and asked the voters to express their opinions on the subject. Halfway through the conversations about gay marriage, the gay canvassers revealed they were gay and wanted to get married but couldn’t because of California’s then-ban on gay marriage, while the straight ones “instead described how their child, friend, or relative” was dealing with the same conundrum. The conversations lasted, on average, 22 minutes.

Before getting into the results, a bit of context is important here. This study fits into a broader body of research on the “contact hypothesis”—the notion that interacting with members of a group you don’t understand or trust can lead you to warmer feelings with them. It’s not as simple as it sounds, of course: As LaCour and Green point out, “The question is whether brief or indirect contact is sufficient to produce meaningful and enduring attitude change,” and “[r]ecent literature reviews have been tentative on this point,” partly because there’s a lack of experiments that track people’s beliefs in the long run.

It’s part of a challenge inherent to most studies aimed at examining how people’s political views change. Even when it appears a given message nudges someone’s views, there’s no way to know, once a study is over, how permanent the effect is. So even if a researcher can nudge someone to take climate change more seriously in an experimental setting, their beliefs may, for all anyone knows, snap back to their previous state a day or a week later. (Think about people you know with strong political opinions: Can you imagine any of them changing their views based on a brief interaction with a researchers?)