Scientists around the United States are getting ready to do an unprecedented experiment: They plan to march en masse in Washington, D.C., and other cities on April 22, to take a stand for the importance of public policies based on science.Some researchers predict that this March for Science will release much needed energy and enthusiasm at a time when science is under threat; others worry it will damage science's reputation as an unbiased seeker of truth.The idea for the march emerged soon after the inauguration of President Trump, and the Women's March that took place the next day. Jacquelyn Gill, a paleoecologist at the University of Maine, says she posted a message proposing a march for science on Twitter."And someone else said 'Yeah, that's a great idea,' and then someone else said, 'Yeah, I had the same thought,' " Gill recalls. "And so then we all kind of glommed together and started working on it."There's been a lot of concern about the fate of science under President Trump. His appointees include climate change skeptics; he's met with an anti-vaccination campaigner. He regularly cites false numbers on things like voter fraud and crime rates, while his surrogates defend the use of "alternative facts.""Our goal, really," Gill says, "is to bring people together in a strong unifying message that science is important to our citizens, it's important to our nation, and that we are going to hold our elected representatives accountable to that."The March for Science now has a website and a Facebook page that's gotten the attention of hundreds of thousands of people, and affiliated marches are planned from Cleveland to Anchorage.The organizers say all are welcome, not just scientists, and they're billing it as a nonpartisan celebration of science.But not everyone buys that. Jerry Coyne, a biologist at the University of Chicago, says the only thing that binds scientists together is that they all use the same tools: things like hypothesis-driven experiments, replication of results, and peer review."How do you march for something like that?" asks Coyne. "A march for science itself is just simply a march for the mechanisms that find truth. And who is going to pay attention to that?"He says what will get attention is the politics: "It's going to become a partisan march."That worries scientists who do research on some hot-button issues. Rob Young, a coastal geologist at Western Carolina University, recently wrote an op-ed column for The New York Times in, opposing the march.Young works on sea-level rise, a phenomenon that some politicians would rather ignore, and thinks it's best for scientists to interact one-on-one with decision-makers across the political spectrum.After his opinion piece ran at the end of January, Young received hundreds of emails from scientists, he says, and the majority agreed with his position."I'm not saying that we don't have a problem with ensuring that science has a seat at the table when we're making decisions at all levels of government," Young says, "but this march is not going to make that job any easier."In his view, all a march will do is make scientists seem like just another biased interest group, especially since it's scheduled for April 22 — which is Earth Day."Those folks who have been trying to pigeonhole and demonize scientists as having a particular political view and identity will see scientists marching on Earth Day as a part of the environmental movement," says Young.But other researchers say, look, if some protest signs at this march are overtly political or even inflammatory, that's really OK."You just can't hope for perfect control over what a large group of people do when they get up to express themselves," says Michael Eisen, a biologist at the University of California, Berkeley.That's why Eisen thinks scientists, who are used to controlled lab experiments, just have to get comfortable with the rough and tumble of public life."The people who seem to be demanding some kind of pure message, and worry about scientists seeming that they're too engaged or something — I think it is a mistake," says Eisen. "I don't think it's reasonable to expect a group of scientists to get together and not have some of what they talk about be, 'Hey, this administration is ignoring evidence in a really important area — that being changing climate.' It's going to happen."In Eisen's view, science is under threat and it's a good thing for scientists to show they really care about how science gets used.That's one reason why he's not just going to march. He says he's going to run — for the U. S. Senate. Copyright 2017 NPR. To see more, visit http://www.npr.org/.