Alireza Edraki spends weekends in the lab. It's what he does. For the past three years, test tubes full of bacteria have been his constant companions. Not this weekend. "I'm so stressed out that I can't work," he says.

Edraki is a third-year PhD candidate at the University of Massachusetts' medical school in Worcester. You know Crispr/CAS-9, the gene-editing technology that’s in all the headlines lately? That’s what Edraki works on. Last year he was part of a team that published a seminal article in the journal Cell detailing work that could make gene therapies safer. To use a Trumpian phrase, that’s big league. It’s the kind of accomplishment that means Edraki is likely to have a long career in science.

Unless the new immigration ban ruins it. Trump's executive order issued Friday explicitly bans anyone from Iran and six other predominantly Muslim countries from getting new visas for 90 days, among other measures. Though Edraki's family left Iran for the United Arab Emirates when he was a child, he still holds an Iranian passport and an F-1 visa that the Trump administration just put in jeopardy.

'They can take my house, but they can’t take my brain away from me.'

"Even before this stupid new rule it wasn't easy, but it wasn’t like I was trapped here," he says. With a single-entry F-1 visa, visiting family overseas wasn't always easy. "But I always felt like I could go back if I needed to. Now I feel trapped."

Edraki cannot go home, and with just an F-1 student visa he also can't stay long-term. He planned to apply for a permanent green card this month, but is unsure how the new order could change that. He's just one of countless students and scientists whose future in the US is uncertain because of Trump's order. Many from the greater Boston area gathered Sunday to protest—students and professors from MIT, Harvard, Boston University, Northeastern, and more joined an estimated crowd of 20,000 in Copley Square. Similar protests broke out in cities and airports across the country over the weekend. Science, like the tech industry, relies heavily on the intellectual prowess of immigrants. By some estimates, more than half of US post-graduate work in so-called STEM fields is done by international students. "That’s the way science is set up, you want the best—you don't care whether they are American or Iranian, you want the best," Edraki says. Indeed, he is part of a small seven-person lab comprised entirely of international students. The only American-born member of his lab is the leader, Erik Sontheimer.

"This is horrible. It's reprehensible. It's counterproductive. It makes no sense," says Sontheimer. Like many professors who took to Twitter this weekend to express their dismay, Sontheimer believes this ban will hurt America's ability to attract and keep talented people. "It's going to have a very detrimental effect well beyond the seven specific countries named in the order. I think there will be strong disincentives for even Europeans to come here. They may just decide that this is not the kind of country that they want to be in for that long."

Universities and colleges across the US have come out in condemnation of Trump's ban because of this threatened brain drain, from Harvard to the University of California. Former Republican governor of Indiana Mitch Daniels, now the president of Purdue University wrote: "The President's order related to immigration is a bad idea, poorly implemented, and I hope that he will promptly revoke and rethink it."

One scientist who wasn't able to join the protests this weekend was Mehrdad Hariri, a Canadian-Iranian dual citizen who runs a science policy association in Canada. He's now blocked from entering the US. Reached by phone, he explained that he had planned to travel to the American Association for the Advancement of Science conference, the biggest science conference in the world, taking place in Boston in two weeks. This will be the first time in eight years that he's missed it.

Scientists affected by Trump’s ban can take grim comfort in one fact: Knowledge is portable.

At least Hariri wasn't already in transit when the order was issued, unlike Suha Abushamma, a Sudanese-born doctor who works at the Cleveland Clinic. Pro Publica reports that on Saturday night she was forced on a plane back to Saudi Arabia where she had been visiting family—moments before the American Civil Liberties Union won a temporary stay that would have prevented her deportation. For at least the next 90 days, she won't be allowed back. Or Samira Asgari, an Iranian doctor who was supposed to start work at Harvard this week but was turned away–at a time when the Association of American Medical Colleges says the US is facing a shortage of doctors. Her story went viral over the weekend.

But for every Asgari, the lives of so many more immigrants have been quietly interrupted or thrown into chaos. There's Bassam (Sam) Al-Mohamadi, a Yemeni engineering student on an F1 visa finishing his senior year at Minnesota State University—Mankato. His mother called him on Saturday to say she feared she could not come to his graduation in May now. "I have not seen my Mom since 2012. I have not seen any of my family," he says.

Al-Mohamadi has a job lined up in Los Angeles when school is over. He is legally able to work because he has applied for Temporary Protected Status due to Yemen's ongoing civil war, but he has no idea whether the Trump administration will grant it. And like Edraki, he is now stuck.

"It’s a weird feeling to feel like you’re locked in," he says. "But whatever this is right now going on in this country, it’s still not as bad as civil war back home, as bombs are falling all around my family there."

The list goes on, as does the likelihood of the US losing out on the world's top talent. Reza Kahlor, a green card-holder, is an Iranian scientist at Harvard who before this week was deciding between applying for professorships at top US universities or starting a company in Boston based on his biological discoveries. But if this ban restricts his ability to travel, he says he'd maybe rethink and go to Germany, or France, or Canada. That would be one less entrepreneur the US gets to claim as its own, one less potential discovery that could turn into an industry-changing technology that could generate jobs. But scientists affected by Trump's ban can take grim comfort in one fact: Knowledge is portable.

"Let’s say tomorrow Trump shows up at my door and kicks me out. I will leave the country with what matters most: what I have in my head. They can take my house, but they can’t take my brain away from me," says Edraki.

That is little comfort for Edraki in the face of what they actually can take away: his brother. Two years ago, Edraki's younger sibling came to the US to study engineering at UMass-Amherst. He turned down better schools on the West Coast because their mother was happy knowing the brothers were near each other. Like Edraki, his brother is a model student. He flew to Dubai for the Christmas break to see their parents. He now can't re-enter the US to finish spring semester of his sophomore year.

"He is devastated. My mom said he hasn't eaten anything since last week," Edraki says. Ironically, Trump himself in 2015 seemed to sympathize with the likes of Edraki and his brother, tweeting, "When foreigners attend our great colleges & want to stay in the U.S., they should not be thrown out of our country." Today the Trump White House is telling Edraki to take his intellect and expertise elsewhere.