At least 21 people associated with the US diplomatic corps in Cuba have been suffering from an array of mysterious symptoms ranging from hearing loss and dizziness to concussions and brain swelling.

After months of investigation, the US determined that a secret sonic weapon was to blame.

But Dr. Joseph Pompei, a former researcher and psychoacoustics expert at the Massachusetts Institute of Technology, says that’s impossible.

He says loud sounds can definitely cause hearing damage, but “the concussions, brain swelling and other symptoms like that have no possibility to be created by sound.” Pompei says the sound would have no way to enter the brain. If the diplomats were exposed to an alarm, 99.9 percent of the sound would bounce off the body.

Pompei says in order for sound to cause internal damage, “somebody would have to be in a large bathtub, covered in ultrasonic transducers at a very high power.” And then that ultrasound would “need to be focused very carefully at their head, and their head would have to be submerged underwater.”

And that definitely did not happen here.

While scientists like Pompei are skeptical, historians have a different view.

The history

Vince Houghton, the curator of the International Spy Museum in Washington, DC, specializes in the history of espionage. He says history is filled with examples of intelligence agencies going to great lengths to mess with diplomats from adversary nations.

Take Operation Mongoose, for example, a secret program of the US to topple Fidel Castro.

“Castro was an avid scuba diver,” explains Houghton. One of the ideas was to put a colorful seashell on the seabed. “And the shell would be so beautiful that Castro would feel compelled to pick it up and look at it, and then it would blow up and kill him.”

Other ideas included lacing the studio where Castro gave his weekly radio address with LSD, so the leader would be so incoherent that he would lose popular support. The CIA also considered sprinkling Castro’s shoes with thallium salts, which would cause his beard to fall out. “The idea was the Cuban people were so machismo that they would no longer want to follow him because he didn’t have his beard,” says Houghton.

But in thinking about sonic weapons that could potentially cause lasting damage, maybe a closer corollary comes from the Cold War.

The Stasi, the East German secret police, would use radioactive chemicals to track suspected dissidents, says Anna Funder, the author of the book, "Stasiland."

“They developed radioactive tags, including irradiated pins that they could surreptitiously insert into a person’s clothing, radioactive magnets on cars and radioactive pellets in tires,” she says.

The Stasi would also break into suspects' homes and spray the floor with scandium-46. When people walked through, the radioactive chemical would stick to their shoes, and they would leave radioactive footprints wherever they went. The Stasi would then follow the suspects through crowds with Geiger counters tucked in their armpits.

So, in a world of spy dust and exploding seashells, a sonic weapon doesn’t sound so far-fetched.

Alternative theories

But for Houghton, some of the specifics of the alleged Cuban sonic weapons plot don’t add up.

“The Cuban intelligence agency is very good, but they don’t have a ton of resources,” he says. And no doubt, developing a sophisticated sonic weapon would require a lot of cash.

“That said, they have some very rich friends.”

Houghton suspects the Russians are behind this latest incident.

He thinks the most likely scenario is that this was a beta test of new Russian technology that went bad. He says the Cubans have no incentive to cause American diplomats permanent damage. "They were probably like, 'Let’s just make the [Americans] throw up,' and then, "Oh wow, whoops!" It went way too far."

There are other theories floating around, too — that it wasn’t a sonic weapon at all, but maybe a virus, poison or radiation.

“I mean, we have no proof of any of this,” says Houghton. “But it’s fun to speculate.”