(CNN) — About 41 years ago, a man said he was abducted by a UFO while returning home from work in Arizona.

His name is Travis Walton, and he reappeared five days after his alleged abduction on November 5, 1975.

He's just one of the people featured in the upcoming photo book, "Phenomena," which is an investigative look into American beliefs about UFOs and aliens. The book is a project by Danish photographers Peter Helles Eriksen Sara Galbiati and Tobias Selnaes Markussen

"We just had a mutual interest in it," Galbiati said. "Not as us being believers and talking about how we believe in UFOs, but more in that we thought that it was interesting that there was this group of people that believes so much in this that they see the world completely different than the majority."

All of the images were shot last year in Arizona, New Mexico and Nevada, including Area 51 , the remote U.S. Air Force facility near the small Nevada town of Rachel.

Photographers Peter Helles Eriksen, Sara Galbiati and Tobias Selnaes Markussen

Galbiati said each area they went to has some sort of significance or meaning. Phoenix, for instance, is where an alleged UFO sighting known as the Phoenix Lights was reported on March 13, 1997.

"In Denmark or in Europe, it's kind of taboo: If you believe in UFOs, you keep it to yourself. It's not something you go around talking about, because the majority will think that you're kind of mad," Galbiati said. "But in America, especially, of course, the places we went, it was more like an understanding -- 'If you believe in this, I'm not going to question you.' It's almost like a religion -- 'I won't judge you, everybody has their right to believe in what they want.' "

Open to telling their stories

Galbiati, Eriksen and Markussen were pleasantly surprised at how many people let them into their homes and were open to sharing their stories. She said the three of them approached this project with openness. They were not out to ridicule or make fun of anyone for their beliefs. They were simply out to investigate a subject they had a "genuine curiosity" in.

"I can't tell somebody who's telling me a personal story about how they were abducted that it's a lie, because I wasn't there," Galbiati said. "And if that's what they believe and that's what they say they believe, I'm not going to tell them they're wrong."

The first night is documented in photo No. 5 of the gallery above. In it, a man holds a crystal pendulum during a group meeting about UFO and alien experiences.

"We thought maybe there would be like two people at this event, maximum. We thought this would be very small," Galbiati said. "But there were like 15 people there, so actually it was a big event. And people just told all kinds of stories. ... (It was) like we stepped into another world. A world we never knew of."

Galbiati said this project made them realize just how many conspiracies and theories exist within this community.

Some people they met, for example, believe that there are "35 different races" of aliens. Some said they think aliens are here on Earth, collaborating with our governments. And whether the aliens are friendly creatures or not is also up for debate.

"Some think that their agenda is not friendly, and some think that they're just here to protect Earth and the reason why they're here is actually to protect us from ourselves because we're a destructive race -- we made the atomic bomb, we made things that we can't quite control," Galbiati said. "So they're actually kind of afraid of what we would do with our Earth and the universe."

The name of the photo book stems from the idea that there is a phenomena of some kind that does exist. It might not be a physical one, but it is a commercial and social one, Galbiati said, noting the tourism, conspiracies and groups that make up this particular community.