A fellow at New York City's Weill Cornell Medical Center, Dr. Sam Parnia is one of the world's leading experts on the scientific study of death. Last week Parnia and his colleagues at the Human Consciousness Project announced their first major undertaking: a 3-year exploration of the biology behind "out-of-body" experiences. The study, known as AWARE (AWAreness during REsuscitation), involves the collaboration of 25 major medical centers through Europe, Canada and the U.S. and will examine some 1,500 survivors of cardiac arrest. TIME spoke with Parnia about the project's origins, its skeptics and the difference between the mind and the brain.

When your heart stops beating, there is no blood getting to your brain. And so what happens is that within about 10 sec., brain activity ceases - as you would imagine. Yet paradoxically, 10% or 20% of people who are then brought back to life from that period, which may be a few minutes or over an hour, will report having consciousness. So the key thing here is, Are these real, or is it some sort of illusion? So the only way to tell is to have pictures only visible from the ceiling and nowhere else, because they claim they can see everything from the ceiling. So if we then get a series of 200 or 300 people who all were clinically dead, and yet they're able to come back and tell us what we were doing and were able see those pictures, that confirms consciousness really was continuing even though the brain wasn't functioning.

How does this project relate to society's perception of death?

People commonly perceive death as being a moment - you're either dead or you're alive. And that's a social definition we have. But the clinical definition we use is when the heart stops beating, the lungs stop working, and as a consequence the brain itself stops working. When doctors shine a light into someone's pupil, it's to demonstrate that there is no reflex present. The eye reflex is mediated by the brain stem, and that's the area that keeps us alive; if that doesn't work, then that means that the brain itself isn't working. At that point, I'll call a nurse into the room so I can certify that this patient is dead. Fifty years ago, people couldn't survive after that.

How is technology challenging the perception that death is a moment?

Nowadays, we have technology that's improved so that we can bring people back to life. In fact, there are drugs being developed right now - who knows if they'll ever make it to the market - that may actually slow down the process of brain-cell injury and death. Imagine you fast-forward to 10 years down the line; and you've given a patient, whose heart has just stopped, this amazing drug; and actually what it does is, it slows everything down so that the things that would've happened over an hour, now happen over two days. As medicine progresses, we will end up with lots and lots of ethical questions.

But what is happening to the individual at that time? What's really going on? Because there is a lack of blood flow, the cells go into a kind of a frenzy to keep themselves alive. And within about 5 min. or so they start to damage or change. After an hour or so the damage is so great that even if we restart the heart again and pump blood, the person can no longer be viable, because the cells have just been changed too much. And then the cells continue to change so that within a couple of days the body actually decomposes. So it's not a moment; it's a process that actually begins when the heart stops and culminates in the complete loss of the body, the decompositions of all the cells. However, ultimately what matters is, What's going on to a person's mind? What happens to the human mind and consciousness during death? Does that cease immediately as soon as the heart stops? Does it cease activity within the first 2 sec., the first 2 min.? Because we know that cells are continuously changing at that time. Does it stop after 10 min., after half an hour, after an hour? And at this point we don't know.

What was your first interview like with someone who had reported an out-of-body experience?

Eye-opening and very humbling. Because what you see is that, first of all, they are completely genuine people who are not looking for any kind of fame or attention. In many cases they haven't even told anybody else about it because they're afraid of what people will think of them. I have about 500 or so cases of people that I've interviewed since I first started out more than 10 years ago. It's the consistency of the experiences, the reality of what they were describing. I managed to speak to doctors and nurses who had been present who said these patients had told them exactly what had happened, and they couldn't explain it. I actually documented a few of those in my book What Happens When We Die because I wanted people to get both angles - not just the patients' side but also the doctors' side - and see how it feels for the doctors to have a patient come back and tell them what was going on. There was a cardiologist that I spoke with who said he hasn't told anyone else about it because he has no explanation for how this patient could have been able to describe in detail what he had said and done. He was so freaked out by it that he just decided not to think about it anymore.

Why do you think there is such resistance to studies like yours?

Because we're pushing through the boundaries of science, working against assumptions and perceptions that have been fixed. A lot of people hold this idea that, well, when you die, you die; that's it. Death is a moment - you know you're either dead or alive. All these things are not scientifically valid, but they're social perceptions. If you look back at the end of the 19th century, physicists at that time had been working with Newtonian laws of motion, and they really felt they had all the answers to everything that was out there in the universe. When we look at the world around us, Newtonian physics is perfectly sufficient. It explains most things that we deal with. But then it was discovered that actually when you look at motion at really small levels - beyond the level of the atoms - Newton's laws no longer apply. A new physics was needed, hence, we eventually ended up with quantum physics. It caused a lot of controversy - even Einstein himself didn't believe in it.

Now, if you look at the mind, consciousness, and the brain, the assumption that the mind and brain are the same thing is fine for most circumstances, because in 99% of circumstances we can't separate the mind and brain; they work at the exactly the same time. But then there are certain extreme examples, like when the brain shuts down, that we see that this assumption may no longer seem to hold true. So a new science is needed in the same way that we had to have a new quantum physics. The CERN particle accelerator may take us back to our roots. It may take us back to the first moments after the Big Bang, the very beginning. With our study, for the first time, we have the technology and the means to be able to investigate this. To see what happens at the end for us. Does something continue?