alk to almost any doctor or scientist about near-death experiences, and chances are they will look at you like you just started jabbering about how aliens in flying saucers are recording your thoughts with the aid of undetectable transmitters implanted in your brain.
The conventional view is that anything you're able to remember and talk about is caused by the firing of specific neurons in the brain. Thousands of careful experiments over the past 100 years have demonstrated that memories are biochemical changes in the synapses that transmit signals between neurons. Even if it were possible to be outside of your body, according to this materialist view, there is no way you could possibly remember what you experienced, because there would be no way for those synaptic changes to occur. In this respect, the brain is a machine like the human body or the computer under your desk: if the physical processes that create memories don't happen, the memory isn't stored, there is no way to retrieve it, and there is no mechanism by which you could tell us about it.
Religious people might call this materialist dogma, but it's not; it's where the evidence has led us. Anyone who does the experiments will get the same results. If you block those biochemical processes, the memory is gone. If we are going to call ourselves rational beings, we have to accept that observations and measurements represent the real world. Of course, anyone is free to make new measurements and present new evidence. If you can make a repeatable observation about what happens after you're dead, scientists will have to believe you. The catch, of course, is that you would have to be alive to tell them about it. The other catch is that there has to be some way for someone else to verify the observation. Well, no one ever said that doing science was easy.
A non-materialist viewpoint has a strong appeal. If perceptions and memories could exist without a physical substrate, it would mean that we and our loved ones would never really die. We would just depart the body and go elsewhere. Much of our culture and religion is based on the idea that there could be billions of spirit-beings, ghosts, and demons all around us that influence our world, and which can be persuaded to work for us by using appropriate incantations. People are reluctant to give up this feeling of power and the comfort it provides.
Science does not say any of this is impossible. But so far, the evidence suggests that the world simply does not work this way.
Believe it or not, the ancient Buddhists said much the same thing as modern science. The Tibetan Book of the Dead, which was an instruction manual that was supposed to be read to a recently deceased person, describes a sequence of progressively more terrifying visions of deities that appear to a person after death. These are explained in no uncertain terms as products of the deterioration of the patient's brain:
"Do not be afraid of him, do not be terrified, do not be bewildered. Recognize him as the form of your own mind. He is your yidam [tutelary deity]."
The idea is that, by explaining to the deceased person what is really happening, he or she will be able to avoid making embarrassing mistakes, like wandering into hell or accidentally getting reincarnated as a duck-billed platypus. Of course, the patient at this point is not really paying much attention. At this stage, it is probably too late to give them advice. So the Book of the Dead was really written to help the living.
In Buddhist psychology, the vijnana, the part of the mind we would call the superego, creates a complete universe of its own. Instead of perceiving the real world, it projects images of a world it has created to explain its experiences, like the images on the walls of Plato's cave. These images are said to disintegrate after death, producing the visions that closely resemble those reported by near-death experiencers.
The first week after death, according to the book, the patient is said to enter a realm of dazzling light accompanied by a feeling of peace, like entering a womb. It is a realm filled with gods and goddesses. This is remarkably similar to the descriptions given by Dr Eben Alexander, a neurosurgeon and author of Stereotactic Radiosurgery. In his latest book, he writes about the near-death experience he had while in a coma suffering from bacterial meningitis. He reports having intense visions of shimmering beings, butterflies, and big, pink, fluffy clouds while he lay unconscious and near death.
Although this story and the hundreds like it are fascinating, they are not evidence, because they are not verifiable. Scientists have learned from experience that personal anecdotes and stories, as provocative as they may be, are useless as a source of factual information because they are unreliable. This is not to say that near-death experiences are necessarily imaginary or false, just that there is no known way of distinguishing an anecdote from a made-up story. Sadly, it is a well-documented empirical fact that people are often mistaken in what they see, and they even lie from time to time.
Realistically, if there were an afterlife it's likely to be so far removed from our everyday experience that any description of it would sound like nonsense, as this description does to many people. Our language is specifically designed to talk about real, physical objects. Additionally, anesthesia is well known to create long-lasting cognitive difficulties. Patients often require months or even years for their mental faculties to fully recover from deep anesthesia. So it is perhaps not surprising that descriptions of near-death experiences sometimes sound a bit fuzzy.
The Gautama Buddha (a k a Shakyamuni), the guy who started all this Buddhism stuff, was at first quite specific about the afterlife: nothing of the original person remained after death. One's personality, knowledge, and intelligence were completely destroyed, and all that remained was an almost formless quality that might be called "subjectivity." It seems that this was not very satisfying to his disciples, and the story is that after encountering much resistance he decided it was better to keep his opinions about the afterlife to himself. As time progressed, and the Buddha passed into history, some Buddhist philosophy evolved so that more and more of the personality was said to survive transmigration. This might have helped ancient Indians to explain, in the absence of any knowledge of genetics, how personality traits could be transmitted from ancestors to their descendants. Buddhism may also have taken on these characteristics to broaden its appeal to the masses. Giving people a reason to believe that the personalities of their loved ones and the memories it took a lifetime to acquire could be preserved after death is bound to make your religion more popular.
As the patient's brain continues to disintegrate, according to the Tibetan monks, their psychological makeup becomes more chaotic, as primitive brain regions, expressing fear, hatred, and other emotions, break down and are said to create visions that increasingly resemble the Western concept of hell.
Of course, the patient at this stage is still experiencing phenomena generated by their dying brain, just as Dr Alexander was. What, if anything, happens afterward? Before we can begin to answer this question, we have to know the answer to the question "What is a soul?" —or of you prefer, what is "consciousness." Without understanding what we're talking about, we have no better chance of finding a definitive answer than religion, which historically has finessed the question by falling back on bald assertions backed up by (occasionally brutal) appeals to authority, or, in recent times, raw speculation backed up by personal anecdotes. Neither of these will get us very far.
First, let us be clear about what we are discussing. The word 'consciousness' has many different meanings. Here I am referring to the "subject" in so-called subject-object duality. Consciousness is that property that determines why you are you instead of me. Its most fundamental property is that it defines a specific reference point in time that we refer to as "the present."
To a rock, or to the unconscious universe, there is no particular favored point in time. But for us, the events we perceive as happening to the rock or to ourselves in the past, present, or future differ from each other because our consciousness defines one point in time as being special. Time matters to us because we are conscious, but it is meaningless to the rock, because it lacks consciousness and therefore has no preferred reference frame.
Consider a past version of yourself. This person appears to us in exactly the same way as other people appear to us: as an animated being, whose subjectivity or inner existence is alien and inaccessible, even though we may remember clearly that we were once living as that person. However, if time were not connected in some way to consciousness, you would perceive no fundamental difference between your present self and that much younger and handsomer version.
This connection between time and consciousness is severed when the person dies. So what happens to your consciousness at that point? Does it return to a conscious universe like a drop of water returning to a vast ocean, or does it just snap out of existence like a computer program when the computer is turned off? Maybe the brain is like those old DOS computers, where a program would sometimes start writing to video memory, creating a spectacular display of garbage on the screen right before it crashed, crossing over to the place where all badly written programs go.
To answer this question will take a new branch of science, and a new vocabulary (and probably lots of very complicated mathematics and some very expensive research grants). But there is every reason to believe that science will someday answer this question. And who knows, we may discover that, indeed, there are pink fluffy clouds up there.
I would be remiss in not mentioning what quantum mechanics has to say about the subject. Don't panic, it's really very simple.
For small particles such as photons and electrons, quantum mechanics tells us that measuring some property of the particle changes its behavior. To make a measurement, you have to make the particle interact with a measuring device. Somehow, this causes the particle to stop acting like a wave, which is spread out in space, and instead makes it act like a point-sized particle. This is one aspect of what is called "quantum weirdness."
As we start looking at larger particles, these quantum effects become smaller and smaller. By the time we reach the size of a neuron, quantum effects are so small as to be negligible. Thus, regardless of whatever other weirdness is in there (and it's been conclusively demonstrated that there can be a great deal), it's very unlikely that any quantum weirdness is going on inside our brains.
Making a measurement also means observing something, and for really small things the act of observation changes what is being observed. Some scientists, including Roger Penrose and Henry Stapp, have speculated that this might be a key to understanding consciousness. The majority of physicists are highly skeptical about that, but most think that it could lead to new insights into the nature of matter. In either case, it will be exciting. Cause and effect have not been overthrown yet, and materialism is by no means "dead." But at the smallest levels, particles are definitely doing some weird stuff.
Another scientific theory that relates to life after death is information theory. Information, we have learned from scientists like Claude Shannon, is a real form of energy that has a measurable physical existence. The astounding implications of the discovery that information is a form of energy (known as entropy) are not as well appreciated as they should be. Back in the 1960s, an IBM researcher named Rolf Landauer calculated the amount of heat that corresponds to storing a single bit of information. This so-called Landauer Limit has nothing to do with heat given off by transistors; it is a property of the information itself. It applies when the storage is thermodynamically irreversible, which is to say in the real world, where particles interact with each other. It says that if you have enough knowledge, you could theoretically use the knowledge alone to heat your coffee (or cool it down, since entropy has a negative sign).
If information has a physical and thermodynamic existence, then all that knowledge stored in your brain that makes you you can't just disappear, because information cannot be destroyed. Once we figure out how to relate the inner (subjective) and outer (objective) worlds to each other, we may be able to deduce where the information that comprises the inner world (that part that makes you you) goes, if indeed it goes anywhere.
Thanks to Einstein, we also know if something has energy, it is equivalent to mass. It may be only a matter of time before some ambitious person comes along and gives us a theory that puts all these pieces together to solve the mind-body problem. That is how science progresses: by answering small questions as definitively as possible, one step at a time. The question of life after death won't be solved overnight. But if I were a supreme being, I would place my bets that the humans will figure it out eventually.