One of my favourite experiments from the world of quantum science is the double-slit experiment and, amazingly, it seems to confirm what shamans have been telling us for years: that reality really is what we make it.

Firstly, the experiment. Imagine a photographic plate that records when light touches it. A short way in front of this is a board with two vertical slits cut into it. A short way in front of that is a light source. When the light shines through the two slits, the pattern it makes on the photographic plate will comprise several vertical lines of light with darker patches in between. This is because light travels as a wave and, as it passes through the two slits, it is broken up before meeting again on the other side. This is rather like two ripples meeting on a pond. Where the converging waves form a peak, it registers as a light patch on the photographic plate and where the waves form a trough, it registers as a dark patch. So the effect of shining light through two slits is to cause a striped effect on the photographic plate.

Now things get odd. By using a machine capable of shooting only a single photon of light – the smallest unit of light there is; think of it like a bullet – and using it to fire many discrete photons over time, we would expect the photographic plate to register two vertical lines of light. This is because each separate photon can only pass through one single slit before hitting the photographic plate. Over time, some photons will go through both slits and two lines should form on the photographic plate. But that’s not what happens. Instead, the pattern recorded by the photographic plate is the same as when waves of light passed through the slits. That, realised the researchers, is impossible.

Somehow, the single photon of light divides before passing through the slits, making itself into a wave. Except that photons can’t physically divide in this way. Something else is happening. Scientists decided to investigate further and put small sensors just before the slits, trying to find out what happened to the photon. Remarkably, the result was now totally different and the photographic plate registered two lines of light as expected; the photons when observed behaved like normal photons. The implications of this are profound.

To sum up: photons of light act like a wave (which is impossible), unless we try to watch them do it, when they act like normal photons. Again and again the researchers got the same results. And there was no cheating; the photons always knew they were being watched. So what exactly is happening?

Now things get really odd. We know that the photon, in acting like a wave, cannot divide and so it must therefore replicate itself and, effectively, be in two places at once. This turns the photon into a wave. But not if we’re looking at it, in which case the photon can be in only one place and acts like a normal photon. It seems that we can determine whether and where something exists merely through observing it. As Einstein said: how do we even know that the moon exists unless we are looking at it? You can see why this is starting to look a little shamanic; we can determine where the photon exists and the outcome of the experiment purely through our intention: whether we observe it or not. That’s what shamans would tell us: our intention determines the outcome. But there’s more.

Some scientists do not believe that the photon replicates itself when it acts like a wave but that the entire universe replicates itself and there become many slits that a single photon can pass through, leaving the tell-tale wave pattern on the photographic plate beyond. So this experiment – providing we don’t directly observe it happening – shows a continuing process whereby the universe – our reality – consistently and continuously replicates itself into an almost infinite number of possibilities. The double-slit experiment just catches it at it.

That means that every time there is a change in our world (and there must be a finite number of changes but it’s a pretty gargantuan number) the universe replicates and the future will be different in each. But can we determine how it replicates and, in effect, which future we chose to experience? Shamans would say, yes, we can, and this is what they have been telling us for years. We can make our own destiny through our intention or, to use a phrase from the Shuar of South America: the world is how we dream it. Scientifically speaking, what this actually means is deciding which version of the universe you want to move into as it replicates and which you want to leave behind. Despite the double-slit experiment, scientists would be cautious and pronounce this impossible. But is it?

When you decided to read this blog, another you – now in a different universe – decided not to and is now doing something else (maybe that was a sensible move). Over your lifetime, there must be zillions of universes with you living different lives in each. If we return to the example of the photon of light, what is most important is that you didn’t replicate into two on each occasion but that the universe did. That means that you are the same in every single universe where you exist. But where does this leave your consciousness, the bit of you that looks around and believes that what you see is the only reality that exists? Where does that reside?

Perhaps we have only one consciousness but with many parallel lives. The immediate reality around us now swamps our senses until we believe that this is all there is. Maybe that happens in every life we are living. But if we use techniques that expand our usual consciousness – just as shamans do – then maybe we can connect to our other lives and access an almost limitless wellspring of information and knowledge. This may be why some people can predict the future, why some people can remember past lives, why some are telepathic, and others (such as shamans) seem to have access to information they could not possibly know under everyday circumstances. There is no trick; they are merely accessing information from the almost infinite lives they are living in different universes.

We must be careful not to run away with the science (and I am the first to admit that I am fond of doing so) but, as the scientists studying the nature of reality consider stranger and stranger possibilities, perhaps it is time to ask those other masters of reality: the shamans, who may just quietly nod and say, yes, we knew it all along.

I think, therefore I am. Rene Descartes was onto something writing that line since it is our ability to recognise our consciousness that makes us human; the only species that science considers capable of such a feat.

All other animals are aware of things in the world but not of a past or a future, and certainly not of themselves as a conscious being. Scientists call this ‘primary consciousness’. Humans, by contrast, are aware of both past and future, as well as having an awareness of ourselves as conscious beings. Scientists call this ‘higher-order consciousness’. An awareness of ourselves is probably one of the most basic facts that ever confronts us – I think, therefore I am – and yet asked to describe consciousness, most people come unstuck. Is my consciousness like yours? If my computer can be programmed to recognise it’s own existence, would it have self-consciousness? Can consciousness survive remote from the body and, if it can’t, does that mean it can be located within the body? Explaining consciousness is at the very limit of our ability.

Our consciousness is rather like the stage where all other thoughts and actions take place. It is both our ego and our subconscious. All our thoughts arise from our consciousness. It is like our personal repository of wisdom.

For most people, consciousness is a single state that is constant and unchanging. Besides dreaming sleep (which is often dismissed as irrelevant), consciousness is what defines people as awake, alert, and able to function in the world. There are other states of consciousness, however. Trance, for example, is every bit as real as the usual state of consciousness but is all but ignored in our modern world. Shamanic communities, by contrast, consider altered states are as real as anything in this world and, what’s more, they can be incredibly useful.

When in altered states of consciousness, many shamans describe journeying to an otherworld and interacting with the spirits that reside there. These spirits impart help and information to the shaman that seem to be beyond anything he or she could have learned in any other way. This can include premonitions, remote viewing, or gaining information about events at which the shaman was not present. It seems that being in an altered state of consciousness allows the shaman access to other sources of knowledge. Similarly, many shamans describe working with teacher plants. The shaman ingests the plant to effect an altered state of consciousness and then learns directly from the plant itself. Shamans revere these plants as teachers. But just where does this information come from?

It would be easy to conclude that the shaman accesses scraps of knowledge buried deep in his or her unconscious and then puts them together to form a coherent whole. But this does not come close to explaining how shamans obtain the depth of knowledge or the level of detail that they do. Some of the information that they bring back from the otherworld is so precise and specific that it could never have arisen from the shamans themselves.

There is another possibility. Consciousness may not be something that humans have but something that we have access to. Instead of our minds holding knowledge, perhaps they are like antennae receiving and filtering an external source of knowledge. Rather as a radio receives signals, then unscrambles them to provide music and speech, so our minds also receive signals, unscrambling only those parts we need. Since the knowledge we could potentially access is unlimited, our minds work hard filtering this information to provide only what is relevant.

When we enter an altered state of consciousness, this filter breaks down and our minds now receive vastly more information than before. We can tap into sources of wisdom that usually lie beyond our reach, and we can communicate with plants, animals, and everything else around us. To access an altered state of consciousness is to remove the filter of our mind and plug ourselves into the seething mass of information that always surrounds us but that we usually tune out. For someone unused to this realm, such as an individual experimenting with hallucinogenic drugs, the experience can be mind-blowing. There is sensory and information overload. Shamanism is a means of controlling the flow.

Could it be that animals also have a higher-order consciousness but that their mind filters are set to receive only what they need to survive? And if that is true of animals then what about plants, trees, even my computer. Shamans argue that everything has a spirit and for spirit, we could read self-consciousness. To connect, however, we need to go to a place where the filters are removed and we can interact freely: an altered state of consciousness. Maybe animals do this all the time and we are just unaware of it.

Ultimately, there is no limit to the wisdom we can access or to the knowledge we can hold. If we remove the filter of our mind then the entire universe becomes knowable. If this sounds a little like obtaining the wisdom of God, perhaps it is. God may be the sum of all wisdom: He (or she) thinks, therefore he (or she) is.

Although shamanism takes many and varied forms around the world, what a shaman actually experiences whilst in trance is remarkably uniform. Almost all report leaving their bodies to journey to an otherworld where they meet and interact with spirits. The reason for such similarity lies within the mind itself and the shared neurobiology of every human. In fact, any one of us could have the same experience as a shaman if we put ourselves in trance.

Shamans have varied ways of entering trance but all attempt to slow brain waves from a beta state, the usual rhythm, through an alpha state (which corresponds to light meditation or engrossment in an activity), to a theta state or trance. Whereas some shamans might stay very still and concentrate on breathing or praying, others move about in frenetic dances or whirl like Dervishes. Both types of activity, paradoxically, lead to trance.

The reason for this paradox relates to the way our brains regulate our bodies. The ‘sympathetic system’ of brain activity reacts to external stimuli. It creates arousal in the body through pleasure or pain. The ‘parasympathetic system’ manages automatic processes such as breathing, sleeping, and digesting. It tends towards quiescence, that is, complete still and calm. The two work in opposition and keep our bodies in balance. Is it possible, however, to push either system to extreme. If we undertake physical activities that lead to hyper-arousal, we load the sympathetic system and the activity completely takes over so that we begin to lose ourselves in a state of flow. Similarly, if we undertake activities that lead to hyper-quiescence, we load the parasympathetic system and the mind begins to empty and turn inward.

Beyond hyper-arousal or hyper-quiescence lies a further state, where one system, usually quite separate, overflows and begins to spill over into the other. With hyper-arousal, this happens when our strenuous activity brings waves of tranquillity and stillness, such as the sensation after vigorous sex. The sympathetic system has overflowed and feelings now arise from the parasympathetic system. Similarly, with hyper-quiescence, there can be a point where deep meditation brings a rush of energy that quite overwhelms us. The parasympathetic system has overflowed and feelings now arise from the sympathetic system. In both cases, when one system overflows into another and our feelings no longer correspond to our actions, we experience an out-of-body sensation that is at the heart of shamanic trance.

Many shamans report that gravity no longer tethers their bodies to the earth and they can fly through the air with little effort. Since the active neurons in the brain at this stage of trance have a spiralling tendency, a tunnel opens up before them, formed entirely within the eye retina itself. Shamans recognise this as a portal to the otherworld and they leave their physical bodies behind to travel down it. Limbs might grow longer or detach from the body as the perception of being in a physical form diminishes. These are the first signs that self-identity is breaking down as the overflow of the sympathetic and parasympathetic systems of the brain excludes any outside stimulus. The mind turns entirely inward. This overflow also causes a leaking of imagery from the unconscious mind into the conscious and, as the shaman steps out of the tunnel and enters the otherworld, they find themselves in a startling new reality.

The disintegration of the self continues and some shamanic communities now speak of terrible violence inflicted upon the body. This self-generated fear response stems from the over stimulation of the amygdala, a bunch of neurons that are responsible for orientating the body in space. When a shaman drums and dances with frenzied intensity, the amygadala starts to malfunction and this causes waves of fear, heightening the expectation of violence. Alternatively, with less frenzied activity, it may provoke feelings of religious awe.

Hallucinations start and one of the most common entities to appear is an animal. Scientists call this ‘zoopsia’, whereas shamans call them spirits. Although hallucinations arise from the preconscious part of the brain, there appears to be a definite pattern to them. Jung calls these archetypes and the ‘wise teacher’ seems a particularly prevalent example from many cultures.

Since the body is losing its self-awareness, it appears to someone in trance that knowledge comes from a point outside the mind. Coupled with zoopsia it is not surprising that many shamans speak of guardian or power animals being a rich source of otherworldly wisdom: the wise teacher. Since the unconscious mind is leaking into the conscious mind, much of this wisdom might also appear novel and new.

It is not always an animal that fulfils the wise teacher archetype but it could also be another human, either living, dead, or entirely mythical. Seeing the dead whilst in trance may reveal the origin of belief in an afterlife and the survival of the soul after death. Many shamans speak of contacting their deceased ancestors whilst in shamanic trance.

As the self breaks down, there is a corresponding sense of unity with the rest of existence; there is no longer any individual identity. This may mean a person merges with whatever appears in front of them, such as their animal guide. Shamans often describe turning into an animal’s form and they call this shapeshifting. Others feel that they are one with the universe, as if all existence connects at this higher level. Everything appears to pulsate with energy and contain its own life force, giving rise to ‘animism’, the shamanic belief that all things are alive.

Eventually, any lingering sense of the self disappears entirely and all thoughts and experience appear to emanate from outside the body. Some discern an ultimate authority at this point; a controlling influence that lies beyond human existence and possibly beyond the world itself. It is not difficult for them to put a name to this supreme being: God.

The neurobiology of the human mind explains the similarities that underpin shamanism (and possibly all religions) around the world. Shamans see what they do because of their minds. Whether the otherworld and its spirits are merely hallucinations or are actually real is less easy to determine. That, like most other aspects of religion, is entirely a matter of individual faith and belief.