A bizarre experiment took place in 1907 when American doctor, Duncan MacDougall, tried to measure the weight of the human spirit.

He put the beds of six dying men on an industrial weighing machine and found that one lost three-quarters of an ounce when he died (the other five results were dismissed as unreliable). The experiment has not been successfully replicated under controlled conditions.

Most scientists would say that something you can’t see and can’t measure doesn’t exist. However, discussions about the human spirit (or mind) occupy a surprising number of pages in current journals of psychology and brain science. The problem is, human consciousness is difficult to understand in purely physical terms.  


The Bible differentiates between ‘soul’ and ‘spirit’ in a surprisingly consistent way. The words for ‘soul’ (Hebrew nephesh and Greek psuch) are used for animals as well as humans but never for God or angels, while ‘spirit’ (Hebrew ru’ach and Greek pneuma) is used only for humans, God and angels (with one exception in Ecclesiastes 3:21, which may be quoting a well-known proverb). It is a divine attribute.

The ‘soul’, which we share with animals, could be described as our ‘personality’. It includes emotions, memory and idiosyncrasies. The ‘spirit’ is what makes humans different from animals. It includes a sense of wonderment, the instinct to pray, the conscience, the fear of an imagined future and a longing for ‘something’ that many find fulfilled in God.  

Anthropologists have discovered worship of some kind in every type of human culture, but animals do not exhibit similar behaviour. Although atheism has become a mainstream viewpoint for the first time in the last century, it could be argued that this has left a gap that is filled by other forms of awe, fear and fascination: from the deification of celebrities to the New Age pursuit of ancient rituals. It appears to be difficult to escape Pascal’s God-shaped hole, which the Bible calls ‘eternity in the human heart’ (Ecclesiastes 3:11). It is part of being human.  


Is the spirit something physical? Conceivably, all of our human characteristics could be housed in our brains without any need for a non-physical ‘spirit’. But if the spirit is entirely physical, this would mean that we do not have true free will because the actions of all physical matter are predictable, in theory at least. If we really can make decisions originating in our subconscious and conscious mind that cannot be predicted by outsiders, something non-physical must be involved.  

One way of thinking about this is to ask yourself whether you are as predictable as the balls on a snooker table. Once a player has hit one of the balls, the outcome is a matter of mathematics. The same is true of any set of atoms, and if we had a large enough computer and enough information we could predict what happens in any physical system, including our brains. But if there is a non-physical ‘person’ in your brain, it could move atoms in an unpredictable way. This person would be equivalent to the snooker player. Once he has struck a ball the outcome is predictable, but until then it is unknown. Theologians call that person the ‘spirit’, while philosophers and brain scientists call it the ‘mind’.  


In quantum physics, however, a tiny area of uncertainty has been found, which may account for free will in physical matter. The Heisenberg Uncertainty Principle states that although we can predict exactly where an electron will be or exactly how fast it is moving, there will always be a miniscule amount of approximation when we try to measure both. This gap theoretically allows for free will, because it means it is impossible to predict exactly what will happen. So perhaps the human spirit could be non-physical because it could potentially make decisions in the brain without breaking any laws of physics.  

This solution to the problem of free will in a physical brain has two potential problems. First, some theoretical physicists (such as John Polkinghorne, a keen Christian) say that the Uncertainty Principle will turn out to be an illusion because there are yet-undiscovered laws at work. Second, some neurologists (such as Peter Clarke, also a Christian) point out that the tiny amount of uncertainty isn’t sufficient to fire a signal in the brain. (See more at bit.ly/1AtDv7d). This is an ongoing area of research.  



The Bible implies something much more exciting about the human spirit: that it connects us to God. Animals and plants have a body, animals have a soul and angels have a spirit, but humans are the only beings that have all three (Hebrews 1:14; 1 Thessalonians 5:23). This Trinitarian nature of our make-up could be dismissed as coincidence, but it is our spirit that creates an interface between us and God. David found that the Holy Spirit enabled him to enjoy the presence of God (Psalm 51:11), and Isaiah spoke about ‘desiring’ God with his soul and ‘seeking’ God with his spirit (Isaiah 26:9).  

So, is the human spirit just a communication system, or does it also house personality? Is our sense of humour, for example, due to something in the spirit or something in the brain? We know that emotions are greatly influenced by internal chemicals such as serotonin, and by external chemicals such as cocaine. We also inherit emotions from our genes and culture; for example, people who laugh easily tend to have parents who laugh a lot.  

So where is the person who is ‘me’? In my body or in my spirit? The Bible implies that it is in both, because God would not need to give us resurrection bodies if our ‘person’ was completely independent of matter.  

When we put neurology and theology together, we find out a great deal about ourselves. We aren’t just physical; there is a non-physical part of us that may explain how we can have true free will. But we are also made up of a body and emotions, and the totality of who we are is bound up with that physical body.  

Our resurrection bodies, without our weaknesses and imperfections, will be very different. However, Jesus implied that we will still recognise our friends (Luke 16:9), so presumably we will still have the characteristics that make us the people we are.

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