The other day my friend Miki and I got into a debate over whether there is such a thing as an "objective reality." She was telling me about a discussion about altered states of reality in her Antro class.
Example: In order to pass into adulthood, males in a certain Native American tribe went out into the wilderness, in solitude, to fast until they entered an 'altered state of reality' in which they have visions which tells them something about themselves.
Another example: this certain other group of people built granaries, and often people would rest under them for shade. However, termites often eat away at the structures and occasionally the structures would collapse on a person underneath. Despite knowing about the termites, the people still come up with some other reason to satisfy their need of needing meaning in reality, needing to know "why me?".
In both these examples, Miki contends, all that matters is how real the belief is to the believer. Everyone has different beliefs and no one belief is more or less valid than any other as long as the believer finds validity in it. Therefore, everyone experiences "subjective reality," based on each individual's perceptions. In addition, she claimed that science is no more or less valid than any other set of explanations; that is, "starvation-induced hallucination" is as correct as "starving yourself allows you to see a higher plane of existence that can only be detected when you are in that state", just because the latter seems real to that person and that tribe.
If you know me, you won't be suprised to find out that I largely disagreed. To the latter, I responded that what they see isn't telling them anything about a separate, external reality but rather is telling them something entirely about their own internal nature. Put another way, no two people in the same state would agree on what they're seeing; the hallucinations are not real objects on some higher plane of reality. Rather, they're generated by the person's mind even though they are percieved as existing outside the person. Further, psychologists studying phenomenon like this have looked at the brain's activity, and are discovering what happens in a person's brain in one of these alternate states. And with the granaries, what happens is that the termites are busily chewing away at these structures nonstop, and eventually they'll weaken it to a point where it can no longer hold itself up. Since people often rest under these, probability dictates that sometimes the structures will collapse when someone is underneath. Wrong place at the wrong time.
At this point, she replied that while she personally believes that my logic is probably correct, the worldview of science is not any superior to any other worldview and it is entirely possible that some other worldview is more correct than science. Hence, no objective reality.
This cannot possibly be true, and there must be an objective reality in which we all exist. Indeed, we could not possibly exist if there was not an objective reality. Consider color. Look at the trees outside; assuming it isn't fall, the trees are green. Now get a friend and ask what color the trees are, and she will agree that they are green. Two separate people, two separate minds, agree about some property about something that exists external to either mind. Expand this to all other things around you, and you will find that there is a hell of a lot that you both agree about regarding the world around you. Now add a third person, and you will find he also agrees with your observations. Expand this to the entire human population and you will find that almost everyone agrees on almost everything that you previously observed with your one friend. Now I say almost everything and almost everyone because there will be some people who cannot detect the things that other humans can. For instance, some people are color-blind, fully blind, or deaf; obviously they won't agree on things they can't detect in the first place. And further, the things that people disagree on here (remember, we're only talking about physical external environment) are not due to some "alternate reality," but rather are due to some difference in the way they detect the outside environment. While I would agree that, to those people who, for instance, are blind, all that matters to them is what they experience themselves, as that the reality they must navigate in is without light. However, that does not mean they can conclude that there is no such thing as light; they just have no way to detect it. Similarly, just because someone is having some spirtual vision after starving and isolating themselves, doesn't mean that the vision is part of some external reality that someone only in that state can detect. The sheer number of things that so many humans can agree on about the world we live in suggests that there is an objective reality in which we all exist. If there was not such an objective reality, it would be absolutely incredible that any two people could agree on any one thing about the outside world, let alone several billion people agreeing on a near-infinite number of things; even groups of people who have been isolated for a long time from other people can still agree on all of these things. Indeed, it would be suprising that we aren't each our own world.
The central assumption of the science "worldview" is that we all live in an objective reality. If we didn't live in such a single, consistent reality, it should become immediately apparent in the unexplainable inconsistencies in the set of all observations made about one aspect of the world. But this isn't so: we see that things behave very consistently. Science would not exist if this central assumption wasn't true. However, science itself isn't the objective reality. Science is the attempt to describe that objective reality, looking for more consistencies about the external world more obvious than the color of trees. This description of the objective reality is true, on the whole, regardless of anyone's subjective perceptions and beliefs.
My example was gravity: we see that all objects cause all other objects to accelerate toward them in proportion to their masses and the inverse square of the distance between them. Scientists call this phenomenon gravity, and attribute it to a not-entirely-understood phenomenon called the gravitational force. Miki suggested that another worldview might have another reason for why things are that way. At that point, though, the other culture's reason and science's reason are just two names for the same observation. (Until, that is, we find that gravity is related to other things which that culture's explanation doesn't describe.)
My next example was a common plastic cup. We can all agree that it looks like it does, and that it has the shape it does, and science can take atoms and molecules and build them up into such a cup. Miki then said that other cultures may not agree with that. But lets look at a nuclear weapon. Scientists know very well how atomic bombs work, and it depends entirely on the existence of atoms of certain sizes and properties. If I were to detonate an atomic bomb in the village of a culture which doesn't believe in the existance of atoms, their belief wouldn't keep their village from being incinerated and their region from being saturated with lethal levels of radiation in exactly the way our science describes. One's subjective beliefs do not affect the reality they live in. There is an objective, shared reality.
Science however, doesn't depend on human experience and perception for their observations. Science understands that parts of the world are not observable with our limited senses. For example, the light we see by is a select range of frequencies of electromagnetic waves, and color itself is only a result of how our detection apparatus works. Thus science uses nonbiological apparati whose workings we understand very well in the context of the many consistencies science has previously described.
As we all live in the same objective reality, our detection systems all receive the same input from the world. And as we are all humans, our detection systems all function in the same way. Since we all receive the same input, where does the variation come from? Where do our different perceptions arise? The mind. Each one of us has a unique mind which is shaped by numerous factors, including our genes, our prenatal environment and the culture we grow up in, as well as additional experiences we accumulate through our lives. Perception comes from the application of our unique minds to the incoming stimuli from the world. In cognitive psychology, this is called "top-down processing"; that is, we apply our mental structures to the incoming stimuli, which results in perception. Therefore if the stimuli is the same and the perception is different, it arises from our differing mental structures. And if something is in our minds, it's not in the world, regardless of how real something may seem.