How do we know what is real? This is a question that has occupied philosophers and scientists for as long as we humans have been pondering the nature of reality.
I don't pretend to know the answer, but I resonate with physicist David Deutsch's approach to the question. In his book, "The Fabric of Reality," Deutsch views explanations as being key to understanding what is real. He writes:
Explanations are not justified by the means by which they were derived; they are justified by their superior ability, relative to rival explanations, to solve the problems they address. That is why the argument that a theory is indefensible can be so compelling. A prediction, or any assertion, that cannot be defended might still be true, but an explanation that cannot be defended is not an explanation.
Now, I realize that this quote isn't exactly crystal clear. Which is understandable, because Deutsch's scientific world view isn't reducible to a couple of sound bites. But I'll try to do just that with another nibble at his philosophical perspective regarding understanding.
What is an explanation, as opposed to a mere statement of fact such as a correct description or prediction?
In practice, we usually recognize the difference easily enough. We know when we do not understand something, even if we can accurately describe and predict it (for instance, the course of a known disease of unknown origin), and we know when an explanation helps us to understand it better.
But it is hard to give a precise definition of 'explanation' or 'understanding'. Roughly speaking, they are about 'why' rather than 'what'; about the inner workings of things; about how things really are, not just how they appear to be; about what must be so, rather than what merely happens to be so; about laws of nature rather than rules of thumb.
They are also about coherence, elegance and simplicity, as opposed to arbitrariness and complexity, though none of these things is easy to define either.
Deutsch uses Galileo as an example of how mere prediction is much different from genuine understanding. He says that at first Galileo didn't get into trouble with the Catholic Church even though he promoted a sun-centered (heliocentric) view of the heavens. The reason: the Church viewed Galileo's theory as just a way of predicting the motions of the planets.
Thus the Church was able to keep on believing that the Earth was at the center of the cosmos by considering that the planets behaved as if they orbited the Sun, not that they actually did so.
To our modern sensibilities this doesn't make sense. But we live in scientific times that are far different from the religion-dominated era of Galileo.
Deutsch says that one reason the sun-centered view won out was that the Church's perspective required a belief in everything that Galileo taught (because that was how fairly accurate predictions of planetary motions could be made), plus an additional belief that somehow reality was responsible for making it seem as if the sun was at the center of the cosmos, even though it actually wasn't.
For example, if one were asked why a planetary conjunction occurred on such-and-such a date, or why a planet backtracked across the sky in a loop of a particular shape, the answer would always be 'because that is how it would look if the heliocentric theory were true'.
So here is a cosmology -- the Inquisition's cosmology -- that can be understood only in terms of a different cosmology, the heliocentric cosmology that it contradicts but faithfully mimics.
Religions obviously fail to produce the same sorts of understandings about reality that science does. In fact, it is difficult, if not impossible, to come up with a single fact about the world that any religion has produced that science didn't already know.
This is a major stumbling block for those who consider that religion has a privileged view of reality. If this is the case, why hasn't a saint, prophet, or other holy person ever come up with an explanation of some phenomenon that was so persuasive, that explanation eventually came to be added to the world's common store of knowledge?
Here's one reason: religion deals largely with supernatural entities that lack what David Deutsch calls "kick back." This term is derived from the story of Dr. Samuel Johnson responding to Bishop Berkeley's solipsistic view that matter doesn't really exist by kicking a rock and saying, "I refute it thus."
Philosophers correctly point out that Johnson didn't really refute Berkeley's assertion by kicking the rock. Rather, Deutsch uses this episode to point out a criterion for reality:
But Dr. Johnson's idea is more than a refutation of solipsism. It also illustrates the criterion for reality that is used in science, namely, if something can kick back, it exists. 'Kicking back' here does not necessarily mean that the alleged object is responding to being kicked -- to being physically affected as Dr. Johnson's rock was.
It is enough to say that when we 'kick' something, the object affects us in ways that require independent explanation. For example, Galileo had no means of affecting planets, but he could affect the light that came from them. His equivalent of kicking the rock was refracting that light through the lenses of his telescopes and eyes.
The light responded by 'kicking' his retina back. The way it kicked back allowed him to conclude not only that light was real but that the heliocentric planetary motions required to explain the patterns in which light arrived were also real.
I was a religious believer for about thirty-five years, so I'm intimately familiar with the many ways people convince themselves that God, Jesus, a guru, angels, spirit, or some other form of divinity is "kicking back' within their consciousness.
Prayers seem to be answered. Unusual events are viewed as miracles. Sights and sounds are perceived in meditation. God is viewed as working in mysterious ways that are plainly apparent to believers.
Yet there is scant evidence that any of this adds up to reality "kicking back" with evidence of a supernatural realm. If there were, converted atheists like me wouldn't be so skeptical of religious claims that fail to stand up under not only close scrutiny, but any kind of serious examination.
Science progresses with its understandings of the universe. Religion doesn't. This alone points to the failure of religious believers to demonstrate that reality does indeed "kick back" when someone attempts to understand divinity.
Yes, all sorts of phenomena do transpire within the minds of believers. However, almost certainly this is their own psyches kicking back against themselves. Meaning, religious beliefs result in mental phenomena produced by those same beliefs. This isn't the sort of really real reality that Deutsch, along with along scientists, are looking for.
Me neither. I'd much rather know something demonstrably true about the world, even if this is a small thing, than believe in the grandest religious fantasy.