Before discussing miracles in detail, it helps to have a firm definition of what exactly "miracle" actually means. The Collins English Dictionary defines it as "an event that is contrary to the established laws of nature and attributed to a supernatural cause." In order for something to qualify as a miracle, it must be more than statistically unlikely; it must be physically impossible without some sort of supernatural intervention.

This definition separates "true miracles" from events that are simply statistically unlikely. These latter events are noteworthy because of their rarity, but they exist within natural laws. For example, a person surviving a disease believed to be terminal only shows that the disease may not be fully understood or that the prognosis was not accurate. Our understanding of the natural world can be modified by new knowledge without needing to throw out our understanding of the laws of the universe entirely.

An Unknown Cause Is Not the Same as Divine Intervention

As a case study of perceived miracles, let’s examine the belief in thunder gods within certain cultures. Throughout history, there have been many thunder gods, spread out across multiple continents and civilizations ⁽¹⁾. In most cases, the god created thunderstorms directly through his actions, whether this meant Zeus throwing lightning bolts or the beating of a thunderbird's wings. Today, when the scientific causes of thunder are well-known, such myths seem absurd and antiquated. At the time, though, believers likely felt that thunder was a miraculous event requiring such divine explanation.

This phenomenon of ascribing supernatural causes to mysterious events is a case of "argument from ignorance" ⁽²⁾. This is a fallacy where a person claims that a statement is true simply because there is no evidence to the contrary, even when there is also a total lack of supporting evidence. The argument takes the form "There is no argument against P, therefore P." In other words, "There is no explanation for this event, so God did it."

Imagine this analogy: let’s say that I claim that the sun runs on trillions of AA batteries. You claim that this is ridiculous. In response, I ask you to explain where the sun gets its energy from. Perhaps you don’t know the answer or assume that no one yet knows the source of sun’s energy. Would it be reasonable to consider this lack of understanding to be proof of my claim? 

Another problem with ascribing supernatural causes to mysterious events is that they are unfalsifiable, meaning that they can’t be disproved. Unfalsifiable claims hold no merit without evidence. For example, there is no way to disprove that there is not a heat-resistant population of giant rhinos living close to Earth’s core. Yet, the inability to disprove such a claim does not make it likely to be true. If a claim is unfalsifiable, the burden of proof for the claim lies on whoever is making the claim.

For any given event without an explanation, an unlimited number of unfalsifiable explanations could be offered, but none of them would necessarily be true. One person might ascribe a miracle to God while someone else claims that space aliens are responsible. Without evidence to back up their claims, these explanations are equally meaningless.

Time and again, events that may initially seem miraculous later turn out to have a reasonable explanation. For example, near-death experiences are often held up as proof of the afterlife. During such an experience, a person may feel as though she is outside of her body, looking down on it, or she may experience the feeling of traveling down a dark tunnel toward a source of light. Some people report hearing the voices of departed loved ones, with these disembodied voices sometimes urging them back away from the light, which some believe may be the afterlife.

These accounts can be compelling and, for the person experiencing them, very real. However, scientific evidence suggests a biological mechanism behind these responses, and the results can be triggered manually by doctors stimulating parts of a person's brain ⁽³⁾.

Just because an event's cause is not immediately apparent or understandable does not mean that it must have a supernatural origin. It might simply mean that more research should be completed to understand it or even that we may never fully understand it.

Many Events Are Inherently Meaningless

The human brain is hardwired to recognize patterns, even in random, meaningless noise. Michael Shermer calls it patternicity in his 2008 Scientific American article, "Patternicity: Finding Meaningful Patterns in Meaningless Noise" ⁽⁴⁾. According to Shermer, this tendency toward identifying patterns and assigning causal relationship is crucial regarding our ability to survive in nature, and it’s something we’ve evolved to do very well. As Shermer explains in a 2010 TedTalk, “[Imagine] you are a hominid three million years ago walking on the plains of Africa, and you hear a rustle in the grass. Is it a dangerous predator, or is it just the wind? Your next decision could be the most important one of your life. Well, if you think that the rustle in the grass is a dangerous predator and it turns out it's just the wind, you've made an error in cognition…but no harm. You just move away. On the other hand, if you believe that the rustle in the grass is just the wind, and it turns out it's a dangerous predator, you're lunch. You've just won a Darwin award. You've been taken out of the gene pool.” This example helps demonstrate how natural selection can favor assigning causality between events ⁽⁵⁾. In a 2008 paper in the Proceedings of the Royal Society B, “The Evolution of Superstitious and Superstition-like Behaviour,” Kevin R Foster and Hanna Kokko conclude that “the inability of individuals—human or otherwise—to assign causal probabilities to all sets of events that occur around them will often force them to lump causal associations with non-causal ones. From here, the evolutionary rationale for superstition is clear: natural selection will favour strategies that make many incorrect causal associations in order to establish those that are essential for survival and reproduction” ⁽⁶⁾.

This type of learning by association is prevalent in all types of animals. In the case of humans, our ability to spot patterns is quite sophisticated. Unfortunately, the brain can also be easily tricked into seeing patterns where none exist (e.g., shapes in the clouds, faces in wood grain or voices in white noise).

We're also quick to attribute meaning to things we experience, even if the event itself is inherently meaningless. As emotional human beings who form strong personal ties to one another and may care deeply for others, we cling to falsely perceived patterns possibly as a way to make sense of both tragedy and success and to, in some way, feel like we have some kind of reliable solution in situations where we sense a lack of control ⁽⁷⁾.

All of this explains why many people are so prone to believe in miracles. It does not make those miraculous experiences true. Without hard evidence to prove both the existence and cause of miracles, such events say little about the existence of God.

Improbable Events Are Not Proof of the Supernatural 

Many people turn to the supernatural when they witness a highly improbable event and consider it to be a miracle rather than looking for a natural explanation. Yet an understanding of basic properties of probability laws shows that even extremely improbable events happen all the time ⁽⁸⁾. There are many examples that show that events with very small probability are not miraculous. In fact, they're commonplace. Mathematician J.E. Littlewood suggested that each one of us should expect one-in-a-million events to happen to us about once every month. Failing to recognize this is due to us ignoring the astronomically high number of events that occur which we find insignificant. Events that we do find significant, such as winning a lottery or dreaming about your mother calling you right before waking up to her call are just a tiny fraction of many other insignificant events with the same or even lower probability of occurring, such as the chance that you had a dream of your mother calling you and also running out of milk five days after at 7:21 am. As statistician David J. Hand explains, “Lives are full of events, minor and major. With so many events to choose from, it's only to be expected that some surprises will occur, even though they are incredibly unlikely when taken by themselves.”

After witnessing events with very small probabilities, we might think that the laws of nature have been broken and attempt to use supernatural explanations to make sense of observing such events. But no matter how unlikely an event is, it doesn’t mean that a supernatural explanation would be more likely, especially when you consider the fact that in order for us to accept such an explanation, we have to agree that scientific models of nature that have consistently and accurately explained and predicted many natural events are completely wrong simply because we have witnessed an unlikely event. Yet close analysis of such “miracles” have never led to any proof for a supernatural explanation, and, in fact, many have proven to be cheap magic tricks, hallucinations or primitive misunderstandings of natural phenomena ⁽⁹⁾.

References:

1. Jordan, Michael. Dictionary of Gods and Goddesses. Second ed. New York: Facts on File, 2004.
2. Bennett, Bo. "Argument from Ignorance." Logically Fallacious: The Ultimate Collection of Over 300 Logical Fallacies. EBookIt.com, 2012.
3. Blanke, Olaf, and Sebastian Dieguez. "Leaving body and life behind: Out-of-body and near-death experience." The neurology of consciousness: Cognitive neuroscience and neuropathology (2009): 303-325.
4. Shermer, Michael. "Patternicity: Finding Meaningful Patterns in Meaningless Noise." Scientific American. November 17, 2008. Accessed September 1, 2014.
5. Shermer, Michael. "The Pattern behind Self-deception." TED. February 1, 2010. Accessed September 4, 2014.  
6. Foster, Kevin R., and Hanna Kokko. "The evolution of superstitious and superstition-like behaviour." Proceedings of the Royal Society B: Biological Sciences 276, no. 1654 (2009): 31-37.
7. Shermer, Michael. The Believing Brain: From Ghosts and Gods to Politics and Conspiracies---How We Construct Beliefs and Reinforce Them as Truths. St. Martin's Griffin, 2012.
8. Hand, D. J. The Improbability Principle: Why Coincidences, Miracles, and Rare Events Happen Every Day. Scientific American, 2014.
9. Nickell, Joe. Looking for a Miracle: Weeping Icons, Relics, Stigmata, Visions & Healing Cures. Buffalo, N.Y.: Prometheus Books, 1999.