We attach a lot of meaning to coincidences. On the one hand, we see them as significant; on the other hand, you have the TV show detective pronouncing that he doesn't believe in coincidences.

The first thing to understand is that everything is a coincidence.

All a coincidence is, is two events happening at the same time. In that sense, everything is a coincidence because whenever one event is happening, a near infinitude of other events are happening at the same time. 

What we CALL "a coincidence" is two events happening at the same time TO WHICH WE ATTACH SOME MEANING OR SIGNIFICANCE.

Some meaningless coincidences exist against astronomical odds. Let me think back to two events I can correlate in my mind. Here's one. I remember getting home from a movie, turning on the TV, and learning that Princess Di had been killed in a traffic accident. Clearly, it happened while I was watching the movie.

Now, what are the odds against Princess Di dying while I was watching a movie? They are so great that the odds against that correlations must be in the billions if not trillions to 1. Yet, that isn't an interesting coincidence. Coincidences with much better odds turn out to be more interesting, such as running into an old girlfriend who was back in town for a visit in the movie theater lobby.

Think about coincidence and you'll see it's a concept you probably should have thought about before. 

Once you understand the nature of coincidence, you can catch people misusing the concept all the time. For example, theists will use the existence of humankind and other life on Earth demonstrating the existence of God due to the astronomically high odds against it. 

What I hope I've shown is that things happen all the time against astronomical odds and that this fact in a particular case really proves nothing at all.

In the case of life popping up in a universe that, so far, seems largely barren of it, one has to bear in mind that as long as it's possible for life to exist, however difficult it may be to come into existence, we now know that there are at least billions of galaxies, each with billions of stars, so that as long as life is possible at all, it's almost certain to happen somewhere at some time, even if we'll never where and when. 

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You posted this while I watched a TV show with detectives. Clearly, this cannot be coincidence. *dum dum duuuum!*

Ah, yes, but paradoxically anything that cannot be coincidence is also coincidence.

Coincidentally enough.

They are more like opposites. The butterfly effect basically states that a relatively minor action in one place can have huge effects somewhere else. The way you set your dinner table causes the destruction of a galaxy far far away. That is the opposite of coincidence which is simply two unrelated things happening at the same time. Sometimes seeming significant but most of the time not.

BTW, when the whole chaos theory/butterfly effect thing came on the scene was overwhelmed with guilt thinking that perhaps some minor thing she did was having serious consequences elsewhere that she would never be aware of.

That's a prediction, prognostication, or prophecy, but not a coincidence. Why? Because they are temporally separate. They don't coincide.

It would have been a coincidence if he had made those predictions just as they were coming true. But then, of course, they would have been a lot less interesting. 

This video really had a impact on my life. Enjoy!


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I like to point out a hypothetical incident where a pebble tumbles down a hillside (due to random chance from erosion) and happens to plunk straight into a gopher hole.  What are the odds of that happening?  Well, if it happened, then 100%.  Now if you want to sit by the hill and wait for the next pebble to tumble down to see if it lands in the gopher hole, then the odds of a successful observation are astronomical.

Statistics don't apply to individual events - they describe the distribution of numerous events.  Selecting one of those possible outcomes and waiting for it leaves you facing long odds.  Noticing an event that has already occurred gives you 1 out of 1 or 100%.

The same as for everyone and about equal to the odds of winding up in Valhalla.

Well, one can take a shot at determining the likelihood of something that hasn't happened, but once it happens there's no point. It's happened and the "odds" are 1/1. Not interesting. 

I'm just recalling probably the greatest interesting coincidence of my life. Back decades ago when I was married, my wife worked at a software development firm and due to limited space, almost all employees shared an office with another employee. Only bigwigs got offices to themselves.

She shared an office with a man named Josh. He and his wife became occasional dinner partners, sometimes at their place and sometimes at ours. 

The company chose a four-week period in July, I believe, and required everyone to take their vacation then. Dates were staggered in a way to keep the company approximately half-staffed during July. It turned out that she and her office mate got the same 2-week period.

Her parents were visiting us at that time so we rented an RV and took a trip that included a visit to Arlington National Cemetery. We parked and spent an hour or so walking around. When done, we were in the parking lot approaching our RV when my wife stopped in her tracks and pointed saying, "I don't believe it!" I looked and there was Josh and his wife who had just arrived to visit the cemetery. They were as astonished as we were. 

We had decided our itinerary on a short notice and so my wife hadn't discussed our itinerary with Josh, and he affirmed that he hadn't mentioned it to her. But even if he had, it would have taken some coordination to bump into him and his wife in the parking lot at a particular moment. 

Arlington National  Cemetery gets 4 million visitors a year, which is about 11,000 on an average day, though I imagine July is one of the heavier months, so let's say it was probably closer to 15,000 on that day. Not only did we have to be in that location on the same day but at the same time and parked in locations that had us using the same aisle.

Once it happened, the odds were 1/1, of course, but I wonder what the odds against that coincidence would have been beforehand.

** Reverend Bayes discovery show statistics which do apply to single events

The statistical theory of probability certainly applies in contexts in which it is physically impossible or logically impossible to provide a well-defined measure of a single event happening. Statistical mechanics among the "classical" theories of physics can represent the first and quantum mechanics can represent the second.

However, another branch of probability theory called Bayesian Statistics does assign probabilities to individual events -- and does so in a coherent and convincing manner.

Bayesian analysis simply does not show up in elementary accounts of statistics -- but in principle it is not difficult to understand. Just look it up and you'll see.

A related aspect is that some people don't have a good grasp on math and probability. A die has a 1 in 6 chance of rolling each number. Roll it 6 times and some people think you should get one of each number. Wrong - it isn't a perfect correspondence - the 1/6 probability only works for sufficiently large numbers (assuming the die is not uneven).

And the reverse is true also - many people don't grasp large numbers well or how frequently a low probability event could occur. "Oh, that's a 1 in a billion chance of that happening to me." First of all, 1/1000,000,000 over what period of time? 1/1000,000,000 each day means that it potentially happened 7 times today (if there is a perfect correspondence) across the world's population or 2555 times in a year. Now if it's 1/7000,000,000 per year then the average would be once per year for 1 person (out of the Earth's population). So a 1 in a billion chance per day makes it a not uncommon occurance contrary to what too many people think.

For me, when I notice a coincidence, my basic response is "Oh, that's cool." Because it's interesting but not really significant of anything.


@Roger, Using those numbers, the chance of dozens or hundreds of parts failing is excellent, unfortunately. With a perfect correspondence, a thousand parts are likely to fail. Fortunately, they know their math and build in redundancy and ways for the failures to be circumvented. But, yes, the astronauts are brave men and women.



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