“You know, the most amazing thing happened to me tonight. I was coming here, on the way to the lecture, and I came in through the parking lot. And you won’t believe what happened. I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing!”
The point that Feynman was trying to make is that you can’t just hunt for anomalies after the fact and then say they are somehow significant. You have to make predictions and do the test and see if those predictions bear out. In the same way it’s not amazing (at least statistically, although perhaps biologically) that any one person is born. It’s just like that license plate. Of course, the license plate ARW 357 is one of millions of possibilities, but that doesn’t mean that it’s amazing every time you see a license plate. They’re all one of millions, and it has to be one of them.
No one places much significance on the random people who win the lottery. But if that random person happens to be you, you feel incredibly lucky (and rightfully so).
The flip side is that, of course, it can be meaningful - not scientifically, but emotionally - to talk about probabilities after the fact. If a meteorite falls and smashes a car next to you, the first thing to your mind wouldn't be that it's not that special because the probability of its happening is 1.
My issue is that the author doesn't really give a good reason for stopping at the probability that two human beings will reproduce and reproduce until they eventually create you.
Some interesting further probabilities to factor in:
- Chance that two human beings evolved from single-celled organisms
- Chance that life came into existence on Earth
- Chance that Earth formed at all
- Chance that the laws of the universe among all the possible universes were conducive to the creation of Earth
I should hope by this point I've made a reasonable claim that the probability of my own existence is 0.
It's a meaningless "probability" on several counts.
1) It applies to everyone reading it, and it would apply to me if I were different and reading it. It tries to convey a specialness which doesn't seem to exist. If a billion people win a penny each then winning a penny isn't miraculous, even if it is a 1 in 1,000,000,000 chance that you win any particular penny - but the 'particular' part has no significance.
2) I am reading it, so my existence probability is ~1.
3) I wasn't waiting in the wings somewhere with a dice roll choosing whether I would be born or not, I am what was born to and raised by my parents. Birth and youth happened before "I", not the other way around.
I appreciate point #2: "The probability that I exist, given that I exist, is 1."
However, the question addressed by the OP is not "What is the probability that I would exist in this world?" but "What is the probability, across the space of all possible continuations of the world from the dawn of humanity, that the world would end up in a state that includes me?"
But given that "me" includes all my experiences as well as my genetics, we have to throw the probability of all those into the equation as well.
At the very least, if you're going to take these sorts of calculations seriously you're going to have to ask what the probability is not only that I exist, but that everyone I've ever met also exists.
> "What is the probability, across the space of all possible continuations of the world from the dawn of humanity, that the world would end up in a state that includes me?"
Not particularly more or less probable than most particular states that don't include me, I imagine?
I don't understand talking about possibility when discussing the past. Probability reflects our uncertainty about what outcomes will happen. Uncertainty is a property of our understanding, not of macro reality. When looking backwards, we know what happened and what didn't, I happened (probability: 1) and those other worlds didn't (probability: 0). Saying "they could have happened" seems to me a sentence with no real meaning.
Even if you go with a many-worlds view, that only means that all things happened with a probability of 1.
People seem to habitually miss point #3. See, for example, many hypotheticals that ask you to imagine yourself in another person's shoes. (Not sure what a succinct alternative would be, though.)
This reminds me of a bit from the introduction to "A Short History of Nearly Everything", by Bill Bryson. To wit:
"Not only have you been lucky enough to be attached since time immemorial to a favored evolutionary line, but you have also been extremely — make that miraculously — fortunate in your personal ancestry. Consider the fact that for 3.8 billion years, a period of time older than the Earth's mountains and rivers and oceans, every one of your forebears on both sides has been attractive enough to find a mate, healthy enough to reproduce, and sufficiently blessed by fate and circumstances to live long enough to do so. Not one of your pertinent ancestors was squashed, devoured, drowned, starved, stuck fast, untimely wounded or otherwise deflected from its life's quest of delivering a tiny charge of genetic material to the right partner at the right moment to perpetuate the only possible sequence of hereditary combinations that could result — eventually, astoundingly, and all too briefly — in you."
That said, the calculation is exactly as meaningful as the Drake Equation: you can plug in wild variations in equally "probable" values for the several steps in the equation, yielding staggeringly divergent end results, all of which mean precisely fuck-all, because nearly every number is little better than a wild-assed guess.
It's an interesting thing to think about, certainly, and a great way to remind yourself how stupendously fortunate you are to have been given the incredible, inestimably valuable gift of being, but in the end, it's naught more than sophistry dolled up in an equation that passes muster as well as a 16-year old kid using an fake ID saying he's 35.
You think that's impressive? 14 billion years ago a big bang occurred and particles too numerous to count were unleashed. Throughout all that time, these particles danced a particular pattern and interacted with each other through quantum effects that we don't even fully understand today. Just think of all the collisions that have occurred between all the particles in the universe; the ebb and flow of forces acting on the smallest of every single subatomic particle and quantum of energy that exists.
Looking at it from a macro perspective these particles, energy quantums, and forces have resulted in innumerable acts of learning and knowledge. People more learned than you and I have developed all manners of science and technology. Wars have been fought. Nations conquered. Virulent plagues unleashed with millions of people dying. A veritable tapestry of human achievement has been women together due to the interactions of countless tiny little particles, bundles of energy, and forces.
And all this rich history of the universe has been building up like a fantastic crescendo in the most amazing symphony every conducted, culminating in a singular event so that here and now I would post this comment on Hacker News. What are the odds of that?
Interesting thing is that when people are faced with a very rare poker hand, e.g. a royal flush, they go "OMG, what's the probability of that happening", without thinking about the fact that any hand they are dealt has a similar low probability, e.g. there are 1,302,540 no pair hands (http://en.wikipedia.org/wiki/Poker_probability), so the probability of your uninteresting, stupid hand being dealt is 1 in 1.3 million!
It is us who give meaning to probabilities and deem some events as interesting and others not.
But people think that way because of the utility of the hand. Worthless hands are abstracted into the same category (junk) because they all have about the same value. A royal flush, however, has by definition a guaranteed value with no risk involved. You cannot lose with a royal flush, thus the variance is 0, which is the rarest of all things at a poker table.
The Buddhist parable of the blind turtle is actually a metaphor for how long it takes to be reborn as a human after being reborn as a non-human.
"Suppose a man threw into the ocean a yoke with one hole in it, and then the east wind blew it west and the west wind blew it east and the north wind blew it south and the south wind blew it north; and suppose there were a blind turtle that came up to the surface once at the end of each century. How do you conceive this, bhikkhus, would that blind turtle eventually put his head through that yoke with the one hole in it?"
"He might, Lord, at the end of a long period."
"Bhikkhus, the blind turtle would sooner put his head through that yoke with a single hole in it than a fool, once gone to a lower realm, would find his way back to the human state."
M. 129
[Nanamoli, The Life of the Buddha, p. 250]
As the post says, the probability of the turtle surfacing with his head in the yoke on any one try is about 10^-15. Since the turtle tries once per century, the expected length of time as a non-human is 10^17 years, or 10 million times longer than the amount of time since the most recent Big Bang. It's actually kind of cool to visualize this. Let one penny represent the amount of time since the Big Bang (about 10 billion years). Then here's a picture of the amount of pennies representing the expected length of time as a non-human: http://www.kokogiak.com/megapenny/seven.asp
This is a fun thought experiment, but I think it over dramatizes the reality.
There's a huge potential set of humans, of which the current population represents one infinitesimally tiny subset of that potential set. But there's a lot of people, and the fact that one of them is you is largely unremarkable. If it hadn't been you, it would've been someone overwhelmingly similar to you.
In other words, we're not unique snowflakes. Humans are more alike than they are different, so don't get so excited about the miracle of your existence.
The chances of a pack of cards being dealt out in a particular order are incredibly low (I'll leave it to the math's whiz kids to work out exactly how low) but you would hardly say it was a miracle if they came out in that order. Same with the chances of you existing. Things are always going to turn out some way, even if the likelihood of that outcome is very low.
Or in other words, the chances of the outcome having a very low probability are very high.
Very good really. Because mutations in sperms are very low. So out of the million or so sperm running the rat race to the egg they all hold basically the same info 50% (DNA) of you from your father and the egg will hold the other 50%(DNA) of you from the mother that will make 100% you. Environment factors will play relatively the same if spermA or spermB had made it to the egg. Only other factor is that the role of environment based on if the egg developed as a male or female factor.
They get new chromosomes that are a combination of the two corresponding chromosomes from the father (or mother). The exact points in each chromosome where the crossovers happens are different (perhaps almost random), so each one of the sperms (eggs) is a very different unique snowflake.
(And there are also a few mutations that make them slightly more unique.)
There is another angle through which you could attempt to determine the probability of you existing. It's by dividing number of people on Earth today, by total number of genetic permutations possible. Of course that would remove cultural factors from the equation... but calculating actual probability of cultural factors are pretty damn hard!
The total number of bases in human DNA is ~3E9, so there are 4^3E9 ~= 10^2E9 possibilities. But this number includes a huge kind of variations, from humans to cows, to whales, to bats, to cats, to algae, to fungus, to pines, to orange trees, to roses, to petunias, to artichokes and probably even to vulcans, and to unicorns :).
(Different species have different number of bases in their DNA, but all the eukaryotic cells have the same order of magnitude, so we will just ignore this fact.)
If we consider only single nucleotide polymorphisms, the difference between two humans is in only 1/1000 of the bases (and let’s suppose that in each case the difference is in the same bases, and that the variations are independent) . So with this restriction there are 4^(3E9/1000)~=10^2E6 "possible" humans. Using that the total number of people that have ever lived is estimated as 10^11, the probability is 10^11/10^2E6 ~= 1/10^2E6.
But, please, don’t take these numbers very seriously.
But identical twins have the same genes, so even if your gene sequence came into existence, it doesn't mean that you would exist (whatever that means). Sentience is weird.
but even the most die-hard skeptic can be absolutely certain that they themselves exist.
I could potentially be non-existing or not-me in ways that I'm not clever enough to speculate about, let alone the ways I could speculate about (simulation, Boltzmann brains, Dust theory, dreams).
This assumes that my lineage is the only one that could produce me. Which, I believe, is wrong at least at the genetic level. As to the other levels - this starts getting tricky, cuz we quickly find out that the definition of 'me' is quite fuzzy.
The chance of anything is either 0 or 1. One in 400 trillion is just a number that might have been calculated by someone with incomplete knowledge. As their knowledge improved, their estimate of my chance of existing would approach 1.
That is a fun question to ask oneself. Ultimately, you come to the conclusion that it is a logical fallacy. Asked this way, it would imply that there is a pool of unborn people waiting for the right chance to come into existence.
“You know, the most amazing thing happened to me tonight. I was coming here, on the way to the lecture, and I came in through the parking lot. And you won’t believe what happened. I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing!”
The point that Feynman was trying to make is that you can’t just hunt for anomalies after the fact and then say they are somehow significant. You have to make predictions and do the test and see if those predictions bear out. In the same way it’s not amazing (at least statistically, although perhaps biologically) that any one person is born. It’s just like that license plate. Of course, the license plate ARW 357 is one of millions of possibilities, but that doesn’t mean that it’s amazing every time you see a license plate. They’re all one of millions, and it has to be one of them.
I came to say that, but it's eloquently copied from: http://surplusgamer.tumblr.com/post/1114853865/derren-brown-...