[HN Gopher] 40k coin tosses yield ambiguous evidence for dynamic...
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40k coin tosses yield ambiguous evidence for dynamical bias
Author : geocrasher
Score : 153 points
Date : 2022-06-03 14:57 UTC (8 hours ago)
(HTM) web link (www.stat.berkeley.edu)
(TXT) w3m dump (www.stat.berkeley.edu)
| wly_cdgr wrote:
| I guess to be more fair we better flip a coin to determine which
| way the coin should initially face when we flip it
| Imnimo wrote:
| I used to play a MUD (a text-based proto-MMORPG). It had a
| command to let you flip a coin. After many years, a player felt
| like they were noticing more tails than heads. They ran some
| experiments, and eventually an administrator checked the code -
| it turned out there was an off-by-one error in the coin flip
| logic (which inexplicably relied on generating a random number
| 1-10), such that coin flips had been 40/60 since the release of
| the game, and no one had noticed for over a decade.
| nicoco wrote:
| 30/60 maybe?
|
| EDIT: probably not after reading the comments. I thought I was
| smart ;)
| feoren wrote:
| 40/50 probably. One of the 10 numbers never showed up. 1-5
| tails, 6-9 (should be 10) heads.
|
| I ran into the same thing when I made a custom dice roller
| for Settlers of Catan. Rand(1, 6) never produced a 6, which
| you could tell if you inspected the comments closely, but
| still feels counter-intuitive to me.
| finnh wrote:
| Our Catan set has noticeably nonuniform dice. They roll
| high numbers much more frequently than low numbers;
| presumably bc the high-numbered sides weigh less (?). We
| haven't buckled down and done the science but it definitely
| tilts the game play, to the extent that we're considering
| swapping them out for new dice.
|
| (or this could just be Catan Crankiness (TM), but we've all
| noticed it quite a bit...)
| sshine wrote:
| On the subject of Catan and dice:
|
| https://www.chiark.greenend.org.uk/~sgtatham/dice/
| infinityio wrote:
| Either could be the case - if it was generating numbers from
| 1-9 instead of 1-10 30/60, if it was comparing <= 5 vs <5 it
| could be 40/60
| Imnimo wrote:
| Yeah, I'm almost certain it was the latter. I remember they
| shared the code snippet, but that was in 2007 and the
| game's forums have been replaced since then. I did find a
| recounting of it:
|
| https://forums.achaea.com/discussion/comment/249213/#Commen
| t...
|
| (and the associated quest to discover the easter egg of a
| coin landing on its edge with 1 in a million odds that was
| added when the bug was fixed)
| dekhn wrote:
| Huh. I once wrote a MUD client that didn't have an obviously
| documented way to quit and got email for years after
| complaining that I had "made the application too addictive".
| ycombinete wrote:
| Which MUD was this?
| Imnimo wrote:
| Achaea
| 0des wrote:
| What are the odds wow
| strbean wrote:
| My favorite baffling RNG bias was in the game Maplestory. It
| always seemed like RNG was extremely "clumpy". For example,
| critical hits would frequently come in bursts - you might get
| around 5 seconds of non-stop crits.
|
| The crafting system was heavily chance based. You'd get say 7
| attempts to augment a piece of gear, using 'scrolls' that had a
| certain percentage chance of succeeding. The lower the chance,
| the bigger the improvement to your gear. So a pair of gloves
| that had 7 successfully applied +attack 10% scrolls would be
| incredibly valuable. The superstitious method to crafting
| (which, anecdotally, worked incredibly well) was to get a ton
| of gloves and a ton of scrolls, and apply one scroll to one
| pair of gloves and throw them away if it failed. Once you had a
| single success, you would apply the scrolls as quickly as
| possible to try and ride the RNG wave. In my experience, this
| would very frequently result in getting 3+ successes in a row.
| mertd wrote:
| I'm fixated on the fact that they used a dime. That's a very
| small coin. I can't say I fully understand the dynamical bias
| mechanics but u had expected that they use a quarter. It's much
| larger and easier to toss.
| btilly wrote:
| They wanted to test the dynamics on long tosses (with lots of
| flipping). It is easier for a toss to be long if the coin is
| small.
| dekhn wrote:
| "We adjusted the methods of the experiment for the
| convenience of the experimenter" is a common detail most
| papers leave out.
| frogger8 wrote:
| From the article
|
| The experiment
|
| Over the Spring 2009 semester two Berkeley undergraduates,
| Priscilla Ku and Janet Larwood, undertook to do the required
| 40,000 tosses. After preliminary experimentation with practical
| issues, there was formulated a specific protocol, described in
| detail below. Cutting to the chase, here is the complete data-set
| as a .xlsx spreadsheet (see sheet 2). This constitutes a
| potentially interesting data-set in many ways -- one could
| compare numerous theoretical predictions about pure randomness
| (lengths of runs, for instance) with this empirical data. For the
| specific question of dynamical bias, the relevant data can be
| stated very concisely
|
| of 20,000 Heads-up tosses (tossed by Janet) 10231 landed Heads
|
| of 20,000 Tails-up tosses (tossed by Priscilla) 10014 landed
| Tails
| [deleted]
| gus_massa wrote:
| From
| https://www.wolframalpha.com/input/?i=binomial+distribution+...
| the standard deviation is almost 71, so it's a 3.3 sigma for
| Janet and .2 sigma for Priscilla. Since this is not particle
| physics, we can conclude that Janet (or her coin) is doing
| something wrong.
| mjburgess wrote:
| p isnt 0.5, which is the point of the article
|
| cf. https://www.wolframalpha.com/input?i=binomial+distributio
| n+n...
| mjburgess wrote:
| If there is the theoretical 50.8% we would expect 20,230 same-
| face-up in 40,000 flips. We find here 20,245. Pretty
| compelling.
| zeroonetwothree wrote:
| The data is consistent with a hypothesis that there is some
| smaller bias in favor of the side you started with (say 50.4%)
| and an additional bias in favor of heads (say 50.4%).
| GartzenDeHaes wrote:
| Coin tosses are not stochastic.
| https://www.npr.org/2004/02/24/1697475/the-not-so-random-coi...
| semi-extrinsic wrote:
| I think you're trying to say that they are not perfectly fair,
| which is entirely unrelated to being stochastic.
| fumeux_fume wrote:
| Thank you!
| t_mann wrote:
| No, the article actually says that sufficiently precise
| machine tosses can be considered deterministic. The
| randomness comes from humans.
| DeathArrow wrote:
| I think that every physical system is a little biased. That's
| what they change the balls at lottery for every game.
|
| I've read an article about a guy who was observing frequencies at
| roulette long time ago and, based on that, he made some wins. The
| casino learned that and switched the tables each day, so he
| wasn't able to win any more.
| bombcar wrote:
| There's someone who built a craps table and perfected exactly
| how to throw the dice. If you control the inputs, you control
| the output.
|
| I could see someone learning exactly how to flip a coin to
| control how it lands, or at least greatly influencing the
| outcome.
| macintux wrote:
| Discussed here: https://news.ycombinator.com/item?id=30489022
| 29athrowaway wrote:
| If you do a movement 40,000 times, you will be memorizing the
| movement.
| dieselgate wrote:
| I didn't read the paper with a fine toothed comb but it seems
| like the two undergraduate researchers were flipping the coins by
| hand? If anyone can confirm or deny I would very much appreciate
| it! Bringing this up because it seems to introduce much
| variability into each flip?
| benibela wrote:
| That reminds me of parapsychology
|
| They have performed lots of experiments where you do a random
| experiment and try to change the outcome with your mind.
| feoren wrote:
| And this comment reminds me of one of my favorite articles I've
| seen linked from HN, "The Control Group Is Out of Control",
| relating to parapsychology as the control group for science and
| how that's not actually necessarily looking great for science
| itself: https://slatestarcodex.com/2014/04/28/the-control-
| group-is-o...
| closeparen wrote:
| > It just means that the standard statistical methods of
| science are so weak and flawed as to permit a field of study
| to sustain itself in the complete absence of any subject
| matter.
| t_mann wrote:
| Interesting experiment! Here's a suggestion for a new protocol:
| set up a stand at some busy places (stadiums, train stations,...)
| and ask random passers-by to toss a coin a few times 'for
| science'. Should be easier to get to statistically meaningful
| orders of magnitude (if not, go to a cosplay event in 'The
| Witcher' costumes, that should help ;)), and arguably far more
| representative for the situations that we care about: the two
| participants will have become far more experienced at coin
| tossing after 20k tosses, but we care more about random people
| who hardly ever toss coins (we already know that people who
| practice a lot can control the outcome of a toss with reasonable
| accuracy).
| dekhn wrote:
| I think my approach would be to build a coin-flip machine (well,
| several) that could operate independently, then use computer
| vision to get the final readout (the result of the flip). Then,
| if it deviates from expected, use a high speed camera to watch
| the coins. Oh, and randomize _everything_ about the trials.
| 2b3a51 wrote:
| As in the paper referenced in the OA?
|
| https://statweb.stanford.edu/~cgates/PERSI/papers/dyn_coin_0...
|
| Wasn't the idea to test the difference between human and
| machine tosses?
| dekhn wrote:
| The link on that page doesn't resolve, nor is that what the
| short writeup about the undergraduate work is about.
|
| Most of what the statisticians conclude about the physics
| seems to be based on poor experimental design. measuring
| human biases in coin flips seems to be a bit off the point--
| you'd do better building a machine that emulates humans
| better, than to take two people and collect a large number of
| samples between them.
|
| Put another way: when somebody builds a robot and collections
| the results of thousands of coin tosses, picking two
| undergrads at stanford and using their physical mechanisms
| does not advance any useful scientific argument about bias in
| coin flipping. It just muddles reality with advanced stats on
| heavily biased data.
| gus_massa wrote:
| Take a look at " _Dice-O-Matic hopper and elevator_ "
| http://gamesbyemail.com/News/DiceOMatic HN discussions
| https://news.ycombinator.com/item?id=14806986 (246 points |
| July 19, 2017 | 57 comments) and
| https://news.ycombinator.com/item?id=626092 (81 points | May
| 26, 2009 | 4 comments)
| dekhn wrote:
| yes, that's a design. It's hard to see the details because
| the video is poor and the explanation is a bit rambling. It
| looks much more complicated than necessary and from what I
| can tell, the rolls themselves aren't truly independent
| because dice can interact with each other.
| williamkuszmaul wrote:
| If the coin were unbiased, we could compute the exact probability
| of getting 10231 or more heads with 20000 flips as:
|
| "sum (20000 choose x)/2^20000 for x from 10231 to 20000",
|
| which Wolfram Alpha evaluates to 0.00056.
|
| The probability of getting a number of flips that differs from
| 10000 by at least 231 is twice that, so about 0.001.
|
| So, in fact, the probability of this happening by dumb luck is
| about 1/1000. That's pretty strong evidence.
| [deleted]
| UberFly wrote:
| Bring on the robot baseball umpires and the NFL robot coin
| flippers.
| 1970-01-01 wrote:
| >>separate the effect of individual tossing style from any
| possible effect arising from the physical difference between
| Heads and Tails. But it is very hard to imagine any such physical
| effect, so we presume the observed difference (if real rather
| than just chance variation) is due to some aspect of different
| individual tossing style.
|
| Much more boring title: "40k coin tosses reveal bad presumption
| and a biased coin"
| TheDesolate0 wrote:
| 40k seems a tad on the low side, by several orders of magnitude.
|
| Seems like a hastily done spring projects
| eklitzke wrote:
| It was an undergraduate research project.
| h2odragon wrote:
| This field of study obviously needs a much larger number of
| tossers.
| [deleted]
| [deleted]
| [deleted]
| a9h74j wrote:
| Next crypto class: Proof of coin tosses.
| _jal wrote:
| Too bad ibankers make too much to want to be study subjects.
| whoomp12342 wrote:
| If we are looking that granular of detail, does the shape and
| weight distribution of the coin matter?
| [deleted]
| sbf501 wrote:
| Referees need to start rolling a d20.
| jonhohle wrote:
| Isn't that why you "call it in the air"?
| segfaultbuserr wrote:
| Or just use von Neumann's debiasing algorithm - toss twice, and
| see if it's head-tail or tail-head, retoss when you get
| repeated heads or tails. It doesn't prevent dishonest tosses
| (if you can manipulate the bias in each toss), but should work
| to eliminate a consistent dynamic bias by an honest tosser.
| mrandish wrote:
| > A first comment is that it would have been better for each
| individual to have done both "Heads up"and "Tails up" tosses
| (which was part of the intended protocol, but on this aspect of
| the protocol there was a miscommunication)
|
| That was a pretty unfortunate error in the experiment. Maybe it
| doesn't matter but now we don't know. It would also have been
| nice to have them swap coins halfway to expose any individual per
| coin biasing. It may seem like an irrelevant thing but I've been
| a lifelong magician specializing in advanced slight of hand coin
| magic. I carry a set of coins with me all day, every day and
| handle them constantly. It started out as practice but evolved
| into both practice and a kind of fidget toy. I have sets of coins
| I've probably handled for thousands of hours over decades.
|
| Most people think of coins as immutable but they actually change
| quite a bit after hundreds of hours of handling. Most advanced
| coin magicians don't tend to use "trick" coins from a magic shop
| because they are actually too limiting. The coins I use are
| completely normal circulated coins but they are very specific
| because there are subtle differences in how coins handle which,
| at the most advanced levels, can matter. I have year-matched sets
| of coins I've carefully assembled because they have the degree of
| surface wear (sometimes called 'softness') and edge-milling which
| works best for the style of slights I do. Coins also vary in
| shape and many aren't quite round. I've actually hired a
| specialized machinist (aka coin-smith) to 'true-up' the shape and
| then re-mill the edges of certain coins.
|
| Based on my admittedly unusual experience in handling coins, I
| suspect that weight, edge and surface variations in individual
| coins could have a material aerodynamic impact at this
| statistical level (sub-half a percent). BTW, there are coin
| magicians who have mastered the ability to flip a normal coin and
| control the outcome to >95%. While the coin is normal in every
| way, it does need to be a coin they've specifically trained with.
| Otherwise the hit rate falls considerably.
| modernerd wrote:
| Please send us further down this rabbit hole, it sounds
| fascinating!
|
| What sort of flourishes/fidgets do you find yourself
| gravitating to most?
|
| What does great sleight of hand coin magic look like? Who do
| you admire most?
|
| Where should someone get started if they want to explore this?
| mrandish wrote:
| > What sort of flourishes/fidgets do you find yourself
| gravitating to most?
|
| There are a huge variety and it's mostly down to personal
| preference. Popular flourishes include coin rolls and coin
| stars. Popular slights include dozens of different palms with
| single and then multiple coins.
|
| > What does great sleight of hand coin magic look like?
|
| Done right it can be absolutely mind-blowing. For an example
| take a look at some of Danny Goldsmith's videos
| (https://www.dannygoldsmithmagic.com/). Danny is very, very
| good but like a lot of specialized skills, those who aren't
| deeply into it won't be able to notice a meaningful
| difference between the top 20% of coin workers.
|
| > Who do you admire most?
|
| That's really down to personal taste and style. One unusual
| thing about magic is that the "best magicians" in the eyes of
| other experienced magicians are generally people you've never
| heard of. Fame doesn't really correlate with the pinnacle of
| skill. While most famous magicians like a David Copperfield
| are skilled, they would be the first to tell you they can't
| hold a candle to the most skilled coin workers or card
| mechanics.
|
| > Where should someone get started if they want to explore
| this?
|
| For _serious_ coin work, Danny 's teaching videos would be a
| good start. Look for ones he flags as being appropriate for
| novices. For learning the art of magic in general, I'd
| suggest not wasting money buying individual "tricks" unless
| you just want a few easy party tricks to amaze (or annoy)
| friends with. Most people who get deep into magic discover
| that the most valuable and broadly applicable knowledge comes
| from books, videos and live learning (called "sessioning" by
| close-up workers). I don't buy much magic in recent years
| because I'm at the point of just perfecting skills, so it's
| hard to recommend an online store but a safe bet for
| beginners would be Vanishing Inc.
| https://www.vanishingincmagic.com/. The guys that run VI are
| deeply experienced and they seem to avoid selling a lot of
| the 'crap magic' that looks amazing to novices but isn't
| actually all that useful. I was at a lecture by the co-
| founder a few weeks ago and the guy not only has deep
| knowledge and mad skills, he clearly loves magic and is good
| at teaching.
|
| If you just want to watch some higher-quality magical
| performances, I'd suggest Penn & Teller's "Fool Us" show
| (lots of clips on YouTube). The technical coordinator on that
| show, Michael Weber, is a long-time magical inventor and
| author who is well-regarded by other magicians. He and Teller
| work together to curate the acts that get on the show and
| you're basically getting to see some top notch talent hand
| selected by guys who know the difference.
| tash9 wrote:
| Well it's not like we're gonna run out of undergraduates, just
| do the experiment again.
| tetris11 wrote:
| Unrelated question: how do your hands look after handling coins
| so constantly as you do? Is there a slight sheen to them? Do
| you have less hair on your hands than you normally would, or
| more?
| mrandish wrote:
| No, there's no noticeable difference in the skin surface of
| my hands. Over years of practice, serious coin workers do
| develop substantial hand muscle strength and joint
| flexibility but that's not visually noticeable. It's also
| just a byproduct of practice and not needed for most of what
| we do. The key physical ability isn't applying force, it's
| actually enhanced sensitivity. I can feel precisely where the
| coins are and feel how the weight is shifting as they move.
| This sensitivity enables precise control which is really the
| key thing.
| spdionis wrote:
| Funnily enough, but also not surprising, it's the same for
| drummers and their preferred type of sticks.
| raincom wrote:
| It is called "kinesthesia", which is important in playing
| musical instruments, sports, flying aircraft, etc. With
| respect to flying, pilots trained by Army (navy, airforce)
| develop these skills far better than those directly
| recruited by carriers from colleges. We can see those
| results in some fatal crashes (Air France 447, Asiana 214).
| I am not blaming the pilots. When one flies with the aid of
| machines (fly by wire, simulators), one doesn't develop the
| kinesthesia required to get out of tricky situations(when
| instruments don't work or when instruments misread, etc).
| AndyNemmity wrote:
| The same is true for card magicians, and card handling. I
| have a lot of things I can do with my hands and joints that
| aren't something you can see.
|
| Same with enhanced sensitivity. I can fairly accurately
| tell you how many cards I pick up from a group. It's just
| practice, once you can do 2, you do 3, all the way up to
| 10, to 15 to 20.
| posterboy wrote:
| Is that a kind of subdigitizing?
| gfodor wrote:
| Imagine being in the room when they realized that, after forty
| thousand coin tosses, they screwed up the experiment. Oops.
| ihattendorf wrote:
| Then it becomes an 80k coin toss experiment :)
| sillysaurusx wrote:
| This is how ML training goes. My longest run was 2 months
| before it collapsed.
| the__alchemist wrote:
| That's super interesting! Of note, the book Quicksilver (First
| book in the Baroque Cycle) goes into a few diatribes about
| subtle differences in coins in Europe a few hundred years ago;
| eg coins being valued by metrics other than their face value.
|
| Eg: > "I say, Daniel, is it true what they say, that those
| coins are perfectly circular?"
|
| > "They are, Isaac--not like the good old English hammered
| coins that you and I carry in such abundance in our pockets and
| purses." ... >"if someone clips or files a bit of metal off the
| edge of a round coin with a milled edge, it is immediately
| obvious."
|
| > "That must be why everyone is melting those new coins down as
| fast as they are minted, and shipping the metal to the
| Orient...?" Daniel began,
|
| > "...making it impossible for the likes of me and my friend to
| obtain them," Isaac finished.
|
| > "Now there is a good idea--if you can show me coins of a
| bright silver color--not that black stuff--I'll weigh them and
| accept them as bullion."
|
| > "Bullion! Sir!"
|
| > "Yes."
|
| > "I have heard that this is the practice in China," Isaac said
| sagely. "But here in England, a shilling is a shilling."
|
| > "No matter how little it weighs!?"
|
| > "Yes. In principle, yes."
|
| > "So when a lump of metal is coined in the Mint, it takes on a
| magical power of shillingness, and even after it has been filed
| and clipped and worn down to a mere featureless nodule, it is
| still worth a full shilling?"
|
| > You exaggerate," Daniel said. "I have here a fine Queen
| Elizabeth shilling, for example--which I carry around, mind
| you, as a souvenir of Gloriana's reign, since it is far too
| fine a specimen to actually spend. But as you can see, it is
| just as bright and shiny as the day it was minted--"
|
| > "Especially where it's recently been clipped there along the
| side," the lens-grinder said.
|
| > "Normal, pleasing irregularity of the hand-hammered currency,
| nothing more."
| 0des wrote:
| Are we all in the same book club or something?
| gibspaulding wrote:
| A substantial chunk of the books I read are based on HN
| recommendations, so... yes?
| robwwilliams wrote:
| Egghead book club. Neal Stephenson, Greg Bear, Greg Egan...
| User23 wrote:
| > BTW, there are coin magicians who have mastered the ability
| to flip a normal coin and control the outcome to >95%.
|
| I managed 11 heads in a row with a quarter when I was in high
| school. I was intentionally going for heads so it was either
| beginner's luck or an absurd statistical fluke.
| onphonenow wrote:
| Even when not trained if you are basically looking to
| "repeat" a motion, you can get a reasonably consistent flip.
| A lot of folks think these far out results are just
| statistics, but statistics actually tells us how incredibly
| rare this would be.
|
| 11 in a row is perhaps still part fluke without training, but
| as long as you were trying to do the same thing again not
| unreasonable.
| [deleted]
| kadoban wrote:
| If you're not using a specific technique, that was just a
| fluke.
|
| I'm not a magician, I just learned this one trick/set-of-
| tricks (and I'm not 95% success at it either).
| [deleted]
| swayvil wrote:
| Would a true rng (electron noise or whatever) be an acceptable
| substitute for physical coinflipping?
|
| Has anybody tried this while under the influence of "psychic
| power enhancers" (psychedelics, meditation, sex, etc)?
| zuminator wrote:
| They mentioned that when A tossed the coin, B would record the
| result on a spreadsheet. But did A know the result of each coin
| toss as it happened and read it off to B, or did B whisk the coin
| out of A's hand without A's knowledge of the outcome? Ideally it
| should be without knowledge of the outcome, so that A's tossing
| style wouldn't be subconsciously influenced by the result in a
| kind of self-inflicted Clever Han(d)s effect.
| deweller wrote:
| > of 20,000 Heads-up tosses (tossed by Janet) 10231 landed Heads
|
| > of 20,000 Tails-up tosses (tossed by Priscilla) 10014 landed
| Tails
|
| Why not do 10,000 Heads-up and 10,000 Tails-up tosses for each
| person?
| pc86 wrote:
| > > _A first comment is that it would have been better for each
| individual to have done both "Heads up"and "Tails up" tosses
| (which was part of the intended protocol, but on this aspect of
| the protocol there was a miscommunication)_
| lumost wrote:
| From a physics stand point, coin tossing is similar to knife
| throwing or axe throwing. It's completely within human capability
| to intentionally or unintentionally time the toss with some
| degree of accuracy. I doubt anyone can be "good" at this
| (otherwise it would be a great grifting trick), but surely this
| creates at least a marginal bias in the data at a high enough
| scale.
| paxys wrote:
| People can definitely get "good" at coin tossing. It isn't even
| too difficult a trick to master. It's not really possible to
| use it in any kind of grift scenario though, because there
| aren't any real world cases where you can win money (or gain
| any advantage) just by tossing a coin a certain way. Rolling
| dice has a lot more potential, but those are in turn heavily
| monitored, e.g. in casino settings.
| JulianWasTaken wrote:
| > there aren't any real world cases where you can win money
| (or gain any advantage) just by tossing a coin a certain way.
|
| Paying off a referee to have the coin turn up heads in
| overtime in a football game seems like it may net you some
| profit.
| paxys wrote:
| If you can pay off a referee then the coin toss would be
| the least effective way to do it. A single bad call would
| gain you a much bigger advantage.
| dTal wrote:
| It has far more plausible deniability, however.
| bluGill wrote:
| Maybe. It only takes one bad call at the right time to
| throw a game. If the ref is consistently bad and missing
| call for both sides what is one more bad call?
|
| I don't care much about bad refs so long as they are
| consistently bad. However a perfect ref who missing one
| critical call is a lot more suspicious. Of course I
| prefer a great ref, but I can work with a fairly bad ref.
| aidenn0 wrote:
| I believe NFL coin tosses let the coin hit the ground. All
| methods I know of biasing a coin toss involve catching the
| coin. As long as the coin hits the ground and bounces at
| least once, a lot of randomness is re-introduced.
| samatman wrote:
| Forcing a coin toss of the sort described in the article is
| well within reach of the interested stage magician.
|
| Forcing a coin toss of the kind used in sport, where the coin
| hits the ground, is more difficult.
| feynmanalgo wrote:
| You don't have to be a magician. I was impressing other kids
| doing exactly this, you just toss so the coin goes high but
| turns slowly and catch it in your hand rather than let if
| fall to the ground. After not so many tries you get a pretty
| good intuition on how you have to throw to get the desired
| result.
| samatman wrote:
| It works the other way around, this kind of trick is
| (stage) magic so if you're doing it, hey presto, you're a
| magician.
| kadoban wrote:
| There's also a particular method to get the coin in a
| tilted spin that looks (and sounds) _remarkably_ like a
| real flip, and is I think going to be more repeatable than
| what you're describing.
| posterboy wrote:
| It wouldn't be. People who fall for shell games have to accept
| that it's fishy and just want to show they are better.
| bitcurious wrote:
| When I was around 15 I tried to master the controlled coin
| flip, having been exposed to the idea in one of the Stainless
| Steel Rat books by Harry Harrison. I reached around 80% success
| flipping for heads, so long as I used the catch-and-show
| method. It was easier with heavier and bigger coins, tougher
| with lighter and smaller ones. Letting the coin drop the the
| ground and bounce took me back to 50%.
|
| Satisfied that it could be done, I moved on - never used the
| skill, except as a party trick.
| gfodor wrote:
| This is why the casino people get upset when you roll the
| dice at a craps table and continually avoid hitting the back
| wall. The rubber pyramids lining the wall are critical to
| ensuring they maintain their edge :)
| raegis wrote:
| Same here. Long ago I tried to generate an encryption key by
| flipping a coin. After getting a rhythm and flipping heads 20
| consecutive times I gave up.
| titzer wrote:
| You could still XOR longer runs together, reducing the
| bitrate but mostly eliminating the bias.
| TimesOldRoman wrote:
| Even that poses a fun test. What flipping method is needed to
| ensure some level of randomness.
|
| I love that idea of a grifter being able to flip a coin as they
| choose.
| MisterBastahrd wrote:
| Probably a device that would uniformly toss the coin with
| regards to force applied at X number of different strengths.
| ChadNauseam wrote:
| Or have both people flip a coin secretly, then reveal the
| coins and XOR the results :D
| faheel wrote:
| Maybe letting the coin fall on a hard surface, so that it has
| a chance to bounce/spin randomly before falling flat (or
| staying on its side!)
| Jaepa wrote:
| Antidotally I can confirm that it is possible toss a coin like
| that. It helps have a larger coin and to impart it with
| relatively little rotation.
| TedDoesntTalk wrote:
| I can consistently flip a US quarter and get the desired
| outcome. I have not measured accuracy but is definitely 80%
| or more. This can be with a quarter I just picked up at a
| store... no special wear.
| williamkuszmaul wrote:
| From what I've heard, Perci Diaconis (one of the authors of the
| original paper) actually could do this. He was a magician
| before he became a mathematician, and a lot of his early
| mathematics work focused on math relating to the magic tricks
| he used to do
| dhosek wrote:
| Art Benjamin at Harvey Mudd College is another
| magician/mathematician. The two skills line up pretty well,
| it seems. When I got my math teaching credential there were
| two people in my cohort who did magic tricks as well as at
| least one teacher at the school where I did my student
| teaching.
| [deleted]
| kloch wrote:
| In roulette this is known as the "dealers signature" where a
| bored zoned out dealer can sometimes hit the same region/sector
| of the wheel on consecutive spins.
|
| I've seen this happen (or at least appear to happen) in real
| life where an obviously bored dealer was consistently hitting
| the same 1/3'd of the wheel and players were taking advantage
| of it. After a while a suit shows up and starts giving heat not
| to the players but to the _dealer_. Chatting them up with
| nonsense conversation to distract them out of their zone. This
| wasn 't a pit boss/supervisor but casino security - guys that
| emerge from back rooms to give heat to card counters in
| blackjack.
|
| The distraction worked: the now very awake and nervous dealer
| was no longer hitting similar areas and the players moved on to
| other tables.
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