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Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

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Re: Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

#21

Post by roywiggins »

chillingeffect wrote: post #17
jpswade wrote: post #10

tl;dr: Occam’s Razor demands the simplest explanation and so it probably was a stowaway piece of gravel

I came here to post that it was a great article - except for the needless invocation and anthropomorphization of Occam's Razor. I. It is not clear that a rock falling out is _simpler_ than a meteorite falling out. How exactly is a meteor less simple? Sure, it's rarer and less likely, but it is not simpler. II. A simple explanation of a how an iPhone works is "magic." But we know that's not the case. Our invocation of…

Unless you know magic exists and works, postulating "magic" fails Occam's Razor, since you're needlessly postulating that magic exists as part of your explanation. The hypothesis that an iPhone works by elecricity and clever engineering- since we have similar objects like TVs that work that way- is favored by Occam's razor.

You're right that it doesn't seem like you can apply Occam's razor to the falling rock. Really it seems like an example of Bayesian reasoning: we know the prior probability of someone coming anywhere near a falling space rock is very, very small. We know the probability of a piece of grit falling out of a chute is orders of magnitude larger. Shakey video evidence by itself barely shifts our confidence that it actually was a meteor.

Re: Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

#22

Post by certainly_not »

tc_ wrote: post #11

The article's discussion of golf balls reads completely opposite to standard well-accepted theory. The author writes: > [The "drag catastrophe"] is when an object is falling so fast that the boundary layer of gas separates off the object and the drag force suddenly drops by a factor of almost 10. The reason why golf balls have dimples is to cause this drag catastrophe to happen at slightly slower speeds, so the ball…

I'd never heard of "drag catastrophe" before either, but I think you're right that he's referring to the onset of turbulent flow that reduces drag on a bluff body.

That's the sudden drop at the right in all of these graphs: www.google.ro/search?q=drag+reynolds+number (same as his own Figure 9, really).

There are a lot of surprising nonlinearities in those graphs. I wish there was a more detailed article/paper somewhere.

Re: Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

#24

Post by khafra »

chillingeffect wrote: post #17
jpswade wrote: post #10

tl;dr: Occam’s Razor demands the simplest explanation and so it probably was a stowaway piece of gravel

I came here to post that it was a great article - except for the needless invocation and anthropomorphization of Occam's Razor. I. It is not clear that a rock falling out is _simpler_ than a meteorite falling out. How exactly is a meteor less simple? Sure, it's rarer and less likely, but it is not simpler. II. A simple explanation of a how an iPhone works is "magic." But we know that's not the case. Our invocation of…

Restrict yourself to explanations which can be rendered as a series of individually simple steps--something you could reduce to math; something you could program into a computer. Note that "magic" does not qualify, here.

The shortest such series of steps that successfully outputs your observation is the most likely explanation for those observations. In this case, we would either need an exception to well-known rules of fluid dynamics, or an explanation why 2 years of searching in a small area yielded no meteorite. Either one of those is an added complication to the explanation which predicts stowaway gravel: P(A & B) <= P(A).

Re: Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

#25

Post by TeMPOraL »

chillingeffect wrote: post #17
jpswade wrote: post #10

tl;dr: Occam’s Razor demands the simplest explanation and so it probably was a stowaway piece of gravel

I came here to post that it was a great article - except for the needless invocation and anthropomorphization of Occam's Razor. I. It is not clear that a rock falling out is _simpler_ than a meteorite falling out. How exactly is a meteor less simple? Sure, it's rarer and less likely, but it is not simpler. II. A simple explanation of a how an iPhone works is "magic." But we know that's not the case. Our invocation of…

You think of the wrong meaning of the word "simple" here.

http://en.wikipedia.org/wiki/Occam's_razor#Probability_theor...

Some background reading that addresses the concerns in your comment:

http://lesswrong.com/lw/jp/occams_razor/

Re: Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

#26

Post by simias »

jpswade wrote: post #10

tl;dr: Occam’s Razor demands the simplest explanation and so it probably was a stowaway piece of gravel

Previous discussion on this topic: https://news.ycombinator.com/item?id=7522586

That's my not-so-subtle way of claiming a late victory on an internet argument since in this thread all the people claiming that it was more likely that it was something else were systematically downvoted.

On a less narcissistic note it's interesting to see the effect of different articles taking different angles on the comment section, I guess even HN is not proof to confirmation bias and hivemind.

Re: Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

#27

Post by runarberg »

jpswade wrote: post #10

tl;dr: Occam’s Razor demands the simplest explanation and so it probably was a stowaway piece of gravel

This isn't just about the Occam's Razor. The author goes through a thorough analysis of the evidence. Surely a forged video is a simpler explanation, but given the fact that the trajectory and the timing of the rock matches a simulated timing and trajectory and timing of a gravel falling out of the parachute, than the most probable explanation is the stowaway piece of gravel.

Re: Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

#28

Post by hammock »

jerf wrote: post #18
chillingeffect wrote: post #17

Earlier quoted context omitted.

I came here to post that it was a great article - except for the needless invocation and anthropomorphization of Occam's Razor. I. It is not clear that a rock falling out is _simpler_ than a meteorite falling out. How exactly is a meteor less simple? Sure, it's rarer and less likely, but it is not simpler. II. A simple explanation of a how an iPhone works is "magic." But we know that's not the case. Our invocation of…

"Simpler" is how it was formulated at the time... nowadays we'd probably formulate it in terms of going with the possibility that least amount of "luck" in its explanation. Something that requires four events with 99% probability is still more likely than an explanation that requires one at 0.004%, even if it is not "simpler". (Those numbers are just made up, not my guess at the odds in question... in reality, the gu…

Your reformulation reduces Occam's Razor to tautology- "the most probable explanation is the most probable." You might want to rethink that.

http://en.wikipedia.org/wiki/Occam%27s_razor#Formulations_be...

Re: Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

#29

Post by ghkbrew »

hammock wrote: post #28
jerf wrote: post #18

Earlier quoted context omitted.

"Simpler" is how it was formulated at the time... nowadays we'd probably formulate it in terms of going with the possibility that least amount of "luck" in its explanation. Something that requires four events with 99% probability is still more likely than an explanation that requires one at 0.004%, even if it is not "simpler". (Those numbers are just made up, not my guess at the odds in question... in reality, the gu…

Your reformulation reduces Occam's Razor to tautology- "the most probable explanation is the most probable." You might want to rethink that. http://en.wikipedia.org/wiki/Occam%27s_razor#Formulations_be...

Isn't that sort of the point? It's true, because it's a disguised tautology.

Re: Forensic Ballistics: How Apollo 12 Helped Solve the Skydiver Meteorite Mystery

#30

Post by debt »

tc_ wrote: post #11

The article's discussion of golf balls reads completely opposite to standard well-accepted theory. The author writes: > [The "drag catastrophe"] is when an object is falling so fast that the boundary layer of gas separates off the object and the drag force suddenly drops by a factor of almost 10. The reason why golf balls have dimples is to cause this drag catastrophe to happen at slightly slower speeds, so the ball…

I'm confused if a low-enough Reynolds number implies that laminar flow is still happening, how would the dimples on a golf ball even create turbulent flow given they have such a low Reynolds number?

EDIT: Ah, the velocity determines increases so does the Reynolds number. So at around 55 mph, the Reynolds number is high enough to induce turbulent flow.

This article is fascinating and now I understand why golf balls have dimples.

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