π = 3 (sometimes) for Nobel laureate • Hacker News Board

Re: π = 3 (sometimes) for Nobel laureate

#21

Post by jessriedel » Wed, Apr 06, 2011, 10:06 PM UTC

Jabbles wrote: post #5

Hmm, whilst it's true physicists often simplify equations to really understand the problem, I can't think of a variable in quantum mechanics we "don't know to within 2 orders of magnitude". Especially one called alpha, which usually denotes the fine structure constant, which we know to better than 1 in a billion... Anyone have some thoughts on what it could be, if true? http://en.wikipedia.org/wiki/Fine-structure_con…

> I can't think of a variable in quantum mechanics we "don't know to within 2 orders of magnitude".

Maybe the neutrino masses differences? In my intro QM class, we did a problem where we calculated the distance it took for one neutrino flavor to mix into another, which depends on the mass differences. You wouldn't want to take a square root of eV, though.

Or it could be it's one of the CKM angles. The latter are known to 1 part in 10^4, but only because of the relatively recent BaBar and BELLE experiments. Maybe back when this guy was an undergrad they only know them to 1 part in 100. Seems kinda advanced for 3rd semester of QM...

Re: π = 3 (sometimes) for Nobel laureate

#22

Post by itsnotvalid » Wed, Apr 06, 2011, 10:12 PM UTC

omh wrote: post #15

dmnd wrote: post #13

Earlier quoted context omitted.

Proof for the curious: http://www.google.com/search?q=number+of+seconds+in+a+year+d...

I understand what you did, but the mathematician in me cringed at the word "proof" in that comment.

May be the word "fact" would be better to describe these kind of numbers.

Re: π = 3 (sometimes) for Nobel laureate

#23

Post by ez77 » Wed, Apr 06, 2011, 10:26 PM UTC

splat wrote: post #12

It's a little unrelated, but if you ever need to know the number of seconds in a year, it's pi x 10^7 to within .5%.

Or, as stated in Bertley's "Programming Pearls":

  Pi seconds is a nanocentury.

Re: π = 3 (sometimes) for Nobel laureate

#24

Post by tygorius » Wed, Apr 06, 2011, 10:35 PM UTC

Jabbles wrote: post #5

Hmm, whilst it's true physicists often simplify equations to really understand the problem, I can't think of a variable in quantum mechanics we "don't know to within 2 orders of magnitude". Especially one called alpha, which usually denotes the fine structure constant, which we know to better than 1 in a billion... Anyone have some thoughts on what it could be, if true? http://en.wikipedia.org/wiki/Fine-structure_con…

Two aspects spring to mind. First, we don't know how long ago this course was, so it's quite possible some of the story is either dated or a slightly misremembered anecdote for a physicist who was brought up with slide rules for his calculations. Second, the quote specifies "experimentally", which implies measurements limited to two orders of magnitude, i.e., measured vs theoretical. Alas, while I have a few slipsticks in the closet, I am not now nor have I ever been a physicist, so I could be totally wrong on this.

Re: π = 3 (sometimes) for Nobel laureate

#25

Post by lukeschlather » Wed, Apr 06, 2011, 11:33 PM UTC

guylhem wrote: post #17

I will never forget an high school assignment in physics in France, where we were asked to calculate how a wheel of a given diameters would put marks to the road if it had a pen attached at a given position. Our teacher always said she accepted all result with an error of less than 10% if we did that by making the calculus easier. So I started by "let's define pi=3" I got a bad grade on that one, even after I protest…

>Our teacher always said she accepted all result with an error of less than 10% if we did that by making the calculus easier.

In English, calculus and calculation are two different things. And there are a number of grammatical errors in that sentence that make the meaning unclear.

I'm noting this because if the teacher allowed you to do simpler calculus so long as you maintained an error margin of 10%, that's different from allowing you to do simpler calculations provided you keep an error margin of 10%. Calculus is specifically the branch of mathematics involving limits, functions, derivatives, and integrals, and from the English it sounds like she, if we are being perfectly pedantic, was giving you the option do do approximations with your integrals and derivatives, not with any value you like.

Re: π = 3 (sometimes) for Nobel laureate

#26

Post by syncsynchalt » Wed, Apr 06, 2011, 11:35 PM UTC

FaceKicker wrote: post #19

Off topic, but why is the "pi" character in most common fonts so poorly designed? It always seems to have a straight line at the top rather than a tilde-like stroke and it confuses me just about every time.

I had the same problem, I thought the author mistakenly used ∏ but I see in my browser tab that it's correctly lowercase.

Re: π = 3 (sometimes) for Nobel laureate

#27

Post by ciupicri » Wed, Apr 06, 2011, 11:59 PM UTC

As my programming teacher used to say when talking about floating numbers and their errors, π is 5 in agriculture and 3.14159 in civil engineering.

Re: π = 3 (sometimes) for Nobel laureate

#28

Post by kwantam » Thu, Apr 07, 2011, 12:01 AM UTC

lukeschlather wrote: post #25

guylhem wrote: post #17

I will never forget an high school assignment in physics in France, where we were asked to calculate how a wheel of a given diameters would put marks to the road if it had a pen attached at a given position. Our teacher always said she accepted all result with an error of less than 10% if we did that by making the calculus easier. So I started by "let's define pi=3" I got a bad grade on that one, even after I protest…

>Our teacher always said she accepted all result with an error of less than 10% if we did that by making the calculus easier. In English, calculus and calculation are two different things. And there are a number of grammatical errors in that sentence that make the meaning unclear. I'm noting this because if the teacher allowed you to do simpler calculus so long as you maintained an error margin of 10%, that's differe…

You're being pedantic in English in response to an exchange that presumably happened in French. :)

Re: π = 3 (sometimes) for Nobel laureate

#29

Post by jberryman » Thu, Apr 07, 2011, 12:23 AM UTC

omh wrote: post #15

dmnd wrote: post #13

Earlier quoted context omitted.

Proof for the curious: http://www.google.com/search?q=number+of+seconds+in+a+year+d...

I understand what you did, but the mathematician in me cringed at the word "proof" in that comment.

proof by googlization

Re: π = 3 (sometimes) for Nobel laureate

#30

Post by wging » Thu, Apr 07, 2011, 12:43 AM UTC

goalieca wrote: post #3

This guy sounds like every microelectronics prof ever. :) I took that to heart when doing the exams and it make the impossible possible.

My favorite one of these comes from physics.

Simple harmonic motion impossible to deal with? Voila, assume |sin(x) - x| is small and just deal with x instead of sin(x)--magic!