Riddle Definition and 152 Threads

It was Eric Barber from t'other village, they shave each other, obviously they don't trust anyone else because cutthroat razors.

I'm no expert in this stuff, and perhaps I don't understand these diagrams, but having said that, I don't understand why the typical Penrose diagrams I see of black holes look the way that they do. They all have a 45 degree (light speed) angle for the event horizon of the black hole, and they...

It's about problem 106 and 107 in Gauge Fields, Knots & Gravity. There's a wormhole of topology ##\mathbf{R} \times S^2## on which has been defined a spherical metric ##g = \mathrm{d}r^2 + f(r)^2 (\mathrm{d} \phi^2 + \sin^2{\phi} \mathrm{d} \theta^2)## as well as a 1-form ##E =...

A theoretical astrophysicist was absentmindedly working through papers on Mossbauer spectroscopy, eventually coming to the Pound Rebka experiment, a remarkable test of GR. (Gamma rays were sent from the top of a building to a receiver, so as to measure the gravitational blueshift in such an...

That question came from one of the students in my classical mechanics class, it took me unprepared at first but was able to give the correct answer in like half a minute. They liked it a lot and it initiated a useful discussion about laws of nature extending even to some particle physics...

At 12.00h a specific event is being expected in Berlin, whether the wall ist teared down, or not. The sender is in Berlin and wants to send the information about the event to the recipient on the moon. Both sides know about the possibly upcoming event. As the light takes 1 second to the moon...

Hi, I got a problem I am trying to solve. An airplane flies at a fixed air speed which is unknown. There is a wind with unknown heading and unknown speed. The airplane has a known ground speed and direction. The airplane changes heading (with reference to ground), and now there is a different...

The original thread was closed << Mentor's Note -- the previous thread was closed because of age, not a rules issue >>, but I am really interested in hearing your opinions on a couple of theories I had. I am baffled at the idea that someone, with the ability to understand the math language to...

Just for fun and for community participation, I offer the following riddle. The person who answers first (with complete explanation of how the answer is deduced) wins a free copy of Understanding Our Unseen Reality: Solving Quantum Riddles. Question: Susie and Paula's teacher gives Susie the...

What will happen? And why?

Assume the water flows from the faucet sufficiently slow.

I saw in an other topic the following thought experiment: In the middle of a train there is a bom with two lightdetectors. At both ends of the train there are two switchable lightsources. The two lightdetectors measure the respective light from both sources. We switch on both switches...

The inspiration for this puzzle can be found here: http://mindyourdecisions.com/blog/2016/07/31/spies-sharing-secrets-sunday-puzzle/ . However, as is obvious from the unnecessarily convoluted character of the following two problems, the rest is original. Part 1: James Bond, Ethan Hunt...

As per the title, apologies for bringing this up again, but all previous threads were closed. Now, I can accept the answer and experimentation done, however as both a pilot and mechanical engineer, I just can't get my head around it. It's been bugging me for years, and created the account just...

First a definition: given a natural number ##a_na_{n-1}...a_0##, a subnumber is any number of the form ##a_k a_{k-1}...a_{l+1}a_l## for some ##0\leq l \leq k \leq n##. I think an example will be the easiest way to illustrate this definition: the subnumbers of ##1234## are...

Following the "enormous success" (it received a single like) of the last riddle, I decided to waste some bandwidth with a sequel! This one doesn't have an interesting concept or an unexpected solution, it's just hard to solve, so if you're looking for such a riddle, do yourself a favor and...

Below are ##6## riddles. Everybody completing a riddle has a chance on winning the book "Dark Matter and the Dinosaurs". Rules: For an answer to count, the complete reasoning must be given, not just the answer. Do not answer a question you already know the answer to. If a question is already...

Homework Statement son and father and granpa have same value for their birthday (except the year ostensibly) father is nine times the son's age now. calculate the granpa's age now. clues - five years ago, grandpa was 32 years older than what the father was at five years ago. -in five years...

I'm reading Cosmology by Harrison and in Chapter 21 he discussed the horizon riddle, I understood the problem that he posed but his solution was confusing. "Consider two widely separated observers, A (for Albert) and B (for Bertha). We suppose they can see each other. Each has a horizon such...

A teenager is looking at his father's beautiful mechanical swiss made watch, and asks him: 'Dad, is there a time of the day, beside noon and midnight, where the hour and minutes needles are aligned and pointing in the same direction ? '. What would you answer at the nearest second ?

This is a Riddle, one of my own so the answer isn't on the web anywhere and you all will be the first to see it. I have 4 legs and a very strong back, my name suggest riding but movement I lack. I do work faithful and true, its dangerous and dirty no one would want to do. By my strength so much...

http://img-9gag-fun.9cache.com/photo/aX9zqD2_460s.jpg

I was listening to a rerun of "http://www.cartalk.com/" today on NPR and was reminded of this riddle. It's been on PF before, but not for several years (at least that I'm aware of). I thought I'd repeat it for those who haven't heard it yet. I'm going to make a small modification to it though...

I've found this video about conditional probability: All steps look correctly, but the result does not make any sense. I'm ok with the part about frogs, but not so with the boy/girl computation. To sum it up: 1) I have two children and at least one of them is a boy. What is a probability I...

I once heard about Einstein's Riddle. I wanted to investigate a bit further so I looked it up and I found it. Einstein's five houses riddle. Some friends and I wanted to test if the 98% estimation was right, so we got together and wrote the rules down (our rules). There were ten of us, we had...

Hi, Every year, my youth group goes on a summer trip, the location of which is kept a complete secret from us until a certain deadline. Before the deadline, our leaders usually give us a riddle to the location of our trip. Specifically, one of our leaders, who has a degree in Physics from the...

Is there a solution to this game https://prlbr.de/2011/08/hundepuzzle/alle-karten.png in the form of an equation that only requires high school mathematics but no higher maths and informatics?

What am I? Ice women a knack weary yum Andy tall thevish feud. Mine aim kennel sobe agree klet her? the answer is.... "Siamese fighting fish" Can anyone explain to me how the hell this is the answer. My chemistry teacher gave this as a random extra credit question on our test. I am convinced...

I say 7, could I be wrong ? :cool:

Imagine two experiments A and B. In experiment A I load a gun with a cartridge and shoot a bullet. Total energy in this experiment will be E(heat) + E(projectile). I include recoil in E(projectile). E(heat) in its turn will heat the muzzle and some air. Done. In experiment B I do...

So perhaps I'm not the only one here on PF who's heard about this .That said, besides the gas cloud G2 concealing a low-mass star, I cannot help but wonder what azimuthal angle G2 made its closest approach to the supermassive black hole Sagittarius A*. The reason this is relevant is because...

Hello I am Badshot! I mainly created this account to reply to a thread about Albert Einstein's 5 houses riddle ( https://www.physicsforums.com/threads/Albert-einsteins-riddle.149083/ ) and because i just found out that i have insufficient permission to comment there, I thought I'd just put it...

Riddle me this. If it was possible to vibrate at near the speed of light, would that still create the effect of time passing faster for you but your surrounding passing through time at the same rate? Just wondering. I am aware that A) Time travel backwards would not function, due to the...

First of all, this is NOT a homework question. So I give you three barrels, one has 50 apples, the second has 50 oranges, the third has 50 - a mixture of both apples and oranges. However, I have intentionally placed the wrong labels on all of them. Find the minimum number of fruits you need...

Hello computer science people, riddle me this... you have three black boxes and three red boxes. You want to connect each black box with the three red boxes without making the lines interact with each other. can you do it ? or is it unsolvable ? Like this :

I have two children. One is a boy born on a Tuesday. What is the probability I have two boys?

What will happen to the balance:

Hi guys, My boss gave me a riddle. He says that you have a "black box" with a polynomial inside it like f(x)=a0+a1x+a2x^2+a3x^3 ... you don't know the rank of it or the coefficients a0, a1, a2 ... You do know: all of the coefficients are positive you get to input two x numbers and...

Suppose a bowler is standing on the edge of platform of a train speeding at 100 m/s, a bowl in his hand (m=1Kg) has KE 5000 J. The bowler throws his ball at 10 m/s giving the ball 50 J of KE , so the balls has total KE 5050 J, right?. Suppose now that the ball falls outside the platform on...

Homework Statement A famous lawyer takes on an apprentice on one condition: the lawyer will train the apprentice on the business, and the apprentice will have to pay the lawyer only after she wins her first case. Right after the end of the apprenticeship, the lawyer sues his own apprentice...

I'm doing battle with someone in a debate and I need some help here as, perhaps, I'm not articulating my side well or he's just so stubborn that he doesn't want to learn the error of his ways. :) It's the stupid old riddle where if you have 1000 birds in a plane or a truck (or any enclosed...

Albert Einstein wrote the following riddle this century when he was in his prime. He believed 98% of the people would not be able to solve it. Good luck! There are five houses in a row. Each of the five houses is a different color. In each house lives a person of a different nationality. The...

Hi, First time poster and I believe that the people on this forum may have a greater chance of solving this riddle or making sense of we have so far. http://imgur.com/eUAete2 http://imgur.com/eUAete2 I am more than happy to go into the background of all of this, but in short, this is...

What is the force that makes a neutron eject an electron, and how strong is it?

Give this riddle a read. As an avid fan of math riddles and brain teasers, this may be the most difficult one I've ever encountered. I posted this in the Set Theory forum, but thought this audience might enjoy it as well. Let me know what you think! Be aware that the solution is at the...

I've asked many people about the incredible conclusion of this riddle, whose solution applies the axiom of choice, and have yet to find a satisfying response. I understand the solution, but I would like to know why the axiom of choice leads to such a bizarre result, while being so compatible...

Hello everybody Here is a wicked math riddle. Go ahead and see if you can solve it A commuter is in the habit of arriving at his suburban station each evening at exactly five o’clock. His wife always meets the train and drives him home. One day he takes an earlier train and...

You are given eight coins of same denomination, out of the eight coins one coin is very very slightly heavy than the remaining seven such that you cannot separate it by weighing it in your palms. You are given a beam balance with the help of which you have to separate out the very slightly...

You have got two buckets of capacity 3 litres and 5 litres each and a tap. How will you exactly measure out 4 litres of water with the help of two buckets and the tap.

Two impatient people agree to meet up sometime between 3pm and 4 pm, in the era before mobile phones, just near Nelson's Column in London. They are so impatient they will only wait 15 minutes before leaving. What is the probability they actually meet up?