Riddle Me Physics

Physics is all about riddles. What are we made of? How did we get here? How do you cool down a group of particles to a millionth of a degree above absolute zero when you can only build a refrigerator that gets down to 4 Kelvin? Physicists must find the answers.

If you like riddles and puzzles, physics probably tickles your fancy. There’s a great deal of creativity involved in uncovering lines of cause and effect. Here’s one puzzle that me and my friends in undergrad would pitch to newbies:

Start with a room. The room has no windows and one door. Inside the room is a lightbulb. Outside the room there are three switches. One of the switches turns on the light. You are allowed to open the door once, but you cannot flip any switches while the door is open. So, you could open the door while one of the switches is flipped on, but you can’t flip the switch off or flip on another switch until the door is closed.

How do you find out which switch turns on the light?

There’s a hint and more riddles after the jump.

Here’s one I love.

Surrounded by loved ones, you die a peaceful death and go to the crossroads of the afterlife. You are presented with two roads. One leads to heaven and one leads to hell (or whatever desireable/undesireable locations you want to imagine). You can only take one path and you cannot change your mind or turn back once you have chosen. The paths look the same from where you stand, and you cannot tell which one leads where. To find out, you must ask the advice of The Twins. But beware: one Twin is good and wants you to take the road to heaven. He will only tell the truth. The other Twin is evil, wants you to take the road to hell, and can only tell you a lie. Like the roads, you cannot tell which Twin is which. And to top it all off, you can only ask The Twins one question to try to figure out which path leads to heaven (only one question, not one per Twin). What question do you ask to guarantee you will find the road to heaven?

The hint for riddle number 1 is that finding the answer has to do with heat. The hint for riddle number 2 is, try to figure out what question they will both give the same answer to.

Answers at the bottom.

The first riddle is about manipulating a system. How do we get the information we want out of it when we can’t manipulate it however we please. Limitations in our ability to collect information arise all the time. Some people might say that the answer to quesion one is to smash a hole through the wall so you can see which switch turns on the light. And I guess that doesn’t violate the rules. But the better solution is to use what resources you have to get the information indirectly. We cannot, for example, pin down an electron and see exactly where it was and when. So we find indirect ways to detect its presence.

The second riddle is more about knowing the right questions to ask. Sometimes that can impact results as much as the answer. Lost fans know this all to well – it’s not where are they but when are they? Ugh.

OK – answers at the bottom, and maybe more examples of physics riddles next week. More riddles here. Happy weekend!

Riddle one answer: The door is closed. Turn on one of the switches and wait a few minutes. Turn off the first switch and turn on the second. Open the door right away. If the bulb is on, it’s switch number two. If the bulb is off, check to see if it is warm. If it is, it is bulb number one. If it is neither on nor warm, it must be switch number three.

Riddle two answer: Ask either twin which path the other twin would recommend you take. Either way, take the opposite road.

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