# Reading too much into a riddle

1. Dec 7, 2003

### Hurkyl

Staff Emeritus
Here's a classic riddle (whose statement I am totally butchering, but that's ok!):

"A man is carrying a canister of liquid which he claims to be a universal solvent. How do you know he's lying?"

This text here is a bit of filler warning you that I'm going to spill the answer to this riddle in the next paragraph. So, if you want to figure out the riddle first, stop reading now before you accidentally get to the answer, because the answer is coming up soon. Ok, if you're reading at this point you don't mind having it spoiled.

The answer is that if it was a universal solvent, then it would dissolve the canister which contains it!

Now, for some odd reason I was thinking about this riddle, and realized I don't like the answer; couldn't a universal solvent become saturated, in which case it thus couldn't dissolve its container?

2. Dec 7, 2003

### Ambitwistor

I don't know, but another objection is that the solvent could be slow-acting and the container simply hasn't dissolved yet.

3. Dec 7, 2003

### turin

time is the universal solvent.

4. Dec 7, 2003

### jimmy p

I thought or ur answer as i read it Hurkyl and that led me to think that the man couldnt really carry it...he'd have no arms left so it should be

"a man with no arms is standing in front of a burnt and bottomless canister, claiming it contained universal solvent, is he lying?"

but then i suppose it would dissolve some of the ground so he must be lying...maybe he is holding Ribena

5. Dec 7, 2003

### Nereid

Staff Emeritus
Here's another take ... 'universal' carries quite a deep set of hidden assumptions, so he must be a mind-reader (to know that his 'universal' is close to what you'd understand by the word), or setting an exam question (exam questions frequently fail to define the scope well; hence the one about the physics student, the barometer, and the tall building), ignorant, ...

Examples: if it's 'universal' it would work as a solvent on Mars, at the equator of Mercury, on Pluto, at the metalic hydrogen surface in Jupiter, ... there could be a substance that's liquid under all those conditions?

6. Dec 8, 2003

### jimmy p

so bottom line, the guy's a liar

7. Dec 8, 2003

### NateTG

There are certainly also other scenarios. For example, the container does not need to be conventional, like electromagnetic containment systems.

It's also possible that the rate of solution of the container is quite low so that it dosen't need to be changed.

A third possibility is that the container consists of aligned macromolecules, and the solvent needs to get to the other side before it can dissolve the container.

8. Dec 8, 2003

### turin

Re: Re: Reading too much into a riddle

Can you elaborate?

9. Dec 8, 2003

### NateTG

Re: Re: Re: Reading too much into a riddle

Let's say the container is built out of molecules that are somewhat like lego bricks. When they crystalize (form a solid) then they are aligned in stacks.

Lego bricks can relatively easily be stacked, but it takes a lot of work to pull a brick out of the middle of a stack of them. Similarly, it might be difficult for a solvent to act on the material from one direction, and not from another, or in one region, and not in another. A container has an interior and an exterior, so if the vulernable regions are on the exterior, then the interior might still be able to hold the solvent.

Of course, the notion of universal solvent is somewhat unclear, so this may not be an effective response.