# The Naked Scientists Forum

### Author Topic: Sandtimer Riddle  (Read 3883 times)

#### latebind

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##### Sandtimer Riddle
« on: 15/09/2009 16:01:26 »
This is originally from a post on Quantum Mechanics [http://www.thenakedscientists.com/forum/index.php?topic=20330.0]
I really like this one so I'll devote a seperate thread to it if that is allright with moderators?

The Sandtimer Riddle

Suppose you have two identical,sealed sandtimers. These are identical in every way, from the number of grains to the number of atoms and particles in each sandtimer, and the placement of all other particles is identical in every way. [Remember this is a thought experiment http://en.wikipedia.org/wiki/Thought_experiment]

Now, you flip both of these over at exactly the same nanosecond and watch the grains fall through. [Remember everything is exactly the same in both sandtimers]

Do you think that each timer would have the exact same grain(s) falling through at any given time?
Do you think that both sand timers would be perfectly synchronized in every single possible way?

My belief is that the answer is 'NO' to both questions, and I believe it is because of the inherent unstability of atoms returning to home base in different positions as described in the post where this experiment came from [http://www.thenakedscientists.com/forum/index.php?topic=20330.0]

« Last Edit: 15/09/2009 16:34:12 by latebind »

#### JP

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##### Sandtimer Riddle
« Reply #1 on: 15/09/2009 18:25:38 »
Do you want a classical or quantum answer?  Your language suggest classical mechanics, since you're talking about grains of sand, placement of particles, etc.  In that case, to the accuracy of classical mechanics, the two timers would produce identical results.

If you want to bring quantum mechanics into it, you need to be more specific about what you mean by "identical."  You can only specify that things are identical up to certain limits due to uncertainty principles.  If they're identical up to those limits, then their quantum mechanical states should evolve identically, but upon measuring them, you might get different results.  In your case, it could tell you "there's a 50% chance that a grain of sand has fallen through" for both timers, but when you measure the sand, you might see that it has fallen in the left-hand timer and hasn't in the right-hand timer.  This result is perfectly consistent with the two timers having identical states before you measure them.

#### latebind

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##### Sandtimer Riddle
« Reply #2 on: 15/09/2009 23:24:26 »
Allright, I'll make this slightly simpler.

Take a single sandtimer, and clone it perfectly so that all quantum and physical states are cloned.
Now there is no grey area with regard to state deeper than ordinary physics, they are both identical in all dimensions.

I still believe they will not be synchronous due to the inherent instability of atoms returning to home base(center of gravity), and BTW this is actually what I believe causes gravity in the first place as you'll see from the original blog...

#### JP

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##### Sandtimer Riddle
« Reply #3 on: 16/09/2009 01:02:52 »
Again, my answer would be the same.  Classically they'd be identical.  If you use quantum mechanics, you cannot clone the original sandtimer perfectly.  The uncertainty principle won't allow you to do so.

As I said before, the best you can do is to have a quantum sandtimer manufacturing plant that made the sandtimers in identical manners.  In that situation, the quantum states of the sandtimers would be identical, but measurements have a good chance of producing different results.

As a thought experiment, this doesn't in any way violate quantum mechanics or the laws of physics in general.

#### latebind

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##### Sandtimer Riddle
« Reply #4 on: 17/09/2009 11:54:37 »
I appreciate your opinion, but you are lacking imagination here, as this is a thought experiment and is supposed to model the impossible (thats the whole point)

« Last Edit: 17/09/2009 11:57:46 by latebind »

#### LeeE

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##### Sandtimer Riddle
« Reply #5 on: 17/09/2009 14:01:49 »
I think JP has answered correctly and the real problem is that you're demanding a sensible solution to a nonsensical situation.

As you say, it "is supposed to model the impossible (thats the whole point)", so if you start from a position that is, by definition, impossible how can you expect a real answer that reconciles the impossibility?  You could, of course, come up with an impossible answer that might solve the problem, but then it wouldn't apply to reality, would it?

#### latebind

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##### Sandtimer Riddle
« Reply #6 on: 17/09/2009 14:33:59 »
Hahaha!

That was funny, really, how much you missed the point.

#### syhprum

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##### Sandtimer Riddle
« Reply #7 on: 17/09/2009 15:08:01 »
I feel JP has said all there is to say on the matter, in the classical world cloning is possible ( at least in theory ) but in the quantum world it is not.
Thought experiments can only model what is possible in theory at least it is futile to try to model what is known to be impossible.
« Last Edit: 17/09/2009 15:11:44 by syhprum »

#### BenV

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##### Sandtimer Riddle
« Reply #8 on: 17/09/2009 15:16:08 »
If the two are identical, with identical forces acting upon them, why would one assume they would do anything other than the same thing?

#### lending

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##### Sandtimer Riddle
« Reply #9 on: 21/09/2009 12:49:20 »
I am interested in the topic. And there is good discussion here. But i could not understand anything.

#### Don_1

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##### Sandtimer Riddle
« Reply #10 on: 21/09/2009 12:58:11 »
I am interested in the topic. And there is good discussion here. But i could not understand anything.

That's because you are too busy being spammy.

#### The Naked Scientists Forum

##### Sandtimer Riddle
« Reply #10 on: 21/09/2009 12:58:11 »