andrel wrote:
> Invisible wrote:
>> Suppose that every atom in the known universe had a unique serial 
>> number. Suppose I picked a serial number at random, and then asked you 
>> to go find out where that particular atom is. (Let us assume that 
>> there is no particular correspondence between serial numbers and 
>> position in space.)
> 
> I don't want to spoil your gedanken experiment, but in modern physics 
> you can not distinguish one (e.g.) hydrogen atom from another.

Sure. You're probably right. And anyway, how the heck would you write 
serial numbers on them, even if you could? More to the point, how would 
you catelogue them all in a giant database? And what if they move 
around? What if an atom is created or destroyed? etc.

My point is really just the staggering difference between complexity 
classes, rather than physical correctness. The same argument would apply 
to *anything* that there's 10^100 of - atoms in the universe is about 
the only [remotely] comprehensible way to describe just what a big 
number that is. ;-)

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> BTW, what if when you finally reach the area the atom was at originally it
> already moved on to an area you had already inspected?  concurrency problems?
> :)

Oh yeah.

I think your "database" would have to be at a specific point in time - 
which leads us nicely to the fact that time is not universal...

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Jim Henderson wrote:
> Actually, the real problem would be that electronic representation of the 
> atomic data would require atoms for storage purposes....So you'd have to 
> have the database operating outside the space/time continuum to begin 
> with. :-)

Yes, I believe I meantioned that one. ;-)

Other obvious problems include the clear impossibility of obtaining this 
data in the first place (uncertainty, anyone?), the subjective nature of 
both time and space, and the sheer craziness of the idea in the first 
place...

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Darren New wrote:
> andrel wrote:
>> I don't want to spoil your gedanken experiment, but in modern physics 
>> you can not distinguish one (e.g.) hydrogen atom from another.
> 
> You say this, but it's not actually true.  You cannot distinguish two 
> hydrogen atoms as long as you ignore the stuff that lets you distinguish 
> them.  Like, say, their positions.

no.

> Certainly the hydrogen atoms in my coffee are distinguishable from the 
> hydrogen atoms emitting light eight minutes ago in the sun.

nope

> Basically, science has a list of "things it's safe to ignore when 
> replicating an experiment."  Given that list, hydrogen atoms are 
> indistinguishable. But there's still a list.
Sorry, no. It may sound counterintuitive but there isn't. A proton does 
not have a position, but a peaked distribution in one place with a small 
but finite change that it is somewhere else entirely. If you have two 
protons, you have a distribution with two peaks with an amplitude large 
enough for two protons. Nothing more and individuality is a meaningless 
concept here. I am trying to find a macroscopic equivalent, but I can't, 
yet.
> 
> It's like saying "pennies are indistinguishable, from a spending point 
> of view. I can replace one penny with any other penny."  

There is a difference between the (sub)atomic and the macroscopic range. 
In the latter common sense is just that, in the former not.

> Yet I'll still 
> get arrested for putting all your pennies in my bank account.
> 
No as long as we assume that you exchanged all your pennies with mine 
simultaneously, I don't see why anyone would bother. ;)
Don't try this at home though, the number of pennies in this house will 
probably not exceed 2, mainly because we use a different currency.

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On Mon, 12 Nov 2007 19:05:34 +0000, Orchid XP v7 wrote:

> Jim Henderson wrote:
>> Actually, the real problem would be that electronic representation of
>> the atomic data would require atoms for storage purposes....So you'd
>> have to have the database operating outside the space/time continuum to
>> begin with. :-)
> 
> Yes, I believe I meantioned that one. ;-)

Ah, yes, so you did. ;-)

> Other obvious problems include the clear impossibility of obtaining this
> data in the first place (uncertainty, anyone?), the subjective nature of
> both time and space, and the sheer craziness of the idea in the first
> place...

Heisenberg would be proud. :-)

Jim

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Orchid XP v7 nous apporta ses lumieres en ce 2007/11/12 13:23:
> Warp wrote:
>> Invisible <voi### [at] devnull> wrote:
>>> Alternatively, you could perform an index lookup.
>>
>>   It's enough for the values to be sorted. Then you can simply perform
>> a binary search. Assuming fast random access the search should take
>> much less than a second.
> 
> Indeed. A binary index lookup and a binary search are equally efficient.
> 
> However, inserting a record for a new atom becomes somewhat 
> compute-intensive if we have to keep all the data in sorted order. (If 
> it's a typical array-like structure, O(n) complexity again. For an 
> index, it's just O(log n) - assuming any rebalancing you choose to do 
> doesn't blow it up.)
> 
> Of course, whether you have an unordered table and seperate index or 
> whether the index *is* the table doesn't matter too much. (Depending on 
> just how much data you store per atom...)
If you have a sorted list of serial numbers, the next item will have it's number 
set as n+1, or 1 after the current last element.
In the case of a balanced tree structure, concidering a tree with about 10^80 
elements, randomly adding a few billions elements is prety much insignifient.

-- 
Alain
-------------------------------------------------
At the feast of ego everyone leaves hungry.
	Bentley's House of Coffee and Tea, Tucson, AZ

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nemesis nous apporta ses lumieres en ce 2007/11/12 12:33:
> Invisible <voi### [at] devnull> wrote:
>> (We casually ignore for the moment the minor detail that a database
>> describing the known universe would obviously be very much larger than
>> the actual universe itself, and hence could not possibly exist inside it...)
> 
> Asimov solved this long ago!
> http://www.multivax.com/last_question.html
> 
> :)
> 
>> Assuming that you could somehow examine several million million million
>> records per second (highly implausible), to find the atom you're looking
>> for would take... several tens of billions of times the current age of
>> the universe.
> 
> BTW, what if when you finally reach the area the atom was at originally it
> already moved on to an area you had already inspected?  concurrency problems?
> :)
> 
> 
The data will, of course, include the precise speed and direction of every 
atoms, along with it's mass, magnetic momentum and spin, and how it can interact 
with other atoms and any photons. With that information, you can predict where 
it will be at any time of your choosing within a Km radius.

-- 
Alain
-------------------------------------------------
Lutheran: If shit happens, don't talk about it.

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Darren New wrote:
> You say this, but it's not actually true.  You cannot distinguish two 
> hydrogen atoms as long as you ignore the stuff that lets you distinguish 
> them.  Like, say, their positions.

	Have to agree with andrel here.

> Certainly the hydrogen atoms in my coffee are distinguishable from the 
> hydrogen atoms emitting light eight minutes ago in the sun.

	Nope. Just that the wavefunction will be such that most likely that if 
we ignore that there is another H atom near the sun, the physics near 
your coffee will barely change.


-- 
Give a man a fish and you feed him for one day. Teach him to use the Net 
and he won't bother you for weeks.


                     /\  /\               /\  /
                    /  \/  \ u e e n     /  \/  a w a z
                        >>>>>>mue### [at] nawazorg<<<<<<
                                    anl

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Alain wrote:
> The data will, of course, include the precise speed and direction of 
> every atoms, along with it's mass, magnetic momentum and spin, and how 
> it can interact with other atoms and any photons. With that information, 
> you can predict where it will be at any time of your choosing within a 
> Km radius.

You're joking, right? :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Mueen Nawaz wrote:
> Darren New wrote:
>> You say this, but it's not actually true.  You cannot distinguish two 
>> hydrogen atoms as long as you ignore the stuff that lets you 
>> distinguish them.  Like, say, their positions.
> 
>     Have to agree with andrel here.

Hmmmmm.... OK.  I can see that.  How does space-like separation affect 
that, tho?

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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