# How can we identify an object

1. Jun 19, 2008

### enricfemi

if one day we have a machine which can records every atoms' position and kind,and breake down the object into atoms,then rebuild the object use the record before.

is the object after such process still the same object before it?

if we have a clock,and we tear down it. is it still a clock? of course not. but if it is broken,and we just change one part of it, is it the same clock? if it is ,which part should we change ,then it's not?

2. Jun 19, 2008

### lzkelley

Last edited: Jun 19, 2008
3. Jun 19, 2008

### Crosson

Scientifically, it is not clear that this well ever be possible. There is already one rigorous impossibility result in this area:

http://en.wikipedia.org/wiki/No_cloning_theorem

Philosophically, the ability to make perfect copies would be a bedrock shift in our understanding of what it means for two things to be the same.

Right now it maybe silly to say:

"I know this is the same cup I used yesterday."

But in this future with perfect duplication this could be bonafide knowledge, since when pressed for evidence you could say:

"After all, I am sure it has never been recorded by a duplicate machine."

In other words, we will deal with this issue as it arises; it is a non-problem.

4. Jun 23, 2008

### enricfemi

thanks,but i still confused.
to make this thing more clearly, i decided to use another example:
suppose a drop of water, i drop it to sea, is it still exist?

5. Jun 30, 2008

### robheus

The water molecules and whatever else was in the water are still there, but there is a very small change you will ever be able to poor out that same configuration of water and other molecules out of the ocean ever before.
However, please consider that molecules are supposed to be identical, so that dramatically increases your chances, just that it needs to have the same number of each molecule.

6. Jun 30, 2008

### DaveC426913

When the atmoic world is as finely-definable as the digital world, we will have that.

Question: is a copy of a file in your computer distinguishable from its original? The answer to this question will answer your real-world question.