Re: Identity

christophe delriviere (
Sat, 21 Nov 1998 04:17:05 +0100

Eugene Leitl wrote:

> Randall Randall writes:
> > The very language you use betrays the assumption that they
> > are not, in fact, identical. To wit, "positions" is plural,
> > and perfect identity would require that they have an identical
> > position, no?
> Hang language. Can you give me a measurement procedure how you are
> supposed to distinguish between these copies if your observation of
> their spacetime trajectories is interrupted? Space itself isn't
> labelled, nor are system's particles.

We could, for example, guess by their previous respective positions and what we know of their respective environments some properties they will respectively have after the interruption of the observation of their space-time trajectories. couldn't we? of course i can't imagine an universal way to distinguish, the way to distinguish is dependent of the configuration of the system. I didn't say here there will not exist situations in witch distinction is impossible, i say there exist plenty of situations where we could easily distinguish between the two brains.

example :

for the demo, we consider we really could have true identical copies of a brain at a same time.

system : our universe including a brain1 and a brain2.

(concept of identity without considering the respective positions of the brains)

Consider brain1 is separated by (10c * 1 second) of brain2. (c= light speed in meter/second)

Say the interruption of observation of their space-time trajectories is of 1 second.

By witch physical process can you exchange (in 1 second) the two brains who where truly identical at the beginning of the interruption of the observation of their space-time trajectories ? As far as i know, i think it's impossible. If you think it's possible and you can provide facts, then i agree with you.

we could thus be able to distinguish between these two brains after the interruption of the observation of their space-time trajectories. Respective positions of the two brains, even if they are truly identical (without position concept) at the beginning, do matter.

> I'd presume otherwise identical objects is indistinguishable, since
> space is rotationally and translationally invariant. (It's actually
> not enantioinvariant, but you'll find that out if you look _very_

I fail to understand the point... how can two macro objects be truly identical at quantum level? by chance?Space is very probably rotationally and translationally invariant, but the universe is not empty and what happen in a place at a certain time doesn't necessary happen in another place at the same time, so there is variations of the *macro* properties of the universe in function of the position relative to an arbitrary object.

I think the identity concept you are claiming for is very useful in quantum mechanics, but doesn't apply for a macro object like a human brain. Perhaps i'm not correcty understanding what you are asking for or i'm fooling myself, but if you are able to prove me that position doesn't matter, i will be in debt to you.