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Just because physics doesn't have a notion of identity, doesn't mean there is no such thing. Identical particles have different identities because they have a

by ericb 13y ago

Just because physics doesn't have a notion of identity, doesn't mean there is no such thing. Identical particles have different identities because they have a different location in space-time. The location in space-time creates the identity. There's also a problem with the math of your claim. They can't "be the same particle" if you can have two of them. 1 != 2

endtime 13y ago
> Just because physics doesn't have a notion of identity, doesn't mean there is no such thing. How is that not exactly what that means?
- ericb 13y ago
  Because physics is not done?
- randallsquared 13y ago
  Identity, like beauty, fun, and spiciness, is[1] something that's built on physics, not requiring a fundamental property, just as asking how much spiciness an electron has is futile. [1] Well, presuming it actually does exist as something other than confusion, which I'm not currently arguing, though I'm sympathetic to the notion.
  - endtime 13y ago
    Beauty has physical structure on a couple levels. You can either talk about certain synapses lighting up (or whatever happens in the brain when someone experiences beauty) or you can talk about facial symmetry and 1.618. Fun is an extremely vague notion, I'm not sure what it means or if it even has a consistent set of synaptic patterns (or whatever), but I think that's probably because people don't use the term consistently (or are confused, etc., as you say). Spiciness is absolutely purely chemical.
- johnday 13y ago
  I think the problem there is with the first half of that statement, > Just because physics doesn't have a notion of identity I inferred that the intended meaning was "Just because the field of physics has no notion of identity". Obviously in philosophical and sociological circles there is absolutely a concept of identity.
loup-vaillant 13y ago
You should read the Quantum Physics sequence I mentioned above. There is no Royal Road, and the whys and hows just cannot be explained in a few lines[1]. If you want a short-cut nonetheless, try here[2] to understand what is a configuration space, then proceed there[3] to understand what "no identity" really means. I won't repeat Eliezer here, you really have to follow the links. Now I did made some language abuse. First, there is no such things as a particle at the basic level. I mean, there are particles, but in the same sense that there are houses: particles are not the fundamental stuff, they are made up of the fundamental stuff, just like houses are made up of bricks. Second, It is possible to test whether two situations are the same, or not. And I don't mean "nearly the same", I mean exactly the same. The difference is rather drastic: in one case you end up with |x|²+|y|² (where x and y are two complex numbers), and in the other case, you end up with |x+y|². Third, there are no labels attached to particles. The universe is not like "photon A here, photon B there". It is more like "photon here, photon there". We know that because of my second point: there is just no difference between "photon A here, photon B there" and "photon B here, photon A there", it is the same configuration. Now, when you move a particle from point A to point B, those are certainly different configuration. (So you do have a point). On the other hand, the way you move the particles doesn't matter in the slightest, as long as the end result is the same: having the particle at point B. Well, the same goes for a human. Flying from London to New-York doesn't destroy your identity. The only thing that matters it that you end up in New-york. So, whether you took the plane, or have been wired across the internet just doesn't matter. You end up in New York. Now, sure there is some difference: locally, you are the same. But the world around you is different. So this is a different configuration[4]. The plane didn't fly, computers did some more work, bandwidth got consumed… But that doesn't sound like the kind of difference that destroys your identity, even intuitively. I mean, by writing this text, I have a much greater influence over your than the motion of a plane could ever have (unless you're in it, or watching it). And I don't destroy your identity. Now that's about it. Those who hunger for more should really read the whole Quantum Physics Sequence. [1]: http://lesswrong.com/lw/kg/expecting_short_inferential_distances/ http://lesswrong.com/lw/kg/expecting_short_inferential_dista... [2]: http://lesswrong.com/lw/pi/classical_configuration_spaces/ http://lesswrong.com/lw/pi/classical_configuration_spaces/ [3]: http://lesswrong.com/lw/pl/no_individual_particles/ http://lesswrong.com/lw/pl/no_individual_particles/ [4]: http://lesswrong.com/lw/pf/distinct_configurations/ http://lesswrong.com/lw/pf/distinct_configurations/

by ericb 13y ago

endtime 13y ago

> Just because physics doesn't have a notion of identity, doesn't mean there is no such thing. How is that not exactly what that means?

ericb 13y ago
Because physics is not done?
randallsquared 13y ago
Identity, like beauty, fun, and spiciness, is[1] something that's built on physics, not requiring a fundamental property, just as asking how much spiciness an electron has is futile. [1] Well, presuming it actually does exist as something other than confusion, which I'm not currently arguing, though I'm sympathetic to the notion.
- endtime 13y ago
  Beauty has physical structure on a couple levels. You can either talk about certain synapses lighting up (or whatever happens in the brain when someone experiences beauty) or you can talk about facial symmetry and 1.618. Fun is an extremely vague notion, I'm not sure what it means or if it even has a consistent set of synaptic patterns (or whatever), but I think that's probably because people don't use the term consistently (or are confused, etc., as you say). Spiciness is absolutely purely chemical.
johnday 13y ago
I think the problem there is with the first half of that statement, > Just because physics doesn't have a notion of identity I inferred that the intended meaning was "Just because the field of physics has no notion of identity". Obviously in philosophical and sociological circles there is absolutely a concept of identity.

loup-vaillant 13y ago

You should read the Quantum Physics sequence I mentioned above. There is no Royal Road, and the whys and hows just cannot be explained in a few lines[1]. If you want a short-cut nonetheless, try here[2] to understand what is a configuration space, then proceed there[3] to understand what "no identity" really means. I won't repeat Eliezer here, you really have to follow the links. Now I did made some language abuse. First, there is no such things as a particle at the basic level. I mean, there are particles, but in the same sense that there are houses: particles are not the fundamental stuff, they are made up of the fundamental stuff, just like houses are made up of bricks. Second, It is possible to test whether two situations are the same, or not. And I don't mean "nearly the same", I mean exactly the same. The difference is rather drastic: in one case you end up with |x|²+|y|² (where x and y are two complex numbers), and in the other case, you end up with |x+y|². Third, there are no labels attached to particles. The universe is not like "photon A here, photon B there". It is more like "photon here, photon there". We know that because of my second point: there is just no difference between "photon A here, photon B there" and "photon B here, photon A there", it is the same configuration. Now, when you move a particle from point A to point B, those are certainly different configuration. (So you do have a point). On the other hand, the way you move the particles doesn't matter in the slightest, as long as the end result is the same: having the particle at point B. Well, the same goes for a human. Flying from London to New-York doesn't destroy your identity. The only thing that matters it that you end up in New-york. So, whether you took the plane, or have been wired across the internet just doesn't matter. You end up in New York. Now, sure there is some difference: locally, you are the same. But the world around you is different. So this is a different configuration[4]. The plane didn't fly, computers did some more work, bandwidth got consumed… But that doesn't sound like the kind of difference that destroys your identity, even intuitively. I mean, by writing this text, I have a much greater influence over your than the motion of a plane could ever have (unless you're in it, or watching it). And I don't destroy your identity. Now that's about it. Those who hunger for more should really read the whole Quantum Physics Sequence. [1]: http://lesswrong.com/lw/kg/expecting_short_inferential_distances/ http://lesswrong.com/lw/kg/expecting_short_inferential_dista... [2]: http://lesswrong.com/lw/pi/classical_configuration_spaces/ http://lesswrong.com/lw/pi/classical_configuration_spaces/ [3]: http://lesswrong.com/lw/pl/no_individual_particles/ http://lesswrong.com/lw/pl/no_individual_particles/ [4]: http://lesswrong.com/lw/pf/distinct_configurations/ http://lesswrong.com/lw/pf/distinct_configurations/