Your position within our universe is giving you a bias toward one side of a mostly symmetrical situation.
Let’s throw out the terms “real” and “simulated” universe and call them the “parent” and “child” universe.
Gravity in the child universe doesn’t affect the parent universe, true; creating a simulation of a black hole doesn’t suck the simulating computer into the event horizon. But gravity in the parent universe doesn’t affect the child universe either—if I turn my computer upside-down while playing SimCity, it doesn’t make my Sims scream and start falling into the sky as their city collapses around them. So instead of saying “simulated gravity isn’t real because it can’t affect the real universe”, we say “both the parent and child universes have gravity that only acts within their own universe, rather than affecting the other.”
Likewise, when you say that you can’t point to the location of a gravitional force within the simulation so it must be “nowhere”—balderdash. The gravitational force that’s holding Sim #13335 to the ground in my SimCity game is happening on Oak Street, right between the park and the corporate tower. When discussing a child-universe gravitational force, it is only necessary to show it has a location within the child-universe. For you to say it “doesn’t exist” because you can’t localize it in your universe is as parochial as for one of my Sims to say you don’t exist because he’s combed the entire city from north to south and he hasn’t found any specific location with a person named “dfranke”.
if I turn my computer upside-down while playing SimCity, it doesn’t make my Sims scream and start falling into the sky as their city collapses around them.
This calls for a port of SimCity to a mobile device with an accelerometer.
This is a digression, but… I’m not sure it actually makes sense to claim that what holds Sim #1335 to the ground is a gravitational force, any more than it would make sense to say that what holds an astronaut connected to the outside of their shuttle via magnetic boots is a gravitational force.
What it is, exactly, I don’t know—I haven’t played SimCity since the early 90s, and have no sense of how it behaves or operates. But I’d be really surprised if it were something that, if I found myself in that universe having my memories, I’d be inclined to call gravitation.
In addition it should probably be pointed out that real things in general don’t need to have a location. I think we can all agree that the electromagnetic field is real, e.g., but the question “Where is the electromagnetic field?” is nonsense.
The question itself is not quite nonsense. There is a perfectly reasonable answer of “everywhere”. It’s just not a particularly useful question, and this is because of the hidden assumptions behind it, which are wrong and can easily lead to nonsense questions. “What is the value of the electromagnetic field at X?” is a much more interesting question that can be asked once those incorrect assumptions are removed and replaced.
Eh. You can force an answer in English, sure, but it’s still not really the “right” answer. The electromagnetic field is a function from spacetime, to, uh, some sort of tangent bundle on it or something? My knowledge of how to formalize this sort of thing isn’t so great. My point is that it’s a function taking spacetime locations as inputs; it doesn’t really have a location itself any more than, say, the metric of spacetime does. When we say “it’s everywhere” what’s meant is something more like “it’s defined everywhere” or “at every location, it affects things”.
The EM field is used both for the function, and the values of that function. (I think it’s actually a skew-symmetric linear operator on the tangent space T_x M at a given point. This can be phrased in terms of a bivector at that point. A “bundle” TM = Union_x T_x M talks about an extended manifold connecting tangent spaces at a different points.) I think it’s entirely reasonable in common language to use “where” to mean “where it’s non-negligible”. Consider that physical objects are also fields. It’s entirely reasonable to ask “where an electron is” even though the electron field is a function of spacetime. Once we’re able to ask the right questions, this becomes a less-useful question, as it only applicable in cases where the field is concentrated. The EM field case just breaks down much sooner.
The claim that the simulated universe is real even though its physics are independent of our own seem to imply a very broad definition of “real” that comes close to Tegmarck IV. I’ve posted a followup to my article to the discussion section: Eight questions for computationalists. Please to reply to it so I can better understand your position.
Your position within our universe is giving you a bias toward one side of a mostly symmetrical situation.
Let’s throw out the terms “real” and “simulated” universe and call them the “parent” and “child” universe.
Gravity in the child universe doesn’t affect the parent universe, true; creating a simulation of a black hole doesn’t suck the simulating computer into the event horizon. But gravity in the parent universe doesn’t affect the child universe either—if I turn my computer upside-down while playing SimCity, it doesn’t make my Sims scream and start falling into the sky as their city collapses around them. So instead of saying “simulated gravity isn’t real because it can’t affect the real universe”, we say “both the parent and child universes have gravity that only acts within their own universe, rather than affecting the other.”
Likewise, when you say that you can’t point to the location of a gravitional force within the simulation so it must be “nowhere”—balderdash. The gravitational force that’s holding Sim #13335 to the ground in my SimCity game is happening on Oak Street, right between the park and the corporate tower. When discussing a child-universe gravitational force, it is only necessary to show it has a location within the child-universe. For you to say it “doesn’t exist” because you can’t localize it in your universe is as parochial as for one of my Sims to say you don’t exist because he’s combed the entire city from north to south and he hasn’t found any specific location with a person named “dfranke”.
This calls for a port of SimCity to a mobile device with an accelerometer.
Simcity has been ported to a mobile device with an accelerometer. No, I don’t think it uses it (at least, not in that way).
This is a digression, but… I’m not sure it actually makes sense to claim that what holds Sim #1335 to the ground is a gravitational force, any more than it would make sense to say that what holds an astronaut connected to the outside of their shuttle via magnetic boots is a gravitational force.
What it is, exactly, I don’t know—I haven’t played SimCity since the early 90s, and have no sense of how it behaves or operates. But I’d be really surprised if it were something that, if I found myself in that universe having my memories, I’d be inclined to call gravitation.
For the Sims, yes, I’d agree. For a more physical based simulation, I would not.
(nods) As I say, it’s a digression.
In addition it should probably be pointed out that real things in general don’t need to have a location. I think we can all agree that the electromagnetic field is real, e.g., but the question “Where is the electromagnetic field?” is nonsense.
The question itself is not quite nonsense. There is a perfectly reasonable answer of “everywhere”. It’s just not a particularly useful question, and this is because of the hidden assumptions behind it, which are wrong and can easily lead to nonsense questions. “What is the value of the electromagnetic field at X?” is a much more interesting question that can be asked once those incorrect assumptions are removed and replaced.
Eh. You can force an answer in English, sure, but it’s still not really the “right” answer. The electromagnetic field is a function from spacetime, to, uh, some sort of tangent bundle on it or something? My knowledge of how to formalize this sort of thing isn’t so great. My point is that it’s a function taking spacetime locations as inputs; it doesn’t really have a location itself any more than, say, the metric of spacetime does. When we say “it’s everywhere” what’s meant is something more like “it’s defined everywhere” or “at every location, it affects things”.
The EM field is used both for the function, and the values of that function. (I think it’s actually a skew-symmetric linear operator on the tangent space T_x M at a given point. This can be phrased in terms of a bivector at that point. A “bundle” TM = Union_x T_x M talks about an extended manifold connecting tangent spaces at a different points.) I think it’s entirely reasonable in common language to use “where” to mean “where it’s non-negligible”. Consider that physical objects are also fields. It’s entirely reasonable to ask “where an electron is” even though the electron field is a function of spacetime. Once we’re able to ask the right questions, this becomes a less-useful question, as it only applicable in cases where the field is concentrated. The EM field case just breaks down much sooner.
The claim that the simulated universe is real even though its physics are independent of our own seem to imply a very broad definition of “real” that comes close to Tegmarck IV. I’ve posted a followup to my article to the discussion section: Eight questions for computationalists. Please to reply to it so I can better understand your position.