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1. Double-slit experiments with humans or cars are impossible in any meaningful sense. If you compute the deBroglie wavelength of humans or cars with feasible momenta, you find that their wavefunction we would naively associate to them won't diffract measurably on any slit you can manufacture since diffraction occurs less the smaller the wavelength is, i.e. you will not get any measurable interference, even if you could guarantee that they behave "quantumly" during the experiment without decohering.

2. Macroscopic objects like cars or humans do not, for any practical purpose, exist in such superposition states of position. They are constantly interacting with their environment in many ways, forcing them to occupy a state of definite position. Depending on your interpretation of quantum mechanics, you may, as in Many Worlds, assert that some other results of such decohering interactions also "exist", but this "existence" cannot influence "our world" at all, so this is a moot point. Creating superposed position states is impossibly hard, if not outright impossible for objects the size of a human.

3. On the level of particles, such superpositions are perfectly feasible. However, no additional "dark mass" appears - the total rest mass of all states of a given particle is just the mass of the particle. That you have some probability to find it in one place, and some to find it in another doesn't mean that it is in "both" places before you look. It means the question of where the mass is only has an answer after you look. Of course, it is hard to see how this may be reconciled with gravitation - impossible since we don't know the correct quantum theory of gravity - but that the solution is not to adopt each possible location as exerting gravity can be seen in analogy to a force whose quantum theory we do understand: Electromagnetism.

Think of an electron, smeared out over space in that "electron cloud" commonly pictured. If you want the classical electrical field it exerts, it is the field of one electron charge. Its charge has not magically multiplied just because it's not certain where it is. Now, if the electron has two disjoint locations where it can be, talking about the classical field becomes harder - but you can either be semiclassical, where you would compute the electric field then from the average position of the electron, or also quantize the electric field, whence you only can talk about expectation values of the electric field to begin with.

4. Lastly, I want to mention that relativity is not the problem as such - quantum field theory does unify quantum mechanics and special relativity. It is general relativity, hence gravity, whose proper quantum theory is unknown. But, in any case, talking about particles and position states already becomes rather hard and sometimes unhelpful in quantum field theory, so one should not expect that thinking on this non-relativistic quantum mechanical level will result in something that can extend QFT.

1. Double-slit experiments with humans or cars are impossible in any meaningful sense. If you compute the deBroglie wavelength of humans or cars with feasible momenta, you find that their wavefunction we would naively associate to them won't diffract measurably on any slit you can manufacture since diffraction occurs less the smaller the wavelength is, i.e. you will not get any measurable interference, even if you could guarantee that they behave "quantumly" during the experiment without decohering.

2. Macroscopic objects like cars or humans do not, for any practical purpose, exist in such superposition states of position. They are constantly interacting with their environment in many ways, forcing them to occupy a state of definite position. Depending on your interpretation of quantum mechanics, you may, as in Many Worlds, assert that some other results of such decohering interactions also "exist", but this "existence" cannot influence "our world" at all, so this is a moot point. Creating superposed position states is impossibly hard, if not outright impossible for objects the size of a human.

3. On the level of particles, such superpositions are perfectly feasible. However, no additional "dark mass" appears - the total rest mass of all states of a given particle is just the mass of the particle. That you have some probability to find it in one place, and some to find it in another doesn't mean that it is in "both" places before you look. It means the question of where the mass is only has an answer after you look. Of course, it is hard to see how this may be reconciled with gravitation - impossible since we don't know the correct quantum theory of gravity - but that the solution is not to adopt each possible location as exerting gravity can be seen in analogy to a force whose quantum theory we do understand: Electromagnetism.

   Think of an electron, smeared out over space in that "electron cloud" commonly pictured. If you want the classical electrical field it exerts, it is the field of one electron charge. Its charge has not magically multiplied just because it's not certain where it is. Now, if the electron has two disjoint locations where it can be, talking about the classical field becomes harder - but you can either be semiclassical, where you would compute the electric field then from the average position of the electron, or also quantize the electric field, whence you only can talk about expectation values of the electric field to begin with.

4. Lastly, I want to mention that relativity is not the problem as such - quantum field theory does unify quantum mechanics and special relativity. It is general relativity, hence gravity, whose proper quantum theory is unknown. But, in any case, talking about particles and position states already becomes rather hard and sometimes unhelpful in quantum field theory, so one should not expect that thinking on this non-relativistic quantum mechanical level will result in something that can extend QFT.

There are several misconceptions here to correct:

1. Double-slit experiments with humans or cars are impossible in any meaningful sense. If you compute the deBroglie wavelength of humans or cars with feasible momenta, you find that their wavefunction we would naively associate to them won't diffract measurably on any slit you can manufacture since diffraction occurs less the smaller the wavelength is, i.e. you will not get any measurable interference, even if you could guarantee that they behave "quantumly" during the experiment without decohering.

2. Macroscopic objects like cars or humans do not, for any practical purpose, exist in such superposition states of position. They are constantly interacting with their environment in many ways, forcing them to occupy a state of definite position. Depending on your interpretation of quantum mechanics, you may, as in Many Worlds, assert that some other results of such decohering interactions also "exist", but this "existence" cannot influence "our world" at all, so this is a moot point. Creating superposed position states is impossibly hard, if not outright impossible for objects the size of a human.

3. On the level of particles, such superpositions are perfectly feasible. However, no additional "dark mass" appears - the total rest mass of all states of a given particle is just the mass of the particle. That you have some probability to find it in one place, and some to find it in another doesn't mean that it is in "both" places before you look. It means the question of where the mass is only has an answer after you look. Of course, it is hard to see how this may be reconciled with gravitation - impossible since we don't know the correct quantum theory of gravity - but that the solution is not to adopt each possible location as exerting gravity can be seen in analogy to a force whose quantum theory we do understand: Electromagnetism.

Think of an electron, smeared out over space in that "electron cloud" commonly pictured. If you want the classical electrical field it exerts, it is the field of one electron charge. Its charge has not magically multiplied just because it's not certain where it is. Now, if the electron has two disjoint locations where it can be, talking about the classical field becomes harder - but you can either be semiclassical, where you would compute the electric field then from the average position of the electron, or also quantize the electric field, whence you only can talk about expectation values of the electric field to begin with.

4. Lastly, I want to mention that relativity is not the problem as such - quantum field theory does unify quantum mechanics and special relativity. It is general relativity, hence gravity, whose proper quantum theory is unknown. But, in any case, talking about particles and position states already becomes rather hard and sometimes unhelpful in quantum field theory, so one should not expect that thinking on this non-relativistic quantum mechanical level will result in something that can extend QFT.

There are several misconceptions here to correct:

1. Double-slit experiments with humans or cars are impossible in any meaningful sense. If you compute the deBroglie wavelength of humans or cars with feasible momenta, you find that their wavefunction we would naively associate to them won't diffract measurably on any slit you can manufacture since diffraction occurs less the smaller the wavelength is, i.e. you will not get any measurable interference, even if you could guarantee that they behave "quantumly" during the experiment without decohering.

2. Macroscopic objects like cars or humans do not, for any practical purpose, exist in such superposition states of position. They are constantly interacting with their environment in many ways, forcing them to occupy a state of definite position. Depending on your interpretation of quantum mechanics, you may, as in Many Worlds, assert that some other results of such decohering interactions also "exist", but this "existence" cannot influence "our world" at all, so this is a moot point. Creating superposed position states is impossibly hard, if not outright impossible for objects the size of a human.

3. On the level of particles, such superpositions are perfectly feasible. However, no additional "dark mass" appears - the total rest mass of all states of a given particle is just the mass of the particle. That you have some probability to find it in one place, and some to find it in another doesn't mean that it is in "both" places before you look. It means the question of where the mass is only has an answer after you look. Of course, it is hard to see how this may be reconciled with gravitation - impossible since we don't know the correct quantum theory of gravity - but that the solution is not to adopt each possible location as exerting gravity can be seen in analogy to a force whose quantum theory we do understand: Electromagnetism.

Think of an electron, smeared out over space in that "electron cloud" commonly pictured. If you want the classical electrical field it exerts, it is the field of one electron charge. Its charge has not magically multiplied just because it's not certain where it is. Now, if the electron has two disjoint locations where it can be, talking about the classical field becomes harder - but you can either be semiclassical, where you would compute the electric field then from the average position of the electron, or also quantize the electric field, whence you only can talk about expectation values of the electric field to begin with.

4. Lastly, I want to mention that relativity is not the problem as such - quantum field theory does unify quantum mechanics and special relativity. It is general relativity, hence gravity, whose proper quantum theory is unknown. But, in any case, talking about particles and position states already becomes rather hard and sometimes unhelpful in quantum field theory, so one should not expect that thinking on this non-relativistic quantum mechanical level will result in something that can extend QFT.

There are several misconceptions here to correct:

1. Double-slit experiments with humans or cars are impossible in any meaningful sense. If you compute the deBroglie wavelength of humans or cars with feasible momenta, you find that their wavefunction we would naively associate to them won't diffract measurably on any slit you can manufacture since diffraction occurs less the smaller the wavelength is, i.e. you will not get any measurable interference, even if you could guarantee that they behave "quantumly" during the experiment without decohering.

2. Macroscopic objects like cars or humans do not, for any practical purpose, exist in such superposition states of position. They are constantly interacting with their environment in many ways, forcing them to occupy a state of definite position. Depending on your interpretation of quantum mechanics, you may, as in Many Worlds, assert that some other results of such decohering interactions also "exist", but this "existence" cannot influence "our world" at all, so this is a moot point. Creating superposed position states is impossibly hard, if not outright impossible for objects the size of a human.

3. On the level of particles, such superpositions are perfectly feasible. However, no additional "dark mass" appears - the total rest mass of all states of a given particle is just the mass of the particle. That you have some probability to find it in one place, and some to find it in another doesn't mean that it is in "both" places before you look. It means the question of where the mass is only has an answer after you look. Of course, it is hard to see how this may be reconciled with gravitation - impossible since we don't know the correct quantum theory of gravity - but that the solution is not to adopt each possible location as exerting gravity can be seen in analogy to a force whose quantum theory we do understand: Electromagnetism.

Think of an electron, smeared out over space in that "electron cloud" commonly pictured. If you want the classical electrical field it exerts, it is the field of one electron charge. It's charge has not magically multiplied just because it's not certain where it is. Now, if the electron has to disjoint locations where it can be, talking about the classical field becomes harder - but you can either be semiclassical, where you would compute the electric field then from the average position of the electron, or also quantize the electric field, whence you only can talk about expectation values of the electric field to begin with.

4. Lastly, I want to mention that relativity is not the problem as such - quantum field theory does unify quantum mechanics and special relativity. It is general relativity, hence gravity, whose proper quantum theory is unknown. But, in any case, talking about particles and position states already becomes rather hard and sometimes unhelpful in quantum field theory, so one should not expect that thinking on this non-relativistic quantum mechanical level will result in something that can extend QFT.

There are several misconceptions here to correct:

1. Double-slit experiments with humans or cars are impossible in any meaningful sense. If you compute the deBroglie wavelength of humans or cars with feasible momenta, you find that their wavefunction we would naively associate to them won't diffract measurably on any slit you can manufacture since diffraction occurs less the smaller the wavelength is, i.e. you will not get any measurable interference, even if you could guarantee that they behave "quantumly" during the experiment without decohering.

2. Macroscopic objects like cars or humans do not, for any practical purpose, exist in such superposition states of position. They are constantly interacting with their environment in many ways, forcing them to occupy a state of definite position. Depending on your interpretation of quantum mechanics, you may, as in Many Worlds, assert that some other results of such decohering interactions also "exist", but this "existence" cannot influence "our world" at all, so this is a moot point. Creating superposed position states is impossibly hard, if not outright impossible for objects the size of a human.

3. On the level of particles, such superpositions are perfectly feasible. However, no additional "dark mass" appears - the total rest mass of all states of a given particle is just the mass of the particle. That you have some probability to find it in one place, and some to find it in another doesn't mean that it is in "both" places before you look. It means the question of where the mass is only has an answer after you look. Of course, it is hard to see how this may be reconciled with gravitation - impossible since we don't know the correct quantum theory of gravity - but that the solution is not to adopt each possible location as exerting gravity can be seen in analogy to a force whose quantum theory we do understand: Electromagnetism.

Think of an electron, smeared out over space in that "electron cloud" commonly pictured. If you want the classical electrical field it exerts, it is the field of one electron charge. Its charge has not magically multiplied just because it's not certain where it is. Now, if the electron has two disjoint locations where it can be, talking about the classical field becomes harder - but you can either be semiclassical, where you would compute the electric field then from the average position of the electron, or also quantize the electric field, whence you only can talk about expectation values of the electric field to begin with.

4. Lastly, I want to mention that relativity is not the problem as such - quantum field theory does unify quantum mechanics and special relativity. It is general relativity, hence gravity, whose proper quantum theory is unknown. But, in any case, talking about particles and position states already becomes rather hard and sometimes unhelpful in quantum field theory, so one should not expect that thinking on this non-relativistic quantum mechanical level will result in something that can extend QFT.