3 ms·

At 16 T you can levitate a frog purely through diamagnetism. I imagine you could do the same for a human as well if you could create a chamber that large with a

by dheera 5y ago

At 16 T you can levitate a frog purely through diamagnetism. I imagine you could do the same for a human as well if you could create a chamber that large with a uniform field of that magnitude. https://www.youtube.com/watch?v=KlJsVqc0ywM https://www.youtube.com/watch?v=KlJsVqc0ywM That said, assuming 16 T cancels gravity, I imagine being imaged in a MRI machine at 7 T horizontal magnetic field would probably feel like a net gravity vector at an angle, i.e. lying on a steep slope of arcsin(7/16) = 0.452 radians, which is pretty steep.

pfdietz 5y ago
That levitation is based on their being a large field gradient (diamagnetic levitation is based on the field gradient), so you could not do the same for a human.
- lend000 5y ago
  Do you have a source for this? I don't believe it is true. Diamagnetism is a fundamental quantum mechanical property related to the quantum mechanical analog to the Lorentz force. Spin 1/2 electrons have exactly 2 states: opposing or attracting a static magnetic field, regardless of direction of the field or orientation of the particle. When all electrons are paired (and the spin fields cancel), all that is left is that Lorentz force and you get diamagnetism. Otherwise, you generally get paramagnetism (attractive because of the net dipole created by net spin). See the Stern Gerlach experiment: https://en.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experiment https://en.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experime...
  - pfdietz 5y ago
    The energy of a diamagnetic material is lower in a lower magnetic field, so there's a force pushing it away from higher fields. This force is proportional to the gradient of the field. In a constant magnetic field, there will be no change in energy and so no force on the diamagnetic material.
    - lend000 5y ago
      Okay, there are a few misunderstandings here. That is the 1800's classical explanation of electric charge, which is not consistent with experiments, nor does it line up with magnetism, which is inherently quantum. 1. Even in your classical description, what you just described (following field lines) does not require there to be a gradient. If there is a gradient, yes, the forces will follow it. But there is still a force in a static infinite applied field, and potential energies still change as things move. 2. Diamagnetism is a quantum property, not a classical one. It exists due to the polarity of spins in an electron pair (although frankly, this explanation is weak and magnetism is one of the less understood subjects in physics). Even if a macroscopic field has a gradient, it will look like a static field at the scale of an atom, at which scale diamagnetic forces exist.
      - pfdietz 5y ago
        Sigh. 1. Yes, a gradient is required. If the energy of the diamagnetic material does not change, there cannot be a force, as this will violate conservation of energy. You are proposing a perpetual motion machine of the first kind. 2. The quantum nature of diamagnetism doesn't matter in the slightest to the argument being made, so why are you bringing this up?
        lend000 5y ago
        It appears that you are conflating a field gradient with a potential energy gradient. Potential energy changes when moving parallel to any field force, regardless of whether that field is static or has some gradient.
        pfdietz 5y ago
        Let us consider an experiment. Take a long cylindrical coil, so that in most of the coil the magnetic field is constant. In the center, place a diamagnetic material. Does it experience a force toward either end of the coil? If not, why not, according to your reasoning? If so, why does it experience a force toward that end of the coil and not the other?

by dheera 5y ago

pfdietz 5y ago

That levitation is based on their being a large field gradient (diamagnetic levitation is based on the field gradient), so you could not do the same for a human.

lend000 5y ago
Do you have a source for this? I don't believe it is true. Diamagnetism is a fundamental quantum mechanical property related to the quantum mechanical analog to the Lorentz force. Spin 1/2 electrons have exactly 2 states: opposing or attracting a static magnetic field, regardless of direction of the field or orientation of the particle. When all electrons are paired (and the spin fields cancel), all that is left is that Lorentz force and you get diamagnetism. Otherwise, you generally get paramagnetism (attractive because of the net dipole created by net spin). See the Stern Gerlach experiment: https://en.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experiment https://en.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experime...
- pfdietz 5y ago
  The energy of a diamagnetic material is lower in a lower magnetic field, so there's a force pushing it away from higher fields. This force is proportional to the gradient of the field. In a constant magnetic field, there will be no change in energy and so no force on the diamagnetic material.
  - lend000 5y ago
    Okay, there are a few misunderstandings here. That is the 1800's classical explanation of electric charge, which is not consistent with experiments, nor does it line up with magnetism, which is inherently quantum. 1. Even in your classical description, what you just described (following field lines) does not require there to be a gradient. If there is a gradient, yes, the forces will follow it. But there is still a force in a static infinite applied field, and potential energies still change as things move. 2. Diamagnetism is a quantum property, not a classical one. It exists due to the polarity of spins in an electron pair (although frankly, this explanation is weak and magnetism is one of the less understood subjects in physics). Even if a macroscopic field has a gradient, it will look like a static field at the scale of an atom, at which scale diamagnetic forces exist.
    - pfdietz 5y ago
      Sigh. 1. Yes, a gradient is required. If the energy of the diamagnetic material does not change, there cannot be a force, as this will violate conservation of energy. You are proposing a perpetual motion machine of the first kind. 2. The quantum nature of diamagnetism doesn't matter in the slightest to the argument being made, so why are you bringing this up?
      - lend000 5y ago
        It appears that you are conflating a field gradient with a potential energy gradient. Potential energy changes when moving parallel to any field force, regardless of whether that field is static or has some gradient.
        pfdietz 5y ago
        Let us consider an experiment. Take a long cylindrical coil, so that in most of the coil the magnetic field is constant. In the center, place a diamagnetic material. Does it experience a force toward either end of the coil? If not, why not, according to your reasoning? If so, why does it experience a force toward that end of the coil and not the other?