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Consider two flat infinitely wide and high rectangular magnets located a distance $L$ from each other in what is otherwise a vacuum. Visualized below:

If the magnets are aligned properly there will be an attractive force between them. One interpretation of this attractive force is that there is a sea of virtual photons between the magnets and "if the virtual photons have a negative energy, they contribute to the electromagnetic force as an attractive force", so the QED vacuum between the plates has less average energy content than the vacuum external to the plates.

Superficially this sounds similar to the situation with the Casimir effect where the QED Vacuum between the conducting plates ALSO has less average energy than the outside but they are subtly different.

1. The Casimir Effect is strictly because there is a lack of virtual photons between the plates (any photons whose wave length is too big are excluded)

2. The Magnets here could be argued to either:

   a. have a surplus of virtual photons with negative energy between them

   b. have a lack of virtual photons of positive energy between them.

Nevertheless by carefully tuning the magnet strength, and distance between the magnets we can make two identical setups, one being a casimir conducting plate setup, the other being this magnet setup where both setups have identically shaped plates an identical distance apart, experiencing identically strong attractive forces (assuming they are held in place and not moving and the magnets have less conductivity than the conducting plates).

So how really are their vacuums different?

One way to shed light on exactly what's happening might be to ask how does light behave between the plates? In the Casimir effect it's predicted that very subtly light might travel faster in an effect called the Scharnhorst effect. Between these two magnets we also have vacuum with lower energy density than the surrounding vacuum so its natural to ask the same question: "is the speed of light between the magnets different at all compared to the classical vacuum?" intuitively we would expect "is it faster?"

Ideally I would have the technical skillset to repeat Scharnhorst's derivation of computing $e_0,\mu_0$ between the plates and then checking for myself but I lack the technical knowledge in QFT to do this at this time.

Consider two flat infinitely wide and high rectangular magnets located a distance $L$ from each other in what is otherwise a vacuum. Visualized below:

If the magnets are aligned properly there will be an attractive force between them. One interpretation of this attractive force is that there is a sea of virtual photons between the magnets and "if the virtual photons have a negative energy, they contribute to the electromagnetic force as an attractive force", so the QED vacuum between the plates has less average energy content than the vacuum external to the plates.

Superficially this sounds similar to the situation with the Casimir effect where the QED Vacuum between the conducting plates ALSO has less average energy than the outside but they are subtly different.

1. The Casimir Effect is strictly because there is a lack of virtual photons between the plates (any photons whose wave length is too big are excluded)

2. The Magnets here could be argued to either:

   a. have a surplus of virtual photons with negative energy between them

   b. have a lack of virtual photons of positive energy between them.

Nevertheless by carefully tuning the magnet strength, and distance between the magnets we can make two identical setups, one being a casimir conducting plate setup, the other being this magnet setup where both setups have identically shaped plates an identical distance apart, experiencing identically strong attractive forces (assuming they are held in place and not moving and the magnets have less conductivity than the conducting plates).

So how really are their vacuums different?

One way to shed light on exactly what's happening might be to ask how does light behave between the plates? In the Casimir effect it's predicted that very subtly light might travel faster in an effect called the Scharnhorst effect. Between these two magnets we also have vacuum with lower energy density than the surrounding vacuum so its natural to ask the same question: "is the speed of light between the magnets and normal to the magnets different at all compared to the speed of light in the classical vacuum?" intuitively we would expect "is it faster?"

Ideally I would have the technical skillset to repeat Scharnhorst's derivation of computing $e_0,\mu_0$ between the plates and then checking for myself but I lack the technical knowledge in QFT to do this at this time.

Consider two flat infinitely wide and high rectangular magnets located a distance $L$ from each other in what is otherwise a vacuum. Visualized below:

If the magnets are aligned properly there will be an attractive force between them. One interpretation of this attractive force is that there is a sea of virtual photons between the magnets and "if the virtual photons have a negative energy, they contribute to the electromagnetic force as an attractive force", so the QED vacuum between the plates has less average energy content than the vacuum external to the plates.

Superficially this sounds similar to the situation with the Casimir effect where the QED Vacuum between the conducting plates ALSO has less average energy than the outside but they are subtly different.

1. The Casimir Effect is strictly because there is a lack of virtual photons between the plates (any photons whose wave length is too big are excluded)

2. The Magnets here could be argued to either:

   a. have a surplus of virtual photons with negative energy between them

   b. have a lack of virtual photons of positive energy between them.

Nevertheless by carefully tuning the magnet strength, and distance between the magnets we can make two identical setups, one being a casimir conducting plate setup, the other being this magnet setup where both setups have identically shaped plates an identical distance apart, experiencing identically strong attractive forces (assuming they are held in place and not moving and the magnets have less conductivity than the conducting plates).

So how really are their vacuums different?

One way to shed light on exactly what's happening might be to ask how does light behave between the plates? In the Casimir effect it's predicted that very subtly light might travel faster in an effect called the Scharnhorst effect. Between these two magnets we also have vacuum with lower energy density than the surrounding vacuum so its natural to ask the same question: "is the speed of light between the magnets different at all compared to the classical vacuum?" intuitively we would expect "is it faster?"

Ideally I would have the technical skillset to repeat Scharnhorst's derivation of computing $e_0,\mu_0$ between the plates and then checking for myself but I lack the technical knowledge in QFT to do this at this time.

Consider two flat infinitely wide and high rectangular magnets located a distance $L$ from each other in what is otherwise a vacuum. Visualized below:

If the magnets are aligned properly there will be an attractive force between them. One interpretation of this attractive force is that there is a sea of virtual photons between the magnets and "if the virtual photons have a negative energy, they contribute to the electromagnetic force as an attractive force", so the QED vacuum between the plates has less average energy content than the vacuum external to the plates.

Superficially this sounds similar to the situation with the Casimir effect where the QED Vacuum between the conducting plates ALSO has less average energy than the outside but they are subtly different.

1. The Casimir Effect is strictly because there is a lack of virtual photons between the plates (any photons whose wave length is too big are excluded)

2. The Magnets here could be argued to either:

   a. have a surplus of virtual photons with negative energy between them

   b. have a lack of virtual photons of positive energy between them.

Nevertheless by carefully tuning the magnet strength, and distance between the magnets we can make two identical setups, one being a casimir conducting plate setup, the other being this magnet setup where both setups have identically shaped plates an identical distance apart, experiencing identically strong attractive forces (assuming they are held in place and not moving and the magnets have less conductivity than the conducting plates).

So how really are their vacuums different?

One way to shed light on exactly what's happening might be to ask how does light behave between the plates? In the Casimir effect it's predicted that very subtly light might travel faster in an effect called the Scharnhorst effect. Between these two magnets we also have vacuum with lower energy density than the surrounding vacuum so its natural to ask the same question: "is the speed of light between the magnets different at all compared to the classical vacuum?" intuitively we would expect "is it faster?"

Ideally I would have the technical skillset to repeat Scharnhorst's derivation of computing $e_0,\mu_0$ between the plates and then checking for myself but I lack the technical knowledge in QFT to do this at this time.

Consider two flat infinitely wide and high rectangular magnets located a distance $L$ from each other in what is otherwise a vacuum. Visualized below:

If the magnets are aligned properly there will be an attractive force between them. One interpretation of this attractive force is that there is a sea of virtual photons between the magnets and "if the virtual photons have a negative energy, they contribute to the electromagnetic force as an attractive force", so the QED vacuum between the plates has a more negative average energy content than the vacuum external to the plates.

Superficially this sounds similar to the situation with the Casimir effect where the QED Vacuum between the conducting plates ALSO has more negative average energy than they outside but they are subtly different.

1. The Casimir Effect is strictly because there is a lack of virtual photons between the plates (any photons whose wave length is too big are excluded)

2. The Magnets here could be argued to either:

   a. have a surplus of virtual photons with negative energy between them

   b. have a lack of virtual photons of positive energy between them.

Nevertheless by carefully tuning the magnet strength, and distance between the magnets we can make two identical setups, one being a casimir conducting plate setup, the other being this magnet setup where both setups have identically shaped plates an identical distance apart, experiencing identically strong attractive forces (assuming they are held in place and not moving).

So how really are their vacuums different?

One way to shed light on exactly what's happening might be to ask how does light behave between the plates? In the Casimir effect it's predicted that very subtly light might travel faster in an effect called the Scharnhorst effect. Between these two magnets we also have vacuum with lower energy density than the surrounding vacuum so its natural to ask the same question: "is the speed of light between the magnets different at all compared to the classical vacuum?" intuitively we would expect "is it faster?"

Ideally I would have the technical skillset to repeat Scharnhorst's derivation of computing $e_0,\mu_0$ between the plates and then checking for myself but I lack the technical knowledge in QFT to do this at this time, so I guess I am asking this because I'm too stupid to even begin to answer it on my own.

Consider two flat infinitely wide and high rectangular magnets located a distance $L$ from each other in what is otherwise a vacuum. Visualized below:

If the magnets are aligned properly there will be an attractive force between them. One interpretation of this attractive force is that there is a sea of virtual photons between the magnets and "if the virtual photons have a negative energy, they contribute to the electromagnetic force as an attractive force", so the QED vacuum between the plates has less average energy content than the vacuum external to the plates.

Superficially this sounds similar to the situation with the Casimir effect where the QED Vacuum between the conducting plates ALSO has less average energy than the outside but they are subtly different.

1. The Casimir Effect is strictly because there is a lack of virtual photons between the plates (any photons whose wave length is too big are excluded)

2. The Magnets here could be argued to either:

   a. have a surplus of virtual photons with negative energy between them

   b. have a lack of virtual photons of positive energy between them.

Nevertheless by carefully tuning the magnet strength, and distance between the magnets we can make two identical setups, one being a casimir conducting plate setup, the other being this magnet setup where both setups have identically shaped plates an identical distance apart, experiencing identically strong attractive forces (assuming they are held in place and not moving and the magnets have less conductivity than the conducting plates).

So how really are their vacuums different?

One way to shed light on exactly what's happening might be to ask how does light behave between the plates? In the Casimir effect it's predicted that very subtly light might travel faster in an effect called the Scharnhorst effect. Between these two magnets we also have vacuum with lower energy density than the surrounding vacuum so its natural to ask the same question: "is the speed of light between the magnets different at all compared to the classical vacuum?" intuitively we would expect "is it faster?"

Ideally I would have the technical skillset to repeat Scharnhorst's derivation of computing $e_0,\mu_0$ between the plates and then checking for myself but I lack the technical knowledge in QFT to do this at this time.