Mentz114

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## Main Question or Discussion Point

I understand that the quantities

[tex]E^2 - B^2[/tex]

[tex]\vec{E} \cdot \vec{B}[/tex]

(the dot is vector inner product).

where E and B are the electric and magnetic components of an EM wave,

are invariant under Lorentz/Poincare transformations.

Can someone explain the physical significance of this ? Is either quantity related to the velocity of light ( or the invariance of the velocity of light ) ?

The second expression must be zero at all times surely ?

[tex]E^2 - B^2[/tex]

[tex]\vec{E} \cdot \vec{B}[/tex]

(the dot is vector inner product).

where E and B are the electric and magnetic components of an EM wave,

are invariant under Lorentz/Poincare transformations.

Can someone explain the physical significance of this ? Is either quantity related to the velocity of light ( or the invariance of the velocity of light ) ?

The second expression must be zero at all times surely ?

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