Explore Fundamental Physics Formulas 

Extract a list of the physical quantities in every formula that contains Planck's constant, the speed of light, or the gravitational constant.

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X quantities = Flatten[If[ MemberQ[FormulaData[#], "PlanckConstant" | "ReducedPlanckConstant" | "SpeedOfLight" | "GravitationalConstant", \[Infinity]], Subsets[Union[ FormulaData[#, "QuantityVariablePhysicalQuantities"][[All, 2]]], {2}], {} ] & /@ FormulaData[], 1];

Show which pairs of physical quantities most often appear together in formulas.

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X pairs = Select[{UndirectedEdge @@ First[#], Last[#]} & /@ Tally[quantities], Last[#] > 4 &];

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X Graph[First /@ pairs, EdgeWeight -> 1/(Last /@ pairs), VertexLabels -> "Name", ImagePadding -> 50]

Out[3]=