In the context of the strong nuclear force, which binds quarks together to form composite particles such as protons and neutrons, the bond between quarks is indeed very strong. The strong force is characterized by a property known as color confinement, which means that quarks cannot exist as isolated free particles but are always found in combinations that are color-neutral.
In a complete vacuum without the presence of other particles, the strong force between quarks would still act to bind them together. However, it's important to note that the strong force becomes stronger as quarks are pulled apart (a phenomenon known as asymptotic freedom). As the separation between quarks increases, the energy stored in the strong force field also increases. At some point, the energy becomes large enough to create a quark-antiquark pair from the vacuum. This pair formation is known as quark confinement.
So, even in a vacuum, if the quarks are pulled apart with sufficient force, the energy stored in the strong force field will be enough to create a new quark-antiquark pair, resulting in the formation of new color-neutral particles. As a result, the original quark bond is "broken," but new quark-antiquark pairs are created, and the strong force ensures that quarks are always confined within color-neutral combinations.
It's worth noting that the concept of a complete vacuum without any particle-antiparticle pairs is a hypothetical scenario. Quantum field theory describes the vacuum as a seething sea of virtual particles constantly popping in and out of existence due to the inherent uncertainty principle. These virtual particle-antiparticle pairs can still influence the dynamics of quarks even in seemingly empty space.