I know what a virtual particle is.   Sometimes they come up when we discuss whether something can exist without a cause.  Certain folks will say that virtual particles have no cause.

Virtual particles have cause. They exist because empty space isn't really empty, but has structure. This structure is called the quantum vacuum. Although Einstein kicked the "ether concept of space" out the front door of the physics building, it quickly snuck in the back door relabeled as the quantum vacuum. The big difference between the two is that the quantum vacuum is compatible with relativity and quantum mechanics, whereas the ether was modeled as a classical jello-like substance.

Quantum field theory postulates that the quantum vacuum (ie, space) has a structure which supports modes of vibration or excitation which we recognize as elementary particles such as photons, electrons, etc. Like all things quantum, these modes have a ground-state (minimal energy) which is non-zero.

So the quantum vacuum, which is the sum of all these modes, has a real energy. This energy can and has been measured as producing a real force, the Casimir force between two very flat surfaces brought very close together.

If the vacuum is stressed it can produce particles. For example, very close to an atomic nucleus the electric field is so strong it can cause an electron-positron pair to briefly appear. This "virtual-particle" effect, known as vacuum polarization, is detectable in the frequency shift of light spectra (the Lamb shift) from atoms. Quantum field theory can calculate this shift with an accuracy of about 6 decimal places, which is strong confirmation of the theory.

In any case, misunderstandings that virtual particles are without cause is mainly due to the inaccurate writing of popular science articles.