That I did not know, virtual photons carriers of electromagnetism?
How do you detect something "virtual"?
Within the context of what we currently know,
real photons are the carriers of electromagnetism. Virtual photons play an important role in some portions of QM theory and vacuum energy. There is no significant experimental evidence, to suggest that virtual particles are the carrier of electromagnetism or gravity.
While there may be and probably are portions of the electromagnetic spectrum that are not within our ability to detect and measure, within the range that we are currently aware of, we can easily detect electromagnetic waves through the effect that they have on the atoms of which we and all of our detectors and measuring devices are composed.
We see photons in the visible spectrum. We measure the changes in electric circuits that result from exposure to radio waves. We measure the heat that exposure to microwave and other EM radiations generates... All of these represent changes that occur within or to, atoms and/or complex materials made of atoms, exposed to EM radiation or photons.
Virtual particles, including virtual photons are far more elusive. There are a few experiments, like those involving the Casimir and Dynamical Casimir effects, that support the existence of virtual particles/photons. If you are interested in how something that is virtual is detected look up those experiments.
It may be that we will come to understand the origin of gravity within the context of photon like particles, the as yet theoretical graviton. We are not quite there yet, though there are what appear to be some promising theoretical models. That would be the subject of quantum gravity.
Could virtual particles, as in zero point fluctuations of the vacuum, be involved in what we experience as gravity? Yes, but so far we have no completely successful model or theory. That is to say, theories that approach inertia and gravity from this perspective, have not been successful in duplicating the scope and accuracy of general relativity, or our observations and experience, of either inertia or gravity.
I have been trying to work my way through a number of papers, on the inertia side of this question. I cannot say that I completely understand, though the more in read the more questions I have and the idea(s) are interesting. As far as Gra ity is concerned.., there the work moves into the realm of quantum gravity and far beyond me...