I think and believe there is gravity between viruses and cells. As is well known, the specificity between cellular receptors and protein structures on the surface of the virus, whether on the capsid or the envelope, plays an important role in attachment, adhesion, and absorption, which then trigger endocytosis and professional entry into the cell cytoplasm. However, the question remains: how does the virus navigate towards the target cell from among millions of different cells and travel long distances to reach it? Yes, in addition to specificity and affinity, there is the theory of Virogravity.
Interesting question, but I think the whole thing is reducible to viscosity physics rather than gravity. From here (https://physics.aps.org/articles/v5/s140) the weight of a human cells is given at 27 fg; here (https://www.quora.com/What-does-a-virus-weigh) they estimate the weight of vaccinia virus (one of the biggest) at 9 fg. We can approximate the mass with the weight.
Thus, at a 1 cm distance, the gravity force would be:
F = gmMd−1 = 6.7 × 10−11 m3⋅kg−1⋅s−2 × (27 × 9 ⋅ 10−18 kg) ÷ 1 ⋅ 10−2 m.
Solving the equation using https://www.omnicalculator.com/physics/gravitational-force to reduce errors, one gets the value of (using 27 and 9 grams instead of femtograms, since the values must be above 0) 1.6 × 10-10 N, therefore (re-converting for femtograms):
F = 1.6 × 10−25 N,
which I think is a negligible force, especially considering the viscosity of solutions at the nanoscale.
The correct answer is that the relationships are purely electromagnetic.
Of course, if attraction exists, it is not related to gravity. But other effects similar to bacterial chemotaxis are possible.
Viruses are far too small for gravitational forces to play any meaningful role in their interaction with cells—the gravitational pull between them is effectively zero.
What actually brings a virus to its target cell is random motion in fluids (diffusion, flow, Brownian movement) combined with molecular recognition.
Viral surface proteins have a very high biochemical affinity for specific receptors on host cells, and once chance contact occurs, this “lock-and-key” interaction ensures attachment and entry.
In other words, viruses do not navigate by gravity but by probability and molecular specificity, with selective binding replacing the role that “gravity” metaphorically suggests.
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