In: Physics
The vanishing jelly marbles phenomena happens because the jelly marbles have the same refractive index as the water they are placed in.
We are able to see normal transparent object in water because they have a refractive index different from that of water. This bends the light as per Snell's Law, allowing the observer to make out the surface of the object.
In the case of the vanishing jelly marbles, since they have the same refractive index of the water, they don't bend the light, and it passes through as it would if the medium was only water. Because of this, we can't see the marbles.
In the case of an object which has different refractive index than water
The ray emerges skew in relation to the initial incident ray.
In the case of vanishing marbles that have a refractive index similar to water
The emergent ray is parallel to the initial incident ray.