What makes glass or water transparent (what is the scientific explanation for this)? Do you think it would be scientifically possible for a man to become invisible, or transparent? (Keep in mind that writers of science fiction have often turned out to be prophetic in their imagination!)

In simple terms, you see an object only when it reflects light, and that falls on your eyes. Here the glass molecules can absorb some part of the light and pass most of the light through them. It makes the glass transparent. The same is the case with water molecules.
If the human body could somehow pass all the light, it would become invisible (Practically impossible). But having said that, we have the latest inventions of metamaterials that could pass light spectra without reflecting it.

Water and glass both have reflection is far less than one for visible light. So it passed torch through it and reflected for visible light, that's why it becomes transparent than translucent. Even the human body also invisible to radio rays than visible light rays. Finally, it is not possible to make the human body with today's technology, but there is not is impossible. I say it not philosophy; it's a fact proven by modern science explorations. We know about human 3-4% of biological recreation knowledge. My thanks for ask scientific philosophy question of origin for life explorer.
 

All transparent objects allow light to pass through them, without any hindrance. Take a bowl of clear water; it's open. If you mix Ink to it, it loses the property of transparency. Similarly, our body has the feature of allowing light to pass through, but we have substances like Ink mixed to it. If it is possible to separate Ink from clear water, we might also find a way to do the same with the human body.

Transparency depends on the molecular structure of atoms decided the slide; then ice and snow would also have been transparent. Yes, it is possible. The person should have some energy field or cover around him so that light bends around him and merges to the same path as it should have if the person were not there. Through the body not possible. Cause if we had even successfully penetrated organs and skin what about the bones. Even x rays cant neglect them.