The heaviest thing in the world is a highly debated topic, as there are many different factors to consider when weighing different objects. Some people might argue that the heaviest things in the world are celestial bodies like black holes, while others might consider the mass of entire galaxies or clusters of galaxies. However, if we're talking about tangible, physical objects, then one of the contenders for the title of the heaviest thing in the world is osmium.

Osmium is a chemical element that is part of the platinum group of metals. It is known for being extremely dense and heavy, making it one of the heaviest elements on Earth. Its high density is due to its high atomic number and the number of electrons in its outermost shell. This makes osmium incredibly dense and difficult to work with, which is why it's not used as a metal in many applications.

Despite its high density, osmium is also a very brittle metal, which makes it difficult to shape and use in construction. However, its high density and strength make it a valuable metal in some industrial applications, including as a material in electrical contacts and fountain pen nibs.

In conclusion, osmium is considered one of the heaviest elements on Earth and is certainly a contender for the title of the heaviest thing in the world. Its high density and strength make it a valuable metal for certain industrial applications, despite its brittleness and difficulties in working with it.