What is the difference between the words 'world' 'earth' 'universe' and 'cosmos'?

Answer 1

All four words refer to the environment, of whatever scope, that humans find themselves living in. 'World' is the most general of the four and has many definitions. Strictly speaking, 'world' refers to the totality of human existence, especially on planet Earth. It can refer to humanity's existence not just in space (e.g. the Western world) but in time as well (e.g. the ancient world). Put simply, it is the summation of all of human society, civilization, and culture throughout history. The term can also be used without reference to humanity to denote the planet Earth physically with all its continents, oceans, and living things. The term can even be extended further to denote any of the celestial bodies, especially the other planets, and even to the whole universe. Theologically, 'world' can mean humanity's present mortal existence on Earth with all of its interests and activities as opposed to a future existence in an afterlife living eternally in any of the transcendent realms such as heaven and hell.

'Earth' specifically refers to the planet that humans live on together with all other living things. Of the four words, it is the smallest in scope. The word can refer not just to the planet itself, but also to the hard material that the planet is made of such as the land or soil as opposed to the liquid water that covers most of its surface. Like 'world', 'earth' can refer theologically to mankind's mortal existence on this planet with all of its concerns and activities as opposed to future existence in a transcendent realm.

'Universe' refers to all that exists, whether material or spiritual. Scientifically, the term denotes all of space and time together with all matter and energy, including humans and all other living things, as well as all physical laws, forces, and constants. All material entities large (e.g. planets, stars, and galaxies) and small (e.g. atoms, molecules, and subatomic particles) are part of the universe. Theoretically, there can be other 'universes' each having separate domains of space and time and configurations of matter and energy as well as different physical laws, forces, and constants. Theologically, 'universe' can be extended to include spiritual entities such as angels or demons.

'Cosmos' refers specifically to the universe as an ordered system. However, recently scientists have begun using 'cosmos' to refer to physical reality of the largest scope, larger even than 'universe'. 'Universe' has been downgraded somewhat to refer to a specific domain of space, time, matter, and energy with its own physical laws, forces, and constants coexisting with other such domains in a 'multiverse' or 'mega-verse'. Theoretically, the cosmos refers to this 'multiverse' with all of its 'parallel universes'.