Breakdown of Nichts auf der Welt ist ewig.
sein
to be
nichts
nothing
auf
on / to (down/up to a level)
die Welt
the world
Questions & Answers about Nichts auf der Welt ist ewig.
Why do we use auf here instead of in to say "in the world"?
In German, the standard phrase for "in the world" is auf der Welt. You can think of it as being "on the Earth" or "on the globe". While in der Welt exists, it usually sounds much more abstract, like "within the realm of existence". For everyday statements about things existing on Earth, always use auf der Welt.
If Welt is a feminine noun, why does the sentence use der Welt?
Welt is indeed feminine (die Welt). However, auf is a two-way preposition. Because it describes a static location here (answering the question "where?" or wo?), it requires the dative case. In the dative case, the feminine article die changes to der.
Could I use für immer instead of ewig in this sentence?
Yes, you could say Nichts auf der Welt ist für immer and native speakers would completely understand you. However, ewig is an adjective meaning "eternal" or "everlasting," which pairs perfectly with the verb sein (to be). Für immer translates to "for always" and acts like an adverb, so ewig sounds slightly more natural and philosophical as a descriptive adjective here.
Is Nichts capitalized here because it is a noun?