Why will the sun not shine forever?

Answer 1

The deeper answer is this: a long time ago, when we were not, even, here, the stars of our galaxy were just forming. Though stars have long lifetimes, many have already died, and some are just being born. They go through a life cycle from having much mass, and burning that mass, through nucleosynthesis, until the fuel for burning has run out (hydrogen). Most stars end their lifetimes by either slowly cooling or exploding. Stars live a long time because they are such gigantic entities. The estimated lifetime for the sun is a total of 10 billion years. No one knows what the situation will be at that time, as far as planet earth goes.

Answer 2

The sun will not shine forever because it is a star that will eventually deplete its fuel source and undergo changes in its life cycle. Eventually, it will expand into a red giant and then collapse into a white dwarf, ceasing to shine in its current form. This process is estimated to occur in about 5 billion years.

Answer 3

Our sun is a star and ALL stars have life spans - just like us. When stars die, the elements get blasted out into space and end up forming other planets and stars.