what the bible really says about when the world will end

Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and [by] our gathering together unto him,

That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand.

Let no man deceive you by any means: for [that day shall not come], except there come a falling away first, and that man of sin be revealed, the son of perdition;

Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, showing himself that he is God.

---2 Thessalonians 2:1-4

Watch therefore, for ye know neither the day nor the hour wherein the Son of man cometh.

---Matthew 25:13

For yourselves know perfectly that the day of the Lord so cometh as a thief in the night.  

For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape.  

But ye, brethren, are not in darkness, that that day should overtake you as a thief.  

Ye are all the children of light, and the children of the day: we are not of the night, nor of darkness.  

Therefore let us not sleep, as [do] others; but let us watch and be sober.

---1 Thessalonians 5:2-6