What is the difference between torpedoes in World War 1 and torpedoes now?

Answer 1

nothing. Not true.

WW1 torpedoes were designed to run in a straight line and explode on impact and little else.

By WW2 they had better explosive and some even had guidance systems that would permit them to search for a target if the did not hit the one they were fired at.

Also several different types were developed with different kinds of propulsion including electric. While electric torpedo were not as fast as the earlier steam driven ones they did not leave a trail of bubbles leading right back to the launching Submarine.

Modern torpedoes are self guided , computer controlled and therefore incredibly versatile and accurate. The have on board sonar systems enabling them to find a target by simply hearing the sounds that it makes or actively seeking it with sound. this is in addition to the Wire guidance system that can be used to manually control and steer the torpedo from the launching Submarine. There are also many variant's that are aircraft launched or launched from surface ships.