If I could witness everything, I would like to see world war two minus human suffering. Just the technological advancements. Sophisticated weapons like the Tiger tank the RAT, the V2 rockets, First jet fighter, The dominance of the carrier, development of sarin/tarin, the Beast computer and the rise of Enigma, guided bombs, the atomic bomb, The scientists of Blechley park, and others like Albert Einstein, Werner von broun, etc etc The Generals Think Patton, MacAuthor, Rommel, the leaders Roosevelt, Churchill, Stalin, Hitler.
Imagine being able to tell people you know how the story ends when they see pictures of Hitler at the Eifle tower when France fell or the Battle of Britain, or the pacific theater like Midway When the whole of the USA carrier fleet could have been destroyed by the Japanese. Or just before Pearl Harbor happened or after the launch of the Enola Gay. More technological advancements occurred in WW2 then probably any other time period in history!
Another great time to witness first hand would be like the show "the men who built america".
Conversations with Vanderbilt, Andrew Carnegie etc etc, would be awesome!
Or going back to see Alexandria before it was burnt or Ancient Egypt or the biblical Babylon *I would have too much fun with a time machine!*
I would of course need some kinda translation device too though
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