Historical clue formulations

• Stuff that's the opposite of stuff — 2023-07-04
• Warp drive power source on "Star Trek" — 2022-11-14
• "Star Trek" warp drive fuel — 2015-09-28
• Fuel for a warp drive engine on "Star Trek" — 2013-09-14
• Physicist's study — 1999-05-07