Cooper doesn’t physically “push” the watch from the outside; inside the tesseract, he uses gravity as the only force he can still influence to nudge the second hand in Morse code.

What happens

  • He is trapped in a higher-dimensional space where he can access moments in Murph’s room from different times.
  • By applying tiny gravitational pulls to the watch’s second hand, he makes it tick in a pattern that encodes the quantum data.
  • Murph later notices the watch still behaving oddly because the message was effectively “stored” in the repeating motion.

Why gravity

In the movie’s logic, gravity can cross time more easily than the other forces, so it becomes Cooper’s communication channel. The result is a time- loop style message: Cooper sends the information to younger Murph, and older Murph later uses it to help save humanity.

Simple version

Think of it like Cooper tapping the watch from a place outside normal time, and the taps show up as Morse code.

If you want, I can also explain why the books and dust fall differently from the watch in the same scene.