Comment on wat

IAmNorRealTakeYourMeds@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

• skisnow@lemmy.ca ⁨3⁩ ⁨weeks⁩ ago

  The end of the stick would respond at the speed of sound travelling through the medium of a stick.

  source

  • Korhaka@sopuli.xyz ⁨3⁩ ⁨weeks⁩ ago

    Now I wish I had a nice big wall about a light second away and a massive laser to draw things on it.

    Bonus: angle the wall so that the left side is a light second and the right side is a light minute away. Alternate the laser on/off.

    source

    • starman2112@sh.itjust.works ⁨3⁩ ⁨weeks⁩ ago

      Good news! We do have a nice big wall about a light second away! Hard to find a laser that’ll make a visible dot on the moon, though

      source

      • NannerBanner@literature.cafe ⁨3⁩ ⁨weeks⁩ ago

        what-if.xkcd.com/13/

        Lovely how xkcd seems to have the answers to life and its mysteries.

        source
  • IAmNorRealTakeYourMeds@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

    but how will it look like?

    for a short scale it’ll be a straight line. but a few light years away? where the abstract dot is moving faster than the speed of light? what shape would you see? definitely not a straight line. and definitely some time issues. like it’ll hit you and then you’ll see it hit other planets you’re left and right?

    source

    • SaraTonin@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

      Think of it like a hosepipe. You’re on the lawn with s long stream of water coming out of the hose. If you flick it quickly it doesn’t stay in a straight line. The beam of water curves as you move.

      Because the beam of water isn’t an object. It’s a stream of particles which are constantly being emitted from the tip of the hose

      Same thing with a laser beam. It’s a stream of photons being emitted from the laser. If you flick the laser, the photons which have already been emitted will continue in a straight line. Any which are emitted during the flick will head off in a straight line in the direction the laser was pointed. End result:a curved beam

      source

      • IAmNorRealTakeYourMeds@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

        that makes sense, but I’m trying to imagine how that beam would look like a few light years away before it hits you, when it hits you, and after.

        source

        • -> View More Comments
• midribbon_action@lemmy.blahaj.zone ⁨3⁩ ⁨weeks⁩ ago

  First question: two reasons that wouldn’t work: the stick would just break, obviously, but if it was a super duper stick, the torque required to accelerate the end past the speed of light is directly related to how long the stick is, so any increase in speed from a longer stick will be offset by the need to apply more force at your end. Therefore the energy required to flick a stick to the speed of light does not depend on the length of the stick, you are simply creating a reverse lever of sorts. It’s still an infinite energy requirement, assuming the stick has mass.

  The second question is a lot easier. The light is traveling directly away from you at all times, there is no sideways motion.

  source

  • sneezycat@sopuli.xyz ⁨3⁩ ⁨weeks⁩ ago

    It’s actually simpler: the stick will deform because whatever movement you do travels at the speed of sound of the material the stick is made out of.

    source

    • midribbon_action@lemmy.blahaj.zone ⁨3⁩ ⁨weeks⁩ ago

      Why does it matter how long it takes for the torque to travel down the stick? The question was about the speed of the tip in the orbital direction, not the speed of the wave in the radial direction outward.

      source

      • sneezycat@sopuli.xyz ⁨3⁩ ⁨weeks⁩ ago

        I see your point. Still, it shows there’s no such thing as a “super duper stick” because there’d be shearing forces pulling the atoms apart faster than they can move together.

        source

        • -> View More Comments
    • Knock_Knock_Lemmy_In@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

      Movement across the stick travels much faster than the speed of sound (which is related to air density).

      source

      • sneezycat@sopuli.xyz ⁨3⁩ ⁨weeks⁩ ago

        The speed of sound of the material. So, if the stick is made of steel, it’d be like ~6000m/s. Which is way faster than the speed of sound in air, but not even close to the speed of light.

        source
• spicehoarder@lemmy.zip ⁨3⁩ ⁨weeks⁩ ago

  The Information that the stick has begun to move takes time to travel through the stick. Kind of like bending, but not really.

  source
• Brkdncr@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

  That’s where things get weird. The tip won’t exceed the speed of light. You could have a section near you moving at the speed of light and the tip will also be moving at c, because c is the limit.

  If you were on a train moving at 100mph, and threw a baseball at 50mph in the direction of travel, then the baseball is moving at 150mph. But if you were moving at c and threw that baseball it would not go faster than c.

  source

  • Duke_Nukem_1990@feddit.org ⁨3⁩ ⁨weeks⁩ ago

    In fact, everything would move very very rapidly away from the baseball hitting the first air molecule it touches (assuming you yourself have no mass in this scenario).

    source
  • IAmNorRealTakeYourMeds@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

    but from the point of view of the guy throwing the ball, the ball will move away from me at c faster than me. but time experienced by all involved would be a mess

    source
• Knock_Knock_Lemmy_In@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

  The tip of the very long stick would still move at sub light speeds. Also, the atoms at the far end will not immediately know what your hand is doing at the other. The forces the atoms make on each other also travel at (sub) light speed.

  source

  • IAmNorRealTakeYourMeds@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

    I guess imagining a perfect unbendable stick would break physics somewhere else.

    source

    • Knock_Knock_Lemmy_In@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

      You must define exactly what you mean by unbendable using existing physics.

      There may be a different definition that makes a paradox.

      source