• Question: Why is gravitational force known as 'action at a distance force'?

    Asked by 232grak26 to Daniel, Hannah, Maggie, Ry, Scott on 15 Nov 2017.
    • Photo: Ry Cutter

      Ry Cutter answered on 15 Nov 2017:

      Action at a distance force is a force that seemingly acts on two objects without them interacting. Magnetism is another one. So an ordinary force (like pushing a cat of your keyboard), requires the force giver to be in contact with the object that is moving.
      However, with things like gravity and magnetism. We can see objects moving even though nothing has ‘seemingly’ touched them.

      We know however, that there is a physical process going on. If two magnets repel then we know that they’re magnetic fields are interacting. We know that the moon is influenced by the Earth’s gravitational field. So while they look like they aren’t touching, there are things we can’t see interacting with each other.
      Great question,
      Ryan 😀

    • Photo: Scott Melville

      Scott Melville answered on 15 Nov 2017:

      Things seem to interact gravitationally without touching, i.e. ‘at a distance’, you can still feel the Sun. Why is this a problem? Well, it made Einstein upset because it makes causality weird. Like, right now, you must be feeling the gravity not just from the Sun, but also from EVERY star out there in the sky. And they feel you. If you jump up and down, every star all over the Universe IMMEDIATELY knows about it (and may even wiggle a bit, if you were really heavy). If light travels at a finite speed, so does information – but this ‘action at a distance’ picture allows information to instantaneously get everywhere. So to fix this, Einstein came up with gravity waves – the idea is that if you jump up and down, really you’re making little waves in space and time, and these travel (over millions of years) out into the Universe – not instantaneously 🙂

    • Photo: Maggie Lieu

      Maggie Lieu answered on 15 Nov 2017:

      The gravitational force is an action at a distance force because any 2 objects don’t have to touch for the force to happen. For example you can get pulled into the gravity of a black hole even though the black hole isn’t grabbing you

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