• Question: How does gravity work? Do different things have different gravitational pulls?

    Asked by infintaneousdeath to Joel, Kristian, Tim, Venus, Zachary on 18 Nov 2013. This question was also asked by white69chocolate.
    • Photo: Kristian Harder

      Kristian Harder answered on 18 Nov 2013:

      Now, that is one *very* good question. Please let scientists know if you find out. 🙂 I think Tim and Venus might be on it already, and I hope they’ll give you a better response to your question than I can, but I’ll give it a go anyway.

      I guess the best explanation of how gravity works is still from Albert Einstein, who thought that gravity isn’t actually a force, but a geometric effect. Massive objects bend space (and time, actually spacetime 🙂 ) in such a way that nearby objects, minding their own business and moving along on their own favourite straight line, actually end up on a curve, because curved space bends their straight line. So the moon is actually moving straight along because Earth twists space enough for straight lines to become elliptical. Sounds easy, doesn’t it? 🙂
      The other side of the story is that gravity behaves suspiciously similar to the electromagnetic force (gets weaker with one over radius squared), and all other forces are described by a common theme in particle physics – quantum field theories, where we describe a force as the exchange of a force carrier particle (or boson) like the photon. Could gravity be such a force as well, with a hypothetical force carrier particle, the graviton? Then we should see gravitational waves like electromagnetic waves, and scientists are on the lookout for that, with special detectors called interferometers (see experiments LIGO and LISA).

      Second part of your question: if it has the same mass, it has the same pull. At least if you are far enough from it that the shape of the object and the distribution of its mass makes no difference. It might not always look that way – for example, a feather and a metal sphere have quite different ways (and speed) of falling down to the ground if you drop them, but that difference is due to different air resistance. In vacuum, they both fall exactly the same way. Even if they have different mass.

    • Photo: Tim Hollowood

      Tim Hollowood answered on 19 Nov 2013:

      Hi, great question. Einstein figured out that gravity works in a completely different way than the other forces. Any mass or energy (since E=mc^2) has the effect of curving space and time around it. If other masses are moving through the space-time then their trajectories will be changed and this is what we see as the force of gravity.
      The amount of gravitational pull depends on how much the space-time is curved and that depends on the mass of the object. So the sun curved space-time more than planet earth because it has a bigger mass.
      Some object curve space-time so much they actually rip it….these are called black holes!

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