• Question: why is there gravity?

    Asked by cjay_is_not_here to Simon, Julia, Delma, Andrew, Alex on 10 Dec 2015. This question was also asked by enya kneeshaw.
    • Photo: Andrew Winnard

      Andrew Winnard answered on 10 Dec 2015:

      Hi Cjay, this another awesome physics question!

      Here is a video that tries to explain things for you:

    • Photo: Simon Challis

      Simon Challis answered on 10 Dec 2015:

      Hey cjay_is_not_here!

      I think Andrew nailed it! But I have my own question about gravity that I need an astronomer or a cosmologist to answer…. If the speed of gravity is not infinite as Newton assumed but rather equivalent to the speed of light, how is it possible for super huge structures like galaxies to form which are hundreds of thousands of light years across? Anyone wanna answer that for me?

    • Photo: Alexander Finch

      Alexander Finch answered on 11 Dec 2015:

      Oh wow, that’s an almost philosophical question! I don’t think anyone knows why there is gravity. We know a lot about it and how it works, but not where it comes from really. Lots of scientists are trying to work it out!

Comments

  • Photo: Alex

    Alex commented on :

    Hi Simon – I’m no cosmologist, but there are two things that pop into my mind:
    1 – Stars don’t move very fast in the scheme of things! For example, stars 10 light years away around our part of the galaxy would move 0.2% of a lightyear in the time the gravity would travel between them – a small angular change. In a local area, where the strongest gravitational attractions would be, motion would be similar for stars in the same area. Ditto over larger scales – even with speed-of-light delays, starts are approximately in the same part of the sky as they “appear”.
    2 – The galaxy has so many stars in that it the shape is dictated more by the distribution of stars in general, rather than individual positions. That’s to say – if one star sends out a gravitational attraction and then “moves” out of place, another start will have, statistically, moved to take its place.

    Not sure if those are the actual explanations, but it’s what I’d conjure 🙂