Question: how big is the univers

Asked by smilliyface12345678910 to Bev, Posty, Edward, Kate, Nathan on 16 Jun 2011. This question was also asked by cloud.

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  1. Photo: Kate PattersonKate Patterson
    answered on 16 Jun 2011:

    Cool question. This sounds like a question for Edward – the universe guru.

    I thought that the universe is continuously expanding and we don’t actually know how big it is – and its measured not in kilometeres but in light years right? ie how long it takes to go somewhere when travelling at the speed of light?

    Edward can you help too? Thanks

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  2. Photo: Edward ShinEdward Shin
    answered on 16 Jun 2011:

    Hi Smilliyface,

    A proper answer to that question is very deep and complicated, because when you start looking at distances on big scales, it turns out that it becomes hard to say what ‘distance’ is…

    But let me try to give you an idea of how unbelievably BIG the universe is — but you have to promise not to ask what I mean by ‘distance’ in my answer below!

    Suppose that you made the earth the size of a marble, 1 centimetre across. The distance to the Sun would then be about 120 metre; the size of the solar system (measured to the orbit of Neptune) would be about 7 kilometre; the nearest star would be 31,000 kilometre away; and the distance to the centre of our Galaxy (The Milky Way) would be more than the distance between Earth and Sun!

    And that’s just one galaxy. So, now you have some idea how impossibly large our Galaxy is, let’s say that the Galaxy is the size of a marble (1cm across, again). Then, the size of the “observable universe” would be about 5 kilometre.

    The “observable universe” is the part of the universe that physics says we could possibly ‘see’ if we had infinitely good, high-technology telescopes. Nobody really knows how much more of the universe there is beyond the observable universe. But in the observable universe alone, there are probably more than 100 billion (10^11) galaxies.

    So you see how incredibly, unimaginably HUGE the universe is!

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