• Question: how far does space go on for if it is a vaccuum and there are no particles then surely we can se all the way through as there is nothing to block our vision.

    Asked by mantha to Adam, Catherine, Karen, Leila, Nazim on 14 Mar 2012.
    • Photo: Nazim Bharmal

      Nazim Bharmal answered on 10 Mar 2012:

      Space isn’t exactly a vaccuum, there are tiny ammounts of dust in the solar system, even less between the stars and even less (but still some) traces of gases between the galaxies. So eventually light bounces off something and we can’t see through it. But actually the further something is, you see it further back in time so we can eventually see to the near the start of the universe which is where all light is blocked. (So yes, looking at the stars is like using a time machine!)

    • Photo: Adam Stevens

      Adam Stevens answered on 10 Mar 2012:

      Like Nazim says, space isn’t actually a vacuum. There’s still loads of particles whizzing around – hydrogen left over from the formation of the solar system, cosmic rays, bits of antimatter and matter created by radiation.

      It’s just that there’s so much less stuff than we’re used to, we call it a vaccum.

      In certain places there’s also lots of dust, ice, bits of rock. Our solar system is far from a vaccum, and there are massive dust clouds in our galaxy (the Milky Way). In fact, the milky way stops us from seeing a large part of the universe. If you look into the bulk of the Milky Way, you can’t really see through it. So we have to look out of the plane of the galaxy to see things far away.

      Even then there are clouds of stuff obscuring our view of parts of the universe, other solar systems, places where stars are being born (look up the Orion Nebula).

    • Photo: Leila Battison

      Leila Battison answered on 10 Mar 2012:

      Even though most of space is more or less a vacuum, we can still see that there are lots of stars, which are tiny patches that are definitely not a vacuum.

      Lots of theories suggest that the universe is infinite, and so must contain infinite numbers of stars. In that case, you would be asking: ‘If space is full of stars, then why isn’t it bright all the time’. One of the best explanations for this is that space is not infinitely old – it is only about 14 billion years old, and so we can only see light from 14 billion light years away (that has been travelling at the speed of light, obviously). The rest of space between the stars we can see is black because we *are* seeing through it – there’s just not enough light to see what we are seeing through it *toMATOMO_URL

      Hope that makes sense – I always feel incredibly tiny and confused when thinking about the vastness of space!

    • Photo: Karen Masters

      Karen Masters answered on 14 Mar 2012:

      Well this is an interesting question, and has previously even been given a name – Olbers Paradox, after a German amateur astronomer who wrote about it in the 1800s.

      The way Olbers put it it goes like this – if the universe is infinite then every sight line through it should end on a star, and so the night sky should be as bright as the surface of a star. This said Olbers proves that the Universe is not infinite.

      The original get out was the idea of interstellar dust. This definitely exists, and it’s what causes it to be difficult to see the centre of our own galaxy, although there’s not thought to be masses of it in the space between galaxies – certainly not enough to explain Olbers paradox.

      The solution instead is that while the universe is thought to be infinite, it has only been around for a finite time (about 14 billion years is the current bust estimate), so light can only reach us from stars within a sphere from which light has had time to travel to us during the age of the Universe.

      Great question!

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