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How big is the universe?

How big is the universe?
Form 8P from Northamptonshire (Age 5-14)
Abid Hossain + Jack Huang + Eddy Liou from Swansea (age 5-14)

How big is space?
Jessica from Kent (Age 5-14)

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One Response

  1. It’s actually rather difficult to put a number on this, because you get a different answer depending on how you measure the distance! The reason for this is that the universe is expanding all the time, so if, for example, you try to work out how long light took to reach us from the most distant thing we can see and use the speed of light to work out how far it could have come, you’d get the wrong answer because the space covered in the first part of the journey would have expanded to be even bigger since then.
    It’s also difficult because since the universe began about 13.7 billion years ago light could only have come to us from distances it could cover in that time (allowing for what I said just above), but there could be lots more universe beyond that distance we’re not able to see.
    However, we can look back to a point in time about 380,000 years after the start of the universe at the Big Bang, at which point the universe first formed hydrogen atoms. Before this time light couldn’t travel through the universe without being scattered, but after this point the light is able to travel largely unimpeded to us now, which we see as the ‘cosmic microwave background’. This is the furthest distance we can see. If you factor out the expansion effect I mentioned, this is about 46 billion light years away (so in those 13 and a bit billion years light has covered a distance which is now 46 billion light years – even though light only does one light year per year!). So roughly speaking the bit of the universe we can see is a little under a hundred billion light years from one side to the other (in miles this is something like 5 followed by 23 zeros).
    Of course as the universe gets older light has more time to reach us from distant areas so in principle we see a little bit further all the time. In a human lifetime this growth isn’t measurable in any way, just as a human lifetime isn’t very long at all compared to the age of the universe.

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