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It certainly seems that everything, on a galactic scale, and apart from our 'local group', are all moving away from each other, so yes, it does make sense that everything was closer together in the past.The reason that it has taken so long for the light from something that was closer to us when the light was emitted is that during the journey of the light, the distance it has had to travel has increased.Imagine that someone sets off walking towards you, from ten metres away, at a speed of 1m/s. If you stand still then after one second they'll be 9m from you and it will take them a total of ten seconds to reach you. If you're walking away from them though, at say 0.5m/s, instead of standing still, then after one second the person still has a further 9.5m to walk instead of just 9m. In the end, it will take them 15 seconds to catch up with you instead of just ten, and they will have traveled 15m instead of ten.This is very simplified, of course, and instead of you walking across the ground and away from the person walking towards you it is more as though you are standing still on the ground but the ground itself, where you are standing, is moving, being forced away from where it was because new ground is appearing between you both.
Tom Nawalinski asked the Naked Scientists: On a recent podcast, your guest was explaining how he was able to detect the most distant object ever seen. My question is: if the light from the gamma ray burst left the star over 13 billion years ago, wouldn't the Earth have been much closer at the time since the universe was only nine percent of it's current size? And if the Earth was closer, wouldn't the light have arrived long ago? How is it that we can see it now?Tom NawalinskiWhat do you think?
Taking the original example, the gamma-ray burst actually occurred 13 billion years ago when the universe was one ninth of its present size. Lets say 10% for clarity. In that case, it would have happened 13 billion years ago minus 90% meaning that is was 1.73 billion light years away from us when it went off. But surely, however fast it moved away from us, the light from that single transient event, would have reach us 1.73 billion years later - ie 11.27 billion years ago?