If the universe is 13 billion years old how do we have stars 45 billion light years from earth? Wouldn’t that light take 45 billion years to reach us?
In: Physics
They weren’t 45 billion lightyears away when the light starting heading towards us. The light has only travelled 13 billion lightyears, but we can calculate the rate of expansion of the universe based on redshift, and so we know that the origin of the 13 billion year old photons reaching us is currently 45 billion lightyears away.
Suppose you’re standing by the road, and a car drives past you. After it’s, say, 10 meters past you, someone in the back seat throws a bottle out of the window in your direction. The bottle is travelling towards you at 1 m/s. After 10 seconds, the bottle reaches you, but at this point the car itself is 100 meters away. The bottle couldn’t have travelled 100 meters in 10 seconds, and indeed it didn’t – it only travelled 10 meters. But you can then take that bottle, and read the note inside, and learn things about the occupants of the car who now *are* 100 meters away.
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