April 3, 2013 Science fact

What is metric expansion? What does it mean when we say the universe is expanding?
The individual parts of the universe, the galaxies, are not expanding. They are simply moving farther away from each other. So imagine an empty balloon with dots drawn on it. At t = 0, the dots on the balloon are very close to one another. Now imagine that the balloon is pumped. Over time, the dots will grow further away from each other, but they will remain the same size.


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