According to Einstein's Special Theory of Relativity, time moves at different paces depending on your frame of reference;
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Special relativity is an explanation of how speed affects mass, time and space.
The theory includes a way for the speed of light to define the relationship between energy and matter.
Small amounts of mass (m) can be interchangeable with enormous amounts of energy (E), as defined by the classic equation E = mc^2.
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Astro-Physics before Einstein
Before Einstein, astronomers (for the most part) understood the universe in terms of three laws of motion presented by Isaac Newton in 1686.
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Time dilation
One of the many implications of Einstein's special relativity work is that time moves relative to the observer. An object in motion experiences time dilation, meaning that when an object is moving very fast it experiences time more slowly than when it is at rest.