How is the universe expanding faster than the speed of light?

Question

Olivia Aldridge · Accepted Answer

The resolution of this apparent problem comes down to understanding the difference between the idea of expansion, and that of motion. Read on...

The issue is solved if we understand that what we mean when we say "the universe is expanding" is the expansion of spacetime, which is distinct from the motion of the material objects that are inside the universe. Spacetime is the rather abstract construct of three spatial dimensions and time that acts as the "container" for all material in the universe; it is not a material body. My understanding is that the galaxies we see travelling at speeds greater than that of light are being swept along with the continual growth of spacetime. They are not moving through spacetime at a speed greater than #c#, but are being carried away from each other by the expansion of spacetime. A common analogy is to picture two dots on a balloon's surface; when we inflate the balloon, the dots move apart because the surface is expanding rather than because they are traveling over it. In the case of galaxies, these are moving apart, and are also being carried to greater distances by the expansion. Thus, they can appear to move away from each other at greater than #c#. It is believed that the universe expanded at a rate that was many times faster than the speed of light during the inflationary phase, when it was still very, very young and smaller than your house!

Hazel Asher · Answer

undefined The speed of light is not the limit to the expansion of the universe; galaxies can expand faster than the speed of light due to the metric expansion of space, but individual objects within galaxies cannot expand faster than the speed of light.