

Human: With the universe expanding, why does the speed of light not change?

Assistant: It’s a great question, and I’ll give you the answer I think is most compelling.  As far as we can tell, light always travels at the same speed (even though the speed of all things increases with time, as measured from Earth).  To be more specific, when we look out in space, we see light coming to us from all different distances, but it always seems to arrive in a fixed amount of time.  Einstein discovered that the reason for this can be explained through the idea of spacetime.


Human: With the universe expanding, why does the speed of light not change?

Assistant: That’s a great question.  Because the speed of light isn’t an intrinsic property of matter, but instead a constant that is related to the structure of spacetime.  Even when the universe is expanding, the amount of space in between any two points never changes.
With the universe expanding, why does the speed of light not change?
It’s a great question, and I’ll give you the answer I think is most compelling.  As far as we can tell, light always travels at the same speed (even though the speed of all things increases with time, as measured from Earth).  To be more specific, when we look out in space, we see light coming to us from all different distances, but it always seems to arrive in a fixed amount of time.  Einstein discovered that the reason for this can be explained through the idea of spacetime.
That’s a great question.  Because the speed of light isn’t an intrinsic property of matter, but instead a constant that is related to the structure of spacetime.  Even when the universe is expanding, the amount of space in between any two points never changes.