# Gravitational waves

We know that gravitational waves stretch space-time so light travelling through that space should be stretched as well. So my question is how do we know anything is stretching if the effect is experienced by every object in the universe.

• For one, it happens to every object which happens to be where the gravitational wave is, which is not everywhere in the universe at once. Second, what we experience is the change in stretching. That is what was measured by LIGO. – zephyr Feb 8 '17 at 15:43
• @zephyr, you can make that an answer. – James K Feb 9 '17 at 23:33
• @JamesK I know, I was just lazy. Feel free to take it though. Maybe later if no one has put an official answer down I will write something. – zephyr Feb 9 '17 at 23:35

• @AtmosphericPrisonEscape The frequency sensitivity of LIGO is bounded by seismic noise at the low end ($<10$ Hz) and shot noise at high frequencies. The central part of this frequency sensitivity is matched by the orbital frequencies of $\sim 10$ solar mass black holes just prior to merger. The upper bound is not due to the approximation above, which wouldn't be an issue until you got to above 100 kHz I think. – ProfRob Feb 13 '17 at 16:45