In this demonstration, you can operate a virtual interferometer with a red laser (632 nm wavelength), and you can alter the path length of each beam arm to see how this affects the resultant signal. LIGO keeps its two lasers completely out of phase, so that no light enters the photodiode unless a gravitational wave changes the arm lengths. Use the sliders in the top-right corner to change the two path lengths by different amounts and note the effect on the recombined beam. What value for the net length difference produces the largest resultant signal? What happens if the two beams are offset by more than half a wavelength (316 nm)? (Click the “Close Controls” button to hide the controls and show the path lengths.) What about when you change each path length by the exact same amount? What happens when you press the “Simulate Gravitational Wave” button?