Let Wigner now ask his friend for the result of the measurement. Whichever answer the friend gives (0 or 1), Wigner would then assign the state "system is in state 0 — friend has measured 0" or "system is in state 1 — friend has measured 1" to the laboratory. Therefore, it is only at the time when he learns about his friend's result that the superposition state of the laboratory collapses.
Let Wigner now ask his friend for the result of the measurement. Whichever answer the friend gives (0 or 1) Wigner wo,uld then assign the state "system is in state 0 — friend has measured 0" or "system is in state 1 — friend has measured 1" to the laboratory. Therefore, it is only at the time when he learns about his friend's result that the superposition state of the laboratory collapses.