Question

Recordings show that SN 1987A was detected by neutrinos on February 23, 1987. About 3 hours later, it was detected in optical light. Why did this time delay occur?

Answer 1

This is due to time dilation.

According to Einstein's special theory of relativity, objects travelling near the speed of light will experience length contraction and time dilation.

If the neutrino took time in its own frame and time in our frame of reference then,

v is the velocity of the neutrino and c is the velocity of light

For v<c the denominator is always less than one resulting

So, the neutrinos were detected at a later time.