Final answer:
The neutrinos from SN1987A were observed almost simultaneously with light, which allows scientists to place an upper limit on the mass of neutrinos. By calculating the relativistic factor gamma and considering the time of arrival, the mass of the neutrino is inferred to be negligible due to its minimal impact on travel time compared to light. This event confirmed that neutrinos have mass but it is extremely small.
Step-by-step explanation:
The observation of neutrinos from supernova SN1987A arriving almost at the same time as light can be used to put constraints on the mass of neutrinos because particles with mass cannot reach or exceed the speed of light (c), according to relativity. However, if neutrinos have a small mass, they can travel very close to c, displaying high relativistic velocities. By analyzing the time difference between the neutrinos' arrival from SN1987A and the arrival of photons (light), scientists concluded that the neutrinos' velocities were close enough to the speed of light to suggest they have an incredibly small but finite mass. This places an upper limit on the mass of the neutrino since a significant difference in the arrival times would have indicated a larger mass and, hence, a slower speed.
An equation to understand this concept involves the relativistic factor gamma (γ), which relates to the neutrino's velocity (v) and mass. Considering a neutrino with a mass and a certain kinetic energy, we can calculate γ using relativistic mechanics. The smaller the mass, the closer the velocity is to c, and the larger the γ factor becomes. If neutrinos were observed within hours of the brightening of a supernova, the time difference compared to light is not large enough to measure directly, but it does limit the possible mass of a neutrino to be very small because a larger mass would have resulted in a more noticeable delay.