How long can light live? Can it die? - Explained
Updated: Oct 18, 2018
Everything in this universe dies; everything that has a start also has an end. To many, this seems to be the one absolute truth to the universe, but what about light? Can it die, or will it exist for infinity? This whiteboard animation video explains all about it.
Light has remained one of the most difficult things to understand in science. Light seems simple but has many theories based on it. Many mysterious things are related to light. Light is also considered as fastest thing in universe. Everything about light is fascinating and so does its lifetime.
Well, there were always been various deep discussions on theories based on light and the light itself. The theories always got modified as understanding light was always been difficult.
Light is an electromagnetic radiation caused by a stream of photons so, Life of light depends on whether photons die or not.
Typically photons are said to have zero mass. But, the question is how anything without mass can ever die, it will be immortal. Well, there are theories according to which photons possess mass. But, that mass is not the actual mass; here the mass is “Relativistic mass” which is due to photon’s energy and momentum.
This thing proves that photons can die. But, what will be its lifetime? Well, Julian heeck of Max Planck institute for nuclear physics, Heidelberg Germany, set to tackle this issue. To find the limit on the photonic lifetime, Heeck analyzed observations of the cosmic microwave background radiation—light pervading the universe that dates from a few hundred thousand years after the Big Bang—gleaned from the now defunct NASA's Cosmic Background Explorer (COBE) satellite, launched in 1989. This light fits a very specific pattern—called blackbody radiation that tells scientists how intense the light should be, based on its wavelength. If any photons were decaying as they traveled across the universe, however, COBE would see less low-energy (redder) light than predicted by the blackbody radiation law, because red light would be expected to decay sooner than blue light. "If the photons come from very far away, say from the beginning of the universe, then they might have had enough time to decay on their way here," says physicist Emanuele Berti of the University of Mississippi, who has studied the mass of the photon but was not involved in Heeck's research. "That's the idea, which I think is very elegant."
But according to COBE's measurements, the cosmic microwave background appears to behave like a perfect blackbody. No low-energy light seems to be missing, indicating that very few photons, if any, have decayed since the Big Bang some 13.7 billion years ago. This analysis enabled Heeck to calculate that the minimum lifetime of a photon is 1018, or one billion billion, years.
Heeck's paper, published July 11 in Physical Review Letters, represents the first calculation of the minimum lifetime of a photon.