I was reading an article on Huffington Post (link to article) about the Multiverse theory. In the article it said this:
The big news last week came from the Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) experiment at the South Pole, which saw imprints in the cosmic microwave background—the oldest light in the universe, dating from shortly after the big bang...
I am far from scientific, actually just a web dev, but I have an interest in learning and reading about science, so please explain your answer in a way I can understand it. My question is in regards to the bold type in the quote. Does light ever actually end, go away, or just cease to exist once it is created? Will this "oldest light in the universe" ever completely cease to exist, or does light stay around indefinitely.
Answer
Will this "oldest light in the universe" ever completely cease to exist, or does light stay around indefinitely.
Light at the micro level is composed out of photons, the elementary particles of light . In addition to reflections light/photons undergo absorptions when hitting/interacting with matter. Photons can be completely absorbed or change in energy after such a scatter and slowly the intensity of light will diminish. Thus how long a beam of light will survive will depend on the matter found in its path.
The oldest light that we managed to see as Cosmic Microwave Background arrives into our instruments, is measured, and that is the extent of its lifetime , 13,9 billion years according to the prevailing cosmological model. In order to measure it some electrons and atoms/molecules have absorbed it. The same is true of its fellows which were intercepted in their path by the earth.
If the non interacting part will exist until the death of our universe is matter for speculations because there is no standard model on how the universe will end, and there may never be. As long as they do not interact some photons will remain though whether they will still carry a coherent snapshot of universe at the time they decoupled about 380000 years after the beginning, is also a moot point.
The CMB is shown here at 380000 thousand years after the Big Bang
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