Ask Ethan: When A Photon Gets Redshifted, Where Does The Energy Go? (Synopsis) [Starts With A Bang]

“…in every kind of chemical change no loss of matter occurs […] in all the varied modes of physical change, no loss of energy takes place.” -Sir Henry Enfield Roscoe

When it comes to the physical laws of the Universe, perhaps the most unbreakable of all seems to be the law of conservation of energy. In every mechanical, chemical, or even nuclear reaction, the total amount of energy, when all sources are considered, appear to be conserved.

Image credit: NASA / SDO.

Yet in General Relativity, no strict definition of energy exists. So when the Universe expands, the photons within it get redshifted, which means they lose energy. Yet there’s no discernible location which gains a commensurate amount of energy. Is it truly lost? Is energy not conserved? The answer, as best as we can determine it, lies in the physics of the expanding Universe.

Image credit: E. Siegel, from the book Beyond The Galaxy.

Find out the story on this edition of Ask Ethan!

from ScienceBlogs http://ift.tt/1NZoF1J

“…in every kind of chemical change no loss of matter occurs […] in all the varied modes of physical change, no loss of energy takes place.” -Sir Henry Enfield Roscoe

When it comes to the physical laws of the Universe, perhaps the most unbreakable of all seems to be the law of conservation of energy. In every mechanical, chemical, or even nuclear reaction, the total amount of energy, when all sources are considered, appear to be conserved.

Image credit: NASA / SDO.

Yet in General Relativity, no strict definition of energy exists. So when the Universe expands, the photons within it get redshifted, which means they lose energy. Yet there’s no discernible location which gains a commensurate amount of energy. Is it truly lost? Is energy not conserved? The answer, as best as we can determine it, lies in the physics of the expanding Universe.

Image credit: E. Siegel, from the book Beyond The Galaxy.

Find out the story on this edition of Ask Ethan!

from ScienceBlogs http://ift.tt/1NZoF1J