Top Document: [sci.astro] Cosmology (Astronomy Frequently Asked Questions) (9/9) Previous Document: I.16. What about objects with discordant redshifts? Next Document: There are different ways to measure distances in cosmology? See reader questions & answers on this topic!  Help others by sharing your knowledge Author: Peter Newman <p.r.newman@uclan.ac.uk> The energy of a photon is given by E = hc/lambda, where h is Planck's constant, c is the speed of light, and lambda is its wavelength. The cosmological redshift indicates that the wavelength of a photon increases as it travels over cosmological distances in the Universe. Thus, its energy decreases. One of the basic conservation laws is that energy is conserved. The decrease in the energy of redshifted photons seems to violate that law. However, this argument is flawed. Specifically, there is a flaw in assuming Newtonian conservation laws in general relativistic situations. To quote Peebles (_Principles of Physical Cosmology_, 1995, p. 139): Where does the lost energy go? ... The resolution of this apparent paradox is that while energy conservation is a good local concept ... and can be defined more generally in the special case of an isolated system in asymptotically flat space, there is not a general global energy conservation law in general relativity theory. In other words, on small scales, say the size of a cluster of galaxies, the notion of energy conservation is a good one. However, on the size scales of the Universe, one can no longer define a quantity E_total, much less a quantity that is conserved. User Contributions:Top Document: [sci.astro] Cosmology (Astronomy Frequently Asked Questions) (9/9) Previous Document: I.16. What about objects with discordant redshifts? Next Document: There are different ways to measure distances in cosmology? Part0  Part1  Part2  Part3  Part4  Part5  Part6  Part7  Part8  Single Page [ Usenet FAQs  Web FAQs  Documents  RFC Index ] Send corrections/additions to the FAQ Maintainer: jlazio@patriot.net
Last Update March 27 2014 @ 02:11 PM

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