
#19
Nov2408, 11:21 PM

Sci Advisor
PF Gold
P: 9,182

When space expands, a photon redshifts. This nicely fits the conservation of energy principle. The total energy of the photon is diluted across a larger volume of space. Incidently, this phenomenon refutes the notion of space as a propogation media for photons [i.e., aether]. If space were such an entity, photons would blue shift when it was tensioned  like the note emitted by a guitar string being tightened. If space behaves more like a fluid, you should get shear when it is stretched. In that sense, dark energy could be equated with turbulence.




#20
Nov2508, 07:32 AM

PF Gold
P: 513

Marcus,
I hope you don’t mind, but I thought your previous response was so useful I made a reference to it in the sticky thread at the beginning of this forum. See following link: http://www.physicsforums.com/showpos...9&postcount=51. As implied, I found this to be a very useful summation of the stateofplay concerning what appears to be some of the more critical assumptions of the LCDM model. I might still be a little sceptical of the `serendipity` theory regarding the energy density of dark energy at this time, but need to research some of the background issues a little more before commenting. Therefore, started to do some figures on the energy issues related to the observable universe now and at CMB decoupling, i.e. z1090, as the following figures can be checked against the cosmological calculators. However, I was wondered if anybody had any comments on the results so far? Energy Density at z=0;So we are considering a comoving volume expanding from 41.80 million lightyears to 45.58 billion lightyears. Therefore, we can estimate the unity change in energy of this volume as follows: Baryon:… 1.145e70 / 1.172e70 = 0.977So under expansion and within the limits of accuracy of the calculation, the baryon and cold dark matter energy within this comoving volume remains unchanged, as we would expect. The radiation energy falls due to the additional (1/a) wavelength expansion factor, while there is an exponential increase in dark energy because it scales with volume. However, the bottom line appears to be that our comoving volume now has 2.7212 times the energy at decoupling, i.e. +370,000 years! I guess one immediate question that comes to mind is whether this energy analysis should consider any change the gravitational potential energy due to expansion?After reading Chronos` post could I clarify a few points: In the context under consideration, the expansion of space, wherever that means, leads to an increase in the wavelength of a photon in transit. As frequency is the inverse of wavelength, it falls as a function of expansion and so does energy by virtue of E=hf? 



#21
Nov2608, 06:46 AM

P: 622

Mysearch: You originally asked: The actual observational measurements are (a) H now (finally wellestablished by observation at 72 Km/sec/Mpc) (b) the Universe's flat spatial geometry (inferred from the WMAP power spectrum) and (c) the observed matter density (via the complex of observations discussed by Coles and Ellis in Is the Universe Open or Closed?; C.U.P. 1997), together with more recent observations of gravitational lensing caused by dark matter). When these observations are interpreted in the usual way with GR, assuming the isotropiceverywhere cosmological principle, they determine the present value of Lambda  and rightly focus attention on the puzzle of why that most mysterious quantity (or H, if you prefer) has the value it does. 



#22
Nov2608, 09:26 AM

PF Gold
P: 513




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