Share this thread: 
#73
Dec1611, 12:20 PM

PF Gold
P: 6,500




#74
Dec1611, 12:22 PM

P: 728

I mostly expect to be completely wrong or missing a fundermental understanding when I ask these kind of questions, but at least I am still asking, which I think is a good thing.



#75
Dec1611, 12:51 PM

PF Gold
P: 6,500




#76
Dec1611, 02:22 PM

Mentor
P: 12,005




#77
Dec1811, 01:19 AM

P: 186

If space was infinite before the Big Bang event and the entire mass/energy of the Universe was confined to a small volume and that volume expanded something like an explosion at the BB event, then it could be difficult to postulate a homogeneous and isotropic Universe. The outer regions of the Universe could see a very lower mass/energy density in the direction of expansion, as compared to a higher mass/energy density in the opposite direction. Given this scenario, it’s possible that the Universe wouldn’t be homogeneous and isotropic.
Seems to me that one way of having a homogeneous and isotropic Universe is if space is finite (i.e. compact). 


#78
Dec1811, 02:14 AM

PF Gold
P: 6,500

If the U was infinite at its inception, that does NOT mean that it could not have expanded exactly as it did. 


#79
Dec1811, 02:17 AM

Mentor
P: 12,005




#80
Dec1911, 08:54 AM

P: 728

In my earlier unanswered question I was asking if special relativity type effects have to be included in estimates for either the rate of inflation or even the age of the universe?
So I had a look around to see if photons which begin their journey in a higher density medium, with lower gravitational potential to a modern day lower density medium with higher gravitational potential, might undergo a red shift, and came up with the following: Source: http://en.wikipedia.org/wiki/Selfcr...onal_red_shift Gravitational red shift The local conservation of energy, and the consequential variation in rest mass, demand that gravitational mass is treated under the de Broglie wave theory. Mass is defined by the DeBroglie frequency of that particle. The red shift caused by the curvature of spacetime, a time dilation expressed by the metric component, is suffered not only by the photon but also by the atom with which it interacts and is thus undetectable. The red shift that is detectable is caused by the increase in rest mass that fundamental particles undergo when raised to the higher level. Gravitational red shift in this theory is interpreted not as a loss of gravitational potential energy by the photon but as a gain of gravitational potential energy by the apparatus measuring it. The red shift predicted is hence equal to the difference in Newtonian potential and thus identical with that of GR as confirmed in the PoundRebka experiment. Firstly, I hope this is acceptable science and that it is ok to post this, I am finding that posting genuine science questions here is getting somewhat risky of terse replies. So does this effect, if real, make any contribution to CMBR red shift and thus estimates for the age of the universe? Oh  and I am sure that if it does, that it has already been included. I also saw at the end of the wikipedia article a section on Dark Matter which looked interesting. Is this view accepted science? 


#81
Dec2111, 11:50 AM

P: 728

This page explains the concept of Gravitational Red Shift very well:
http://en.wikipedia.org/wiki/Gravitational_redshift At the bottom there is also a discussion on gravitational time dilation: Gravitational redshift versus gravitational time dilation When using special relativity's relativistic Doppler relationships to calculate the change in energy and frequency (assuming no complicating routedependent effects such as those caused by the framedragging of rotating black holes), then the Gravitational redshift and blueshift frequency ratios are the inverse of each other, suggesting that the "seen" frequencychange corresponds to the actual difference in underlying clockrate. Routedependence due to framedragging may come into play, which would invalidate this idea and complicate the process of determining globally agreed differences in underlying clock rate. While gravitational redshift refers to what is seen, gravitational time dilation refers to what is deduced to be "really" happening once observational effects are taken into account. So is there anyone here who can speak to the level of contribution of gravitation red shift to the CMBR redshift and also the possible effect of gravitational time dilation on the estimated age of the Universe? 


#82
Dec2111, 11:29 PM

P: 186

We are embedded within the BB event. A compact space model of the Universe can allow for closed spacelike and closed lightlike geodesics. A compact space model can explain a U that is homogeneous and isotropic. And to all PF participates, Merry Christmas and Happy New year! 


#83
Dec2211, 12:43 AM

Mentor
P: 12,005




#84
Dec2211, 12:54 AM

PF Gold
P: 6,500




#85
Dec2211, 12:55 AM

PF Gold
P: 6,500




#87
Dec2411, 12:44 AM

P: 186

My inclination is a U with a compact space (i.e. finite). 


Register to reply 
Related Discussions  
Topological space, Euclidean space, and metric space: what are the difference?  Calculus & Beyond Homework  9  
How does the space station survive the damages caused by debris in space?  Astronomy & Astrophysics  6  
Would an energy diffraction ring in five space form a Minkowski space?  Differential Geometry  2  
Solution space of linear homogeneous PDE forms a vector space?!  Calculus & Beyond Homework  2 