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Universe expansion is slowing down 
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#19
May612, 04:09 PM

P: 6

I'm confused about the standoff here.
As an observer so far of this exchange we seem to be talking at cross purposes. The point under discussion appears to be is .51 older or younger than .49 in terms of observed phenomena. So which is it? Have I missed a trick here or should this be obvious? 


#20
May612, 05:21 PM

P: 98

It's not about age. It's about dark energy. Current theories state that space expansion was accelerating, decelerating and is accelerating again, and that we have this repulsive (i guess, source isn't described) and unknown force called dark energy.
Instead of this it could be simply explained by deceleration. And known force  gravity? It's a hypothesis, same as dark energy. 


#21
May612, 06:05 PM

P: 150

But the problem is that the acceleration is not a hypothesis, it's a measurable fact. Your hypothesis of decelerating expansion is contradicting known evidence, therefore it's not true.



#22
May612, 06:08 PM

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#23
May612, 11:13 PM

P: 98

Dead Boss, what fact my hypothesis contradicts? Collected data is a fact, data interpretation isn't. You clearly don't understand what I'm saying. My hypothesis does not contradict collected data. I pointed out the mistake in dark energy interpretation.
I would appreciate if you point a mistake in my interpretation. Drahhith, we can leave inflation alone. It doesn't change the fact of "accelerating" expansion. Bet on Nobel price winners sure is better than on random guy. But i would like to see some reasoning. 


#24
May612, 11:44 PM

P: 98

Dark energy:
* Expansion is accelerating * Velocities of distant objects will increase with acceleration over time relative to us * Universe will end up in big rip if dark energy continues to dominate, spacetime expands faster then c. * Time will come when CMBR and other galaxies will not be visible due to faster expansion then c. * unknown force. My hypothesis: * Expansion is not accelerating, it's constant (was decelerating earlier) * Velocities of distant objects will not increase with acceleration over time relative to us * Universe is flat, spacetime always expands at the speed of c. * All galaxies and CMBR will be visible all the time, at least till Planck's limit. * No additional force. I bet against DE due to Occam razor principle and due to the error in the interpretation. 


#26
May712, 12:00 AM

P: 98




#28
May712, 12:52 AM

P: 366




#29
May712, 02:00 AM

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P: 9,437

Myslius, you are arguing against mainstream scientists. Show your math, or, better yet, how their math is wrong. Logic is not better, or even equivalent to math.



#30
May712, 05:37 AM

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#31
May712, 05:46 AM

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P: 4,800

The rate of expansion [itex]H[/itex] has always been decreasing. However, lately it has been decreasing more slowly, slowly enough that it leads to an accelerating expansion. How is this possible? Well, the rate of expansion [itex]H[/itex] is defined as: [tex]H(t) = {1 \over a(t)}{da(t) \over dt}[/tex] I think the easiest way to see why a slowlydecreasing [itex]H(t)[/itex] leads to an accelerating expansion is to consider a constant [itex]H(t) = H_0[/itex]. [tex]H_0 = {1 \over a(t)}{da(t) \over dt}[/tex] [tex]{da(t) \over dt} = H_0 a(t)[/tex] So a constant rate of expansion [itex]H(t)[/itex] means that change in the scale factor is proportional to the scale factor: this is exponential growth! Specifically: [tex]a(t) = a(t=0) e^{H_0 t}[/tex] So a constant rate of expansion means that objects within the universe are accelerating away from one another exponentially fast. This isn't the situation we're in yet, but it appears that our universe is approaching this situation. 


#32
May712, 07:13 PM

P: 659

We just published an alternative in Class. Quant. Grav. last month whereby the universe is a decelerating EinsteindeSitter model (no cosmological constant, no dark energy, no acceleration) http://arxiv.org/abs/1110.3973. Our model fits the supernova data as well as the accelerating LambdaCDM (EinsteindeSitter plus cosmological constant). Don't get me wrong, LCDM has also fit WMAP and BAO data better than alternatives (we haven't even tried that yet). So, the safe bet is accelerating expansion per LCDM. But, I wouldn't go so far as to claim the accelerating expansion has been "measured." It is a model dependent "acceleration." 


#33
May712, 07:25 PM

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Interesting Ruta. I'll be sure to take a look at the paper as soon as I get a chance. Thanks for the link.



#34
May712, 10:27 PM

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#35
May812, 12:57 AM

P: 334




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