Acceleration of expansion: less gravity, not dark energy?

[newtonian]

I was staring at a diagram in Time magazine (I think it was 9/4/06) showing the expansion of the universe since the big bang and inflation. It showed gradual slowing and then acceleration of expansion. The slowing was due to gravity, the acceleration was due to <br />dark energy.<br /><br />And I was thinking – what if instead of dark energy, the gravity slowing expansion was becoming weaker.<br /><br />The gravity, I assume, is from what is not the center of our universe – involving the density of matter in space(/time).<br /><br />But, I ask – what if less of our universe’s gravity is influencing the expansion of our universe – due to less of our universe being in the gravity equivalent of a light cone – to wit: a gravity cone (or whatever it would be called).<br /><br />Couldn’t that lower gravity be causing acceleration of expansion?<br /><br />Now, of course, that begs the question: has more of our universe left this portion of our universe’s gravity cone, so to speak?<br /><br />That leads to other questions, but I will stop there for now.<br /><br />It may not be until Friday that I will be able to post again, btw. <br /><br />I have the flu and a very long day at work tomorrow.<br /><br />[Note: This is a variation of another model I have considered where the acceleration is caused by our section catching up with more mass beyond our visibility horizon that is already travelling above the speed of light away from us - by a domino effect attracting us to catch up.

 

[border_ruffian]

<font color="orange">The gravity, I assume, is from what is not the center of our universe </font><br /><br />Thought there was no center....?<br /><br />I'm fascinated by your less gravity idea, though.

 

[SpeedFreek]

For an object to accelerate, there has to be a force acting upon it. If you remove gravity completely, an object travels at a constant speed, it does not accelerate.<br /><br />Gravity may cause the universes expansion to slow down. But lack of gravity would not cause it to speed up, it would just slow down less and less until it travelled at a constant speed. Something else is required to make it accelerate. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[kyle_baron]

Just speculating, but I think that it's the space outside our light cone or gravity well, which is traveling faster than the speed of light (due to inflation from the BB). I think it's this 156 bly space pulling at our visible 13.7 bly space, causing it to accelerate. It would be similar to streching a rubberband. But I like your less gravity idea also. Maybe MOND has something to do with it:<br /><br />http://en.wikipedia.org/wiki/MOND <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[SpeedFreek]

<font color="yellow"> I think it's this 156 bly space pulling at our visible 13.7 bly space, causing it to accelerate. </font><br /><br />But the 156 bly space is actually just a description of the comoving distance which means our visible universe of 13.7 bly in <b> radius </b> is supposedly 78 bly in radius by <i> now. </i><br /><br />Science tells us that the things we see 13.7 bly away were there 13.7 billion years ago. Today they are 78 bly away. Which makes our visible universe 156 bly across now.<br /><br />So what you are suggesting is that the universe as it is now is pulling on the universe as it was then... but it is the same space, pulling on itself through time. Which I doubt is what you actually meant. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[kyle_baron]

<i><br />So what you are suggesting is that the universe as it is now is pulling on the universe as it was then... but it is the same space, pulling on itself through time. Which I doubt is what you actually meant. </i><br /><br />Well, not exactly, but your statement is close enough. <img src="/images/icons/wink.gif" /> Remember, the so called BB had 2 explosions, not 1. The 1st was this inflated space traveling faster than the speed of light. I also believe it is connected to the 2nd explosion, which is the physical energy part, which we are a part of, and includes the physical universe. This inflated space, which from reading your post, has to be much farther than the 156bly. Simply, because it is traveling faster than the speed of light. So what I'm saying is, this inflated space is pulling our visible universe space (both energized, and each a part of the other). Therefore, this inflated space could be the source of the dark energy, or accelerated expansion. <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[newtonian]

speedfreek - Its a relative thing. Your post is accurate.<br /><br />Actually, the universe's expansion rate is very close to omega=1.<br /><br />That would be the critical point where density and speed and gravity are balanced exactly between eternal expansion and eventual collapse.<br /><br />If gravity is less, then expansion becomes eternal. This is the effect that is being observed, I think.<br /><br />Feel free to correct me if I am wrong.<br /><br />BTW, I am not rejecting the dark energy model - merely adding another factor/model.<br /><br />I do not know which model is correct.<br /><br />There is always the possibility that more than one cause is involved with the effects scientists are observing.<br /><br />Like universal spin, aka global rotation; and also my domino effect model involving catching up to distant masses via gravity cones overlapping like dominoes from beyond our visibility horizon.

 

[SpeedFreek]

Your description of the expansion rate being close to omega=1 is correct as far as I know, so at this stage we don't know whether the universe will collapse or continue to expand.<br /><br />If gravity becomes less, the expansion would indeed become eternal.... but it would not cause acceleration of the expansion, just expansion at a constant speed. We observe the expansion accelerating, so the weakening of gravity (i.e. the gravity "cone" you mention) cannot be the cause of the acceleration.<br /><br />Something with gravity at the edge of the expansion could, however, cause the universe to accelerate as it expanded towards it.<br /><br />Universal spin wouldn't cause the "edges" to accelerate - again they would move away at a constant speed.<br /><br />A model involving catching up to distant masses of some kind could account for it though.<br /><br />As could something like what Kyle posted, i.e. the <i> unknown </i> rest of the universe that is outside of our visible universe. There is nothing to say that the universe is of uniform density, we can only suppose that. So it could be that our visible part of the universe is less dense than other parts, and thus they attract us towards them. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[newtonian]

kyle_baron - That is essentially one model I thought of independently.<br /><br />The objection posted on SDC (I forget by whom) was that we are out of reaction (gravity) range with matter from beyond the visibility horizon, aka light cone.<br /><br />My answer was my domino effect model - which involves overlapping light cones, and therefore overlapping gravity cones.<br /><br />Granted the matter cannot DIRECTLY attract our area of universe, but it can attract matter near our visibility horizon because said distant matter in our light cone is also in light cones from beyond our visibility horizon - and so on in a domino effect out to the edge of our universe or perhaps even out to another universe!<br /><br />On MOND - perhaps the equation is correct, but the reason for this is not understood correctly.<br /><br />I also wonder if the slowing of the space probes has something to do with one of the causes of the effects we are observing.<br /><br />On occam's razor (from your excellent link) - I would counter that sometimes the simplest explanation is not the correct one.<br /><br />As an example, consider genetics. It was assumed Mendel's model, which is quite simple, was all that was needed. Now we know genetic variation is far more complex - including not only methylation of DNA genes but also even epigenetic (outside the gene) coding involving methyl and acetly links to histones on the chromatin - once thought to be the inert backbone of the chromosome but now realized to be dynamic and involved in inheritance of traits.<br /><br />I would say that the simplest explanation is the easiest, and sometimes is correct - however, sometimes reality is very complex (another example is the complexity of the living cell compared to older views of simplicity of the cell.)

 

[newtonian]

speedfreek - On my model for matter pulling on our universe from beyond our visibility horizon, see my post to Kyle.<br /><br />But note this would involve matter that is beyond the co-moving distance for the furthest matter currently observed.<br /><br />And you have introduced another factor - time.<br /><br />The effects from the cause could be slowed.<br /><br />Have we confirmed that the speed of gravity is always constant at exactly the speed of light - also have we confirmed the speed of light is always constant? (in a vacuum - another problem btw.)

 

[newtonian]

speedfreek - Your user name may indicate you would be interested in this model:<br /><br />At the big bang, or at later inflation stage, or...., black holes have been accelerated to escape velocity from the gravity and light of our universe, thus in effect leaving the effective (i.e. the cause and effect edge) edge of our universe.<br /><br />In that case our universe would gradually have less mass and therefore less gravity!<br /><br />All do to speed!

 

[newtonian]

speedfreek - What if the truth turns out to be complex and both are true?<br /><br />To wit: dark energy does exist.<br /><br />But gravity is also less.<br /><br />In that case, less gravity to counteract dark energy with the result: acceleration!<br /><br />I trust you understand I have no faith in these models - I just feel one should explore all possibilities to see which model conforms more with the actual observations in astronomy (and physics).

 

[nexus555]

I personally don't think that is the case. Let's say you have a galaxy, and an intergalatic object hurling through space with nothing to be attracted to. The galaxy will be somewhat uniformly bound by gravity, however the galaxy itself is still in motion, just like the intergalatic object.<br /><br />We really and truthfully don't know what's causing the acceleration. What if we're on our way to a massive blackhole? The Big Bang calls for expansion, but cannot define acceleration. There has to be some force reacting to the acceleration to the universe. <br /><br />I really don't buy the Dark Energy/Mass thing yet. I think it's a convienent form of matter to justify the big bang and other mysterious of the universe (missing matter/energy.) Honestly, we really don't know at this point. Dark Energy and matter may be proven to be real, I don't know.<br /><br />But to me it seems like we're being attracted to something as a whole. What if we're really contracting instead of expanding? What if you went to the opposite side of the universe and the acceleration was going in the opposite direction? We cannot prove much with 1 small perspective of the massive universe.

 

[SpeedFreek]

I see where you are coming from here Newtonian, and I can see the connections you are making.<br /><br />But the simple fact is that however reduced gravity is, it cannot account for acceleration. There <i> has </i> to be another cause.<br /><br />As you say, dark matter could be involved, but whatever the cause is, it can't be reduced gravity as that would only cause reduced deceleration which is not the same as acceleration. Reduced deceleration can only end with constant speed. Acceleration requires something else. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[jamesbdunn]

I propose the Universe as we see it is much different than it appears to us.<br /><br />We already believe that light can be sucked in by a Black Hole. So photons are influenced apparently by Gravity and perhaps other forces of the Universe. So it seems to me that a photon traveling millions of years in the presence of gravitational forces would wander to some degree. Take into account all the stars that have previously died and their mass is simply floating around out in space but with just as much a gravitational force as when it was active, I have to believe the photons move around.<br /><br />Also, consider the causal effects of graviton resonance that I recently have been reading.

 

[jamesbdunn]

I was browsing one of the slide shows regarding graviton resonance.<br /><br />Might Dark Energy be potentially explained by Graviton Resonance at extremely long wavelengths. A bending in graviton densities with nodes spaced unequally and with increasing occurrence further from the Universe. The local graviton densities are distributed somewhat evenly so it is difficult to detect locally. Matter and energy are influenced by the warpage of graviton node densities on a macro scale. <br /><br />Matter as one of the mediators of gravitons expands outward, the graviton resonant nodes continuously redistribute and a shift occurs that begins pulling matter back towards each other.<br /><br />The effect like a glob of mercury on a surface with a vibrating vertical component. Thus, Omega =1.<br /><br />Just a thought<br />

 

[newtonian]

jamesbdunn - Hi!<br /><br />Well, photons are influenced by gravity - that is the cause of gravitational lensing. (e.g. double images or stretched images of distant galaxies or quasars due to a mass in between.<br /><br />On gravitons - I am not familiar with that aspect so I will need to study it before responding properly.<br /><br />Excellent post, btw.