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sabianq
2010-Jan-28, 01:16 AM
hi all,
a while back i suggested that the fundamental forces we see around us, the electromagnetic, weak and strong force are an artifact of the expansion of spacetime, meaning that these forces are manifested by stress of the expanding fabric of spacetime...

regardless, i got a lot of flack for posting such a hair brained and crazy idea...

but one comment has really been bugging me...

http://www.bautforum.com/against-mainstream/83483-higgs-particle-field-gravity.html#post1409578


The problem with this, outside of not having any supporting mathematics, is that spacetime doesn't expand "locally" due to gravity.

i asked for a source for this statement and tensor politely suggested that i was joking by suggesting that everyone knew that gravity overcomes the expansion.


You're arguing for some highly speculative ideas, with no support or presenting any sources and and you want sources for an idea (gravity overcoming expansion) that is well known? You're joking right?


anyways, i cannot find a straight forward answer...

it seems that about half of the places i look suggest that the expansion will eventually rip everything apart, even the quanta that makes up matter...
like this article
http://www.abc.net.au/science/news/stories/s942245.htm


In Caldwell's scenario, the universe will last about 20 billion more years. Sixty million years before the end, dark energy will cause the Milky Way galaxy to fly apart. Three months before the end solar systems will break down, flinging planets helter-skelter. Finally, at a tiny fraction of a second before the end of everything, dark energy will be so great that it will overcome the powerful forces that hold matter together, throwing apart atoms.

"It's as plausible as the other [scenarios]," said astrophysicist Professor Abraham Loeb of Harvard University. "And it's good to know what the possibilities are".

and the other half say...
well, the other side of the argument...


so what is the real story?
does gravity overcome expansion or will expansion overcome gravity?
does anybody really know..

thanks

01101001
2010-Jan-28, 02:20 AM
does gravity overcome expansion or will expansion overcome gravity?

Sean Carroll Cosmology Primer FAQ (http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#dess)


Could we detect the expansion of the universe by trying to measure the expansion of the solar system?
No. Any system that is bound together by internal forces -- whether it is a table, the solar system, or the galaxy -- does not expand along with the universe. (Not just that it only expands slightly; it really doesn't expand at all, or at least not because of the expansion of the universe.) To observe the expansion, we need to study objects that are very distant, not directly bound to us by gravity or anything else.


does anybody really know..


Sean Carroll Cosmology Primer FAQ (http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#finite):


Is the universe finite or infinite? Will it recollapse or expand forever?
We don't really know in either case. [...] Similarly, we can straightforwardly extrapolate the current evolution of our universe, dominated by dark energy, to predict a future in which the universe continues to expand for all time (see the dark universe). However, the dark energy might someday change its character into something different, in which case the universe might very well collapse. So, given how little we currently understand about the nature of dark energy, we can't say anything for sure about the ultimate fate of our universe.

sabianq
2010-Jan-28, 04:17 AM
hi, thanks for the links,

but that is not really answering my question.
i understand that we cannot detect or even see the expansion of the universe at a local level,

the question is will the expansion eventually rip everyting apart as astrophysicist Professor Abraham Loeb of Harvard University agrees is a possable senario as cited in the reference posted in the OP.
http://en.wikipedia.org/wiki/Big_Rip

or it wont as Captian Swoop says in this statment?
http://www.bautforum.com/against-mainstream/83483-higgs-particle-field-gravity.html#post1410237

It's not a controversial or little known piece of information.
Maybe what you need to do is some reading on the basics. I am sure that the other posters in the thread can suggest some good basic books.


so what is the consensus thus far?

the big rip
or the big crunch?

thanks!

sabianq
2010-Jan-28, 04:42 AM
or something else?

i saw a Universe episode recently where Michio Kaku was talking about the possibility of the expansion eventually ripping everything apart even atoms.

the deeper i dug, the more information i found supporting the scenario.

it surly doesn't validate my original crazy ATM claim/idea,
rather i was a bit bothered that i perceived a vehemence that i would even ask such a question and then ask for a reference to a "fact" that the expansion is weaker than the force of gravity and receive in reply, "It's not a controversial or little known piece of information"

when at the same time, such a scenario may actually be well within the realm of possibility.

so my other question is, is Michio Kaku and other astrophysicist in error when they say this scenario is a possibility?

Cheers!

WayneFrancis
2010-Jan-28, 05:10 AM
I had a similar question and I got the feeling that the most accepted current theory states that the big rip won't get powerful enough to unbind gravitationally bound systems let alone atoms.

But I'll qualify this with the issue that we don't understand DE at all so it, in my eyes, is no more then an educated guess and in that case I don't question educated guesses for which I'm woefully uneducated.

My specific question was if the "big rip" does happen and gets to the point where DE > strong force wouldn't that cause a cascade of quarks getting produced exponentially as DE attempts to rip the quark pairs apart.

The answer I got was "no" because it will never get to that point with a bit more information. I accepted that and moved on.

01101001
2010-Jan-28, 05:46 AM
the question is will the expansion eventually rip everyting apart as astrophysicist Professor Abraham Loeb of Harvard University agrees is a possable senario as cited in the reference posted in the OP.

I though Sean Carroll was explicit in stating that we don't know enough to say which possibility may be the outcome. Sean Carroll Cosmology Primer FAQ (http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#finite):


So, given how little we currently understand about the nature of dark energy, we can't say anything for sure about the ultimate fate of our universe.

astromark
2010-Jan-28, 06:00 AM
hi all,
a while back i suggested that the fundamental forces we see around us, the electromagnetic, weak and strong force are an artifact of the expansion of spacetime, meaning that these forces are manifested by stress of the expanding fabric of spacetime...

regardless, i got a lot of flack for posting such a hair brained and crazy idea...

but one comment has really been bugging me...

http://www.bautforum.com/against-mainstream/83483-higgs-particle-field-gravity.html#post1409578



i asked for a source for this statement and tensor politely suggested that i was joking by suggesting that everyone knew that gravity overcomes the expansion.



anyways, i cannot find a straight forward answer...

it seems that about half of the places i look suggest that the expansion will eventually rip everything apart, even the quanta that makes up matter...
like this article
http://www.abc.net.au/science/news/stories/s942245.htm


and the other half say...
well, the other side of the argument...


so what is the real story?
does gravity overcome expansion or will expansion overcome gravity?
does anybody really know..

thanks

---* The late Andrew Lange * ---
Had contributed much to this subject and will be sadly missed. The answer is...
Absolute. No doubt about it. Yes and No. :eh:

The gravitationally bound components of this Universe are not part of this accelerating expansion.

WayneFrancis
2010-Jan-28, 06:32 AM
I have heard Leonard Susskind say the DE could have an effect on atoms but it would not be detectable. He gave the analogy that you could think of the strong force as a spring and dark energy would just stretch that spring a little bit. I'm not sure if he still holds this view but seeing the lecture was only recorded last year I'd think there isn't a big risk that he still holds this view. I'll try to find and link where he describes this view.

Cougar
2010-Jan-28, 02:28 PM
so what is the real story?
does gravity overcome expansion or will expansion overcome gravity?

It is difficult to make predictions, especially about the future*.

________________________
* Who said it first? (http://www.larry.denenberg.com/predictions.html)

GOURDHEAD
2010-Jan-28, 03:48 PM
Would the Lens-Thirring effect play a significant role in the generation of dark energy at the galactic super cluster level of organization? I have little, if any, understading of either dark energy or Lens-Thirring effects, but it seems reasonable to assume that "space distortion" requires some energy and when all the chips are in something similar to a conservation rule must apply. Consequently, if Lens-Thirring is compressing space due to the twisting action near a center of gravitation, space must be stretched in the regions more distant from the center. The space between adjacent superclusters would be subjected to maximum stretching, and if the hierography of clustering is of a fractal nature, this may lead to the sort of expansion we have perceived that we are observing.

Argos
2010-Jan-28, 03:54 PM
The big rip scenario assumes that the increasing strength of Dark Energy will ultimately overcome gravity.

Ken G
2010-Jan-28, 08:21 PM
so what is the real story?
does gravity overcome expansion or will expansion overcome gravity?
A big problem here is that you are mixing two different questions: does expansion overcome gravity now, and will it ever. tensor's comments that you quoted were all about the situation as it is now, yet you seem to be asking about some very distant future. That's the fundamental disconnect. tensor is right that it does not overcome local gravitational binding now, and the question of will it ever is unknown (but either possibility seems plausible when so little is certain).

publius
2010-Jan-29, 02:10 AM
There is a lot of confusion over this, and I get confused too.

First, "expansion" is a matter of coordinate choice, as we've gone on about before. But all the confusion doesn't lie there either, but in other areas.

Imagine a universe with no dark energy/cosmological constant. The expansion is an *initial condition*. The Newtonian version of this would be a spherical glob of non-interacting dust that was thrown apart radially with some initial velocity. FLRW is the GR version of this, which is a bit more complicated, but all the basic behavior can be gleaned from considering the Newtonian limit version.

So the matter is flying apart. This is the expansion (for the record I stress the GR version is more complex -- it's not matter flying apart in static space). Now, the self gravity of all that matter is going to slow it down. If the initial velocity profile is below some critical value, the thing will stop flying apart and collapse back on itself.

If equal to or greater than this critical value, it flies apart forever. But note that gravity is always *slowing down* the expansion. The local tide due to the global matter distribution is always *compressive*. There's no ripping apart at all, but quite the opposite.

Now, add dark energy/cosmological constant. Here we get a term whose Newtonian limit is equivalent to filling space with a negative mass density, and we get a repulsive component, something acting against the attraction of the matter distribution.

This changes things, and adds another term to balance with the critical "initial velocity". If the universe expands enough for this repulsive term to "take over", the expansion *accelerates*. Here the tide will be stretching, pulling apart in all directions.

In regions of this expands forever profile, the expansion will initially slow where gravity dominates, then start accelerating once the cosmological constant term takes over.

-Richard

transreality
2010-Jan-29, 11:37 AM
Perhaps it is like a 2D fabric continuous subject to stretching, and thinning from an external flux, and into the thinning gaps these virtual particles appear to fill the gaps. If two objects are gravitically bound within the plane of the fabric, then the fabric would to have to bunch up between them, or flow around. hmm.. then, gravity should directionally distort space in an expanding universe.

01101001
2010-Jan-29, 02:54 PM
Perhaps it is [...]

As long as we're perhaps-ing, perhaps not.

Jeff Root
2010-Jan-29, 04:30 PM
So the matter is flying apart. ... Now, the self gravity of all that matter
is going to slow it down.
That is clearly true for a finite and bounded Universe. I think it is
pretty clearly untrue for an infinite Universe. I'm unsure about a finite
but unbounded Universe. I want to be convinced one way or another.
If the finite but unbounded case is too difficult, I'd be happy to start
by examining the infinite case.

In an infinite Universe it seems obvious that the gravitational pull by
every particle on every other particle is, on average, the same in every
direction, so that there can be no net slowing of the expansion.

-- Jeff, in Minneapolis

sabianq
2010-Jan-29, 04:47 PM
would the "Big Rip" scenario be more plausible if the energy that holds together atoms and subatomic particles (the fundamental forces) are subject to the laws of ever increasing universal entropy?

will the energy that was realized from the Big Bang eventually simply dissipate and become equal to nothing?

Argos
2010-Jan-29, 05:02 PM
will the energy that was realized from the Big Bang eventually simply dissipate and become equal to nothing?

If the conservation of energy holds, the energy will still be there, although incapable of producing work.

sabianq
2010-Jan-30, 02:00 AM
so is the strong force doing work?
is the weak force doing work?
is the electromagnetic force doing work?

will all mass eventually fall apart due to entropy....
if it does, then eventually dark energy will indeed simply pull everything apart on a particle level..
is this one reason we are looking for the higgs particle?


particle man particle man
can do anything a particle can.
when he's underwater doe he get wet,
whats he like?
nobody knows, particle man...

cosmopaul67
2010-Jan-30, 05:59 AM
Now, add dark energy/cosmological constant. Here we get a term whose Newtonian limit is equivalent to filling space with a negative mass density, and we get a repulsive component, something acting against the attraction of the matter distribution.

This changes things, and adds another term to balance with the critical "initial velocity". If the universe expands enough for this repulsive term to "take over", the expansion *accelerates*. Here the tide will be stretching, pulling apart in all directions.




Perhaps it is like a 2D fabric continuous subject to stretching, and thinning from an external flux, and into the thinning gaps these virtual particles appear to fill the gaps. If two objects are gravitically bound within the plane of the fabric, then the fabric would to have to bunch up between them, or flow around. hmm.. then, gravity should directionally distort space in an expanding universe.

In all seriousness (honestly, from my own limited knowledge), I ask : how realistic is the hypothesis of the “Big Rip” ? Do physicists really know ?

Why do we need a “Dark Energy” at all ? Are theoretical physicists looking for something that needn’t exist at all ?

How well does a notion of the “fabric” of space-time suit observation ? Is there a “fabric” to rip at all ? Or is space, just that ... space ? Not something tangible that is attached to the matter of the universe, and becomes detached or ruptured with expansion. Space just expands where there isn’t enough mass to gravitationally overcome expansion. And that time is just that ... a unit of measurement. Not attached to space or matter; just another descriptor of events.

Maybe Inflation never “stopped”; it was just interfered with for the last 13.7 billion years by gravity, after the splitting of the fundamental forces. After nucleosynthesis , when gravity at last had something to act upon, that Inflation slowed. Super hot hydrogen cooled and condensed into clouds. The clouds collapsed under gravity to form stars. The stars burned and collapsed into black holes. That’s just what mass does on the relatively small scale of galactic superclusters and filaments. It’s just that now, the expansion has reached a point where the redshift of light, and possibly gravity along with it, prevents gravity from “wrestling” with Inflation finally; and Inflation is free again on a large scale.

Maybe this is a piece of evidence that gravity is a force carried by a particle, the graviton. And that this particle has a fantastically minute rest mass and a finite speed that eventually is overcome by the redshift that affects photons in an expanding universe. These gravitons simply can’t reach over the expanding distance, in time to be exchanged with other masses’ gravitons.

The Strong force still exists on the atomic scale. And Gravity still exists on the large-scale, but it’s just an inescapable eventuality that happens to gravity in all universes, after time.

This is simply my own conjecture, speculation that doesn’t depend on something invisible, and possibly impossible to detect, to explain anything. I certainly don’t pretend to have the mathematics and physical experimental evidence to support this. I just think : "if it’s simpler, isn’t it more likely ?"

pzkpfw
2010-Jan-30, 12:01 PM
cosmopaul67, the Q&A section is for asking questions and getting mainstream answers. Personal claims or conjectures go in the ATM section.

cosmopaul67
2010-Jan-30, 08:28 PM
cosmopaul67, the Q&A section is for asking questions and getting mainstream answers. Personal claims or conjectures go in the ATM section.

... point graciously accepted. :)

And I'll reiterate my conjecture about Dark Energy, etc in a new thread in the ATM section.

Honestly, the point of my post, and the detail I put in it, was not intended to attack or challenge concepts that members were posting, but just to point out, hopefully constructively ... alternatives that may bring about even more relevent discussion. And I look forward to more ! :)

George
2010-Jan-30, 10:59 PM
...i understand that we cannot detect or even see the expansion of the universe at a local level,

the question is will the expansion eventually rip everyting apart as astrophysicist Professor Abraham Loeb of Harvard University agrees is a possable senario as cited in the reference posted in the OP.
http://en.wikipedia.org/wiki/Big_Rip

or it wont as Captian Swoop says in this statment?
http://www.bautforum.com/against-mainstream/83483-higgs-particle-field-gravity.html#post1410237

There are a couple of questions that seemed to be before us. Allow me rephrase the first one I thought was being asked and in a way that may limit the common ambiguity:

Are galaxies a tiny bit larger due to expansion?

If gravity neutralizes, somehow, the effect of the expansion, then the answer should be "no". Otherwise, it should be "yes". I think the answer is yes, but it is often ignored or stated in ways that only imply, at best, a yes answer.

An analogy is gluing buttons (ie galaxies) to the proverbial expanding balloon -- the balloon analogy, though without buttons, was originally introduced by Eddington, or at least he popularized it in his 1933 book - The Expanding Universe. Only the space between the buttons will be expanding, which is how it is described in books. But put a microscope to those buttons and these buttons will indeed expand but only according to their elastic properties. The force causing the balloon to expand will be much too little to produce a noticeable size effect upon the buttons. The same is true of our Solar System, but with much smaller expansion effects. Perhaps the orbit of Pluto is a tiny, tiny bit greater due to the expansion. Assuming, of course, this view is correct.

I have been curious about this question for some time. The expansion is quite enigmatic. Speaking of Eddington....

"But the theory of the expanding universe is in some respects so preposterous that we naturally hesitate to commit ourselves to it. For it contains elements apparently so incredible that I feel almost an indignation that anyone should believe in it - except myself." :)

[Oh how I had presumed too little the sense of humor of astronomers and physicists! Gotta love 'em.]

Another reason I think the above view is mainstream is partly because of what Publius has stated. He described an isotropic view for the universe, which was the approach Freidman took and it greatly simplified Einstein's equations, reportedly. If gravity neutralized the expansion, there would be significant anisotropy results in things like the "Great Wall", for instance. That doesn't seem likely, but I'm no expert on any explicit evidence showing favor or disfavor of the view.

It seems obvious that if the above view is indeed correct and the rate of acceleration will always increase, then at some point in time everything will rip apart. Such a view can be described in one word -- jerk. [I think that's funny. :shifty:]

Jeff Root
2010-Jan-30, 11:40 PM
My recent versions of the expanding balloon analogy use sequins (because
they are lightweight, and metallic, so one could imagine them as being
magnetizeable) stuck to a balloon covered with thick oil or thin grease.
The magnetic attraction between the sequins simulates the gravitational
attraction between nearby galaxies, while the oil or grease allows them
to slide around with some resistance, so they don't all slide together
instantly. Still isn't a perfect analogy, of course!

If the "dark energy" is everywhere in the Universe, evenly distributed, then
it pushes or pulls apart on everything. But things held together by nuclear,
electromagnetic, or gravitational forces currently resist the pulling enough
that they are only put under very slight tension.

If the "dark energy" only exists in or is stronger in the spaces between
galaxies, then it might actually push things inside galaxies together very
slightly. Instead of a microscopically tiny tension, there would be a
microscopically tiny compression. That compression might decrease as
the galaxies get farther apart, and farther away from the source of the
pushing force.

-- Jeff, in Minneapolis

Luckmeister
2010-Jan-31, 03:14 AM
Can someone tell me if mainstream theory considers it possible that all of space is expanding an equal amount everywhere, even within atoms. If it were, could the forces somehow be consistent with that expansion so that the tug of war between them would not be a factor? That would eliminate the need for local gravity overriding expansion to explain why we don't observe said expansion. That expansion, magnified by the extreme galactic distances, would explain the redshift we observe.

I certainly can't account for the reason that would be the case mathematically (I don't have the skills), but perhaps someone here who does can tell me if that idea has been discounted, and if so why? It just seems like Occam's Razor would indicate that as the simplest cosmic scenario. Or does it open up a dimensional bag of worms we're not yet equipped to theorize on?

Mike