Dark energy

[thomma]

If dark energy pervades the universe and is responsible for inflation, and that the space between galaxies is inflating, how do galaxies collide? Would inflation not keep them apart and why does dark energy only seem to work on galactic scales? Why, or is it, not working within our solar system?

[Airbrush]

Your title should be "Expansion of the Universe", since dark energy has nothing to do with the expansion, only the acceleration of expansion.

 

The expansion of the universe takes place ONLY between superclusters of galaxies. Galaxies are bound together by gravity. Clusters of galaxies are bound together by gravity. And superclusters (clusters of clusters of galaxies) are bound by gravity. But all superclusters are moving away from all other superclusters.

 

This is a very common misunderstanding of the expansion of the universe. Dark energy has nothing to do with it. Dark energy is the term they use to address the strange fact that superclusters are moving faster and faster way from other superclusters.

Edited January 19, 2012 by Airbrush

[zapatos]

Your title should be "Expansion of the Universe", since dark energy has nothing to do with the expansion, only the acceleration of expansion.

 

The expansion of the universe takes place ONLY between superclusters of galaxies. Galaxies are bound together by gravity. Clusters of galaxies are bound together by gravity. And superclusters (clusters of clusters of galaxies) are bound by gravity. But all superclusters are moving away from all other superclusters.

 

This is a very common misunderstanding of the expansion of the universe. Dark energy has nothing to do with it. Dark energy is the term they use to address the strange fact that superclusters are moving faster and faster way from other superclusters.

I understand that DE had nothing to do with the beginning expansion of the universe, but I question your statement that DE currently has nothing to do with expansion.

 

My understanding is that universal expansion was slowing down until about 5 billion years ago, at which point the expansion began accelerating. If without DE the expansion could have slowed and possibly reversed, then wouldn't it be true that DE is solely responsible for our current expansion (whether that expansion is accelerating or not)?

[Airbrush]

That's a very good question Zapatos. I hope someone here can answer it.

 

If dark energy pervades the universe and is responsible for inflation, and that the space between galaxies is inflating, .....

 

I don't believe DE is responsible for inflation. Inflation is something that happened very briefly shortly after the big bang. Your question seems to be about universal expansion.

Edited January 19, 2012 by Airbrush

[JustinW]

Wouldn't expansion be the creation of new space? Or is it just the expansion of what we see moving out through space that already exists?

 

To the question about DE. As my layman way of thinking only provides to me, is the simple understanding that DE is a simple force that is acting on a large portion of matter(superclusters) constantly. A small amount of energy applied over a long period of time can reach very high speeds. Kinda like an ion engine. Anyway. . This small amount of energy is connected with both, the expansion and the acceleration of that expansion, since the density pressure of the universe is at a level close to 1 the expansion should logically slow to 0. Some say this would lead to a big crunch, but I would logically think that that would only happen if everything was close enough to be attracted by gravity. But I am an ameteur thinker, in that I have not been thinking about much of anything until recently. So if I have made an assertion that contradicts mainstream science then I would appreciate any correction.

[thomma]

Wouldn't expansion be the creation of new space? Or is it just the expansion of what we see moving out through space that already exists?

 

To the question about DE. As my layman way of thinking only provides to me, is the simple understanding that DE is a simple force that is acting on a large portion of matter(superclusters) constantly. A small amount of energy applied over a long period of time can reach very high speeds. Kinda like an ion engine. Anyway. . This small amount of energy is connected with both, the expansion and the acceleration of that expansion, since the density pressure of the universe is at a level close to 1 the expansion should logically slow to 0. Some say this would lead to a big crunch, but I would logically think that that would only happen if everything was close enough to be attracted by gravity. But I am an ameteur thinker, in that I have not been thinking about much of anything until recently. So if I have made an assertion that contradicts mainstream science then I would appreciate any correction.

 

Thanks for the replies dudes,or even dudettes. Why does the inflation, whatever is responsible for it, only work on Super cluster scale?

[IM Egdall]

Thanks for the replies dudes,or even dudettes. Why does the inflation, whatever is responsible for it, only work on Super cluster scale?

 

I think you mean the expansion of space. Gravity within galaxy clusters overcomes the expansion. As I understand it, things inside galaxy clusters are expanded by the expansion of space, but this expansion has been stopped by the strength of gravity (spacetime curvature). But out there in so-called empty space, there are no galaxies, thus so little gravity that the expansion dominates.

[dimreepr]

I understand that DE had nothing to do with the beginning expansion of the universe, but I question your statement that DE currently has nothing to do with expansion.

 

My understanding is that universal expansion was slowing down until about 5 billion years ago, at which point the expansion began accelerating. If without DE the expansion could have slowed and possibly reversed, then wouldn't it be true that DE is solely responsible for our current expansion (whether that expansion is accelerating or not)?

 

 

May be it's another example of cyclic fluctuation, like the flipping of the magnetic poles on earth, just over a much longer time frame.

Edited January 20, 2012 by dimreepr

[Airbrush]

Just today I was watching a program about the universe and someone said that ALL galaxies are moving away from us, and they are moving faster and faster away from us. That is only partly true. Not ALL galaxies are moving away from us faster and faster. The galaxies within the Virgo supercluster, our home, are bound together. They are not speeding away from us, but rather they are all orbiting the center of mass of the Virgo supercluster. The galaxies of our Local Group are also orbiting the center of mass of the Local Group.

Edited January 21, 2012 by Airbrush

[thomma]

I still don't get if inflation, or whatever you call it, is roughly the speed of light, how gravity within local clusters can overcome the rate of expansion.

[zapatos]

Inflation and expansion refer to two different things. Inflation refers to the rapid expansion of the universe very early in its history, while expansion refers to the increase of distance between super clusters in the universe over time. Inflation is no longer happening, expansion is happening now.

 

It is thought that dark energy (DE) pervades all of space and attempts to increase the amount of space between objects. It tries to increase the space between the atoms in your body, the moon and the earth, the earth and the sun, etc. The force of DE is relatively weak. It tries to increase the space between stars in the galaxy, or galaxies in our supercluster, but it is not strong enough to overcome the strength of gravity between these relatively close objects. On the scale of distance between superclusters, it is strong enough to overcome gravity (because gravity loses strength over distance) and the space between superclusters increases. DE is causing an accelerated expansion.

Edited January 23, 2012 by zapatos

[Doughnut]

I read recently a theory that: "Dark matter is not matter but a state – a structural pre-existent existencethat precedes matter – the submerged iceberg, the tip of which is manifested inthe universe as matter." Presumably this 'state' leaves a solid footprint. Any thoughts?

[imatfaal]

I read recently a theory that: "Dark matter is not matter but a state – a structural pre-existent existencethat precedes matter – the submerged iceberg, the tip of which is manifested inthe universe as matter." Presumably this 'state' leaves a solid footprint. Any thoughts?

 

Although we have yet to isolate or identify a dark matter particle - it behaves as if, and fits the prediction that follow from, it being a (weakly interacting) massive particle. Your quote might fit dark energy a little better as we know very little about dark energy, and that which we do know is a bit strange

[ncook90]

Couldnt dark energy simply be the ripples created by the big bang in which we are kind of "surfing" on?

[imatfaal]

Couldnt dark energy simply be the ripples created by the big bang in which we are kind of "surfing" on?

 

Ripples in what?

 

Waves only tend to get faster when the medium through which they are travelling changes - the expansion of the universe is accelerating; so what is changing?

[ncook90]

Ripples in what?

 

Waves only tend to get faster when the medium through which they are travelling changes - the expansion of the universe is accelerating; so what is changing?

 

am not good with physics so please dont laugh when i say stupid things but, couldnt the density of the universe be changing, the more we stretch out from the point of origin then surely the density is decreasing causing less restriction for waves to move and therefore speed up?

[imatfaal]

am not good with physics so please dont laugh when i say stupid things but, couldnt the density of the universe be changing, the more we stretch out from the point of origin then surely the density is decreasing causing less restriction for waves to move and therefore speed up?

 

No one's laughing apart from the little yellow guy

 

a lowering of the density would tend to speed up a compression wave - but it is still a bit tenuous. what is the wave in?

[DrRocket]

Couldnt dark energy simply be the ripples created by the big bang in which we are kind of "surfing" on?

 

no

 

Although very little is understood about dark energy, enough is known to answer your question.

 

Dark energy behaves like a positive cosmological constant in general relativity. What is not known is why there should be a positive cosmological constant.

 

The vacuum energy of quantum field theory ought to act as a cosmological constant. The "only" problem is that calculations based on quantum electrodynamics overpredict the observed cosmological constant by a factor of about [math]10^{120}[/math] which is probably the all-time record for error in physics.

 

So, basically we are clueless about the mechanism behind dark energy.

[G Anthony]

no

 

Although very little is understood about dark energy, enough is known to answer your question.

 

Dark energy behaves like a positive cosmological constant in general relativity. What is not known is why there should be a positive cosmological constant.

 

The vacuum energy of quantum field theory ought to act as a cosmological constant. The "only" problem is that calculations based on quantum electrodynamics overpredict the observed cosmological constant by a factor of about [math]10^{120}[/math] which is probably the all-time record for error in physics.

 

So, basically we are clueless about the mechanism behind dark energy.

 

 

Dr R is such a wonderful delightful skeptic, I do hesitate to proffer this idea. http://www.fotothing.com/Gak/ image 96 Hyperbolic P.E. vs. Inverse Square P.E. <--- This web address points to an image of a graph of (1.) y = ln(x) compared to an equally scaled graph of (2.) the hyperbola y = -1/x + 1. These are supposed to represent the potential energies (P.E.) of the gravitational fields associated with (2.) the inverse square F = GMm/r² and (1.) F = GMm/kr, k = the unit vector of r for dimensional integrity, where F is the hyperbolic ultra-massive black hole "inflaton" super-excited "inflaton field", the primordial hyper-excited gravitational field of Alan Guth's Inflation Hypothesis.

 

Suppose, just for argument's sake, that (1.), as the P.E. stemming from a super-excited hyperbolic gravitational field, was the potential energy source that fueled inflation in the first place (see how much higher it, P.E. of F, is nearer the abscissa) and it was the source of potential energy that fuels "re-inflation" - acceleration of Hubble expansion seen in the latter era (see how it becomes significantly higher again to the right of x = y = 1). This P.E. of F in (1.) became available to objects in the universe which were under the influence of equation (2.) where its P.E. curve is seen to be generally significantly lower than in (1.). The mechanism of transition from (1.) to (2.) is the time dependent quantum transition of one excited state to a lower state. Such transitions release energy. This transition energy forces the expansion of space and thus the increase in kinematic properties of objects within it at an accelerating rate.

 

There is a major objection. See the graphs here ---> http://www.fotothing.com/Gak/ image 97 Hyperbolic 1/kr versus inverse square 1/r² gravitational fields. It is said that GR cannot tolerate a hyperbolic 1/kr gravitational field unless there are only two spatial dimensions in spacetime. Otherwise, Birkhoff's theorem applies and the inverse square gravitational field is de rigeur. But, Birkhoff and its sibling theorems and corollaries all presume that the black hole or other massive body is stationary and spherically symmetric. This is never the case. This is always grossly unreal. All Black holes rotate at great rates and they are always distorted massively by tremendous external gravitational fields. These theorems just do not apply. They are good only for approximate estimates of black hole properties, not for "precision cosmology".

 

Furthermore, so what? If we must putatively endorse a 2-D spacetime continuum for the inflaton particle and the inflaton field, then fine. The holographic principle says that all relevant information may be stored on the 2-D surface or quasi-surface of any 3-D parcel of space. It is the basis for the black hole entropy law. So the inflaton ultra massive black hole singularity might have existed in a 2-D false vacuum continuum surface (an ultra massive black hole event horizon quasi-surface?) that began to unfold or deconvolve into our 3-D + time continuum thereby commencing inflation and fueling "re-inflation" in the current epoch. The hyperbolic field may reside comfortably on such a 2-D surface. And, such a surface need not be "flat", after all. And, there are ways to represent curvature that do not necessitate a 3rd spacial dimension.

 

All that I am saying is that it may be worthwhile to consider the hyperbolic black hole singular gravitational field. The HBHF also explains every other phenomenon associated now with Dark Matter. It ratifies GR and Friedmann by "explaining" Dark Matter and even Dark Energy as well. DE is seen as purely a gravitational effect, not quintessence. But, Dark Matter is still real. The P.E. wrapped up in the hyperbolic gravitational field is real. It contributes to the total mass/energy of galaxies, galactic clusters and super-clusters. So, it adds to the inventory of matter and energy in the universe consistent with current formulations of the Friedmann equations according to comments under the image in (1.).

 

 

 

The vacuum energy of quantum field theory ought to act as a cosmological constant. The "only" problem is that calculations based on quantum electrodynamics overpredict the observed cosmological constant by a factor of about [math]10^{120}[/math] which is probably the all-time record for error in physics.

 

 

 

 

What if the appearance of virtual particles, say, in a Casimir effect experiment, obeys an inverse square law too? Studies of virtual particles using particle accelerators also probe very small distances. If the Casimir effect falls off exponentially with distance or even much much faster, quantum electrodynamic extrapolation to cosmic distances would not be 10¹²⁰ too large. If anything, the numbers would be too small. But, surely we could fudge that too.

 

But, why does the continuum seethe with virtual particles in the first place? Because it CAN? This form of the anthropic principle is highly unsatisfying and physicists are loath to embrace it, Stephen Hawking notwithstanding.

Edited January 29, 2012 by G Anthony

[Klaynos]

!

Moderator Note

G Anthony, you've been told about posting non-mainstream replies to others threads before.

DON'T DO IT!

Do not reply to this modnote, and please no one reply to G Anthony's post.

[Doughnut]

Before ascribing a personality to our subject perhaps we ought, first, to ask what is matter? If dark matter acts as if it were matter, does it follow that it must so be? Could be be talking about a proto-particle having the essence but not (all of?) the elements associated with matter as generally understood? Just a thought.

[Widdekind]

Could DE be "Hot Dark Matter", whilst 'DM' is "Cold Dark Matter" ? I.e. I understand computer simulations are run, with either CDM, or HDM; but what about both, in the same simulation ?? Perhaps 'DM' = CDM ("brown dwarves" ?); and 'DE' = HDM ("primordial neutrinos" ?).

[guenter]

Could DE be "Hot Dark Matter", whilst 'DM' is "Cold Dark Matter" ?

No, matter - whether hot or cold - exerts attractive gravitation whereas DE works repulsive.

Edited February 4, 2012 by guenter

[Kryptex]

I had a thought recently - What if Dark Energy and Gravity are two sides of the same coin? Akin to electricity + magnetism = electromagnetic force.

 

And yes, I realise this is an extremely old topic.

Edited March 19, 2014 by Kryptex

[Schneibster]

So-called "dark energy" is a consequence of General Relativity.

 

Just as with gravity, Cosmological Constant, aka "dark energy," is a curvature of spacetime. However, this particular curvature is not dictated by the presence of mass-energy; it is an inherent property of spacetime itself, just as the FLRW metric (Friedmann-Lemaître-Robertson-Walker, for its discoverers) is. However, because it is associated locally and not globally, as the FLRW metric is, the expansion of space increases Cosmological Constant. That is, as space expands, the total amount of Cosmological Constant in the universe increases.

 

As Cosmological Constant increases, so does expansion; that's what Cosmological Constant governs, the acceleration of expansion.

 

I should give Cosmological Constant its standard name, lambda, or Λ, and note that it is one of the components of ΛCDM cosmology, which is currently being referred to as "The Standard Model of Cosmology."

 

I'm prepared to have a long discussion on the subject, but will wait to see what others have to say.