before everyone gets overexcited...don't forget, time/space is man made...anthropogenic, if you will...it only exists in yer gourd...so, the whole premise is flawed...the universe explained/contracted to fit within our realizeable confines...don'tcha think?

It seems obvious.  As expansion moves objects farther apart, the effect of gravity on each object, trying to keep it near its neighboring objects, becomes less.  This allows expansion to accelerate.

could it be possible that dark matter moves as fast or faster than the speed of light, thus would not be visible?

Albert Einstein introduced his "cosmological constant" because he was working with a model of the Universe that was 'steady-state' in nature.  Under that scenario, all of the galaxies would be attracted towards each other by gravity, and the universe would be collapsing.  That was known to be not the case, so he introduced his "cosmological constant" that served as a 'repelling force' against gravitational attraction, keeping everything in place.  When he later learned that the Universe is actually expanding [from Hubble's red-shift measurements], with all of the galaxies moving away from each other, he realized that his "cosmological constant" was not required.

This latest information in no way 'vindicates' Einstein's original error.  It does point out that the more we learn, the more we learn how little we still know.  This raises the question of whether the "large extra dimension" scenarios proposed for the Large Hadron Collider products, including micro-black-holes, might be correct. http://en.wikipedia.org/wiki/Large_Hadron_Collider#Safety_concerns_and_assurances

Regards,

Walter L. Wagner

Not Again!

I always thought this "dark energy" thing was bull...and everytime there is an article to disprove it, another article comes out saying it exists. I still don't believe it exists, but I wish you guys would just pick one side and stop printing articles that continually contradict each other.

It's universal gravity already and we are hardly advanced enough to detect it properly. The numbers don't add up because we don't have the ability to collect all thoses "numbers" or travel where we need to be to detect it accurately. And if you don't think the rules are even a little different outside our solar system and our galaxy, then you are probably going to settle on the "dark energy" thing...kinda makes it easier, doesn't it?

The acceleration makes sense. At the beginning of this era, the gravitational pull of the mass as it was closer together would create a drag on the expansion. As objects move farther away from the center and other objects, the drag should decrease, resulting in an acceleration.
The only thing that slows the acceleration of explosions here on Earth is the planet's larger gravity slowing the expanding matter down. When that force of gravity decreases due to the expansion, it follows that the expansion would increase. What's out there to slow it down?

In response to Deborah's point - "What's out there to slow it down?" - it's simple physics. It's not enough that there be nothing to slow something down to explain why something would be undergoing acceleration.

Since we're looking at the position of 'matter' where it was those billions of years ago, are we not also seeing it as it was then and cannot 'know' just where it is now or its current speed or its present condition?

When the Big Bang occurred all the bits in it were propelled outwards in all directions.  Following two lines of those bits, one going "north" and the other "south" I would expect the Alpha bit going north to exhibit extraordinary velocity but then to start slowing down since there would be nothing in front of it to help pull it forward, but the entire universe behind it to pull it back.  

By the time the Omega bit started going north, it would have only half of the universe in front of it to pull forward and half to pull it back.  The discrepancy in velocities would serve to 'tumble' the universal matter into the galactic bubbles, walls and haphazard arrangements we have observed.

Since we are now observing the earlier stages of faraway development, would we not also be seeing their greater speed of initial expansion, while the closer and later stages would seem to be moving more slowly?

First, the rules are the same everywhere.  Certainly, hydrogen and the rest of the elements act the same way everywhere.  We can tell because spectral analysis shows the same lines everywhere, adjusting for Red shift.  Second, gravity acts the same everywhere because the same kinds of stars are produced in distant galaxies as are produced in our own Milky Way.  But galaxies seem to be grouped more closely and, individually, packed more densely than the amount of visible matter can account for.  So, we call the unseeable difference Dark Matter.

Third, the expansion of the Universe is not an acceleration whereas gravity is.  If there weren't some extra push, as in Dark Energy, we would not be seeing that extra Red shift that says distant galaxies are moving faster away from us than they should be.

Finally, Space-Time exists everywhere and solipsism is it's own reward.

Maybe there IS no gravity...Consider dark energy PUSHING in all directions, instead of an "attraction of bodies",

Yes, it follows that the expansion would increase as the gravitational pull lessoned. But what would cause the acceleration? As the speed at which the matter was accelerating away from the big bang was slowed by the gravity of other objects around it, then how could it gain speed later as it moves farther and farther away form any object that may have a gravitational influence on it?

"EVERYTHING WE KNOW ABOUT GRAVITY IS WRONG."
 One might say that our THEORIES about gravity may be wrong, but "everything we know about gravity is wrong" is either a slip of tongue or exposes (supports?) a belief that all science, human experience, etc. is an hallucination. Indeed, there are those who believe such is our plight and one cannot PROVE them wrong (no more than one can PROVE an atheist wrong or a theist right), However, belief that truths (laws?) of our universe do exist, independent of human existence or the human mind (it is NOT all a giant hallcination) was one of Einstein's (and, certainly, all bona fide scientists) fundamenal beliefs. It is this fundamental belief, because it can't be PROVEN true, scientifically or otherwise, that makes all bona fide scientists have a religious bent whether they like to admit it or not.
 There are many in the bona fide scientific community and other truth-seeking communities that have come to BELIEVE that our universe is such that its truth can be uncovered by bona fide observers (human beings included therein).
 Finally, along these lines, it is important to remember the fact (truth?) that the successful physics theories do not show "everything about prior theories was wrong"  because such successful theories have, under proper limitations, been shown to agree with, reduce to, the theories that they are replacing. General Relativity did NOT show that everything (predictions etc.) about Newtonian gravitation was wrong; but, indeed, showed that Newtonian gravitation was RIGHT (accurate enough) if the masses ("weights") involved were sufficiently small. TODAY we use the Newtonian equations (because they are much simpler and do NOT introduce significant error) for our high precision, space exploring missions in our solar system (have not gone outside yet) because they do not get near enough to massive enough bodies to require General Relativity's refining. As long as the factor GM/(Rc²) (found by General Relativity and impossible to get from Newton) is sufficiently small compared to 1, General Relativity Gravitation reduces to Newtonian gravitation. "G" is NEWTON'S universal constant of gravitation, "M" is the mass involved at distance "R", and "c" is the maximum speed of light. Isn't it NEAT that Einstein's Theory discovers Newton's "G"? It is such mingling and reduction agreement that is essential for acceptance of new theories
by the physics community because, said community, has so much evidence yielded by old theories. Any "new" theory that shows all the "old" theory predictions to be wrong has to be wrong itself because the existing scientific evidence is not going to go away. like an hallucination. It is the belief of the physics community that any alien scientist's theories on gravity will, under any necessary restrictions, verify or reduce to Newton's and Einstein's. The Cosmological Principle of Physics (a matter of belief or faith until shown otherwise), which in essence says that there is no galaxy that has an advantage over any other in uncovering the truths of our universe; or, our universe presents the same physical evidence, universal truths, to any galaxy, supports the idea (belief, truth?) that our universe is such that its truths can be discovered from any galaxy (humans there or not and a self-consistent requirement if life, or whatever, can arise in more than a preselected galaxy). Incidentally, current physics and logic show that such "preselection" is impossible for self-consistency in our physical universe.  
 

It amazes me the people that comment on these stories that don't even have a basic understanding of physics.

You can not have acceleration without a force being applied.  If there is no force, there is no acceleration.  Gravity, in this case, is a negative force, slowing expansion.  But since there is acceleration in expansion there must be some greater positive force being applied, which is the basis behind "dark energy".

If there were no positive force being applied, once objects were out of the range of gravity's effect, they would simply continue to move at a constant speed.  They would not accelerate.

HubbleSite.org recently did a nice interactive on dark energy that gives folks a better understanding of some of the concepts involved:
http://hubblesite.org/hubble_discoveries/dark_energy/

The whole idea that gravity lessening as things spread out would cause them to accelerate doesn't make sense.  The expansion of the universe is supposedly caused by the initial explosion of its creation, the big bang.  Even as the force of gravity lessens as things spread out, it is still acting on objects and slowing them.  It is not like there is a rocket strapped to the back of the galaxy that is giving it some sort of new or continued thrust away from the center of the universe.  The initial blast of the big bang is all the force that caused the expansion.  Any gravity no matter how miniscule would act againts it and slow it.  The only explanation for the speeding up would have to be that there is some other force acting upon the universe other than the big bang, and gravity.

Accually, I think the dark energy idea is a way to account for the possiblity that the rules might be a little different outside our solar system or beyond.

Yes, it is just a modeling convienience. I don't think that the theorists intended it be interperted as anything else.

What's exciting is that there may be a way to test some variations on string theory, like determining how many extra dimension there might be. Time being the fourth that we added our model to account for the fact that the physical world is not static.

Walter T, Dark Energy and Dark Matter are not the same thing.  I don't think they're even related.

There is a book called "Understanding Thermodynamics" by H. C. Van Ness.  Find it and read the first chapter.  Or you can get the first volume of Feynman's Lectures on Physics.  We have a model of how we think things work.  The model works for somethings and not for others.  For the things that don't work out like we expect, we need to understand them.

We consider our method of measurement and the margin of error.  If the effect isn't too much greater than the expected error, we don't need to account for it.  If the 'effect' is too big, though, it's probably real and we need to find a way to account for it.  We might do this in several ways, but one way is to say, "There's this extra energy we don't know about ... we could call it X, but we use X all the time, we'll call it 'DARK'"  Then they go about determining other properties of this hypothetical energy to help us figure out what its source might be and how we might go about looking for it.

Science does this all the time.  When the orbit of Uranus wasn't as predicted, scientists didn't throw out Newtonian mechanics.  Instead they predicted that there must be another planet that was perturbing its orbit.  They then figured out (computed) the hypothetical planet's orbit and new just where to look for it.  The Dark Energy problem is a much harder, but it's the same kind of reasoning.

I think that as far as the debate is concerned that we dont nearly have enough information to really formulate an accurate hypothesis, and I to am getting sick of the conflicting articles that pop up here every so often but we must remeber that its the quest for the truth that will continually drive our ideas and theorys and eventually over time the answer come out as time and society progresses. I for one dont imperticularly dont like the concept of dark matter and energy for reason's that im sure have been well debated but im still willing to keep and open mind because of progress we must often try to re-learn what we know to seek out greater truths because the proposition of everything that we have learned is wrong is one that tends to scare us because it leads to a sense of chaos but it also will lead to more important truths because it was only a couple hundred years ago that we belived that the earth was the center of the universe and that everything revolved around us.... The notion is funny now but when the theorys were incomplete and even when the facts were in people were skepticle and refused to believe that we revolved around the sun but as time progressed we became endowed with these views and based are society upon these truths but we must remember that although we have come a far way we are far from realizing all the information in the universe and it is very naive to belive that our rules although advanced and all based in the logic we know are flawless and not open to change.....

Actually Deb your logic is faulty. Acceleration requires energy of some kind. While it's true that "drag" will decrease over time, nothing will accelerate without a driving force behind it. Your explosions on Earth example is also flawed, as the explosion expands its energy is dissapated over a larger and larger area, with or without gravity. While in a vacuum it would continue to expand, it would not accelerate, and if it contained enough mass it would be slowed by its own size.

How quickly we forget. This whole dark matter/dark energy thing reminds me of the concept of ether before Einstein came along. Anyone who thinks of these phenomena represent something besides merely a place holder for something we don't understand should read into the history of scientific ideas. The old addage does hold true, history does repeat itself.

The universe is a tangent wave. Gravity is compressing matter into more complex matter within the fusion factories of stars, as it does, space expands.

What does not make sense to me, posted in a couple of comments, is why something would "re"-accelerate as gravitational pull diminished.  When you take your foot of the brakes, you don't speed up again unless you add gas.  Where's the cosmological "gas"?

I've wondered if the acceleration was an optical illusion.  That as the universe stretches the objects within appear to be moving faster, but they are still moving at the same speeds?  Perhaps this is what is meant by "but they say a finer-scale survey could tell whether it's an exotic characteristic of the space-time continuum – or whether it's just that everything we know about gravity is wrong."  the first part of this quote that is . . . I mean I'm not a physicist, I'm a math Grad. so I've never really learned a lot about this, but it seems to me that as space increases it would be elegant if the universe was in some kind of an equilibrium and tried to maintain it's previous state of motion/time, but then maybe that contradicts the idea of entropy?

I cant wait for the LHC to kick off in April. :P

There may be some misunderstandings here.  If an object in a vaccum was moving in a direction free of gravity and outside influences, it would do so ad infinitum.

If gravity were introduced sufficient enough to produce 'drag' on the object to alter its course or slow it down, then that effect would reduce the speed of the object.

REMOVING the gravitational force would not cause the object to ACCELERATE back to its original speed.  In other words, the absence of gravity does not cause acceleration.  There must be some other outside influence.

The simplest explanation of explosive force resulting in accelerating expansion and lessening gravitational influence is to me the better choice without esoteric presumed phenomena such as black matter or “extra” dimensions. However, until we know exactly what life and death are, what animates and departs with death, there can be no “theory of everything.” For me, this is the primary weakness of attempts to understand a universal constant. We may accept such a constant, but not be able to understand it and perhaps it will remain an “unknowable” part of such a constant. I think Einstein believed this, but drew back from the potential “paranormal” implications.

@Deborah - The question isn't, 'What's out there to slow it down?', it's, 'What's out there to speed it up?'...

Any kind of matter is just a form of energy. One of the laws of our universe is the law of opposites.  If you have matter that you can see and feel then you should also have matter that you can't see and feel.
Einstein came up with a lot of fantasy laws. Hey, even a thought is faster than light. And everything is relative to the viewer and the creator, since they are one and the same.

In response to Bloggerrich,

Belief has nothing to do with observable data and testable hypotheses. Multiple interpretations are a sign of a healthy scientific endeavor. Scientists are not searching for truth; they are simply assigning the best approximation to their observations. When numbers are very large or very small approximation becomes problematic within a chaotic system.

Truly, "some completely different theory of gravity is needed." Dark Energy is a dominant factor though not proven, its presence evident in the different 'light speed' stages; I expect Dark Energy will prove relative in gravity, magnetism, and electromotive force.
Ben Winter

Someone should do a study on the advancing gap between scientific knowledge and the public's perception of scientific knowledge, because it's hilarious reading some of these comments.

Dark matter is evil

But what makes expansion accelerate?   That's the problem.  What force is accelerating expansion.  I like the idea.  Maybe this force or matter originates from the point of singularity and maybe it does move faster than light making it invisible.  It's slightly stronger than gravity in the open universe and it's fight with gravity is only getting easier as gravitational bodies move further apart.  There's something to dark matter, it may not actually be some thing or force but just a miscalculation.  Nevertheless interesting.

Three thoughts.  
First, we need to keep in mind that all our scientific "theories" are just generally accepted models of the relationships between "things" we observe.  Some of these models appear quite accurate and useful, but the model is not the thing itself and never will be.

Second, the expansion and development of useful theories has been spectacular over the last several hundred years. However, each time researchers have embraced a theory, a few decades later new information provides the need to re-look at our assumptions and the observed data to develop a new and more comprehensive theory.

Third, this search for a more accurate model of reality continues today while the physicists search for something to connect gravity to quantum mechanics and the astrophysicists search for something to explain the observed distribution and motion of galaxies.

I suppose that all I am trying to say is that there is a great deal that we now think we know, but we remain somewhat ignorant of how the universe actually works.  "Dark energy" is just another name for a relationship of matter that we do not understand yet. It seems likely to me that many of our prized theories will need future modifications.  Science is still an explortion of the universe and search for truth.  

Objects that are moving will either slow down because of gravity or continue at the current speed. Just because gravities effect is lessened by distance will not allow an object to accelerate. Acceleration requires some kind of force to move the object beyond it current state. Comments?

Or, perhaps the speed of light is simply slowing?  The result would be that objects appear to be moving apart from each other.

I'm no genius and I hope I don't prove it with these comments, but it seems to me that these equations are based on the assumption that the ‘Big Bang theory’ is correct as opposed to the theory that the universe has always existed and always will exist.  I’ve always had a problem with the BB theory as it seems to me it over simplifies the universe.  The BB theory won popularity when someone declared that the white noise you pick up with any radio receiver is actually the echoes or remnants of the Big Bang.  I’m fairly certain that those who believe that are not taking into account that the billions or trillions of stars, planets, and other celestial bodies that produce radio waves.  Not to mention all of the other possible sources such as the ever more popular ‘multiverse’ theory.

I recently read a theory on gravity that states, in this overly simplified explanation, that gravity is a bleed over from some other energy based in another dimension…or something like that.  The same could be said for this so called ‘Dark Energy.’  Maybe it does exist but that doesn’t mean the source of it resides in our dimension.

Ok, I’ve now exhausted my reservoir of brain cells this morning.  I gladly welcome any comments.

Marv and Deborah, with all due respect I think you're making a common mistake when it comes to accleration.  If we assume that the Big Bang happened, and matter was ejected at high velocity from a single point, that would explain why everything is moving apart.  Nevertheless, the Big Bang is over, it's done -- after that intital explosion it wouldn't continue to "push" on anything.  As a result gravity would start to slow down the rate of expansion caused by this explosion, causing everything to move apart at a slower and slower pace.  Even if Big Bang gave enough momentum to all the galaxies in the universe to keep moving until they broke free from one another's gravity, they wouldn't suddenly speed up once they were free -- they would continue to move apart at the exact same speed they were moving at the time of release. In order for this expansion to acclerate, it requires that something either be pushing or pulling on these galaxies (or simply creating new space inbetween); as gravity diminshes, this other force would have more influence and things would speed up.  This is what scientists refer to as "dark energy".  There are a lot of possible explanations as to why this might be happening -- but it isn't happening just becasue gravity gets weaker the farther apart things are.  Expansion wouldn't suddenly incresae unless there was another force at work.

The universe expands.

The farther away an object is, the faster it appears to move.

Does it not follow that as an object gets farther away, it appears to move faster?

To Deborah in Seattle:

I think you're confused about the difference between velocity and acceleration.  When an explosion happens in a vacuum, the initial force provides an acceleration that results in the velocity of the debris -- but the debris doesn't continue to accelerate, because there's no force acting on it.  This is exactly the distinction with what is being observed on cosmological scales; not only is the universe expanding, it's expanding at an *accelerating* rate, which means (1) there's something we don't understand, and (2) from Newton's Second Law of Motion, it is some sort of force acting on the mass in the universe.  And since it's a force acting over a distance, it does work, i.e., energy, hence the term "dark energy."

Same thing with respect to the effects of gravity becoming less noticable with distance:  there still has to be a force accelerating mass in opposition to gravity.  

Correct me if I'm wrong, but don't they use "red shift" to determine a body's distance from Earth as well?  If the emitted light is affected by both the speed of the body, and the distance of the body, it cannot give an accurate measurement of either.

Not to mention the assumption that has to be made of the emitted wavelength to get any measurement at all.

And to the previous posts about the lessened effect of gravity due to the increased distance:  The greater distance would decrease the gravitational effect, but this will not result in acceleration.  It will only serve to lessen the decceleration due to the gravity.  Without any gravity, the rate of expansion will at best remain constant.  An resultant exteral force is required for any change in that rate.

Are we justifying the idea that the expansion of the universe is accelerating by the fact that we are traveling faster than a body that is theoretically closer to the center, at a time that is theoretically closer to the beginning of the expansion?

If it's closer to the "center" of the universe as we see it now, might it have been traveling slower than the Earth was at that observed time either?  In any uncontained explosion, there are discrepancies in the speed of individual pieces.  We can't assume that the farthest flung piece was travelling at the same rate as the nearest at any time after the explosion.

A reduction in drag will not cause an increase in acceleration unless energy is added at the same time. If you are ridding your bicycle at a given rate and all factors causing friction and drag on you and your bike suddenly disappear you will not accelerate unless you are peddling or producing energy. If you are coasting you will go at the same speed forever or until you hit something. As far as I know the same rules as apply here apply everywhere.  So if the universe is expanding at an increasing speed there must be energy being added to the system. Call it Dark Energy or whatever…It has to be.

The expansion of the visible universe and the confusion over the cause shows the need for a re-examination of the interpretations of our existing physical basis for physics.  The equations of physics require that our common experience of time is wrong, that block time is correct and that gravity will be united into the superstring theory.  If the theories that describe time are re-interpreted to allow time to flow from the past to the future many new ideas will follow.
I have been looking at the nature of time and have come to the conclusion that Einstien made a crucial error in accepting Mach's proposals about time and the basis for inertia.  I believe that we, and our visible universe are embedded in the present moment, "now", and that the past is a different dimension from "now" and the future.  By modifying Wheeler's many worlds theory that every quantum event creates a new universe to one that puts those extra universes into the future with only "our" universe to be real, with the future alternate universes extinguishing themselves as events occur in the real universe.  The energy tied up in the alternate worldlines then becomes the inertial energy we see in our universe, which passes thru our present time dimension and goes into the past dimension, adding energy to a closed dimension, thereby causing the past dimension to expand, since adding energy to a closed volume makes it expand.  Gravity is the physical scaffold only and does not increase during accelerations like the present theories describe.  Inertial energy comes from future worldlines being extinguished by events at time "now" with that energy creating the effects of acceleration ( increased mass and physical distortion).
This is only a very brief explanation of my thinking on the nature of time and the effects on our visible real universe.

If the farther apart something is from a gravity producing whatever is you would not assume that it would speed up but slow down as gravity pulls at it. speed is a constant as it is when it is slowing down not accelerating. Question! What would cause it to accelerate if the gravity were somehow turned off?

I was curious how a decrease in gravitational drag would result in an acceleration?  F=ma of course, which would mean to have a positive acceleration would mean u need a positive, non zero, force pushing.  That would mean there is some force constantly pushing galaxies?  Or creating energy?  Everything was given an inital push from something such as the Big Bang, but how is that "instantanious" force continuing?  Being an explosion and all.  I'm just having a hard time seeing this.  Clarification would be appreciated =)

why do we assume that anything would accelerate once gravity is lessened?. Is it under it own power? false assumptions maybe?

I think the posts that talk about induced acceleration due to the decreased gravitational effect could be valid if you establish that gravity isn't the only force at work. For instance, if there were some constant force at play in addition to gravity, bodies which are close to eachother would feel an attractive force until you cross some threshold distance where the gravitational attraction becomes less powerful than the constant force. After that point, decreased gravity would essentially cause acceleration because the net repulsive force between two objects would become greater as a result of the attractive force of gravity decreasing. I don't claim to know what the force would be (maybe the expansion of space), or if it even exists, but its a hypothetical situation where decreased gravity would cause acceleration.

You kids really need to start with a basic physics class.

A previous poster asked: "why something would "re"-accelerate as gravitational pull diminished.  When you take your foot of the brakes, you don't speed up again unless you add gas.  Where's the cosmological "gas"?

But consider a sailboat.  If you pull up the anchor, the boat accelerates.  We know of "solar wind", but what if there was a "big bang wind", so to speak, acting on these bodies, and as gravitational drag is reduced, acceleration occurs?

What if the effects of gravity eventually just stopped completely at x number of light years instead of continuing to attenuate?

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