Necessity of Dark Energy Questioned

ttnuagmada points us to an article about scientist David Wiltshire's suggestion that theorized dark energy is not needed to describe the expansion of the universe. His work challenges assumptions made about the distribution of matter in the universe. Early solutions to general relativity were based on a "smooth distribution" of matter. Wiltshire's approach focuses on a "lumpy" dispersal, which more accurately fits data from modern studies. We have discussed other theories about dark energy in the past. Quoting: "Through observational projects like the Sloan Digital Sky Survey and the 2 Degree Field survey, we now have a much better picture of the large-scale structure of the universe and we know that galaxies are not uniformly distributed. 'Rather, they are in clusters sprinkled thinly in filaments and "bubble walls" surrounding huge voids hundreds of millions of light-years across,' Wiltshire says.

Skeptical

[Black Parrot (19622)]

Mostly because of this:

we now have a much better picture of the large-scale structure of the universe and we know that galaxies are not uniformly distributed. 'Rather, they are in clusters sprinkled thinly in filaments and "bubble walls" surrounding huge voids hundreds of millions of light-years across,'

which we have already known for decades. He seems to think all the cosmologists who have signed on with the dark energy model are unaware of it.

Re:Skeptical

[sam_handelman (519767)]

Just because you know that something is happening doesn't mean that you account for it correctly or fully appreciate the implications; I'm a biologist, all the systems I deal with are heterogeneous, and it's always a major bitch to deal with. That said, I share your skepticism but this doesn't strike me as implausible - although I know essentially nothing about astrophysics.

Re:Skeptical

[Bill, Shooter of Bul (629286)]

From the article, it seems like he believes that this lumpiness was always there, rather than an earlier smooth distribution they've been assuming.

While we might not ever know who is correct in this regard, I tend to prefer theories that don't have the need for dark energies, or matter,even if that really really screws up the equations we use to model the early universe. I think at some point every physicist just stares at a black board somewhere and says to himself " thats fucked up". We really have lost the elegance of the universe being a series of spherical shells rotating around the earth. Since that point we've managed to go through cycles of discovering elegance in the universe on a deeper level (the simple math of kepplar and Newton), and having to reject it for more complexity( Einstien's huge matrix of PDE's ). Let this be a lesson to us all, Don't let what should be prevent you from seeing what is.

Re:

[John Hasler (414242)]

> From the article, it seems like he believes that this lumpiness was always there, rather
> than an earlier smooth distribution they've been assuming.

The assumption of uniformity was an approximation intended to ease computation. The lumpiness has to have always been there or it would not be there now. It is postulated that it originated as quantum fluctations in the inflaton field.

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[ceoyoyo (59147)]

I don't know, I quite like my GPS, global communications and satellite TV (satellites are not possible with the ancients' spherical shells, overturned by Kepler and Newton, among others). I'm also fond of my electronics, which are made possible by quantum mechanics and special relativity. I'm having trouble thinking of an in-the-home consequence of general relativity at the moment, but there probably are some and are likely to be more in the future.

The math might get harder, but the conception has gotten

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[Bill, Shooter of Bul (629286)]

No, I don't think the math can get any simpler than " Because God made it that way". I don't know what you mean my conception. take a look here [wikiquote.org] to see how "easily" the leading scientific minds understood ( if thats what you mean by conception) quantum mechanics. I'm just saying we live in a complex world, where things aren't as simple as we sometimes would like them to be. And I think as you pointed out, we are all better off for it.

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[Cylix (55374)]

Initially, I was a firm believer of dark matter expansion, but then I was hit with some major insight one morning while preparing breakfast.

I started making pancakes and after I stirred the batter I noticed it was quite lumpy.

I thought,"Eureka!, these same constants in my pancake batter help me better to understand the expansion of the universe!"

Why it's so lumpy and not smooth at all... you would need to stir the universe for a billion or two more years before it's smooth.

That my friends, is generally how

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[Cylix (55374)]

Actually, the big bang usually comes after consuming the chili. (I'll share the recipe if you like, it's quite tasty)

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[John Hasler (414242)]

He isn't saying that they didn't know about it: just that they didn't realize that they couldn't get away with simplifying their calculations by ignoring it.

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[bigpicture (939772)]

Exactly, even though we don't need to postulate the presence of "Dark Matter" to construct mathematical models of the expanding Universe, Einstein did not need the "ether" theory to construct "relativity" mathematical models that incorporated how light seems to behave.

Still that does not prove that the "ether" either exists or doesn't exist. Just that it is not necessary to incorporate into a mathematical model, that will more or less express what is observed. But we still have the question of "zero point

Re:

[servognome (738846)]

which we have already known for decades. He seems to think all the cosmologists who have signed on with the dark energy model are unaware of it.

We all know the Ideal Gas Law is incorrect, but that doesn't stop it from being used.

Re:

[sgt_doom (655561)]

The math in Einstein's Cosmological Constant is highly suspect - but he was a pretty good physicist after all! I suspect Neal Turok of Cambridge has the right theory to end all theories - dark energy not required.....

Meanwhile, on the Neutral Planet

[davidwr (791652)]

As Zapp Brannigan is in lukewarm discussions with the Neutral Planet president, the planet's scientists are holding a lukewarm debate over the possible existence of Grey Matter.

I need my dark energy

[russlar (1122455)]

'Dark energy', which researchers have spent years trying to fathom, isn't necessary to explain our universe after all

I don't know about those guys, but I usually do my best work after a cup of dark energy.

Relatively readable survey of solution approaches

[gyepi (891047)]

... can be accessed here: http://arxiv.org/abs/astro-ph/0510059 [arxiv.org] . A bit less recent (but even more readable) account is http://xxx.lanl.gov/abs/astro-ph/0310342 [lanl.gov] . The first linked article also mentions the approaches featured in the slashdot post (this is an ongoing business for a while). For starters the flow diagrams in the front pages describing the options might be particularly useful.

Re:Relatively readable survey of solution approach

[Chemicalscum (525689)]

You picked on a particularly apposite article in your ref: http://arxiv.org/abs/astro-ph/0510059 [arxiv.org]

from the article

A central question for this approach is whether the feedback of non-linearities into the evolution equations can significantly modify the background, volume-averaged FRW universe and explain the accelerated expansion without the introduction of new matter, or a cosmological constant [13]. Key to this issue is that interpreting observations made on a particular scale tacitly also requires the s

Re:

[vtcodger (957785)]

***"God does not use flowcharts!"***

Of course not. I mean, she draws them because her boss says she has to. But use them? That'd be like ... like ... That'd be like reading the spec before doing the creative work.

Can someone please explain?

[martyb (196687)]

I did some googling and found David Wiltshire's home page [canterbury.ac.nz] which had links to his recent publications [canterbury.ac.nz]. That brought me to this full article [iop.org] which I am guessing is the one that corresponds to what was discussed in the original /. article here.

I had a couple courses in astronomy and cosmology way back in my college days. That said, I can't begin to understand the details. I'm hoping someone with more knowledge and experience could elaborate. Is he really onto something that can dispense with the need for dark energy? And, if he is, am I correct in thinking this would be Nobel-Prize-Candidate-Worthy?

Re:Can someone please explain?

[SoberVoiceOfReason (1209826)]

I am, for the record, a physicist.

Here's the slightly more condensed version of this story. Einstein's theory of General Relativity (GR), which incidentally should the Law of GR by today's standards, gives a large set of differential equations to be solved. When this was first being applied to Cosmology in the 1920's, some basic assumptions about the universe had to made in order to solve the GR equations: it is isotropic (same in all directions), and homogeneous (uniform everywhere). They were primarily made for two reasons: mathematical expediency (this is the simplest sort of non-trivial universe you can have), and this didn't conflict with any observations at the time. Solving the GR equations with these assumptions gives fairly simple equations for the time evolution of the universe, leading to the standard model of Cosmology (called the Lambda-CDM model).

As you would imagine, we have vastly more astronomical data now then we did in the 20's. To explain what we observe now, particularly the cosmic microwave background data, with these evolution equations we need to include a constant expansion term. This expansion would have to be from something uniformly distributed throughout the universe with negative pressure (very reminiscent of phlogiston, isn't it?) which we call "Dark Energy". So, based on current data and using the standard model to explain certain properties of the universe, it must consist of around 73% dark energy. Considering that this is the bulk of the universe and that, other than negative pressure, we have no idea what dark energy is or what it's properties are, this leads to a scientifically troubling state of affairs.

However, modern sky surveys show that the universe is neither isotropic nor homogeneous. Instead there is a tendency towards a bubble-like structure with large empty spaces surrounded by thin "filaments" of galaxies. Even still, the standard model which requires dark energy ignores these differences. So, Wiltshire's contribution is to replace the standard assumptions with this "bubble" model, re-solve the GR equations, and get new equations for the evolution of universe based on it's *observed structure*, not some simplified model. In his new equations, dark energy is completely unnecessary. Since the structure of these "bubbles" is so large, fits to the data with Wiltshire's model are statistically just as good (actually indistinguishable) as the standard model, though as a caveat not all of the calculations have been done. Not only is Wiltshire's model much better from an Occam's Razor standpoint, it may actually solve some mysteries which the standard model cannot explain.

I really can't go any further and still call this a "condensed" version with a straight face. In /. articles in other fields, I enjoy reading the commentary from experts, so here's an attempt to reciprocate. Hope this helped.

Thank you

[John Hasler (414242)]

Very helpful.

Re:

[X_Bones (93097)]

fantastic post. thanks.

That makes sense, but

[shadowofwind (1209890)]

Why have they been wasting our time with this dark energy stuff for the last decade then? Why posit the dark energy if its only needed to fix a model that was derived with what has for a while now known to be a false assumption? It seems stupid. Instead of endless science articles on dark energy, instead there should have been articles on scientists working to solve pde's with really hard constraints that match modern astronomical observations. I don't get it. Is there more to the story?

Re:

[John Hasler (414242)]

> People always talk about the "fabric" of spacetime. GR says massive objects warp
> spacetime, and that's what we see as gravity etc. So what is the actual "fabric" made of?

Strained analogies.

Mini-Inflation events in Voids

[skeptictank (841287)]

The fact that matter forms bubbles around the voids intuitively make me think that some force is pushing matter away from the center of each void. Perhaps the center of each void is location where mini-inflation events have happened and what we see today is the reslut of these events pushing shells of matter up against each other so that they form filaments and bubbles. Just a though, IANAP though.

Re:Mini-Inflation events in Voids

[LionKimbro (200000)]

I don't think so; My understanding is that it's the force of gravity.

Here is the picture I have heard:

The universe basically, from any point, stretches out in all directions. Gravity pulls a given lump in all directions at a given time. But local things are more powerful by the law of gravity, than far things. So things start lumping with their neighbors.

Some lumpings occur earlier than other lumpings, which cause then to exert a stronger pull. These become the super-clusters [wikipedia.org] (joining points between filament; such as the Virgo Cluster. [wikipedia.org])

So masses are basically pulled towards the closest super-cluster. But, ah-hah, some are pulled strongly by *two* super-clusters. These become the filament ("bubble walls.")

If you download Mitaka, [nao.ac.jp] you can see a lot of these things first hand, with data directly from the Sloan Digital Sky Survey. [sdss.org]

Re:

[bunratty (545641)]

No, gravity causes matter to clump and contract. As that happens, the voids grow more sparse and larger. It's pretty simple, isn't it?

Re:

[Nazlfrag (1035012)]

Well, isn't the pull of gravity and the push of the void the same thing from different perspectives? As in, both are valid ways to view gravity - as an attracting force caused by mass or a repulsive force caused by lack of mass. How can one interpretation be valid and not the other?

Re:

[John Hasler (414242)]

> Otherwise they should just sit there, riding along with the expansion of the universe as
> a whole - no?

They do, pretty much. Here is a crude, oversimplified summation:
Since there is less matter in the voids than there would be in a homogeneous universe time runs faster in them then it would in a such a universe. Therefor the universe is older seen from the voids and so they seem bigger than they should be. Meantime down here in the matter concentrations where contraction due to gravity dominates

Dark matter balloney

[flyingfsck (986395)]

If you cannot detect something at all with light or gravity effects, then it very likely isn't there. So, the whole dark matter thing is equivalent to calling in the gods to explain the unexplained with something even more inexplicable.

Re:

[mark-t (151149)]

Well, bringing in gods to explain things isn't exactly working on the same playing field, as it's more or less understood that gods are supposed to be supernatural, which by its very definition can defy any explanations that would be consistent with nature.

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[vertinox (846076)]

If you cannot detect something at all with light or gravity effects, then it very likely isn't there.

Are you so sure there aren't other spectrum's yet to be discovered? We just might not have the technological know how to detect certain things. Doesn't mean they aren't there.

Take radiation for example. You can't see it, can't taste it, can't feel it and without the proper tools you'd never know you're sitting in it.

Same thing for "dark matter". Yes it could be a bunch of baloney, but its the only thing that

Re:

[geekoid (135745)]

"Are you so sure there aren't other spectrum's yet to be discovered?"

To date, that is the stupidest thing ever said on slashdot.

Re:

[Nazlfrag (1035012)]

Yet this is exactly what dark matter would imply, matter or energy that cannot be detected in the EM spectrum. There may be a WIMP spectrum analogous to the electromagnetic spectrum, a gravity wave spectrum, there may be other interpretations like TFA that don't require this invisible mass, there may be other forces at work only noticeable on a galactic scale. His comment is no more or less stupid than the current use of dark matter in equations.

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[Tablizer (95088)]

If you cannot detect something at all with light or gravity effects, then it very likely isn't there. So, the whole dark matter thing is equivalent to calling in the gods to explain the unexplained with something even more inexplicable.

I would compare it to just calling something "X". However, sticking the name "energy" or "matter" onto an unknown may be a bit presumptuous. But frankly, I can't find a better description that rolls off the tongue nicely in popular press science articles. You can't just kee

Re:

[cnettel (836611)]

It's a matter of making the equations nicer. If it seems like matter in a significant way (i.e. gravity, possibly weak interactions, but no electromagnetic ones), it makes sense to call it matter and add it as matter in the equations, rather than adding it as an independent second-order correction or something that just happens to coincide...

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[ceoyoyo (59147)]

Well, we can detect dark matter by it's gravitational effects. That's how we know it's there.

Which reduces your argument to "if you can't detect something with light (see it) then it's not there). Well, you can't see any subatomic particles with light!

Now maybe you mean "if you can't detect something through electromagnetic interaction then it's not there." In that case neutrons and neutrinos don't exist either, as they have no charge, just like dark matter.

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[nagora (177841)]

Well, we can detect dark matter by it's gravitational effects.

No: we can detect gravitational effects we were not expecting. Some people have suggested dark matter as an explanation. You're jumping the gun a bit.

TWW

Re:

[ceoyoyo (59147)]

All right, but clearly dark matter, AS POSTULATED has gravitational effects. We're talking about the dark matter hypothesis here.

Re:Dark matter balloney

[John Hasler (414242)]

You confound dark energy with dark matter. They are very, very different concepts. This paper deals with dark energy.

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[jbengt (874751)]

If you cannot detect something at all with light or gravity effects, then it very likely isn't there

So I guess that I should forget all about radioactivity, what with all the weak forces and strong forces that govern subatomic particles rather than light and gravity?

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[arminw (717974)]

..... It's a set of procedures that have a great success rate for developing working models of how the world works........

These procedures are based in experiments and observations, not arcane, complicated math. Physics is NOT equal to math, but math is only a useful tool to describe discoveries and experimental results.

Much of cosmology and astrophysics is pure mathematical fiction, having no basis in the increasing flood of data coming from sophisticated space probes which severely contradicts so

Re:Dark matter balloney

[ceoyoyo (59147)]

You do know that the temperature of the corona has been explained by observation of the sun's magnetic field lines right? Your confusion stems from modeling the sun as a light bulb, rather than the physics.

The shortage of detected solar neutrinos was explained by hypothesizing that neutrinos actually have a very small mass. That would imply that they oscillate between types, only one of which we were detecting. That implies that the shortage is made up by neutrinos of the two other types that we couldn't detect. Now, with better equipment, we've discovered that neutrinos do have some very small mass and everything adds up nicely. Sorry, but that's a TRIUMPH of quantum mechanics, nuclear physics and the standard model, not a failing.

But if you don't like all that math, that's no problem. Please sell or recycle your computer, which is only possible due to all that math.

Re:

[ceoyoyo (59147)]

Sigh, says the anonymous coward, who won't even put his (fake) name to his convictions.

Great Rip?

[LionKimbro (200000)]

Does this have any implications for long-term scenarios, such as the "Great Rip" ..?

Re:

[John Hasler (414242)]

It probably obviates the "Great Rip".

KISS

[WindBourne (631190)]

It seems like physicists LOVES complex answers, but life prefers the simplest possible solution.

Re:KISS

[ceoyoyo (59147)]

Actually, physicists hate complex answers. The overwhelming guiding principle of physics is to describe the universe with as few axioms and rules as possible. Leon Lederman (former director of FermiLab) has a neat little passage in his book about the goal of physics being to produce the ultimate t-shirt: everything that's needed to describe everything written on a shirt. And not one of those XXXL shirts couch potatoes wear.

If this guy is correct then it's a nice advancement of cosmology. From what's described in the article it appears that at least the sign of the effect in his argument is correct. You hear a LOT of these claims though, that explain one or two observations and conveniently omit a hundred or so others.

And the article is terrible. It sets this up somehow as a battle between this guy and Einstein. Einstein postulated a cosmological constant (the equivalent of dark energy) because he wanted a STATIC universe and then retracted it when Hubble came up with experimental evidence that the universe isn't static at all. Einstein's theories have nothing to do with whether matter is smoothly distributed or not.

Re:

[morcego (260031)]

Wasn't there something about the original formula being EL=mc^2, and that after a time, they discovered that L was always 1 ? I think I read about it somewhere, but I'm not sure how reliable that source was (if I could remember the source).

If that is really the case, I think it is a good example for the gp.

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[arminw (717974)]

Is the Universe expanding?

There I fixed it!

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[boot_img (610085)]

IAAAP: The explosion model was ruled out in the late 1980's. Why? velocities of galaxies are not compatible with observations.