No Dark Energy? New Puzzling Discovery

[ZapperZ]

This should throw another spider into the web:

http://www.physicsweb.org/articles/news/10/2/4/1

As far as I can tell, this is not MOND, is it?

Zz.

 

[Garth]

This is here on the physics arXiv, but it is not MOND.

This theory, like MOND, treats gravitation as a two regime phenomenon with a modification to GR/Newton that disappears in the 'close' regime inside a threshold.

MOND treats that threshold as an acceleration a₀ ~ 10^-8 cm.sec^-2.

This theory, "generalized modified gravity", treats the threshold as a distance from the solar system of r ~ 10 pc.

This is a three parameter theory, beginning with a complicated modified gravitational action. The authors find a parameter fit with the distant supernovae data and intend in future to study its fit with large scale cluster structure and CMB also. I wish them well!

This may be the 'next big thing', or, on the other hand it could just be a case of "you can prove anything if you try hard enough" (or have enough variable parameters to fit).

By adapting the gravitational action they are introducing new physics, are we allowed to ask whether such physics may be tested in a local laboratory?

Garth

 

[SpaceTiger]

This should throw another spider into the web:

Well, I would say it's more like a step forward in understanding one of the spiders. The paper is parameterizing and evolving alternative gravity models that attempt to explain dark energy. There has been no shortage of these theories in recent years, but they're usually proposed by field and GR theorists who don't do a thorough check of their model with astronomical data. Also, it's important that we have a simple framework within which we can work to test the models. It's unrealistic to expect observers to independently evolve every alternative gravity model out there to check with their data.

As far as I can tell, this is not MOND, is it?

No, in fact, the paper says that they still require dark matter.

 

[Chronos]

I would be bold enough to assert dark matter has not been ruled out by any existing model. In some respects, however, it is even more difficult to rule out dark energy. Unless GR is very wrong, there is no viable alternative that explains expansion, much less accelerated expansion in the observable universe. WMAP and SN1a studies offer independently derived, and powerful evidence supporting this conclusion.

 

[Chronos]

Unfortunately, no one else seems to be interested in this discussion. I kinda miss the crackpots. Lurkers? I think there are plenty of them. That is annoying. If you have something to say, just say it. I quit, I am tired of this nonsense.

 

[vanesch]

I kinda miss the crackpots.

There you have it ! First we clean everything up, crack down on crackpots, and now we miss them !

 

[selfAdjoint]

Well, I've been lurking - I thought the paper itself was substantively handled by Garth - but I will comment on this:

Also, it's important that we have a simple framework within which we can work to test the models. It's unrealistic to expect observers to independently evolve every alternative gravity model out there to check with their data.

What you need here is a middleman. In particle physics such middlemen are called phenomenologists; they specialize in working out the hopefully empirical consequences of abstract theories. It is a valuable job description there, and the current proliferation of different explanations for dark matter and dark energy suggests that it would be a productive specialty in cosmology.

 

[Garth]

In some respects, however, it is even more difficult to rule out dark energy. Unless GR is very wrong, there is no viable alternative that explains expansion, much less accelerated expansion in the observable universe. WMAP and SN1a studies offer independently derived, and powerful evidence supporting this conclusion.

[Second attempt, my computer crashed just as I was trying to post at the first ]

The evidence from SN1a would be powerful and more robust if:
a) We knew definitely what SN1a actually are.
b) We knew that there was no evolution over cosmological time scales and therefore we knew that they can be taken as 'standard candles'.
c) That all IGM absorption has been properly accounted for.
d) That the degeneracy between expansion (R(t)) and curvature (k) effects has been robustly resolved.

The WMAP evidence for a spatially flat universe would be powerful and more robust if:
a) There was no 'axis of evil'.
b) There were no low l-mode anisotropy deficiencies, particularly with the quadrupole.
c) That conformally flat geometries, which could explain these deficiencies, and would also affect the interpretation of the SN1a apparent luminosities (expansion/curvature?), have been ruled out.

Furthermore, as far as:

there is no viable alternative that explains expansion, much less accelerated expansion in the observable universe

is concerned, consider Figure 2, pages 23/4 in Perlmutter et al's seminal paper Measurements of $\Omega$ and $\Lambda$ from 42 high-redshift supernovae

The middle solid curve is for ($\Omega_M$, $\Omega_{\Lambda}$) = (0,0). Note that this plot is practically identical to the magnitude residual plot for the best-fit unconstrained cosmology of Fit C, with ($\Omega_M$, $\Omega_{\Lambda}$) = (0.73,1.32).

Garth

 

[ubavontuba]

Unfortunately, no one else seems to be interested in this discussion. I kinda miss the crackpots. Lurkers? I think there are plenty of them. That is annoying. If you have something to say, just say it. I quit, I am tired of this nonsense.

Oh! Now you want crackpot ideas to consider? Fine, here's mine:

"Dark energy" may be nothing more than an apparent effect of relativity at a distance. View this thread: https://www.physicsforums.com/showthread.php?t=106841"

"Dark matter" may be nothing more than a macroscopic effect of the Heisenberg uncertainty principle. Basically, VPs pop in, emit a graviton, absorb a graviton, and pop out. At the edges of large regions of space, they exchange these gravitons with ordinary matter. The matter reacts to the absorbed gravitons, but the VPs simply take the gravitons from ordinary matter as a necessary replacement in order to pop out. Conservation holds, and yet galactic orbits are affected.

See? Anyone can come up with a zany hypothesis that isn't testable locally. Why should mine be any less valid? At least mine doesn't require any unexplainable/unknown mass and/or energy. Remember Occam's razor?

P.S. To the moderator: I can provide references to establish the validity of the concepts expressed in this post if required. However, I'd like it to be understood that the context of this post was in response to questions raised above and is not intended to present any new theory.

 

[Chronos]

That's more like it! Thanks SA. Garth raises the issues that are truly worth discussing - the ones I find interesting. Starting from the top - SN1a are believed to be accretion events. Your basic binary star system where a white dwarf star is accreting mass from it's big, red giant buddy. After accreting a certain mass of hydrogen [?], it detonates. The resulting explosion may, or may not destroy the white dwarf. A few of them have been known to explode more than once.

 

[Garth]

Starting from the top - SN1a are believed to be accretion events. Your basic binary star system where a white dwarf star is accreting mass from it's big, red giant buddy. After accreting a certain mass of hydrogen [?], it detonates. The resulting explosion may, or may not destroy the white dwarf. A few of them have been known to explode more than once.

That is the standard model, however, there are more than one possible routes to such a conflagation such as A New Evolutionary Path to Type Ia Supernovae: Helium-Rich Super-Soft X-Ray Source Channel

We have found a new evolutionary path to Type Ia supernovae (SNe Ia) which has been overlooked in previous work. In this scenario, a carbon-oxygen white dwarf (C+O WD) is originated, not from an asymptotic giant branch star with a C+O core, but from a red-giant star with a helium core of $\sim 0.8-2.0 M_\odot$. The helium star, which is formed after the first common envelope evolution, evolves to form a C+O WD of $\sim 0.8-1.1 M_\odot$ with transferring a part of the helium envelope onto the secondary main-sequence star. This new evolutionary path, together with the optically thick wind from mass-accreting white dwarf, provides a much wider channel to SNe Ia than previous scenarios. A part of the progenitor systems are identified as the luminous supersoft X-ray sources or the recurrent novae like U Sco, which are characterized by the accretion of helium-rich matter. The white dwarf accretes hydrogen-rich, helium-enhanced matter from a lobe-filling, slightly evolved companion at a critical rate and blows excess matter in the wind. The white dwarf grows in mass to the Chandrasekhar mass limit and explodes as an SN Ia. A theoretical estimate indicates that this channel contributes a considerable part of the inferred rate of SNe Ia in our Galaxy, i.e., the rate is about ten times larger than the previous theoretical estimates for white dwarfs with slightly evolved companions

A different elemental relatative abundance would be expected to produce a different luminosity.

Garth

 

[ubavontuba]

Okay, so you didn't like my crackpot hypothesis. Sheesh, no sense of humor around here!

Anyway, here is an interesting hypothesis published in http://news.scotsman.com/scitech.cfm?id=253972006 that doesn't require dark matter either. Unfortunately, since it throws Newton and Einstein out the window, I doubt it'll be seriously received.

 

[scott1]

It says that they're "theorist".Sounds like it's short for crackpot theorist...

Okay, so you didn't like my silly hypothesis. Sheesh, no sense of humor around here!

Anyway, here is an interesting hypothesis published in http://news.scotsman.com/scitech.cfm?id=253972006 that doesn't require dark matter either. Unfortunately, since it throws Newton and Einstein out the window, I doubt it'll be seriously received.

It thorws both einstein and Newton out the window That's pretty thowring out 2/3 of physics and pretty half of cosmology...These crackpots are starting get support popluar secience this isn't good ...
Edit:Diffently a crackpot theory

and have thrown down a challenge for their doubters to prove them wrong.

 

[ubavontuba]

scott1,

Ah, but they're crackpots with degrees that got published! Isn't that all that matters around here?

In seriousness, I have a problem understanding the dark matter hypothesis. Isn't dark matter supposed to consist of weakly interacting massive particles (WIMPs)? If so, how do scientists explain the stability of such a particle. Wouldn't Hawking radiation preclude this hypothesis?

 

[Nereid]

scott1,

Ah, but they're crackpots with degrees that got published! Isn't that all that matters around here?

In seriousness, I have a problem understanding the dark matter hypothesis. Isn't dark matter supposed to consist of weakly interacting massive particles (WIMPs)? If so, how do scientists explain the stability of such a particle. Wouldn't Hawking radiation preclude this hypothesis?

One thing at a time ...

"DM" is what you need, in the form of 'mass' (per Newton, or Einstein) to account for things like the observed X-ray emission from rich clusters, the observed 'peculiar' motion of galaxies in said clusters, and the observed gravitational lensing in said clusters (the estimates of the amount of such Newtonian mass, from the three independent sets of observations, are consistent, within the error bars).

What the 'mass' is is the subject of a very great deal of work. Certainly some of it is boring old baryonic mass (dust, gas, pebbles, rocks, rogue planets, brown dwarfs, red dwarfs, white dwarfs, ...) - though these are usually excluded in modern analyses (cf Zwicky's landmark papers). There are some interesting reasons to think that some of the 'non-baryonic' mass may be sparticles.

So, it depends on your taste - the observations are sound, the explanations variously interesting, crazy, compelling, ... - but if you fail to understand just what sort of shorthand 'dark matter' is, you will be lead willy-nilly into making some pretty darn silly statements.

 

[ubavontuba]

One thing at a time ...

"DM" is what you need, in the form of 'mass' (per Newton, or Einstein) to account for things like the observed X-ray emission from rich clusters, the observed 'peculiar' motion of galaxies in said clusters, and the observed gravitational lensing in said clusters (the estimates of the amount of such Newtonian mass, from the three independent sets of observations, are consistent, within the error bars).

What the 'mass' is is the subject of a very great deal of work. Certainly some of it is boring old baryonic mass (dust, gas, pebbles, rocks, rogue planets, brown dwarfs, red dwarfs, white dwarfs, ...) - though these are usually excluded in modern analyses (cf Zwicky's landmark papers). There are some interesting reasons to think that some of the 'non-baryonic' mass may be sparticles.

So, it depends on your taste - the observations are sound, the explanations variously interesting, crazy, compelling, ... - but if you fail to understand just what sort of shorthand 'dark matter' is, you will be lead willy-nilly into making some pretty darn silly statements.

I understand that "dark matter" is a term used to plug a hole in theory versus observed reality, as is "dark energy." Basically, either the standard model is wrong, or there's something out there, correct?

"Sparticles" are an interesting concept of SUSY, but as far as I know no one has detected any. I suppose they might when the LHC gets fired up. However, I think I read somewhere that they supposedly only existed for only a fraction of a second during the big bang. Is this correct?

I was referring to the common references that dark matter might be micro-blackholes. If they are, wouldn't this blow a hole in Hawking's hypothesis? Also, considering that sparticles might be like a thousand times more massive than ordinary matter, shouldn't they fall apart too (rapidly radiate away)?

 

[Nereid]

I understand that "dark matter" is a term used to plug a hole in theory versus observed reality, as is "dark energy." Basically, either the standard model is wrong, or there's something out there, correct?

Well, it's old news that the Standard Model (of particle physics) is incomplete - there is a good article by Gordon Kane (sp?) a few years ago, in Scientific American, that covers the bases pretty well (neutrino oscillations will do as a good example for now).

And isn't it wonderful? There are wonderful things still to learn about the universe!

"Sparticles" are an interesting concept of SUSY, but as far as I know no one has detected any. I suppose they might when the LHC gets fired up. However, I think I read somewhere that they supposedly only existed for only a fraction of a second during the big bang. Is this correct?

Who knows? If you've not captured one and sat it down on your lab bench, how do you know what it looks, tastes, smells, and feels like? Maybe DM is axions, or wimpzillas, or something truly wonderous that we haven't even got the faintest hint of so far?

Again, it's old news that the universe is capable of generating tonnes of particles with energies that will make the LHC running flat out to make just one or two barely noticable (you do know, don't you, how many OOM - in energy - the most energetic cosmic rays detected so far are above that of the best the LHC will possibly reach? IIRC, it's something like 9). If you've got an amateur astronomer friend, ask them to point their telescope at a BL Lac object, and take a peek ... you'll be looking 'down the barrel' of a cosmic gun that emits in one second more high energy particles than the LHC is likely to produce if it ran for a billion years (I'm guessing).

Have you read up on the history of the neutrino? How Pauli 'created' it? How it was many, many decades before any were detected? How many, many more decades passed before the 'solar neutrino problem' was solved? Is there some requirement that all unknowns in science be solved within a year or two of discovering 'something fishy' going on? (If you don't like neutrinos, think of Darwin/Wallace and Crick et al.)

I was referring to the common references that dark matter might be micro-blackholes. If they are, wouldn't this blow a hole in Hawking's hypothesis?

Maybe they are (though so far no Hawking radiation has been detected), maybe they aren't (how many ways can one say "We don't know yet"?). And what "Hawking hypothesis"? And why a hole?

Also, considering that sparticles might be like a thousand times more massive than ordinary matter, shouldn't they fall apart too (rapidly radiate away)?

I guess that depends somewhat on what sparticles are, doesn't it? Perhaps the LSSP (lightest super-symmetric particle) is stable?

 

[Nereid]

I understand that "dark matter" is a term used to plug a hole in theory versus observed reality
[snip]

You seem to have skipped over something rather important.

There are three, independent methods that give the same result, re 'dark matter' in rich clusters. In other words, whatever it is that's there, it behaves like mass.

I think it's just too easy to be blase about this ... the challenge is of developing an alternative (to the sets of independent observations pointing to something which behaves just like mass) is extraordinarily difficult. What is it that leads folk to say 'plug a hole in theory' rather than to marvel at how powerful the theories we have actually are? Where do such muddle-headed attitudes come from?

 

[Chronos]

I second Nereid's point. How long did it take to experimentally confirm the existence of the atom after its existence was postulated [a couple thousand years as I recall]? Unexplained gravitational affects that have been found using many different techniques, as Nereid pointed out, is what led scientists to conclude [reluctantly] there is a huge amount of some sort of hitherto unknown form of matter in the universe. This suggests our theories are incomplete, but, not necessarily wrong. Standard theory does not forbid the existence of cold dark matter, it merely never anticipated it. I call this a discovery, not a flaw in the theory. Isn't this how Pluto was discovered - detection of anomalous perturbations in Neptune's orbit? Did this not present scientists with the same dilemma - choosing between the existence of an hitherto unseen mass, or that Newtonian gravitational theory was wrong? History has taught us it is unwise to throw out the old model until it has been proven flawed beyond a reasonable doubt.

Attempts to reverse engineer observations into a new, improved theory [e.g., MOND] have not been terribly successful to date. They create at least as many headaches as the mainstream model. That is not what I would call progress. Getting the right answer is not as important as knowing why it is the right answer.

 

[ubavontuba]

Well, it's old news that the Standard Model (of particle physics) is incomplete - there is a good article by Gordon Kane (sp?) a few years ago, in Scientific American, that covers the bases pretty well (neutrino oscillations will do as a good example for now).

And isn't it wonderful? There are wonderful things still to learn about the universe!

You bet! What would be the fun of knowing everything? Where would the adventure be?

Who knows? If you've not captured one and sat it down on your lab bench, how do you know what it looks, tastes, smells, and feels like? Maybe DM is axions, or wimpzillas, or something truly wonderous that we haven't even got the faintest hint of so far?

Right, like I so flippantly stated above, everyone's hypothesis is about as good as the next at this point, don't you think (like my Dad used to say, "it's anyone's guess")?

Again, it's old news that the universe is capable of generating tonnes of particles with energies that will make the LHC running flat out to make just one or two barely noticable (you do know, don't you, how many OOM - in energy - the most energetic cosmic rays detected so far are above that of the best the LHC will possibly reach? IIRC, it's something like 9). If you've got an amateur astronomer friend, ask them to point their telescope at a BL Lac object, and take a peek ... you'll be looking 'down the barrel' of a cosmic gun that emits in one second more high energy particles than the LHC is likely to produce if it ran for a billion years (I'm guessing).

Yeah, but these cosmic rays have a lot of relative momentum to Earth and the solar system. If cosmic rays create micro-blackholes (MBHs) in our system, the MBHs should pass right on through, right?

Have you read up on the history of the neutrino? How Pauli 'created' it? How it was many, many decades before any were detected? How many, many more decades passed before the 'solar neutrino problem' was solved? Is there some requirement that all unknowns in science be solved within a year or two of discovering 'something fishy' going on? (If you don't like neutrinos, think of Darwin/Wallace and Crick et al.)

Oh sure. It's a good story (and a great demonstration of the veracity of QM). I still remember seeing pictures of neutrino trails(?) in my 4th grade science class!

Maybe they are (though so far no Hawking radiation has been detected), maybe they aren't (how many ways can one say "We don't know yet"?). And what "Hawking hypothesis"? And why a hole?

I was referring to Hawking's black hole radiation hypothesis. If they don't evaporate, then his hypothesis is incorrect. And, if they don't evaporate, wouldn't this mean that creating them at CERN might not be such a good idea (considering that they might have no relative mometum to the earth)?

I guess that depends somewhat on what sparticles are, doesn't it? Perhaps the LSSP (lightest super-symmetric particle) is stable?

Who knows? I certainly don't. All I really know is that I know less than I thought I knew! :)

You seem to have skipped over something rather important.

There are three, independent methods that give the same result, re 'dark matter' in rich clusters. In other words, whatever it is that's there, it behaves like mass.

I think it's just too easy to be blase about this ... the challenge is of developing an alternative (to the sets of independent observations pointing to something which behaves just like mass) is extraordinarily difficult. What is it that leads folk to say 'plug a hole in theory' rather than to marvel at how powerful the theories we have actually are? Where do such muddle-headed attitudes come from?

Muddle headed? Perhaps. I certainly apologize if I seemed blase about it. I have the greatest respect for the work that's gone into the development of our understanding of physics. If the standard model didn't exist, then no one would've known to look for anything, right?

 

[ubavontuba]

Chronos,

You are right. I do not mean to imply that there's anything wrong with the standard model. I was just trying to ephasize the point that the standard model has provided parameters to narrow the search.

I saw a recent reference that states that dark matter is much warmer than expected (sorry, I didn't save the reference).

 

[SpaceTiger]

In particle physics such middlemen are called phenomenologists; they specialize in working out the hopefully empirical consequences of abstract theories. It is a valuable job description there, and the current proliferation of different explanations for dark matter and dark energy suggests that it would be a productive specialty in cosmology.

We do, of course, have papers like that, but the problem is that the number of cosmologists in the world is much smaller than the number of particle physicists. Most of the manpower has to go into conducting the observations and constructing the theories in the first place. Unless the model is extremely popular (like $\Lambda$CDM), it's usually left to up to the theorist to compare their model to the observations. Also, it's hard to get a faculty job with a lot of papers that test other people's theories with other people's observations.

 

[Nereid]

[snip]

Right, like I so flippantly stated above, everyone's hypothesis is about as good as the next at this point, don't you think (like my Dad used to say, "it's anyone's guess")?

[snip]

I missed this last time ... as several folk have mentioned (welcome back Space Tiger!), it isn't at all 'anyone's guess'

Of course, anyone can make a guess, but to show that such a guess meets the 'three consistencies' tests¹ is an awful lot of hard work (and rarely do 'anyone's guess' pass even weak versions of those tests - just ask Garth how hard it is!)

¹My shorthand for the core 'doing' part of science:

• internally consistent
• consistent with well-established theories, where the domains of applicability overlap
• (the most important one) consistent with all relevant, good observational and experimental results.

 

[wolram]

After the air crash only 5% of the black box data could be recovered, the
tribunal recorded pilot error as the cause.

 

[SpaceTiger]

(welcome back Space Tiger!)

I haven't been away that long, have I?

Of course, anyone can make a guess, but to show that such a guess meets the 'three consistencies' tests¹

I like your list. An additional way to critically assess theories is to do a sort of "Occam's Razor" type analysis. If your proposed theory satisfies all of those three tests, but has a large number of free (unconstrained) parameters, then it will be considered less likely (or, perhaps, less likely to be useful) in the eyes of the scientific community. This is why, for example, we usually only consider single-component models for "dark energy" and "dark matter".

 

[JBash]

Local Charter Member of the Crackpot Brotherhood

Anybody ask for a crackpot?...here are my qualifications:
No formal educational background in physics, cosmology, etc.
Logged hundreds of hours watching the Science Discovery channel.
I have nothing silly like science preventing me from my off the wall thoughts.
This is my question having to do with dark matter, using visual aides so I can understand it better.

Lets say, you have a bucket of water and in that bucket you spill some oil. Then you drop soap right in the middle of the oil "puddle" and watch the oil break up into little "clumps" and disperse from the the original point where the soap was introduced.

Does the soap in this model act like dark matter/energy?
...or am I just plain cracked.

 

[wolram]

I haven't been away that long, have I? [QUOTE/] yes you are on jankers for
two weeks, and think your self luky.

 

[Chronos]

Anybody ask for a crackpot?...here are my qualifications:
No formal educational background in physics, cosmology, etc.
Logged hundreds of hours watching the Science Discovery channel.
I have nothing silly like science preventing me from my off the wall thoughts.
This is my question having to do with dark matter, using visual aides so I can understand it better.

Lets say, you have a bucket of water and in that bucket you spill some oil. Then you drop soap right in the middle of the oil "puddle" and watch the oil break up into little "clumps" and disperse from the the original point where the soap was introduced.

Does the soap in this model act like dark matter/energy?
...or am I just plain cracked.

Try this: Place an ink droplet on the surface of a barely inflated balloon. Rapidly inflate it to 1000 times it's preinflated diameter. The ink droplet will disperse in a filamentary pattern. This is very similar to the observed distribution of matter in the universe. The interesting part is dark [non-baryonice] matter is not predisposed to re-clump after the 'balloon' is inflated, as is ordinary [baryonic] matter. This tends to produce clumps [e.g., galaxies] of baryonic matter aligned in filamentary patterns throughout the universe.

 

[JBash]

Thanks for that interesting analogy, Chronos

In your analogy, is air in the balloon is dark matter? And if so, would that also make it it's own dimension, meaning that if would be faster to get to the exact opposite side (surface of the balloon) by going through the balloon then around it on the surface?

 

[Chronos]

Dark energy would be the air in the balloon. Dark matter resides on the surface, and would disperse in the form of droplets that slide across the surface of the balloon. The more dispersed baryonic matter would be drawn to these gravitational seeds and clump into galaxies.