Do we know what Dark Matter/Energy is?

[harry]

G'day from the land of ozzzzzzz

Do we know what Dark matter and Dark energy is?

What is Dark matter/energy importance in the evolution and structure of the space objects?

[Chris Peterson]

Do we know what Dark matter and Dark energy is?

Dark matter and dark energy are different things, and have no connection with each other. This is like asking, "Do we know what rocks and trees are?" The question makes little sense.

If you want to discuss dark matter, start a discussion about it. Or start one about dark energy. Placing these things together under a single topic is just confusing.

[canuck100]

More different than chalk and cheese, I would say.

The existence of dark matter is inferred from it's gravitationally ATTRACTIVE properties and accounts for the 'missing' mass that must be present to account for the speed of rotation of galaxies, among other things. It accounts for 22 - 23% of the mass/energy of the universe. Reading a variety of sources seems to suggest that while not observed directly, observations continue to mount supporting the case for its existence and describing its properties and distribution in the universe. However, http://en.wikipedia.org/wiki/Dark_matter

some alternative theories such as modified Newtonian dynamics and tensor-vector-scalar gravity have been proposed. None of these alternatives, however, have garnered equally widespread support in the scientific community.

OTH dark energy seems more enigmatic, to my way of thinking and it's existence is inferred from it's gravitationally REPULSIVE properties. It accounts for the acceleration of the expansion of the universe. However, as it accounts for a whopping 73% of the mass/energy of the universe, if it does not exist, any alternative theory has a lot to account for.

As I see it, dark matter and dark energy in particular are the preferred vehicles to account for the 96% of the mass of the universe largely due to the law of parsimony or Occam's razor "entia non sunt multiplicanda praeter necessitatem" which basically states that all other things being equal, choose the simplest explanation.

Given that all mass can be viewed as energy density, therefore energy arranged in a particular fashion, it is not far fetched to consider that energy will be found to be arranged in forms that are not easily observed by techniques available to us mere mortals whose existence occupies such a minute slice of space-time.

I won't for one minute pretend to be qualified to debate brane theory or its alternatives but in the interests of balance note that http://en.wikipedia.org/wiki/Dark_energy describes a number of contending approaches to dark energy including

• string theory, brane cosmology and the holographic principle
  failure of general relativity on very large scales and modification of the law of gravity at intergalactic distances
  multiverses and anthropics
  information energy
  early electroweak symmetry breaking

None of these has yet met the standard of the cosmological constant and dark energy in predicting the observed behaviour in the cosmos and so none are embraced by a majority of cosmologists. But debate continues.

Let's be clear. The validity of a scientific theory rests on how well it predicts observable outcomes and how verifiable it is. Pure speculation that does not predict testable behaviour is not a scientific theory.

Many folks expect a scientific theory to be some kind of ultimate explanation but it is not.

Cosmological speculations that lie outside the limits of verifiability are valid exercises. They are, however, not science and are more properly undertaken within philosophy and/or theology. By this definition, much of cosmology lies at the outer limits of what can be considered science. This is why it is important to be disciplined in thinking and discussing these matters so as to try to be aware of when one is in or out of bounds as far as science is concerned.

http://www.scientificamerican.com/artic ... dark-matte

The stars make up less than 1 percent of its [the universe's] mass; all the loose gas and other forms of ordinary matter, less than 5 percent . . . The terms we use to describe its [the universe's] components, "dark matter" and "dark energy," serve mainly as expressions of our ignorance.

[harry]

G'day Bystander

I think you missed the point by a mile.

How do you differentiate matter and energy at subatomic levels?

Is there a difference?

[bystander]

G'day Bystander

I think you missed the point by a mile.

How do you differentiate matter and energy at subatomic levels?

Is there a difference?

No, Harry, you missed the point. This forum is not the place for you to post your personal reading list for the world to see. If you can't stay on topic your reading list will be removed. If you don't post the relevance to the topic at hand, with the article(s) and in your own words, your post will be removed. You are wasting my time and many others with your off topic postings. This means you need to read the paper and explain what it has to do with the current subject. Posting abstracts is not sufficient. Stay on topic. Read your PMs.

[canuck100]

How do you differentiate matter and energy at subatomic levels? Is there a difference?

E=mc^^2 equates mass and energy. Mass and therefore matter is energy. I would say, no, there is really no difference. Convenience, convention and semantics accounts for the usage of one term vs the other.

There is an excellent discussion of mass at http://en.wikipedia.org/wiki/Mass which outlines the history of the concept from inertial mass to gravitational mass to the relation between mass and weight and finally to relativistic mass energy equivalence.

The concept of mass is pretty old whereas the concept of energy did not congeal until the 19th century and of course Einstein's mass-energy equivalence is of 20th century origin. It seems to me that term mass or matter is preferred when referring to inertial or gravitational properties or when discussing the particle-like characteristics of sub atomic entities. The term energy seems to be preferred when discussing wave-like characteristics or motion-related phenomena. Some of the usage seems to be due to convention more than anything else.

I suppose that because 'dark matter' manifests itself through its gravitationally attractive properties and explains missing mass, the term matter as opposed to energy has been coined.

The term 'dark energy'

was coined by Michael Turner in 1998, a term similar to Fritz Zwicky's "Dark Matter" coined in the 1930's.
http://en.wikipedia.org/wiki/Dark_energy

I wish that they had called it something else because the similarity of the two terms is very confusing. I suppose that the term 'energy' might be preferred because it contributes to motion and is certainly not matter-like or mass-like in any sense except for energy equivalence.

There is a neat video/audio of Michael Turner at http://research.uchicago.edu/highlights/item.php?id=31 in which he mostly refers to 'dark energy' as 'vacuum energy' -- I wish they had kept this term.
In this 2003 video Turner talks about the relationship between theory and observations and how the standard model and inflation in particular predicted the existence of dark energy.
He discusses the various candidates for dark matter in particular, citing neutrinos (observed as 1% of dark matter) and the yet to be observed neutralinos and axions.
He uses the analogy of the 6 blind men and the elephant and likens various aspects such as dark matter, dark energy, inflation, quark soup etc. to the various observations of the blind men and says that what is needed is the overall concept akin to the elephant that successfully unites all these pieces into a coherent whole.

What seems to be accepted overall, though, is that the bulk (as in 95%!!) of the universe consists of 'stuff' that is different from the 'stuff' from which we (and the stars and planets) are made and that this exotic stuff mostly consists of what we presently term dark matter and dark energy. Hopefully the next few years will result in these 'dark' terms being replaced by descriptions that better reflect the discovered properties of the stuff these dark entities are made of.

Until then, though, despite the E=mc^^2 equivalence of mass (matter) and energy, the terms "dark matter" and "dark energy" are conventionally used to describe two extremely different aspects of the content of the universe.

[canuck100]

There is an excellent, brief overview of Dark Matter & Dark Energy at http://nasascience.nasa.gov/astrophysic ... ark-energy
(The above link does not work! To get there, use http://www.google.ca/search?q=nasa+what ... =firefox-a and then click on Dark Energy, Dark Matter — NASA Science)

Synopsis:
Dark Energy
Known?

• 70% of the universe is dark energy
  it is responsible for the acceleration of the expansion of the universe.

Three kinds of theories attempt to explain it:

• 1. Einstein’s cosmological constant – i.e. vacuum energy, a property of space itself
  2. a strange energy-fluid that fills space
  • ~ fluid of virtual particles coming in/out of existence – this theory had serious problems
    ~ “quintescence” - a new kind of dynamical energy fluid/field
  3. the theory of gravity needs to be modified - no gravitational theory modification has yet proven compelling

Dark Matter
Known?

• 25% of the universe consists of dark matter.
  (Note: other sources show maps of dark matter inferred from gravitational effects.)

Ruled out:

• ~ not thin clouds of normal (i.e. baryonic) matter (no absorption spectra)
  ~ not antimatter (no antimatter annihilation gamma rays)
  ~ not large black holes (insufficient gravitational lenses)

Current proposals include:

• ~ MACHOs (massive compact halo objects) baryonic matter consisting of brown dwarfs and dense chunks of heavy elements
  ~ WIMPs (weakly interacting massive particles) non-baryonic matter such as neutralinos or axions
  ~ so far, the WIMPs seem to be winning -- yay wimps

I'm rooting for dark energy=vacuum energy and dark matter=neutralinos etc. but the universe doesn't give a hoot for my opinion and observations will determine which theories win out.

When I google " 'dark matter' research and experiments" I get many projects that are underway to detect candidate particles. Perhaps better explanations for dark matter are close at hand.

On the other hand, when I google " 'dark energy' research and experiments" most projects are focused on improving the accuracy of the rate of expansion. No one seems to have tangible testable models for what 'dark energy' actually might be. From this I'm guessing that 'dark energy' will remain mysterious for some time to come.

[harry]

G'day canuk100

Before I go onto another point in matter.

Please explain how dark matter and dark energy are explained by the BBT.

[Chris Peterson]

Please explain how dark matter and dark energy are explained by the BBT.

It's the other way around. Dark matter and dark energy are part of what explains the Lambda-CDM model in cosmology. Lambda-CDM is the more proper name of what you are calling "the BBT", since this is the model that is widely accepted. The theory is too complex to explain in detail in a forum like this. Since you like reading, start with the Wikipedia article on LCDM, and work your way through the references. You'll find plenty of publicly accessible scientific papers on the model, as well.

[harry]

G'day Chris

You are right in what you say.

I was asking to see what he knows.

You said that the BBT is widely accepted means very little to me. I have seen Standard models in the past fall by the side and through History people just follow the MOB.

As for information backing the BBT there are lots of papers and yet very liitle evidence, just theoretical here say.

The redshift is one data that is coming under fire due to the lack of info on the intrinsic properties of supernovas.

As for the BBT being too complex, i do not think so.

[canuck100]

As for information backing the BBT there are lots of papers and yet very liitle evidence, just theoretical here say.

The BBT and in particular the LambdaCBM version of BBT is not just theoretical hearsay. It is well supported by a variety of observations and has emerged from years of debate on its merits as an overwhelmingly supported theory.
It did not garner it's support from scientists following a MOB mentality. It has become the dominant theory in genuine, fierce competition with steady state theories and cyclic theories that were equally well supported before observation counted them out.
For example:
Hubble-type expansion, redshifts of galaxies, the abundance of light elements and various properties of the large-scale structure of the universe have all been observed to be in agreement with LambdaCBM.
The age of the universe as estimated from the Hubble expansion is in good agreement with the ages of the oldest stars, by various types of measurements.
The prediction that the cosmic microwave background radiation was once at a higher temperature has been borne out by observations.

Are there aspects of the theory that are not well understood? Yes.

For starters, inflation and baryogenesis are seen as speculative. I have no idea even theoretically how observation could count these in or out as they are predicated on parts of the theory that lie beyond what is knowable. However, it has been pointed out that these aspects of the theory could be changed significantly without negating the theory over-all so most folks don't regard this as a serious problem.

However, inflation does account for the horizon problem, the flatness problem and other difficulties so I guess it will be kept until something better comes along.

Some folks think that the lack of antimatter is still a problem but there was a Nobel Prize awarded for the theory that explains how this can be though I don't claim to understand it, LOL!

The nature of dark matter still needs further explanation but so far observations are supporting WIMPs as the preferred explanation. Dark matter doesn't explain BBT and it wasn't predicted by BBT either. It's existence is implied even by classical, non-relativistic, non-quantum mechanical analysis of observations though it's nature will eventually be explained in relativistic and quantum mechanical terms I'm sure and it is implicit in LambdaCBM - CBM standing for cold dark matter.

In many ways the discovery of the acceleration of the expansion of the universe the invocation of 'dark energy', while not completely explained by any theory as yet, lends support to BBT/LambdaCBM as it brought us full circle back to Einstein's cosmological constant, however with the potential for various interpretations from which one has yet to be chosen.

The redshift is one data that is coming under fire due to the lack of info on the intrinsic properties of supernovas.

I disagree here. I can find no credible research quoted that suggests that redshift data is 'under fire.' There are, however, many projects underway seeking better data as far as the rate of expansion is concerned so if this data is truly in doubt, we will soon hear about it.

As for the BBT being too complex, i do not think so.

I believe that he said that a DETAILED analysis of LambdaCBM was too complex for this forum and on this, I agree. That shouldn't stop us from trying to understand as much of it as our mental and math skills allow but I am not going to presume to be capable of a detailed debate.

I was asking to see what he knows.

I don't know anything

[The Code]

canuck100

Thank you for your posts.. very interesting.

Some folks think that the lack of antimatter is still a problem but there was a Nobel Prize awarded for the theory that explains how this can be though I don't claim to understand it, LOL!

Unless anti matter is the wrong name to call it?

[bystander]

Unless anti matter is the wrong name to call it?

• What's in a name? That which we call a rose
  by any other name would smell as sweet.
  
  • Romeo and Juliet (II, ii, 1-2)

[Chris Peterson]

Unless anti matter is the wrong name to call it?

The name seems reasonable. Most particles have antiparticles; usually these are particles with the opposite charge, although the situation is a little more complicated for neutral particles and those particles (like photons) that are their own antiparticles.

In any case, most particles and antiparticles are well understood, and this includes the behavior of antiparticles that combine into atoms, which pretty much defines "antimatter". There's nothing very mysterious going on with all of that.

[canuck100]

You said that the BBT is widely accepted means very little to me. I have seen Standard models in the past fall by the side and through History people just follow the MOB.
. . .
The redshift is one data that is coming under fire due to the lack of info on the intrinsic properties of supernovas.

On the supernova thread at http://asterisk.apod.com/vie ... 91#p111291 I quote two 2009 research papers that document techniques for improving the measurement results obtained from type 1a supernovae.

I also quote a third paper that documents various concerns with their use that arise from the need to better understand the processes and recent progress in this area as well. No MOB mentality at work here!!

[The Code]

The name seems reasonable. Most particles have antiparticles; usually these are particles with the opposite charge, although the situation is a little more complicated for neutral particles and those particles (like photons) that are their own antiparticles.

In any case, most particles and antiparticles are well understood, and this includes the behavior of antiparticles that combine into atoms, which pretty much defines "antimatter". There's nothing very mysterious going on with all of that.

http://newscenter.lbl.gov/feature-stori ... ihydrogen/

Unless when antimatter and matter annihilate ,,they unite to a higher or lower realm ... Shall I compare thee to a summers day? Or is that Dark antimatter/anti-energy//// Anti-anything you can think of..

[Chris Peterson]

Unless when antimatter and matter annihilate ,,they unite to a higher or lower realm ... Shall I compare thee to a summers day? Or is that Dark antimatter/anti-energy//// Anti-anything you can think of..

I don't know what that means. Matter and antimatter annihilate to produce photons, in a well understood and well observed process.

As far as "dark antimatter", theory suggests it doesn't exist, because the non-baryonic particles that are the current best fit for dark matter are probably their own antiparticles.

[The Code]

I don't know what that means. Matter and antimatter annihilate to produce photons, in a well understood and well observed process.

http://www.astro.utu.fi/~cflynn/astroII/l10.html

How did these get past annihilation?

[bystander]

How did these get past annihilation?

These what? Try reading the articles at the CERN Antimatter Academy. For that matter, try reading the articles you posted.

[canuck100]

How did these get past annihilation?

If you are referring to the annihilation at the end of the big bang hadron epoch etc., these are not the same anti particles.

The article you cite clearly states that the positrons responsible for the high energy gamma rays are created at the center of our galaxy by "high energy particle or gamma ray decay" and that the galactic center is "rich in high energy sources which could provide the high energies needed"

As far as antimatter in the cosmos is concerned, other than routine antiparticles expected as results of high energy collisions, none has been detected. The AMS-02 Experiment will attempt to detect anti-helium nuclei in an effort to discern whether or not antimatter stars exist.

Seeing a mere antiproton or antielectron [positron] does not mean much - after all, these particles are byproducts of high-energy particle collisions. However, complex nuclei like anti-helium or anti-carbon are almost never created in collisions. But they would be made abundantly by nuclear fusion in an anti-star! So, AMS will search for anti-helium nuclei.
http://cyclo.mit.edu/~bmonreal/antimatter.html

Launch of AMS-02 was originally scheduled for 2005 but currently

Launch is targeted for July 29, 2010 on Space Shuttle Endeavour flight STS-134. http://en.wikipedia.org/wiki/Alpha_Magn ... ectrometer

when it will be installed on the ISS.

Until then, the poets and sci-fi writers are still in charge of antimatter

[canuck100]

Antimatter is, in fact, so common that the PET scan (Positron Emission Tomography) medical imaging procedure uses it!
http://www.sciencedaily.com/articles/p/ ... graphy.htm

The Space.com antimatter article is very readable http://www.space.com/scienceastronomy/a ... 30929.html

and a search of antimatter at ScienceDaily.com http://www.sciencedaily.com/search/?keyword=antimatter lists many interesting, very readable articles.

Of course, Wikepedia has a good article as well.

[canuck100]

Please explain how dark matter and dark energy are explained by the BBT.

They are not.
They are not 'explained' per se by LambdaCDM either.
I have yet to find a time-line for the evolution that includes the creation of dark energy and dark matter. I thought for sure I would find one but nada.
ΛCDM uses dark energy as a cosmological constant and therefore treats it as a sort of 'vacuum energy' (not to be confused with the Casimir effect - they are not the same thing.)
I've intuitively thought of dark energy as one of the repulsive aspects responsible for inflation but I've never seen it characterized this way and based on my recent re-reading of all this stuff, I now believe that this is wrong.

ΛCDM says that dark matter is dominant and 'cold' (v<<c) by the Matter domination era at BB + 70,000 years. But it does not say how or when it arose.

The current details of BBT developed as the Standard Model of particle physics developed firmly anchored in experimental observations. There are no detailed detection projects or experiments yet to described dark energy or dark matter so there is no basis for their detailed incorporation into cosmological theory.

I finally got around to reading the Wikipedia article on LamdaCDM and it has an interesting, humbling statement:
http://en.wikipedia.org/wiki/Lambda-CDM_model

However, ΛCDM is a model. Cosmologists anticipate that all of these assumptions will not be borne out exactly, after more is learned about the applicable fundamental physics. . . Moreover, ΛCDM says nothing about the fundamental physical origin of dark matter, dark energy and the nearly scale-invariant spectrum of primordial curvature perturbations: in that sense, it is merely a useful parameterization of ignorance.

So as to the questions stated at the top of this thread:

Do we know what Dark matter and Dark energy is?

My own answer is No more than Yes.
The second question

What is Dark matter/energy importance in the evolution and structure of the space objects?

Well we know that both are extremely important today because they are required to explain accelerated expansion (dark energy) and the gravitational behavior of all normal matter (dark matter).
If dark energy is indeed a cosmological constant, a property of space, it will be extremely important as without it normal and dark matter would fall in on itself.
Similarly, without dark matter, the force of dark energy would blow us apart.
So they are extremely important.
However, more is known about their detailed nature, we will not know how they interact with normal matter at each stage of the evolution of the universe.

[The Code]

mark swain wrote:How did these get past annihilation?


These what? Try reading the articles at the CERN Antimatter Academy. For that matter, try reading the articles you posted.

Was Not quite, the info i was looking for. it was just a guide line ... to help put my minds eye across. bystander.. I read Hubble's book 40 years ago... time to climb on his foundations. And build higher.

canuck100

great info...

[canuck100]

I read Hubble's book 40 years ago... time to climb on his foundations. And build higher.

Back when you were 5? You must be a genius

[The Code]

Back when you were 5? You must be a genius

It was the book my father taught me to read with. I still own it.