PDA

View Full Version : Dark Matter and Dark Energy



pakoppan
2007-Oct-12, 07:11 PM
Hello,

If both exist at the same time and at the same or very close place then in which way, if any dark energy and dark matter interact between themselves.

They are not for all I now mutually exclusive. Both permeates the Universe if I don't read this wrong.


Thank you

antoniseb
2007-Oct-12, 10:55 PM
Welcome to the BAUT forum.

As far as we know dark matter and dark energy only interact gravitationally, and in whatever way dark energy affects *all* matter.

3dknight
2007-Oct-13, 01:18 AM
oh come on you couldn't of added that to my thread? It has the same title. I can't believe this

antoniseb
2007-Oct-14, 11:56 AM
I can't believe this
What? I think I responded to your thread. I didn't say the same thing there because you seemed to have a different misconception about Dark Matter and Dark Energy. It's not the title that drives what I post.

We get a lot of people who join the forum wanting to propose some alternative idea for what dark matter and dark energy are.

01101001
2007-Oct-14, 01:46 PM
oh come on you couldn't of added that to my thread? It has the same title. I can't believe this

Are you asking pakoppan why he/she didn't add the question to your thread Dark Matter and Dark Energy (http://www.bautforum.com/astronomy/65338-dark-matter-dark-energy.html)?

They are different questions, no? I think a problem is that the reused title is too general in both cases, but its generality shouldn't force subsequent people to apply their specific questions in either. If tomorrow I decide to ask, say (and I'm not asking here), if dark matter and dark energy are related by E=mc2, I wouldn't use either topic.

I'm sure I wouldn't use the same title either, because I like my topics more focused, and I like titles that explain better what the reader is going to see. Titles are important.

3dknight
2007-Oct-15, 06:18 AM
yes i was talking to pakoppan

Cougar
2007-Oct-15, 08:05 PM
Both permeates the Universe if I don't read this wrong.
Well, dark energy would seem to permeate the universe, but not dark matter, which appears to hang out within and around galaxies and galactic clusters.

As to how they interact, uhhhh.... the effect of dark energy really only seems to come into play on very, very large scales, in the super large distances out between large galaxy clusters, so these two things don't appear to be in the same ballpark to be doing much interacting....

alainprice
2007-Oct-18, 11:07 PM
Is it so much that dark energy only acts on large scales or rather that the effect is only measurable on large scales? Wasn't there dark energy in the seconds old universe?

blueshift
2007-Oct-20, 11:19 PM
Is it so much that dark energy only acts on large scales or rather that the effect is only measurable on large scales? Wasn't there dark energy in the seconds old universe?
The density of dark energy remains the same even though the universe expands. Dark energy has been called a smooth tension by Sean Carroll.

Since the density of dark energy remains the same, it provides a continual source for spacetime curvature. This curvature keeps the universe expanding since curvature and acceleration are the same thing.

Cougar
2007-Oct-21, 09:16 PM
Is it so much that dark energy only acts on large scales or rather that the effect is only measurable on large scales?
I would say the latter.


Wasn't there dark energy in the seconds old universe?
Yes, see below....


The density of dark energy remains the same even though the universe expands.
Yes, if the cosmological constant accurately describes it. So the ratio of the density of dark energy to that of matter in such a universe varies with the expansion, which brings more dark energy (but with the same density) and reduces the matter density.


This curvature keeps the universe expanding since curvature and acceleration are the same thing.
You lost me there. :confused:

Mike Holland
2007-Oct-22, 12:38 AM
Interesting connection there. The expansion of the universe would eventually be stopped by gravitational forces if there is enough dark matter - about 10 times as much as normal matter. But the dark energy keeps it expanding. So is there just enough dark energy to counteract the effect of the dark matter?

Ok, I know it is much more complicated than that, and the situation is not in equilibrium anyway as the expansion seems to be accelerating. But just a passing thought about one way they do interact.

Farsight
2007-Oct-22, 11:47 AM
The density of dark energy remains the same even though the universe expands. Dark energy has been called a smooth tension by Sean Carroll.

I would challenge this density remains the same, blueshift. Can you provide a link please? IMHO the "density" of Dark Energy cannot remain the same. Energy does not come for free. Intergalactic space expands, but the space within a galaxy does not. IMHO it is the difference between the two that is currently interpreted as Dark Matter.

Cougar
2007-Oct-22, 01:45 PM
I would challenge this density remains the same, blueshift. Can you provide a link please?
Hmm, odd that Wikipedia doesn't mention this. I can, however, vouch for the fact that if the vacuum energy is accurately described by a cosmological constant, then the "new" space resulting from expansion has the same vacuum energy density as the "old," and there is no dilution, as one would ordinarily expect. Look at that equation in Wikipedia - lambda is a constant, after all....

Nereid
2007-Oct-22, 05:11 PM
I would challenge this density remains the same, blueshift. Can you provide a link please? IMHO the "density" of Dark Energy cannot remain the same. Energy does not come for free. Intergalactic space expands, but the space within a galaxy does not. IMHO it is the difference between the two that is currently interpreted as Dark Matter.As Cougar has already noted, if a little obliquely, 'dark energy' is just a shorthand for the mechanism behind the observed accelerated expansion of the universe.

In GR, it's not an 'energy' of the usual mass-energy kind; the simplest kind of such is, as Cougar has noted, just the cosmological constant, lambda.

So, a question for you: if lambda is to produce an acceleration of expansion, in a GR description of the (present-day) universe, should it be > 0, or < 0?

blueshift
2007-Oct-22, 11:01 PM
I would challenge this density remains the same, blueshift. Can you provide a link please? IMHO the "density" of Dark Energy cannot remain the same. Energy does not come for free. Intergalactic space expands, but the space within a galaxy does not. IMHO it is the difference between the two that is currently interpreted as Dark Matter.All of the space is expanding and here is one of 1,500,000 links on the subject as you requested:(Scroll down to "Gravity on the Fly".) Hey, who put that frown face in this paragraph? I didn't.

http://www.sciencenews.org/articles/20040522/bob9.asp

blueshift
2007-Oct-22, 11:06 PM
You lost me there. :confused:No I didn't.

Fortunate
2007-Oct-23, 02:16 AM
I am pretty sure that the question of whether the density of dark energy is constant is still open. After the discovery that the expansion was accelerating, two categories of theories were proposed - one category in which the density was constant, and another, called quintessence, in which the density varied. Neither of these alternatives postulated a convincing mechanism; they arose simply from placing constant or variable terms into the Einstein equations.

Since then, I believe that subsequent observations have seemed to favor a constant or nearly constant energy density. More sensitive experiments such as SNAP and HETDEX are planned, and the South Pole Telescope and the Atacama Cosmology Telescope are currently collecting data, which will be analyzed utilizing the Sunyaev-Zeldovich effect. The goal of these projects is to determine the rate of expansion as a function of time.

blueshift
2007-Oct-23, 03:00 AM
Fortunate,

from what I have looked into, you are on the mark and then some..but I think that some of the questions asked were of the Standard Model's explanation and that is what many of us were posting.

Experimentation is going on right now with quintessence. It involves measuring the acceleration of little balls made of different substances in the direction of the sun. The force of the sun on the balls can be measured by looking at how much they move in that direction at one time of the day verses another time of the day. So far there is no eveidence for a new force of nature, a quintessence field and its associated massless or near massless boson. One supposition is that there is some symmetry or dynamical mechanism that is preventing its detection at the moment.

Other dynamical dark energy proposals exist and one includes cosmic strings while another involves a possibility of variable mass particles. If there are particles whose masses increase as the universe expands, then density doesn't change while the number density does. The trouble is that it is full of too many holes. Explaing how mass changes and inventing a scalar field that leads right back to quintessence seems to run into a wall unless some observations in the future bring out something new that fits.

We know too little about DE right now

Cougar
2007-Oct-23, 03:21 PM
I am pretty sure that the question of whether the density of dark energy is constant is still open.
Quite so. Hence my conditional, "If it's described by lambda, then the density remains constant (even though space is expanding).

Kwalish Kid
2007-Dec-16, 05:55 AM
That the "pressure" term of the energy density of vacuum energy is negative is a consequence, in part, of demanding that it obey the conservation of energy. (I can't remember the exact equations and I'm away from my books, but it is described in James Rich's cosmololgy textbook and it probably is discussed in others.)

Jerry
2007-Dec-21, 10:05 PM
The density of dark energy remains the same even though the universe expands. Dark energy has been called a smooth tension by Sean Carroll.

Since the density of dark energy remains the same, it provides a continual source for spacetime curvature. This curvature keeps the universe expanding since curvature and acceleration are the same thing.
This is all nonsense, and I don't mean Blueshift is wrong, I mean the theory lacks thermodynamic roots: Lord Kelvin would not have let it fly.

It also lacks roots in the quantum mechanical world. Dark energy is simply a place holder for the unknown, a characterization of the difference between what is observed, and what should be observed if prevailing theories of expansion and supernova events are correct.

Ken G
2007-Dec-22, 12:51 AM
That the "pressure" term of the energy density of vacuum energy is negative is a consequence, in part, of demanding that it obey the conservation of energy. (I can't remember the exact equations and I'm away from my books, but it is described in James Rich's cosmololgy textbook and it probably is discussed in others.)

Another way to say that is, if expansion of featureless vacuum leads to an increase in dark energy, then the pressure must be negative, in order for the work done by expansion to yield the increase in energy. But there's not necessarily conservation of energy in general relativity, so it's no more than a plausibility argument. As Jerry says, the thermodynamics of it is not on very solid footing, but I view that as a problem for thermodynamics not general relativity. We build our theories to fit our science, not the other way around (a point that Kelvin himself tripped over a few times).

Kwalish Kid
2007-Dec-22, 02:37 PM
I apologize, I was wrong about the origin of the negative pressure.

The pressure term is negative because the density of the vacuum must be Lorentz invariant. This then means that, in order to preserve local conservation of energy, the density remains constant.

undidly
2007-Dec-28, 12:24 AM
There is no dark matter and no dark energy.The so called dark matter is to account for unexplained mass.Here is the real explanation.
Mass 1 plus mass 2 adds to more than the sum of each mass.
Proof?.All the parts that make the earth add to make it one part in 10^9 more
massive than the sum.That is why time runs slower on the surface by that amount than outside the G well.That is why light generated on earth is red
shifted by that amount when viewed from outside the G well.There is no such thing as G red ****,it is red when generated.
On the very large scale of supermassive gallaxies the mass increase is enough
to cause obvious orbital effects and a larger than expected red shift but it is not caused by dark matter.It is caused by the effect of the non linier adding of mass.
Enough for one post.
No dark energy either.There is a simple explanation(voyager too).

Kaptain K
2007-Dec-28, 02:02 AM
Enough for one post.
No doubt! I'd be tired too after all that hand waving!

undidly
2007-Dec-28, 10:03 PM
Kaptain K
>hand waving!>

What does that mean?.

YOU tell me why a tuning fork (or any oscillator)in the G well of earth runs at a lower frequency
(viewed from outside the G well) than the same tuning fork outside the well.

Viewed from outside it seems that the mass is larger than when it is outside.
Should we look for dark matter inside the metal of the tuning fork?.
Where does any dark matter go when the tuning fork is taken outside the G
well and the frequency goes back up to what it was.

Ken G
2007-Dec-29, 04:06 AM
YOU tell me why a tuning fork (or any oscillator)in the G well of earth runs at a lower frequency
(viewed from outside the G well) than the same tuning fork outside the well.If Kaptain K doesn't mind, I will: it doesn't. Not for the observer holding the tuning fork (and who is more qualified to discuss its properties!)-- such an observer will always get the normal frequency for that fork. To get the lower frequency, you have to be an observer who is somewhere else in the well, inferring the frequency of the fork in what seems like the most natural way. The amount of the change in frequency is predicted by relativity, the explanation for "why" that happens is not unique. One might say that it is a feature of relativity to generate non-unique explanations of why things happen the way they do. Some see that as a flaw or a weakness, but in fact it is one of the most profound strengths of the theory-- it not only tells you what will happen, it explains your limitations in specifying why it happened.



Viewed from outside it seems that the mass is larger than when it is outside.That is true-- but the problem is not with the fork, but where we view the fork from.

Should we look for dark matter inside the metal of the tuning fork?.Why would we, when we already have a wonderfully adequate theory for that phenomenon: relativity. But relativity does not resolve the dark matter problem in astrophysics-- one still needs dark matter even with relativity. The example is thus completely moot.


Where does any dark matter go when the tuning fork is taken outside the G
well and the frequency goes back up to what it was.As I mentioned, the frequency will also go back to what it was if the observer moves-- it is not necessary to do anything to the tuning fork to get the result you quote. Thus we see this is not a phenomenon that fundamentally involves the fork, but rather the observation of the fork. So it is with relativity, it is not really a theory of local physics, it is a theory about how nonlocal observations must be interpreted to use them to describe local physics. A lot of people don't see that subtle but important difference, so they get all confused about what relativity is telling them about reality-- and what it isn't. Dark matter, on the other hand, is indeed a property of the local physics-- it doesn't go away when you change the state of the observer. At least, that's how the theory of it works-- of course we don't know how well that theory will stand up, but so far it is doing just fine, and is clearly the best game in town at present. I make no predictions about its future-- what would be the point.

Kaptain K
2007-Dec-29, 05:01 AM
>hand waving!>

What does that mean?.
It means that you threw a lot of words around with very little (if any) science to back them up.

Thanks Ken G!

undidly
2007-Dec-30, 10:14 PM
Ken G
>Quote:
Viewed from outside it seems that the mass is larger than when it is outside.>

>That is true-- but the problem is not with the fork, but where we view the fork from.>

We are outside the distant galaxies which appear to have too much mass.
We are viewing it from here.

Kaptain K

Thanks for explaining "hand waving".
I gave the fact that all oscillators run slowly on earth ,when viewed from
outside the G well, exactly as they would IF their mass was that much (1/10^9) greater.
IF their mass is NOT larger ( viewed from outside) then why do they run slowly?.
I know they appear normal when the observer is in the G well but then
everything outside appears to run faster.

Ken G
2007-Dec-31, 12:00 AM
We are outside the distant galaxies which appear to have too much mass.
We are viewing it from here.
You are misinformed. Our own galaxy also has "too much mass"-- and we're smack dab in the middle of it.

undidly
2008-Jan-05, 11:41 PM
Ken G

>> Originally Posted by undidly View Post
We are outside the distant galaxies which appear to have too much mass.
We are viewing it from here.>>


>You are misinformed. Our own galaxy also has "too much mass"-- and we're smack dab in the middle of it.>

I never said that.Observers in these distant would look at our galaxy and say
"That galaxy has too much mass.Let us invent dark matter and the goverment will give us money to find it."

They are outside.They infer missing mass because star orbit speeds do not
match theory.

Nereid
2008-Jan-06, 12:45 AM
Ken G

>> Originally Posted by undidly View Post
We are outside the distant galaxies which appear to have too much mass.
We are viewing it from here.>>


>You are misinformed. Our own galaxy also has "too much mass"-- and we're smack dab in the middle of it.>

I never said that.Observers in these distant would look at our galaxy and say
"That galaxy has too much mass.Let us invent dark matter and the goverment will give us money to find it."

They are outside.They infer missing mass because star orbit speeds do not
match theory.
And gas, and dust, ... and because the mass inferred from (GR) lensing is greater than can be accounted for by the (observed) mass of stars, gas, dust, black holes, ... and because ...

In other words, the inference that there is rather a lot of (non-baryonic) DM in distant galaxies, not-so-distant galaxies, and the galaxy we just happen to be 'in the middle of' comes from a range of independent observations, based on a range of independent physical mechanisms.

Oh, and the real kicker is that the amount of (consistently inferred) DM varies, enormously, by object type: globular clusters, for example seem to have almost none; certain dwarf irregulars seem to be almost nothing but ...

undidly, the real challenge of (non-baryonic) DM is that, as a postulated input, it has extraordinary explanatory power, no inconsistencies*, and no alternative explanation comes even remotely close to being as powerful.

*well, there are some; for example, the inferred radial DM profiles/densities, for both galaxies and (rich) clusters, can't seem to make up their minds as to whether they are isothermal or NFW (Navarro-Frenk-White) or (occasionally) something else.

Mike Smith
2008-Jan-27, 07:46 PM
Well, dark energy would seem to permeate the universe, but not dark matter, which appears to hang out within and around galaxies and galactic clusters.

As to how they interact, uhhhh.... the effect of dark energy really only seems to come into play on very, very large scales, in the super large distances out between large galaxy clusters, so these two things don't appear to be in the same ballpark to be doing much interacting....

Some recent thoughts about Dark and a little about Dark Matter

Ahmet Oztas and I become worried about the predictable past and future of Dark Energy in 2005. When we took a look at the mathematics used by the Kirshner and Perlmutter groups we found significant problems. They all use a version of the Friedmann model within the Robertson-Walker framework, designated the FRW model. The Dark Energy arises from the cosmological constant, a separate term, within this model. The cosmological constant was placed into the equations of General Relativity by Einstein so people should take this seriously.

The math is very uncomfortable with this extra term - solutions about our present situation are warped and even disappear at lower matter densities. So models with “Dark Energy” suffers inconsistencies. We have pointed this out in an article in the International Journal of Theoretical Physics

http://www.springerlink.com/content/5228552224410ul3/?p=086852aaa89046d480c1948b9358a79b&pi=5

The article can often be obtained by students and profs. via university on-line libraries for free or by credit card if one is a “civilian”. I don’t think one has to be too savvy in math to appreciate the many figures. What these inconsistencies mean is that the Universe must "jump" between states because it cannot exists according to model allowing Dark Energy. When we published this article in 2006 the supernovae data (SNe Ia) were not of "red hot" quality, so we decided to wait for a larger and better public data for examination of real data.

Ahmet and I have now used the most recent, public data set, 192 SNeIa (these are available on-line) to recently examine the FRW solution and have found inconsistencies springing up everywhere. These solution are presented on-line for free at

http://www.m-hikari.com/astp/forth/smithASTP1-4-2008.pdf

The inconsistencies can be viewed in Fig. 1. This figure rather reminds me of Swiss cheese. We perform a task, the analysis, using significantly different method from astronomers in that we use the data and errors as true distances with distance errors and not log(data) and log (error).

People in many other branches of science gave up using log(data) many years ago because this type of evaluation tends to place too much emphasis on distant data with large errors rather than discriminating against poor data. Some people continue to use log(data) because it is convenient and because one can more easily visualize the data as straight lines. Computers have allowed us to move beyond this and determine the best models using data vs data, rather than log(data) vs data, etc. Another problem with log(data) is the underestimation of the errors associated with distant measurements. Log(data) tend to fool you into thinking that data from 6 billion year old emissions are better and more trustworthy than there really are.

Anyway, I told Sean Carroll, a Dark Energy man about this problem over a year ago and just watched him on a recent TV show discussing the virtues of Dark Energy. Dr. Carroll has suggested that Dark Energy only functions on the scale of galaxies and does not affect atomic interactions. Prof. Perlmutter claims that Dark Energy is working on atomic scales, too. This is one example of scientific inconsistency. As for me, whenever I model data and my model then returns inconsistent results over the domain or range of interest I look at my model for a few minutes then discard it as being fundamentally flawed. I have spent many years modeling baskets of data, with some models ending in the basket where it belongs.

The reader might also check out recent articles by Oliviera and Hartnett in "Foundations of Physics" and "Foundations of Physics Letters", where they take a look at these 192 SNe Ia and and find these fit best with very low matter densities which can be best explained without reference to Dark Matter.

He (Carroll) didn’t sell me with his presentation on TV but there are hundreds of people in physics and astronomy who don’t mind math with questionable results.

Kaptain K
2008-Jan-29, 05:48 PM
Originally Posted by Cougar
Well, dark energy would seem to permeate the universe, but not dark matter, which appears to hang out within and around galaxies and galactic clusters.
I think it would be more accurate (cause and effect wise) to say galaxies and galactic clusters hang out within and around dark matter.