Further proof or disproof for dark matter

[BoJangles2]

Further proof or disproof for dark matter

I guess there would be an easy formula to calculate whether the apparent mass and velocity of 2 or more galaxies (without the added mass of dark matter) should be interacting using general relativity, i.e. there would seem to be a cut off point where 2 galaxies and their particulars just won’t significantly interact to keep them bound.

At that point would the effect of the dark energy outweigh the affects of dark matter (i.e. extra mass), and if not, would that help calculate the extra mass/energy needed to keep seemingly interacting galaxies/clusters together, and does this discrepancy if found equal the mass a galaxy needs to keep its rotation curve as eluded to with dark matter.

Forgive me if this sounds a little disjointed, as this has been scrawled together.

Ill try and refine this a bit more.

If we look at any 2 galaxies or cluster of galaxies, calculate the apparent mass of each individual galaxy, (i.e. the mass we can calculate from what we see), use some GR and plot their course, then compare it against what the theoretical mass needed for dark matter to keep each galaxies rotation curve, we should be able to find fringe cases which either do fit or don’t fit the added weight of dark matter, fully dependent on whether dark energy is playing a significant role at this distance.

I’m sure this has been done in every 1st year cosmology class, however id like to see if the results fit perfectly, i.e. is everything in equilibrium as far as our current theories go with DM, DE, interacting galaxies, and a galaxies rotation curve.

 

[ramparts]

First, easy formulae pretty much never exist in general relativity. Sorry :lol:

I'm a bit confused, and I think it's because I don't understand all of the assumptions you're making. What do galactic rotation curves have to do with whether galaxy clusters are bound together?

Chances are the things you'd like to calculate can't easily be calculated. Interactions between galaxies and galaxy clusters, especially in the context of general relativity, is extremely complicated and requires supercomputer simulations to solve. That said, people have made plenty of simulations involving those ingredients - dark energy, dark matter, and normal gas - in the amounts that we expect, and the results look very, very similar to what we observe in the universe. So these simulations lend weight to the dark matter hypothesis in a way similar to what I think you're getting at.

 

[BoJangles2]

Hi thanks for your reply

I’m not sure even if I understand what I’m saying, so I guess we’re in the same boat 

Basically as I understood, dark matter is needed to keep a galaxies rotation curve flat as a certain amount of extra mass is needed.

Basically all I’m alluding to is, when you add up that extra mass needed for each galaxy in regards to what’s needed to keep its rotation curve flat (I think is the correct expression) then plug it in to the formula for interacting galaxies, you should be able to look at fringe cases within interacting pairs or clusters (ie ones on the limit of being bound), and determine whether or not the extra mass (as needed by the rotation curve) is contributing

 

[EarthlingX]

Check this video :

[youtube]http://www.youtube.com/watch?v=hLfZntbMAHg[/youtube]

 

[ramparts]

Hi thanks for your reply

I’m not sure even if I understand what I’m saying, so I guess we’re in the same boat 

Basically as I understood, dark matter is needed to keep a galaxies rotation curve flat as a certain amount of extra mass is needed.

Basically all I’m alluding to is, when you add up that extra mass needed for each galaxy in regards to what’s needed to keep its rotation curve flat (I think is the correct expression) then plug it in to the formula for interacting galaxies, you should be able to look at fringe cases within interacting pairs or clusters (ie ones on the limit of being bound), and determine whether or not the extra mass (as needed by the rotation curve) is contributing

Hmm, sorry I missed this, BoJangles. The rotation curves are one of several reasons we suspect dark matter exists, and really the first big reason we found. There are other, independent lines of evidence now, however.

I'm still having trouble understanding the question. What formula for interacting galaxies? You don't just have a formula for something (for example, there is no formula for a cat, or the Earth), but formulae providing certain calculable properties (for example, a formula for the Earth's gravitational force). What would you want this formula to calculate?

This may not be what you're looking for, but it might be: check out the Bullet Cluster (wiki).

This is the prime example of interacting clusters providing strong evidence for dark matter. The Bullet Cluster is a pair of colliding galaxy clusters. This color-coded image shows where the light is (in pink), as measured by x-rays, and where the mass is (in blue), as measured by gravitational lensing:

Note that most of the mass is coming from places besides where the light is! This suggests that most of the cluster's mass is in something which isn't emitting light. Also, the fact that it stays on the outside suggests that it's collisionless and only interacts via gravity, while the x-ray emitting gas does interact with other forces, having friction, etc. The standard dark matter models predict exactly this. Hopefully this helps!

 

[EarthlingX]

chandra.harvard.edu : Einstein's Theory Fights off Challengers

• Via different methods, two separate teams have tested gravity and General Relativity using Chandra observations of galaxy clusters
• The results from each show that Einstein's famous theory works even on some of the largest scales
• Such studies are necessary to understand the evolution of the Universe and the nature of dark energy, one of the biggest mysteries in science

 

[acsinnz]

Dark energy is not a mystery; I believe that it is caused by a magnoflux force which as all stars have positive surface voltages gradually push the outer stars further out.
CliveS

 

[MeteorWayne]

Well that's balony, and dark energy has nothing to do with the subject of this discussion, which is dark matter.

 

[StarRider1701]

Well that's balony, and dark energy has nothing to do with the subject of this discussion, which is dark matter.

Really MW? Since we know almost nothing about either Dark Matter or Dark Energy, how do you know that the two are not somehow related?

 

[ramparts]

Because we know quite a lot about their properties, and at the moment there's no more reason to believe that dark energy and dark matter are related than there is to believe that dark energy and unicorns (which are also poorly understood) are related.

 

[Saiph]

dark matter is the source of an attractive force, while dark energy is the source of a repulsive force. Through observations we know some other characteristics of dark matter, or rather characteristics an object/force requires to fit the list of symptoms that is currently attributed to dark matter, such as general dispersal characteristics, electromagnetically inert, and a few other things.

These two ideas don't share much in common, and while they may be due to a single source, so far there is nothing to suggest that's the case.

 

[Woggles]

than there is to believe that dark energy and unicorns (which are also poorly understood) are related.

Wow, that cracked me up!!!

 

[StarRider1701]

dark matter is the source of an attractive force, while dark energy is the source of a repulsive force.
These two ideas don't share much in common, and while they may be due to a single source, so far there is nothing to suggest that's the case.

Ok, if you say so. Yet now there is the theory out there that Gravity as we knew it in the Newtonian sense does not exist. Rather what we feel is dark matter pushing us against the Earth. Would that not suggest a repulsive force rather than an attractive one for dark matter? Couldn't that repulsive force be called dark energy?
Given that we are observing these phenomenon at extreme distances, appearances could be deceiving.

than there is to believe that dark energy and unicorns (which are also poorly understood) are related.

She is upset that you don't understand her, so you might hop back onto your Unicorn and ride, ramparts.
Obviously, Unicorns are not the only things that are poorly understood. Because while nothing currently says that the two are related, neither does anything say they are not.

 

[ramparts]

Ok, if you say so. Yet now there is the theory out there that Gravity as we knew it in the Newtonian sense does not exist. Rather what we feel is dark matter pushing us against the Earth.

There is?

She is upset that you don't understand her, so you might hop back onto your Unicorn and ride, ramparts.
Obviously, Unicorns are not the only things that are poorly understood. Because while nothing currently says that the two are related, neither does anything say they are not.

Well, that's kinda my point. Lack of evidence against isn't the same as evidence in favor. That's what unicorns are supposed to illustrate - there's no scientific evidence saying that dark energy isn't related to invisible pink unicorns, but we can be pretty sure it isn't, anyway. Similarly, the fact that there's no evidence suggesting dark energy and dark matter are unrelated (what would that evidence look like anyway? What kind of experiment could you run to see that?) doesn't really mean much when there's no evidence in favor of them being related either.

Think of it as a probability argument: most things in the Universe aren't the same thing on a fundamental level. Unicorns aren't kettles. Friction isn't gravity. Dark energy is almost certainly not the strong nuclear force. So a lack of evidence for two things being related is necessarily stronger than a lack of evidence against their being related.

 

[Saiph]

I haven't heard of such a theory, nor do I accept it without a lot of work. Such a set up would have problems explaining the decrease in gravitational strength with distance (1/r^2)

 

[ramparts]

Nor would it make any sense, especially given that general relativity, which is extremely well-tested outside of Earth (as well as on it) reduces to Newtonian gravity in weak fields.

 

[csmyth3025]

...So a lack of evidence for two things being related is necessarily stronger than a lack of evidence against their being related.

I nominate you for the 2010 George W. Bush Abstrusiness Award.

Chris

 

[EarthlingX]

www.newscientist.com : Black holes + dark matter = light

27 August 2010

by Kate McAlpine

Dark signs from Centaurus A (Image: NASA/CXC/SAO/M.Karovska et al)

TWO of the darkest things in the universe may be making light - or at least, radiation. When jets spat out by a supermassive black hole at the centre of a galaxy collide with dark matter, they could produce gamma rays detectable from Earth - possible evidence of the elusive dark stuff.

Jets of particles are propelled away from black holes at near the speed of light. Akin to a cosmic belch, they are thought to be connected with matter falling into the black hole. Stefano Profumo of the University of California, Santa Cruz, and his colleagues calculated how electrons in one of these jets would interact with any surrounding dark matter.

They looked specifically at the types of dark matter particles predicted by two major theories: one is supersymmetry, which proposes that each ordinary particle has a superpartner, and the other assumes that the universe is hiding a fourth spatial dimension.

They found that rather than simply ricocheting off one another, some of the electrons and dark matter particles could fuse together, transforming into a single, supersymmetric or extra-dimensional version of the electron. This particle would be heavy, and much of the electron's kinetic energy would be dumped into making the new particle. As a result, the particle would be almost standing still.

If the particle were then to decay into an electron and a ground-state dark matter particle, the electron would release gamma rays. Unlike a particle travelling fast, like those in the jets, the slow-moving particle would emit rays that could travel in any direction. This could potentially make them easier to distinguish from the flood of photons in the jet, says collaborator Mikhail Gorshteyn of Indiana University in Bloomington.

 

[acsinnz]

Earthling, I agree with your view that dark hidden matter is somehow attracted by gravity and also that dark energy is a repulsive dark force. If that dark force was a negative 4 times gravity force would the universe then balance I wonder. I have chosen of a dark force of = -4G on the basis that we appear to have lost 75% of the observed universe to dark energy.
CliveS

 

[EarthlingX]

Earthling, I agree with your view that dark hidden matter is somehow attracted by gravity and also that dark energy is a repulsive dark force. If that dark force was a negative 4 times gravity force would the universe then balance I wonder. I have chosen of a dark force of = -4G on the basis that we appear to have lost 75% of the observed universe to dark energy.
CliveS

If i understand the article correctly, this has not been proven yet, and includes a lot of 'if's, 'could's and 'maybe's, but shows a hypothetically possible way to check what is going on, or at least exclude some of the possibilities.

 

[kk434]

The latest data says that ordinary matter is 4%, dark matter 23% and dark energy the rest (about 73%).
I understand that Dark matter is some kind of "matter", but why is Dark energy counted in the equation? Dark energy sounds more like a force (against gravity) and no one counts gravity as some kind of "missing mass". Is the LambdaCDM model messed up?

 

[Woggles]

Hi everyone. I like to add to this discussion; however I am no expert in this, as most of you already know lol.

Ok here is my thinking. I was watching Through the Wormhole the other night and the topic of brane cosmology was discussed.

http://en.wikipedia.org/wiki/Brane_cosmology

Now, as it was shown in the show, a brane look like a flat piece of paper turn on edge. When the brane (or our universe) cools enough, say in a trillion years, two parallel branes touch and create a big bang. And all the stuff in our universe restarts again. The cycle repeats over and over again

So as show in their model, the stuff in our universe is cold now but not gone. Could this cold matter actually be dark matter?

Could Dark energy actually be the gravitation pull of this cold matter?

Thanks

 

[acsinnz]

Thanks. If only we could forget about all the ifs,buts and wherefores then we could get on with the search for the dark massless electromagnetic force of 4Gs that is in reality pushing the universe apart. Why not forget about negative matter and look unblinkered for the dark force
CliveS

 

[csmyth3025]

The latest data says that ordinary matter is 4%, dark matter 23% and dark energy the rest (about 73%).
I understand that Dark matter is some kind of "matter", but why is Dark energy counted in the equation? Dark energy sounds more like a force (against gravity) and no one counts gravity as some kind of "missing mass". Is the LambdaCDM model messed up?

As I understand it, various lines of evidence indicate that the overall curvature of spacetime in our observable universe is very nearly "flat" (like a sheet of paper) as opposed to being positively curved (like a beach ball) or negatively curved (like a saddle). I don't pretend to know what this really means, except that cosmologists say that in order for the geometry of the universe to be "flat", it must contain a certain critical density of matter/energy. The reason that energy is included is that energy possesses an equivalent mass according to Einstein's famous equation, E=mc^2. For the purpose of this calculation the preceding formula would be rearranged in order to give the equivalent mass thus: E/c^2=m.

The amount of ordinary matter in our observable universe is estimated by taking the stuff we can see (mostly stars, dust and molecular hydrogen) and extrapolating from that what we think is the "average" amount of matter in the universe.

The amount of "dark" matter in our observable universe is estimated based on the amount of gravity that is needed to make stars in galaxies orbit at the speeds we observe them orbiting in their galaxies - as well as galaxies clustering in galaxy clusters. Since the amount of matter we can "see" in these galaxies and galaxy clusters is not nearly enough to cause the orbital speeds and clustering we observe, we attribute the "missing" mass to "dark" matter.

When we add up all the ordinary matter and "dark" matter we think there is in the universe there isn't nearly enough to make up the "critical density" needed to make space appear "flat". So, the cosmologists subtract the ordinary matter and "dark" matter from the amount of mass required and what is left over is called "dark" energy (that is, its mass equivalent).

The Wikipedia article here http://en.wikipedia.org/wiki/Density_pa ... _parameter explains it this way:

To date, the critical density is estimated to be approximately five atoms (of monatomic hydrogen) per cubic metre, whereas the average density of ordinary matter in the Universe is believed to be 0.2 atoms per cubic metre. [4] A much greater density comes from the unidentified dark matter; both ordinary and dark matter contribute in favor of contraction of the universe. However, the largest part comes from so-called dark energy, which accounts for the cosmological constant term. Although the total density is equal to the critical density (exactly, up to measurement error), the dark energy does not lead to contraction of the universe but rather accelerates its expansion. Therefore, the universe will expand forever.

I don't know how gravity fits in to the whole energy thing when calculating "omega" (the ratio of the observed mass/energy in the universe to the "critical density" of mass/energy).

Chris

 

[csmyth3025]

...Why not forget about negative matter and look unblinkered for the dark force...
CliveS

I haven't heard the term "negative matter" used before. Are you referring to anti-matter, or something else?

I have heard the term "negative energy" used to describe the portion of a virtual particle pair that falls within the event horizon of a black hole (in descriptions of the mechanism of Hawking radiation). I'm still unable to grasp the concept of how "negative energy" is different than "positive energy". This isn't as simple as just saying an electron has a negative charge and a positron has a positive charge, since both - as far as I know - have "positive energy" in this context.

Chris