"[I]f there were no light in the universe and therefore no creatures with eyes, we should never know it was dark. Dark would be without meaning." -C.S. Lewis
I've told you the entire history of the Universe, from before the Big Bang into the far distant future, and yet many of you noticed there was a conspicuous missing piece to the story: dark matter.
Living in halos around our galaxies and clusters, dark matter, at present, makes up 23% of the energy density of the Universe. This makes it second in overall importance to dark energy, which has become important only recently, but makes it about five to six times as abundant as normal matter.
Yes, normal matter -- protons, neutrons, electrons, etc. -- all the stuff our everyday world is made out of, is only 4-5% of the total energy in the Universe.
But in the past, before dark energy was important, dark matter was the dominant thing, as far as energy is concerned, in the Universe. Hugely important, gravitationally, for the formation of structure in the Universe, including galaxies, clusters and superclusters, dark matter is mind-numbingly upsetting to physicists and astronomers everywhere for two simple reasons.
- We can see its gravitational effects. It is the best explanation for what we see in all aspects of physical cosmology, from fluctuations in the microwave background to large-scale structure, from supernovae data to gravitational lensing, dark matter is far and away the most superior explanation.
- And we have no idea how, other than gravitationally, to interact with it.
Image credit: NASA / ESA / Richard Massey.
But, if we knew what it was, we could figure out how to interact with it. Because dark matter wasn't always important. Back when the Universe was just a few thousand years old and earlier radiation was the dominant thing. Not just photons (light), mind you, but any high-energy particle that moves close to the speed of light.
From the moment of the Big Bang and onwards, the Universe was full of it. Perhaps one of the more bizarre things, though, is if you think about all the particles we know exist in our Universe. They come with different spins and charges, they come in matter and anti-matter varieties, they come in lots of different types and flavors. You know most of them already: they're in the standard model.
The thing is, they all acted like radiation in the Early Universe, even the heaviest one: the top quark. It was too hot, and they had too much energy. And they weren't the only things around, either.
Image credit: University of Glasgow.
There were likely more, as-of-yet undiscovered particles, because the temperatures back then were far in excess of what we've ever created or observed on Earth. Supersymmetry is the leading example of this: a new set of particles that are heavier, but should be able to be created at high enough energies.
The Early Universe, shortly after the Big Bang, surely has enough energy to create these in abundance, if they exist. And as the Universe cools, they annihilate away and/or decay, leaving us with nothing.
Except, of course, if the lightest one is stable.
Image credit: Sandbox Studio.
Dubbed the "neutralino," these are almost completely gone from annihilating away from the Universe when it's just a second or so old. The Universe, at this time, is still dominated by radiation. But as we expand and cool, the radiation becomes less and less important, and the little bit of matter suddenly, by time the Universe is many thousands of years old, comes to dominate.
And at this moment, when you look up, you discover that these neutralinos, most of which were destroyed a long time ago, are now the dominant form of energy in the Universe, and will be for billions of years, until Dark Energy takes over.
And that's one dark matter candidate, although many others (such as the Lightest Kaluza-Klein Particle) have very similar stories.
But dark matter has another interesting option.
Much like the Antarctic Fur Seal, dark matter could be born cold, due to something like a phase transition. An example of this is the axion, which -- when it's first produced, again when the Universe is less than a second old -- is a tiny, tiny fraction of the total energy density. It's completely negligible, as only the radiation is important. But as the Universe cools, the radiation's energy density drops faster than the matter density, and by time the Universe is around 10,000 years old, these axions have surpassed radiation, and come to dominate the Universe.
In either of these cases, interacting with them should be possible: we just need to re-create the conditions of the Universe where their interactions were abundant, or, barring that, to be very clever about how it might interact today.
Image credit: CDMS collaboration.
So we search for dark matter. And we make assumptions as to how it interacts, and we poke around in the dark, trying to get it to interact with us. We haven't successfully done it yet, but that's ok: this is science in progress. I have every confidence that we'll figure it out, just as hundreds of years ago we figured out first how to interact with electricity, and then later, how to master it.
And if you thought discovering how to interact with and master electricity and magnetism led to some advances, just imagine what learning how to control our interactions with dark matter would allow us to do.
Limitless energy. Not in some silly-but-untrue way, but in the 100% efficient, perfect sort of way. How's that?
For most candidates for dark matter, including both of the leading ones explained above, dark matter is its own antiparticle, which means that if you collide it with another dark matter particle, it turns into pure energy, the same way as if you collide matter with antimatter.
But dark matter is innocuous, and doesn't run the risk of annihilating with us the way antimatter does.
Safe, clean, abundant, 100% efficient energy. Yes, it's on the very, very distant horizon, the same way Benjamin Franklin probably couldn't have imagined the laptop computer I'm writing this post on. But it's one of the goals we aspire towards, and if we can not only interact with, but master our interactions with dark matter, this is what awaits us.
And so we look. We look for neutralinos, above (credit: CDMS collaboration), and axions, below (credit: ADMX collaboration).
And, long-term, if we can figure out how to interact with it, control/harness it, and collide it with more dark matter under controlled conditions, we'll have a free, virtually limitless source of energy, with no waste.
So if learning about the Universe wasn't enough reason for you to want to look, now you've got a practical one, too.
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Perhaps whoever designed this simulation never expected us to measure it so thoroughly... ;)
Hmm... if dark matter interacts gravitationally with normal matter, shouldn't that mean it gets drawn in towards stars, black holes and galaxies? And won't it meet other dark matter there? And then.. ka boom!! annihilation. Or am I missing something? No friction I guess, so no way to adjust orbits except by the other gravitational effects... which should still either pull the particle in or spit it out I'd think. But really, 5-6 times as much dark matter as matter, you'd think it would be pretty crowded out there with regular annihilation...
Maybe my incredulity is off the mark. There it is anyway.
Dude, cool post but totally wrong image for the kind of power DARK matter will give us:
http://static.tvtropes.org/pmwiki/pub/images/Unlimited_Power_9591.jpg
:)
Paulino
(1 GeV/cm^3)* x (220 km/s)** = 35 W/m2
Kinda diffuse though.
*current high estimate of local CDM density
**Sun's galactic orbital speed
For most candidates for dark matter, including both of the leading ones explained above, dark matter is its own antiparticle, which means that if you collide it with another dark matter particle, it turns into pure energy, the same way as if you collide matter with antimatter.
It astonishes me how so many cosmologists can observe two clouds of Invisible Dark Matter in the bullet cluster pass through each other, completely friction free and without exhibiting even the slightest trace of so-called âannihilationâ and then, without needing a moment to pause for breath, follow up this observation with an unsubstantiated assertion that IDM annihilates with itself.
Nowhere on the web have I been able to find anyone willing or able to substantiate this 'annihilation' assertion.
if supersymmetry partners follow the same kinds of lagrangians as the original partners, why isn't the Sproton stable? or the Selectron? how can they preserve "supersymmetry" but be able to experience interactions that regular particles can't?
Make some sort of arbitrary assumption about the mutual interaction cross-section of DM particles. Figure the velocities necessary to keep them from all falling into the nearest black hole, plus the density of the particles. Figure rate of interaction.
Now you know why you don't see enough annihilation events to stand out of the background.
It is quite possible that Normal baryonic matter does not interact with Dark matter, yet Dark matter does gravitationally interact with normal baryonic matter. Due to dark and normal matter spatial conformance difference normal matter may be neutral towards dark matter, while dark matter exhibits gravitational bounds upon normal matter, yes this would be odd, yet to assume dark matter annihilations to radiation is unfounded, and only based upon the presumption that dark matter is itâs own antiparticle.
Lack of annihilation events may be a illusion forced upon us by physics as usual paradigm.
I find most candidates lacking in their ability to define dark matter is based upon the predetermined theories of a standard particle system that can only express normal matter and is limited in itâs predictive powers due to differing dynamics between different forms of matter.
Perhaps I've been dense, or missed something entirely, but is dark energy the result of dark matter annihilation?
If so, it seems that would both explain and further entrench the difficulties in detecting dark matter annihilation events. Ethan, I hope you'll tell me if I'm way off in my thinking.
@D. C. Sessions
The spectacular fireworks display in the bullet cluster is caused by colliding particles of baryonic matter and absolutely nothing else.
Invisible Dark Matter is powerful enough to keep large galaxies and galactic clusters firmly in some kind of gravitational grip, yet it has never been observed to undergo any so-called âannihilationâ anywhere at all. Not in the bullet cluster, not in galactic halos, nor in any other place in the universe.
Itâs all based on assumptions and speculations about what things ought to be like and further based on a near complete lack of knowledge of what an IDM particle is made of. Even the Standard Model, as currently interpreted and understood, is of no help here.
Science is supposed to be firmly grounded on observation, not arbitrary assumptions and wishful thinking.
They may well be. They're just too heavy for us to make (so far), they're bosons, and they don't interact with normal matter or with each other except through gravity.
Why "yet"?
Why do you think this is a contradiction?
Dark-matter particles do not notice each other, except by gravity, which is weak, and perhaps by the weak force, which is... weak.
Of course, this probably means they cannot collide unless they get close enough to each other for long enough to feel each other's gravity (or weak force), which means just about never.
Photons are their own antiparticles. They cannot, apparently, collide at all, because they have no mass and no weak charge (or electromagnetic charge or color charge).
What does that mean?
Frankly, does it mean anything?
Calculations.
Hard math -- extrapolation from equations that are already known to describe the universe pretty well indeed.
@Ethan: Thanks! :-)
@Sphere Coupler:
Err, ever heard of actio = reactio ...?
This is now my new bumper sticker.
@Alan L:
Dark matter (e.g. the bullet clusters) interact with baryonic matter at the galactic level via gravity -- but that doesn't require a particle density high enough to ensure significant numbers of DM-DM collisions unless you assume interactions (e.g. electromagnetic) which produce large cross sections.
There are a lot of neutrinos in the Universe, but don't expect to detect any neutrino/neutrino interactions. Just too weak an interaction.
The "we might see DM annihilation" theory took another damper here http://arxiv.org/abs/1106.3416 .
And one question (with apologies to Pete Seeger): Where did all the neutrinos go? In the 380,000 year graphic, there's nearly equal parts neutrinos and atoms, and neutrinos are constantly produced. Nevertheless they're completely absent in the now picture.
I'm not sure what the point of the snark from Alan L is. This seemed to me to be pretty explicitly a fun, speculative discussion rather than a bald assertion that "This is what dark matter is!" But also a reminder that there might (MIGHT!) be real technological advantages that came out of it... though Zeno's point about dark matter's diffuseness seems sort of important here.
As for the Bullet Cluster, like others have said, given the lack of EM interaction that dark matter would require, it's hardly a surprise that there's not much in the way of annihilations visible from millions of light-years away.
David M
"Non-interacting" particles can indirectly interact via the uncertainty principle.
"If the energy.. of the two photons is large enough, matter can be created... within the bounds of the uncertainty principle, (a photon can) fluctuate into a charged fermion-antifermion pair, either of which the other photon can couple." Wiki
Ethan
I'm interested in understanding the experiments and reasoning that leads theorists to consider the various dark matter candidates (e.g. axion or Kaluza-Klein Particle).
The problem with "free, virtually limitless.. energy, with no waste" is the "virtually limitless" unintended consequences. oops!!!
First I wanted to share this with you in case you haven't seen it, this has potential to open some eyes...maybe.
http://www.eso.org/public/news/eso1120/
Regarding an isolated galaxy;
It would be prudent to assume that Dark Energy has a more profound effect on Dark matter halo than on normal matter due to normal matter being closer to the balance point or middle ground between Dark energy and the Attempted Singularity inclusive of a Super Massive Black Hole (which by the way are almost identical if not the same).DE=ASSMBH (=almost equal to)
Dark Matter space expansion due to Dark energy is likely a stronger effect due to differences in the density matrix and distance from ASSMBH. The natural occurrence of DM(as of the type I discuss later) on Earth is not possible, it would take a massive disturbance such as a galactic merger to mix the two.
Dark Matter and Normal matter do not mix under standard actions of non-merging galactic phenomena, only when you have a disturbance in the normal baryonic configurations will there be any non-interacting mixing of components.
Perhaps, while we are embedded in normal matter and also consisting of normal matter, other spatial non-conformity's apply, take for example we reside in non-Euclidean geometry,
From Wiki
âIn general, there are two forms of (homogeneous) non-Euclidean geometry, hyperbolic geometry and elliptic geometry. In hyperbolic geometry there are many distinct lines through a particular point that will not intersect with another given line. In elliptic geometry there are no lines that will not intersect, as all that start separate will converge.â
An implication of Einsteinâs theory of general relativity is that Euclidean space is a good approximation to the properties of physical space only where the gravitational field is not too strong. Einsteinâs theory of general relativity shows that the true geometry of space time is non-Euclidean geometry.
Misner , Thorne, and Wheeler (1973)
I would amend this to include (and only where expansion is not too strong)
If we were made of dark matter and were embedded in dark matter, might we not *see* experience a different geometry?â¦perhaps a hyperbolic geometry, and conversely black hole matter (behind the curtain/event horizon) resides in an elliptical geometry. The determination of the geometry of space (taken as a whole Universe concept)as one or the other is a completely different concept, In reality it is a complex relation of all geometries that without the theory of relativity (all mass moves) we would reside as normal matter in an Euclidean Geometry.
A Universe where spatial non-conformity's unite to give us a view that space is flat within 2% only because of the relativity of expansion and coalescence does not allow us a simultaneous view of position and velocity of Dark Energy.
(I realize the above paragraph is incomplete and wanting but I'm not writing a book here ;?)
Once again ,it is only from our view point, (our view point being between opposing geometries) that we see the Universe as almost flat, if we resided outside of normal matter influence (beyond the halo) we could appreciate this concept.
In still other words, it is not just the actions of Dark matter that make it weakly interacting, it is the condition of space it inhabits(hyperbolic)â¦gravity follows the same laws, it is still the same, space takes on a different form under a different density matrix, given a differing matter construction.
This is why I think that(the majority of) Dark matter is a close coupled (yet not fully coupled)pre-meson that exhibits baryonic gravity and a fictitious binding force(a complex manifestation from expansion and acceleration) against normal matter yet itself is weakly interacting with it self due to the nature of a semi-free quark in constant free-fall against the expansion in a hyperbolic geometry.
And as I have said before but bears repeating âDark matter becomes normal matter on the very long galactic time scales.
This is how I see this, be it right or wrong.
OK this really is the last time I will post this,
for fun
Jokers(in coalescing black)=black hole matter/able to consume normal matter, under normal conditions
Clown(in expanding attire)=dark matter/unable to consume normal matter, under normal conditions
Let's see - it has gravitational attraction and annihilates itself, and yet there's still far more of it than our normal matter? Has anyone come up with a model for patches of dark matter which includes the annihilation? Is dark matter expected to produce energy which we can harness?
"For most candidates for dark matter, including both of the leading ones explained above, dark matter is its own antiparticle, which means that if you collide it with another dark matter particle, it turns into pure energy, the same way as if you collide matter with antimatter. "
This is the first place I've seen the idea of dark matter annihilating itself. Isn't the fundamental problem with detecting dark matter that it only reacts gravitationally? If there were annihilation events, they should be detectable, no?
Have I been missing something all these years, or is this a novel theory?
So I have a question as a result of all this, and I know it can't actually be measured because it's all relative, but are the atoms that go into the making of our bodies and all the matter around us expanding? What I mean is, is dark energy pushing the atoms away from each other so we're getting bigger without increasing our mass, kind of like a cartoon animal after they swallow a lit stick of dynamite?
It would be prudent to assume that Dark Energy has a more profound effect on Dark matter halo than on normal matter due to normal matter being closer to the balance point or middle ground between Dark energy and the Attempted Singularity inclusive of a Super Massive Black Hole (which by the way are almost identical if not the same).DE=ASSMBH (=almost equal to)
Dark Matter space expansion due to Dark energy is likely a stronger effect due to differences in the density matrix and distance from ASSMBH and likely to show up as a fictitious force mimicking gravity. The natural occurrence of DM on Earth is not possible, it would take a massive disturbance such as a galactic merger to mix the two.
Dark Matter and Normal matter do not mix under standard actions of non-merging galactic phenomena, only when you have a disturbance in the normal baryonic configurations will there be any non-interacting mixing of components.
Perhaps, while we are embedded in normal matter and also consisting of normal matter, other spatial non-conformities apply, take for example we reside in a non-Euclidean geometry,
From Wiki
âIn general, there are two forms of (homogeneous) non-Euclidean geometry, hyperbolic geometry and elliptic geometry. In hyperbolic geometry there are many distinct lines through a particular point that will not intersect with another given line. In elliptic geometry there are no lines that will not intersect, as all that start separate will converge.â
"An implication of Einsteinâs theory of general relativity is that Euclidean space is a good approximation to the properties of physical space only where the gravitational field is not too strong. Einsteinâs theory of general relativity shows that the true geometry of space time is non-Euclidean geometry".
Misner , Thorne, and Wheeler (1973)
I would amend this to include (and only where expansion is not too strong)
The spatial geometry that cosmologist speak about is derived from an overall concept of the complete whole Universe, and is observed from our perspective/viewpoint/(our solar system).
If we were made of dark matter and were embedded in dark matter, might we not *see* experience a different geometry?â¦perhaps a hyperbolic geometry, and conversely black hole matter (behind the curtain/event horizon) resides in an elliptical geometry. The determination of space (taken as a whole concept)as one or the other is misleading, it is a complex relation of both geometries that without the theory of relativity (all mass moves) we would reside as normal matter in an Euclidean Geometry.
A Universe where spatial non-conformities unite to give us a view that space is flat within 2% only because of the relativity of expansion and coalescence and our position in the galaxy does not allow us a simultaneous view of position and velocity of independent geometries governed by Dark Energy.
Once again ,it is only from our view point, (our view point being between opposing geometries) that we see the Universe as almost flat, if we resided outside of normal matter influence (beyond the halo) we could appreciate this concept.
In still other words, it is not just the construct of Dark matter that make it weakly interacting, it is the condition of space it inhabits(hyperbolic)â¦gravity follows the same laws, it is still the same, Space takes on a different geometric form under a different density matrix, given a differing matter construction.
This is why I think that Dark matter is a close coupled (yet not fully coupled)pre-meson that exhibits baryonic gravity and a fictitious binding force(a complex notion from expansion and acceleration) against normal matter yet itself is weakly interacting with it self due to the nature of a semi free quark in constant freefall against the expansion in a hyperbolic geometry..
That is how I see this, be it right or wrong
OK this really is the last time I will post this,
Jokers(in coalescing black)=black hole matter/able to consume normal matter, under normal conditions
Clown(in expanding attire)=dark matter/unable to consume normal matter, under normal conditions
I've tried several times to post a comment and been unsuccessful, the last being at 5;33, so as another attempt I'll break it up into parts...
Previewing your Comment
It would be prudent to assume that Dark Energy has a more profound effect on Dark matter halo than on normal matter due to normal matter being closer to the balance point or middle ground between Dark energy and the Attempted Singularity inclusive of a Super Massive Black Hole (which by the way are almost identical if not the same).DE=ASSMBH (=almost equal to)
Dark Matter space expansion due to Dark energy is likely a stronger effect due to differences in the density matrix and distance from ASSMBH and likely to show up as a fictitious force mimicking gravity. The natural occurrence of DM on Earth is not possible, it would take a massive disturbance such as a galactic merger to mix the two.
Dark Matter and Normal matter do not mix under standard actions of non-merging galactic phenomena, only when you have a disturbance in the normal baryonic configurations will there be any non-interacting mixing of components.
Perhaps, while we are embedded in normal matter and also consisting of normal matter, other spatial non-conformities apply, take for example we reside in a non-Euclidean geometry,
From Wiki
âIn general, there are two forms of (homogeneous) non-Euclidean geometry, hyperbolic geometry and elliptic geometry. In hyperbolic geometry there are many distinct lines through a particular point that will not intersect with another given line. In elliptic geometry there are no lines that will not intersect, as all that start separate will converge.â
"An implication of Einsteinâs theory of general relativity is that Euclidean space is a good approximation to the properties of physical space only where the gravitational field is not too strong. Einsteinâs theory of general relativity shows that the true geometry of space time is non-Euclidean geometry".
Misner , Thorne, and Wheeler (1973)
I would amend this to include (and only where expansion is not too strong)
The spatial geometry that cosmologist speak about is derived from an overall concept of the complete whole Universe, and is observed from our perspective/viewpoint/(our solar system).
If we were made of dark matter and were embedded in dark matter, might we not *see* experience a different geometry?â¦perhaps a hyperbolic geometry, and conversely black hole matter (behind the curtain/event horizon) resides in an elliptical geometry. The determination of space (taken as a whole concept)as one or the other is misleading, it is a complex relation of both geometries that without the theory of relativity (all mass moves) we would reside as normal matter in an Euclidean Geometry.
A Universe where spatial non-conformities unite to give us a view that space is flat within 2% only because of the relativity of expansion and coalescence and our position in the galaxy does not allow us a simultaneous view of position and velocity of independent geometries governed by Dark Energy.
Once again ,it is only from our view point, (our view point being between opposing geometries) that we see the Universe as almost flat, if we resided outside of normal matter influence (beyond the halo) we could appreciate this concept.
In still other words, it is not just the construct of Dark matter that make it weakly interacting, it is the condition of space it inhabits(hyperbolic)â¦gravity follows the same laws, it is still the same, Space takes on a different geometric form under a different density matrix, given a differing matter construction.
This is why I think that Dark matter is a close coupled (yet not fully coupled)pre-meson that exhibits baryonic gravity and a fictitious binding force(a complex manifestation from expansion and acceleration) against normal matter yet itself is weakly interacting with itself due to the nature of a semi free quark in constant freefall against the expansion in a hyperbolic geometry..
That is how I see this, be it right or wrong
We live in a Universe that is;
open/hyperbolic(saddle shaped),
closed/elliptcal(sphere shape)
and attempted flat.
It's not one or the other, it's all three.
OK this *really* is the last time I will post this song,
For fun
Clown(in expanding attire)
=dark matter/unable to consume normal matter, under normal conditions
Jokers(in coalescing black)
=black hole matter/able to consume normal matter, under normal conditions
Stuck in the middle with you...
I canât believe that I was unaware of this critical endpoint.
Gerald "Gerry" Rafferty (16 April 1947 â 4 January 2011)
A star that will shine indefinitely...he had something to say.
Someone should have told me.
He made this place...better
Dark matter??? So every bit of matter has to give off energy? Yea, it's out there.
correction...perceivable energy
I jumped in too fast..the article seems on a road to something, but I always had a logical and non dreamer approach also...keep in touch.
I simply think that all matter reacts with other matter....but...as we think it should????
i am thinking that when the end of the will come?
thanks for the knowledge....
You can't see light unless it hits your eye.
Every point in the universe has light passing through it, which we can not see. That does not mean it is not there. That is a lot of dark energy.