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Dark Matter Measurements
ksp0704 writes: "According to this article at space.com, scientists have finally measured the approximately 90% of the universe we can't see (the dark matter)." I'm sure it will continue to be a topic of debate for years, but two independent measurements agreeing is a good sign.
As I understand it, they can estimate how much matter there *should* be, based on what we know of the universe and of physics, and also based on the matter was can see now. They aren't just pulling the numbers out of thin air.
:)
Always remember: Weezer ain't rocket science!
"Tell me doctor, with all of your defenses, are there any provisions for an attack by killer bees?"
Okay, I just read the article, and I'm down with it. There is nothing illogical about it, assuming their methods actually work, and I have no evidence that they don't. But, after re-reading the section on the "Creation of normal matter", I have one complex question that I hope can spark a bit of discussion: And how on earth (pun intended) did we get here from all of that?
All the "normal stuff" is thought to have been made in two steps, one occurring when the universe was roughly three minutes old, and the other some 300,000 years later.
:0)
See? Even "God" needs to get it in production, then issue a revision some time later before it's really running right.
(P.S.- My first thought was of "Dork Matter", but then I saw the StarWars DVD ad on the page. *sigh* Too easy...)
Soko
"Depression is merely anger without enthusiasm." - Anonymous
Heh. What's the difference, if it's all just theoretical anyway? I mean, really, how is the amount of matter in the universe ever going to mean anything more to us than simply a numerical value?
Of course, one can assume that, by knowing the ammounts of normal matter compared to dark matter as they change, scientist could predict approximately when the universe would collapse on itself. You know, if the big bang theory has any truth to it. Of course, that prediction wouldn't mean much to us either, as our sun will likely die out long before the universe itself will.
I'm only in high school physics, maybe someone more familiar with the field could provide an explanation and how it relates to the facts presented in this article?
Is your company running tools written by ma
Gack. How do they figure an explosion of spacetime is nuclear? There were no nuclei to fuse or split. My cynicism is telling me that the author just though "nuclear" sounded big and bang-y.
If 10 percent of all matter in the universe is made of "stardust" and the other 90 percent of the matter is made up of dark matter, we've got a pretty serious problem. There may yet be some other sort of matter out there that we don't know about yet, since the 10% of all regular matter occupies only a tiny fraction of the actual space available and dark matter is ,by the accounts in the article, clumped together into pockets. So what about all the rest of that space? Is is occupied by purple matter?
Still, it's all very confusing. I don't think it's a "serious problem", because the assumption seems to me to be that much of the dark matter has not materialized into what we recognize as matter yet. This means that the universe is young yet... When we reach the point when normal matter and dark matter are split 50/50, then my guess is that the universe will begin to shrink back toward its state before the big bang, only to explode all over again. Of course our planet will be long gone by that time (but that doesn't mean we have to go with it)... "In the beginning, there was nothing. Then it exploded."
Sanders : Kapteyn Astronomical Institute
Finzi : Dunno
Bekenstein : Weizmann Institute, IL
Milgrom : visiting Cambridge/Oxford/England
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Of course, it had to fuse into all those other tiny particles that make up the protons and neutrons first, but why would they want to bore us by explaining all of that too? My question in relation to that: How small was this "stuff" before the explosion? Would it be fair to wonder if it had been rapidly exploding outward from a much smaller size than we could possibly imagine for much longer than we think?
Oh yeah, Bekenstein is of the Hawking-Bekenstein Fame. He is the guy who suggested the Entropy/Area correspondance. So I think he's smarter than Hawking (who set out to prove it wrong but ended up proving it right).
Modified Dynamics that you talked about have no covariant formulation (i.e. the theories are all coordinate-system dependent, which is bad since physics should not care about coordinates).
(I spent a year looking around for a covariant formulation...with no success of course.)
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Scientists can measure ALL the dark matter in the universe, but can't build a fortune-telling weight machine that can get my weight right.
Pfft.
-Kasreyn
Kasreyn: Cheerfully playing the part of Devil's Advocate to hairtrigger
Only further testing will be able to prove that this match is not simply coincidence. They're right, this doesn't "have to be the answer", so let's not jump to conclusions from two friendly tests. (But certainly get excited for the potential! Heh.)
Yes if you believe in a homogenous and isotropic Universe.
You can construct all sorts of universe where there are "matter" only in some parts and not others. But they violates our observations (we see stuff everywhere). Of course you can say "oh we don't see the parts where there are no stuff". You are allowed to say that, but then "why bother if we never see them?". Basically, postulating that there are "empty" regions that we cannot see violates Kant's principle that theories need to be falsifiable.
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You can have whatever creationist theories you like, but you can't contradict what we *know*.
That's a very humbling thought. Not enough of humanity gets put in their place by the sight of millions of stars anymore. Gives me hope.
Dark matter is the packing material the Universe came in...
No theory of everything could ever be complete without allowing for this.
When the whole universe collapses because of the reversal of the big bang energy by gravity, then you may care.
One of the biggest debates IMHO, is whether the gravitational pull of the universe can overcome the expanding motion of the universe. This expansion caused by the big bang was theorized to be decreasing and gravity would eventually overcome it, thus pulling the entire universe back together in the same manner of pre-big bang time. It could also be said that this would cause the universe to be a periodic function of explode, expand, contract, explode... The problem with this is that there is not anywhere near enough matter in the universe to create a gravitational pull strong enough to overcome the big bang energy. There is also not enough visible matter to explain many gravitational effects scientists perceive. Thus, dark matter was theorized to explain these phenomenons. However, it could never be measured. This could go a long way to supporting various theories about the universe and it's workings.
WikiAfterDark.com It's a sex wiki, go now!
Picture the surface of a balloon. The galaxies are dots on the balloon.
Now inflate the balloon. Any galaxy will see all the others moving away, speed proportional to distance.
You'll notice that since the surface of the balloon has no boundaries, you can go forever in any direction (assume the balloon is expanding so that the circumference is growing at a rate faster than the speed of light, so you can never get back to where you started).
There's our 2-d curved space. We live in a 3-d one. It may not be curved that way, and galaxies change the local curvature (think the dots sinking the surface of the balloon)..but you get the idea. We don't need infinite matter for a boundless universe.
Sure.... why is it that no one ever talks about an infinite number of big bangs occuring constantly? Our big bang might just be a fairly small one compared to the one that happened last night a gazillion miles away. Our little "universe" could simply be a little puddle of matter in our little side street of the real infinite universe.
I sure hope you're Ross Tessien, who posted this article to Usenet!
an enormous nuclear explosion called the Big Bang happened 13 billion to 15 billion years ago. From it, the universe appeared in an instant, but as a billion-degree mess of neutrons, protons and electrons.
If ever Big Bang there was, it was not a giant nuclear explosion! Damn at those temperatures there are no nucleus (as they themselves state a few sentences afterwards). It is rather a very FAT release of energy, which later congregated into quarks and antiquarks, neutrinos, etc. definitly not nuclear. And what a hell is "dark matter". They state that "dark matter" congregated and formed gravity pools...
At the time of the original release of light, dark matter had congregated in clumps, which created small fields of gravity that eventually pulled in normal matter as well.
Dark matter does not emit radiation by definition. It thus has to have enough gravitational pull to keep all EM radiation in. That is a freakin big chunk of matter, not small gravity fields! And what do they mean normal and not normal matter... it's all the same stuff, energy. The energy is just "stored" differently.
"The nature of these 'wiggles' is basically saying how the normal matter was responding to that crazy dark matter," explained Fields, "by amplifying the places where the extra density was."
Errhhmmm... that is called matter falling in the black hole to make it larger and thus increase the gravity....
Imperium et libertas
Autocracy and freedom
This slashdot comment also looks like this Usenet post.
This slashdot comment also looks like this Usenet post.
How about I speculate; we discover that dark matter exists, and that it outnumbers regular matter 9:1
Knowing it exists, we can start trying to find, create, and control it.
N years later we have dark constructs.
Without even having the theories about the universe showing there is dark matter, we don't find it or about it's properties, capabilities, and uses.
GPL Deconstructed
I believe that the universe has always existed, and will continue to exist forever. It is also infinitely large in every direction. The only reason we can't see the rest is because the light hasn't gotten here.
Hmm.
The universe is infinitely large, and infinitely old.
Since the universe is infinitely old, light from luminous objects in all parts of the universe has been radiating for infinite time.
But you think light from distant objects "hasn't gotten here yet?"
I wish I'd had you on my side during my last tax audit!
I believe I've got some under my couch. A rather more important discovery will be, I suspect, that all that dark matter is all the socks of every culture ever to evolve clothes dryer technology. Clothes dryers create minature wormholes which teleport your socks to random points in the universe. This revelation will ultimately lead to a faster than light drive with a clothes dryer at its core. Its mission will not be to explore new planets yadda yadda. Its mission will be to retrieve all those socks.
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
They look at the galaxies, and estimate how many stars and stuff there is in the galaxy. Any rotating galaxy. And They figure out how fast the galaxy is rotating.
They notice a problem. For any rotating galaxy there is not enough star stuff to hold the galaxy together. The spiral arms should never be there.
The star stuff in the galaxies do not have have enough gravity to hold galaxies together. Galaxcies should not exist at all. Stars should be all flying about because that is how weak the gravity is.
Just how much too weak? The Star stuff has one tenth the gravity needed to do the job. so something has to be doing the other 90%.
That is what the dark matter is. It is a term to label what the other 90% is. The don't know what it is yet. but they are working on it.
"It is a greater offense to steal men's labor, than their clothes"
The stars you see are all within our own galaxy, which is "only" about 100,000 light years across, so all the star light is from well after the dinosaurs bit it. There is a lot of light from other galaxies that are over 65 million light years away, but it's relatively faint, so you've probably not really noticed it.
Yes, by seeing farther away objects we can raise the lower bound for the age of the universe. Astronomers are working on that. Yes, we think the universe is expanding, and we have a lot of proof for it too, mostly the red-shift that Hubble (the man, not the telescope) noticed. And yes, maybe the universe had a creation date (you've heard of the big bang theory, right?). (How did this get modded up?)
Okay, top paragraph: distance doesn't stop light, only matter, and there's relatively very little of it in space. Light from far away objects
Your belief that the universe has always been here is unsupported. (Again, big bang theory.) You're belief that it is infinite in all directions is also unsupported.
Yes, they can guess how much dark matter there is. By definition, the part of the universe we can't see is dark matter...it's called that because we can't see it. It's not any different from normal matter (as far as we know), it's just not emiting any light, so we can't see it. And by the calculations for the estimated mass of the universe, and the calculations of the total mass of all the matter we can see, yes, there must be some (up to 90% of the total mass, by the measurements in this article).
(I ask again... why did this get modded up?)
Those who fail to understand communication protocols, are doomed to repeat them over port 80.
I call blatant matterism!
It's not dark matter you unenlightened cretins!
It's matter of color!
Heathens.
Hilary Rosen's speech was about her love of money and her desire to roll around naked in a pile of money.
Something very odd just happened...
I clicked the link to space.com to read the article. When the page loaded, the big central advertisement was for "Star Wars: Phantom Menace" videos... Kinda threw me off for a moment. Perhaps I haven't recovered yet beause I'm posting this here. hmmm
Skiers and Riders -- http://www.snowjournal.com
If bright matter truly makes 10% of the universe, then by definition the remaining 90% of the universe must be dark matter.
The reason is that neither the terms "bright matter" nor "dark matter" specify a single type of matter. Rather, they define two values of a single common characteristic of all matter. The characteristic in question is how the matter interacts with photons. If you shine a light on something and you can see it, then it's bright matter. If you heat something up and you can see it, then it's bright matter. If you energize something then let its energy level drop and you can see it, then it's bright matter. Otherwise it's dark matter.
Therefore we can't measure dark matter directly merely because we can't see it. All astronomical observations depend on photons. Radio. Light. X-Ray. Gamma. Just different frequencies of photons. Since dark matter neither reflects nor emits photons, astrophysicists can't observe it. Or perhaps it does emit photons, but then immediately reabsorbs them (as in the case of black holes). Either mechanism comes down to the same thing. They can observe its effects indirectly by watching, for instance, the effect that its gravity has on surrounding bright matter, but no direct observation is even theoretically possible.
But there really aren't any theories about the nature of dark matter, because it's fundamentally impossible to observe remotely. Maybe it's some truly strange substance. Maybe its just a whole bunch of black holes. No one knows. The only reason that we know about black holes is that some brilliant physicist who'd been downing a few too many beers one night did a thought experiment about the implications of gravity's inverse square strength. So we had a theoretical phenomenon that astrophysicists could later go and look for. But that's not true of other forms of dark matter.
All that's important is that "dark" matter is every piece of matter that isn't "bright" matter. It's still matter, and will still behave exactly the same as bright matter behaves. But it may come to be discovered that some characteristic that we thought was endemic to all matter is, in fact, only endemic to bright matter. We have no comparison yet, so we can't make that determination.
I don't think that anyone believes that all dark matter is in the form of black holes. Who knows, maybe so. I'm certainly not an astrophysicist (though I know a number of them who are on the bleeding edge), so someone can easily have come up with some theories about all this of which I'm unaware.
But this is my current understanding, and with the rate that astrophysics moves, I'm probably at least 5 years out of date.
Oh, explaining this caused me to remember a theory about dark matter that I heard from my undergraduate adviser back in my college days (Dr. Douglas Lin: he was and is a big shot in the astrophysics circles). The idea is that there actually isn't any special dark matter. It's all bright matter. But some matter might be in locations where so few photons fall on them that we just never get a chance to observe that matter. For instance, it's known that all the galaxies of the universe exist on the surfaces of voids in the universe (that observation is what gave rise to superstring theory). Think of soap suds. We've got complex surfaces, where all the soap is, each surrounding a small void with no soap. Small from our perspective, but from the point of view of a technological civilization living in one of the "galaxies" within the soap film, those voids are huge. The universe has the same structure. And these voids are just monstrously huge. In the center of one of these voids, there would be very little light, because all the light sources are very far away. So you could stick a whole lot of matter there and no one would ever see it. These voids are so huge that you could easily fit 90% of the universe's mass in them and still have a very low density of matter. It's normal "bright" matter, but insufficient light reaches it for us to observe it. The problem with the theory is that if you have 90% of the universe stuck in these voids, then the voids should collapse from gravity and make the galaxy distribution homogenous. And we don't see that. Perhaps this problem has been resolved by now. I don't know. And, of course, there are other locations where matter can be hidden, where we wouldn't be able to observe it. Those voids are just a single example.
-- Nolite audere delere orbiculum rigidum meum.
1) Get Jon Katz to write a book full of book reviews and post a topic about it on Slashdot.
2) The amount of trolls accumulating around that single topic on Slashdot will be so intense that it creates a giant gravity field that sucks everything in the universe together.
3) The universe is saved from flickering out into nothingness due to endlesss expansion! No dark matter required, yay!
Men believe what they want. - Caesar
Well spotted, dude. And from 1996 too!
For many Slashdotters, Kantor's central idea of basing physics on information, rather than things like matter and energy, might seem inherently appealing.
We have three methods to calculate the mass of the universe. Two are based on electromagnetic interactions. Those two agree. The other is based on observations of gravitational interactions. It gives a result 10X as large for the total amount of matter. Therefore 90% of the universe is made of particles that interact gravitationally but not electromagnetically. The only way to observe them is to observe their gravitational effects. Like, duh. Why is this such a difficult concept to grasp? It's an empirical observation.
Keep in mind that if something only couples gravitationally, it's going to be extremely hard to see. You're prejudiced by your own experience with the world, which is mostly based on electromagnetism- meaning interactions with photons (real and virtual). Get rid of electrodynamics, and most concepts and phenomena you're familiar with- atomic physics, chemistry, biology, optics, materials science, friction, pressure, radiation, viscosity, resistance, reflection, transparency, iridescence, impenetrability- all this stuff goes out the window! Your ass would sink through your chair, right through the ground, until you reached the center of the earth with everything else. Don't underestimate the importance of photon-mediated interactions. Everything else is gravitation, beta decay, and the strong nuclear force. Of those three, only gravitation operates over non-microscopic distances. And it is very weak. There could be up to several tons of dark matter in the room with you right now. You would never know it's there.
Of course, the mass could be ordinary matter that we're just not seeing. Many people like the idea of lots of Jupiter-sized objects. Lots of black holes might also work (although a black hole can feed off either kind of matter).
All the aether physicists came up with a new, marketable name for the aether - the quantum vacuum. All those virtual particles popping in and out of existence are pretty much the same as an aether concept, when you get right down to it. They just don't dare say it.
Choice of masters is not freedom.
If the universe is an evenly distributed thin soup of cold dark mass, would it not then be in a state similiar to the one that precipitated the Big Bang? What I mean is, if the universe was an evenly distributed pinpoint-sized ball of hot mass (relative to it's "surroundings")that "exploded", then wouldn't the massivly-large ball of cold mass not be the same thing at a larger scale/perspective?
No, because space and time were also created at the instant of the Big Bang and in the event of an open Universe we already have these things, plus an energy density quite ridiculously low - one electron/positron pair for every trillion cubic light years is not enough to make any kind of explosion!
Unless superstring theory comes up with some better explaination of what happened before the Big Bang (which I believe it explains as the decoupling of our 4-dimensional macrospace from the other 6 dimensions that are curled up real small), then something like Linde's chaotic inflation seems to be the best bet - an unstable "false" vacuum within which quantum fluctuations can cause a Big Bang-like event at any time...
What happens when black holes get hold of other black holes? Does the bigger suck in the smaller? Do they combine into a super black hole? Are they the force behind my theory that the universe will recompress itself for another bang?
Did no one else get it? Am I the only Pink floyd fan reading here? Or maybe no one had the moderator points to use. Anyway, to paraphrase a little bit closer to the original:
"There is no dark side of the universe, really.
Matter of fact, it is all dark."
(Kudos to nukebuddy for thinking about it first!)
Tongue-tied and twisted, just an earth-bound misfit, I
Learning to fly, Pink Floyd.
How about this. What if everything is preordained, but because of its complexity our minds cannot possibly, no matter the scope of our computing and math, understand it all. Therefore, because it is defined but unknowable (i.e., just like quantum mechanics, that electron certainly is somewhere, but we are not able to know where it is by a law of nature) we can ACT like we have free will.
I think there is some kind of interaction between knowing the truth and the truth being true. So, okay, your entire fate is preordained, but you cannot get at that info, therefore, why live your life like you have no free will? The absence of the knowledge yields effects similar to true free will. Effects similar enough that you can get on with life.
Maybe. IMHO.
So, what is outside the balloon? Anti-space?