Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chimera on 23/02/2005 23:56:42
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http://news.bbc.co.uk/1/hi/wales/south_east/4288633.stm
What do you think? Is this a confirmation of dark matter, or could there be other explanations?
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I think Dark Matter is spooky.
'Men are the same as women...just inside out !'
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Black magic, that's what it is... or maybe just an alien revving up his engine, which unfortunately also bends space a bit out of whack. There's probably a dead-ordinary explanation, eventually. Maybe best ignore it, until we come up with something. [:)]
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I think dark matter is already confirmed. It has been found in galaxies filled with stars. What is fascinating here, is that there can be radio galaxies. What we may be seeing is a relic, a fossil galaxy from the "dark age" of the universe, before star formation began. This could be very important, and not just about dark matter.
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quote:
Originally posted by gsmollin
I think dark matter is already confirmed. It has been found in galaxies filled with stars. What is fascinating here, is that there can be radio galaxies. What we may be seeing is a relic, a fossil galaxy from the "dark age" of the universe, before star formation began. This could be very important, and not just about dark matter.
So that would make them very old aliens. OK. Point taken. [^]
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Old aliens? I guess its a joke, son, but I don't get it. The galaxy would be full of darkerons, the elementary dark matter particle.
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Can you speculate as to what a handful of Dark Matter would look like (yes...I gather it would be dark ( or would it ? ) but is it possible to elaborate ?) and what it might feel like ?..would it be just be like a black rock......or is it something less tangible which you can not touch or feel ?
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OBTW the "darkeron" bit is just a joke, son. There hasn't been an elementary dark-matter particle identified. I suppose whoever discovers it would have the privilege of naming it. But maybe it would be fun to run a poll for "name the dark matter".
What would it feel like? Well, everything we see, hear, feel, smell, and taste is a result of electromagnetic forces acting on atoms and molecules. That's our level. Nuclear stuff is out-of-reach, and that's not even dark. I am pretty sure that dark matter feels like absolutely nothing. We cannot feel it at all, and it cannot form objects like rocks.
Whatever gravitational binding energy the dark matter was endowed with at the beginning of time must still be with it. Dark matter cannot radiate its gravitational binding energy like baryonic matter. There is an analog in baryonic matter. Momentum is conserved in baryonic matter. That is why galaxies and solar systems collapse into flat disks. The rotational momentum of the collapsing nebula cannot be radiated, it can only be transferred. So to form a star, a large solar wind must shed the rotational momentum. The gravitational energy can be radiated away, and the rise in temperature in the star eventually ignites nuclear fusion.
Dark matter cannot radiate, so its energy and momentum are conserved. Without the ability to shed the gravitational energy, it cannot reach a critical density and collapse into stars, planets, and rocks. It just stays in a diffuse mass, and collects baryonic matter by gravitational attraction. The baryonic matter then can collapse into stars and galaxies, but the dark matter is unperturbed by all this, and remains in the diffuse mass. Astronomers call it a "halo", but I think that is misleading. A halo is a thing overtop of something else. The dark matter was there first, and attracted baryonic matter to it. A baryonic matter galaxy is submerged in the dark matter halo.
Anyway, what does it feel like? Well, nothing, but it is there, and it must be right in front of you all the time. It is just too diffuse and non-reactive to be seen, or felt.
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quote:
Originally posted by gsmollin
OBTW the "darkeron" bit is just a joke, son.
Sounded too much like 'mysteron' from the old Captain Scarlet series, indeed ...
Anyway, given its rather mysterious nature, and intangible properties, what does it actually DO, besides helping to balance the books gravitywise (since without black matter, the standard model cannot explain a difference of 2 orders of magnitude in observed vs. required mass).
I know they need it to explain things, but does it do anything more than being mysterious? Scientists talk about properties and repeatable experiments a lot, but what with their own creations? Why are they always safely out of reach of any such rigour?
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quote:
Originally posted by chimera
... what does it actually DO, besides helping to balance the books gravitywise ...
I think that covers it. Without the mass provided by dark matter, there is no reason why baryonic matter should have clumped together to form structures such as galaxies, stars, planets, and us. Without a balanced universe, space itself would be hyberbolic, and we would be far flung hydrogen and helium.
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.... according to theory, yes.
Problem is, that's circular reasoning. If our theory wasn't right, we would not be discussing this, sort of.
Sorry, don't prove a thing, as they used to say. It could just as well be argued it's a stop-gap for an erroneous theory that's off by a factor 100 in explaining something.
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Is dark energy just another name for dark matter ?
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fimg.photobucket.com%2Falbums%2Fv286%2Fneilneil%2Fdarkenergy.jpg&hash=511fc68a2aae9060a585d496d5000bea)
A supercomputer-produced cross-section of part of the universe shows galaxies as brighter
dots along filaments of matter, with a sea of dark energy filling in between the galactic
islands. Credit: James Wadsley, McMaster University, Hamilton, Ontario
More info..go here http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=957&whichpage=6
Men are the same as women.... just inside out !!(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.com%2Fhtml%2Fimages%2Fsmilies%2Fmini%2Fmini018.gif&hash=43d4f680fb1e52aecb14b539cb9eba2c)
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No, dark energy would be more like Einsteins cosmological constant, pushing things apart (working against gravity).
But there is growing doubt about both, even in academic circles...
http://www.economist.com/science/displayStory.cfm?story_id=2404626
and let's face it, my previous remarks cannot be discredited in any sense. You have to take a lot of things on faith in modern cosmology if you wish to make ends meet (and a large hammer to get them pesky square pegs into those round holes would be handy).
I find that a highly unsatisfactory state of affairs, to put it mildly.
I highly respect what I've seen so far from gsmollin's approach, but he has no ground to stand on here, since there is no empirical data. It's all conjecture, and more a matter of consensus, or lack of it.
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quote:
Originally posted by chimera
...I highly respect what I've seen so far from gsmollin's approach, but he has no ground to stand on here, since there is no empirical data. It's all conjecture, and more a matter of consensus, or lack of it.
There is good empirical data for dark matter. First of all, the rotational rates of nearby galaxies can't be explained without it. The rotational rates and movements of far galaxies also can't be explained without it. If the universe weren't more massive than it appears to be, there is no explanation for the observed universe being observable at all. Many other details of cosmology demand a universe far more massive than what we observe.
Since we observe only stars and highlighted nebulae, the other mass is known as dark matter. What it is, is still somewhat mysterious. There has been a lot of work done to determine what it is, and there will be much more before this is found, but it has to be out there. There is, indeed, a wealth of empirical data that it exists. There is not so much empirical data on what form this matter takes. You can Google dark matter and get a lot of reading material about it.
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There is a lot of empirical, raw data. (period)
How you interpret it, depends on your theory and subsequent observations.
After your interpretation, you cannot say the empirical data is proof on that ground alone, though.
As soon as a new, and better theory is achieved, or one of the current flavours makes it to prominence, you will probably say the 'empirical data' is proof of THAT theory, however conflicting with the previous.
In that sense we have to be careful in not going into circles, which normally works as a kind of refining process, but can also go haywire in the sense it feeds on delusion, which can also reinforce itself, however wrong.
"When it comes to deciding what kind of exotic particles may make up the non-baryonic dark matter, however, there may be a hint of 'weakness', in that different particle physicists favor different exotic particles. Moreover, as far as I know, there has not been a direct detection of these exotic particles."
Koji Mukai (for Ask a High-Energy Astronomer with help from Dr. Mushotzky")
taken from
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970731a.html
(and google hits don't say a lot about something's existence. millions of urls can be wrong, indeed.)
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Chimera,
I'm having some trouble understanding what your point is. You are clearly a nay-sayer to dark matter, and that does not bother me. I don't understand what your take on this would be. Maybe you could elucidate.
The link you provided was not too much help. It is about calibration issues for interpreting CBR data. I can understand there will be such problems, and it is nothing new. I don't see the authors disputing the existence of dark matter, so much as disputing its form. There is still debate over whether the dark matter is cold or hot.
The analogy (in that article) with the Ptolemic theory of the universe was pretty lame. In the beginning, the Ptolemic explanation was good. It provided adequate structure for many centuries. The bad rap the Ptolemic theory gets is because it was so successful for so long that it became dogma. As better observation came along, and better theories were developed, they were suppressed by the Roman Catholic Church. The Pope did not want to hear that he was not at the center of the universe.
The replacement of one scientific theory by a better one, is a natural progression. A few years ago, the fundamental particles were the proton, neutron, and electron. Now we have different theories, and different fundamental particles. Years from now there will be better theories with perhaps different fundamentals. The empirical support for these theories will contain both direct and indirect evidence. Both types are good. All this is called scientific progress. There is no shame in an old theory being found incomplete, or overly complicated, and replaced by a simpler, better explanation. The only shame is in not keeping an open mind, and sticking to an old favorite explanation as dogma.
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quote:
Originally posted by neilep
...and what it might feel like ?..
I had a run in with some the other day neil so I can tell you... forget all these people who actually know what they're talking about.
First it is what I can only describe as the touch of god upon your cheek follwed by a swift backhand across the other cheek and the sensation of having your crotch set on fire. Then everything goes dark and you wake up in hospital sometime later.
Quite an experience!
Tim
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quote:
Originally posted by gsmollin
Chimera,
I'm having some trouble understanding what your point is. You are clearly a nay-sayer to dark matter, and that does not bother me. I don't understand what your take on this would be. Maybe you could elucidate.
The link you provided was not too much help. It is about calibration issues for interpreting CBR data. I can understand there will be such problems, and it is nothing new. I don't see the authors disputing the existence of dark matter, so much as disputing its form. There is still debate over whether the dark matter is cold or hot.
The analogy (in that article) with the Ptolemic theory of the universe was pretty lame. In the beginning, the Ptolemic explanation was good. It provided adequate structure for many centuries. The bad rap the Ptolemic theory gets is because it was so successful for so long that it became dogma. As better observation came along, and better theories were developed, they were suppressed by the Roman Catholic Church. The Pope did not want to hear that he was not at the center of the universe.
The replacement of one scientific theory by a better one, is a natural progression. A few years ago, the fundamental particles were the proton, neutron, and electron. Now we have different theories, and different fundamental particles. Years from now there will be better theories with perhaps different fundamentals. The empirical support for these theories will contain both direct and indirect evidence. Both types are good. All this is called scientific progress. There is no shame in an old theory being found incomplete, or overly complicated, and replaced by a simpler, better explanation. The only shame is in not keeping an open mind, and sticking to an old favorite explanation as dogma.
Sorry for not responding earlier, was migrating my stuff over to another system... my new love is called Debian Unstable, that's one certainty. Best linux distro so far...
Anyway:
my problems with dark matter is that it is 'ordered' to fit a certain bill. It was not discovered. It's conjecture.
The analogy with epicycles is not so nice maybe from a scientist's viewpoint, but has striking analogies nonetheless. It was accepted for nigh on 2500 years by people, even though they KNEW there were things clearly wrong with it. One of its predictions/implications was that the moon would change distance by a factor 7 from the Earth, each month. This clearly never happened, but it was a useful theory nonetheless.
It's the holding on to a theory when it is no longer productive, that indeed is the crux here. Is dark matter (still) a productive theory?
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"...my problems with dark matter is that it is 'ordered' to fit a certain bill. It was not discovered. It's conjecture. ..."
I'm still having trouble understanding your point. Physical theories are almost always "ordered" to fit a bill. Most times, experimental evidence shows discrepancies to the existing theory, and it is either extended, modified, or scrapped to fit the observations. Dark matter is an excellent case of that. The rotational rates of galaxies do not obey the Keplerian rules. They rotate more like solid bodies than stars orbiting around a center of mass. This is well documented to high precision using Dopler studies. So what do we do? We could modify gravitational theory, and that has been proposed as a competing explanation. Or we could propose that extra mass, that we cannot see, is in the galaxy.
Another instance is big-bang primordial nucleosynthesis. It was one of the great success of big-bang theory, because it explained the 75% hydrogen - 25% helium - trace lithium makeup of the universe when nothing else can. One problem, was that to get the proper mix of primordial isotopes, only ~5% of the mass of the universe can be accounted for. It was throught that the universe was open because of that, however, an open universe would have flung itself apart long ago. Space would curve hyberbolically, and we could not see distant galaxies, let alone the CBR. So there must be another kind of matter holding the universe together. Other theories, such as inflation, also predict a flat universe, but theory still accounts for only a fraction of the observable mass. Here is a case where theory is predicting that there is more mass in the universe than the theory itself can account for. The theory is predicting it's own limitations.
So we have dark matter. There are numerous candidates for it, but we don't have a definite answer. One thing seems sure- it does not react electromagnetically. It seems to be gravitational only, although weak force has not been ruled out. With such weak forces involved, there is little chance of direct observation in the near future, except gravitationally.
"...It's the holding on to a theory when it is no longer productive, that indeed is the crux here. Is dark matter (still) a productive theory?"
If it isn't productive, then I invite the alternate explanation that answers so many other questions as well.
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quote:
Originally posted by gsmollin
[1] Physical theories are almost always "ordered" to fit a bill.
[2] So we have dark matter. There are numerous candidates for it, but we don't have a definite answer. One thing seems sure- it does not react electromagnetically. It seems to be gravitational only, although weak force has not been ruled out. With such weak forces involved, there is little chance of direct observation in the near future, except gravitationally.
[3] If it isn't productive, then I invite the alternate explanation that answers so many other questions as well.
[1] I think there is a difference between trying to explain a phenomenon - normal procedure indeed - and *inventing* something to gloss over discrepancies in a theory.
[2] Since we needed a stop-gap for our gravity discrepancy, there would be 'gravitational' observation? Sorry. Circular thinking, IMO.
No gravitational observation, just a corollary of underlaying theory... there is so much attraction, hence there must be so much mass. If it's not observed, it must be dark, since there MUST be so much mass... etc.
[3] No, I don't need to come up with a better explanation, frankly. Even when invited friendly, or as is more usual, in the form of a challenge. You are one courteous discussion partner, btw. [:)]
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At this silly hour I find this thread captive reading (as i would any other hour of course !)....From what I understand (which is very limited) Dark Matter is a term for a 'thing ' that is only detectable by it's effect on gravity, because it does not radiate light.I assume DARK MATTER is a generic term yes ? If Dark Mattter does not exist then is there an alternative conclusion to what 'it ' is that effects the visible tangible matter ?
It's generally accepted that dark matter and dark energy account for the vast majority of the Universe yes ?...and this is deduced by observation of the visible matter......and it's a logical rational deduction because it's a conclusive explanation eh ?.....
So, if Dark Matter does not exist, what's effecting the 'Light Matter' ?
Thanks for a great thread people.
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Neil, there is more than one explanation for the observed phenomena. Even the big-bang theory itself has competition in the steady-state theory. One other explanation for observed gravitational phenomena modifies the inverse-square law of gravity at large distances. There are also several other general relativity theories, although one by one they have fallen by the wayside with better observation. There is good evidence that we have to allow for dark matter. It shows up in nearby observations. The Pioneer spacecraft may even have discovered dark matter in our own solar system. Nobody knows for certain if the dark matter is made up of "hot dark matter", such as neutrinos, or if it is an exotic form of matter, "cold dark matter". There is quite a debate on that point. I'm not active in that field, so I don't have an opinion.
The argument for dark energy is not as good. It relies on some supernova measurements, and I personally feel the evidence is not good enough. The WMAP spacecraft has also returned data supporting the dark energy hypothesis, but brings us no closer to understanding what it is. It's been called the "repulsive force of the vacuum". I have understood this effect on the subatomic level, but I don't see it on the cosmic level. This leaves me 1/2 like Chimera.
Chimera, I have been courteous because you have been too. I think we understand each other and have respect for our differences. It's nice when that happens. Too often I've been sucked into those pointless sarcastic flame wars. Not here, of course; it was in Newsnet groups where there are much larger numbers of ignorant people present, who apparently delight themselves in their scatagorical abilities.
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A nice change indeed, same here. Flames are bad karma for everyone involved.
As to supernova measurements: I did some research on that recently and was pretty disgusted with the way they treat that raw data, and base their conclusions on heavily filtered stuff. Really un-scientific behaviour if I ever saw it. Don't trust anything coming from that dept. on face value anymore.
Anyway, your frankness forces me to divulge I do have an idea of what causes the missing gravity, but its more green than ripe, so bear with me.
They have observed phenomena in the Earths atmoshpere at very high altitudes involving plasma and very high levels of gamma radiation that makes some suspect there are short-lived mini black holes inside the plasma.
http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/0202513
and
http://seti.it-tallaght.ie/astrophysics/
Now imagine that happening on a interstellar scale: large clouds of that stuff could add up. Strangely, I've never believed in enormous black holes (they violate the rules in my book), but those mini ones make sense, and rapidly decay with interesting side-effects, all in accordance with what we know of Hawking radiation and all that, fortunately.
It might just mean we've been looking in the wrong place...
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Funny update: black holes are dark energy stars, according to George Chapline (respected researcher from Lawrence Livermore Lab)
http://xxx.arxiv.org/pdf/astro-ph/0503200
NOW I'm confused... [:)]
The living are the dead on holiday. -- Maurice de Maeterlinck (1862-1949)
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After reading that paper I don't feel any closer to an understanding between GR and QM. Chapline's hang up with universal time is typical of a QM viewpoint. Requiring universal time is QM's failing, not GR's. The 1957 conference decided QM was wrong on macro scales because all experiments have shown GR to be right. Time is not any more universal than space. QM will have to shuck the fixed spacetime it requires before it can grow beyond microscopic understanding.
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Spot on as usual IMO, gsmollin. My thoughts exactly. Time's inherent to locale.
The living are the dead on holiday. -- Maurice de Maeterlinck (1862-1949)
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Dark Energy/Matter is somewhere between a noun and a verb, it is trying to name the action/result of processes that we can see, but cannot fathom the carrier of, just like gravity[}:)]
Mmmmm - Dark Energy/Matter (E=mc^2 therefore c^2=E/m)
Its Dark Light^2[:D]
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As I said in another thread, only half-jokingly, gravity and vacuum expansion might well turn out to be two faces of one and the same coin. Remember all primordial forces probably interconnect, and although I'm not proposing something along the lines of if-you-only-push-here-it-bulges-there, other things have been found that do tend to be that simple, which is one semi-good reason for overlooking it in the first place. [:)]
The living are the dead on holiday. -- Maurice de Maeterlinck (1862-1949)
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Not being a physicist I have no firm beliefs 1 way or another on dark matter/energy. I'm too much of a layman to be able to understand the raw data & scientific papers & form an opinion. I am, however, surprised that cosmic strings haven't yet reared their ugly head in this thread (strings - thread.. no pun intended).
Now, I may have got this wrong but I thought there was a theory that there were "cracks" in space where these massive strings lurked: crossing thousands, or millions, of light years & that these could be the seeds of galaxy formation.
Also, there is, I believe, a train of thought that gravity is trans-dimensional & its source is locked away in some dimension other than those we can percieve. If that's the case, could not the phenomenon referred to as dark matter be the result of something - particles or energy - being locked up in another dimension and only becoming apparent by its gravitational effects? If so, surely there will never be any empiric evidence for its existence & it will forever continue to exist as no more than a theoretical concept.
It wasn't me - a big boy did it & ran away
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Personally not too taken with strings, especially not with Calabi-Yau manifolds... think our understanding of QCD and QM is still far from complete. We're still missing an essential thing or two in that department, and that stuff has been around for 40 years, and has some amazing insights that have proven right time after time.
The living are the dead on holiday. -- Maurice de Maeterlinck (1862-1949)