What is dark matter?: Philosophy Forums

Calendar

Quick Links open

New Posts Member List

Help

Philosophy Forums » Philosophy of Science » Science » What is dark matter? » What is dark matter?

What is dark matter?

What is dark matter?

smd42
Initiate

Usergroup: Members
Joined: Mar 23, 2008
Total Topics: 2
Total Posts: 11

Posted 03/23/08 - 10:32 PM: Subject: What is dark matter?	#1
What is dark matter? And quarks. What are they? Thanks very much.
_____________________ He felt that his whole life was some kind of dream and he sometimes wondered whose it was and whether they were enjoying it. There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.

Fergus Currie
Blind watcher of the sky

Usergroup: Members
Joined: Jan 11, 2008
Location: Athens Greece
Total Topics: 5
Total Posts: 143

Posted 03/24/08 - 03:46 AM:	#2
Dark matter is the name cosmologist gave to the force that would be required to align the observable facts about the universe with the current physical understanding of it. In other words, we observe an accelerating expansion of space yet our understanding of how matter works suggests that this expansion should be decelerating - in order to 'explain' this they proposed a 'new' force which, when added to the current understanding gives the observed results. This force is known as 'dark energy' and the matter connected with this energy is known as 'dark matter'. Dark, simply because we cannot as yet observe it, not because of any mysterious evil force or metaphysical implication. Quarks are subatomic particles - bits of atoms. Or rather bits of the bits of atoms. Atom is a word which literally means 'indivisible' from the Greek tome which means 'to cut' and the negative sign a- , as in amoral. It was first used by Demokritus over 2500 years ago to describe something that maintained it's properties even in the smallest amount. Today we consider the Chemical elements to be the equivalent of Demokritus's atom. Now we use the word rather loosely to describe the smallest particle of any chemical element that retains its identity amongst its constituent parts and arrangement thereof. The three basic constituent parts were described by Sir Arthur Rutherford at the beginning of the 20th Century as Protons Neutrons and Electrons. Later, as the field of particle physics advanced, even these constituent parts were discovered to have their own components. A quark is one of these components. More than 150 'subatomic' particles have since been discovered and the search still goes on. The Large Hadron Colider - an enormous machine which 'crashes' subatomic particles together and then tracks and analyses the 'debris' is looking for particles so small that they are sometimes not considered as particle at all but traces of energy. The most exciting search at the moment is for the so called 'Higgs Boson' Which was proposed in the sixties by Scottish physicist Peter Higgs. These particles are considered to be zero mass and, according to Higgs, they are responsible for the phenomenon of mass itself. But that's another story! FC Edited by Fergus Currie on 03/24/08 - 03:50 AM
_____________________ ...and so Achilles never reaches the tortoise. ...so never send Achilles to get fags!

Spiral-Architect
I, strange loop.

Usergroup: Members
Joined: Jun 17, 2004
Location: Israel
Total Topics: 20
Total Posts: 137

Posted 03/24/08 - 06:26 AM:	#3
If I might intervene - Fergus, your explanations are very comprehensive, would you mind elaborating a little bit about the Higgs Boson? thanks
_____________________ That young lady is one of the least benightedly unintelligent organic life forms it has been my profound lack of pleasure not to be able to avoid meeting. - Marvin

Fergus Currie
Blind watcher of the sky

Usergroup: Members
Joined: Jan 11, 2008
Location: Athens Greece
Total Topics: 5
Total Posts: 143

1 of 1 people found this post helpful Posted 03/24/08 - 07:38 AM:	#4
Thank you for the compliment about my explanation. The Higgs Boson (You'd better check wikipedia too for this one but here goes) Higgs proposes a field (an array of 'stuff') of very fine material which pervades the whole universe, not unlike the idea of Ether. His idea is that this 'material' has no mass as such but rather reacts to changes in energy differential. That means that if energy levels are higher in one place and lower in another the Higgs field will change so as to indicate this. Here's an analogy: Imagine a room full of people, these will act as our Higgs boson. Now imagine that a rumor (playing the part of energy) that I am posting about Higgs' bosons on Philosophy Forum, starts in one corner of the room. There is a little ripple of activity as the rumor spreads to the other side of the room. What carries this rumor? Well, the initiator of the rumor doesn't travel but some how the rumor itself reaches the other side by means of transfer through the medium of the people. It is this riffling or head-turning in the room (Higgs Field) which produces the perceptual impression of mass. Imagine now, if you will, a rumor that the king is coming! Now there is more head-turning, a veritable riot or rumor breaks out. The higher the 'energy', it seems, the more mass is perceived. This is Higgs tipping his hat to Einstein. Now, imagine this on a sub atomic scale. Between all the electrons, neutrons, protons etc and their neighbors are billions and billions of tightly packed Higgs bosons and they transfer energy from one particle to the other as in the rumor analogy. We just don't 'see' any of this since they are so small and also form a closed field. According to Higgs we assume that there is a vacuum and that action at a distance is the only explanation, but we are a wrong. Now the search is on to find evidence of the Higgs Field. When and if they find it, that may be enough to reconcile Quantum physics and Relativity, but that's another story! FC Now go check wikipedia to see if I'm bullshitting you. Edited by Fergus Currie on 03/24/08 - 08:02 AM
_____________________ ...and so Achilles never reaches the tortoise. ...so never send Achilles to get fags!

Spiral-Architect
I, strange loop.

Usergroup: Members
Joined: Jun 17, 2004
Location: Israel
Total Topics: 20
Total Posts: 137

Posted 03/24/08 - 08:15 AM:	#5
It's times like these that I wonder how neurobiology usually intrigues me more than physics. This is so abstract and arbitrary, it's beautiful Thanks for another well phrased explanation.
_____________________ That young lady is one of the least benightedly unintelligent organic life forms it has been my profound lack of pleasure not to be able to avoid meeting. - Marvin

Kwalish Kid
Tenured Poster

Usergroup: Members
Joined: Sep 26, 2004
Total Topics: 20
Total Posts: 2411

Posted 03/24/08 - 03:51 PM:	#6
Dark matter has been pinned down to more than simply a force that doesn't interact with light. From the available observations, we can be pretty sure that there is an extra mass-energy density roughly homogeneously distributed throughout the universe. This mass-energy density interacts with gravity like matter moving at non-relativistic speeds, that is, if it is broken down into particles, these particles are not moving at close to the speed of light. The particles do not interact through electromagnetism (or do so very, very rarely). It is suspected that dark matter is really particles that are similar to neutrinos and that interact through the Weak Nuclear force.
_____________________ "Scientific truth is always paradox, if judged by everyday experience, which catches only the delusive nature of things." - KM, V, P and P "A fishnet is made up of a lot more holes than strings, but you can't therefore argue that the net doesn't exist. Just ask the fish." - Jeffrey Kluger "…Love of God and compassion and empathy leads you to a very glorious place, and science leads you to killing people." -Ben Stein

Fergus Currie
Blind watcher of the sky

Usergroup: Members
Joined: Jan 11, 2008
Location: Athens Greece
Total Topics: 5
Total Posts: 143

Posted 04/01/08 - 02:03 AM:	#7
Kwalish Kid wrote: we can be pretty sure that there is an extra mass-energy density roughly homogeneously distributed throughout the universe. Actually, it's not. There is next to no dark matter near or around our own Milky Way galaxy. If it was, there would be about 90% more dark matter than normal matter right here in our backyard. So why do CERN have to spend billions of dollars trying to find (or create) just one tiny bit of the stuff? The main school of thought is that these are heavy subatomic particles, some up to 300 times the weight of a proton which can absorb photons and hardly reflect electromagnetic waves at all. There have been some interesting photographs recently of candidates for dark matter. I'll try to find a link to any thing on the net. FC
_____________________ ...and so Achilles never reaches the tortoise. ...so never send Achilles to get fags!

Kwalish Kid
Tenured Poster

Usergroup: Members
Joined: Sep 26, 2004
Total Topics: 20
Total Posts: 2411

Posted 04/01/08 - 06:33 AM:	#8
Fergus Currie wrote: Actually, it's not. There is next to no dark matter near or around our own Milky Way galaxy. If it was, there would be about 90% more dark matter than normal matter right here in our backyard. So why do CERN have to spend billions of dollars trying to find (or create) just one tiny bit of the stuff? Actually, it is more likely that there should be about 900% more dark matter (measured by energy density) than ordinary matter. (However, one should note that the homogeneity of cosmological dark matter is measured on a scale greater than that of galaxies.) And there very well could be. If the distribution is homogeneous throughout the Milky Way, then the influence that the matter has on the mechanics of our solar system is negligible. I would be interested to see the support you have to claim that there is no dark matter in our galaxy. Support for a measurement of a dark matter halo around (and through) the Milky Way can be found here: http://arxiv.org/abs/astro-ph/0506102v2
_____________________ "Scientific truth is always paradox, if judged by everyday experience, which catches only the delusive nature of things." - KM, V, P and P "A fishnet is made up of a lot more holes than strings, but you can't therefore argue that the net doesn't exist. Just ask the fish." - Jeffrey Kluger "…Love of God and compassion and empathy leads you to a very glorious place, and science leads you to killing people." -Ben Stein

Fergus Currie
Blind watcher of the sky

Usergroup: Members
Joined: Jan 11, 2008
Location: Athens Greece
Total Topics: 5
Total Posts: 143

Posted 04/01/08 - 07:21 AM:	#9
Here's a quote from the Wikipedia which supports the idea that the dispersion of dark matter is not even but it does refer to a much I higher amount of Dark matter in the Milky Way than I had originally thought so I apologize for misleading you. An interesting cosmological fact how ever shows just how much space is left for dark matter in any case. If you took all the stars in the universe and put them side by side they wouldn't even reach from here to Proxima Centauri, our nearest star 4.2 light years away! So when they say 'Space' they really mean space! Wikipedia wrote: Recently (2005), astronomers from Cardiff University claim to have discovered a galaxy made almost entirely of dark matter, 50 million light years away in the Virgo Cluster, which was named VIRGOHI21.[9] Unusually, VIRGOHI21 does not appear to contain any visible stars: it was seen with radio frequency observations of hydrogen. Based on rotation profiles, the scientists estimate that this object contains approximately 1000 times more dark matter than hydrogen and has a total mass of about 1/10th that of the Milky Way Galaxy we live in. For comparison, the Milky Way is believed to have roughly 10 times as much dark matter as ordinary matter. Models of the Big Bang and structure formation have suggested that such dark galaxies should be very common in the universe, but none had previously been detected. If the existence of this dark galaxy is confirmed, it provides strong evidence for the theory of galaxy formation and poses problems for alternative explanations of dark matter. Edited by Fergus Currie on 04/01/08 - 07:29 AM
_____________________ ...and so Achilles never reaches the tortoise. ...so never send Achilles to get fags!

Kwalish Kid
Tenured Poster

Usergroup: Members
Joined: Sep 26, 2004
Total Topics: 20
Total Posts: 2411

Posted 04/01/08 - 08:54 AM:	#10
When I say "roughly homogeneous", I mean roughly homogeneous in the same way that ordinary matter is roughly homogeneous. Though ordinary matter is obviously clumped together, on the cosmological scale, it is rather evenly distributed.
_____________________ "Scientific truth is always paradox, if judged by everyday experience, which catches only the delusive nature of things." - KM, V, P and P "A fishnet is made up of a lot more holes than strings, but you can't therefore argue that the net doesn't exist. Just ask the fish." - Jeffrey Kluger "…Love of God and compassion and empathy leads you to a very glorious place, and science leads you to killing people." -Ben Stein

You don't have permission to post.

Please login or register.