Evidence Points to the Detection of Dark Matter

[peggygee]

Fascinating and exciting stuff particularly these two points.

"Dark matter is what created the structure of the universe and is essentially what holds it together. When ordinary matter falls into lumps of dark matter it turns into galaxies, stars, planets and people. Without it, we wouldn't be here," Gilmore said.

Some dark matter particles could explain why ordinary matter is not radioactive, while others may help scientists understand why time – so far as we know – always runs forward.

By the by, did folks get a chance to read some of the comments on the article
at the site, it read like some typical HA responses.

[trish]

If luminous matter (i.e. the stuff bright enough to see) were the only matter there is, the universe would have negative curvature; (i.e. the interior angles of triangles would sum to less than 180 degrees). Measurements indicate the geometry of the universe is nearly zero, which is further evidence that there’s a lot of matter in the universe that is not seen. Indeed, according to general relativity (if it’s right) for the universe to have its present degree of flatness about 70% would have to be dark and only 30% the normal stuff that observation accounts for. Without this extra 70% there probably would not have been enough gravitational “impetus” to draw the uniformly distributed matter of the expanding universe together into clumps that eventually formed stars, galaxies and the folks who inhabit them. This is what I think the commentator is referring to when she says, “Dark matter is what created the structure of the universe and is essentially what holds it together.”

I don't know what DM has to say about the arrow of time. I always thought time ran backwards, i.e. the future runs toward us and recedes behind us as the past.

I only made this thread so that if it turns out to be true, you can say you heard at HungAngels first.

[scroller]

Ummm... stuff like the following always really bothers me about stories like this. Last line of the main article:

Detectors in the mine will be upgraded in the new year before the search for more dark matter continues, Bauer said.

So in other words, they're in need of a bunch of money for refurbishing to continue the project, and they just happened to have a (statistically insignificant) detection right as their current funding/equipment runs out. Fancy that.

Reminds me a of the research facility in Antarctica that announced discovering signs of life on a meteorite from Mars at exactly the time their funding ran out.

[hippifried]

Sorry Trish. More hubris. Mathematics is an intellectual construct, & curvature doesn't change how many degrees are in a triangle as long as we count 360 in a circle. We can change that any time we please.

The truth is that we really don't know jack shit. We don't know how big or how old the universe is, or if there's even an age to measure. We don't know what gravity is. Einstein spent his whole life trying to define it & failed. We've never even seen a planet in another star system. There's mathematical evidence, based on the motions of some stars, so we just assume they're there.

I'm not saying that DM doesn't exist, but I don't see why it has to. Stars don't behave like mathematicle models because they're all different sizes & densities, & we can't really measure them accurately. Why can't there be open space? Who says there's a "structure" to the unicerse?

[trish]

You raise many interesting issues, hippiefried. More than can be adequately addressed in a single post. So I’ll just pick on one of two of your points.

I agree that mathematics is a mental construct. That is why mathematics is one of the few subjects in which practitioners actually prove results. In any particular mathematical field, a set of undefined terms (terms formally without meaning) are listed and a list of statements using those terms is also laid out for all to see. The statements in this list are called axioms (or in prior times postulates). The game is to define new terms from the undefined ones and derive other statements (called theorems) from the axioms using only logical inferences. In some modern geometries (Euclidean, Hyperbolic and Elliptic) the terms “point”, “line” and “plane” are entirely undefined. You can formally practice geometry without ever having in your head a notion of what they mean. The term “incident” is also an undefined term in modern geometry. However, a triangle is defined to be three points that are not incident to the same line. The points are called the “vertices” of the triangle. One of the axioms of Euclidean geometry is that given two points, there is one and only one line incident to both those points. If those two points are vertices of a triangle, the line to which they are both incident is called a side of the triangle. And so on (as Vonnegut would say). The entire subject makes no direct reference to points and lines a[s] ordinary language uses the terms and in that way geometry is entirely a mental construct.

In spherical geometry lines are in fact defined. They are the intersections of the sphere with planes that pass through the center of the sphere. We could call these spherical-lines, but in the context of spherical geometry they’re usually just referred to as lines. In spherical geometry the shortest route between two points lies along a spherical-line incident to both. Now just to help visualize things, imagine a sphere is given a reference frame like the one we use on Earth; there’s a north pole and a south pole, and equator and meridians. Imagine the zero degree meridian (through England). It intersects the equator at a ninety degree angle. So does the ninety degree west meridian (through Indiana). Together the two meridians and the equator determine (by definition) a spherical triangle. The sum of the interior angles is two[-hundred] and seventy degrees (not one and eighty). Yet there are still three-hundred and sixty degrees in a circle! All of this is of course still mathematical and therefore mental construction, though it’s all logically consistent even if sometimes surprising or counter-intuitive.

So what does this have to do with things like physics which purport to have something to do with the world beyond mental constructs; i.e. the real world the parlance of our times?

Well of course we use Euclidean geometry all the time in the real world. Instead of taking the term “line” to be meaningless, our everyday language assumes we know what lines are and how they behave. The assumption through the ages was that the things we call lines follow the axioms of Euclidean geometry. This is the geometry Newton ha[d] in mind when he penned the law of inertia. The law of inertia says the world-line (the graph of its position against time) of an object not acted upon by a force is a line. The world-lines of baseballs are [NOT] lines because baseballs are subject to the force gravity. The weird thing about gravity is that it’s universal. It doesn’t just act on particles with special properties or charges, it acts on everything. Einstein hypothesized an explanation. What if gravity isn’t a force but rather a manifestation of a different, more appropriate set of rules for the geometry of space-time; i.e. what if the assumption that the geometry that’s most applicable to “real-world” space and time isn’t Euclidean? Einstein kept the law of inertia, and just redefined a line in space-time to mean the path traced out by particle not acted upon by a force … and oh, gravity doesn’t count as a force. By this slight of hand, he essentially redefined the term line in space-time geometry so that Newton’s first law is automatically true and gravity is by definition a manifestation of geometry. This is the idea of general relativity (GR) in a nutshell. This simple recasting of the terms of physics might seem to be nothing but redefinition of terms. But this redefinition has consequences that differ from predictions of Newtonian physics. GR predicts th[at] clocks slow down as they near massive bodies, Newtonian physics makes no such prediction. Both GR and Newton predict that massive bodies will bend light rays th[at] pass near, but they make different quantitative predictions as to the amount of deflection. Newton predicts planets travel around the Sun in ellipses, though the orbits are perturbed in predictable ways if there’s more than one planet in the system. Einstein predicts the ellipse precesses even if there are no other planets perturbing it. Einstein predicts the gravitational lensing of images of distant galaxies by a massive galaxy between the observer and the objects of observation. What’s interesting is that all the observations we’ve made so far eliminate Newton['s] theory of gravity in favor of Einstein['s]. Does this mean we know GR is true? Of course not. But it is the best description we have so far. When we need or want to make decisions or venture answers to questions about astronomy, remaining consistent with GR is our current best course of action. This doesn’t prevent perfectly good scientist[s] from writing respected articles on modified gravity which contradict GR.

Back to triangles. Even though there are three-hundred and sixty degrees in a circle, GR predicts that near a massive object, like a star, if you form a triangle with three lasers beams the interior angles won’t add up to one-hundred and eighty degrees.

[edits in square brackets]

[BrendaQG]

What she said.

It's Geometry but it's not Euclidian, entry level geometry. The observed flatness of the universe only exist because there is just the right amount of matter-energy present.

Physics goes through phases where fudging becomes popular and acceptable. This last happened in the 1880-1920 time period. 40 years where something call Lumeniferious Aether was thought to fill all of space much the way Dark matter is now. Numerous numerous experiments had to fail to find it before the idea was abandoned. Even after Einstein's wrote about Special Relativity. He spent many more years as an unemployed physicist. Working in the patent office, or lecturing at various schools for very little money.

I predict that relatively soon dark matter will be considered the stupidest thing serious scientist ever considered.

[zlorg]

Sorry Trish. More hubris. Mathematics is an intellectual construct, & curvature doesn't change how many degrees are in a triangle as long as we count 360 in a circle. We can change that any time we please.

The truth is that we really don't know jack shit. We don't know how big or how old the universe is, or if there's even an age to measure. We don't know what gravity is. Einstein spent his whole life trying to define it & failed. We've never even seen a planet in another star system. There's mathematical evidence, based on the motions of some stars, so we just assume they're there.

I'm not saying that DM doesn't exist, but I don't see why it has to. Stars don't behave like mathematicle models because they're all different sizes & densities, & we can't really measure them accurately. Why can't there be open space? Who says there's a "structure" to the unicerse?

There're a few point here, most of them already replied by trish, but I miss a few ones.

You said: "We don't know what gravity is. Einstein spent his whole life trying to define it & failed." and well, we also don't know what is time or charge or whatever. Science is usually bad at these questions, but better in other as "how does it behave?". By the way, the very best definition you can give is an operational one. i.e. that "time is this thing measured by clocks and that make one day different uppon another". And so on with charge and the rest, we can try another but is easy to mess up.

This rests at the basement of physics; you supose that exists a world (outside our heads), you supose that there some kind of regularity on it , that we can achieve some knowledge about it applying scientific method and that is useful to write this knowledge using maths.

The last statement sets up the relationship between mathematics and the natural sciences. Sure, mathematics are a mental construct. But when we're saying that a given triangle can, o can not, sum 180 degrees for all three angles we're not talking about mental constructs (at least if you don't want to push a very extreme philosophical POW), we're talking about a thing in the real world (whatever it is) and maths are used here as nothing more than a set of tools or language or similar.

And I cut here, because I'm going offtopic. Soory for this lengthy text.

[hippifried]

Relative to what?

If you bend a line, it becomes an arc. The triangle still has three angles, but you're not using straight lines anymore. We can do that without being next to a large mass. But even if the wind catches your tape measure between stakes, the measurement is still figured as a straight line so that Pythagoras can get you that square corner laid out on the ground.

Look Professor Trish; I'm hot for teacher & all that, but I'm not going to pretend to understand high mathematics. It just seems to me though, that we're merely talking about measurement systems that we've invented to explain what's already there & what's already happening, within our limitations. We do rocket science every day in our heads without using a single number. Think about all the calculus that goes into catching a fly ball: You need to judge triangulation, velosity, trajectory, gravity, mass, wind, your own speed to get to where you need to be & all it takes to get that speed, etc... All done in a split second without a thought to the math. We just grok. Common sense works whether there's any science to muddle the thought process or not.

[trish]

The triangle still has three angles, but you're not using straight lines anymore. We can do that without being next to a large mass.

Near a massive object, such as a star, you can pick three points A, B and C. Then find the shortest route from A to B, the shortest route from B to C and the shortest route from C back to A. In ordinary parlance those routes are lines. The interior angles of the triangle just traced out fail to sum to 180 degrees. If to don’t want to call those shortest distance routes lines, that’s fine. The insight of general relativity is that the geometry obtained by thinking of these routes as lines is non-Euclidean and that this is the geometry that applies when one wishes to answer questions about the routes laser beams and material objects take passing near a massive object.

Relative to what?

The word “relativity” in Special Relativity merely meant that the laws of physics should be the same regardless of the inertial frame used to express those laws. This implies there are no “preferred” inertial frames and consequently the values of certain measured quantities (such as velocity) are relative to the inertial frame of the observer. In special relativity though one could say that Nature prefers inertial frames and physicists had a problem with this from the very start. For one thing, how does one decide whether your own frame of reference is inertial or not? Einstein pursued general relativity in part because of these problems and in part because he saw in their solution a way toward a new theory of gravity. In general relativity the laws of physics are to be expressed in the same way in all frames of reference. If a law is not invariant under a switch in frame of reference, then it’s not really a law of physics. At least that’s what Einstein was advocating. A shortcut way of saying this: there are no frames of reference which Nature prefers over others.

We just grok. Common sense works whether there's any science to muddle the thought process or not.

I have great respect for what we can grok but can’t seem to do with mathematics. But sometimes common sense is wrong in the last decimal place while physics gets that most recent decimal right. In fact that’s when the fun begins. Because then we get to reassess all our common sense notions of world and reformulate. It’s gets to be even more fun when science gets the next decimal wrong.

I'm hot for teacher & all that

And your presence on these boards is much appreciated. Whenever you post, if it's not right on the mark, then it's thought provoking.

[scroller]

Sorry Trish. More hubris. Mathematics is an intellectual construct, & curvature doesn't change how many degrees are in a triangle as long as we count 360 in a circle. We can change that any time we please.

You don't know what the hell you're talking about, and this is just the first droplet of you demonstrating that. Non-Euclidean geometry has been well-established for over 200 years now. For example, here is a picture of a curved surface creating a non-180 degree triangle:

http://en.wikipedia.org/wiki/File:Triangles_(spherical_geometry).jpg