The Ur-Quan Masters Discussion Forum

http://www.sciencedaily.com/releases/2006/08/060821133930.htm (http://www.sciencedaily.com/releases/2006/08/060821133930.htm)


You were saying something Deus? ;)

I'm not sure I understand that this is "direct proof" Dark Matter is out there, and meets the definition that has been made for it. It sounds like their calculations are off (perhaps because these collision-ers are so distant and so it is just an educated guess what they are made of,) or some unknown force is at work over there. Perhaps its actually Dark Energy, Zero Point Energy, Prauna, The Force, the Uhl, Alien gas miners, etc. :)

There's two things from the article that seemed weird to me:

"dark matter, which is invisible and can only be detected through its gravity"

"the dark matter was not slowed by the impact, because it does not interact directly with itself or the gas except through gravity."

This doesn't sound a lot like dark "matter" to me. But if it is, that last quote proves it is really "Dwarf" Dark Matter! :p

Matter is stuff which weighs something even when it is stopped. In other words, it moves slower than the speed of light.

If there is matter which does not have a significant coupling to the electromagnetic, weak, or Strong fields, then it would be nearly interactionless.
This is not at all farfetched -- Neutrons do not have much coupling to the electromagnetic field. Electrons do not have any coupling to the strong field at all. Neutrinos are only coupled to the weak field.

So, it's reasonable to suppose that there is something else which isn't coupled to any of the above. But it would still weigh something.

I thought weight was more about how something was effected by gravity or something along those lines, and mass was what stopped matter from ever being able to exceed the speed of light. I didn't know that anything that didn't have one of these two things necessarily had to move at or faster than the speed of light, though either.



But does this mean Dark Matter would be completely uneffected by interactions with light and itself/matter?

On mass vs weight you are correct that there is a difference. However, anything with mass will weigh something, so it works out the same in this case.

Anything with no mass can have no energy unless it is moving at the speed of light, exactly (e.g. photons). A weak exception is granted for particles with extremely short lifetimes (e.g. gluons), as the mass of a particle is constrained to its nominal mass only via resonance. If the particle doesn't last long enough for the resonance to really knock off all the other masses, then it can have a different mass than its nominal mass.


Dark matter would  be coupled via gravity at least; there could also be very weak couplings. Like, if they occupy a fourth 'generation' of quarks, they would undergo normal forces, but just not much with our kind of matter. If they are supersymmetric partners, or are nucleonic axions, then they could undergo normal forces with ordinary matter, but only at such high energies that we haven't been able to probe it yet.

I suppose black suns can exist as well then ...

They prefer African American suns.

I thought it was 'pigmentally enhanced suns'  ;)

Our sun is quite typical in that it is black; any other kind of star would be anomalous to the point that it would require new physical theories to explain.

If you're wondering what I'm smoking, keep in mind that black is the condition of having an emissivity of 1 across the spectrum. If the other object is cool, it will appear dark. If the object is hot, it will appear bright.

So, when iron begins to glow red, a physicist would say that it remains black.

Hey that's that "black body radiation" I heard about. Never quite figured it out. Why the "black" in the name?

Because it doesn't reflect any light?

Black is the color which absorbs all light, right?

Well, the universe (more or less) has time-reversal symmetry. What's the reverse of absorbing light? Emitting light!

So, black objects are also the best at emitting light.

We do not normally see this because almost everything we see does not emit light itself (at least, not thermally), but instead reflects it. In order for us to see the emitted light of an object, it would have to be hot enough to emit in the visible spectrum, which begins around 500 celsius (around 1000 fahrenheit).

Yeah, I haven't posted in, like, forever. but thats not the point.

Anyway, Dark matter is a misnomer. You see, Scientists don't quite understand that light travels faster away from gravity wells, such as planets, stars, and UrQuan Dreadnaughts.
When  taken into account, these pockets of dark matter seem to dissapear

Its just ignorence, really.

WTF? Scientists don't understand the rules that... scientists... made... oh, wait, that doesn't make any sense at all.

So, do you care to explain the way that galaxies are suspiciously failing to fly apart under ther internal momentum, which is what Dark Matter's job is, mainly

So then scientists have a collective consciousness? Thought scientists often disagreed on many theories' accuracies, I did.



I thought that super massive black holes were responsible for keeping galaxies together?



It got layed off, black holes will do the same job for half the pay. ;)

Possibly a stupid question, but my field is electronics/heavy industry so understandable.

What is the difference between dark matter and antimatter? And if they are different, what would the result of their interaction be?
Also, if dark matter's existence can be proven (I'm undecided either way) would it have practical application?

Context, dude. The claim was posited that every scientist was unnecessarily postulating dark matter because they did not even understand basic elements of relativity. If at least one astrophysicist scientist were competent in their field, this claim is trashed.



No, it's not enough. More to the point, it would make galaxies look very different than they actually look. Galactic rotation profiles are indicative of a distributed mass, not a central point mass.



A similar job, sure. But you can tell the difference, and this isn't the work of black holes.

Every kind of particle - electron, proton, neutron, photon, etc. has a particle which is its 'anti'. There are anti-electrons (a.k.a. positrons), anti-neutrons, etc. They have a variety of their properties reversed. In particular, charge. Mass, on the other hand, is not reversed.

So, if you have an anti-electron, it has +1 electron charge (as opposed to -1 for electrons). This means it is involved with electromagnetic interactions.

We have seen antimatter. We are making antimatter. Antimatter occurs naturally in small quantities in the upper atmosphere, but in general there is not very much of it at all.

This is due to one of the more notorious properties of antimatter, that it is capable of annihilating with the same kind of ordinary (non-anti) matter on contact (it doesn't need to do this right away, but in a matter-dominated environment, antimatter will not last long). When this happens, the mass of the two particles is released as energy in photons.

On the other hand, dark matter (if it exists) is ubiquitous. There is more dark matter than any other kind of matter, by several times. It doesn't have electric charge, though it may be involved in the 'weak' interactions that cause nuclear fission. We can't make it (yet), and we have never seen it directly.


Anti-dark-matter particles would annihilate with non-anti-dark-matter particles, probably via the weak interaction. Which means it would probably happen verry slowwwly.


Depends what the particular properties are. Even if it's really useful for something, the apparatus for creating and manipulating them will be enormous, so it will only be used on extremely large projects.

Alas, that would explain why there is so much more dark matter than normal matter. It would also help the theory that the spreading of the universe accelerates, because there is still plenty of anti-dark-matter to reduce the amount of (dark) objects with mass, and thus their gravitational pull. Is this already a real theory yet?

And if so, why has science come up with Dark Energy? If there wasn't even enough matter to explain universal binding forces, why did something else need to be created that does the opposite?

I approve of this way of naming things.  It makes everything better. Now if we could only work a void in with that non...

Yours truly

non-void-non-anti-Lukipela

Thank you for your input. It was most enlightening.

We've known about positrons for a long time, haven't we?
I wonder what the opposite of a neutral charge would be. An anti-neutron would be... interesting.

Heh - I wonder what hybridising nanotechnology and antimatter technology would result in? Or an antimatter fusion reaction, i.e. an antimatter sun? Forgive these fancies, as I mentioned before, I'm totally out of my tree here.

My mother was an English teacher, and all of my siblings and myself have a heavy mathematical/scientific/linguistic background, so translating something like non-anti-etc is a simple matter of maths. Not always accurate, but almost guaranteed to have hilarious results when inaccurate. Almost.

Juffo-Mugz

It's made up (http://en.wikipedia.org/wiki/Anti-neutron) of anti-quarks. Rather than just ordinary non-anti-quarks.

Finally I get Terry Pratchett's joke about the five flavours of magic particles, based on the quark flavours!

Time to flex my science muscles...Heres what I have a problem with...Remember when people didn't know about the ionisation of gas to produce light and thus had no handle on lightning? They invented gods to explain it, lacking the laws to explain it scientifically. Dark matter is something of the same. The article is saying that they've discovered gravity with no source, which MUST mean dark matter, this substance they invented because they lack the laws to fully explain the gravity of the universe.

Gravity, according to string theory (which I've started to warm up to recently) is the only one of the 4 fundamental forces which is not 'tied' to this membrane (basically M theory states that the universe is contained on a membrane in a higher dimensional order and we are stuck to the brane like paint to paper and cannot escape). THerefore, this explains the dramatic weakness of gravity compared to the electromagnetic forces, as most of the gravitons that are emitted by mass is escaping our branes and potentially showing up in other branes nearby. Therefore it is not hard to imagine that gravitons from a large graviton emitting location (black hole...?) on another brane is showing up as a gravitational anomaly on our brane, which is what has occured in this article.

I used to be a doubter but string theory is really starting to come together now.

Umm... dark matter == Zeus. Wow.

Note, if you have these other 'branes', and gravity is leaking, then the contents of these other branes is... DARK MATTER.

Whoa, that was just too shocking, I've got to rest and dismantle my altar to the supersymmetric top quark.

dark matter as the 21st century equivalent of ancient deities, for the purpose of explaining odd phenomena? Hmmm.....

actually, this concept does make sense. Back then, we didn't even know that we didn't know. Now we know that there are huge gaps in our knowledge...

aaargh, now I have a headache...

string theory? how does that work?

Let's consider a simple string theory, it has only 3 dimensions -- two spatial, and time. To large-scale observers in this system, they would only see one dimension. Why? Because one of the two spatial dimensions is 'compact'.

What does that mean? Take a garden hose. The outer surface of the hose are the spatial dimensions of this space. One way, there's a lot of room to work with. In the other, you go a short distance and you end up where you started.

Now, you can wrap rubber bands around the hose. Each rubber band is a particle. You can have them go around one time, or two times, or three times... etc. Each of these ways of wrapping changes the behavior of the band, so that it acts differently. So, different wrappings are what make the various fundamental particles different.

Of course, it's more complicated than that! Instead of one compact dimension, our theories call for around seven. There are all sorts of ways that you could wrap particles up in these dimensions, going around one, then another, looping around a third and then returning. The details of the topology (i.e. how the space is connected to itself) of these dimensions determine the rules of the universe.

Here's 3 hours of video explaining just that and more. Warning, some pretty heady stuff here, but it is presented in layman's terms so it's not too difficult to understand.

http://www.pbs.org/wgbh/nova/elegant/program.html

I'm curious, what are your opinions on the theory of Modified newtonian dynamics (http://en.wikipedia.org/wiki/Modified_Newtonian_Dynamics) and the proposed theory of Tensor-vector-scalar gravity (http://en.wikipedia.org/wiki/TeVeS)?
I read an article about these theories and thought they seemed like neat solutions, but I don't know enough about physics to say if they can account for everything and/or are reasonable.

Tenser-vector-scalar gravity breaks several "rules" of conventional gravity.

Yes, that's kind of the point...

I don't really like Modified Newtonian Dynamics. The dark matter explanation seems perfectly suitable, and this additional evidance lends yet more weight to it. There are also some galactic rotation curves that don't seem to make sense with TeVeS gravity.
We might learn more on this matter soon, but for now, I wouldn't count on TeVeS gravity being correct.
I wonder how TeVeS gravity would impact universal curvature and explansion models?

I may be a high school physics teacher, but I am no physicist. That said:

A common misconception is that anti-particles are the same as regular particles, but they have opposite charge. But we know there are anti-neutrons, so that doesn't work. A better description is anti-particles are the same as regular particles, but experience time in the other direction.  I cannot defend this statement except to say that I got it from a real physicist who makes a living looking for neutrinos and teaching particle physics at a good university.

My last year at that school left me seriously questioning ideas of truth and knowledge - Schroedinger's cat, and all that jazz leave me completely weirded out.

Both the neutron and the antineutron have no charge, and the opposite of no charge is no charge.
But the neutron isn't an elementary particle. A neutron consists of two down quarks and one up quark. An antineutron consists of two anti-down quarks and one anti-up quark.
The quarks that form the antineutron do have opposite charge of those of the regular neutron.

They aren't exactly the same, but they're awfully similar. Another difference beside the one mentioned by meep-eep is that... well, let me back up a little. Neutrinos are peculiar particles in that they only come in one 'handedness', that is, they spin only one way in respect to their direction of motion. Anti-neutrinos have this backward as well.

Also, there are some more subtle asymmetries which are harder to describe, buried in the way that antiparticles mix quark flavors.


This is a kind-of-okay description under certain circumstances, like if you're only interested in a momentary look at the mathematics of their interactions. However, once you get into a large enough system that entropy makes sense, it really screws around with the concept of time. Most physicists I know, including myself and also including my quantum field theory professor, think this description is pretty awful. He stressed that the field equations maintain causality, he showed how they do. We had to show how a different set of field equations maintained causality as part a homework assignment.

Now, the time-reversal symmetry, as an abstract tool, is an extremely useful description; but that does not mean that  the particles actually are time-reversed.


It does that more than it needs to because of the weird interpretations that people have come up with. To a great extent, these interpretations are optional.

Schroedinger's cat is one of them, kind-of. The state of the universe contains some live cat and some dead cat, whether or not we look. But when we look, the parts of us that go with the live or dead cat are no longer similar.

The cat is not saved or killed by our looking at it.