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"Dark energy" and "Dark matter"...What is it?

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SoHiAllTheTime

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I was just reading a discovery magazine this morning and it was talking about how stars ONLY make up %0.4 of the space in the uni. They were talking about how %4 of the uni is something called “dark matter” and the other %96 is called “dark energy”, both of which we cannot see or detect what it actually is, we just know its there.

Before I get to the “dark” stuff, i want to say that I find it mind boggling that stars make up such a small % of all of the uni! That is crazy, and it almost makes my head spin trying to visualize it.

About this “dark matter/energy”, I have heard of it before, but have never really thought about it at all. I mean there is something that exists that we cant see/feel/ or detect, but yet we know it is there. Does anybody else find that mind-boggling? Maybe it’s just me but I can’t comprehend this concept for some reason…”Something” physically exists that we cant determine “what” it is, but we know it is there. Wow... So when we use the word “universe” we are actually talking about “dark energy”, because after all, it is what makes up %96 of the “universe”.

The uni is so amazing in so many ways that I cant even find words to describe my thoughts about it, does anyone else feel this way?


BTW, I had a much better post almost finished when my computer crashed and I lost it, so this post was kind of a shortened quick version of the last :\
 
When we look up at the sky with visual or radio telescopes, we see whatever is radiating sufficient light or radio waves for us to detect.

Dark matter is just not radiating enough of either for us to detect it.

It's not all that complicated.

As an analogy, think if a pair of heat-sensing goggles like you sometimes see in movies. If everything in the room was the same temperature, you'd see nothing. That doesn't mean nothing is there. We just couldn't see it.
 
Petersko said:
Dark matter is just not radiating enough of either for us to detect it.
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Thats not the way it was explained in the magazine...I dont have it on me, but according to it, it has nothing to do with how much it radiates, it has to do with the fact that we dont have any way of detecting what the substance atually is made up of.

Like with wind, we cant see it , but we know what it is. But with this dark stuff we DONT know what it is, it is a "substance" unkown to man. I find that amazing...I dont know, maybe its just me :\
 
SoHiAllTheTime said:
The uni is so amazing in so many ways that I cant even find words to describe my thoughts about it, does anyone else feel this way?
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i agree. i think part of the problem are the numbers involved. understanding the scale of the universe requires some numbers so large, it's hard to deal with them from the place we deal with numbers on a day to day basis.

alasdair
 
SoHiAllTheTime said:
The uni is so amazing in so many ways that I cant even find words to describe my thoughts about it, does anyone else feel this way?
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:D Yeah... I think that's what drives most everyone who goes into science. :D

Dark energy is especially weird -- it's this odd sort of anti-gravitational force, that's pushing space apart, making the universe expand at a faster and faster pace. It probably is something to do with the vacuum energy, but all our calculations of it come out terribly wrong. As in either you get no vacuum energy, or an energy 10^120 times larger than we actually see -- that's 10 with 120 zeroes after it. It's one of the greatest mysteries in physics today...

Dark matter is not quite as weird but still crazy... some of it is probably the cold, dark remnants of dead stars: brown dwarfs, and black holes. Some is probably exotic, mostly invisible particles that fill the universe mostly unbeknownst to us. There are good reasons to believe in something called supersymmetry, though no solid proof so far. (With a good amount of luck, we'll find some when the world's new huge particle accelerator, the LHC in Switzerland, starts up in 2007.) If supersymmetry is true, each type of regular particle has a corresponding 'superparticle,' a ghostly mirror-image of it... :)
I do not know what I may appear to the world; but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding of a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.
-Isaac Newton, 1642-1727
 
Petersko said:
http://www.eclipse.net/~cmmiller/DM/ <- If you're interested, here are some theories.

We can't see it because it doesn't emit enough light or radio waves. How can you argue that?

WHY it doesn't emit it is another question.

Anyways, that's why it's called "Dark" matter.
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dude, i am not arguing anything...I was just telling you what i read...Besides there are other things that dont give off light that we can detect, but that is what makes this different, it not only doesnt give off light, it doesnt give off ANYTHING at all that we can detect, but yet we know it is there. That is what i find amazing! I am not trying to argue whether it gives off light or not because that isnt the only way to detect something, it gives off NOTHING, but yet exists. Crazy.
 
Zorn, about the uni expanding, i read that people believe that someday it may retract and crunch everything together. I guess like a nuclear eruption does. What do you think about that?

BTW, i read the same thing you wrote about the numbers being way off (regarding the energy vacuum), they said each time they try to calculate this stuff the numbers are almost completely different from the last time. All this stuff just is so awesome it makes me want to get into the study of it all, but it all just seems way to intimidating!
 
as far as my understanding of dark matter goes, it was discovered when scientists found objects that seemed to be moving very oddly... they worked out where something should be to make the star move like that, and how massive it would have to be... but yet, they still couldn't fnd this "dark matter" that was making these stars behave so strangely... and that is about as far as we come to proving dark matters existance... it's alot like a black hole, just on a much smaller scale... we can't actually see the dark matter, only the effect it has on objects around it... we are, however reasonably certain that dark matter does exist, as the universe would be expanding much faster if the only matter out there was what we could see... another interesting fact, the universe must have at least 5 times the amount of dark matter as it does matter we can see for us to be living in a "closed" universe... that is a universe that will stop then start to fall in on itself... but if the univerese fails to reach that critical density, then we are living in an "open" universe, which will expand forever, long after the last star burns out...

Dark energy I am not as sure on, but I believe it refers to zero point energy, which is the most abundant energy in the universe... this energy exists on the quantum level between sub atomic particals... I'm not enitrely sure what role it plays, or even how it's percieved, but I know that it is a very promising energy sourse... scientists are working on ways to harness it as a clean, unlimited power source to power the world, and perhaps even future space ships if the technology can be sufficiently compacted...
 
Few cosmologists believe in the "Big Crunch" nowadays, as observations suggest that there is still too little mass to halt the universe's expansion; the addition of dark energy into the equation with observation actually indicates that the expansion is accelerating. In any event, current science suggests that the universe will eventually expand into a cold, dark, and by the reckonings of our times, lifeless void. But oh well...

By the way, there are still a few cosmologists who think dark matter is just a fudge factor...a new theory that a couple of cosmologists are toying with is that the nature of gravity itself may change at extremely weak accelerations. Others near the fringe think that dark matter may be the imprint of a phantom universe interspersed with our own, which we can't contact. The prevailing theory though, is that dark matter consists of some exotic, massive, yet almost completely unreactive subatomic particles, known as WIMPS ("Weakly-Interacting Massive ParticleS"). These have not been discovered yet, but experiments are underway to find them. In the past, they thought that a wandering population of brown dwarfs, planets, black holes and other stellar remnants in the galactic halo were the culprits--called MACHOS, by the way;) , for "Massive Compact Halo ObjectS"--but microlensing experiments seem to indicate that these are far too rare to be responsible.
 
but I know that it is a very promising energy sourse
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Perhaps zorn has some knowledge of this, but my understanding is that zero point energy as a source of usable power is pretty much espoused only by crackpots, marketers and scam artists.

And it certainly wouldn't be "promising", since no zero point contraption ever designed has produced a measurable net gain in power.

[edit]I guess I should say that no zero point contraption ever designed has produced a measurable net gain in power that was actually confirmed as being zero point in origin. Apparently some people have machines that claim to work, but have yet to be subject to any kind of rigorous scrutiny to see "how" they work.
 
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Zorn, about the uni expanding, i read that people believe that someday it may retract and crunch everything together. I guess like a nuclear eruption does. What do you think about that?
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Like Bel said, doesn't look like it's gonna happen. Up until 10-15 years ago, nobody really knew what the eventual fate of the universe was: it depends upon the universe's density. There's a critical density; if the universe is less dense than that critical value, it'll keep expanding forever, into a cold dark void. If the universe is denser, it'll eventually stop expanding and collapse into a "Big Crunch" like you said. (It's just like the escape velocity a rocket needs to escape Earth's gravitational pull.)

Anyways, until 10-15 years ago, all the evidence pointed to a universe with really close to the critical density, but we couldn't tell which side. But recent evidence -- finally confirmed by the WMAP results, which came out just this year! -- indicates that a lot of the universe is this "dark energy," which actually has somewhat of an anti-gravitational effect. So unless our current laws of physics turn out to be entirely wrong, the universe will not only keep on expanding, but at an ever-accelerating rate...

--

A good book if you're fascinated by this stuff (for non-scientists, no math/phys background required) is Steven Weinberg's The First Three Minutes. I've heard good things about Wald's Space, time, and gravity: the theory of the big bang and black holes but haven't looked at it myself. :)
Petersko said:
Perhaps zorn has some knowledge of this, but my understanding is that zero point energy as a source of usable power is pretty much espoused only by crackpots, marketers and scam artists.
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Naaa, that's pretty much it. I'd maybe add in "kooks and cranks."
 
^Wow. So it is expanding faster and faster? Wont that eventually pull things out of place? I cant understand how if it expands forever and keeps getting faster and faster that things wouldnt get "overstretched" or pulled out of place. What would make sense (to me) is if it did eventually start to "crunch", but i guess that isnt possible :\

Zorn, my next question is this...What is the uni expanding into? I mean if it is expanding, what exists prior to its expansion? Like, as the uni is moving "forward" what is ahead of it? It makes it sound like there is something "outside" of the uni, right?

If i am blowing up a balloon (which represents the uni expanding), the air inside the balloon represents the inside of the uni, all the stars, planets, and galaxy's, and the air outside the balloon would be the area where the balloon/uni is expanding into. Does anyone have any terms or ideas as to what that is?

There has to be something bigger than the uni if the uni is expanding or the uni wouldnt have space to expand into, right? So what is that area (outside the uni, that the uni expands into) called?
 
SoHiAllTheTime said:
^Wow. So it is expanding faster and faster? Wont that eventually pull things out of place? I cant understand how if it expands forever and keeps getting faster and faster that things wouldnt get "overstretched" or pulled out of place.
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Yups, it's expanding faster and faster. That won't tear things apart though: See, the dark energy that's driving the expansion is really, really weak. The amount of dark energy in a space 1000 times as big as the entire volume of the Earth is the about the same as is stored in a single AA battery. Not much. ;)

The only reason it has any noticeable effect at all is because it's present everywhere, and the universe is so incredibly huge. What happens is that it drives galaxies (actually clusters of galaxies) apart because there is tons of empty space in between them full of nothing except dark energy. But galaxies and smaller are virtually unaffected because the gravitational force holding them together vastly overcomes the small amount of dark energy they contain.

It's like what happens when you throw sand in the air on a windy day: the wind is powerful enough to scatter the grains of sand (galaxies) but nowhere near enough to tear the individual grains apart.
Zorn, my next question is this...What is the uni expanding into? I mean if it is expanding, what exists prior to its expansion? Like, as the uni is moving "forward" what is ahead of it? It makes it sound like there is something "outside" of the uni, right?
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Not quite. As far as we can tell, the universe continues on indefinitely. It looks pretty much exactly the same in all directions, as far out as we can see.

What we mean by expanding is that distances between things are increasing -- not that it's moving into new regions. It might well continue on infinitely and be expanding; even if it's finite though there doesn't have to be an outside because space might be "curved."

This picture helps me see it: each dot represents a galaxy here, (the red arriws are light emitted by the green ones right after the big bang.) Infinite but expanding.

cphotons.gif


There's some more discussion of this in these threads:
http://www.bluelight.ru/vb/showthread.php?s=&threadid=93066
http://www.bluelight.ru/vb/showthread.php?s=&threadid=103550

And if you're interested in this stuff, I highly recommend UCLA prof Ned Wright's site: http://www.astro.ucla.edu/~wright/cosmolog.htm

*especially* the FAQ at http://www.astro.ucla.edu/~wright/cosmology_faq.html

It's at a level non-scientists can understand, lots of stuff, and accurate.
 
Dark energy" and "Dark matter"...What is it?

It's unChristian matter and energy, stuff like the Koran, a porno mag, a speech by Howard Stern, me etc..
:p

(sorry Sohi, I just couldn't resist ;))
 
Zorn, it still seems (to me at least) that the uni is "expanding" and that there would have to be something for it to "expand" into. From the exapmle you posted, everything gets further and further apart from each other, so therefore it is getting larger. The box that surrounds the dots would HAVE to get bigger and bigger to be able to keep all of the dots inside of itself.

But you are saying the area "outside" the box does not exist? I cant see how that is possible (not that i am saying i dont believe you, but that i am not understanding)...I am going to check out those links...Is there a term or phrase in science that refers to this paticular subject? Thanks a lot!
 
SoHiAllTheTime - Why are you asking for a rerun of this topic?

Until you let go of the idea that the universe has to expand into something else, the point will continue to elude you.
 
^How could it not expand into something else? If it is expanding then there is something else for it to expand into...

Why should i let go of the idea? Because you or someone else says so? IF you dont like me trying to understand this concept and/or make sense of it, or even question it, then just skip over the thread and read something else.

The answer that the uni is expanding but not getting larger is not accpetable to me, maybe for you it is, but not me.

Do you have anything to add to the discussion? If so, i would love to hear it.
 
SoHiAllTheTime - Do you also use Tr6ai0ls4 as an online handle? If not, my apologies. Your posting styles seem somewhat similar to me. I thought it was you who participated in a large discussion about this very topic recently, and it was Tr6ai0ls4.

Regardless, go HERE - this topic was discussed at length.
 
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