[Ace]

STILL ONLY HAS ONE DIMENSION OF TIME

Time is a human concept to observe motion, most of the physics I've read about in Discover, etc. are now working on removing time which would allow for a grand unified theory, but then leads to more questions on why we're here in the first place. (much more then if time is a dimension and a true measure)

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Ace
Staff member FreeSpace Watch
 http://freespace.volitionwatch.com/

[Sushi mk. 2]

Alright, skimming the topic...

The definition of dark matter that I am familiar with is matter that does not emit detectable energy, and thus doesn't show up in conventional calculations of the total mass of everything floating around in the universe. So that includes quite a few things... black holes, black dwarfs, neutrinos, some kinds of dust clouds. Dark matter is NOT the opposite of matter- just like cold is not the opposite of heat. Heat is measured relative to absolute zero(on the Kelvin scale) and it can't go any lower than 0. Most dark matter discussions are in reference to "missing mass," the idea that the known universe doesn't seem to have as much stuff in it as various measurements can detect. All the stuff that we think should be there usually ends up under the category of dark matter.

Last I checked, there were two main camps on the state of dark matter: the "wimps" and the "machos." The Wimps go for the idea that most of the dark matter is contained in neutrinos and other subatomic particles spread throughout the universe- not very massive, but there's an awful lot of them, and their combined weight makes up a greater portion of dark matter/missing mass than actual stellar bodies like black holes and black dwarfs. The Machos take the opposite view- that most of the mass is in large clumps, consisting of things like black holes and black dwarfs. Mikheal, for example, seems to take that view.  

Anyway, the idea of "Dark energy" being associated with dark matter kind of bothers me, since it isn't consistent with the idea of dark matter at all. Sorry if I'm mishearing that. It looks like the discussion's gotten away from that idea anyway.  

Feel free to correct me if I've actually made an error somewhere- I haven't done this for a while.  

[mikhael]

 

Originally posted by Ace:
STILL ONLY HAS ONE DIMENSION OF TIME

Time is a human concept to observe motion, most of the physics I've read about in Discover, etc. are now working on removing time which would allow for a grand unified theory, but then leads to more questions on why we're here in the first place. (much more then if time is a dimension and a true measure)

Time is not merely a 'human concept to observe motion'. Time is a convenient simplification of a universal concept.

When we think about time, we think of it always marching forward. Events take place after causes. You push a teacup off a table (the cause) and it crashes on the floor (the event). We also think of time as 'duration'. This event took this much time, meaning 'this event started at this time, ended at this time, and the difference (the duration) is such'.

The problem is that 'time' isn't exactly either of these things. A specific 'time' is actually a point on a line and a 'duration' is actually a segment of the infinite line of time. Time is an axis of a multidimensional coordinate system, much like X, Y and Z of traditional 3-space. The main differences between time and the XYZ axes are that it only seems to have a positive end and has a distinct starting point. However, as all dimensions actually have a starting point at the Planck time and Planck length, all of them have a starting point and direction is strictly arbitrary.

The way humans look at time is strictly based on thermodynmics. Entropy increases, and thus an observable universal metre-stick exists by which to scale time. Since order never increases (well, it does increase, locally, but this is always overshadowed by the overarching increase of disorder everywhere else), we can 'see' time's passage. As Hawking said, broken teacups do not spontaneously reform themselves.

Sushi's mention of WIMPs and machos made me laugh. I had never seen the term 'macho' before as a back construct of 'WIMP'. WIMP stands for 'weakly interacting massive particles'. Its nice to know that in something, at least, I'm a macho.  

[wEvil]

id have to say WIMP is a more plausable theory.

The problem with massive clumped matter is gravity decays in line with the inverse square law.

Thus a "macho" model would only distort local space, not empty space, which in no way would provide enough mass to curve the universe.

The latest figures say about 5% of the matter in the universe is visible, i can understand maybe another 4% could be collapsars or cold masses...but 95%?!

The universe is only 15 billion years old, there hasnt been enough time for that many stars to collapse into enough matter to explain such a huge proprotion away.  A short-lived star might go for about 20 million years, a long lived star might last up to 10 billion.  It doesnt seem to hold up for me.

[mikhael]

 

Originally posted by wEvil:
id have to say WIMP is a more plausable theory.

The problem with massive clumped matter is gravity decays in line with the inverse square law.

Thus a "macho" model would only distort local space, not empty space, which in no way would provide enough mass to curve the universe.

The latest figures say about 5% of the matter in the universe is visible, i can understand maybe another 4% could be collapsars or cold masses...but 95%?!

The universe is only 15 billion years old, there hasnt been enough time for that many stars to collapse into enough matter to explain such a huge proprotion away.  A short-lived star might go for about 20 million years, a long lived star might last up to 10 billion.  It doesnt seem to hold up for me.

Last I checked, and I could be wrong, the visible matter in the universe totaled up to around 10% of the critical mass required to 'close' the universe.

Gravity does not 'fall off'. Its pull lessens as distance increases. All objects in a system gravitationally affect all other objects, no matter how far away. This effect may be great or it may be negligible, but it is still there. All of those effects, no matter how negligible add up to the total gravitational pull to 'close' the universe--if there is sufficient matter. If gravity 'decayed', in an expanding universe, gravity would never be enough to close the system.

Also, remember that not all dark matter consists of blackholes. Dark matter refers to all unobserverable mass, so black holes, dwarfs and neutraon stars in close orbit to their primaries, etc are 'dark' matter even though they are luminous. It has been estimated that MACHOs (I found the reference)  may take up as much as 35% of the unobserved mass. MACHOs are 'MAssive Cometary Halo Objects', and are thought to consist of burned out (not collapsed) stars and massive chunks of matter that did not become stars.

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--Mik http://www.404error.com
ruhkferret on ICQ/AIM

"Your guy was a little SQUARE! You had to use your IMAGINATION! There were no multiple levels or screens. There was just one screen forever and you could never win the game. It just kept getting harder and faster until you died. JUST LIKE LIFE." --Ernie Cline

[This message has been edited by mikhael (edited 01-22-2002).]

[CP5670]

I'm sort of learning towards the "MACHO" view. As mikhael said, the gravitional force always exists in the system as long as anything with mass exists, so the combined force might be sufficient to pull everything back together.

One other theory I have heard is that there might be an extremely massive black hole (masses of several galaxies combined, enough to account for most of universal mass) in the area that the big bang is thought to originally have taken place. After the explosion, some of the matter might not have gained enough momentum to fully escape the gravitational fields of the other nearby particles, which caused much of it to accrete together once again over time. As this object gained enough mass to pass the Oppenheimer-Volkoff limit and turn into a black hole, it might have drawn much of the surrounding material into it. The bodies of matter that had enough momentum from the bang to escape formed the galaxies and stars, but this "central" black hole might still be pulling on them.

[This message has been edited by CP5670 (edited 01-22-2002).]

[wEvil]

I did state that gravity decreases in line with the inverse square law, therefore the further away you are, the less it affects you.

35% is a massive amount of data, and surely if there were so many of these floating around they would have been detected by occluding stars the drift in front of relative to the earth?

[mikhael]

 

Originally posted by wEvil:
I did state that gravity decreases in line with the inverse square law, therefore the further away you are, the less it affects you.

The direct effect lessens, yes, but the gravity is still there, and thus the attraction between two objects, regardless of where they are in the universe, is never zero. Even you, here on earth, have a gravitational effect on a plant on a planet in the Greater Magellanic cloud.

 

35% is a massive amount of data, and surely if there were so many of these floating around they would have been detected by occluding stars the drift in front of relative to the earth?

The key here is that H in MACHO. Halo. The matter in question would exists in a halo on the outer edge of galaxies. We would not be able to see our own ring as it is whited out by the stars between us and it (as they are luminous and it is not) and we couldn't observe it occluding anything.


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--Mik
http://www.404error.com
ruhkferret on ICQ/AIM

"Your guy was a little SQUARE! You had to use your IMAGINATION! There were no multiple levels or screens. There was just one screen forever and you could never win the game. It just kept getting harder and faster until you died. JUST LIKE LIFE." --Ernie Cline

[wEvil]

my point is that gravity becomes a negligable force deterministically speaking at a certain point.

Of course my presence effects something on the other side of the universe, but even quarter the pressure of a single photon would negate that.

As for the halo theory...Halos up to 200,000 solar masses have been observed but I would assume that the most recent calaculations have already taken such large molecular clouds into account?

[Sandwich]

  You guys never cease to amaze me! Sheesh - I think I have a headache now...  

FYI, zero-point dark energy is the quantainium sublification of the inericate expultion inherent in every subloop and quiggle.  

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[wEvil]

then you edit your courgette, go to the slice modifier, boolean in your banana and lettice and after collapsing it and fiddling with the diffuse surface characteristics you should have a decent fruit salad

[Bobboau]

as for the gravity decreseing as you move away from it's sorce,
this is true as you are a static point on a sphere of effect that grows larger as you move farther away, however if you are a ring or sphere (sort of like the universe) the effect exerted on you to colapse you would remaind constant no mater how far you're perimiter reached (note the universe has these gravity sorces within it thus it never realy moves away from them)

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Bobboau, bringing you products that work.............. in theory

[mikhael]

Bah! Bobboau beat me too it.  

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--Mik
http://www.404error.com
ruhkferret on ICQ/AIM

"Your guy was a little SQUARE! You had to use your IMAGINATION! There were no multiple levels or screens. There was just one screen forever and you could never win the game. It just kept getting harder and faster until you died. JUST LIKE LIFE." --Ernie Cline

[Grey Wolf]

Just remember, there's no certainty that any particle will be where you expect it to be at any given time. And of course, you can't forget Schroedinger's cat.

[Bobboau]

poor kittie caut in limbo between life and death

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Bobboau, bringing you products that work.............. in theory

[CP5670]

lol

[Bobboau]

so, what is gravity?

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Bobboau, bringing you products that work.............. in theory

[mikhael]

 

Originally posted by Bobboau:
so, what is gravity?

Sure, ask the hardest damn question in all of quantum physics.  

We got all kinds of Gravity here, take your pick. We got Quantum Gravity, Supergravity, plain vanilla Gravity. We've got gravitational radiation, and gravitons (and gravitinos!).

Loosely speaking, gravity is the weakest of the four forces of nature, but has the longest reach and therefore has the most impact at the macroscopic scale. Its also the most elusive force, because it, when combined with other reasonably well understood theories of physics/quantum-physics, you get these nasty infinities that imply that the universe is a singularity (among other things).

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--Mik
http://www.404error.com
ruhkferret on ICQ/AIM

"Your guy was a little SQUARE! You had to use your IMAGINATION! There were no multiple levels or screens. There was just one screen forever and you could never win the game. It just kept getting harder and faster until you died. JUST LIKE LIFE." --Ernie Cline

[wEvil]

you forgot gravity waves

or they could be said to be the wave funtion of gravitons.

Either way...we havent detected them yet.  Most of the math after 1983 is pretty hard to verify with observation because we were pissing around with making movies instead of working on space telescopes.

[Setekh]

 

Originally posted by mikhael:
...that imply that the universe is a singularity (among other things).

The universe? Try the multiverse.  

As for the general idea of this discussion, I'm afraid I'm going to have to agree with Sandwich here. Positronic dongle what the thingy?