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yifan
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It is said that most mass in the universe consists of dark matters which don't emmit light. What is the difference between dark matters and planets?
Thank u.
Thank u.
there's certainly a distniction between cold baryonic matter and baryonic dark matter,
I could be accused of being obtuse, because to be honest it doesn't matter wheehr or not you include cold gas as part of the dark mass as gas could only make up a very small amount of the dark mass, as gas in general is pretty easy to observe.mathman said:The above sounds confusing. The important distinction is between baryonic matter(visible or dark) that we all know about (it's what everything we experience is made of) and non-baryonic matter (known only by its gravitational effect).
I'd be very surprised if anyone deleted any of your posts meemoe_uk! Do you happen to recall which one(s) you think got deleted? Perhaps you kept a copy of them?? AFAIK, only Phobos, Janus, Greg, and chroot can delete posts here in the Astronomy and Cosmology area.meemoe_uk said:Sorry you feel the need to delete my posts.
I know you dark matter dudes get very upset when anyone opposes your undoubtably correct theory. Oh well, time will tell.
Nereid said:I'd be very surprised if anyone deleted any of your posts meemoe_uk! Do you happen to recall which one(s) you think got deleted? Perhaps you kept a copy of them?? AFAIK, only Phobos, Janus, Greg, and chroot can delete posts here in the Astronomy and Cosmology area.
Would you be so kind as to tell us who you consider to be 'dark matter dudes' who 'get very upset when anyone opposes [our] undoubtably correct theory'?
Leaving aside the question of whether I'm a 'dude' or not, I'm not married to any 'dark matter theory'! However, I do rather insist that those with a different view be able to account for the observations that are posited as evidence for dark matter.
Apart from MOND, do you have any alternatives to propose? As for MOND, how do you reconcile your support for the idea with observations that are clearly inconsistent with it?
Thanks mee, an interesting website.meemoe_uk said:Hi All,
Not an expert in physics, so I can`t give precise analytic reasons for why I support MOND and not DM.
But I can give common sense reasons...
DM been studied for at least 30 years, still no direct evidence for existence, still very imcompatible with observations. MOND gives far better predictions.
If you want to see why DM theory is so outclassed, the best webpages are at
http://www.astro.umd.edu/~ssm/mond/
which is in easy layman language, and is a very good summary of the problems in modern theorectical cosmology.
Most of the arguments I'd hold against DM are expressed properly there.
MOND cannot be considered anything other than a stop-gap theory, and that why so many love to hate it! For the many romantics, a theory must be all or nothing! But physics is physics, the best theory is the one that gives best results, no matter how ugly it is. Having said that, MOND isn't that ugly.
After they've digested everything on those webpages, anyone who still goes for DM, must be a fanatical DM dude, because, as it stands, it simply isn`t logical to stick with it.
shrumeo said:Look, we ASSUME whole truckloads of stuff about the universe and our theories about it. We ASSUME that the redder the light is from an object, the farther away it is, but no one has difinitively proven that, really. We ASSUME that the universe is expanding based on the first assumption. We ASSUME that the expansion is accelerating based on the second. We build on assumptions that sound so right, and MUST be true because they sound so right and fit nifty models.
Actually, the Hubble relationship (distance vs redshift) is pretty well established, with multiple types of observations giving consistent and (mostly) independent results.shrumeo said:Yea, ever since I heard of "dark matter" and "dark energy" I thought it was bunk.
Look, we ASSUME whole truckloads of stuff about the universe and our theories about it. We ASSUME that the redder the light is from an object, the farther away it is, but no one has difinitively proven that, really. We ASSUME that the universe is expanding based on the first assumption. We ASSUME that the expansion is accelerating based on the second. We build on assumptions that sound so right, and MUST be true because they sound so right and fit nifty models.
Yes, but ... while there are lots of questions and not a few inconsistencies, the approach is precisely to make predictions and go test them (through observation).Then we say, "this part of our theory matches pretty well with observation, so the other part MUST be true also. Our theory, based on this observation here, says that there must be 10 times more of something we've never detected than all the rest of the matter in the universe." When something like that happens, why the hell arent' we questioning the theory? Why aren't we doing our damnednest to rework the theory to fit observation? (I know, I know, that's what it feels like we're doing with this dark matter garbage.)
I'm sure I sound totally high here, but I must agree with anyone who wholly doubts the existence of the elusive 90% of the matter in the universe, especially if it has to be something exotic (90% of the matter in the universe wouldn't be exotic, it would be us that's exotic.)
don`t jump the gun.actually passing another with Gravity probe B,
What do you think the results from GPB will be? What predictions does MOND make about these results?meemoe_uk said:don`t jump the gun.
The GPB test will be the stiffest test ever for GR. There's a fair chance it won`t pass.
Great! Care to make an estimate of how much more?meemoe_uk said:I think GPB will detect more space warping than predicted by GR!
MOND? It doesn`t predict anything in the GPB test, no galaxys see.
correct, but then again it doesn`t incorparate any other bit of physics in any form either. It has no theoretical frame work at all. That is why anyone is free to propose theory for why MOND works. So I am justified in making this theory.IIRC, MOND doesn't incorporate relativity in any form.
It's not obvious to me how 'space warping' would account for galaxy rotation curves,
Dark matter is a hypothetical form of matter that is thought to make up approximately 85% of the total matter in the universe. It does not emit or interact with electromagnetic radiation, making it invisible to telescopes. Planets, on the other hand, are celestial bodies that orbit a star and do not produce their own light.
The main difference between dark matter and planets is their composition and behavior. Dark matter is believed to be made up of particles that do not interact with light, while planets are made up of solid materials and can reflect or emit light. Additionally, dark matter is spread out throughout the universe, while planets are more concentrated in a specific orbit around a star.
Currently, there is no known relationship between dark matter and planets. Dark matter is believed to play a role in the formation and evolution of galaxies, while planets are formed within solar systems. However, some theories suggest that dark matter could potentially influence the orbits and movements of planets in a solar system.
Scientists use various methods to study dark matter and planets. For dark matter, they use observations of gravitational lensing, galaxy rotation curves, and the cosmic microwave background radiation. For planets, scientists use telescopes and space probes to observe and gather data on their physical characteristics, orbits, and composition.
The study of dark matter and planets has unveiled many mysteries, such as the true nature and composition of dark matter, the formation and evolution of galaxies, and the potential for habitable planets beyond our solar system. It has also raised questions about the origin of the universe and the possibility of other forms of life in the vastness of space.