Science
05 Mar 14
07 Mar 14
Originally posted by FabianFnasMuch much less. I am afraid I cannot give an exact figure, but definitely less than a millionth of a gram per litre. The universe is mostly an empty place.
Is it uniformely distribuated through the space, even in our vicinity, like within the solar system?
And what would then the average density be? Like one kg / litre? More? Less?
07 Mar 14
Originally posted by Metal BrainBut does it affect our measurement of the mass of the black hole using he orbit of a star?
The spin affects how close stars orbit black holes.
This is a variable that needs to be taken into account and you have not.
I am not convinced.
It is very relevant. I have proved what you "work out" can be wrong because the spin variable makes those calculations relative.
Relative to what?
07 Mar 14
Originally posted by FabianFnasIt depends on the atom nucleus, although in that case it is more accurate to say the nucleus decays to another nucleus.
And what is its half-time within a atom nucleus? Is it stable there? If so, why there and why not when it's free?
(I like this discussion, I learn a lot!)
Generally speaking (and oversimplifying a bit), "stability" is determined by whether there is a lower energy state available to the system and whether such a lower energy state is accessible without violating certain conservation laws (e.g. conservation of momentum).
08 Mar 14
Originally posted by twhiteheadHow can you not be convinced? Are you saying that the frame dragging does not exist? Are you an idiot?
But does it affect our measurement of the mass of the black hole using he orbit of a star?
[b]This is a variable that needs to be taken into account and you have not.
I am not convinced.
It is very relevant. I have proved what you "work out" can be wrong because the spin variable makes those calculations relative.
Relative to what?[/b]
08 Mar 14
Originally posted by KazetNagorraGreat simple explanation of stability!
Generally speaking (and oversimplifying a bit), "stability" is determined by whether there is a lower energy state available to the system and whether such a lower energy state is accessible without violating certain conservation laws (e.g. conservation of momentum).
08 Mar 14
Dark Matter is probably not Anti-Matter right? What I was reading is that the boundary between where matter and antimatter met would be detectable because of the energy that would be given off at the boundary where the two meet and would be a constant annihilation of the two.There would be emissions that would be detectable. Something is pushing around the visible mass however hence dark matter
Manny
08 Mar 14
1 edit
Originally posted by menace71Dark Matter could not possibly be Antimatter for several reasons. One such reason would be that antimatter is not 'dark' which means, if it made up most of the mass of the universe just like dark matter is supposed to, it should be at least as visible as the matter we see.
Dark Matter is probably not Anti-Matter right? What I was reading is that the boundary between where matter and antimatter met would be detectable because of the energy that would be given off at the boundary where the two meet and would be a constant annihilation of the two.There would be emissions that would be detectable. Something is pushing around the visible mass however hence dark matter
Manny
There would also be the thorny problem that, if dark matter was antimatter, that would mean we would extremely precariously be surrounded my massive amounts of the dangerous stuff which would beg the question of why we haven't yet been annihilated by it a long time ago!
09 Mar 14
Originally posted by humyYour statements make sense if you view anti-matter the same way as matter in that it attracts other matter, but what if it repels?
Dark Matter could not possibly be Antimatter for several reasons. One such reason would be that antimatter is not 'dark' which means, if it made up most of the mass of the universe just like dark matter is supposed to, it should be at least as visible as the matter we see.
There would also be the thorny problem that, if dark matter was antimatter, that would ...[text shortened]... stuff which would beg the question of why we haven't yet been annihilated by it a long time ago!
09 Mar 14
Originally posted by menace71Dark matter particles, if they exist, probably also have antiparticles, but those are not related to the antiparticles that we can currently observe. An anti-up-quark, for instance, is not dark matter by definition since it interacts strongly through forces other than gravity.
Dark Matter is probably not Anti-Matter right?
09 Mar 14
Well we do know antimatter is basically the same as matter but opposite charge right ? Like Electron / Positron so visibly it looks just like ordinary matter but it annihilates when it comes in contact with matter. I guess I answered my own question LOL so we really have no clue on what dark matter is other than we know that there is an unaccounted force acting on the mass that we do see in the universe.
Manny
09 Mar 14
1 edit
Originally posted by Metal BrainIf it repels then we would have surely already observed this with the antimatter experiments but we didn't observe this. In addition, even if it does 'repel' matter, antimatter still annihilated matter in the experiments so, evidently, it doesn't 'repel' well enough, at least in all our experiments to date, to stop contact and annihilation thus this still begs the question of why we haven't been annihilated yet (and this is not to mention the several other significant problems with the idea of dark matter being antimatter)
Your statements make sense if you view anti-matter the same way as matter in that it attracts other matter, but what if it repels?
09 Mar 14
1 edit
Originally posted by twhiteheadThe business of measuring or computing the mass of a star orbiting a black hole close enough to be effected by frame dragging is a valid point, if the drag is enough to effect the velocity of the star's orbit around the BH.
But does it affect our measurement of the mass of the black hole using he orbit of a star?
[b]This is a variable that needs to be taken into account and you have not.
I am not convinced.
It is very relevant. I have proved what you "work out" can be wrong because the spin variable makes those calculations relative.
Relative to what?[/b]
For instance, frame dragging is what delays the orbit of Mercury by such a tiny amount it was almost not measurable but it was one of the proof's of relativity when they first made the measurement. I think they knew about the tiny excess precession measured in 1915:
http://en.wikipedia.org/wiki/Tests_of_general_relativity#Frame-dragging_tests
Another related effect is called the Geodetic effect:
http://en.wikipedia.org/wiki/Geodetic_effect
Such effects are hard to even measure with our technology on masses like our sun but would need to be taken into account near the incredible bending of spacetime near a black hole where such effects would be extremely magnified, I suspect enough to alter the measured orbital velocity of a star unfortunate enough to get within grabbing distance of a black hole.
Space time itself is wound into a small spindle near a black hole so it makes sense such alterations of physics would have to be taken into account when trying to make such measurements as the orbital velocity of a star trapped by a black hole.
09 Mar 14
Originally posted by sonhouseBut we do not measure the obit of just one star, but rather a number of stars with various orbits, including highly elliptical orbits. Surely such frame dragging if significant would be detectable and could then be taken into account?
Space time itself is wound into a small spindle near a black hole so it makes sense such alterations of physics would have to be taken into account when trying to make such measurements as the orbital velocity of a star trapped by a black hole.
To what extent would it affect our estimate of a supermasive black hole?
http://en.wikipedia.org/wiki/Supermassive_black_hole#Milky_Way_galactic_center_black_hole
Wikipedia says the one in our galaxy was estimated from the orbit of a particular star, but then shows a diagram of the orbits of 6 stars.