Dark matter and Dark energy

Reality Check said:
That is unlikely since there are no nearby universes.
Click to expand...

http://www.trustedlog.com/2007/11/26/parallel-universe-exists-we-have-evidence/ "Last August, astronomers working on the analysis of data being acquired by NASA’s WMAP (Wilkinson Microwave Anisotropy Probe) satellite announced that they found a huge void in the universe. A void is a region of space that has much less material (stars, nebulae, dust and other material) than the average. Since our universe is relatively heterogeneous, empty spaces are not rare, but in this case the enormous magnitude of the hole is way outside the expected range. The hole found in the constellation of Eridanus is about a billion light years across, which is roughly 10,000 times as large as our galaxy or 400 times the distance to Andromeda, the closest “large” galaxy. The dimension of the hole is so big that at first glance, it results impossible to explain under the current cosmological theories, although scientists put forward some explanations based on certain theoretical models that might predict the existence of “giant knots” in space known as topological defects. However, University of North Carolina at Chapel Hill physics Professor Laura Mersini-Houghton made a staggering claim. She says, “Standard cosmology cannot explain such a giant cosmic hole” and goes further with the ground-breaking hypothesis that the huge void is “… the unmistakable imprint of another universe beyond the edge of our own“ ... snip ... The implications of this possibility are obviously of huge importance for everybody, but it also has further relevance for the astrophysics community as it would bring support for the hotly debated string theory and other central debates."

:D
 
BeAChooser said:
http://www.trustedlog.com/2007/11/26/parallel-universe-exists-we-have-evidence/ "Last August, astronomers working on the analysis of data being acquired by NASA’s WMAP (Wilkinson Microwave Anisotropy Probe) satellite announced that they found a huge void in the universe. A void is a region of space that has much less material (stars, nebulae, dust and other material) than the average. Since our universe is relatively heterogeneous, empty spaces are not rare, but in this case the enormous magnitude of the hole is way outside the expected range. The hole found in the constellation of Eridanus is about a billion light years across, which is roughly 10,000 times as large as our galaxy or 400 times the distance to Andromeda, the closest “large” galaxy. The dimension of the hole is so big that at first glance, it results impossible to explain under the current cosmological theories, although scientists put forward some explanations based on certain theoretical models that might predict the existence of “giant knots” in space known as topological defects. However, University of North Carolina at Chapel Hill physics Professor Laura Mersini-Houghton made a staggering claim. She says, “Standard cosmology cannot explain such a giant cosmic hole” and goes further with the ground-breaking hypothesis that the huge void is “… the unmistakable imprint of another universe beyond the edge of our own“ ... snip ... The implications of this possibility are obviously of huge importance for everybody, but it also has further relevance for the astrophysics community as it would bring support for the hotly debated string theory and other central debates."

:D
Click to expand...
So you acknowledge that this cosmological theory quoted in the article is the correct one - not plasma "cosmology", "electric universe" or Big Bang cosmology? :D
 
Ziggurat said:
By coming together at a saddle point. Here, I'll make it easy. Consider the following field:
[latex]$\vec{B}=by\hat{i}+ax\hat{j}$[/latex]
where the hats are the unit vectors. This field has a saddle point at the origin. The divergence is zero, so it satisfies the magnetism version of Gauss's law for any and all values of a and b. If a and b are both equal, magnetic field lines along the diagonals will point towards the origin, forming a sort of X. If a is greater than b, then there will still be magnetic field lines which are straight and come together at the origin to form a sort of cross, but it will be stretched in the vertical direction. If a is less than b, it will be stretched in the horizontal direction. Now consider a field line starting at (x=-1,y=1). If a<b, this point lies above the X, and the field line passing through this point will connect to (x=1,y=1). If a>b, then (x=-1,y=1) lies to the left of the X, and the field line passing through this point connects to (x=-1,y=-1).

But the field satisfies Gauss's law for ALL a and b. So if we change a and b so that we go from a<b to a>b, then the field line passing through (x=-1,y=1) has experienced reconnection. And it does so by passing through a saddle point (when a=b) where it touches another field line, which is what I said before. There was even a little picture someone had posted showing how this happens, can't remember who.

Long story short: magnetic reconnection doesn't require any violation of Gauss's law. And once again, your math skills prove themselves inadequate to the task of comprehending electromagnetism.

attachment.php
Click to expand...
.
Having rediscovered your post, I thought I would try and comment, bearing in mind that my knowledge of reconnection (also called magnetic merging) isn't great (and others are welcome to have a free pop at my expense over this admission). In no particular order:
  1. That “the field satisfies Gauss's law for ALL a and b" is correct. But...
  2. The two cases (1) a<b and (2) a>b, (see your image above) respresents two static magnetic vector field, which must obey Gauss's Law
  3. However, the static field line vectors say nothing about the movement, and mechanism of reconnection.
  4. So if this is how "magnetic reconnection" is described, with static two-dimensional vector fields, then there is no violation of Guass's Law.
  5. However, if reconnection implies the breaking and reconnection of field lines, a process which implies the creation of open field lines, then I believe this does violate Guass's Law.
  6. In which case the term "reconnection" may mislead some people into thinking (incorrectly) that field lines (a) move (b) may break and reconnect (c) may "anchor" to certain points (d) may be "frozen into" a plasma.
And I think this was Hannes Alfvén's point; the term "Reconnection" may give the false impression that the process is understood.
 
iantresman said:
[*]That “the field satisfies Gauss's law for ALL a and b" is correct. But...
[*]The two cases (1) a<b and (2) a>b, (see your image above) respresents two static magnetic vector field, which must obey Gauss's Law
Click to expand...

And if a and b are time-dependent? Then it's not static.

[*]So if this is how "magnetic reconnection" is described, with static two-dimensional vector fields, then there is no violation of Guass's Law.
[*]However, if reconnection implies the breaking and reconnection of field lines, a process which implies the creation of open field lines, then I believe this does violate Guass's Law.
[*]In which case the term "reconnection" may mislead some people into thinking (incorrectly) that field lines (a) move (b) may break and reconnect (c) may "anchor" to certain points (d) may be "frozen into" a plasma.
Click to expand...

Semantic debates are about the most uninteresting debates one can have. EU folks seem to have confused a semantic debate with a physics debate. This is an issue of how to describe what's going on. It is not an issue of the actual math. The objection to magnetic reconnection always and ONLY centers around the language used to describe the fields. At no point do any of the critics object to the fields themselves, or show that they have nonzero divergence.

And as for fields being "frozen in", well, that happens with any good conductor, given the appropriate time scale. Plasmas aren't special in that regard. The time scale is set by how good the conductor is, and physically larger conductors are better conductors (the resistance scaling as 1/L).
 
Since I think I understand about 4% of the posts in this thread, and concede that 96% are clearly over my head, the following question may have been asked and answered already in this thread without me recognizing it, but...

If dark energy apparently has an anti-gravity effect on regular matter, would it be possible for a black hole to absorb enough dark energy to start itself evaporating?
 
bokonon said:
Since I think I understand about 4% of the posts in this thread, and concede that 96% are clearly over my head, the following question may have been asked and answered already in this thread without me recognizing it, but...

If dark energy apparently has an anti-gravity effect on regular matter, would it be possible for a black hole to absorb enough dark energy to start itself evaporating?
Click to expand...

Dark energy does not have an "anti-gravity effect on regular matter" since anti-gravity is unlikely to exist (it requires negative mass).
Dark energy increases the rate of expansion of space-time so that the universe is expanding faster than the calculations without dark energy. This has no effect on black holes or other matter.
 
Reality Check said:
Dark energy does not have an "anti-gravity effect on regular matter" since anti-gravity is unlikely to exist (it requires negative mass).
Dark energy increases the rate of expansion of space-time so that the universe is expanding faster than the calculations without dark energy. This has no effect on black holes or other matter.
Click to expand...
Why couldn't the black hole's absorption of dark energy cause the space-time in the vicinity of the black hole to expand to the point where the black hole would become less dense?
 
bokonon said:
If dark energy apparently has an anti-gravity effect on regular matter, would it be possible for a black hole to absorb enough dark energy to start itself evaporating?
Click to expand...

In can, in a certain sense, absorb enough dark energy to stop itself from evaporating...
 
bokonon said:
Why couldn't the black hole's absorption of dark energy cause the space-time in the vicinity of the black hole to expand to the point where the black hole would become less dense?
Click to expand...
My understanding is that dark energy is not something that can be absorbed, i.e. it is not the same as energy but dark. But as far a a black hole is concerned there is no difference between mass and energy (good old E=mc2). So any absorbed energy (dark or otherwise) will add to the black holes mass.
You should also note that density is not that applicable once a black hole has formed - the singularity containing all of the mass has zero volume and so infinite density.
 
Reality Check said:
My understanding is that dark energy is not something that can be absorbed, i.e. it is not the same as energy but dark.
Click to expand...

It's all clear now! :D

Reality Check said:
the singularity containing all of the mass has zero volume and so infinite density.
Click to expand...

Now now ... didn't we just get done talking about this? And the volume isn't zero because all theory says is that the mass will collapse to a Planck length. And that's not zero. Right?
 
BeAChooser said:
It's all clear now! :D
Now now ... didn't we just get done talking about this? And the volume isn't zero because all theory says is that the mass will collapse to a Planck length. And that's not zero. Right?
Click to expand...

Not all theories. Quantum Mechanics says there is no point in measuring lengths < a Planck length. Black holes are a feature of General Relativity and that allows lengths down to zero. Most scientiests say that something strange happens at < a Planck length and we need a theory to see what it is, e.g. quantum gravity.
 
Reality Check said:
Not all theories. Quantum Mechanics says there is no point in measuring lengths < a Planck length. Black holes are a feature of General Relativity and that allows lengths down to zero. Most scientiests say that something strange happens at < a Planck length and we need a theory to see what it is, e.g. quantum gravity.
Click to expand...

Thanks, that is a straight forward answer.

Look and learn BAC!

:D
 
You must log in or register to reply here.

Back
Top Bottom