the university I work at it is required to spent a significant portion of your budget on library fees. The library uses these fees to pay for the journals, which nobody reads because the content is generally available online (though the author's homepage or through the ieee or acm sites). Some journals even offer free access!
Not really. Most online journals charge $$$. You pay the library fees, the library pays a subscription to these online journals. You can read them off your browser with your university's domain name, but not anywhere else. It may be transparent to you, but try accessing one of the journals with a browser running from home for example. These things cost bombs.
I don't know about IEEE ( I think it is not free). But the astrophysical journal, the citation index, astronomy and astrophysics, physrev etc..are not free.
Yes, I think that ___-ism is the root cause which undermines our collective belief in ___-ism and post-___-ism. Hence, current society gravitate towards ___-ism with a vengence.
It is sad, perhaps, but such ___-vistic ___-ism is an important facet of our ___-ism beliefs. Hence, our dillemma.
We have reached a stage in our development where facts and beliefs are intertwined in both post-___-ism and pre-___-ism thinking. It is impossible to untangle the Giodion Knot without resort to ___-ism, thus we resigned ourselves to ___-visitic thinking.
Pluto is NOT mostly ice : it has the density of TWICE water (and ice is less dense than water). It has a rocky crust! It has an atmosphere! It has a moon! What more can you ask?!
This Tyson fella should be brought up to the next American Astronomical Society (AAS) meeting and asked to repent.
When I read the Hawking's BHOT in highschool, heady with plans to start a career in physics, I wanted to believe I understood it.
But no, I don't understand a single thing : it's utterly incomprehensible.
Now, I _am_ actually doing physics in grad school, and understood the "nuts and bolts" a bit more, I still think that BHOT is one of the worse popular science books ever written about fundamental physics ever. It's terrible.
Anybody who claimed they learned a great deal, or understood clearly what Hawking meant, was either (a) BS-ting for the sake of having an ego boost OR (b) a genius.
I figured that the reason BHOT becomes a bestseller is because people are more fascinated by Hawking the Man himself than his physics (which is while of extreme high quality, is no where near as dominating as those of an Einstein or a Dirac).
GWB : let's send clear submiluminal messages to the Russkies that God is on our side!
Al Gore : I think we have a 76% chance of convincing the Russians there is a 23% probability of destroying the world if we go to war over this. And that has about 62% chance of happening.
Ronald Reagan : We will vanquish the evil empire. The bombs will start dropping immediately.
There is a singularity in the OV equation at R=2m(R). This is a result of the coordinate system we uses, and is not a physical singularity so no worries.
>During the formation event (typically a >supernova), if the collaspe forces (gravitation, >implosion) exceed the neutron degeneracy forces, >there's nothing to stop the continued collapse >(through higher densities) to a black hole.
Well, it's not due to "higher densities".
First, 2 facts to clear up some of the stuff of the previous post(s):
(a) Neutron stars always have densities that are less than nuclear density (i.e. the density of a nuclei, about 10^-15 g/cm3). The point is that there is no "smooth" transition from finite to infinite density : the collapse is catastrophic and highly unstable.
(b) The standard calculation of a "chandrasekhar mass" of a neutron star uses the so-called Oppenheimer-Volkoff equation (which Mitra is questioning : I have not read his paper since I'll let the bigger guns shoot him. There are _a lot_ of crazy people out there....), combined with an equation of state for fermions. In a standard "non-GTR" calculation, a mass of about 6 solar masses is obtained for collapse to BH. In a proper OV-GTR calculation, a mass of about 2.5 solar masses is obtained.
Now, my point : "mass densities" no longer has any meaning at high gravitational fields since the fermions no longer just contribute mass, their mass contributes to increasing curvature which modify the metric. This relationship is highly nonlinear (kind of a "feedback" thingie I suppose. In standard white dwarf Chandra mass calculation, the metric is always fixed in the weak-field Newtonian limit). Usually, in the weak-field limit, increasing density will increase the degeneracy pressure, so adding mass to a fixed radii will increase the pressure. However, in strong fields adding mass pass a certain point will actually reduce pressure because of the OV equation :
dp/d(rho) = (m(R)+4piR^3)/R(R-2m(R)) (set G=c=1 as usual, and rho = density)
Note the denominator R-2m(R). Usually in weak fields, dp/d(rho) >1, since R>2m(R) so adding mass will add pressure. However, at a certain fixed m(R), R2m(R), and adding mass will _decrease_ the pressure instead.
It turns out that the critical density when this happens actually is less than the nuclear density.
That's a good question that even veteran cosmologists get it wrong (I recalled Alan Sandage I think, this year's Cosmology Prize winner making the same mistake!)
Here is a short primer (without much Jargon I hope) :
The BB DOES not happen at a single point necessarily, contrary to popular belief (and the blasted "primeval atom" picture which is totally wrong). Whether or not it happened at a single point depends on the "curvature" of the Universe.
Currently, the latest results (Cosmic Microwave Background) points to a "flat" Universe, which means that the curvature is zero (a balloon has positive curvature, a table has no curvature). Now , a balloon has a "bounded" surface area : i.e. it is finite. But the flat space we lived in is infinite. Thus, an infinite space, extrapolating backwards the finite age of the Universe, does not have a "single point" start.
The point of all that is to tell you that to impress you that when we look "deep", we are both looking "far" and "into the past". The idea is that "curvature" warps space-time into a continuum, so "far" and "into the past" is not separable : 6 billion light years away is not the "distance light will travel in 6 billion light years _given_ the Universe is static and not expanding." Distance has no meaning without the time component (I know it sounds woozy, and I can't visualize it either : it's all in the equations and I just work at them.)
The 6 billions LY quote in the article is probably the "luminosity distance". Astronomers use the term "luminosity distance", a _defined_ concept with the curvature of the universe embedded in. So
if new data shows a different curvature, the 6 billion LY will have to be revised.
To blow up your brain a little, think about this :
What is the furthest thing you can see?
It is a sad state of affairs to see posts like these from reasonably well educated people.
How the hell does GR and QM filtered into Moral Relativism?! Moral Relativism is a creation of Humainities with a political agenda (yeah, blame the progressives!). Science makes no judgements on Morals or Ethics, she just seeks the truth.
Your ignorance towards what Science is has led you to fear it, and then blame it for the ills of the world. It's very sad. Maybe you should have taken a Physical Sciences degree in College. Then perhaps you will see Science for what she is : a wonderful adventure where Nature is the playground, and the finding the Truth is the game.
Sagan once said,"I prefer the ugly truth then comforting fantasy."
Slashdot Mirror
I guarantee you : your vegetable oil will burn like crazy, as the black spot on the roof of my kitchen will testify.
Man, those things burn like hell.
the university I work at it is required to spent a significant portion of your budget on library fees. The library uses these fees to pay for the journals, which nobody reads because the content is generally available online (though the author's homepage or through the ieee or acm sites). Some journals even offer free access!
Not really. Most online journals charge $$$. You pay the library fees, the library pays a subscription to these online journals. You can read them off your browser with your university's domain name, but not anywhere else. It may be transparent to you, but try accessing one of the journals with a browser running from home for example. These things cost bombs.
I don't know about IEEE ( I think it is not free). But the astrophysical journal, the citation index, astronomy and astrophysics, physrev etc..are not free.
Won't they set up us the bomb first??!
Actually, nothing. I'd rather find out that believe in anything. My post was a joke btw.
Yes, I think that ___-ism is the root cause which undermines our collective belief in ___-ism and post-___-ism. Hence, current society gravitate towards ___-ism with a vengence.
It is sad, perhaps, but such ___-vistic ___-ism is an important facet of our ___-ism beliefs. Hence, our dillemma.
We have reached a stage in our development where facts and beliefs are intertwined in both post-___-ism and pre-___-ism thinking. It is impossible to untangle the Giodion Knot without resort to ___-ism, thus we resigned ourselves to ___-visitic thinking.
(Inspired by the Prof Sokal).
I Want to believe.
You need to get to at least 7 km/s to get into orbit. THat's 1000 times more than a "jet liner" flies.
Energetically speaking, there is negligible "weight" saved by collecting Oxygen from the atmostpher flying at "jet liner" speed.
The actual calculations are left to the student. But I bet a lot of pop (I don't drink) on it.
.
Their idea is to use standard hydrogen-oxygen rockets with the O collected from the atmostphere.
Blame Canada?
for making pencils so I can copy books....
/. editors might be sloppy lately, but the titled did state "SOME demote Pluto....".
So RTFH (RTF Headline)
Pluto is NOT mostly ice : it has the density of TWICE water (and ice is less dense than water). It has a rocky crust! It has an atmosphere! It has a moon! What more can you ask?!
This Tyson fella should be brought up to the next American Astronomical Society (AAS) meeting and asked to repent.
Besides, nobody is going to listen him anyway.
When I read the Hawking's BHOT in highschool, heady with plans to start a career in physics, I wanted to believe I understood it.
But no, I don't understand a single thing : it's utterly incomprehensible.
Now, I _am_ actually doing physics in grad school, and understood the "nuts and bolts" a bit more, I still think that BHOT is one of the worse popular science books ever written about fundamental physics ever. It's terrible.
Anybody who claimed they learned a great deal, or understood clearly what Hawking meant, was either (a) BS-ting for the sake of having an ego boost OR (b) a genius.
I figured that the reason BHOT becomes a bestseller is because people are more fascinated by Hawking the Man himself than his physics (which is while of extreme high quality, is no where near as dominating as those of an Einstein or a Dirac).
So there.
GWB : let's send clear submiluminal messages to the Russkies that God is on our side!
Al Gore : I think we have a 76% chance of convincing the Russians there is a 23% probability of destroying the world if we go to war over this. And that has about 62% chance of happening.
Ronald Reagan : We will vanquish the evil empire. The bombs will start dropping immediately.
>Ironic that nuclear bombs are much more likely to go off today than 30 years ago, but pols don't worry about it much
/. crowd seemed so gleeful when they bash them.
How do you quantify "much more likely"?
Such rhetoric is typical of a piece not well researched, but written by ear instead.
I am always amused by Katz's pieces : they resemble mega-trolls.
No wonder the
It's 10^(15) g/cm3 not -15. (silly me)
There is a singularity in the OV equation at R=2m(R). This is a result of the coordinate system we uses, and is not a physical singularity so no worries.
>During the formation event (typically a >supernova), if the collaspe forces (gravitation, >implosion) exceed the neutron degeneracy forces, >there's nothing to stop the continued collapse >(through higher densities) to a black hole.
Well, it's not due to "higher densities".
First, 2 facts to clear up some of the stuff of the previous post(s):
(a) Neutron stars always have densities that are less than nuclear density (i.e. the density of a nuclei, about 10^-15 g/cm3). The point is that there is no "smooth" transition from finite to infinite density : the collapse is catastrophic and highly unstable.
(b) The standard calculation of a "chandrasekhar mass" of a neutron star uses the so-called Oppenheimer-Volkoff equation (which Mitra is questioning : I have not read his paper since I'll let the bigger guns shoot him. There are _a lot_ of crazy people out there....), combined with an equation of state for fermions. In a standard "non-GTR" calculation, a mass of about 6 solar masses is obtained for collapse to BH. In a proper OV-GTR calculation, a mass of about 2.5 solar masses is obtained.
Now, my point : "mass densities" no longer has any meaning at high gravitational fields since the fermions no longer just contribute mass, their mass contributes to increasing curvature which modify the metric. This relationship is highly nonlinear (kind of a "feedback" thingie I suppose. In standard white dwarf Chandra mass calculation, the metric is always fixed in the weak-field Newtonian limit). Usually, in the weak-field limit, increasing density will increase the degeneracy pressure, so adding mass to a fixed radii will increase the pressure. However, in strong fields adding mass pass a certain point will actually reduce pressure because of the OV equation :
dp/d(rho) = (m(R)+4piR^3)/R(R-2m(R)) (set G=c=1 as usual, and rho = density)
Note the denominator R-2m(R). Usually in weak fields, dp/d(rho) >1, since R>2m(R) so adding mass will add pressure. However, at a certain fixed m(R), R2m(R), and adding mass will _decrease_ the pressure instead.
It turns out that the critical density when this happens actually is less than the nuclear density.
I think it's Net Access, not email.
I think we need to pour hot grits down Timothy's pants.
Try xxx.lanl.gov for the preprints.
It is.
PhysRev is Slashdotted!!!! Yay!!!!!!!
The furthest thing you can see is the Cosmic Microwave Background Radiation! 5 pts for Good Try.
That's a good question that even veteran cosmologists get it wrong (I recalled Alan Sandage I think, this year's Cosmology Prize winner making the same mistake!)
Here is a short primer (without much Jargon I hope) :
The BB DOES not happen at a single point necessarily, contrary to popular belief (and the blasted "primeval atom" picture which is totally wrong). Whether or not it happened at a single point depends on the "curvature" of the Universe.
Currently, the latest results (Cosmic Microwave Background) points to a "flat" Universe, which means that the curvature is zero (a balloon has positive curvature, a table has no curvature). Now , a balloon has a "bounded" surface area : i.e. it is finite. But the flat space we lived in is infinite. Thus, an infinite space, extrapolating backwards the finite age of the Universe, does not have a "single point" start.
The point of all that is to tell you that to impress you that when we look "deep", we are both looking "far" and "into the past". The idea is that "curvature" warps space-time into a continuum, so "far" and "into the past" is not separable : 6 billion light years away is not the "distance light will travel in 6 billion light years _given_ the Universe is static and not expanding." Distance has no meaning without the time component (I know it sounds woozy, and I can't visualize it either : it's all in the equations and I just work at them.)
The 6 billions LY quote in the article is probably the "luminosity distance". Astronomers use the term "luminosity distance", a _defined_ concept with the curvature of the universe embedded in. So
if new data shows a different curvature, the 6 billion LY will have to be revised.
To blow up your brain a little, think about this :
What is the furthest thing you can see?
Define it for us then.
It is a sad state of affairs to see posts like these from reasonably well educated people.
How the hell does GR and QM filtered into Moral Relativism?! Moral Relativism is a creation of Humainities with a political agenda (yeah, blame the progressives!). Science makes no judgements on Morals or Ethics, she just seeks the truth.
Your ignorance towards what Science is has led you to fear it, and then blame it for the ills of the world. It's very sad. Maybe you should have taken a Physical Sciences degree in College. Then perhaps you will see Science for what she is : a wonderful adventure where Nature is the playground, and the finding the Truth is the game.
Sagan once said,"I prefer the ugly truth then comforting fantasy."
I guess you prefer the other one.