Martin

Blike, I wish there were a little tick mark or check that appears by threads that I've written to... [Edit: Cap'n R responded to this and solved my problem. Thanks Cap'n]

If I had it to do over I would order from Amazon.co in the UK. Postage from UK to US is not all that bad and i would get the cheap UK price (21 pounds, less than 40 bucks) and I would already have the book by now. Instead I found a US supplier who claimed they had it for $54 and I ordered it two weeks ago and still dont have it. they discovered it wasnt in their warehouse yet and put the order on hold. When it finally comes out in US it is likely, I am told, to be more expensive than the 21 pound price in UK. trouble is, I at least am not used to ordering from UK my wife has done it a bunch and it's worked for what she's ordered. the atlantic ocean may not be such a big obstacle except in the mind

Thales, one thing Stecker says is that cosmic rays have been observed with energies as high as 300 E18 eevee that is something like a carbon nucleus whizzing along with several joules of kinetic energy (a joule is 6E18 or 6 quintillion eevee) Reflect that accelerator energies are measured in Tev or trillion eevee. so the very high energy cosmic rays are particles or nuclei whizzing with energy that is on the order of a million times greater than what one gets in man-made accelerators. meanwhile in accelerator world one struggles tooth and nail, and makes heroic efforts to secure funding, just to raise the energy a few tens of percent. Stecker is a gentleman and makes no such comparison. It is a good paper, I urge you to have a look. His figure of 300 quintillion eevee corresponds to 50 joules. I also had heard this 50 joule figure elsewhere. It is incredible to me that a little thing like a proton or the nucleus of an atom could be hurtling so fast that it could have even one joule (enough to raise a kilogram weight up 10 centimeters!) 50 joule is to raise a kilogram weight up by 5 meters! how could a such a thing have such energy! but there it is---on rare occasions sees UHECR (ultrahigh energy CR) with 300 E18 eevee. ------------------ Stecker also gives an upperbound on observed energies of Gammaray. they go up to 50 TeV... well visible light is on the order of 1 eV-----several eV like 3 IIRC. the thermal light at the core of the sun is X-ray----around 1000 eV so 50 TeV light is like the light you would get glowing from something that is a billion times hotter than the core of the sun. some light. I can't picture what could emit a photon of light with 50 TeV. and cosmic gammaray comes in the sudden huge flashes called Gammaray Bursts. so there is a lot to explain-----I hope this guy Arnon Dar really has some adequate explanations----Stecker doesnt explain he just gives data and describes the ongoing efforts to get data.

I am sure you can figure the basic differences----it is two different approaches and the accelerator has some clear advantages you have a beam you can repeat something millions of times you can set up a specific target and an specific array of detectors you can automate the counting of just the event you want observing what comes down from the sky, by contrast, is haphazard and imperfectly localized, statistical inference is more difficult but there are a number of ambitious projects underway or planned. the success of the neutrino observatories (under Antarctic ice, using huge tanks of heavy water and other liquids, in abandoned mines etc.) has been dramatic there is a trend I think towards observing the weird stuff from the sky with larger and more exotic detectors it has been proposed to put up a bunch of satellites to look down at our upper atmosphere and detect flashes caused by particles from space crashing into the upper air------incredibly enough, observing neutrinos this way may be possible. (just as in a cubic kilometer of ice in Antarctica, where they also look for flashes) this is pretty boggling, at least for me there is an expert on all kinds of high energy CR and Gammaray observation named Floyd Stecker and he has a survey article about what has been done and what is planned the article is called, IIRC, "Cosmic Physics: The High Energy Frontier" you might search arxiv.org, in the astro-ph department, by author Floyd Stecker. [edit: I found the paper. it is http://arxiv.org/astro-ph/0309072]

there is a new paper by Arnon Dar: http://arxiv.org/astro-ph/0408310 "The Origin of Cosmic Rays - A 96-Year-Old Puzzle Solved?" It is important to understand how GammaRay Bursts (GRB) and how Cosmic Rays (CR) are produced because more and more these days this stuff is taking the place of Particle Accelerator beams in testing new theories and exploring new high energy physics. there is a new field of "Astroparticle Physics" with conferences and people specializing in it. It is people getting out of conventional HEP (High Energy Physics) and going into the high energy physics of GRB and CR and also I guess neutrinos which are interesting particle physics if not so high energy. One has to understand how these huge releases of energy happen and what the particle reactions are and then what reactions go on when stuff hits our own atmosphere. One has to know what detectors to set up and all that. So this is basic knowledge people want: what makes Cosmic Rays, and GRB too. this was an invited talk at a conference---some credibility attaches to that. ---------here's the abstract-------- "There is mounting evidence that long duration gamma ray bursts (GRBs) are produced by ultra-relativistic jets of ordinary matter which are ejected in core collapse supernova (SN) explosions. Such jets are extremely efficient cosmic ray (CR) accelerators which can accelerate the swept up ambient particles on their way to the highest observed CR energies. The bulk of the jet kinetic energy is used to accelerate CRs while only a tiny fraction is used to produce the GRB and its afterglow. Here we use the remarkably successful cannonball (CB) model of GRBs to show that the bipolar jets from SN explosions, which produce GRBs most of which are not beamed towards Earth, can be the main origin of cosmic rays at all energies. The model explains very simply the elemental composition of CRs and their observed spectra at all energies. In particular it explains the origin of the CR knees and ankle. Above the CR ankle, the Galactic magnetic fields can no longer delay the free escape of ultra-high energies CRs (UHECR) from the Galaxy, and the CRs from the intergalactic medium (IGM), which were injected there by SN jets from all the galaxies and isotropized there by the IGM magnetic fields, dominate the Galactic CR spectrum. A Greisen-Zatsepin-Kuzmin (GZK) effect due to the interaction of UHECRs with the microwave background radiation is expected. The CR nuclei which diffuse out of galaxies, or are directly deposited in the IGM by the relativistic SN jets, may be the origin of the IGM magnetic fields. Inverse Compton scattering of the cosmic microwave background radiation (MBR) by the CR electrons in the IGM produces the diffuse extragalactic gamma-ray background radiation (GBR)." --------end quote----- Invited talk at Conference on Frontier Objects in Particle Physics and Astro Physics, Vulcano, Italy, May 24-29, 2004 Anybody want to put this in simple terms? what makes this high energy sh*t rain down from the sky? Sometimes a single particle can be carrying amazing amounts of energy----way more than you get from human-built accelerators----what process could accelerate stuff to such levels.

Thales, thanks much for the link to Seth Major's green page of further QG links! It is a valuable concentration of good leads for gravity in general as well as QG. On my monitor it is a deep sort of green, a bit Robin Hoody but not by any means ghastly. Seth seems to be a neat guy and enthusiastic teacher, he has a paper explaining spin networks at around sophomore college level, or trying to, in basic terms without a lot of prep. Anyway, great link and you will add more to this sticky!

formula (1) in http://arxiv.org/astro-ph/0303062 [math]\frac{M_{hole}}{M_{sol}} = 3.37\sqrt{\frac{\lambda L_{3000}}{10^{37} W}}}(\frac{\text{speed of ring}}{km/s})^2 [/math] the mass of the hole, measured in solars is equal to 3.37 times the square root of the 3000 Angstrom line brightness measured in units of 10^37 Watt time the square of speed of the ring measured in km/s --------------- what they put in for the speed in the case of this quasar was 6000 km/s, and their symbol for the speed is FWHM(MgII) which means "full-width-half-maximum speed reckoned from width of Magnesium II line" the 3.37 is an empirical coefficient gotten by studying hundreds of closer quasars where they could use time-variation ("reverberation") to determine the radius of the speeding ring and determine the mass reliably. then they found a correlation with the brightness of the 3000 line. And using that they could reckon the mass of more distant quasars (assuming they are the same as nearby ones at least in this respect)

Wouldnt you say though that mankind poses a greater threat to our planet than do asteroids. I'm trying to assess the risk of accidental death by impact versus Greenhouse Geocide, meanwhile the water is inching up on the beach.

I plugged the numbers into Morgan's calculator to get the basic data on this quasar http://www.earth.uni.edu/~morgan/ajjar/Cosmology/cosmos.html using concordance model parameters (0.27, 0.73, 71) in the calculator age of universe when light was emitted: 0.87 billion years distance from us when light was emitted: 3.8 billion lightyears recession speed when light was emitted: 2.9 c present distance: 28 billion lightyears present recession speed: 2.03 c So this light we are now seeing, when it was emitted by the quasar (almost 13 billion years ago) the quasar was only 3.8 billion LY away from us and it was going away from us at 2.9 times the speed of light. Of course the light, even the part of the light "aimed" at us, at first was swept back and did not get any nearer to us, but eventually after almost 13 billion years it did make it (the expansion of the universe having slowed markedly until comparatively recently is what permitted this) To imagine the thing is more detail. the whole quasar then, as we see it today, was receding at around 3 times the speed of light. And on top of that the gas on one side was going away from us at 6000 km/s and on the other side coming towards us at 6000 km/s. As the gas circled the black hole. This is two percent of the speed of light. what I'm wondering is why do you say the mass of a black hole is 3 billion solar, based on observing that the gas circling the hole achieves a speed of 2 percent of c. have to turn in, think some more about it tomorrow. this link may help http://arxiv.org/abs/astro-ph/0204473 it looks like they studied reverberation of closer quasars---brightness fluctuations over time periods like a year---there being a delay between when we see peak excitment of the gas between the hole and us and when we see the same peak in the gas off to the side, and that delay gives an idea of the distance the ring of gas is out from the hole. then knowing the distance and the speed of the ring of gas they got the mass of the hole. then they correlated the radius of the gas ring to the brightness of a 3000 angstrom line and this let them estimate masses of more distant quasars. hope to clarify this tomorrow

I dug up the actual journal article that the news article was based on. It gives more information. Like the redshift of the quasar is z = 6.41, which the science journalist didnt bother including http://arxiv.org/abs/astro-ph/0303062 "We present near-infrared H and K-band spectra of the z=6.41 quasar SDSS J114816.64+525150.3. The spectrum reveals a broad MgII 2799 emission line with a full-width half-maximium of 6000 km/s. From the peak wavelength of this emission line we obtain a more accurate redshift than is possible from the published optical spectrum and determine a redshift of z=6.41+/-0.01. If the true peak of the Lyman alpha emission is at the same redshift, then a large fraction of the flux blueward of the peak is absorbed. The equivalent width of the MgII emission line is similar to that of lower redshift quasars, suggesting that the UV continuum is not dominated by a beamed component. Making basic assumptions about the line-emitting gas we derive an estimate for the central black hole in this quasar of 3x10^9 solar masses. The very high luminosity of the quasar shows that it is accreting at the maximal allowable rate for a black hole of this mass adopting the Eddington limit criterion." Some of the gas spiraling into the hole is coming at us at 6000 km/s and some is going away from us at 6000 km/s. they tell that from the width of the Magnesium line. these speeds are superimposed on the recession speed that goes with redshift z = 6.41. we can calculate that using Morgan's calculator. this will help make imagining the thing more concrete.

back in March 2003 blike posted a news item about people measuring the mass of a distant black hole and finding that it was 3 billion solar masses. http://www.spaceflightnow.com/news/n0303/20blackhole/ this is a good mass for a quasar-core black hole the mass of the stars in Milky galaxy is about 200 billion solar, IIRC anyway it is on the order of 100 billion so this hole in the news item is massing a few percent of all the stars in our galaxy how big is such a hole? the radius of a solar mass BH is about 2 miles and it is proportional] so the radius of the hole they got a mass for must be 6 billion miles. that is not so big for something far away How did they estimate the mass? can anyone suggest a way or ways to determine the mass of a distant BH. As it happens this one is about 13 billion lightyears away. How can you tell its mass? They give some hints in the news article. Does anyone understand the method, from these hints, and want to explain? --------------------- I understand how they measured the mass of the black hole at the center of our galaxy. It is only some 30,000 lightyears away and they can see objects ( stars) orbiting it. So they can easily estimate the mass from the orbit. IIRC it was I think around 6 million solar masses---not very big. this one in the news item is 3 billion solar--much bigger. But how did they tell since it is too far away to image things orbiting it.

hello Keebs, I have had those kind of thoughts too it is sometimes called a version of the "anthropic principle" but the trouble is it is not predictive in such a way as to make it falsifiable the way a normal scientific theory has to be a normal scientific theory bets its life constantly on its predictions. If in some future experiment you get results different from what it predicted then the theory is shot down the "anthropic principle" model just says Whatever. whatever turn out from any experiment it must be right because we are here and the world has to be right for us to be here. So it can accommodate any outcome of any experiemnt without batting an eye. this means that it predicts nothing So it is bogus---anything that depends on invoking the A.P. is not part of empirical science. (it can still be good religion or philosophy or poetry, just not science) this is why people have been making a gigantic stink over the past year's behavior of Leonard Susskind. the harder-headed string people seem opposed to taking the easy way out and invoking A.P which is seen as a diminishment or a defeat. Fortunately Smolin recently came out with "Scientific Alternatives to the Anthropic Principle" which does some of the good Multiverse things but makes predictions which enable it to be falsified if some future observation turns up such and such size neutron star and so on. I'd say dont give up on the possibility that a quantum theory of space and time (which is what Quantum Gravity is) will explain its dimensionality as so many other aspects of nature have been explained. Cant say why I feel so confident about this, just do. Come to think of it, it might even be possible to get d = 3+1 out of Smolin's evolutionary Multi. In which case it would already come with predictions to check experimentally.

this is one by a Cambridge guy Hendryk Pfeiffer http://arxiv.org/abs/gr-qc/0404088 Quantum general relativity and the classification of smooth manifolds ---quote--- ...It turns out that differential topology distinguishes the space-time dimension d=3+1 from any other lower or higher dimension... ---end quote---

So far no kind of string theory-under-construction or any approach to Quantum Gravity has offered an explanation for why there are visibly 3 spatial dimensions. If a theory has, say, 11 dimensions it will not explain why 7 remain rolled up out of sight and just 3 + 1 come out in plain view. Other Quantum Gravity approaches do not need extra (rolled up) dimensions but instead they work all right with just 3 + 1, or any number indiscriminately. They dont explain why it happens to be 3 + 1. So this is a problem that some smart people have been working on in QG. If we had a really good quantum theory of spacetime, they say, then it would explain not only gravity but also why the world has 3 spatial dimensions. This thread is to collect links to mathematical physics papers which tackle this problem. If you have run across a journal article bearing on this problem of "why three spatial dimensions and not some other number?" please put a link. I have seen some, so I'll try to find the links.

I find this interesting too. I suspect it is not coincidence or anthropic either' date=' but something else. [bTW No one else in this thread pointed out that you said [b']stable[/b] If gravity were 1/r3 then I think you could still have an exactly circular orbit, but it would not be stable and if something should accidentally come by and tug the planet slightly it would drift away. It can only stay orbiting if it keeps exactly in a circle and is never disturbed. Have you ever met a person like that?] Just a wild guess about the 1/r2 law. It seems to me to come from the fact of 3 spatial dimensions. Area increases with the square of distance. Illumination falls off with the square of distance. If only we could explain why there are 3 spatial dimensions! A mathematician (at Cambridge?) named Hendryk Pfeiffer has published some papers trying to say what is special about 3D. Someone else published something about that recently but I forget his name. If people can find a lot of things that are mathematically special about 3 dimensions (instead of 2 or 4 spatial dimensions) then perhaps they can get an idea about why Nature chose that number. Maybe we should have a thread where people can put links to research showing specialness of 3 spatial dimensions

http://www.space.com/scienceastronomy/mystery_monday_040503.html Toutatis comes close every 600 years and this year is one of those times. On 29 September this year, it will pass 1 million miles from earth (visible with binoculars under dark sky), that is about 4 times distance to moon. Toutatis is about 3 miles long and 1 and 1/2 miles wide. The last encounter this close was around 1350 AD and the next close one will be around 2550 AD.

hey shards venus surface doesnt get enough light besides being too hot (like the others said) so put these CO2-users on MARS! Mars atmosphere is mostly C02. the sunlight on mars is roughly 500 watts per square meter and human metabolism is roughly 200 watts so if you had a big green ass and went sunbathing like Earth people do on the beach you could soak up a good meal of energy If mobile green plants were engineered to handle the low pressure (one percent of earth normal) and severe cold, then they might run around happily, grubbing for subsurface ice to eat, visiting the famous polar caps and canyons. they could build greenhouses to live in that would help provide a better temperature and retain moisture-----the main thing is to tolerate low pressure and to have chlorophyl in your skin. Maybe they should grow leaves for extra area.

BTW keebs, Janus is an excellent fellow I believe I have seen his posts elsewhere and they are quite good. I havent seen him around here at SFN much so far but if he decides to stick around it will be a bit of luck for us. At the other place he had this sig which said let's see, it was a quote from the philosopher and mathematician Betrand Russell, it said IIRC "The whole trouble with the world is that fools and fanatics are always so certain of themselves, and that wiser people are so full of doubts." Lot of truth there. Even greens (who I sympathize with for loving the planet and nature etc.) are beginning to bug me because of this passionate selfrighteous certainty they get. they are as bad as neocons. Well this is off topic.

You are heartily welcome! Anytime you want to try using LaTex, just do the same "quote" trick on any post with a sample of it My post about 7 posts back has a sample you will see that the important thing is to put "math" and "/math" in brackets at the beginning and at the end of what you write [m*th]E = m c^2[/m*th] this, with * replaced by letter a, will make [math]E = m c^2[/math]

hello keebs You are cordially invited to try this for superscripts put the words "sup" and "/sup" in brackets if you want to see how somebody writes something, press "quote" under their post as if you were going to quote and reply-----this doesnt obligate you to reply, you just get to see what they typed E = m c2 I will damage this by replacing the u in sup with an asterisk just so it will explicitly show what I typed E = m c[s*p]2[/s*p]