Martin

yourda, there is a conventional distinction---but we are free to use the words however we want the conventional distinction goes like this: cosmologists study the parameters of the universe like the Hubble parameter (a kind of "expansion rate") like the estimated age: 13.7 billion years like the energy density needed for spatial flatness, the so-called "critical density" which is now estimated at around 0.83 joules per cubic km they want to estimate the density of dark energy and the density of ordinary (baryonic) matter they want to see how close to spatially flat the universe is, or to see if they can detect spatial curvature (so far it looks flat to them, but there is uncertainty in the measurements and it may have some slight positive curvature) they want to see if it is possible to detect evidence of inflation---there are many different ideas or "scenarios" of inflation and they would like to be able to distinguish they model conditions at very early times (near big bang) to see which chemical elements formed then and which only formed later in stars here is a mainstream survey article about Cosmology by a prominent cosmologist named michael turner. It is online Turner "Making Sense of the New Cosmology" http://arxiv.org/abs/astro-ph/0202008 --------------- Cosmologists study global parameters which describe the whole universe (age, temperature and density at certain time, energy density, expansion rate, acceleration of expansion, abundance of various chemical elements) Astronomers study specific objects: galaxies, clusters of galaxies, quasars, neutron stars, black holes seen in centers of galaxies, planets, comets, asteroids, young stars, old stars, big stars, little stars, variable stars, gas clouds, jets, large scale magnetic fields, they study the details. they leave the overall study of the universe and its beginnings and its history and future destiny to be studied by the cosmologists

it sure is high energy! planck energy is 2 Gigajoules! a huge whallop for a little thing like a photon to deliver (speaking very informally) but please answer the question, how big is the BH your choice 100 planck mass 1,000,000 planck mass it should be easy for you, given who you are

OK I guess it is time to take the mask off. You said rather sweetly in another thread "I'm an undergraduate, so I could be wrong" but you are not an undergraduate at Toronto for present purposes you are isomorphic with Jeffery Winkler a diehard string loyalist who used to post a lot on sci.physics.research nobody has for-sure identities on the internet but isomorphic you sure are because you talk and act the same IIRC Jeffery was born around 1970 and didnt finish a physics major at Longbeach but taught himself a lot of string theory. So every once in a while he gets hung up with basic undergraduate level mistakes (like sets of measure zero, and gravitational mass of binary systems and stuff) but he sounds brilliant when he is flinging around the highlevel QFT acronyms. I reckon he's very smart. You could re-register here as Jeffery Winkler and I wouldnt know the difference except it would be more staightforward than your coming here pretending to be someone you are not----like a 20 year old woman. Anyway, in whatever future life or persona, good luck Jeff!

Jana you said that transplanckian mass implied enormous if you dont know the basics and make elementary mistakes then it is clear that when you start slinging around terminology from quantum field theory it is pretentious, not authentic. Just tell me the size of an ordinary BH with 100 planck mass. Or if that is not "transplanckian" enough for you, 1,000,000 times the planck mass.

just tell me, in meters or kilometers or whatever you think is appropriate the radius of a Schwarzschild black hole which is 100 times the planck mass so we can see if it is enormous or microscopic or what

Few people could combine "toilet" and "physics community" in the same sentence with such verve. Tell us what it's like being "part of the physics community" up there in Toronto

Jana could you please explain why a black hole with mass larger than the planck mass (a "transplanckian mass" black hole) must necessarily be enormous?

Here is a illustrative sample of what you wrote in that other thread: "In fact the argument I studied says that there can be no background-independent QG theories since the (conjectural) domination in quantum gravity of transplanckian scattering processes by the production of correspondingly extremely massive and hence very large black holes (tom banks calls this conjecture “asymptotic darkness”) ruins universality. The idea is simply that asymptotic darkness means that transplanckian scattering instead of probing short distances, instead probes distances of order the size of these very large black holes. The resulting entwining of large scale geometry with the high energy spectrum means that the fundamental degrees of freedom depend on vacuum dynamics thus preventing background-independence. This is an example of the celebrated but still mysterious “UV/IR connection” which is yet another idea intimately related to holography." here's the link to your post (I hope, otherwise its to one of mine right after it so back up to find yours) http://www.scienceforums.net/forums/showthread.php?p=60966#post60966 jana this is such tortured reasoning! background independence is something very simple that 1915 gen relativity has in a simple extremely obvious way---its a fundamental characteristic of GR: there is a basic continuum set of points (a manifold) and you start with no metric on it---so there is no prior commitment to a geometry the metric, which determines the shape by giving distances between points, IS the graviational field---and the point of the theory is that the field (the metric, the geometry) emerges dynamically as a solution to the main equation any theory that wants to be free of a prior commitment to geometry, and let the geometry emerge, can be background indep but string theory isnt background independent so it does not have the fundamental characteristic of General Relativity You know all this So what I have heard over and over from string-boosters is ways to obfuscate and duck this issue One says "background indendence is impossible, any theory that tries to get it will fail" Another says "background independence is really not background idependence but something else entirely" lost in a fog of arcane acronyms. Another says "background independence is really something else and furthermore it is impossible to achieve this something else" And then "furthermore it is impossible that a quantum version of General Relativity can have true background independence". But the Loop gravity and Foam gravity and Simplex gravity people dont seem to make it so obscure. They just go ahead and build their theories to agree with Gen Rel and not have prior fixed geometry for the spacetime. And these are smart people so if there is some reason this is impossible that you, the undergrad, can think of (like in that quote) then they might well have thought of it themselves, I reckon, and decided it was impossible and not be trying. It is always possible that Tom Banks "asymptotic darkness" scenario does not apply----that scenario was in a paper he wrote with a very glum prognosis for string theory in it----IIRC it was his "A Critique of Pure String Theory"----or maybe it was his "Is there a string theory Landscape". He is an internal critic of string who is worth listening to. But that black holish scenario argument of his may just apply the purposes he made it for and not mean much about the progress of other approaches to quantizing GR. I think you get my point---there are background independent approaches to quantum gravity going ahead, quite a lot of current progress. the arguments you came up that this progress is impossible seem rather strained and far-fetched (depending on Tom Banks asymptotic darkness business etc) and likely to be contradicted in a straightforward way by events. they sound like denial of what you wish were not happening (this is in reply to your BTW question as to why I suspected you might be a True Believer type instead of a student)

In your last post there was this interesting BTW question "... I am happy to discuss anything since I need the practice. If I don't understand something that you do understand, would you mind helping me out a bit on that topic? btw, what is it that I posted that made you think I may be some kind of string zealot?" this will take some introspection. I take it you know the type of zealot I mean "Loop gravity cannot possibly be right. String/M theory is the language in which God wrote the World..." and so on. Most of the time you dont sound like one of the Faithful, the fervent believers etc. But I was worried by your series of rather lengthy essays in the other thread which gave logical arguments, it seemed to me, that the Lorentzian dynamical triangulations approach of the new Ambjorn et al paper could not possibly succeed. You may have noticed that a some experienced people were excited by that paper and/or hopeful about the approach----Matt Visser, Thomas Larsson, John Baez. With a breakthrough that is obviously just getting started and has a lot more room to grow it is premature to try to argue from purely logical grounds that it must necessarily fail. This is a reaction not appropriate to a young college student (as you introduced yourself) but to someone with a substantial investment in string theory who feels threatened. there is a tendency, which you may have noticed, for those heavily invested to abhor any competition for the limelight, and vigorously deny that alternatives are making progress, and even to argue that they cannot possibly succeed! What would it cost you, as a 20 year old entering senior at Toronto, to share my hopes that the Ambjorn paper, with its computer simulation of the geometry of the universe, opens up a real avenue to quantum gravity? but to a zealot, such thoughts would be anathema. you see my point I think

oops I missed your latest reply before I posted, to catch up, first I will find out the papers you cited:

Well let's see what we have! Jana bless your heart! You have provided links!!!! http://xxx.lanl.gov/abs/gr-qc/9908031 http://xxx.lanl.gov/abs/gr-qc/9603063 http://xxx.lanl.gov/abs/hep-th/9601029 I see you have left it to me to fish up the authors and titles, so I will do that presently. Off hand from the numbering I am puzzled. You are a Toronto U undergrad taking a senior class in the fall, so you are, like 20 years old in 2004---born around 1984 You are referring back to 1996 papers, stuff written when you were 12 years old!!!!! Maybe not much has happened in some lines of research since the 1990s but a lot has happend in the various approaches to quantum gravity (not string) that I follow. I will get back to that. but anyway you are a sweetheart for getting links to sources. there is such a lot of intellectually dishonest hype in the world and such misconceptions that sources are a virtual necessity----dont take anything on faith!---here I am giving the young college student my sage advice but I am sure you know this already. No I dont actually. the sources for claims made about scholarly research are as important as the conversational claims i have been exposed to string propagandists who were so dishonest that when they say something you could practically take it that the opposite was true. So I dont trust anyone I suspect might have an ax to grind unless they regularly cite references. Yes it does doesnt it? No offense intended to jana the Toronto U undergrad student! You can probably understand where I'm coming from, I'm bored with string propagandists constantly hyping string theory---like it is some sacred crusade---and using phony arguments to badmouth more recent alternative approaches to quantizing gravity! As an undergraduate-age person you are presumably more open-minded and I would hope you dont suffer from a neurotic need to believe in something. Personally I have no commitment to any one approach---I believe in nothing and have no interest in promoting or persuading anybody. I see nothing interesting has happend in string since around 2001 so i look on it as (at least temporarily) a dead field----so I watch other areas where a lot HAS been happening since 2001 or so and developments are hopeful: barrett-crane spinfoam Hawking path integral (recently some signs of action, tho almost disappeared off the map for a while) Loop gravity Simplex gravity If you, as a Toronto U undergrad, are interested only in making up arguments why none of these approaches can possibly work---which is something we cant know ahead of time---all I can do is smile and listen politely. If you know something about any of them and can discuss it I would love that. Cant stress this enough. I am looking for other people who have an interest in discussing recent advances in quantum gravity and can supply links to recent research papers to substantiate what they say. You seem like the ideal person since IIRC you say your background is in Loop and Simplex gravity----what recent papers have you read in simplicial? Have you looked at the Ambjorn, Jurkiewicz, Loll paper? hep-th/0404156 I think it is dynamite. Very exciting

YT and others who have chipped in, thanks! it's great to have a collection of astronomy favorites from a bunch of different people, hope more will contribute. here's some pedagogical links for cosmology: This article by Lineweaver (he was one of the team in charge of COBE an earlier CMB satellite observatory) "Inflation and the Cosmic Microwave Background" http://nedwww.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver_contents.html http://arxiv.org/astro-ph/0305179 the second link has a PDF version that is more readable but takes more time to download Lineweaver's essay has been made into a chapter of a book now in press called "The New Cosmology" (world scientific 2004) I will repost this link to Ned Wright, because of his FAQ which is famous on the web and has been translated into several languages IMO it is the overall best online cosmology FAQ http://www.astro.ucla.edu/~wright/cosmolog.htm http://www.astro.ucla.edu/~wright/cosmology_faq.html he teaches the undergrad and graduate level courses in cosmology at UCLA and is also one of the team in charge of the WMAP satellite observing the CMB

I will try to direct you to a standard cosmology FAQ maybe Ned Wright's cosmology tutorial FAQ will work for you http://www.astro.ucla.edu/~wright/cosmolog.htm http://www.astro.ucla.edu/~wright/cosmology_faq.html he teaches the undergrad and graduate level courses in cosmology at UCLA and is also one of the team in charge of the WMAP satellite observing the CMB You are mistaken. Light can lose its energy. there is no global energy conservation law in General Relativity. the expansion of space has two effects: one (which you pointed out) is that there are fewer photons per cubic kilometer-----they get spread out into a larger volume the other is that an individual photon loses energy as its wavelength gets stretched out the energy of a CMB photon is hc/lambda where h is Planck constant and lambda is the wavelength-----stretching out the wavelength reduces the photon's energy roughly speaking: each CMB photon has individually lost 1100/1101 of its energy since the time when they were all last scattered besides which, since space has expanded by a factor of 1100 a sample volume has expanded by a factor of (1100)3 so CMB energy-per-volume has declined by a factor of (1100)4 this fourth power relation is a standard fact you get taught in an introductory cosmology course or will find referred to in pedagogical articles it is surprising the density of matter only goes down as the cube but the energy density of radiation falls off as the fourth power Try this article by Lineweaver (he was one of the team in charge of COBE an earlier CMB satellite observatory) Inflation and the Cosmic Microwave Background http://nedwww.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver_contents.html http://arxiv.org/astro-ph/0305179 the second link has a PDF version that is more readable but takes more time to download this essay of Lineweaver has been made into a chapter of a new book now in press called "The New Cosmology" (world scientific 2004) here's the part of my post I believe you were responding to: ---quote--- also think about this: the universe is full of CMB photons which have experienced a redshift of 1100 that is, each photon has lost 1100/1101 of its energy---it has lost over 99 percent of its original energy from the 'recombination' era when those photons originated where has this huge amount of energy gone? is there a global energy conservation rule in Gen Rel that says it has to have gone somewhere? ---end quote---

If we are going to cite references I will start with what i think is a kind of model unbiased survey of quantum gravity by someone whose research is mostly string Enrique Alvarez "Quantum Gravity" http://arxiv.org/abs/gr-qc/0405107 I dont particularly like Alvarez or his survey papers, but he has never done any Loop Gravity or Simplicial gravity he has done a bunch of String and he has a balanced perspective. some HEP people---particle theorists---stringy folk--invited Alvarez to give a survey last year at a conference July 2003 and it was Enrique Alvarez "Loops versus Strings" http://arxiv.org/abs/gr-qc/0307090 those are offered as benchmarks for a fair balanced perspective and also (you may not like this as much if you are strongly pro-string) Lee Smolin has done research both in String and Loop and several related areas as well and he did a survey last year where I think he bent over backwards to be fairminded and to compare progress (and prospects for experimental testing) point by point in a bunch of categories So what do you say to this survey? Lee Smolin "How far are we from the quantum theory of gravity?" http://arxiv.org/abs/hep-th/0303185 I also really like a 1998 survey by Rovelli of ALL the different approaches to quantizing gravity then being pursued Carlo Rovelli "Strings, loops, and others" (plenary lecture on quantum gravity at the GR15 conference) http://arxiv.org/gr-qc/9803024 Now I am hoping to get a selective bunch of links from you to back up some of your claims. so I have started by tossing out some general surveys by reputable people that kind of scope out the whole quantum gravity area. Im eager to see what sources you come up with! regards,

Hi jana, wouldn't you please give a reference to the basic paper on that so a casual passerby has a chance to look up what you mean? IIRC it is in arxiv. We should get into the habit of citing sources. In balanced (not biased) comparisons of the various approaches what I usually hear is that it is six of one versus half a dozen, because one approach gets the right number four, but is restricted in applicability, while the other applies very generally for all kinds of holes, but has an undetermined coefficient in the formula. But if you want to present it that "only" string theory succeeds in that department then maybe you should give a bit of a lecture on this. I would love to hear your exposition. I am not worried about anyone here getting deluded---just come out boldly and deliver your pro-string message if you have one. I have to point out that your slant on it differs considerably from what an authoritative professional survey article would say, like by Enrique Alvarez recently---he is primarily a string theorist but knows something about non-string approaches and he has been invited several times to give a loop/string comparison at various conferences because he seems able to give a balanced view. Or perhaps Steve Carlip or Gary Horowitz, or Lee Smolin (for whom i will say that he gives a less one-sided picture than you) or whoever might have fairly recent (2003-2004) survey articles that compare progress in the different approaches. You have indicated you are an undergraduate at Toronto U and will be taking a course for seniors in the Fall. You also say your main familiarity is with loop and simplicial quantum gravity and you are psyching yourself up to learn string theory. but sometimes you sound to me oddly like a much older person---the string cheerleader who got religion in the 1990s, or the type of diehard string booster i've had plenty of experience with---they talk with a verneer of authority but give a real lopsided view. So I would urge you to talk more like a student at Toronto U and give some references to papers in arxiv---back up what you want to say with some arxiv links. (even Urs Schreiber the moderator of sci.physics.string does that, even jacques distler at string coffee table does that----you can do it too) just assume I wont believe anything you say unless you give a link to the paper like. for the area-entropy relation for extremely fast-spinning or highly electrically charged black holes IIRC there is Vafa 1996 so say http://arxiv.org/hep-th/9600000 but please fill in the number so I dont have to do a search for your references and if the result has been extended to any type that is more like an ordinary black hole such as astronomers witness then please give the arxiv number for that. I would be delighted to see the paper! If you give sources it will be more fun, and I will learn a lot more, AND who knows you might even succeed in educating me

Hi jordan, I didnt look to see I assume it was what you said----especially if you assure me of that. I was just playing around with this LaTex notation it is so wonderful to be able to share formulas easily can you do the basics with it? just, like do "quote" on a Dave post and then dont bother to carry through and reply just look at how he does the type-setting

[math]10^{10^{34}} = \underbrace{10 \cdot 10 \cdots 10}_{\displaystyle 10^{34} \mbox{ times}}[/math] [math]10^{10^{10^{34}}} = \underbrace{10 \cdot 10 \cdots 10}_{\displaystyle 10^{10^{34}} \mbox{ times}}[/math]

that I doubt the trouble comes when you have to do a lot of copy/paste operations and forget to erase things---LaTex is a marvel but can be a pain in the butt as well

something looks wrong here it would seem that [math]10^{10^{34}} = \underbrace{10 \cdot 10 \cdots 10}_{\displaystyle 10^{34} \mbox{ times}}[/math]

Every three years there is a big-time world conference on General Relativty and this year it is in Dublin 18-23 July three years ago it was in [edit:correction] South Africa and back in 1998 it was in India so anybody in UK, now is your chance this conference is about every facet of gravity theory and research the gravity wave detectors what observing binary pulsars and other neutron stars tells about gravity all kind of gravity experiments, in space and on ground theories of quantum gravity (john Baez will talk on Loop Quantum Gravity, quantum geometry, and spin foams) here is the website, it has the program of talks, with brief summaries, on the lefthand sidebar----click on "recent additions to the program" http://www.dcu.ie/~nolanb/gr17.htm Stephen hawking made a surprise announcement that he had a solution of the BH information paradox and would be coming to GR17 to talk that up ---- There is also a public lecture by Roger Penrose that I believe will have a lot to do with String Theory and related fancy mathematical doodads. Penrose talk is called FASHION, FAITH AND FANTASY IN THEORETICAL PHYSICS and it is at the Dublin concert hall at 8PM on Friday 23 July String theory has had a kind of tulip-mania fad or craze and now seems to be in decline. But it is also a kind of religious faith for some of those who have invested a lot of effort in understanding it. so there are some diehard believers who will give you elaborate specious arguments why it is impossible that any of the newer approaches to quantizing gravity can work and it lives in a kind of fantasy realm, making no testable predictions and ungoverned by experimental evidence, so the researchers indulge in untrammelled mathematical inventiveness finally such an embarrassing richness of possibilities has emerged that the distinct variations of the theory have been estimated by its insiders (Susskind, Douglas) at ten-to-the-100 different base states and things like the Anthropic Principle, a latterday Hand of God, are being invoked in a desperate effort to find the right one. So it has gotten bogged down in its own fecundity. Well people are beginning to point this out and i guess Penrose's title "Fashion, Faith, and Fantasy in Theoretical Physics" will call attention to plight of string theory, whatever he turns out to say. he could have made the title shorter if he had just said "Pseudo-science" a good place to follow the Decline of String melodrama is at Peter Woit's website---a mathematician at Columbia with a specialty in (non-string) mathematical physics----he as a fairly regular web-log and lots of academics drop in to comment and respond---and a certain amount of the latest gossip and conference news here's the link to Peter's blog http://math.columbia.edu/~woit/blog/

Hello J'Dona, I will try to find one of the bunch of papers about that----that you asked about---very high energy gamma rays slightly exceeding c. BTW I agree in general with what you said in your post about the best available evidence point to gravity going at same speed as light, namely c. And also I agree that (whereas tachyons are more SciFi) gravitons are generally predicted by respectable theories-under-development and they merely have not (yet) been observed. As a minor point I think that it is not the graviton but the higgs boson that is supposed to interact with other particles in a way that gives them mass------mass means inertia basically. the Higgs field (THEORETICALLY) would interact with other particles in a way that keeps them moving just the way they are moving, and makes them resist changes of speed and direction so if it doesnt interact with some particle then that particle would have mass = zero and if it does interact then how strongly it interacts determines how much inertia ( = mass) the particle has it would be wonderful if that theory could be confirmed by actually detecting Higgs particles. but this has not happened so we really should not believe in them too hard.

AFAIK there has never been an observation of either a tachyon or a graviton there is no experimental evidence that they exist ------------ here is another point: if gravitons are ever observed, it is widely expected that they will obey the speed limit----the idea that gravitons will exceed the limit is a fringe idea (that does not mean it is wrong, the mainstream is not always right, maybe gravitons exist and maybe they can go faster than light, but THEORETICAL reasons would convince most people, i think, that if they exist they must obey the speed limit) anyway so far there is no sign they exist---they just come up in this or that unproven theory---and if they did exist they probably wouldnt break the limit any more than light does ----------------- here is another point: tachyons sound good but when they turn up in a theory they are treated as something to get rid of---if it predicts them then somethings wrong with the theory and it needs to be fixed In other words at least to many if not all, if a theory predicts tachyons then that is a problem with the theory they are generally seen to be fairyland mathematical creatures, not the daily stuff of physics -------------------- You need to rephrase the question. Strike out the reference to tachyons and gravitons and ask a question that has some empirical meaning: do photons of light ever go faster than c? it is possible that some very high energy gammaray photons do go faster than c and this is going to be tested in the next few years by a satellite observatory called GLAST (gamma ray large array space telescope or something like that) there is a NASA website about GLAST there are a bunch of mainstream technical journal articles about the possibility of testing whether very high energy light can go just slightly faster than c which some new theory suggests might happen for a definite reason and this can be tested because the most energetic light in the universe comes in these gammaray bursts which come in a pulse, and it will be possible to check with very sensitive instruments like GLAST whether some of the more energetic photons have gotten just a bit out ahead of the others in the pulse so this is a real empirical thing to look for, not "tachyons", maybe it will be found, maybe not---a good experiment can go either way I should try to find a link about this. GLAST website says they plan to launch in 2007 which is still pretty far away and Bush might cut NASA's unmanned space instrument budget so GLASt could die on the ground--- lot of uncertainty here

Was immer du tun kannst oder träumst es zu können, fang damit an! Mut hat Genie, Kraft und Zauber in sich. (gefunden von Gerhard Bendig) -------end quote----- Freeman, this is from a German famous quotations site: http://www.daszitat.de/Autoren/G/goethe02.html Notice that it does not say the quote is from the actual play Faust! It says the quote was found (perhaps in a letter or in some of G's papers) by a person named Gerhard Bendig. Be careful about attributing it to the play unless you can learn the act or scene where it occurs. Freeman, also think about the force of the original words which have Goethe's spirit more alive in them. The English translation is a bit slack----I fear the Latin will come out even less energetic. this is not the fault of English and Latin which are wonderful languages, but something that happens often in translation german is a wonderful language which, just as much as Latin, should never die. I would take the motto direct in German and use it proudly

Go Planck! just one little constant more and its c=hbar=G=1