Martin

Kepler spacecraft was successfully launched on 6 March. It's job is to watch a particular patch of 100,000 stars for several years to detect transiting HZ (habitable zone) planets which are roughly about earth size. If anybody knows more about the Kepler mission please contribute comment. http://kepler.nasa.gov/ This website has an FAQ. My understanding is that HZ planets are ones whose semimajor axis (average distance to star) is 0.95 - 1.37 AU adjusted for luminosity. That might be wrong but it is something like that. The idea is that for a star as luminous as the sun they look for planets whose distance is around the same as the earth's, namely from 95% to 137% of earth's distance. And for a hotter star they adjust the distance out so that the energy balance and equilibrium temperature is the same. And for a cooler star they adjust the distance in. That band is called the 'habitable zone' and roughly corresponds to the planet having liquid water on part of its surface. But also they want the mass of the planet to be like earth, or a few times earth mass, so that it will hold it's atmosphere. A reasonably thick dense atmosphere is important. Helps the water stay liquid. Shields, protects etc. etc. So Kepler spacecraft will be watching for transits of a not too small and not too large planet disk in front of the star, and it will watch for this to occur on a time period basis that says that the distance to the star is right. In other words, HZ and the right size. If you are curious and want to understand the inference better, try asking. Kepler will orbit the sun at the trailing Lagrange point, if I remember correctly. It will not orbit the earth. It can watch 100,000 stars at once because it has a pretty nice CCD (charge coupled device).

I like this response a lot. I am not an expert on this. What you are saying is that a large amount of gravitational energy is released. That is an alert observation. Like, calculate the gravitational potential energy of two compact masses each of which has a mass of a billion solar----and they are say 100 lightyears apart and they are falling towards each other. I think it is a new field. I think this workshop that the link is to is an early workshop in this line of research. I don't know how or on what timescale the energy is released. They are doing sims and trying to understand the dynamics of this. One reason it's interesting is that they can see this kind of event in process. I think the sheer size may somehow slow the release of energy down. The radius of a solar mass BH is only about 2 miles. (3 km). So when two solar mass BH merge they could be going some goodly percent of the speed of light (I don't know) and it could happen really fast. Radius is proportional. The radius of a 3 million solar BH (like we have at Milkyway center) would be 6 million miles. (9 million km = 30 light seconds). And then some of the BH are a billion solar mass. Offhand I cant figure out what to expect. Maybe if I was in Baltimore MD I'd drop in at Johns Hopkins and visit that workshop.

There was a lot of discussion in the past. Now HZ has a conventional technical meaning. Money and telescope time is being allocated to the research goal of finding HZ planets. Another term that seems to have taken on a practical operational meaning is "earth-like planet". Careers and resources are being allocated to the "earthlike planet search" The technical meaning of these terms is kind of pragmatic. You have to set your goals and define your criteria. And that has been done, because then science policy has to be framed and work has to go forward. HZ means 0.95 to 1.37 AU adjusted for the star's luminosity. Earthlike as I understand means something like a rocky planet with water that is no more than 6 or 7 earth masses and orbits in the HZ. I'm not an expert in this, Widdekind may know the agreed-on definitions. I think we've had enough of these discussions about "what is Life?" and quibbling about terms like "what does habitable mean?" Now the game is to design and launch instruments that can identify planets in the interesting band and find out as much as we can about them.

Cameron, I share your skepticism about Farsight's assertion. I'd like to urge you to use the "quote" button and leave the link back to the post that you are quoting. That way when you quote someone I can click on the link and get back to the post. the little blue square with the arrowhead. Otherwise I have to waste time scrolling back to see who said it and what else their post said, context sometimes matters. so please leave the full quote function intact. Indeed gravity = geometry and geometry is in process of being successfully quantized. New results have come in and will be reviewed at the September 2009 Corfu school. (and also several conferences and workshops leading up). Google "QG school corfu" or just go to http://www.maths.nottingham.ac.uk/qg/CorfuSS.html Quantum gravity is reaching a milestone, or a new stage. It's interesting to watch the current research scene.

Good. Now what do we mean by "too high" in some realistic case? Equilibrium temp goes inversely as square root of distance. So an eccentricity of 0.2 or 20 percent translates into a 10 percent excursion in absolute temp, if unmoderated by the ocean. If absolute temp is 300 K, then 10 percent is 30 K. This is assuming no participation by cloudtop reflection albedo and by greenhouse. It is a really really rough envelope scribble just to get an idea.

Hi Mokele, my impression is that HZ has acquired a kind of consensus meaning among professional astronomers. http://en.wikipedia.org/wiki/Habitable_zone Wiki is often unreliable but I think it may be OK here at least in broad outline. They are saying that for a star with solar luminosity the range of semimajor axis is 0.95 to 1.37 AU And for a star of different luminosity they show how to adjust the band. We could do some calculations and try to see how closely the conventional HZ concept corresponds to your idea of temperature range 0 to 40 Celsius. I'm not sure details like that matter though. There is a lot of latitude implied by albedo and greenhouse variation. Once one finds a planet within the broad HZ range, one has to estimate the atmosphere density and think about those effects. A planet where the top of the cloud layer reflects away most most of the incoming light will be a lot colder than equilibrium black body temp at that distance from star. So one should not interpret the broad HZ range naively. Basically it is just one step in the process of searching for earth-like or habitable planets. The search is just getting started. They cast a wide net. HZ is a fairly arbitrary category defining the first cut. Let's just say that the professional planet-search astronomers' definition of HZ is 0.95-1.37 AU, adjusted for luminosity. Does anybody want to challenge that and say the astronomers should be using different bounds? Merged post follows: Consecutive posts merged DH, can you give us some idea of what you mean by "too high". The point of the OP is that eccentricity needs to be taken into account, so I take it you would agree with Widdekind on that general point. The critical factor seems to be the averaging over the year performed by the ocean. Maybe the planet searchers are right not to worry about eccentricity very much in making the first cut. Maybe for a planet with an ocean orbiting a sunlike star the main thing that matters is simply the semimajor axis*. I don't have an immediate opinion about this. Do you? * assuming say the e < 0.2.

Now I'm confused. I thought that your simple calculation, based on ionosphere circumference and the standard speed c, led you to expect 7.15 Hz. And I thought you found some source that said the actual frequency was (variable but approximately) 7.85 Hz. So I thought you were asking how does the frequency end up higher.

http://www.stsci.edu/institute/conference/blackholemergers An interesting thing you immediately get if you click is eight images. Four on the left are stills from a computer simulation of a merger, calculated step by step using numerical GR methods. The four on the right are actual photographs, some with false color showing temperature, of real things which look like stages in the merger of supermassive BHs. That is, the observed thing looks somewhat like what they got by running the numerical model. This field is just getting started. Maybe at this point they don't have much more than those eight images. But I'd expect they'll be getting more interesting stuff on observing BH mergers in next few years.

In every geometry there is an idea of straightness proper to that geometry. Straight lines are called geodesics, by analogy with great circle lines on earth. Between nearby points, straight follows the shortest distance. Light goes along shortest distance routes. So it follows geodesics. In the 2D balloonsurface toymodel the flatski can see something that is halfway around the balloon from him. Unless the balloon is expanding so fast the light never makes it. Correct. But a very large expanding balloon is experienced approximately like an infinite flat 2D. So it is a good mental exercise to think a lot about the balloon analogy and the 3D hypersphere case and get to understand it. How some distances between things are increasing at a faster rate than c, and so on. How expansion affects what you can see. And then when you have learned what you can, just enlarge the picture and get the infinite flat case in the limit. A lot of the intuitive understanding carries over.

the way to use the balloon is as a 2D analogy for 3D space. analogy, not direct straightforward representation. in other words, concentrate on the surface of the balloon as having zero thickness and being a purely 2D toy model of the 3D reality analogies are tools to help your mind imagine. so to use this balloonsurface 2D toy model analog, to train your mind to imagine living in the 3D version (called a hypersphere) you first think a while what it would be like to be a purely 2D creature (no thickness) sliding around in the 2D balloonsurface. If it wasn't expanding you might eventually make your way all the way around, just by going in one direction. So you could figure out that your world was finite and curved. (I mean curved as experienced from the inside because there is no outside to the universe, all existence is concentrated on the balloon surface as far as you the flatski creature know.) You could also discover internal or intrinsic curvature in your world by making triangles and discovering that the sum of angles was bigger than 180 degrees. In fact by doing this you could learn how to estimate the circumference of your world without having to make a tour. If you assumed it was uniform, then you could sit in one place and study triangles and estimate how big all of space was. So think about the experience of a 2D flatski in a 2D balloonsurface world and then try to project by analogy what it would be like as a 3D creature in a 3D hypersphere world.

Fair question. Someone with a practical experience with waveguides could probably give a responsible explanation. In my case I can either speculate irresponsibly and guess at an explanation, or I can research it, which I don't have time to do right now. But its a good question. Why doesn't the electric noise from a lightning flash act as if it travels exactly along circumference great circle defined by the ionosphere? Why does it behave as if it was taking a shortcut? Notice that the difference in frequency is only 7.85 versus 7.15 Hz by your calculation (which I trust so will not check.) It is not so big. It suggests our general idea is right, our general understanding of the resonance is OK. Maybe the noise does somehow take a shortcut, could it go along a polygonal path? A polygon inscribed in a circle has less circumference than the circle. Or could it be sneaking sideways around the earth? Waves spread out and go different paths and then come back together and reinforce. Maybe we are being too restrictive with the wave if we insist on it traveling a great circle circumference, maybe the wave knows better and gets around faster. So then the resonant freq would be higher, as in fact it is, you point out. Just quick speculation. You might check with Swansont. If he has time to answer you will get more than just this guess.

Absolutely right about the misnomer. The name was given antagonistically by Fred Hoyle who didn't like the theory and had no interest in representing it accurately. (He favored an alternative steadystate model.) I gather that a tachyon is a field whose mass is an imaginary number (like the square root of -1 is an imaginary number.) Usual matter masses are positive real numbers, so this is already pretty exotic. There is no experimental evidence for the existence of tachyons. Airbrush, I really should not be talking on this subject. Don't know enough. Here's what I gather from the Wikipedia article: "Since a tachyon's squared mass is negative, it formally has an imaginary mass. This is a special case of the general rule, where unstable massive particles are formally described as having a complex mass, with the real part being their mass in usual sense, and the imaginary part being the decay rate in natural units[4]. However, in quantum field theory, a particle (a "one-particle state") is roughly defined as a state which is constant over time, i.e. an eigenvalue of the Hamiltonian. An unstable particle is a state which is only approximately constant over time; However, it exists long enough to be measured. This means that if it is formally described as having a complex mass, then the real part of the mass must be greater than its imaginary part. If both parts are of the same magnitude, this is considered a resonance appearing in a scattering process rather than particle, since it does not exist long enough to be measured independently of the scattering process. In the case of a tachyon, the imaginary part of the mass is infinitely larger than the real part, and hence no concept of a particle can be attributed to it. It is important to stress that even for tachyonic quantum fields, the field operators at spacelike separated points still commute (or anticommute), thus preserving causality. Therefore information never moves faster than light." http://en.wikipedia.org/wiki/Tachyon Cosmic inflation may not have happened. People are still working on alternative ideas of how the remarkable degree of flatness and temperature uniformity that we observe might have come about. Inflation is just the earliest conjectured scenario that offered an explanation. Personally i have no opinion. I neither believe nor disbelieve that inflation happened. I kind of suspect that maybe it did, but don't assume it. But just for argument's sake let's assume an inflation episode occurred--the mechanism usually imagined is a scalar field. Sometimes this imagined field is called an "inflaton". Nothing that has ever been observed would serve the purpose. In other words the proposed physical mechanisms of inflation are total fantasy so far---they are exotic physics, resembling tachyon fields in regard. The upshot is that you are right in the sense that if a field could have existed very briefly in the early universe with mass that was an imaginary number (the tachyon property) it might have served as an inflaton field and driven inflation, then an eyeblink later decayed into more ordinary types of matter. Aaargh. I knew I shouldn't have tried to respond to this. But I won't erase it.

If I remember right the full cycle takes 26,000 years. Hmmm. I just checked Wikipedia and it says 25,771.5 years, so 26 thousand is about right. http://en.wikipedia.org/wiki/Precession_(astronomy) So half of one cycle would be about 13,000 years. That would change our northern hemisphere seasons by 6 months. The winter solstice which is now around 21-22 December would then be around 21-22 June, give or take a day or two.

Here's an alternative link to the "Misconceptions about the Big Bang" article from the March 2005 SciAm that has proven generally useful: http://www.astro.princeton.edu/~aes/AST105/Readings/misconceptionsBigBang.pdf The one I've been using has a black page at the beginning of the pdf file, which might confuse people. http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf

But we expect to be able to detect neutrinos from the big bang, from some fraction of a second after start. We just need to get the right instruments to detect neutrinos of the right energy. The energy range has been calculated---I forget what it is. Please read my post again. There is no way that those particles could have "run away". Whatever hasn't gotten absorbed and changed by collision is still here. There is no empty space for them to run away into. It sounds like you are still suffering from the "explosion" misconception. Conventional bigbang cosmology is in no sense pictured as an explosion of stuff flying out from some central point. If it were like that then the CMB photons from 380,000 years after start of expansion would also have "flown away". Everything would be flying outwards from some point, out into empty space. That is not how it is, Airbrush. That is a popular misconception. Get over it . You could try reading Lineweaver's SciAm article "Misconceptions about the Big Bang" again. Have you at least read it once? Here's the link. It's also in my sig. Scroll down. The first page or so of the pdf file is blank. http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf Here's an alternative link that doesn't have the blank page at the beginning. http://www.astro.princeton.edu/~aes/AST105/Readings/misconceptionsBigBang.pdf

There were two first prizes, a Juried prize and a Community prize. In one case it was a select panel of judges, in the other it was a larger group of people who have been made FQXi community members. One essay could not be awarded both first prizes, and Rovelli's was a clear choice for the Community first prize. He got by far the largest number of votes in the open voting. The two essays form an interesting pair, because they have the same message, but Rovelli pushes it farther, writes more, and includes more technical detail. The basic message is that you don't need a designated time-variable to do physics, and at the fundamental level a preferred time variable just gets in the way. It's a hard message to assimilate. Probably the best is to read both firstprize essays. Here's Rovelli's http://www.fqxi.org/data/essay-contest-files/Rovelli_Time.pdf Here's Barbour's http://www.fqxi.org/data/essay-contest-files/Barbour_The_Nature_of_Time.pdf

I don't understand your reasoning, Airbrush. I don't have much faith in the existence of tackies, but suppose they did exist and suppose a bunch were created along with some other stuff shortly after the beginning of expansion. Why wouldn't they be whizzing by here at this moment? If the big bang volume was finite, then space today is finite, and the taxies could have circled around perhaps several times already. Depending on their speed relative to expansion. Think about the balloon model with speckles on the balloon being galaxies. And stuff like photons and the rest moving across the surface. On the other hand, if space is infinite, then the big bang volume also was infinite. This is standard cosmology I'm telling you. So there are plenty of tachyons coming our way, plenty here now, and lots that have already passed us. That is, if tachyons actually exist and if a bunch were produced right after the start of expansion. You seem to disagree! What is your argument?

Hi Widdekind! I am glad you came back and checked your thread. From some other discussion at some other board, I forget what the topic was, I connect you with UCSD. Maybe you did some of your undergrad or graduate work there. If so you may have run into Tytler? I don't know him, just of him. He works with Keck and he seems to be interested in the habitable planet search. Maybe directly involved in it. I think the habitable planet search is exciting, actually in part because it spurs the development of new instruments. And possibly will also spur the development of new methods of inference and mathematical applications (I don't know about this but it could be.) Who else is good in that line of research? Any people or projects I should keep an eye out for? Don't know much about it, just feel it has potential.

The Schumann resonance is a very beautiful phenom, and I like the fact that you are learning stuff like this and sharing it. http://en.wikipedia.org/wiki/Schumann_resonance You are right that the cycle-type wavelength is key to figuring out standing wave modes. In this case it is the earth's circumference (at the ionosphere level). In order to reinforce itself constructively the wave has to stretch all the way around and come in at the same phase. Keep the radian-type wavelength idea alive in the back of your mind, but often the cycle-type version is more natural (here's a case of that!) so use that. The basic Schumann resonance, set off by bolts of lightning, is 7.83 cycles per second. (Multiply that by 2pi to get the angular version of the same frequency, if you want.) The cycle wvlngth of that frequency is, as you say, the circumference of the planet. The angular wavelength, if we cared to know it, would be the radius of the planet. (out to the ionosphere) It is useless to argue about which ideas of frequency and wavelength are the right ones. The ones you are using are more natural in many situations, the others more natural in other situations. But arguing is silly----like trying to say which is the "real" Planck constant. Is it hbar or is it h? The cycle wvlngth is also the natural one to use when talking about organ pipes and musical tones.

Hi Widdekind! I think your conclusion is correct. I haven't checked every detail. And you refer to something you are going to supply in a further post. But it is intuitive. You are assuming a planet with ocean where the ocean serves to stabilize and equalize temp. With that simplifying assumption what matters most is the annual flux. Even so, the effect of eccentricity might be small, even for e = 0.1 or e = 0.2. Worth considering though. Two atmospheric effects are also important, and work in opposite directions: * reflection off cloud-tops (increasing albedo) reducing effective flux that is actually absorbed, and * greenhouse The more massive terrestrial-type planets can be expected to have retained denser atmosphere and to have more of these two effects. ==================== I realize you have a graduate degree and an intense interest in the physics of habitable planet formation. Factors affecting how many habitable planets the current searches are likely to find, and what kinds of habitable-zone planets will be most abundant. I have seen a number of your short message-board "papers" at Astronomy Forum. I note that the Admin at astronomy forum thanked you for sharing. I agree with him that your stuff is interesting and food for thought. === I also think writing it up is a learning exercise for you. I believe you are currently going thru Bradley Carroll's Astrophysics text and it looks to me as if you adapt stuff you are learning about general astrophysics to address habitable planet issues. It is a good strategy for learning. You let your interest in habitable planets drive your assimilation of a textbook almost on a chapter by chapter basis, it appears. Whenever you learn some general fact or equation you think of how it might apply to your special interest. === Also you are learning communication skills by doing this and writing it up for messageboard. Here for instance, as a communication tip, you should have put "Summer" and "Winter" in quotes! To me it's obvious that you did not mean axis-tilt-type seasons, you meant perihelion and aphelion (near and far) seasons. For a planet with substantial eccentricity those are very important to consider! More important in some cases than tilt-seasons. Putting the terms in quotes could have made it clearer to the reader what you were saying. I've noticed in the exoplanet catalogues that many of the planets that have been discovered do indeed have quite large eccentricity compared with earth. As I recall it isn't unusual to see eccentricities as large as e = 0.2! You seem to have a proof here that orbital eccentricity should be included in formulas defining the habitable zone around any given star. I assume this is well-known. Now that you point it out it seems obvious. I am far from being an expert in this kind of thing so I don't know if they typically include it. I don't think this matters. Educationally your contribution can be good (both for you and us) as long as you develop the communication smarts not to excite member antagonism. Welcome, and good luck. === BTW why did you pick Bradley Carroll and Dale Ostlie's book? I don't know the book. Did you consider any others? What's especially good about C&O's text? Wow. OK, I see. C&O is the obvious choice for an introduction to Modern Astrophysics. I checked the amazon listing http://www.amazon.com/gp/bestsellers/books/13445/ref=pd_ts_pg_2?ie=UTF8&pg=2 It is the highest rank astrophysics textbook.

I understand. And what you calculated is a cycle length. The distance over which the wavetrain goes thru one full cycle of phase. There is an alternative idea of a radian of phase which is 1/(2 pi) of a full cycle. That gives an equally valid length to associate with the wave. The corresponding (radian-type or angular-type) wavelength is 1/(2 pi) of the more traditional (cycle-type) wavelength. Wavelength is not God-given, it is a human-made-up concept. You have your choice, associate a length with a full cycle of wave phase, or with a radian. So take your cycle-type wavelength and divide it by 2 pi. You will find it is Planck length. (I'm pretty sure you have been thru this already, so I'm not telling you anything new, but i want to make sure.) The basic lesson is that Planck units are normally defined using hbar, not h. Therefore when you calculate stuff with Planck units you should try to consistently use hbar, not h. In some cases this takes a little mental effort, to kind of shift gears, if you are very used to working with h in formulas. And it means keeping two alternative ideas in mind, to refer to occasionally. The angular freq. which is 2pi times the traditional cycle freq. The angular wvlngth which is the traditional cycle wvlngth divided by 2pi. These are natural quantities of freq and wvlngth to use when working with hbar.

You are doing great until you get to wavelengths. Then you let the fact that both h and hbar are used in physics confuse you. And no, the Planck volume doesn't have any special shape. It's like Swansont says----just a (very small) quantity of volume, like a liter. You can picture it as a cube, with planck length edges. I'm aware of what bothers you. The custom is to define Planck units using hbar. hbar is more used in upperdivision coursework. In my experience people prefer hbar. So they base the units on hbar. But when you use hbar it is more natural to measure frequency in radians per unit time rather than cycles per unit time. So if you are studying a photon, you might give its angular frequency (denoted omega) instead of its cyclic frequency (denoted f). And instead of the old formula E= hf you might write E = hbar omega. It is the same thing because hbar is reduced by a 2 pi factor and omega is increased over f by a 2 pi factor. And sometimes people define a reduced wavelength and write it lambdabar (lambda is the usual symbol for the cycle wavelength, and you put a slash thru it.) the reduced wavelength is c/omega. It is shorter than c/f, the cycle wavelength, by a factor of 2 pi. All this extra notation comes about because some physicists like to use h and some like to use hbar. ====== If a photon has energy E = planck energy, then its angular frequency (radians of phase per unit time) = one per planck time. and its angular wavelength (reduced, ordinary divided by 2 pi.) = one planck length. Maybe you don't like? I'm offering these as a way of getting used to situations where you use hbar a lot. It's really just a matter of getting used.

Cameron, if you wanted a scientific discussion you would need to provide some more coherent basis. Your conjectures and questions here are rather nebulous. For example might help to say what book, and what satellite you mean. Be definite, and give some links so that people can easily see what you are talking about. On the other hand the general tone of your post suggests you may simply wish to speculate and elicit speculative responses from others. In that case perhaps you don't need to give links or any solid detail, just give free rein to your imagination and have fun! Good luck, either way.

smart inference. I mean it. I'm not presuming to act condescending. You can learn alot of stuff just playing around with the model. If you ask questions about what some of the other output features are like e.g. "angular size distance" ask. Some I don't happen to know. some I do

Well now the data suggests that we may be in a spatially finite universe that will expand forever. What do you want to call that case, "closed" or "open"? Either way you are going to confuse and possibly mislead some of your audience. The last time this came up at another forum I take part in, folks settled down to the usage that closed meant spatially closed. So you could have a universe that is expected to expand forever and if a certain parameter which can be measured these days to within a few percent uncertainty, namely Omegak turns out to be less than zero then you have spatial closure----basically space like a 2D sphere surface except its 3D. So that would be a closed universe destined to expand endlessly. As the term is used on that forum. At that point we had a Princeton astrophysics grad student helping us get our terminology straight. Maybe the thing to do is never use a term like "closed" by itself. Always say things like "spatially closed" and "eternally expanding". Use enough words to be clear. I'd like to know your opinion.