Martin

You have the story backwards, Piltdown. General Relativity was proposed in 1915, before the discovery of redshift-increase-with-distance (before the discovery of Hubble's Law) General Relativity implies that the universe's geometry is not static. This conclusion could be drawn without anyone observing redshift. In fact Alex Friedman derived the mathematical model of expanding universe in 1921---this was still some years before Hubble observed anything. There are many ways to check GR and many tests have been devised, starting with studying the orbit of Mercury. Including lightbending, binary pulsars, the GPS satellites, and so forth. GR is a coherent whole. If you can check GR by testing it against other kinds of observations, you get the expanding universe model as a byproduct. So far it has passed all the tests with admirable precision. This lends a lot of credibility to the universe model derived from it. The model itself can then be evaluated by fitting observation data to it. It is a simple model with few adjustable parameters and gives a remarkably good fit. Based on the standard model the masses of data which it fits, we then have pretty good idea of what to expect. Well that's an entertaining idea, but it isn't consistent with our theory of gravity which has been tested rather thoroughly (since proposed in 1915) and it is not consistent with our dynamic model of the unverse which dates back to 1921 and has also been well tested (especially since the 1990s with a bunch of new space instruments.) Right now cosmology is in a mode of refining the parameters. (And finding out more about the physics underlying them.) Any damn fool thing is possible, but don't hold your breath.

If by SETI you mean just the activities of the SETI institute then I haven't understood the question. What I mean by SETI is collectively the whole effort of listening for artificial signals (evidence of ETI). Arch has a source from the SETI institute that covers some other activities besides their own, and mentions a 1974 instance of transmission ==quote== Who else is carrying out searches? Astronomers from the University of California, Berkeley, are carrying out a search called SERENDIP IV at the Arecibo Observatory in Puerto Rico. About 3% of these data are made available for processing by the popular SETI@home screen saver software. The Planetary Society, an independent, privately funded organization, operated Project BETA at Harvard University (this search was stopped in 1999 due to damage to the telescope in a wind storm) and in Argentina. Ohio State University conducted a full-time search with a large volunteer effort for 24 years; however, this search ended in 1997 when the university shut down the radio telescope they used. New optical SETI programs are being conducted at the Univ. of California Berkeley's Leuschner Observatory and at Harvard University. Other radio searches are underway in Australia (see links to the SETI Australia Centre) and Italy. Additional SETI experiments, on a smaller scale, have been, and continue to be, conducted by individual scientists and radio amateurs in the United States and other countries. ==endquote== I don't know what the Berkeley/Harvard "optical programs" are. They might be looking for laser signals, which would be interesting to hear about. Are we also sending any signals? ...SETI researchers have not been very interested in broadcasting... Nonetheless, a few, mostly symbolic, intentional messages have been sent. One message, transmitted in 1974 from the Arecibo Observatory, was a simple picture describing our solar system, the compounds important for life, the structure of the DNA molecule, and the form of a human being. The message was transmitted in the direction of the globular star cluster M13, about 25,000 light years away. Personally I have no interest in transmission, but if a political decision were made to transmit then the kind of thing they did is technically smart. Focus on a small target containing a lot of stars, like a globular cluster. That way you can focus a tight beam and put a lot of energy in, and still have a lot of potential listeners. this is not science, it is politics, and of course there is a risk (which I reckon is very slight) of hostile reception. Transmission ought to be a collective political decision, if it is ever done again. The question is not well-posed. Who "hopes"? If you mean SETI the institute? They probably have official policy statements that give estimates of that sort. But what I mean by SETI is the whole collective activity of listening for signals, and an activity does not "hope". One can make a rough estimate of a plausible figure. Presumably the folks at Areicibo did their calculations and could reasonably expect that if they used a transmitter antenna the size of the Areicibo dish and aimed a tight beam at M13 then the folks in M13, 25,000 lightyears away, any who were listening with decent gear, would get it. There is no clear answer to such a vague question since it depends so much on how the listener is equipped. There are a lot of stars in M13 though. And it is a tiny tiny blob, so you can focus tight and bear down. It may have been dumb to transmit in the first place, but they did it technically smart IMHO. I'm not an expert on UFOs. As far as I know there have never been any convincing reports of ETI "Visitors" and no substantiated material evidence of past "Visits" has ever been found. What there is is silly books of garbage put out for the popular media. But I love Men in Black. I identify with Tommy Lee Jones and Will Smith, the good guys, not with that Evil Cockroach, although his character is kind of cool too. Rip Torn isn't bad either. Here's stuff on M13. http://en.wikipedia.org/wiki/Messier_13 It has hundreds of thousands of stars in a cluster only 145 lightyears wide, and is at a distance of 25,000 lightyears, so the angle is real small. Here's a good technical paper on optical SETI http://seti.harvard.edu/oseti/oseti_apj_preprint.pdf'>http://seti.harvard.edu/oseti/oseti_apj_preprint.pdf one of the links in this list: http://seti.harvard.edu/oseti/ Both Harvard and Princeton have optical SETI programs. Maybe it is time to wind down the radio search and get into optical. In the article they give the arguements and trade-offs.

Good! Then I vote for continuing that too for the time being. We need to do a reasonably thorough job. BTW my basic political premise here is what I'd call "astrodemocrat". I aspire that humanity should voluntarily cooperate to establish squishy life on a few earth-like planets. Some political slogan like "extend evolution to the stars by democratic means" That means that even though I consider finding terrestrial planets and planting our kind of life on them to be maybe the greatest goal or purpose of our species, still I would not support a dictatorial government that compelled humans to pursue this goal. So in a sense I don't care whether artificial radio/laser signals are there or not. We should know whether or not they are, so we should check. But regardless of what we find or don't find, we should work democratically and cooperatively to plant life on some earth-like planets. That is what I mean by "astrodemocrat premise". It is a basic value stance that goes beyond science. One has to distinguish clearly. SETI-business already goes beyond science. It involves political will, decisions, values. And likewise an astrodemocrat orientation does too. For example I would favor a nonviolent campaign to reduce world population because I think that woud increase our chances of achieving the goal of spreading our kind of life. Also I would favor developing intelligent machines able to do the planting and nurturing of whatever pioneer organisms. I don't expect the remote work to be done directly by humans because they don't live long enough and have very complicated lifesupport. More efficient to send machines to plant the seeds and hatch the eggs etc. Population reduction and developing intelligent pioneer machines are not scientific goals. They are political/ethical goals. To me this is a lot more interesting than SETI. And it puts SETI in perspective. but I don't knock SETI because it seems simple obvious common sense that you need to check what else is there.

Me too, on both counts! I think continuing support for listening for artificial signals is a voter issue. Not a science issue. Currently my vote is for continuing to scan the radio spectrum. I have no fixed preconception that I assume about what might produce artificial signal, for what purpose. I don't assume anything remotely like "Contact" scenario or any other scenario. I don't assume alien ETI would want to say "Hello". that is a novelistic plot device. Signal could be sent for reasons we cant imagine or would be a waste of time to speculate about. The question for now is, are there artificial signals in the radio spectrum or not. We have to have a plan with an "exit strategy". If we build sensitive receivers and make an honest try and don't get anything, then I would hope we figure out some other signal mode and wavelength band to try. I don't think it is science, it is just a commonsense Intelligence operation. It is about being well-informed about one's surroundings. Really? That is not the impression I got from listening to this guy being interviewed. I got the impression that he was looking for any kind of artificial signal broadcast for any reason. Anything coming down that was not the usual bleep and crackle that quasars and pulsars etc put out by known natural processes. Anything you could identify as not natural. And he stressed repeatability. Somebody else has to be able to look at the same spot and get the same result. This is a good point! I tend to accept it even though I have no confidence in my ability to "think like an alien". It seems to me, without my being at all knowledgeable, that the most likely thing if we get anything at all is to intercept a message from Party A to Party B. If we listen for a while and don't intercept, the that tells us something. Like maybe they don't use radio. Maybe they use lasers. Or there are no ETI. Or they don't communicate over long distance. Lots of possibilities. I wonder if the SETI people have a list of other communication channels besides radio that they think are possible. Might be interesting to see what theyve thought of. Anyway I don't have a scenario in mind. I just want to know are there artifical signals.

Airbrush, I have to disagree. Isn't SETI simply the search for artificial radio signals (coming from off-world)? In what sense does it "assume" anything? To me checking for artificial signals seems like an obvious commonsense thing to do. Even more basic than scientific research. It is a useful, possibly important, piece of information either way. Are there artificial radio signals from outside solar system? Or are there not? I would like to know. Would not you? I don't think of this as primarily science, although their could be science implications, connections to various sciences, science methods used, as with any technological project. Rather than science (discovering and testing laws of nature) I think of it as simply intelligent behavior. Don't you. ========================= 1. I think you and others are confused if you assume fearfulness or paranoia on the part of some ETI. I don't think there is a foregone conclusion. There may be no ETI but if there are they may not consider that they have anything to fear from each other. No scarce resources to compete for, etc. The reality might be violent predatory domineering paranoid battle prone romantic swashbuckly and all that. Stealing watery planets from each other and all that. Or it might not be. In any case, what one wants is to know the social reality of the Milkyway, whatever it turns out to be. Some ETI may have discovered that it is perfectly safe to communicate between parts of their community. That's possible. And they may use radio, if they haven't discovered something superior. 2. I think you and others are confused if you think that sending a radio message on a beam from City A to City B automatically gives away the position. Suppose there are ETI in various locations and they are just carrying on their business and they want to beam some data. Maybe they aren't afraid of revealing position but even were they the risk is not prohibitive. When you intercept a beam all that tells you is the direction it is coming from. As an instance, if someday we point an antenna at the Andromeda galaxy (a small fuzz-blob) and happen to receive an artificial signal, all that means is it is coming from somewhere in Andromeda (hundreds of billions of stars). Probably all it means is that a computer somewhere in Andromeda wanted to talk to a computer somewhere in Milky. And that the first computer didn't reckon it was risky for it to go ahead and talk. You can think of other instances on a more nearby scale involving communication from smaller structures, like the Clouds of Magellan, or within our own spiral arm of Milky. If anybody thinks that life (machine and squishy) could never evolve the ability to communicate by radio beam over a larger distance than 1000 lightyears, then please just scale down my examples to something you find more credible. It's easier to talk in terms of known features like Andromeda.

Certainly. Extraterrestrial microscopic stuff seems much more likely than spacefaring high tech life. Seems like a no brainer. I doubt you offended anyone here. You didn't say anything very original, or that I haven't heard often enough, but that's fine. (I don't excel at originality either.)

Sorry for butting in, I just saw something on Colbert Nation. I dont normally follow that but heard he had a guest on who is an author of a book about the ET hunt http://www.colbertnation.com/the-colbert-report-videos/228301/may-20-2009/seth-shostak The book's name is Confessions of an Alien Hunter and the author is S. Shostak. From what the guy said, in the brief interview, especially at the end, it sounded like he didn't expect to find "squishy things" like us, as intelligent life. What he thought most likely he said was "artificial intelligence" in other words machine life. This agrees with what I had suspected from a simple Darwinian evo perspective. Conscious squishy life is like the larval or caterpillar stage and it matures into an adult phase which is conscious machine life. Colbert suggested "robots?" and Shostak said that gave the wrong picture---machine life doesn't have to have arms and legs that look like like anthropomorphic robots. It doesn't have to be made after our vertebrate image. I was surprised to find someone whose career is SETI and is promoting a SETI book who is thinking along those lines. It is the same old technology. He described the big dish antennas, and the kind of artificial signal (not natural noises) they are looking for. Mentioned the movie "Contact" with Jodie Foster, to help the audience picture the kind of work he's involved in. What I wonder is how do people like that get money if they are honest and say they want to eavesdrop on communications between advanced conscious computers. It doesn't sound sexy or appealing or even scary. No Klingons. No blue-skinned babes with nice boobs. How long will the public put up with it on such sterile terms?

All right. Both you and NowThat think so. I'll try to adapt and use it more flexibly. But I'll sometimes call attention to it's meaning different things. will get back to this, have to go.

observing with photons is limited by scattering---we only see back to about year 380,000 and then there's the hot fog. but what about observing with neutrinos? What are your thoughts on that? How far back in time might that permit observation? How close to the start of expansion, do you think?

Current measurements do not indicate that space is flat, even on average. They indicate that on average it is nearly flat. There is a difference if you are talking about a global frame. Didn't we discuss the WMAP 2008 estimate of the radius of curvature? They said if space is a hypersphere then the radius of curvature (with 95% confidence) is at least 100 billion light years. This was based on the combined data from WMAP, the galaxy counts, and the supernova data available at the time. My understanding of a reference frame is that the spatial part is an infinite flat Euclidean space----orthogonal x,y,z. Obviously you can't fit such a thing onto a hypersphere. You have really good intuition and a lot of inititiative, you think vigorously (is my impression). But you seem to think "reference frame" can mean what makes sense to you for it to mean. My experience is different. I find that when people say "reference frame" they mean something technical with some kind of rectilinear coordinates. Either it is flat Minkowski space of special rel, or it is conventional Euclidean space. That might not be what I would like them to mean---it is simply what they do mean. It is not my choice, it's just how it is. If we could force people to use words the way we want, that makes the best sense to us, then I would agree with you that a hypersphere together with time could be a "reference frame". ======================= where did you hear that space was flat? As far as I can remember I have never said such a thing. We don't know. Of course it is obviously not flat locally. The sun bends light rays. All sorts of things do grav. lensing. Space is very wavy gravy. But it MIGHT be zero curvature if you take a very largescale average. We just do not know, and as far as I'm aware there has never been a scientific journal report that says we do know the overall curvature. Since 2004 anyway, what I have seen always has a confidence interval on the overall average curvature. The confidence interval is always around zero, so it includes zero curvature as a possibility, but not a certainty. I'm getting tired of talking about "reference frame". It is just quibbling about words. We agree that there is a global universe time that is used in cosmology. Only approximately measurable but still practical. And fairly natural. We don't agree that there are natural rectilinear space coordinates. (and we don't even know the largescale overall spatial shape) Instead of talking about "reference frame" I'd like to talk about largescale curvature. The latest data I know about that is March 2008. That is over a year ago. You and I may have discussed it. Did you look at Table 2 in that paper Komatsu et al? Ned Wright was one of the co-authors. Do you remember the confidence interval for the curvature? The data was WMAP+BAO+SN*. Have you seen anything more recent? This was a major NASA report. As far as I know it is still the most reliable and authoritative source. *microwave background+galaxy counts+supernovae data

These are all three thoughtful stimulating posts---thanks Airbrush, Sherlock, Moontanman. I can see a point to what S. says namely consciousness in its various forms is extremely interesting. If future squirrels developed some mathematics I would be really interested in learning how it compared with human-invented mathematics. If super-evolved parrots happened to discover laws of physics, I would be extremely curious to know if they were the same as Newton's. Or Heisenberg's. But if we had interfered and taught the parrots ours before they discovered their own, then it wouldn't be as fun or valuable. I don't mean just counting acorns, or skillful flying. I mean mathematics on par with ours, but presumably different. How different could it be? Are the laws of physics, the concepts like energy and angular momentum, unique. Does every ETI discover the same set of concepts and laws? Does every ETI have some analog of pythagoras, pi, sine and cosine, calculus? If not what range of variation is possible? I can see that every un-interfered-with consciousness is a uniquely valuable asset, if you desire understanding. So I can see the point of not bothering your neighbors if they seem to be in the process of evolving consciousness---if it was a different kind of consciousness that you thought you could learn something from. Maybe learn something new about the universe by watching alien thought and understanding develop. There would be a self-interest motive not to interfere. Because what does interfering get you? That is worth anything. Goes along with Sherlock's idea. =================== I can't contribute to the basic thread topic though. I have no idea how to estimate the number of ETI species in the galaxy. Or star systems inhabited by ETI critters. Basically it is a Darwinian evolution problem. whatever else life does it evolves to fill niches. Most niches I can think of are suitable for selfreproducing robot life, rather than wet meat. And evo is always doing surprising stuff, and altering and creating new niches. So I don't even trust my intuition about the directions of future evo. Whatever intelligent life evolves to (starting say in watery earthlike planets but then evolving more widely viable forms) it probably is life-forms that can live in vacuum and endure hard radiation and wide temperature range----because there are more environments to live in that are vacuum and exposed to radiation (the kind you have to shield astronauts from, solar flare stuff). So when you go thru the logic steps of the Fermi Issue, you need to have a realistic picture of what widespread or galaxy dominant species are like and what their desiderata are. Which I don't expect they would be interested in watery earth-like planets, except to study. Because they don't need liquid water, or atmospheric pressure, or an ozone layer to block UV, or Kentucky Fried Chicken to eat, or someplace to go to the bathroom, probably. If there are any evolved species in the galaxy, I mean. There might not be any, of course. So but if there are some, Fermi asks "where are they?" and I go "why should they come? why would the earth be of interest except as something to study?"

Thanks, that's an interesting bit of news. An observational first of sorts. Some notes on Low Mass X-ray Binaries here: http://en.wikipedia.org/wiki/X-ray_binary Possible explanation for the 511 keV gamma coming from galactic core.

Yes. In cosmology there is an idea of global time. sometimes called universe time. also Friedman time, because it goes with the Friedman model. that gives a standard way to slice spacetime into a succession of spatial slices, 3D hypersurfaces, each of which is a "now" containing all the simultaneous events, events which are simultaneous in the sense of occurring at one particular moment of the global time. But these spatial hypersurfaces are not flat. There is no way to put rectilinear space coordinates on that cover the whole 3D space. No. It wouldn't in the way I understand "frame". I think of a reference frame as involving not only a time coordinate but also spatial x, y, z. Maybe we should have a poll to find out what people here at SFN think a "frame" is. I think we are just having a minor verbal difficulty here. I have never said that cosmo has a preferred reference frame. I have always said that cosmologists have a preferred time. They do. It is involved with their main equations and built into the standard cosmo model and absolutely essential. But personally I always avoid saying preferred reference frame because I have never seen one in cosmology. What I would call that. They use several different systems of space coordinates, whatever is suitable for the purpose at hand. I don't think there is ever assumed one preferred x,y,z that covers the whole. I can't imagine what that would look like or how you could make sure it was right, or how you would define it, or on what basis you would prefer it. I feel a bit inadequate here even talking about it because I just can't imagine what it would mean. Maybe someone else has a different more clear idea, and can talk about it.

There is something I'm missing here. A "preferred reference time" is fine, the professionals already have that and it is standard. But how do you get a global frame from that? What do you do for spatial coordinates? We don't know the largescale topology of space. One set of spatial coordinates might not fit the whole thing! Like one flat map does not cover the whole earth. You can only make flat maps of a curved surface if you work in small local patches. I don't see how anybody can talk about a preferred reference frame (except limited and local, for a given observer). What am I missing?

Well I certainly do not consider widely separated points to be part of the same reference frame. Reference frame is a technical idea belonging to special rel (which doesn't apply over large regions of curved spacetime!) So you can toss the concept of reference frame in this context. But there is of course a criterion of rest, and of simultaneity, which cosmologists use all the time. Their Friedman model employs it, as does the Hubble Law. What do you mean "frame", exactly? There is definitely Friedman time, a preferred time slicing into (curved) spatial hypersurfaces. But I don't know of any frame, in the rectilinear sense of special rel, that is globally applicable. That wouldn't make sense, except perhaps in some special case like a universe without matter. I have to go. Will check in later. MacSwell, we may have a merely verbal misunderstanding here. Cosmologists have a preferred time, universe time, Friedman time, that enters into everything. But they do not have a preferred frame. Anyway I never heard of one. Maybe you are confusing the ideas of global time with global frame (which doesnt occur in cosmology).

Grant (GDG) gave a good answer, I thought. MacSwell asked a question about how distance expansion differs from ordinary motion. MacSwell, in ordinary motion you get somewhere, there is some destination you approach. But in standard cosmo espansion nobody gets nearer anything. It simply means that the geometry (the gravitational field) is changing. All (largescale) distances increase and you don't go anywhere. So naturally special rel time dilation does not apply! How could it? Nobody is moving. NowThat, the 1915 lesson is that when you say gravitational field you mean geometry----the catalog of distances between things. If you want to talk about recession rates (the rate of increase of distance between objects which are not moving) then that necessarily means talking about geometry. Changing geometry is what you are talking about. General rel is our only handle on that (unless you count the newer quantum versions of GR too). So it isn't practical to ignore GR in your scenario. Recession is not ordinary motion (it doesnt go anywhere) and therefore it is not subject to Special Rel.

More accurate measure of supernova brightness means more reliable distances. (Type Ia SNe are used as standard candles.) This will enable more accurate measure of the Hubble rate---the expansion rate/distance ratio basic to cosmology. The SciAm has a news item about this: http://www.scientificamerican.com/blog/60-second-science/post.cfm?id=a-better-way-to-size-up-distant-gal-2009-05-22 ===sample excerpt== the new method can be used to measure a supernova's luminosity, and hence distance, much more quickly, and with a level of accuracy the study's authors say surpasses the traditional approach. The researchers found that the ratio of the brightness of two colors in the supernova's light spectrum strongly correlate with the explosion's magnitude. Specifically, the ratio of 642-nanometer-wavelength (orange-red) light to that of light with a wavelength of 443 nanometers (indigo) gives an accurate estimate of the supernova's brightness, in concert with other observed characteristics. Type Ia supernovae are useful as markers because of their fairly standard brightness, which facilitates gauging their distance across the universe. Their uniformity derives from unusual birth circumstances: they are believed to arise from white dwarfs that have swollen to 1.4 times the mass of the sun by drawing material from a nearby companion star. At that point, says study co-author Greg Aldering, a cosmologist at Lawrence Berkeley National Laboratory, "a white dwarf star cannot support itself against gravity," exploding in a thermonuclear blast that is visible even in distant galaxies. "The conversion of a fixed mass—1.4 solar masses—into energy," Aldering says, "sets a reasonably narrow range to the resulting brightness."... ==endquote== http://arxiv.org/abs/0905.0340 Using Spectral Flux Ratios to Standardize SN Ia Luminosities S. Bailey et al. (The Nearby Supernova Factory) 6 pages, 3 figures, 2 tables; accepted by A&A Letters (Submitted on 4 May 2009) "We present a new method to standardize Type Ia supernova (SN Ia) luminosities ... When combined with broad-band color measurements, spectral flux ratios can standardize SN Ia magnitudes to ~0.12 mag. These are the first spectral metrics that improve over the standard normalization methods based upon light curve shape and color and they provide among the lowest scatter Hubble diagrams ever published." The Hubble diagram is the plot of recession rate (like in kilometers per second) against the estimated distance, for lots of galaxies. Ideally all the dots should fall along a straight line. The slope of that straight line will be the Hubble rate----like 74 km/s per megaparsec. For each additional megaparsec of distance, the recession rate increases by 74 km/s. But there has always been some scatter. So it was uncertain exactly what straight line slope.

That is a really good question. The temp was 3000 kelvin, so it was more orange than the surface of the sun, which is 5800 kelvin. There are stars which are less massive than the sun, which burn a little cooler, and whose surface temperature is 3000 kelvin. Their light would be that color. It is a blackbody thermal mix of wavelengths. Actually the tungsten filament of an oldstyle 100 watt bulb operates at about 3000 K. You know how incandescent lightbulb light is slightly more yelloworange than clear sky sunlight? Your eye adapts quickly so we think of a pure white piece of paper as the same color indoors as outdoors but if you measure the mix of wavelengths in daylight it will be a different lopsided bellcurve distribution from what comes off the paper under artificial illumination. Graphics designers sometimes describe different types of "white" light by their temperature. The closer to 5800 the closer to daylight. There's actually more to the story. It's kind of interesting. Maybe have a look at the Pedia on "black body radiation" http://en.wikipedia.org/wiki/Black_body at each temp there is a standard mix of wavelengths for that temp radiated by a generic object. sunlight is well described by the same blackbody formula (but for 5800 kelvin) as also describes the invisible heat spectrum in an oven (at whatever kelvin baking temperature) you just plug a different temperature in but it is the same blackbody formula and similar looking curve---sort of lopsided bell. Good to know about this. Merged post follows: Consecutive posts merged Good way to put it! Independence day that year was the day all the photons got free and could run forever. Before that, the fog was dense enough that they were constantly being absorbed and re-emitted and scattered. So on July 4 they gained their liberty.

One of the designers of the stanford linear accelerator used to say that the klystrons made waves and the particle (an electron) rode the wave "like a surfer". You don't have to say that it is magnetic waves, you can emphasize the electric component of the wave. The electron is like on a surf board, and it has a big concentration of negative charge behind it pushing and a trough or low point of negative charge ahead of it (or think of it as positive charge pulling). So naturally it accelerates. So the accelerator is several kilometers long and there is this long long line of large klystron tubes all the way along the tunnel. They are big tubes like as big as a man, they are cylinders full of vacuum. They make the wave of positive negative electric force, that the "surfer" electrons ride on. You asked how a klystron works. The klystron tube is used in television broadcast and radar and all places where you need a lot of microwave power. Think of it as an amplifier. It works by "bunching". You put energy into an electron beam by a highvoltage electron gun and at the start or base of the beam you apply a weak little fluctuation which alternately slows down some and speeds up others. Then like cars on the freeway, if some go a little faster and the others go a little slower after they have gone some distance along their road they will be bunched. Then there is a brief concentration of negative charge, as the bunch passes by. This gives an alternation of high and low charge density. The driving beam of each klystron is not the same as the science beam that is going down the long tunnel. The driving beam is just inside each klystron tube and it is only a means of making wave power---of amplifying an originally weak microwave signal. Cam, since you live in Madera, California, you probably drive sometimes on the SF Peninsula and you may know highway 280. The 3-mile stanford accelerator called SLAC crosses 280 at around Sand Hill road exit, a Palo Alto exit. The 280 freeway is very beautiful in the hills and along reservoir lakes. Often fog comes in from the ocean over the hills. As you approach Sand Hill road exit you can see the long straight SLAC shed that goes sort of east-west crossing under the freeway at right angles. You can go off there to main office and arrange to take the tour. They will show you the klystrons and explain. Take your girlfriend, if you have. It is beautiful and impressive at the research facility. After all, it was built for the honor of the human mind.

Some interesting stuff in the Sci Am about Planck and Herschel http://www.scientificamerican.com/article.cfm?id=planck-herschel-launch http://www.scientificamerican.com/blog/60-second-science/post.cfm?id=europes-planck-and-herschel-spacecr-2009-05-14 The second one has a video

The Hubble rate figure of 71 (km/s per megaparsec) has been the standard one to use for over 10 years now, since 1998. One of the main reasons for the HST was the socalled "Hubble Key Project" of determining it. And that team reported in 1998. There was a range of uncertainty though. Now it looks like, using the HST during the years since 1998, they have narrowed the uncertainty to about 4 percent and have a new estimate of 74. It will take some time for this to be accepted, and for changes to be made. Like the default parameters in Ned Wright's calculator are still 0.27, 0.73, 71. I would guess that eventually the default numbers will change to 0.25, 0.75, and 74. That leaves us in a slight dilemma. Should we continue using the old numbers or should we change over to what we guess the new ones will be? Well, what difference does it make, if any? Percentage-wise not much. The CMB redshift stays 1090. Redshifts in general don't change. The age of expansion becomes 13.4 billion years instead of 13.7 or 13.8 or whatever it was. The distance to last scatter becomes 45.2 billion lightyears, which is about what we were saying before. The particle horizon---the radius of the observable---is 46 billion lightyears, which is just what we have been calling it! So since we have been speaking in approximate terms all along, and the percentage changes are not very big, I'm kind of tempted to shift over to the new numbers. Don't want to jump the gun, but if this kind of thing only happens every 10 years or so, why not enjoy it? =============== In case anyone is curious here are technical details. The Komatsu WMAP report, in Table 1, gave a figure of 0.1358 +/- 0.0036 for Omegamh2. Cosmologists have a conventional symbol h to show dependence on the Hubble parameter. It is just the numerical value of H divided by 100, so with the new Hubble rate of 74, this h will be 0.74 To get the matter fraction Omegam we just have to divide 0.1358 by the square of 0.74 That gives 0.248, call it 0.25. To a rough approximation, space she is flat, so let's put OmegaLambda = 1 - Omegam = 0.75. Sources: Riess et al give the new value of 74: http://arxiv.org/abs/0905.0695 Here is Komatsu et al, if you want to check Table 1 for Omegam: http://arxiv.org/abs/0803.0547v2 The figure of 0.1358 is an average determination three datasets: WMAP + BAO + SN, that means the microwave background plus galaxy counts (ripples in the overall distribution of matter) plus supernovae. They tend to prefer that to basing the determination of numbers on just one approach. Table 1 gives the separate estimates and then it gives the average in the column labeled WMAP + BAO + SN

http://www.esa.int/esaMI/herschelplanck/index.html a lot of media stuff about it at this site.

http://www.esa.int/esaMI/Planck/SEMVW10YDUF_0.html Planck mission is a big deal. More accurate observation of the microwave Background. Planned for launch 14 May, along with another satellite observatory called Herschel. Wish 'em luck!

Delighted to see this! Cosmologists love to challenge their own standard model. Constantly trying to catch it at fault some way---at odds with some data or other. Good scientists in that way. Sounds like another wave of interest in MOND (modified gravity). I've seen no indication that Dark Matter is losing support to any significant extent. Too much in its favor. Interest in MOND was stronger back in 2006 before the bullet cluster news. Used to see several MOND articles nearly every week. Not so much research on modified gravity during 2006-2008. But now in 2009 there may be another flurry of interest. I think it is too early to be expecting General Relativity to be overturned. But this development is certainly something to watch! I will get the links to the Metz papers, and try to keep track myself. Meanwhile please let us know if you see anything more. IMHO from the look of the abstracts there is a bit of tub-thumping going on. PhysOrg source was Bonn University, which has an interest in overstating the importance of the local hero's results. And they don't seem to have found much that is earthshaking. DM is based on thousands of galaxies and clusters of galaxies, including maps of DM concentration by weak-lensing. These people have some isolated observations of stuff right around our galaxy which at least for the time being they can't explain otherwise and are promoting MOND to explain it. Gotta be open to this kind of thing but not go off half cocked. http://arxiv.org/abs/0903.0375 Did the Milky Way dwarf satellites enter the halo as a group? Manuel Metz, Pavel Kroupa, Christian Theis, Gerhard Hensler, Helmut Jerjen (Submitted on 2 Mar 2009) The dwarf satellite galaxies in the Local Group are generally considered to be hosted in dark matter subhalos that survived the disruptive processes during infall onto their host halos. It has recently been argued that if the majority of satellites entered the Milky Way halo in a group rather than individually, this could explain the spatial and dynamical peculiarities of its satellite distribution. Such groups were identified as dwarf galaxy associations that are found in the nearby Universe. In this paper we address the question whether galaxies in such associations can be the progenitors of the Milky Way satellite galaxies. We find that the dwarf associations are much more extended than would be required to explain the disk-like distribution of the Milky Way and Andromeda satellite galaxies. We further identify a possible minor filamentary structure, perpendicular to the supergalactic plane, in which the dwarf associations are located, that might be related to the direction of infall of a progenitor galaxy of the Milky Way satellites, if they are of tidal origin. http://arxiv.org/abs/0901.1658 Discs of Satellites: the new dwarf spheroidals Manuel Metz, Pavel Kroupa, Helmut Jerjen (Submitted on 12 Jan 2009) The spatial distributions of the most recently discovered ultra faint dwarf satellites around the Milky Way and the Andromeda galaxy are compared to the previously reported discs-of-satellites (DoS) of their host galaxies. In our investigation we pay special attention to the selection bias introduced due to the limited sky coverage of SDSS. We find that the new Milky Way satellite galaxies follow closely the DoS defined by the more luminous dwarfs, thereby further emphasizing the statistical significance of this feature in the Galactic halo. We also notice a deficit of satellite galaxies with Galactocentric distances larger than 100 kpc that are away from the disc-of-satellites of the Milky Way. In the case of Andromeda, we obtain similar results, naturally complementing our previous finding and strengthening the notion that the discs-of-satellites are optical manifestations of a phase-space correlation of satellite galaxies.

I'm glad you had a look at some of those sources. Check out Einstein Online if you have time. It is a public outreach website of one of the world's top research institutions (Germany's network of Max Planck Institutes). I'm not sure exactly what you have in mind but the hollow cone or "horn" shape is a common and handy way of picturing the whole expansion history. The whole spacetime. In that case the rudimentary toy-model of space is a 1D circular ring. The time axis is along the cone, and it shows the rings getting larger as you go from left to right. It's a trade-off, including a time coordinate, so the whole history is modeled, means an even more rudimentary representation of space. In the balloon we already simplified by having space be 2D. In the horn picture space is a mere 1D circle, with 1D creatures and objects living in it. Remember that spacetime does not expand. The expansion of spatial distances only. So one does not want to have "expansion in all directions". One only wants to model expansion in all spatial directions (which takes place in the course of time without time-expansion, whatever that would mean ) The jury is still out on whether flat or nearly flat. Average density cannot be measured with absolute precision. So far average density says at least it is nearly flat, and possibly flat. But we don't know yet. Yes that is a very real possibility. It just means we have to work harder and build and launch better instruments. This month a new orbital observatory goes up---called Planck Surveyor. It will be able to determine the curvature still more accurately than the previous spacecraft, Cobe and Wmap, did. Planck Surveyor launch is set for May 14, which is in three days from today. Keep an eye on the website and wish it luck! http://www.esa.int/SPECIALS/Operations/SEM45HZTIVE_0.html http://www.rssd.esa.int/index.php?project=Planck http://en.wikipedia.org/wiki/Planck_Surveyor