Spyman

So you would sacrifice millions of lives just because you have an aversion to using nukes on them? That's mighty big of you. Where did I say that I have "an aversion to using nukes" or that I am willing to "sacrifice millions of lives" ? I thought we where talking about Apophis in this thread and I made it very clear that I was by stating the name of the asteroid. My point is that Aphosis won't cause the end of the world and that the pros and cons is not always that simple. I did NOT argue either against or for the use of nukes to deflect asteroids. Nobody is talking about using nukes now, or even in 2029. There simply is no need to do so. There's no need to do anything right now but observe. Where did I say that somebody was talking about launching nukes now ? If you read my post again you can see that I said more or less the same thing you are saying: "There's no need to do anything right now but observe". Again, my point is that Aphosis won't cause the end of the world and there is no need for panic.

The entire human race is NOT on stake here, Apophis could kill millions of people and cause a big catastrophe in an area of thousands of square kilometres, but most of us would survive and continue our lives. Also even the risk for an impact is tiny and it seems to get smaller and smaller with every measurement we make, so I would hold off any nuclear launches for now, there is still plenty of time for more precise observations with later actions if necessary.

Big Asteroid Less Likely to Hit Earth The large asteroid Apophis poses less of a threat of walloping the Earth in the year 2036 than previously thought, new research finds. "Updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036, for Apophis has dropped from one-in-45,000 to about four-in-a million." "The refined orbital determination further reinforces that Apophis is an asteroid we can look to as an opportunity for exciting science and not something that should be feared," said Don Yeomans, manager of the Near-Earth Object Program Office at JPL. http://www.space.com/scienceastronomy/091007-apophis-hazard.html

The Ehrenfest paradox concerns the rotation of a "rigid" disc in the theory of relativity. In its original formulation as presented by Paul Ehrenfest 1909 in the Physikalische Zeitschrift, it discusses an ideally rigid cylinder that is made to rotate about its axis of symmetry. The radius R as seen in the laboratory frame is always perpendicular to its motion and should therefore be equal to its value R0 when stationary. However, the circumference (2πR) should appear Lorentz-contracted to a smaller value than at rest, by the usual factor γ. This leads to the contradiction that R=R0 and R<R0. http://en.wikipedia.org/wiki/Ehrenfest_paradox

Thats more what I meant and I am sorry I missed your comment about this in your post #30. The OP says: Which I interpret as the device could be larger even if it only takes up about 10 cm of the hose lenght at the end, the transmission area for heating could then be made larger. The OP also later says: I wonder why 70º C ? For normal practicall purposes, in a home, you don't need that hot water. And with lower temperature it's also easier both to make smaller and to heat. [EDIT] Could Legionellosis be the cause for the high temp, where I live a heat rise in the hot water heater once a month is recommended to prevent the growth of bacteria. (It could also explain why the thread is in Biology instead of Physics or Engineering.) "Legionellosis is an infectious disease caused by bacteria belonging to the genus Legionella. Over 90% of legionellosis cases are caused by Legionella pneumophila, a ubiquitous aquatic organism that thrives in temperatures between 25 and 45 °C (77 and 113 °F), with an optimum around 35 °C (95 °F)." http://en.wikipedia.org/wiki/Legionellosis

Well, actually the OP want to increase the temp from about 6º C to 70º C, which means that the heater I linked is even more underpowered. I did not say that the your calculations where wrong, what I meant was that it's possible to have a "small" heater in the end of the hose that can rise the temperature to practically needs without extrem power sources or solar surface temperatures. Maybe I was wrong, but I made the assumption that the use of the device in the OP was to take a shower or clean your hands in a summer house or something similar.

I don't have any answer to the question in the OP, but calculations of 67 kW or 22 631º K sounds a "little" to high... This electrical through-flow water heater is small, only uses 3.5 kW and is still able to increase the temperature of a water flow of 2 l/min by 20º C through a water inlet of 1/2": http://www.azp-brno.com/p10421/aum-6-with-through-flow-water-heater-clage-3-5-kw-230v-50hz.html

Even if Dark Matter turns out to be wrong, the phenomens it tries to explain is observed and not something comparable to Santa Claus. According to Wikipedia, Dark matter is not only accepted as an scientific theory, but also the best supported explanation we have right now. "As important as dark matter is believed to be in the universe, direct evidence of its existence and a concrete understanding of its nature have remained elusive. Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in observed galactic rotation, some alternative theories such as modified Newtonian dynamics and tensor-vector-scalar gravity have been proposed. None of these alternatives, however, have garnered equally widespread support in the scientific community." http://en.wikipedia.org/wiki/Dark_matter

Dark matter is postulated to partially account for evidence of "missing mass" in the universe, including the rotational speeds of galaxies, orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. http://en.wikipedia.org/wiki/Dark_matter Stars revolve around the center of galaxies at a constant speed over a large range of distances from the center of the galaxy. Thus they revolve much faster than would be expected if they were in a free Newtonian potential. The galaxy rotation problem is this discrepancy between the observed rotation speeds of matter in the disk portions of spiral galaxies and the predictions of Newtonian dynamics considering the visible mass. This discrepancy is currently thought to betray the presence of dark matter that permeates the galaxy and extends into the galaxy's halo. An alternative explanation is a modification of the laws of gravity, MOND. http://en.wikipedia.org/wiki/Galaxy_rotation_problem

Kinetic energy is not the same as Force. The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. Negative work of the same magnitude would be required to return the body to a state of rest from that velocity. http://en.wikipedia.org/wiki/Kinetic_energy In physics, mechanical work is the amount of energy transferred by a force acting through a distance. http://en.wikipedia.org/wiki/Work_(physics) In physics, a force is any agent that causes a change in the motion of a free body, or that causes stress in a fixed body. It can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate, or which can cause a flexible object to deform. http://en.wikipedia.org/wiki/Force You can use the force of 10N to accelerate a ball during some time and it will then have a certain kinetic energy depending on the time and the mass of the ball. The air molecule or the person would be hit with the kinetic energy and some of the kinetic energy would transfer over to them during the collision. As they gain kinetic energy the ball is loosing the same amount but depending on the difference in mass a small ball is not going to accelerate a human to very high speed and cause the ball to bounce back, while a tiny air molecule is being pushed aside easily by the ball and is hardly able to lower the speed of the ball at all. In both cases they are affecting each other with equal forces, the human/molecule is accelerated with the same force as the ball is deccelerated with. But since the human has more mass than the molecule the influence and thus the force is greater than with the molecule.

I guess we are talking about some electrical fans here and even though they have a "marked" theoretical air flow, it is calculated for air normally standing still and only being pushed by the fan. If the air already is flowing the fans will probably be able to push it up to a little higher flow than rated. Electrical fans don't have a maximal RPM, they have a rating how fast the electrical current will be able to make them go and what air flow there is in the fans with that RPM. They normally don't have any mechanical breaks or other devices that will limit their maximal RPM, if the air flow increase then the RPM will also increase, up to the point where the fan will break, due to bearings failure or wings flying apart. Granted there will be a maximum level where the fans won't be able to increase the flow any further and instead the fan may start to act as an generator and try to draw power from the air flow, but that can be prevented electrically. The only restriction the fans make on the airflow that remains then is the friction in the bearings and the turbulence in the fan, which I think more or less can be neglected. In addition there is also times when the car is not going fast enough for producing higher air flow than what the fans support, where the fans actually raises the cooling and thus smoothes out the temperature in the car engine. More cooling before and after the high speed durations will also lower the overall engine temperature and preventing high peeks in the engine temperature will extend the engine life time. I would recommend installing the fans, the restriction on the air flow during high speed is tiny and the increase in lower speeds is great.

2012 phenomenon The 2012 phenomenon is a present-day cultural meme proposing that cataclysmic or transformative events will occur in the year 2012. The forecast is based primarily on what is claimed to be the end-date of the Mesoamerican Long Count calendar, which is presented as lasting 5,125 years and as terminating on December 21 or 23, 2012, along with plenty of speculation, such as interpretations of assorted legends, scriptures, numerological constructions, prophecies, and alleged channeling from extraterrestrials. A New Age interpretation of this transition posits that, during this time, the planet and its inhabitants may undergo a positive physical or spiritual transformation, and that 2012 may mark the beginning of a new era. Conversely, some believe that the 2012 date marks the beginning of an apocalypse. The 2012 doomsday prediction idea has been disseminated in numerous books and TV documentaries, and has spread around the world as an Internet meme through websites and discussion groups. The idea of a global event occurring in 2012 based on any interpretation of the Mesoamerican Long Count calendar is rejected as pseudoscience by the scientific community, and as misrepresentative of Maya history by Mayanist scholars. http://en.wikipedia.org/wiki/2012_phenomenon

energetix, do you think you are a duplicate of your past self or the past self that has aged ?

When someone use the wording "through space", I assume it's from the perspective of the object going through space. If the ant on the rubber band would have counted every step it took and measured how long each and everyone step was, it could calculate how far it had "walked" on the surface of the rubber band. But relative the ground of Earth it would have travelled a very different distance due to the streaching of the rubber band. Likewise if the photon carried a device to measure the distance it travels "through space", it would have showed 13.73 billion lightyears, but relative us the photon has traversed both "through space" and togheter with space, like how the ant also is brought away togheter with the rubber band when it streaches. The redshift observed is a combination of the emitting objects velocity away "through space" and the effect of expanding space on the lightray, but "velocity away" does not include recession speed of the emitting object due to expansion, you can't double the effects of expansion and have it twice. In theory we should be able to observe stuff with redshift between 10 to 1100 too, but it's not that easy in reality. When the distance to the emitter increases the photons gets more spread out witch causes the intensity to get weaker, our recivers need to be sensitive enough to pick up the signals or the signals needs to be strong enough. The CMBR was more lika a flash of light that then faded and the reason we still see it is because it was emitted from such a large area that light from the far end of the area has still not reached us, and younger light from the CMBR has already passed us and can't be viewed anymore. When the light from the end of Recombination had faded the Universe was dark until the first quasars and stars started to form from gravitational collapse. Quasars and Gamma Ray Bursts are very powerful lightsources and can easier be observed from larger distances than ordinary stars, and with more and more sensitive instruments we will probably be able to see further back in time. But even so, there will be a limit how far back we can see because there is no stellar objects there to see yet, at redshifts greater than 22 there is not thought to be any stars at all yet.

"Sometimes a distinction is made between the visible universe, which includes only signals emitted since the last scattering time, and the observable universe, which includes signals since the beginning of the cosmological expansion (the Big Bang in traditional cosmology, the end of the inflationary epoch in modern cosmology). The radius of the observable universe is about 2% larger than the radius of the visible universe by this definition. The age of the universe is about 13.7 billion years, but due to the expansion of space we are now observing objects that are now considerably farther away than a static 13.7 billion light-years distance. The edge of the observable universe is now located about 46.5 billion light-years away. http://en.wikipedia.org/wiki/Observable_Universe I would calc the radius of the "Visible" to about 0.98 × 46.5 = 45.57 billion lightyears, from that text. At the age ~400 000 years the Hubble Constant was ~1347787 km/sec/Mpc and matter at the distance of 40 million lightyears was receding from us with the speeed of ~57 times lightspeed. (Cosmos Calculator values: Omega=0.27 Lambda=0.73 Hubble=71 and Redshift=1100 for the CMBR.) "Huge strides in Big Bang cosmology have been made since the late 1990s as a result of major advances in telescope technology as well as the analysis of copious data from satellites such as COBE, the Hubble Space Telescope and WMAP. Cosmologists now have fairly precise measurements of many of the parameters of the Big Bang model, and have made the unexpected discovery that the expansion of the universe appears to be accelerating." http://en.wikipedia.org/wiki/Big_Bang It is not just some guesses, we can measure the brightness, spectrum and redshift of different supernovas and draw conclusions to build models. The Cosmos Calculator fits observed data and it's easy to use it to view different values for Hubble values and recession speed in the past by simply changing the redshift. Martin made a good thread about different angular diameter distance here: http://www.scienceforums.net/forum/showthread.php?t=22200 The distance covered by a photon, through space, during 13.73 billion years is 13.73 billion lightyears. The distance changes like the rubber band analogy in post #47.

The Cosmic Microwave Background Radiation is not from some area constantly emitting it, it was emitted from every region in the universe during a very short event in the past. From the closer regions from us, the CMBR has already passed us and from more remote distances it is still on it's way towards us. It has to be this way, because otherwise it should already have been long gone and no longer be observable. "The CMBR is well explained by the Big Bang model – when the universe was young, before the formation of stars and planets, it was smaller, much hotter, and filled with a uniform glow from its white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled enough, stable atoms could form. These atoms could no longer absorb the thermal radiation, and the universe became transparent instead of being an opaque fog. The photons that existed at that time have been propagating ever since, though growing fainter and less energetic, since the exact same photons fill a larger and larger universe." http://en.wikipedia.org/wiki/CMBR We don't know if the universe is infinite or not, but even if it's finite, it's very possible that it's much larger than what we are able to observe. The observable universe is everything we are able to see and observe, hence it's also the same as the visible universe, and it makes no difference if there is or not, a greater finite or infinite universe outside of it, it would still be called "the observable universe". We are due to large distances able to se stars the way they where billions of years ago, we know from other stars closer that they have evolved and changed by now, but they are still included in the observable universe since we can observe them. We are due to expanding space able to observe objects that at that time had a very high recessional velocity and as such we can calculate how much farther out they should be today, and they are also included in the observable universe since we can observe them. Even without the concept of an expanding space, we would still not be able to observe distant stars as they are or where they are today, the difference with an expanding space is that the travel time for light is larger than what the travel distance was when the light was emitted. "The observable universe contains about 3 to 7 × 1022 stars (30 to 70 sextillion stars), organized in more than 80 billion galaxies, which themselves form clusters and superclusters." http://en.wikipedia.org/wiki/Observable_universe Those 80 billion galaxies are inside the region that we can observe today, but the light from some of them could be very old and as such they might be in a different stage and place today, than what they where in when they emitted that light. Just like a good hunter estimates the speed of the prey and then aims and fires his rifle a little further forward, we can from our observations calculate where the objects should be today. Whether or not you prefer to use a calculated model of how our observable universe is thought to be today, a sphere with a radius of 46.5 billion lightyears, or how it's observed today, a sphere consisting of recent to 13.7 billion years old light, the estimate of 80 billion galaxies is still within there. ----- I am not able to follow you, what 2% and what exactly do you mean when you say "visible" ?

If the two ants starts at the same time, traverses the same path and distance, with the same speed, then they also arrive at their respective goals at the same time. It makes no difference if they are going in opposite directions or not.

OK, lets make an simple analogy: Imagine a large rubber band, 100 centimeters long, firmly attached in the end and the start is in your hand. Place a fast ant, with a top speed of 1 centimeters per second, on the band close to your hand. When the ant starts to run towards the end, you play a trick on the ant and start to streach out the band while it is running. Since you are much bigger than the ant, you are able to streach the band with 100 centimeters per second. Now, lets ask your question again, but slightly reformulated: In 100 seconds, the ant can travel 100 centimeters, so why couldn't the ant from 100 centimeters reach the end, (in 100 seconds)? How long do you think it would take for the ant, if you could continue to streach the rubber band forever? (Think about it before you read this thread: http://www.scienceforums.net/forum/showthread.php?t=24039) Now, to answer the quoted question, the light couldn't reach us at the available time because space was expanding to fast. But depending on the dynamic of the expansion it might be able to reach us at a later time.

Sorry, I managed to mess things up... 1) Somehow I misinterpreted the age of 396 000 years as 0.4 billion years, when it really is 0.4 million years or 0.0004 billion years. (Must have been very tired.) 2) Morgans Calculator don't show age values lower than 0.01 billion years and can't handle values higher than 1000 for Hubble. (Didn't have the ability to check it, at that time.) Closest I can get with the calculator, are with Hubble=970 and z=1.7, that takes us back to the age of 1.0 billion years and the larges distance light was able to reach us from, at that time, was 0.42 billions lightyears.

I don't think it's any good to measure distances in the early universe in the term of galaxies, since they are so small compared to the large distances between them and when the universe was ~0.4 billion years old, matter had not yet even started to compact enough to form stars, it was probably more like a soup of Hydrogen and Helium atoms. "The observable universe contains about 3 to 7 × 1022 stars (30 to 70 sextillion stars), organized in more than 80 billion galaxies, which themselves form clusters and superclusters." http://en.wikipedia.org/wiki/Observable_universe "Most galaxies are 1,000 to 100,000 parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs)." http://en.wikipedia.org/wiki/Galaxy (1 parsec is about 3.26 light-years.) Clusters contain from 50 to 1000 galaxies with even larger separation and they in turn, are grouped in superclusters with very large voids in between. About the causally connected distances: It might be possible to trick Morgans calculator to show how far away our area could be reached by light when the universe was ~0.4 billion years old. The Hubble constant changes with time and the calculator uses it among other things to keep track of time. But I am not sure if it will yield correct values or not by changing the Hubble value... If you still want to try it out, here is how: - First, here is the link again: http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html - Put in the values: Omega=0.27, Lambda=0.73, Hubble=71 and change the redshift until you reach 0.4 billion years in age Then. - It will tell you how large the Hubble constant was back Then, take that value and put it in for Hubble and the calculator will assume that the redshift you put in are if we where back in that time. - Now you need to find the redshift that lets you see the farthest distance away. Start with a low value for z and increase it until the distance Then stops increasing and start to decrease with higher z. - The distance Then, at the turning point, should theoretically be the farthest distance that light could have reach us from, at that time.

The thing here is that they are both snapshots of the event, if you want a movie you need a stream of images and if you want to continue to feel the gravity it needs to be updated. When the Moon orbits Earth, the gravity interaction gets updated continually and causes tidal forces as can be seen in the tides. (The speed at which the updates or wave propagates is with light speed.) The gravity wave that reached our area earlier, doesn't stick around any more than light does, it continues outward. So when light reaches us it is togheter with fresh and accurate gravity syncronized with the light. (Like the example with the two movie projectors.)

If Ω > 1 then Universe is shaped like a Hypersphere If Ω < 1 then Universe is shaped in a Hyperbolic shape If Ω = 1 then Universe is truly flat One aspect of local geometry to emerge from General Relativity and the FLRW model is that the density parameter, Omega (Ω), is related to the curvature of space. Omega is the average density of the universe divided by the critical energy density, i.e. that required for the universe to be flat (zero curvature). http://en.wikipedia.org/wiki/Shape_of_the_universe

The image from distant objects reaches us syncronised with the gravitationally attraction as it was, at the same time as the image was transmitted. I try to imagine gravity like a deformation of space that propagates like a wave with the speed of light, but one could also view it like a graviton moving through space. Since the photon and the graviton both starts at the same time and point, travels with the same speed and traverses the same path, they must also both arrive at the same time. Eg. if there is two movie projectors, showing the same movie in parallell, and one of them has the lens blocked in the opening of the movie, they would still be in sync, on the screens, when the lens cover is removed. So even if gravity is able to traverse the early Universe when light is blocked by matter, when the path is cleared light will be able to race through space, side by side with the gravity wave that is emitted at the same time as the photons, and reach the finish togheter.

Thanks for the correction Martin, actually I think I caused the mixup myself and not Wikipedia. They increased Dark Energy and not Omega to simulate the Big Rip in their paper. Here is the correct quote from Wikipedia: Closed universe If Ω > 1, then the geometry of space is closed like the surface of a sphere. The sum of the angles of a triangle exceeds 180 degrees and there are no parallel lines; all lines eventually meet. The geometry of the universe is, at least on a very large scale, elliptic. In a closed universe lacking the repulsive effect of dark energy, gravity eventually stops the expansion of the universe, after which it starts to contract until all matter in the universe collapses to a point, a final singularity termed the "Big Crunch," by analogy with Big Bang. However, if the universe has a large amount of dark energy (as suggested by recent findings), then the expansion of the universe can continue forever – even if Ω > 1. Open universe If Ω < 1, the geometry of space is open, i.e., negatively curved like the surface of a saddle. The angles of a triangle sum to less than 180 degrees, and lines that do not meet are never equidistant; they have a point of least distance and otherwise grow apart. The geometry of such a universe is hyperbolic. Even without dark energy, a negatively curved universe expands forever, with gravity barely slowing the rate of expansion. With dark energy, the expansion not only continues but accelerates. The ultimate fate of an open universe is either universal heat death, the "Big Freeze", or the "Big Rip," where the acceleration caused by dark energy eventually becomes so strong that it completely overwhelms the effects of the gravitational, electromagnetic and weak binding forces. Conversely, a negative cosmological constant, which would correspond to a negative energy density and positive pressure, would cause even an open universe to recollapse to a big crunch. This option has been ruled out by observations. Flat universe If the average density of the universe exactly equals the critical density so that Ω=1, then the geometry of the universe is flat: as in Euclidean geometry, the sum of the angles of a triangle is 180 degrees and parallel lines continuously maintain the same distance. Absent of dark energy, a flat universe expands forever but at a continually decelerating rate, with expansion asymptotically approaching a fixed rate. With dark energy, the expansion rate of the universe initially slows down, due to the effect of gravity, but eventually increases. The ultimate fate of the universe is the same as an open universe. http://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe And here is a quote from the "Phantom Energy and Cosmic Doomsday" paper: (by Robert R. Caldwell, Marc Kamionkowski and Nevin N. Weinberg) As we now show, if w < −1 persists, then the fate of the Universe is quite fantastic and completely different than the possibilities previously discussed. To begin, let us review these other fates. In a flat or open Universe without dark energy, the expansion continues forever, and the horizon grows more rapidly than the scale factor; the Universe becomes colder and darker, but with time the co-moving volume of the observable Universe evolves so that the number of visible galaxies grows. If the expansion is accelerating, as a consequence of dark energy with −1 ≤ w < −1/3, then the expansion again continues forever. However, in this case, the scale factor grows more rapidly than the horizon. As time progresses, galaxies disappear beyond the horizon, and the Universe becomes increasingly dark. Still, structures that are currently gravitationally bound, such as the Milky Way and perhaps the Local Group, remain unaffected. Thus, although extragalactic astronomy becomes less interesting, Galactic astronomy can continue to thrive. ... If Ω ~ 0.3, then the Universe is already dark-energy–dominated, and for w < -1 it will become increasingly dark-energy–dominated in the future. http://arxiv.org/PS_cache/astro-ph/pdf/0302/0302506v1.pdf

Like Airbrush says, gravity and atomic forces overcomes the expansion and keeps stuff in place, but it has been calculated: In their paper they consider an example with ω = -1.5, H0 = 70 km/s/MPsec and Ωm = 0.3, in which case the end of the universe is approximately 22 billion years from now. This is not considered as a prediction, but as a hypothetical example. The authors note that evidence indicates ω is very close to -1 in our universe. http://en.wikipedia.org/wiki/Big_Rip If ω is precisely -1 the Universe will continue to expand forever but not get ripped apart and with ω smaller than -1 the Universe will eventually start to collapse. http://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe