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#12
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what is the intensity of stellar radiation?
Jonathan Thornburg [remove -animal to reply] a écrit :
Of course, if someone is sending us a signal deliberately it could be much, much stronger. The Arecibo and JPL planetary radars are about 20 million times stronger, IF you are in the beam (a big if). We could detect one of these from about 5000 light years if it happened to be aimed at us. (Of course we have never looked at the frequency of the JPL radar, but that's another problem.) Aliens (if they exist) KNOW there is life here since the atmosphere is NOT at equiliobrium. SOMETHING must be producing all that oxygen. This atmospheric signal can be deduced from a spectrum of earth atmosphere, and needs technology slightly more advanced than what humans master now (10-20 years only) So, they know this planet has life since millions of years that this signal has been going on. We are an "interesting" target. THEN It is probable that they would point signals to us, if they want to communicate with us at all... Problem is that they could use other, much better ways of communicating than what we know NOW, for instance modulated neutrino beams. Photons are deviated by many things, neutrinos can pass through a whole planet without losing signal strength. Problem for us: we have no neutrino iPhone (yet). Obviously too, if they live in our immediate vicinity (50 light years) they have received the radio signal already that we are emitting all the time. Conclusion: After watching our TV shows they lost interest in us :-) |
#13
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what is the intensity of stellar radiation?
In article , Eric Flesch
writes: On Sat, 17 Jul 10, Phillip Helbig wrote: As a counter-example, it is not a coincidence in the big-bang model that the age of the oldest known objects in the universe is of the same order of magnitude as the Hubble time. In the steady-state model, however, this would be a complete coincidence. This is actually a pretty good argument against the steady-state model "Order of magnitude"? So if globular clusters are estimated with ages of 18 Gy, that is a confirmation of FRW's 14 Gy age of the universe? No, because there is no such thing as "FRW's 14 Gy age of the universe". The age depends inversely on the Hubble constant and also on the parameters lambda and Omega. For otherwise realistic values, the age is of the order of magnitude of the inverse of the Hubble constant, but can be somewhat larger. All the stuff about "universe older than the objects in it" was based on a too large value for the Hubble constant or (more often) assuming lambda=0 and Omega=1, which, unsurprisingly, is ruled out by observations. |
#14
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what is the intensity of stellar radiation?
On Fri, 23 Jul 10 07:18:16 GMT, Phillip Helbig wrote:
The age depends inversely on the Hubble constant and also on the parameters lambda and Omega. One has to wonder how there can be a Hubble "constant" in an "accelerating expansion" universe. Isn't it time to put the "Hubble constant" out to pasture? [Mod. note: even in a traditional decelerating universe, H is not a constant. In describing H_0 as a constant one is referring to its role as a constant of proportionality in the observed relationship between velocity and distance, not implying that it remains constant over cosmic time. Some people prefer to talk about the Hubble 'parameter' to avoid this confusion -- mjh] |
#15
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what is the intensity of stellar radiation?
On 7/17/10 8:02 AM, Phillip Helbig---undress to reply wrote:
As a counter-example, it is not a coincidence in the big-bang model that the age of the oldest known objects in the universe is of the same order of magnitude as the Hubble time. In the steady-state model, however, this would be a complete coincidence. This is actually a pretty good argument against the steady-state model, but as far as I know no-one thought of it before the steady-state model was no longer a viable candidate for other reasons. Check George Lemaitre Lemaitre predicted the Big Bang based on Einstein's equations before Edwin Hubble's observed universe expansion data http://en.wikipedia.org/wiki/Georges_Lema%C3%AEtre Richard D Saam |
#16
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what is the intensity of stellar radiation?
Thus spake Phillip Helbig---undress to reply
ax.de As a counter-example, it is not a coincidence in the big-bang model that the age of the oldest known objects in the universe is of the same order of magnitude as the Hubble time. In the steady-state model, however, this would be a complete coincidence. This is actually a pretty good argument against the steady-state model, but as far as I know no-one thought of it before the steady-state model was no longer a viable candidate for other reasons. I dare say people did think of the argument, but as there were no accurate age estimates for the oldest objects in the universe until quite recently, no accurate estimate of Hubble's constant or of the other cosmological parameters, it was not of much use. Regards -- Charles Francis moderator sci.physics.foundations. charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and braces) http://www.rqgravity.net |
#17
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what is the intensity of stellar radiation?
In article , Oh No
writes: Thus spake Phillip Helbig---undress to reply ax.de As a counter-example, it is not a coincidence in the big-bang model that the age of the oldest known objects in the universe is of the same order of magnitude as the Hubble time. In the steady-state model, however, this would be a complete coincidence. This is actually a pretty good argument against the steady-state model, but as far as I know no-one thought of it before the steady-state model was no longer a viable candidate for other reasons. I dare say people did think of the argument, but as there were no accurate age estimates for the oldest objects in the universe until quite recently, no accurate estimate of Hubble's constant or of the other cosmological parameters, it was not of much use. The age of the oldest stars was rather accurately know, certainly to within an order of magnitude. The steady-state universe has the Hubble time as the only parameter with the dimension time, but there is, within the steady-state framework, no relation between this and the age of the universe, so even an order-of-magnitude coincidence should appear strange. |
#18
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what is the intensity of stellar radiation?
"robert bristow-johnson" wrote in
message ... On Jul 15, 2:46 am, Steve Willner wrote: In article , robert bristow-johnson writes: For number use a noise temperature of ~18,000 for your calculations use the following. at 30 MHz use 18,000 K at 150 MHz use 450 K at 420 MHz use 47 K. for other frequencies around those I gave you assume the noise temperature goes as 1 over the frequency squared. The noise power from space is the bandwidth times the Boltzmann's constant times the noise temperature. You will have to add the noise power from the other sources. I would make an assumption of the signal noise ratio you would like to have is 10 to 20 since you'll probably will only be doing modulation and no coding. The signal to noise ratio you use will depend on the bit error rate you want the others to be able to detect. |
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