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That brings us quite a bit closer to an interstellar-capable engine. So my question is, would this actually work from a physics perspective? For the purposes of this question, I'm not interested in practical issues. Assume that we have the technical capability to build an absurdly lightweight superconducting dish antenna thousands of kilometers in diameter, a fusion reactor that can generate ridiculous amounts of power, and radiators that can reject arbitrary amounts of waste heat.

If the antenna is very directional and much larger than the waves and before the uniform plasma density distorts it will be like pointing a laser from the center of a mirrored hollow ball, the whole beam will hit you and maximum efficiency will be achieved. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. The interstellar medium reflects extremely low-frequency radio waves. Could we use this fact to build a more efficient photon rocket? Ask Question. Asked 1 year, 4 months ago. Active 1 year ago. Viewed times.

Thorondor Thorondor 1, 8 8 silver badges 29 29 bronze badges. The reflection will be a very? It seems to me that because of the large wavelength, the effective aperture of the antenna would be large compared to the distance the radio waves could travel before being reflected. Thus, there's nowhere for the reflected beam to go besides the antenna. An ordinary MHD drive cannot exchange useful amounts of momentum with the interstellar medium because there simply aren't enough atoms to push against. Hence, one usually attempts to maximise the bandwidth.

The easiest way is usually to follow the example of the above plot and to split the total bandwidth, BW, into a number of smaller channels. The signals are then detected and delayed before summing as described above. Of course, there is still dispersion smearing in each of the smaller channels, so that the channel width is chosen depending on observing frequency and aim of the observations. We will review another de-dispersion method, which removes dispersion completely, below.

The sensitivity of the observation, or the "signal-to-noise" ratio describing the strength of a signal compared to random noise, depends on more parameters than just the bandwidth of the receiving system: The size of the telescope matters, which is described by the "gain" parameter. The larger the telescope, the larger the gain, G. Each piece of equipment involved produces a random thermal noise signal.

This is the reason why one tries to cool receivers to temperatures of only a few degrees above absolute zero. Any remaining thermal noise signal is described by the system noise temperature, T sys. Thermal noise is a random signal, while the pulsar signal arrives periodically with the pulsar period. Averaging "integrating" the received signals over a period of time, will therefore reduce the random noise relative to the real signal. A simple receiver system is only sensitive to one of two orthogonal polarisation directions.

One usually combines two such systems, to measure the intensity in both directions. Effectively, one then increases the used bandwidth by a factor equal to the number of received polarisations, N pol max. All of the above considerations are combined in the equation displayed in Figure 2, where K is a constant of order unity and S the strength of the pulsar. The diagram also summarises the typical situation during pulsar observations.

Figure 2.


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Schematic of pulsar observing system. The pulses emitted by the pulsar upper right propagate through the interstellar medium ISM , before being picked up by a telescope and the installed receiving system. In a standard approach the total bandwidth is split into smaller channels by a filterbank for each polarisation. The signals of each filterbank are acquired by a data acquisition system and recoded along with information from the observatory's atomic clock which is synchronised to an international time standard with GPS. Figure 3.

This new system uses a de-dispersion method called "coherent de-dispersion" which is able to restore the original pulse shape completely. Although this method requires substantial computing power, it removes all dispersion smearing, producing much sharper pulses. Sharper pulses allow us to measure the arrival times of pulses to a much higher precision which is important for pulsar timing see next section.

The residuals between a good model and actual pulse arrival times scatter around zero. Figure 4 d. Deviation with one year period and increasing amplitude due to inaccurate proper motion.

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We have already discussed the effects of dispersion on the arrival time of pulses. Much more fundamental is however, that the arrival time must be different for any telescope and must also change with time of day and time of year as any given telescope is moving in space due to the Earth's rotation and movement around the Sun. For our experiments we should refer to the arrival time at a point in the solar system which is at rest. Such a point is the system's centre of mass, the so-called solar system barycentre.

It will focus on one of the most fundamental issues addressed at the conference.

This is the question of whether the deep underlying structure of language would likely be the same for extraterrestrials as for us. The eminent Linguist Noam Chomsky developed this theory in the middle of the twentieth century. Two interrelated presentations at the symposium addressed the issue of universal grammar. The first was by Dr. Bridget Samuels of the University of Southern California. The second was given by Dr. Jeffrey Watumull of Oceanit, whose coauthors were Dr.

Ian Roberts of the University of Cambridge, and Dr. Noam Chomsky himself, of the Massachusetts Institute of Technology. What are the consequences of this new way of thinking about the structure of language for practical attempts to create interstellar messages? Watumull supposes that while the minds of aliens or artificial intelligences may be qualitatively similar to ours, they may differ quantitatively in having bigger memories, or the ability to think much faster than us. He is confident that an alien language would likely include nouns, verbs, and clauses.

That means they could probably understand an artificial message containing such things. Such a message, he thinks, might also profitably include the structure and syntax of natural human languages, because this would likely be shared by alien languages. Punske and Samuels seem more cautious. Overall, the findings foster new hope that devising a message comprehensible to extraterrestrials is feasible. In the next installment, we will look at a new example of such a message.

It was transmitted in towards a star 12 light years from our sun. What should they be like? Still, a friend of mine recently started a serious effort to build little quartz disks, etc. At first I argued that it was all a bit futile, but eventually I agreed to be an advisor to the project, and at least try to figure out what to do to the extent we can.


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We just have to think about archaeology to know this is hard. What exactly was some arrangement of stones from a few thousand years ago for? For our beacons project, we want to create human artifacts that will be recognized even by aliens. The related question of how alien artifacts might be recognizable has been tackled many times in science fiction. And indeed our current artifacts may look as primitive in the future as many of those produced before modern manufacturing look to us today.

SETI: An Alternate Strategy

True, but having witnessed how we build complexity in software, the evolution of self replicating bots must be more analogous to the evolution of, say, the C-compliler. Only the first iterations of the yet completed compiler are written in assembly language; thereafter, the compiler is completed in the language it is to compile C.

Code to build new things, code to build improved things. In other words, evolving. Finally, if you can build eg print things efficiently, there might be little reason not to clean up and not leave a physical mess around. In a sense you become more informational with few material traces. Even three billion years ago, aliens may have been able to infer life by sniffing out methane and carbon dioxide in the early atmosphere.

But our modern atmosphere—a literal beacon for life—arrived only about million years ago. I think we are safe inviting them over to visit and exchange notes on the cosmos. These biosignatures, described in the journal Science Advances, could offer a key tool in the search for extraterrestrial life. Here, I build on these ideas and attempt to organize the terminology and efforts of SETI within a single framework for SETI as an interdisciplinary and multipronged approach. Presented at the workshop by Sofia Sheikh.

Workshop white papers available at this https URL. Jeff Foust reviews a book that attempts to argue how those civilizations—if they exist—can teach us about how to deal with life in the Anthropocene. There are interesting arguments in the book about the likelihood of intelligent life elsewhere in the universe, and a compelling case that human activities are altering the climate with significant, and deleterious, effects in the years and decades to come.

But the combination of the two seems forced and unnecessary. Why not model our own world, which we know infinitely better? Or, possibly, a SETI search will finally find a signal of extraterrestrial origin. There was a paper a few months back Zackrisson et al. Dyson Swarms. Zackrisson et al. This is unrelated to the kernel, but there is an interesting observation I can make about TYC I did, of course, communicate this curious find to Gary Sacco privately.

Hope, perseverance, and the courage of their convictions sustain those seeking hints of alien civilizations. In March I attended a SETI Institute workshop, where a multidisciplinary group of astronomers, neuroscientists, anthropologists, philosophers, and historians pondered new approaches to expanding the search for extraterrestrial intelligence. To me, the way these topics flowed together at the meeting served as a reminder that the distinction between astrobiology and SETI is completely artificial.

It might exist in terms of bureaucracies and funding streams, but intellectually the quest to know how we — and living things in general — fit into the universe is all part of the same nested series of questions:. How does matter turn into living cells? Is this unlikely or inevitable? What is required of a planet to support this and the subsequent transitions to differentiated cells, multicellular life, cognition, curiosity, and technology?

What planetary transitions accompanied, enabled, or were caused by these biological leaps? Should these have occurred on other types of planets that we know or suspect exist, and how would we recognize them? She currently serves on the board for the Allen Telescope Array, a group of more than telescopes north of San Francisco. What would finding other intelligent life do to our perspective on life in the universe and our own lives? TARTER: Even not finding it but trying to find it is important because it helps to give people a more cosmic perspective.

TARTER: Stephen was a brilliant man, but neither of us has any data on this point other than our own terrestrial history. Next post: Galileo Evidence for Plumes on Europa. Comments on this entry are closed. Michael May 14, , Gary Wilson May 14, , A series of brilliant articles lately. Thanks to Paul and Centauri Dreams. Paul Gilster May 14, , DCM May 14, , John Freeman May 14, , A very interesting idea and article. And, if it were realised…. Both cases are silent and impossible to detect signatures from far away. Harold Shaw May 14, , Dmitry Novoseltsev May 14, , Curious May 14, , Harold Shaw May 15, , Harold Shaw May 16, , Jason Wentworth May 15, , Ivan Vuletich May 15, , Also: The Sun, as was discovered during the radar research conducted in World War II, transmits radio waves having a wavelength of 1 meter, which corresponds to a frequency of MHz the Sun emits radio waves at other wavelengths, of course, but the strongest emission they detected was at 1 m.

Arnaud May 23, , Interesting idea. But I see 2 problems with this approach: 1. Also the beat signal would be oscillating through space as the earth rotates around its own axis and orbits the sun Bill. Now, regarding the quick and free way of testing this idea, to see how it works at radio frequencies: Amateur radio operators ham radio operators often own more than one transmitter they use multiple modulation systems, including AM. AlexT May 15, , AlexT May 16, , AlexT May 17, , Andrew Palfreyman May 15, , Sorry misprint Sun diameter is approximately 1.

Interstellar propagation of electromagnetic signals - Semantic Scholar

Alex Tolley May 15, , Grondine May 15, , One earlier idea was to look for their radars, as these would be their most powerful radio signals Following this line of reasoning, any extra-terrestrial advanced civilization is likely to have an active impactor cometary impactor detection system, either in the optical or radio range. Jason Wentworth May 16, , DCM May 15, , We might learn ABOUT them but not necessarily any useable lessons in self-improvement, One could make the same argument about other ancient or historic cultures or civilizations on Earth.

Also: Life is an extravagantly complex, entirely unnecessary solution to the problem faced by atoms of all elements except the noble gases and, in most cases—unless fluorine is present, which it seldom is—the refractory metals : to combine into compounds as needed, in order to reach the lowest energy states. Plus: If they had searched for other civilizations with no previous success before they and we finally found each other for far longer than we have, that would emphasize, as perhaps nothing else could, the extreme rarity and preciousness of life in the galaxy and, likely, in the rest of the universe as well.

As well: Another possible—though unlikely—case could involve a Bracewell probe from another civilization, which had ceased to exist some time later. Alex Tolley May 16, , AlexT May 18, , DCM May 16, , DCM May 17, , AlexT May 19, , AlexT May 24, , DCM May 19, , Michael Fidler May 16, , Do you know what is interferometer? Michael Fidler May 17, , Michael May 19, , Michael May 16, , Harry R Ray May 17, , Jay Olson Submitted on 15 May We present a simplified description of expansionistic life in the standard relativistic cosmology.

Comments: 7 pages, 3 figures Subjects: Cosmology and Nongalactic Astrophysics astro-ph. If aliens beam us a signal, what should we expect? Is the galaxy awash in the signals of long gone civilizations? How do we get our message across to the extraterrestrials? In the process, they considered the meaning of language as well. John Fluth has long turned his thoughts to the heavens — in more ways than one. Babak Farhang June 8, , It might exist in terms of bureaucracies and funding streams, but intellectually the quest to know how we — and living things in general — fit into the universe is all part of the same nested series of questions: How does matter turn into living cells?

Charter In Centauri Dreams , Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. Now Reading. On Comments If you'd like to submit a comment for possible publication on Centauri Dreams , I will be glad to consider it.

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