Galactic exploration by directed Self-Replicating Probes

… and its implications for the Fermi paradox

Martin T. Barlow
This paper proposes a long term scheme for robotic exploration of the galaxy,and then considers the implications in terms of the `Fermi paradox’ and our search for ETI. We discuss the parameter space of the `galactic ecology’ of civilizations in terms of the parameters T (time between ET civilizations arising) and L, the lifetime of these civilizations. Six different regions are described….
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Figure 1: Galactic ecology parameter space

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Conclusion
Consideration of the points above, and Figure 1, leads to three broad categories of answer to Fermi’s question:
(F1) They have not visited us because they do not exist. (Regions R1 and R2.)
(F2) The ‘zoo hypothesis’: their probes are watching us now (Regions R3 and R4.)
(F3) They have not visited us because civilizations are all too short lived (Regions R5 and R6).
Of these, possibility (F3) relies all all civilizations being short lived, while the zoo hypothesis appears to be deeply unpopular (partly I suspect because it compromises human dignity.) The analysis above reduces the force of some of the objections that have been made to the zoo hypothesis, since in both cases R3 and R4(ii) we would lie in the zone of control of just one ETI.
If we exclude (F2) and (F3), then we are left with (F1), to which there are no objections except that it is uninteresting. It is worth noting that while astronomers have frequently given rather large values to fci – typically in the range 0.01–0.1, many evolutionary biologists have been much more pessimistic. Even if one is not convinced by all the arguments in [10], it seems very possible that the development of intelligent life requires evolution to pass through several gateways, and hence that fci is very small.

Read more: http://arxiv.org/pdf/1206.0953v1.pdf

First VLBI SETI Search Finds No Radio Transmissions

… From Gliese 581

Astronomers have completed the first search for extraterrestrial intelligence on nearby exoplanets using very long baseline interferometry

uv coverage of the LBA observation of the Gl581 system, in units of mega wavelengths. The x-axis plots the u coordinates, while the v coordinates is on the y-axis

A telescope’s angular resolution is its ability to distinguish small details of a distant object. The Hubble Space telescope, for example, has an angular resolution of about 100 milliarcseconds. 

That’s good but by no means the best. In fact, the telescopes with the highest angular resolutions are interferometric radio telescopes, made up of several dishes spread over thousands of kilometres.

Known as very long baseline interferometers (VLBIs), the biggest boast an angular resolution some two orders of magnitude better than Hubble.

So what to point them at? Today, Hayden Rampadarath and pals at the International Centre for Radio Astronomy Research at Curtin University in Australia say they’ve pointed their interferometric radio telescope at Gliese 581, a red dwarf star some 20 light years from here. 

What makes Gliese 581 interesting is its planets, which include two superEarths that probably sit on the edge of their habitable zone. 

That makes them good candidates for life. And if this life is anything like our own, it may already be broadcasting at radio frequencies that we can tune in to.

Although VLBI has extraordinary angular resolution, it has never been used to look for signs of extraterrestrial intelligence. So this is an important proof-of-principle step. 

The Australian instrument, known as the Australian Long Baseline Array, consists of three radio telescopes a few hundred kilometres apart, which gives them an angular resolution that is about the same as Hubble’s.

Rampadarath and pals pointed it at Gliese 581 for a total of 8 hours in June 2007, tuning into frequencies close to 1500 megahertz.  Why they’ve waited so long to publish their result, they don’t say but their paper has now been accepted for publication in The Astronomical Journal.

What they found is interesting. VLBI techniques turn out to be useful for SETI searches because they automatically exclude many terrestrial sources of interference that might otherwise look like SETI signals. That’s because the same signals have to show up at all the telescopes several hundred kilometres apart.

In total, Rampadarath and co found 222 candidate SETI signals. However, they were able to exclude all of these relatively easily using automated analysis techniques, which have become increasingly sophisticated in recent years. (That’s partly because of projects such as SETI@Home which has found billions of interesting signals, all of which have turned out to be false alarms.)  

The false alarms picked up by the Australian Long Baseline Array probably came form Earth orbiting satellites, say the team.

Of course, this doesn’t exclude the possibility of intelligent life in the Giese 581 system or even exclude the possibility that these ETs might use radio signals to communicate. 

Instead, it  places limits on the strength of these signals and not particularly onerous ones at that. Rampadarath and pals say  their instrument would have picked up a broadcast with a power output of at least 7 megaWatts per hertz. 

To put that in context, on the slim chance that Gliese inhabitants had been broadcasting directly to Earth using an Arecibo-style dish, Rampadarath and co would have easily picked up the signal. (Arecibo is a 300 metre radio telescope in Puerto Rico).

On the other hand, the ordinary radio transmissions like those  we continually broadcast into space, would have been far too weak to be picked up by the Australian team.

That’s not to say that this kind of observation won’t be possible in future. The Australian array is by no means the biggest of most sensitive instrument available today. 

What’s more, astronomers are planning a new VLBI telescope called the Square Kilometre Array which will have the sensitivity to pick up broadcasts of a few kiloWatts per Hertz from 20 light years away.

There are no shortage of targets. At the last count, astronomers had found around exoplanets that sit in their habitable zones (meaning they’re warm enough for liquid water). These places are of intense interest.

Time on VLBI telescopes is precious and difficult to come by. But the prize here is of almost incalculable value–the discovery of intelligent life beyond the Solar System. 

So it wouldn’t be a complete surprise if radio astronomers found ways to hunt more often for radio broadcasts from new and exciting exoplanets.

Ref: arxiv.org/abs/1205.6466 :The First Very Long Baseline Interferometric SETI Experiment

Read more: www.technologyreview.com

Read also: ‘No signal’ from targeted ET hunt

Expectation of extraterrestrial life …

… built more on optimism than evidence, study finds

Recent discoveries of planets similar to Earth in size and proximity to the planets’ respective suns have sparked scientific and public excitement about the possibility of also finding Earth-like life on those worlds.

But Princeton University researchers have found that the expectation that life — from bacteria to sentient beings — has or will develop on other planets as on Earth might be based more on optimism than scientific evidence.

Princeton astrophysical sciences professor Edwin Turner and lead author David Spiegel, a former Princeton postdoctoral researcher, analyzed what is known about the likelihood of life on other planets in an effort to separate the facts from the mere expectation that life exists outside of Earth. The researchers used a Bayesian analysis — which weighs how much of a scientific conclusion stems from actual data and how much comes from the prior assumptions of the scientist — to determine the probability of extraterrestrial life once the influence of these presumptions is minimized.

Turner and Spiegel, who is now at the Institute for Advanced Study, reported in the Proceedings of the National Academy of Sciences that the idea that life has or could arise in an Earth-like environment has only a small amount of supporting evidence, most of it extrapolated from what is known about abiogenesis, or the emergence of life, on early Earth. Instead, their analysis showed that the expectations of life cropping up on exoplanets — those found outside Earth’s solar system — are largely based on the assumption that it would or will happen under the same conditions that allowed life to flourish on this planet.

In fact, the researchers conclude, the current knowledge about life on other planets suggests that it’s very possible that Earth is a cosmic aberration where life took shape unusually fast. If so, then the chances of the average terrestrial planet hosting life would be low.

“Fossil evidence suggests that life began very early in Earth’s history and that has led people to determine that life might be quite common in the universe because it happened so quickly here, but the knowledge about life on Earth simply doesn’t reveal much about the actual probability of life on other planets,” Turner said.

“Information about that probability comes largely from the assumptions scientists have going in, and some of the most optimistic conclusions have been based almost entirely on those assumptions,” he said.

Turner and Spiegel used Bayes’ theorem to assign a sliding mathematical weight to the prior assumption that life exists on other planets. The “value” of that assumption was used to determine the probability of abiogenesis, in this case defined as the average number of times that life arises every billion years on an Earth-like planet. Turner and Spiegel found that as the influence of the assumption increased, the perceived likelihood of life existing also rose, even as the basic scientific data remained the same.

“If scientists start out assuming that the chances of life existing on another planet as it does on Earth are large, then their results will be presented in a way that supports that likelihood,” Turner said. “Our work is not a judgment, but an analysis of existing data that suggests the debate about the existence of life on other planets is framed largely by the prior assumptions of the participants.”

Joshua Winn, an associate professor of physics at the Massachusetts Institute of Technology, said that Turner and Spiegel cast convincing doubt on a prominent basis for expecting extraterrestrial life. Winn, who focuses his research on the properties of exoplanets, is familiar with the research but had no role in it.

“There is a commonly heard argument that life must be common or else it would not have arisen so quickly after the surface of the Earth cooled,” Winn said. “This argument seems persuasive on its face, but Spiegel and Turner have shown it doesn’t stand up to a rigorous statistical examination — with a sample of only one life-bearing planet, one cannot even get a ballpark estimate of the abundance of life in the universe.

“I also have thought that the relatively early emergence of life on Earth gave reasons to be optimistic about the search for life elsewhere,” Winn said. “Now I’m not so sure, though I think scientists should still search for life on other planets to the extent we can.”

Promising planetary finds

Deep-space satellites and telescope projects have recently identified various planets that resemble Earth in their size and composition, and are within their star’s habitable zone, the optimal distance for having liquid water.

Of particular excitement have been the discoveries of NASA’s Kepler Space Telescope, a satellite built to find Earth-like planets around other stars. In December 2011, NASA announced the first observation of Kepler-22b, a planet 600 light years from Earth and the first found within the habitable zone of a Sun-like star. Weeks later, NASA reported Keplers-20e and -20f, the first Earth-sized planets found orbiting a Sun-like star. In April 2012, NASA astronomers predicted that the success of Kepler could mean that an “alien Earth” could be found by 2014 — and on it could dwell similar life.

While these observations tend to stoke the expectation of finding Earth-like life, they do not actually provide evidence that it does or does not exist, Spiegel explained. Instead, these planets have our knowledge of life on Earth projected onto them, he said.

Yet, when what is known about life on Earth is taken away, there is no accurate sense of how probable abiogenesis is on any given planet, Spiegel said. It was this “prior ignorance,” or lack of expectations, that he and Turner wanted to account for in their analysis, he said.

“When we use a mathematical prior that truly represents prior ignorance, the data of early life on Earth becomes ambiguous,” Spiegel said.

“Our analysis suggests that abiogenesis could be a rather rapid and probable process for other worlds, but it also cannot rule out at high confidence that abiogenesis is a rare, improbable event,” Spiegel said. “We really have no idea, even to within orders of magnitude, how probable abiogenesis is, and we show that no evidence exists to substantially change that.”

Considering the source

Spiegel and Turner also propose that once this planet’s history is considered, the emergence of life on Earth might be so distinct that it is a poor barometer of how it occurred elsewhere, regardless of the likelihood that such life exists.

In a philosophical turn, they suggest that because humans are the ones wondering about the emergence of life, it is possible that we must be on a planet where life began early in order to reach a point so soon after the planet’s formation 4.5 billion years ago where we could wonder about it.

Thus, Spiegel and Turner explored how the probability of exoplanetary abiogenesis would change if it turns out that evolution requires, as it did on Earth, roughly 3.5 billion years for life to develop from its most basic form to complex organisms capable of pondering existence. If that were the case, then the 4.5 billion-year-old Earth clearly had a head start. A planet of similar age where life did not begin until several billion years after the planet formed would have only basic life forms at this point.

“Dinosaurs and horseshoe crabs, which were around 200 million years ago, presumably did not consider the probability of abiogenesis. So, we would have to find ourselves on a planet with early abiogenesis to reach this point, irrespective of how probable this process actually is,” Spiegel said. “This evolutionary timescale limits our ability to make strong inferences about how probable abiogenesis is.”

Turner added, “It could easily be that life came about on Earth one way, but came about on other planets in other ways, if it came about at all. The best way to find out, of course, is to look. But I don’t think we’ll know by debating the process of how life came about on Earth.”

Again, said Winn of MIT, Spiegel and Turner offer a unique consideration for scientists exploring the possibility of life outside of Earth.

“I had never thought about the subtlety that we as a species could never have ‘found’ ourselves on a planet with a late emergence of life if evolution takes a long time to produce sentience, as it probably does,” Winn said.

“With that in mind,” he said, “it seems reasonable to say that scientists cannot draw any strong conclusion about life on other planets based on the early emergence of life on Earth.”

This research was published Jan. 10 in the Proceedings of the National Academy of Sciences and was supported by grants from NASA, the National Science Foundation and the Keck Fellowship, as well as a World Premier International Research Center
Read more:www.princeton.edu

Scouting the spectrum for interstellar travellers

Scales of speed with respect to the speed of light in vacuum (logarithmic scale). The fastest man-made objects are in the range of velocities from 10−5c to 10−3c. Examples are the fastest manned ship, Apollo 10 on entry (NASA, 1969), the Galileo probe during its descent into Jupiter (NASA, 2003) and the solar probe Helios 2, with its velocity estimated at its periapsis at 0.29 Astronomical Units from the Sun (Freeman, 1998). For comparison, we have included the average speed of Earth during its orbit around the Sun (Cox, 2000) and the motion of the Solar System with respect to the cosmic microwave background frame (Hinshaw et al., 2009). The fastest natural objects, like hypervelocity star HE 0437-5439 (Brown et al., 2010) and neutron star RX J0822-4300 (Hui and Becker, 2006), move in the scale of 10−5c-−2c. We define a region of extraordinary propulsion (REP) for speeds which would point to an artificial object. The REP starts at the estimated speed for the nuclear propulsion Orion ship (Dyson, 1968), which could be built with present human technology.

Juan Carlos Garcia-Escartin, Pedro Chamorro-Posada
Advanced civilizations capable of interstellar travel, if they exist, are likely to have advanced propulsion methods. Spaceships moving at high speeds would leave a particular signature which could be detected from Earth. We propose a search based on the properties of light reflecting from objects travelling at relativistic speeds. Based on the same principles, we also propose a simple interstellar beacon with a solar sail….
Read more: arxiv.org/pdf/1203.3980v1.pdf

Seti Live website to crowdsource alien life

A website has been launched that aims to get the public involved in the search for extraterrestrial life.
Announced at the TED (Technology, Entertainment and Design) conference in Los Angeles, the site will stream radio frequencies that are transmitted from the Seti (Search for Extraterrestrial Intelligence) Allen Telescope Array.
Participants will be asked to search for signs of unusual activity.
It is hoped the human brain can find things the automated system might miss.
The website is the latest stage in a quest “to empower Earthlings everywhere to become active participants in the ultimate search for cosmic company”.
The project is being run by Dr Jillian Tarter, winner of the TED Prize in 2009 and director of the Seti Institute’s Center for Seti Research.
She has devoted her career to hunting for signs of sentient beings elsewhere.
She hopes Seti Live will help build upon the community of scientists and technologists already involved in the search.
“There are frequencies that our automated signal detection systems now ignore, because there are too many signals there,” she said.
“Most are created by Earth’s communication and entertainment technologies, but buried within this noise there may be a signal from a distant technology.
“I’m hoping that an army of volunteers can help us deal with these crowded frequency bands that confuse our machines. By doing this in real time, we will have an opportunity to follow up immediately on what our volunteers discover.”……
Read more: www.bbc.co.uk

Time to give SETI a chance

by Jill Tarter – newscientist

Earth 2.0 is in our sights. Checking it for signs of life will be the next big issue

THE thousands of probable worlds discovered in orbit around other stars are making our corner of the universe appear a lot friendlier to life these days.

The Kepler space telescope, which has its eye on 150,000 stars, is beginning to home in on Earth-size planets. Can Earth 2.0 be far behind? What will it be like?

Earth 2.0 would be a rocky planet the size of our own, orbiting a star like the sun at a distance where the surface temperatures would allow liquid water oceans, assuming the planet was sheathed in an atmosphere containing greenhouse gases.

In other words, it will be a world that we might find habitable. We won’t be able to see this other Earth directly, but we will know it is there because of the influence it has on its star. Even so, we will inevitably ask: “Is it inhabited?”

Answering that question will be hard. It is quite probable that Earth 2.0 will be hundreds or even thousands of light years away; too far from us to detect trace chemical “biosignatures” that would suggest life.

There is another way. We could look for life on Earth 2.0 via “technosignatures” such as radio signals produced by intelligent life. These would be cheaper and easier to find than biosignatures. It is a long shot, but one that is affordable and we can do it now. In fact the Search for Extraterrestrial Intelligence (SETI) has been on the case since the 1990s.

Despite being denied public funds and derided by some politicians for seeking “little green men”, SETI still carries out searches with private money.

For decades we have blindly checked the sky overhead or targeted stars that are old enough, metallic enough and stable enough to have rocky planets in the right orbits. Now, thanks to Kepler, we know where to look. Digital technologies are speeding up the searches, but they require investment to reap the rewards.

SETI is a logical addition to the publicly funded endeavours exploring other worlds. It is time to fund it properly, either with public money or privately.

Now that we know there are planets beyond our solar system, and where to find them, we should give SETI a fighting chance to see if anybody is home.

Jill Tarter is director of the Center for SETI Research at the SETI Institute in Mountain View, California

Type III Dyson Sphere of Highly Advanced Civilizations ….

… around a Super Massive Black Hole

Schematic picture around SMBH. Items are not to scale. In this picture, an example of power plants with transmitters is shown partly. BLR stands for the Broad Line Region. The SMBH and accretion disk will not be fully covered by the collectors of power plants, so as not to prevent jets emanating from somewhere in this area, and accretion flow coming out of the central region. A twin jet is thought to emanate perpendicular to the plane of accretion disk, seen about 10% of AGN. The energy from the power plants is transferred by electro-magnetic waves to habitats of advanced civilizations. In this picture, the beams are directed to a galactic plane on which a galactic club is formed. However, the planes of the accretion disk and the host galaxy may not necessarily be in the same plane

Makoto Inoue, Hiromitsu Yokoo
We describe a new system for a society of highly advanced civilizations around a super massive black hole (SMBH), as an advanced Type III “Dyson Sphere“, pointing out an efficient usage of energy for the advanced civilizations. SMBH also works as a sink for waste materials. Here we assume that Type III civilisations of Kardashev classification [1] form a galactic club [2] in a galaxy, and the energy from the SMBH will be delivered to the club members, forming an energy control system similar to power grids in our present society. The energy is probably transmitted by a sharp beam with coherent electro-magnetic waves, which provide a new concept for the search for extraterrestrial intelligence (SETI) via detection of such energy transmission signals. This expands the search window for other intelligences within the Universe….
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CONCLUDING REMARKS
Figure 1 shows a schematic picture of the power plants and others around SMBH. The condition around SMBH is very promising for an advanced intelligence to manage energy issues in terms of both energy generation and disposition.This idea comes from a combination of Type III and Dyson Sphere. The strong radiation from the accretion disk rotating around SMBH is mainly used, and the waste energy is returned toward the SMBH. The available energy is huge compared to Dyson Sphere of stellar scale, and this type ofcivilization could be called Type III Dyson Sphere. The search for this type of civilization, however, would not likely be revealed from “unintended” communication signal, but detection by coherent radiation from power stations may be more promising….
Read more: http://arxiv.org/pdf