SETI and the Cosmic Quarantine Hypothesis

[emad]

With this essay by Steven Soter, Astrobiology Magazine presents the first in our series of 'Gedanken', or thought, experiments - musings by noted scientists on scientific mysteries in a series of "what if" scenarios. Gedanken experiments, which have been used for hundreds of years by scientists and philosophers to ponder thorny problems, rely on the power of one's imagination to project these scenarios to logical conclusions. They do not involve lab equipment or, often, even experimental data. They can be thought of as focused daydreams. Yet, as in the famous case of Einstein's Gedanken experiments about what it would be like to hitch a ride on a light wave, they have often led to important scientific breakthroughs.

Soter is Scientist-in-Residence in the Center for Ancient Studies at New York University, where he teaches a seminar on Scientific Thinking and Speculation, and a Research Associate in the Department of Astrophysics at the American Museum of Natural History.

In this essay, Soter examines the Drake Equation, which asks how many technically advanced civilizations exist in our galaxy. He also looks at the Fermi Paradox, which questions why, if there are other technological civilizations nearby, we haven't heard from them.


http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1745&mode=thread&order=0&thold=0

[phantom power]

1. New rule...

No scientist is allowed to use the pretentious term "gedanken experiment", unless they are actually German.

[kurth]

14. Yeah... what 'bout eigenvalue? eigenfunction? bremsstrahlung?

[NNadir]

15. Nein. Diese Worter sind auch verboten.

[papau]

2. If the Gestalt fits then the Gedanken is a success - or

do you want to know how the details work?

[mainegreen]

3. I don't understand these lines of reasoning.

Its about as sensible as intelligent design. If all the evidence points to there being no one else out there, and there is absolutely no evidence to the contrary, why on earth would you assume some outrageously complex theory that dictates absurd rules and philosophies of civilizations that we have no evidence about? Occam's Razor folks! None of this faith-based SETI crap.

Now, I'm not saying we shouldn't look, nor should we drop SETI nor the Drake Equation, but seriously folks, should we really overlook the lack of evidence for ET, and a great deal of evidence against ET? 'By golly, there hiding behind that star over there, I just know it, and here is a needlessly complex theory that explains it' is rubbish science.

I've heard far better and simpler theories explaining why ET is not out there as evident than theories explaining that ET is out there and is hiding, as is not evident.

[htuttle]

4. It would take our fastest spaceship almost 12-15,000 years...

...to reach Alpha Centauri right now. That's longer than any single human civilization has ever existed.

All the radio waves ever emitted by human civilizations have only reached a sphere of star systems that's barely 10% of the thickness of the galactic disk in our region of the Milky Way.

In addition, consider the timing issues: What are the odds, with the distances so large, and the timescales so long, that any two civilizations will be both capable and willing to communicate with each other at the same time -- not to mention being lucky enough to happen to find each other? Keep in mind that 100 years from now, human beings may not even be listening with SETI anymore (we may be too busy trying to figure out how to deal with the effects of global warming and the lack of petroleum).

Finally, it may well be the case that the speed of light is indeed an absolute limit for matter. There may be no such thing possible as 'warp drive' or other sci-fi 'interstellar drive' technology.

In other words, the most probably explanation for why there is no evidence of ET life at this point is that space is FRICKIN HUGE! No additional reasons are needed, as far as I'm concerned.

[mainegreen]

7. Clearly no aliens have visited earth.

I'd be suprised if we ever got very far beyond our solar system any time soon in the next million years. My problem is that there is no evidence for aliens, period. You hit the nail on the head when you state space is huge. In the %10 of the galactic disk our transmissions have covered there are a phenomenal amount of stars. Even given low values across drakes equation, the galaxy should be washed in evidence, from broadcasts to evidence of activity. There is none. Anywhere. Period. While this says nothing about how common life is, it says a lot about how common technilogical civilizations are. They aren't. We might be it, the first (at least in this galaxy).

There are so many conditions neccessary to technilogical society its a miracle even we exist. A planet must have life, easily extractable surface metals, hence plate tectonics, not be drowned under liquid (which would happen to most worlds larger than earth), have animals, be around a stable star, generally g-class, exist in a low star dense region. A species must have decent tool using appendages, be good at math, be social, and exist on one of these planets that also has good conditions for technilogical development.

Even given that these conditions are common, where is everyone? Unless malevolent, invisible force is reseting life all across the galaxy, yet has ignored earth, the best fit answer is that there is nobody.

Even the Lock Ness Monster has some evidence!

[htuttle]

8. That's 10 percent of the *thickness* of the galactic disk

...not 10 percent of the whole disk. The disk of the Milky Way is about 1000 light years thick in our neighborhood. If we've been transmitting radio signals for about 100 years, that means our signals haven't even gotten halfway through the thickness of the galactic plane.

I'm just saying that concluding that there is no extraterrestrial life on the basis on what we've seen so far is like concluding that there's no fish in the ocean because you looked for 5 minutes and didn't see any.

I think it's really only few hundred -- maybe a few thousand -- star systems total that have received radio signals from Earth¹ -- probably something like 0.001% of the stars in our galaxy. If we still haven't seen any evidence of extraterrestrial life in 1000 years, THEN I'd be more inclined to think that 'intelligent life' (at least smart enough to use radio) must be incredibly rare if it exists at all.

Even then, if we ever figure out how to actually (and usefully) get physical probes to extra-solar planets, I wouldn't rule out finding archeological evidence of intelligent life. Advanced civilizations might come and go all the time, each being 'radio aware' for only a brief moment, galactically speaking.


¹ Google tells me that there's estimated to be 14,500 star systems within 100 light years of our Sun: http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980123d.html

[Ready4Change]

10. How strong are our own signals?

At this point our earliest major broadcasts are around 100 light years out there. But, they've been spreading out, to cover a spherical volume of 100 ly radius. That's a lot.

How powerful are those signals. If we were 100ly out there, would WE detect those amongst the other random noise of the universe?

[htuttle]

11. Radio waves should propagate 'forever' until they hit stuff

There are going to be shadows whenever something is in the way, like a solid body, or a star, gas clouds, etc..., but for the signals that pass through empty space, I don't think they ever really fall off, though there'd be some sort of doppler effect the farther away it got (and they could get bent and even 'lensed' from gravitational effects).

BTW, I read that there's about 14,500 star systems within a 100 ly radios sphere around our Sun. That is a lot, but we don't know how many of them have rocky planets (I don't think we've ever even seen one outside our own solar system), much less other ingredients for life. And that 14,500 systems only represents a tiny fraction of our galactic neighborhood, much less our own galaxy, much less other galaxies.

I think it's entirely possible that life arises around the universe all the time, but just never ends up finding any other life. It must certainly be an extremely rare event.

[Ready4Change]

12. Space isn't totally empty

When you start looking at distances in light years, space isn't empty. There is dust, scattered molecules of gas, etc...

I've read that the frequencies that may travel best are in the hydrogen band? I'm not up on exactly why, but I gather than most of the "stuff" in space is hydrogen, and transmitting on that band would therefor "pass through" the majority of the junk.

So, of our transmissions, how much is in this hydrogen band, and how strong would it be 100 light years away? how strong would our "non-hydrogen band" transmissions be at the same distance?

[NNadir]

13. We actually have no idea whether aliens have visited the earth.

Of course, it depends on what you mean by "aliens." Intelligent aliens - maybe not, but primitive aliens, who's to say?

If one means by aliens "virus-like particles" or simple bacteria, it may or may not be true.

I think that life is improbable, not impossible obviously, but improbable. The already low probability of life occurring is raised and not diminished by having having a large area over which it can arise, and is raised even higher by something like panspermia, in which certain very simple extremophiles - extremophiles being present on the earth - manage to survive in intragalactic space. We do know that life arose on this planet with amazing speed. One possible explanation for this speed is of course that the universe was seeded, not by creatures in space ships, but by tiny packets of self organizing molecules, catalytic nucleic acids.

I have no doubt that this is possible. This is different from asserting a certainty, but on the other hand, I certainly don't think the question absurd. Indeed at least one organism with extreme Resistance to radiation, something an interplanetary traveler would need, is known: Deinococcus radiodurans.

http://web.umr.edu/~microbio/BIO221_2000/Deinococcus_radiodurans.html

Further exploration of planetary space, robots to places like Europa and Mars may offer some positive evidence of panspermia, although negative results will not disprove the panspermia hypothesis.

By the way, I hate to find myself agreeing with the retarded science fiction writer Crichton - who follows in the steps of that other great science fiction writer L. Ron Hubbard in being totally out to lunch - but I do think the Drake equation is just shy of nonsense, since it will indeed proved very difficult to get any measurement of any of the variables. Therefore the whole equation is just formalized speculation.

[bananas]

5. Frank Drake wrote about it last December

For anyone interested in these things,
I just took a look at the wikipedia entry for the Drake Equation
http://en.wikipedia.org/wiki/Drake_equation
and noticed that Frank Drake wrote about it last December
http://wired.com/wired/archive/12.12/life.html

[Johonny]

6. I found

Peter D. Ward and Donald Brownlee Rare Earth a pretty convincing read on how many advances civilizations are out there.

[Ready4Change]

9. Where can I get employed as a "Gedankist?"

Love that kind of stuff. Particularly if there were a chance to hook up with hard scientists as an anchor into reality.

[nashville_brook]

16. this thread has my two wonderful words: Gedanken and panspermia

mmmm... up there with flummoxed, quotidian and Gemeinschaft

yummy