One Theory to Explain Fermi's Paradox is The Popcorn Theory.

It is similar to the "What if everyone is listening but no one is sending". What if all planets with intelligent life are listening and they have their own SETI-like programs. We have only sent a message out once (that I can remember) and it is not hard to imagine that other planets are just as cautious.

But I call this theory "The Popcorn Theory" because one way or another the life giving environments come to an end and, like a corneal of popcorn the life clinging on the planet pops. Imagine a galaxy of little planets spread across the pan of the galaxy and one by one they pop.

Sadly, if this theory is true, then for all parctical purposes we are alone.

Sagan popped the bubble on this one, we've been transmitting continuously in all directions for more than half a century.

__________________
"God bless thee, my son; I will give thee the greatest jewel I have ...
"The end of our foundation is the knowledge of causes, and secret motions of things; and the enlarging of the bounds of human empire, to the effecting of all things possible."Trying to make sense of computers, The Error Log.

Yes, but our transmissions would be very hard to discern rather soon (was it after some 50 lightyears?). They are just to weak.

About the Popcorn theory. We are alone until we decide to speak as well instead of only listening. Voyager and Pioneer are leaving the solar system, hopefully many more will follow. If other civ's do the same, chances are that one of them may pass us by, and we'll notice it.

It's not hard to make up theories in which we are alone or incommunicado or whatever, but what's the point? The only way to know that SETI or other projects are a waste of time or not is by trying them out. As long as the spending on them doesn't get ridiculously high, I have no problem with them (and even if they find no signs of ET life, they may very well find other things we didn't know about yet, and be worth their money as scientific tools anyway).

__________________
Knowledge is a curse, but ignorance is worse

As I understand it, the methods we use now to detect ETI would not detect the Earth more than 5 or 10 light years away.

We don't look for EM clutter. We look for a signal that was specifically sent as a beacon. We, ourselves, do not send anything like this on a regular basis. I agree with William that we have done this only once.

__________________
Home of the Illumi-Llama:
The Illuminati-R-Us Forums

So here's a wild idea - think of ways to test this idea!

Any suggestions?

The most important and easily detected signals we send are those having to do with atmospheric gases and other signals from the effects of life and of intelligence.

I don’t think the footprint of life is small at all—it’s been broadcast for about four billion years with an antenna of about 600 million square kilometers. Even we, before the end of the next decade, will be able to detect methane or oxygen producing life within 50 light years or so of Earth. By the end of the 21st century, it’s hard to imagine that capability won’t be extended to a distance of many thousands of light years.

I think, almost by definition, advanced ETs will be at least as capable as us, and here are some of the things we know ET can look for (ET, thousands of years more technologically advanced than us, certainly than me, will know a lot more):

1. Oxygen and Ozone at levels higher than possible from non-biological sources of which we are cur-rently aware. More than 20 times higher over the last 600 million years, and more than 12 times higher for more than two billion years.
2. Methane in quantities not possible on a sustained basis from non-biological processes of which we are aware on a planet as hot, as irradiated and with as much oxygen as Earth. With varying strength this signal has been sent out from Earth for about four billion years.
3. One of the human introduced pollutants in our atmosphere is lead, which has been used in metal working for more than 8500 years. The Romans increased the lead identified in Greenland ice cores hundreds of times above normal levels 2500 years ago.
4. Coal has been widely used for more than a thousand years. Burning coal releases radioactive uranium and thorium into the atmosphere, mercury and other gases and particles, many of which could be candidates to announce the presence of a living civilization.
5. Chemicals which came into widespread use in the 19th century, such as DDT (1870s), kerosene, naphthalene and gasoline (1850s), benzene (1860s), and chloroform (1840s).
6. Widespread use of freon has taken place for the last 75 years. For those 75 years we’ve used a 600 million square kilometer antenna to broadcast 24/7-360 degrees that we use refrigeration, have substantial electrical distribution and freight delivery systems, fractional horsepower electric motors, other measures of some kinds of industrial activity, and lots of other implications.

There are lots of other opportunities for advanced ET, such as remote detection of chlorophyll, and a sophisticated understanding of biological and social evolution enabling extrapolation from limited or non- current data.

There will be lots of opportunities for us, in the next thousand years, to exploit all of these possibilities and many more I don’t know about; that no human may know about—yet. We’re on the cusp of doing many of these things within most of our lifetimes.
.
What is ET supposed to think of a planet of about the right size and temperature, with an atmosphere containing water vapor, excessive amounts of oxygen and methane? What are they to make of chlorophyll? Then add elevated levels of atmospheric lead, mercury, DDT and freon. How could advanced ET not know we are here? At least, if they’re within a few thousand light years.

Of course if advanced ET is stupid and backward, they won't figure this stuff out, which will make them not so advanced.

Bob

How does ET sitting 100LY away detect that chlorophyll?

The experiment is easy. Broadcast some powerful beacons for ET to find, then sit back and wait a few hundred years to see if we get a reply.

To say we have been sending for 50 years is a bit romantic, I think. We have been generating noise locally yes, but sending? No. Not any more than the noise my dish washer generates is sending a beacon to the rest of my city.

“How does ET sitting 100LY away detect that chlorophyll?”

From the spectral signature of chlorophyll in the reflected light from Earth, a signature which is observable from the time photosynthesis was invented about two billion years ago.

We’ve been using this 600 million square kilometer antenna called atmosphere for sending signals to technologically advanced ET civilizations for many thousands of years: lead from metal working for at least 8500 years, uranium, thorium, mercury and other things from coal for at least a thousand years. DDT, kerosene, naphthalene, gasoline, benzene and chloroform for around 150 years. Freon, which does not occur in nature, for 75 years.

We will be able detect many of these signals, and others we haven’t thought of yet, before the end of this century. How can it be that advanced ET will be less capable than our children?

ETs a few thousand years ahead of us would have to be pretty weird to not know we are here. They don't have to look for radio signals, probably the least productive way to locate extra-terrestrial life.

Bob

I think, the age of the universe and our own timeframe make it more incredible that two civilisations could overlap and discover each other. The dinosaurs age for instance. If we were visted during that time frame , it's possible that those who visited us have also since expired.

__________________
Round...everything is always round!

They still have to look AT us to see any of this. It’s a big sky and we are a little dot. Not just that, but to (I can't with certainty say majority) but to many other stars systems out there, our sun, the other planets, and other stars will be too much of an interference to see any of these signals coming from our planet. Just because a signal is there, or being “broadcast” doesn’t mean it is able to be seen, or seen easily.

__________________
The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom.
--Isaac Asimov

If our kids will be able to see the signs of life on celestial bodies orbiting a significant fraction of the stars in our galaxy, how could it possibly be that advanced ET won't be able to do at least as much?

Bob

Define significant. 1,000? 10,000? 1,000,000? 1,000,000,000?
1,000,000,000 is still just ~1/2 % of all the stars in the galaxy.

__________________
The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom.
--Isaac Asimov

I think Bobunf is about right. Already we have found 170 planets in star systems in our galaxy; with improved techniques I would expect that terrestrial planets will be found in the next few decades. In a hundred years time we will probably be able to detect most of the earth-sized and larger planets in star systems for thousands of light years around. In a few hundred years time the signs of life and intelligence Bobunf has suggested will be detectable for a large proportion of the galaxy;surveys by patient automatic systems will make it possible to deal with the vast numbers of stars in our galaxy.
Bear in mind that Argelander mapped the position of three hundred thousand stars without any automation in the nineteenth century; computerised surveys using long baselines will efficiently map the visible parts of the sky in the fairly near future. In fact these surveys might be so efficient they could make interstellar probes unnecessary for centuries to come.

We have barely started to survey our Galaxy; I think it is wrong to believe that we have enough evidence to rule out widespread instances of life on the little evidence we have now.

__________________
Orion's Arm . The Starlark . Voices: Future Tense . OA Flickr set

I don't believe it is true.

It is just a notion I had.

I would rather spend time thinking of ways to test the ideas I think really are true.

Lance, you gave me a link once about this but I read the article and I did not get the same conclusion. Can you give me that link again?

BTW, notice any funny usernames around here? We missed out. There is something to say for having a serious scientific discussion and people only know you by "Hugh Jass"

Well said eburacum, I agree with your time-line as well. The only thing is that who says that WE find them? What if they find us before then? chances are that we do indeed find them first, as we know for a fact that we are looking, but we don't know anything about them, so it's difficult to say...but it would defiantly be neat to witness our first contact, just hope it's in my life time.

[quote=Dragon Star]...who says that WE find them? What if they find us before then? chances are that we do indeed find them first, as we know for a fact that we are looking, but we don't know anything about them...QUOTE]

It seems to me that if advanced ET exists, he should have found us already. In which case his behaviour is rather weird since he hasn't let us know about his big discovery.

To me this suggests that a technologically advanced ET civilization does not exist anywhere nearby.

I don't think this suggests there is no ET life nearby, just not any technologically advanced ETs. This shouldn't be surprising. Life existed on Earth for about four billion years before we came along; the beneficiaries of a remarkably perfect environment in which we could evolve.

Life may be common, but complex rare, and technological civilizations extremely rare.

This is all speculation, but in the next few decades we should start to gather good data about ET life, which should be very exciting. Imagine the excitement of the discovery of a planet with oxygen, water vapor, a stable orbit and good size and temperature.

Bob

Hi Bobunf,

I think you assume too much,even though it's speculative, why should ET need to contact us? Who says they haven't been here already? (not saying they are now, but could have in Human history)

ET --"well this place sucks, nothing interesting here, we can just move on"

Bobunf, I am aware we can detect signs of the Roman Empire industry in ice samples and such, but just how much DDT for example is in the atmosphere in forms that would show up in reflected starlight many light years away? Lead too. How many part per trillion are there of chlorophyll in our atmosphere? Uranium?

And in the next star system over, we have no guarantee that chlorophyll even exists in the ecosphere, let alone in measurable amounts. The whole chemical basis for life there - assuming life - might be totally different. Who says ET burns or even has coal? No coal fuel, no chemical pollutant byproducts to detect. WOuld we even recognize ET's equivalent to chlorophyll if we detected traces of it? And would ET know that our traces denote us? That is not an assumption I would embrace.