Shouldn't we have heard alien radio signals by now? Why not?

SeventhSigma

I figure that intelligent life couldn't have formed until, at the very least, the second generation stars that started birthing forth carbon (maybe 3 billion years after the Big Bang?). On Earth, it took something like 2.5 billion years until multicellular life formed, and so maybe we can estimate that intelligent civilizations didn't start popping up until ~7 billion years after the Big Bang.

If this is true, that may imply that radio signals from these intelligent civilizations may have been traveling for ~7 billion years or so prior to today. Shouldn't that be a decent stretch across the cosmos -- about half of our cosmic horizon?

Do you think radio signals are "weakened" to the point where we can't detect them? Is it possible that intelligent life couldn't have formed until much later in the game despite the carbon influxes? Do you think it's some other reason? Let me know your thoughts!

Antiphon

I think that there is a very short window for a civilization, maybe only 5000 years between the time it starts broadcasting radio signals and the time its technology becomes so advanced that they no longer broadcast high power RF signals.

This leaves only the possibility that they are deliberately sending signals for another civilization to pick up. I find this very unlikely due to the inherent danger in the uncontrolled contact between civilizations of widely differing technology.

Chronos

Other issues - how many radio capable [and utilizing] civilizations overlap? How many have the means and desire to transmit sufficiently powerful radio signals during the overlap period? I don't think intelligent civilizations are necessarily unique, just that they rapidly pass through the radio era of communication. I think they are sufficiently rare that funding for sufficiently powerful ET radio studies have a very tiny window.

nicksauce

Yes, of course. Think about how hard it is to see an individual star in a nearby galaxy. Now compare the power output of such a star to the power output of a typical radio transmitter that an intelligent civilization might have. It is pretty much unthinkable that we would ever get ET signals from outside of our galaxy, let alone, from billions of light years away.

phyzguy

Try googling the "Fermi paradox". Basically Fermi asked the same question - "If intelligent life is common, then where are they?" The simple answer is that we don't know. Maybe intelligent life is extremely rare. Maybe intelligent life destroys itself after a short time. Maybe (this is Hawking's recent point) there are predators out there and any civilization that makes "noise" gets quickly found and snuffed out or enslaved. Maybe energetic events like gamma ray bursts periodically sterilize the galaxy. Maybe.... We simply don't know yet.

Radrook

Some believe that the WOW-Signal constituted the necessary evidence to conclude that there are other civilizations out there. Unfortunately, that signal was not sustained and finding it again by scanning that same section of the universe has proven fruitless. Some have said that we might have just listened in a brief ship-to-ship communication. Others a distress signal that was heeded and needed no repetition. Still others say that we don't listen long enough and their transmission schedule might not coincide with our listening one. In any case the signal was impressive enough to warrant a big WOW written next to it and it has referred to by that ever since.

Rasalhague

I got some good replies to a related question:

http://www.physicsforums.com/showthread.php?t=374799

cmarrou

Those who believe radio communication is a temporary development are likely correct. It was barely a century ago that Marconi first sent his three-dot "S"s into the void. Radio and television broadcasting work well for sending content from the few to the many, but today people want more give-and-take. Most TV is now received through shielded coaxial cables, and radio is rapidly becoming outdated through satellite broadcasts that are aimed down at the Earth, not from it into space. In another twenty years or so, we are unlikely to have much of a radio wave signal to show the universe, so, figuring maybe 150 years out of 7 billion for use of radio waves, perhaps one in 50,000,000 planets with intelligent life would show some radio profile. Then again, maybe radio was developed here because we missed the development of greeblatz or some other alternative technology that sends nothing at all skyward. Woe is us!

Vanadium 50

Despite mentor warnings, this thread was getting side-tracked into a non-scientific direction. Those messages have been removed.

I think people are missing something. It is completely plausible that a society will use less and less radio for communications, for all the obvious reasons. However, SETI doesn't have to just look for radio - it also looks for radar. Radar has many advantages. A putative civilization would like some advance notice of nearby asteroids that might collide with them. It's high power. It's aimed up in the sky. It's likely to be reasonably regular and thus easy to spot.

Rasalhague

The article Chronos mentioned in the thread I linked to has some interesting comments on high intensity narrowband radar, as the one kind of signal our civilisation makes which a civilisation of equivalent technological development could be reasonably expected to detect.

http://www.physicsforums.com/showpos...59&postcount=5
http://www.faqs.org/faqs/astronomy/f...ion-12.html%5D

PacketMan

The other question is how much of a sample have we really been able to take so far? We've been looking for what, 50 years? I saw an astrophysicist on some program on the Science Channel put it very well: If you dipped a glass of water in the ocean and looked it at, would you conclude that the ocean has no fish in it?

ThomasEdison

Are you sure about fully developed civilizations being possible as far back as 7 billion years ago?

So you mean a modern type solar system at least 10 billion years old because I can only assume it would take a few billion years to form a civilization from a rocky world.

That seems like a very broad window.



EDIT:
Can someone who is well versed in Astronomy confirm or deny the plausibility of modern (extra)solar systems existing that far back? Modern =A long lived yellow to red sun with rocky bodies made of heavy elements orbiting it. How far back was this even possible?

If we truly want to approach this question shouldn't we start there?

What exactly is the timeline window for the development of solar systems and life on them?

GODISMYSHADOW

Maybe we did, but the source LGM-1 was later downgraded and written off as being a rotating neutron star.

tasp77

We are first.

Ryan_m_b

Care to clarify any reasoning behind this?

drollere

supermassive stars appear to have formed relatively early in the history of the universe (around 13 billion years ago, more or less) and would have very rapidly (within a million years or so) begun spewing out heavier elements.

life on our planet evolved within 1 billion years after the formation of the earth, if not earlier.

the crux here is that there are uncountably more explanations for why something has *not* happened than for why it *has* happened.

surely the inverse square law of radiation, and the sheer scale of the universe, and the disparity between energy requirements and practical motivation, suggests that at some point there is a horizon on the signals one might receive from an advanced civilization elsewhere in our galaxy.

but because i choose something that appears relatively more plausible as a piece of the scheme of things does not mitigate the problem. i'm still dabbling with the toy of my ignorance ... or i work for the SETI foundation.

tasp77

Consistent with data we have on hand,


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being first has to happen to some civilization, mighty profound if it be us.