Is there life in the universe, and if so has it visited Earth?

[StuMyers]

A civilization will have the means to extinguish itself hundreds of years before it can spread to other solar systems.
Once the spreading starts in one million years this civilization could traverse the galaxy. The lack of communicating civilizations in our neighborhood (as far as we know), seems to demonstrate that technological civilizations don´t last this long.

Why one million years? Just curious where that number comes from.

And a lack of communicating civs could just as easily imply that we are the first, right?

 

[SGT]

Why one million years? Just curious where that number comes from.

Our galaxy is 200000 ly across, so an advanced civilization with means to travel at 1/5 c could spread in 1 million years.
Not that the original inhabitants would travel to the other side of the galaxy, but their colonies would spread in the same way that the original Africans never reached Australia, but South Asians, descended from them did.

And a lack of communicating civs could just as easily imply that we are the first, right?

Not necessarilly first, but the only living at the present moment.
Second generation stars, containing all necessary elements for life must have formed one or two billion years after the Big Bang. So, as Ivan said, there could be civilizations billions of years ahead of ours. The fact that they are not swarming the galaxy indicates that civilizations don´t last for billions of years.

 

[StuMyers]

...or, that they are very very rare. If they were common, but short lived, might we not expect to see a universe filled with relics (possibly in the form of radio signals or longwave, or whatever)?

 

[SGT]

...or, that they are very very rare. If they were common, but short lived, might we not expect to see a universe filled with relics (possibly in the form of radio signals or longwave, or whatever)?

Since we have not being outside the solar system we cannot know if there are relics of alien civilizations anywhere. As for radio signals we are loking for them and have found nothing until now.
There are two problems with radio signals.
First, their energy drops with the third power of distance, so even a very strong signal will fall below the background noise after traveling a few light years, unless they are aimed directly on us. So we probably can only detect signals from actually existing civilizations. The signals from the dead ones is immersed in the noise.
Second, even if we detect a coherent radio signal we can´t be sure if they are of natural or artificial origin. When the first quasar was detected, the regularity of its emissions led some astronomers to speculate if they were artificial. Before being named quasar it received the name LGM (from Little Green Men).

 

[StuMyers]

I seem to remember that there was something called the 'watering hole' where the galaxy is naturally fairly quiet in radio, where you might expect it to be loud, were it teeming with intelligent radio users.

 

[Ivan Seeking]

And again, already we are going radio silent. With a window of only about one-hundred years here on earth, radio is probably a very poor signature to be used in the search for ETs. And since we don't know what will be used a million years from now, or even in another hundred years...

 

[StuMyers]

Why do you think Earth would ever go radio silent? Radio is a super cheap and super fast way to communicate around a planet. If anything, I'd guess more and more data will get crammed into louder and louder signals, as we get better at pulling them apart.

 

[Ivan Seeking]

The shortest answer: Directed microwaves... Direct TV is a good example. Also, all analog TV transmissions in the US will be banned in two years.

Soon, with "view on demand" coming along, such as with Joost, you will probably replace your television signal with the internet. Already I watch some of my favorite shows, like Meet The Press, online, and at my leisure.

 

[cshum00]

The talk is usually about intelligent species. But what would humanity do if they find species who are in the process of being intelligent?

Experiments? Slavery? Cooperation? Play the role of God?

Make your guess.

Edit: To make it more general. What would humanity do if any kind of extraterrestrial life is found? Including the intelligent and the unintelligent ones? (Besides announcing it to the public in the news)

 

[Ivan Seeking]

Here is a short blurb about a radio free earth

AM: What do you think of the idea that more advanced civilizations will be radio silent, just as we are becoming more radio silent due to satellite transmission and fiber optics and that sort of thing?

NT: That's correct. That's a scary, very realistic notion. Not only that, but our TV waves aren't escaping Earth anymore because a growing number are receiving their signals via cable. So the total broadcast universe is shrinking.

http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1425

 

[Ivan Seeking]

The talk is usually about intelligent species. But what would humanity do if they find species who are in the process of being intelligent?

Experiments? Slavery? Cooperation? Play the role of God?

Make your guess.

That is not appropriate for this discussion. You could start another thread in General Discussion if you wish to pursue this.

 

[cshum00]

That is not appropriate for this discussion. You could start another thread in General Discussion if you wish to pursue this.

Sorry. I thought i might be appropriate since it is related and i saw a few shifts too (like from life in universe visited Earth to whether there is life other than earth, then extinctions of civilizations, etc).

I just make another thread.

 

[Ivan Seeking]

No problem. It is logically connected but too far off topic for this forum.

 

[StuMyers]

Here is a short blurb about a radio free earth


http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1425

Thanks. I find that blurb pretty surprising. I still just find it hard to believe that something so useful and so cheap (radio) will ever really be abandoned. I'd be interested in seeing the total radio flux from Earth (in the interesting frequencies) over the past decade. I have to wonder if we aren't really becoming silent so much as we are seeing the dominant communication medium shift. In other words, radio keeps its purpose, increases in net, but diminishes as a fraction of the sum total of communication signals?

 

[Ivan Seeking]

I don't see how that would happen. Sure, we may have a billion cell phones transmitting, but only with a few watts of power each. The days of 50KW omnidirectional radio transmissions are likely [soon to be] a thing of the past

 

[SGT]

A practical 14 GHz antenna with a diameter of 20m will have a beamwidth of about 0.08 degrees. This means that at the distance of a medium altitude satellite (10000km) the half power beamwidth is 14 km, much larger than the satellite antenna.
So, most of the power irradiated from Earth to the satellite will be lost in space.
Of course, we could build 14 km diameter antennas on Earth in order to loose only half of the irradiated power, but think of the environmental problems created by those arrays all over the globe.

 

[Ivan Seeking]

What is the typical radiated power in this case?

The added complication here is mentioned by Tyson: As signal encryption becomes more sophisticated, the broadcasts signals will look more and more like noise.

Why would we want to build 14Km antennas?

 

[SGT]

What is the typical radiated power in this case?

I have no idea.

The added complication here is mentioned by Tyson: As signal encryption becomes more sophisticated, the broadcasts signals will look more and more like noise.

I don´t see why.

Why would we want to build 14Km antennas?

In order to keep radio silence against eavesdropping aliens. It is not my idea, it is yours.

 

[Ivan Seeking]

I have no idea.

I would expect that the radiated power is very low as compared to traditional radio.

I don´t see why.

By definition, encryption means less obvious - highly compressed digital data streams do not look like analog radio.

In order to keep radio silence against eavesdropping aliens. It is not my idea, it is yours.

I never said any such thing. I am talking about the logic in using radio for detecting other civilizations. How you came up with that is beyond me.

 

[SGT]

I would expect that the radiated power is very low as compared to traditional radio.

The overall transmitted power is lower than in broadcast transmissions, but remember that these are not truly omnidirectional. The antennas are designed to transmit in the horizontal and most of the power that would escape due to Earths sphericity is reflected back by the troposphere.
A transmission to a satellite is aimed directly out of the planet.

By definition, encryption means less obvious - highly compressed digital data streams do not look like analog radio.

It escapes me why a stream of ones and zeros would be less conspicuous than an analog signal.

I never said any such thing. I am talking about the logic in using radio for detecting other civilizations. How you came up with that is beyond me.

You said that we are leaking less radio signals toward the space. The only way to accomplish this is using huge antennas. Of course, more directional antennas would mean less power loss. I don´t think that the economy in transmitted power would compensate for the environmental problems created. So, the only reason would be to hide against eavesdropping aliens.

 

[Ivan Seeking]

You said that we are leaking less radio signals toward the space. The only way to accomplish this is using huge antennas. Of course, more directional antennas would mean less power loss. I don´t think that the economy in transmitted power would compensate for the environmental problems created. So, the only reason would be to hide against eavesdropping aliens.

Again, you are pulling this from thin air. The entire point of this aspect of the discussion is whether or not radio is a good way to detect other civilizations. We judge this by considering our own. No one has said anything about hiding anything.

One way to leak less radio is to transmit less radio.

As for encryption, do you understand what radio noise is?

 

[SGT]

Again, you are pulling this from thin air. The entire point of this aspect of the discussion is whether or not radio is a good way to detect other civilizations. We judge this by considering our own. No one has said anything about hiding anything.

One way to leak less radio is to transmit less radio.

I don´t think we are transmitting less radio. And if we are looking for space traveling civilizations I don´t see them communicating with spaceships or with colonies without using EM waves.

As for encryption, do you understand what radio noise is?

Yes, noise is an uncorrelated signal. Are you saying that encrypted signals are uncorrelated?

 

[Ivan Seeking]

"I don't think" is not a good argument, but in order to determine the degree of radio silence, it would take a great deal of time to calculate. In the case of directed signals as with satellite, there are a number of additional considerations such as the length of time the signal would be seen, and the intensity of the signal over distance. Of course, we also need to know the minimum detection level of our own equipment for comparison.

SETI began when it was deteremined that to some reaasonable limit, we could detect us. It becomes an interesting question as to when we no longer could have detected us using the technology first used by SETI.

In the past, SETI has been looking at wavelenths longer than those typically used on Earth now. So radio silence is also frequency dependent. The Allen Array will be good to something like 11 GHz, which is an improvement over the previous 3GHz limit.

Without the coding algorithm, a series of ones and zeros may or may not seem to be random depending on the sophistication of the encoding. But for starters, it would be much more complex to decode than modulated analog radio, which requires a tuner and amplifier.

 

[BillJx]

And the Drake equation is possible given the criteria and confirms there must be intelligent life: maybe in the galaxy, but definitely in the universe by the laws of probability.

QUOTE]

The Drake equation doesn't confirm anything. The inputs are guesses.
1) We don't know the likelihood of life arising, although it doesn't seem unlikely at all.

2) We don't know the likelihood of intelligence arising from life. If it weren't for the accidental extinction event 80 million years ago, would there be intelligent life on Earth now? What if the asteroid were bigger?
In any case, even the evolution of human intelligence from primate intelligence was a difficult path and must have had a strong evolutionary conditon driving it.

3) We don't know the likelihood of high technology arising from intelligence. For most of human existence on Earth, people were hunter-gatherers. They presumably used their intelligence for what presumably forced its evolution: border warfare. The development of high technology was possible partly because of chance combinations of readily available metals in south-east Europe. In particular, the discovery of iron seems to have been the lucky result of geological coincidences.

Here's a question: If the Earth's tectonic activity were less, would we have minerals like Iron near the surface at all? And how could an intelligent, technological society evolve if the tectonic activity were a lot greater?

3A) The moon was formed from debris from an object that hit the early Earth. We don't know the odds of that object striking with just enough force to bring a handy selection of minerals to the surface but not enough to drive all the atmosphere into space (at least I don't know, and the formula doesn't include an estimate).
I'm guessing that if it weren't for this collision, iron would be buried under miles of crustal rock.

4) We don't know the probable life span of a technological society that arises from a primitive one.

An equation could be written with pessimistic assumptions, leading to a small number of civilizations capable of space flight, with few of those lasting more than a few generations, so that at a given time the number would be vanishingly small in the vastness of the cosmos. If you wanted to be pessimistic!

Finally, why would they want to visit in person? We can already get more information from a probe than by sending a human being to walk around Mars and have a look. The reasons for wanting to send people instead of probes are emotional. With a technology only a little more advanced than ours, we could get all the information we need, then go hiking on Mars via a virtual reality indistinguishable from the real thing! By the time we can send a ship to the stars, there may be no point in putting people on it.

 

[SGT]

Without the coding algorithm, a series of ones and zeros may or may not seem to be random depending on the sophistication of the encoding. But for starters, it would be much more complex to decode than modulated analog radio, which requires a tuner and amplifier.

True if we are wanting to retrieve the information contained in the signal. Until now we are only trying to detect if there is some kind of information. For this it is irrelevant if the modulating signal is analog or digital, and if digital what sort of algorithm has been used to encode it.
By the way, even an analog signal would be incomprehensible to us unless we found some cosmic Rosetta stone.

 

[ukmicky]

The way i see it is science deals with evidence and as far as that goes we are on our own.I say life on Earth is a fluke ,we are just plain lucky to be here and there's no proof otherwise

Even in a universe as big as ours their has always got to be a first and i say that us as in Earth born life forms, we are on our own.

You have only got to look at the Earth to see how hard it is for life to start from a bunch of amino acids.I ask how many times has life began on earth, how much of the life on Earth is related.

Believing something because their is some evidence for it is one thing but to blindly believe in something without any evidence for it is MADNESS

 

[Ivan Seeking]

i say that us as in Earth born life forms, we are on our own.

...Believing something because their is some evidence for it is one thing but to blindly believe in something without any evidence for it is MADNESS

Aren't you making the very leap of faith in the first sentence that you condemn in the next?

 

[ukmicky]

Sorry IVAN
Please explain what you mean,why is my first sentence a leap of faith,theirs evidence for life on earth.

 

[Ivan Seeking]

There is no evidence to rule out life on other planets. In fact, what we do know suggests that we are almost certainly not alone, so to leap to any conclusion is a leap of faith at best.

 

[ukmicky]

There is no evidence to rule out life on other planets.

But then going by your way of thinking you may as well say that as theirs no evidence that super intelligent alien life forms haven't found a way to manipulate space then theirs no reason to disbelieve someone who tells you that aliens are walking our streets kidnapping and performing operations on us in their cloaked invisible spaceships.

Theirs no harm in dreaming or wishing it to be true but sorry without ANY form of evidence in my opinion common sense should take over..

In fact, what we do know suggests that we are almost certainly not alone,.

Please enlighten me.