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

Several Speculative Scenarios

There are no active civilizations within a few tens of thousands of light years. Active being functional and broadcasting for at least a hundred thousand years time. [radius of the galaxy]

There are no civilizations active within a hundred thousand years in time, don't forget we are separated in time as much as space. There is only a 100,000 year window of detection after a civilizations stops broadcasting in one wavelength

All current active advanced civilizations use different communication systems than we do, perhaps ones we have not thought of. Maybe other frequencies or other ideas we have not tried

We are the first civilization to emerge and activate in the galaxy

We are alone in the galaxy

Communication methods fade into the cosmic background after a distance. (most likely, stuff fades out as distances get larger) You need power to go long.

We are not trying hard enough [money]

Recognitions:
Gold Member
 Quote by tasp77 We are first.
Some people (i.e. this astronomer I heard in a meeting about 12 years ago) think we are last - we arrived when the party is nearly over.

Mentor
Blog Entries: 1
 Quote by Wanderlust There are no civilizations active within a hundred thousand years in time, don't forget we are separated in time as much as space. There is only a 100,000 year window of detection after a civilizations stops broadcasting in one wavelength
I think this is a key point that is often forgotten in science fiction (unless you read hard-SF). Humans/the Homo genus evolved to the point where they could communicate and use tools to the sophistication we see today over the last few hundred-thousand to million years (depending on whether or not you consider the capabilities of other species of human). However we only started to organise into non-nomadic communities in the last ten-thousand years. There is little reason why a species with these attributes couldn't have evolved at any point since the Cambrian explosion but that is just how things have gone. It would seem an extraordinary coincidence if we were to identify an alien species whose history was the same length as us and who were at roughly an equal level of technology. More likely the separation would be measured in megayears.

 "Shouldn't we have heard alien radio signals by now? Why not?" Because you have many hidden assumptions that are probably false: 1. That aliens want or need to communicate with us. The vast likelihood is that they are either way behind us (they are sponges, fish etc) or way ahead of us, in which case we are not of slightest interest to them. 2. That stray alien signals would be easy to pick up. Even human signals are tending more and more towards something that looks like white noise. Why? because white noise contains the most information. White noise is also almost impossible to interpret for patterns by its very definition. 3. That signals would leak to earth. If aliens were speaking to each other, broadcasts in all directions would be massively inefficient so wouldn't be used 4. That we are the peak and the future of evolution. We arrogantly consider ourselves the 'best' animals, but maybe we are just an oddity that over-populates, sucks all the oil then dies out, with rodents the most common animal over time. The long term future may look much like the past, different animals, different plants coming and going. I expect our discoveries in future will come mainly from simulations, rather than trying to set up conversations with aliens with a lag time of thousands of years. So if we aren't likely to be making such conversations, we shouldn't expect ET to be doing that either.

 Quote by TGlad 4. That we are the peak and the future of evolution. We arrogantly consider ourselves the 'best' animals,
No we don't. We simply recognize that, as an animal with
1] the capacity for foresight, and
2] the tools to do something about it,
we are capable of guiding - and thus preserving - our own destiny.

Like evolution, it inevitably leads to greater prosperity - unless something goes terribly wrong (which is a failure not a natural progression).

 Quote by TGlad I expect our discoveries in future will come mainly from simulations,
I think it was Aristotle that made that profound error - the conviction that we can learn all there is to learn from logic alone, that going out and observing - seeking new (and specifically, unexpected) information - is unnecessary. He was wrong.

"Aristotle understood that logic can be used to deduce true consequences from true premises. His error was his failure to realize that we have no absolutely true premises, except ones we define to be true."

 in which case we are not of slightest interest to them.
Ameobas are interesting. You don't realize that groups of people have specialists. I am not interested at all in a new species of slug in borneo, but some people are passionate about it. Some individuals in that society may have a keen interest in new sapient civlizations.

 3. That signals would leak to earth. If aliens were speaking to each other, broadcasts in all directions would be massively inefficient so wouldn't be used
Good idea, havent though of this one before.

 Quote by 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

That's assuming the same types of psychological needs and motivations of course.

Mentor
Blog Entries: 1
 Quote by Wanderlust Ameobas are interesting. You don't realize that groups of people have specialists. I am not interested at all in a new species of slug in borneo, but some people are passionate about it. Some individuals in that society may have a keen interest in new sapient civlizations.
More than that looking at simple life would be intensely fascinating to any biologist, especially biochemists, microbiologists and any branch of evolutionary biology. If the ameoba were to use something other than water as a solvent and biochemistry not based on amino acids, nucleotides or carbohydrates (or even not based on carbon) that would be fantastically interesting.

 Quote by 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?

That's an excellent analogy which becomes even more compelling if we hypothetically add the possibilities of life inherent in the dimensional or multiple universes ideas that physicists are currently tossing around.

Mentor
Blog Entries: 1
 Quote by Radrook That's an excellent analogy which becomes even more compelling if we hypothetically add the possibilities of life inherent in the dimensional or multiple universes ideas that physicists are currently tossing around.
Firstly you are using the term dimension wrong here. Secondly no theory involving a multiverse involves the capability to transfer from one to the other. It's easier to keep it within the realm of known physics in the known universe.

Not that it wouldn't be interesting to view life under different physical laws but a bit moot.

Mentor
 Quote by Ryan_m_b Secondly no theory involving a multiverse involves the capability to transfer from one to the other.
Ahem.

I don't know about you, but I take umbrage when someone describes evolution as "only a theory." The lay community uses the term "theory" to mean "some crazy idea I had when I woke up at 3 AM thanks having eaten a bad batch of seafood." Science views the term differently. Scientific theories are the pinnacle of scientific knowledge.

Let me correct that statement of yours, if you don't mind.
Secondly no theory conjecture involving a multiverse involves the capability to transfer from one to the other.

Sorry for the derailment. Go on back to discussing why we haven't heard alien radio signals by now.

Mentor
Blog Entries: 1
 Quote by D H Let me correct that statement of yours, if you don't mind.
No problem, you're dead right. I put it down to a slip of the tongue/hand.

 Quote by Ryan_m_b Firstly you are using the term dimension wrong here. Secondly no theory involving a multiverse involves the capability to transfer from one to the other. It's easier to keep it within the realm of known physics in the known universe. Not that it wouldn't be interesting to view life under different physical laws but a bit moot.

 Quote by Ryan_m_b Firstly you are using the term dimension wrong here.
Really? How? Strange since I didn't go into a detailed definition of what I think the term "dimension" means.

 Secondly no theory involving a multiverse involves the capability to transfer from one to the other.

 It's easier to keep it within the realm of known physics in the known universe.

Please show me where I said it wasn't.

 Not that it wouldn't be interesting to view life under different physical laws but a bit moot.
Well, it might seem moot if we understand it in a certain irrelevant way and not as intended. The point is that life is life whether we can communicate with it or not and whether it is within our dimension or not but still extraterrestrial or out there somewhere in the general direction where our telescopes are aimed.

Any claim that extraterrestrial life doesn’t exist based on our meager attempts to detect it would be ludicrous. But it would be even more ludicrous when the possibility of multiuniverses and extra dimensions where life might be present, as physicists are currently theorizing, is taken into account. It is such a claim that I was commenting on as I clearly pointed out.

 Brane cosmology String theorists like Neil Turok, Burt Ovrut and Paul Steinhardt discuss the idea that there are no more or fewer than 11 dimensions. These structures, membranes, exist across all these dimensions. Presumably, the one dimension of time and other ten dimensions of spaces have always existed. The physicists suggest that our universe may have formed when two extra-dimensional membranes collided. On this conception, our universe may not be so special, since membrane collisions could cause big bangs all the time. The result is a sort of multiverse - with universes acting like bubbles that generally cannot interact with one another. These ideas have implications for Cosmogony.[1] http://en.wikipedia.org/wiki/Brane_cosmology

Parallel Universes Videos

<object style="height: 390px; width: 640px"><param name="movie" value="http://www.youtube.com/v/Z7SDrj4Tjvk?version=3&feature=player_detailpage"><param name="allowFullScreen" value="true"><param name="allowScriptAccess" value="always"><embed src="http://www.youtube.com/v/Z7SDrj4Tjvk?version=3&feature=player_detailpage" type="application/x-shockwave-flash" allowfullscreen="true" allowScriptAccess="always" width="640" height="360"></object>

Who lives in the eleventh dimension Video

<object style="height: 390px; width: 640px"><param name="movie" value="http://www.youtube.com/v/xE7xRgfPjAI?version=3&feature=player_detailpage"><param name="allowFullScreen" value="true"><param name="allowScriptAccess" value="always"><embed src="http://www.youtube.com/v/xE7xRgfPjAI?version=3&feature=player_detailpage" type="application/x-shockwave-flash" allowfullscreen="true" allowScriptAccess="always" width="640" height="360"></object>

Mentor
Blog Entries: 1
 Quote by Radrook Really? How? Strange since I didn't go into a detailed definition of what I think the term dimension means.
No but the way you are using the term is wrong; only colloquially is dimension synonymous with universe.
I never suggested you did. My point was that talking about life in other universes is a pointless exercise because 1) we can't be sure that such universes exist and 2) even if they did we could never expect to hear from them anyway. As this thread is about detection bringing something to the conversation that cannot be detected wont get us anywhere.
 Quote by Radrook Well, it might seem moot if we understand it in a certain irrelevant way and not as intended. The pint is that life is life whether we can communicate with it or not and whether it is within our dimension or not. Our claim that no extraterrestrial life doesn’t exist based on our meager attempts to detect it would be ludicrous. It would be even ludicrous when we consider the possibility of multiuniverses and extra dimensions where life might be present is taken into account. It is such a claim that I was commenting on as I clearly pointed out.
Again only colloquially is dimension used to mean universe.
 Quote by Radrook Parallel Universes Videos...
Popular science documentaries are not supportive evidence.

 Part of me worries that intelligent life is just so rare, even when taking into account the countless number of planet types/star systems/etc that would be conducive to it.

Blog Entries: 8
Recognitions:
Gold Member
Staff Emeritus
 Quote by Radrook Really? How? Strange since I didn't go into a detailed definition of what I think the term "dimension" means.
The term dimension has nothing to do with parallel universes. We often see in science-fiction shows that "people have been transported to other dimensions", like tey have went to another universe where the laws of physics are different.

The term dimension has absolutely nothing to do with this. Dimension has a very precise mathematical meaning. A dimension actually is "the number of free variables possible in a system". For example, the plane has dimension 2 since you need 2 variables to specifically determine a point in the plane (indeed: you need an x and a y-variable). The space has dimension 3 since you need 3 variables.

So a dimension is not a parallel universe, it is simply a number!!

In physics, a dimension has a related but different meaning. A dimension there can be used to signify whatever units we use. For example, accelaration has units $m/s^2$ and has a different dimension than velocity which has units $m/s$.
Again, there is no talk about parallel universes.

If you want to talk about parallel universes, you are welcome to do so: but do NOT use the term dimension.

 Quote by Ryan_m_b No but the way you are using the term is wrong; only colloquially is dimension synonymous with universe. I never suggested you did. My point was that talking about life in other universes is a pointless exercise because 1) we can't be sure that such universes exist and 2) even if they did we could never expect to hear from them anyway. As this thread is about detection bringing something to the conversation that cannot be detected wont get us anywhere. Again only colloquially is dimension used to mean universe. Popular science documentaries are not supportive evidence.

 Quote by Ryan_m_b No but the way you are using the term is wrong; only colloquially is dimension synonymous with universe.

That is a mere unjustified inference. Even so, it is a totally unnecessary one since inferences derived from the written text should always be firmly based on context and this one isn‘t.. You see, textual context should indicate in this case that if indeed a universe is being spoken about it is a universe in the total sense of the word and not merely a detectable universe. Whether the usage is colloquial or not is totally irrelevant to the intended concept. In short, the colloquial objection is non-applicable and the premise which it represents is fallaciously skewed.

 I never suggested you did. My point was that talking about life in other universes is a pointless exercise because 1) we can't be sure that such universes exist

Inconsistency of policy. You aren’t sure if extraterrestrials exist but that doesn’t stop you from talking about it.

 and 2) even if they did we could never expect to hear from them anyway.

Really? You know that for a fact? Some of the unexplained phenomenon has been hypothesized to be extra dimensionally derived. Electrons which disappear and reappear at unpredictable locations around atomic nuclei are thought to be flitting from dimension to dimension. Gravity itself is presently being hypothesized as extradimensional leakage into our dimension from anther where it is much more powerful. Physicists are even now attempting to explain the enigmatic Dark Energy and Dark Matters by factoring in extra dimensional mathematical equations. So a casual relegation of extradimensioality to the boondocks of the silly and irrelevant isn’t quite at the cutting edge of current scientific thinking to say the least.

 thread is about detection bringing something to the conversation that cannot be detected wont get us anywhere.

Another baseless inference! I made no claim that it was intended to get us anywhere. Why? Well, because getting somewhere in relation to this subject means finding a definite answer to the thread’s topic which is presently impossible. In short, this whole thread is based on hypotheticals which can’t get anywhere unless by somewhere you mean additional hypothesizing that will get nowhere. Which is, BTW, exactly what I did..

 Again only colloquially is dimension used to mean universe.
I never equated dimension with universe. LOL

 Popular science documentaries are not supportive evidence.
It wasn’t offered as irrefutable supportive evidence. It was merely offered as an example that the idea is being seriously considered in scientific circles as the documentary points out. If indeed the physicist who is speaking in that documentary is lying, and you feel justified in brazenly and publicly accusing him of lying, then it is up to you to prove it since you are the one taking serious umbrage with what that physicist is claiming. Your mere personal opinion glibly posted on this forum does not in any way manner r form constitute irrefutable proof otherwise. It is merely an unsubstantiated OPINION.

As for popularity, your premise is completely off since popularity doesn’t invariably equate with the unscientific or with quackery. The Bib Bang Theory and the Dark Matter Dark Energy theories are also popular and they are not diminished by being so or by being shown on any documentary hosted by a physicist.

Of course if indeed this was a full-fledged debate I would present s doctoral dissertations and scientific articles submitted for peer review and ultimately accepted as reputable by the majority. But that would seriously deviate the thread and deviation of the thread wasn’t and still isn’t my intention. Neither does my very brief comment about the possibilities inherent in claiming that there is no life in space based on our inability to detect it derail it.

However, unnecessary quibbling with semantics and demanding extensive documentation for every statement based on personal interpretation concerning what the poster meant does seriously threaten to deviate the thread by attempting to turn it into a personal debate over a relevant albeit slightly side topic about another poster’s pertinent and excellent analogy which was definitely on topic,