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Author Topic: SETI: Fundamentally Flawed?  (Read 19161 times)

Offline Parsiminous

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SETI: Fundamentally Flawed?
« on: 05/11/2007 02:12:11 »
Hi Folks, I have been doing some thinking and reading on SETI and their approach to detecting signals.

I've come to the conclusion that, well, The SETI program, as conceived and executed by The Planetary Society, U of C Berkeley, et al, is fundamentally flawed because they use antennas designed to detect radio waves, light waves, and micro waves at a distance that is beyond their capability.  Antennas (including satellite dishes) collect waves that match the frequency to which they are tuned.  Unbound, waves disperse over time and distance.  They are called "waves" because they behave precisely like a wave in the water.  A signal sent from a planet 130 light years away would have existed for 130 years before it is read, and would have weakened and stretched to a length greater than the length of any wave that can be detected by any equipment currently in use.  Scientists study events that happened in the past, including what they believe to be evidence of the Big Bang singularity, by examining their effects on other things, like the rate that a specific body travels within a fixed point in space.  They do not have at their disposal any instrument that can measure these events directly.

I see this leading to the conclusion that our current technology renders SETI as mere entertainment. Maybe I'm missing something fundamental here? Thanks for your input! Chris


 

another_someone

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SETI: Fundamentally Flawed?
« Reply #1 on: 05/11/2007 02:24:45 »
While I am no particular proponent of SETI, I don't really see your argument as making any sense.

You seem to be saying we cannot say much about a radio wave that has travelled 130 light years; but since radio waves are electromagnetic waves, just like light waves, so the same argument could be said of light reaching us from the same distances.  Are you therefore saying we cannot be sure of the light we see that we believe to be emitted from distant stars?
 

Offline Parsiminous

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SETI: Fundamentally Flawed?
« Reply #2 on: 05/11/2007 03:33:19 »
thanks for the quick reply A_S.

While I know I must be wrong somewhere in thinking about the situation, I can't figure out exactly where -it's been a while since I took a physics class:). I'm not saying that the situation is analogous to light from distant stars, and we can analyze that light for it's properties. But with SETI's detection, they are looking for non-random, or non-naturally, occurring patterns. Any pattern would lengthen out as it progresses through space to the point of incoherence on the receiving signals end, right?

Radio signals travel much slower than light.  I don't know the conversion, so I'll give the benefit of the doubt and say they're the same.  So they're scanning for signals sent 200 years ago. Unfortunately, radio waves spread out over time and distance, so in order for this to work, they would have to cover a very large space with their antennas, and digitally alter the signal that was sent centuries ago.  If they found the beginning of a wave in the 1,200 and 3,000 MHz range right now, how long would it take to read the entire wave, assuming their antennas were locked onto it (which Project Phoenix's antennas were not capable of)?  Multiply that by the chances that the wave they were chasing was actually a meaningful transmission.  The answer is more than the life span of a human.

These constraints seem to point toward SETI never having a real chance of recognizing a radio (or otherwise) signal.
I'm not sure what I'm missing here, and appreciate anybody pointing it out!
Chris
 

another_someone

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SETI: Fundamentally Flawed?
« Reply #3 on: 05/11/2007 06:36:53 »
You are wrong in a number of counts.

First, all electromagnetic waves travel with exactly the same velocity through a perfect vacuum (this is a basic tenet of relativity, and if this is shown not to be so, then it will undermine much of what is believed in modern physics).  Although no real world vacuum is perfect, for all practical purposes, space may be considered sufficiently much a perfect vacuum for our purposes (we know of no significant refraction in space, and if such refraction did exist, it would be something that would be observable).

Secondly, EM waves do not stretch longitudinally (as far as we are aware) as they travel through space.  We would expect red shift of all EM waves due to objects that are further away from us also to be travelling away from us, causing a doppler shift (this is part of the known expansion of the universe, and is something we know about, and adjust for).  That the waves will reduce in amplitude as they travel through space (unless they are focused waves) is also known, and this is what causes more distant stars to appear to be fainter (they will appear fainter in the radio spectrum just as they appear fainter in the visible spectrum).
 

Offline syhprum

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SETI: Fundamentally Flawed?
« Reply #4 on: 05/11/2007 08:07:15 »
I do not believe in SETI not because of waves stretching or any thing like that but because of the utter futility of trying to hold any conversation with any beings 100 light years away.
The technical limits to communication are about 1000 LY but although it would be interesting to receive conformation that there is 'someone out there' two way communication is a no no.
 

Offline Dick1038

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SETI: Fundamentally Flawed?
« Reply #5 on: 05/11/2007 17:18:08 »
We can observe stars located at great distances because of the tremendous power radiated. I haven't done any calculations, but I doubt if we could detect a 50KW radio transmission, typical for commercial radio and TV stations, from a multi-light-year distance. The aliens would have to use tremendously powerful transmitters in order for us to detect the signal. From what I understand, the SETI people receive extremely low signal-to-noise ratio signals and rely on long duration signal processing and hope to average out the noise.  They rely on statistical techniques to look for nonrandom components in the radio signal.
 

Offline syhprum

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SETI: Fundamentally Flawed?
« Reply #6 on: 05/11/2007 18:05:52 »
I believe the 1000 LY range assumed 10MW transmitter, 1 Hz bandwith and Acibro size(300m) Antenna's correctly directed.
They would have to wait 2000 years to know if they got it right!
 

lyner

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SETI: Fundamentally Flawed?
« Reply #7 on: 05/11/2007 18:12:39 »
Antennas have no limit to the 'distance' they can look. They are limited (along with the receivers) by the energy levels they can detect. This, in turn, limits the actual information they can get out of a signal they receive.
The bandwidth for SETI is very narrow, which gives them a huge help. The directions in which they can look are determined by the daily spin of the Earth.

Whilst we can't hope to carry on a conversation with anyone more than a very few light years away, we can get information from them. This could be useful or deadly - and we should have to be very careful in how we acted on anything we collected.

In our limited way, we are spreading information around the Galaxy - to a distance of nearly 90 light years!
 

Offline syhprum

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SETI: Fundamentally Flawed?
« Reply #8 on: 05/11/2007 19:01:05 »
Here is a good analysis of the technical matters involved with extra terrestrial communication


http://home.fnal.gov/~carrigan/SETI/SETI%20Hacker_AC-03-IAA-8-3-06.doc
« Last Edit: 05/11/2007 19:04:11 by syhprum »
 

another_someone

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SETI: Fundamentally Flawed?
« Reply #9 on: 05/11/2007 20:01:16 »
Here is a good analysis of the technical matters involved with extra terrestrial communication


http://home.fnal.gov/~carrigan/SETI/SETI%20Hacker_AC-03-IAA-8-3-06.doc

I do like the notion of an intergalactic computer virus.
 

lyner

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SETI: Fundamentally Flawed?
« Reply #10 on: 10/11/2007 18:15:05 »
Does anyone remember 'A for Andromeda"?
Scientists on Earth receive information from an Alien source on how to make a new computer. The computer then creates a new life form.
It's only through luck that the 'monster' (played by Julie Christie, I seem to remember  and she can take me over any time!) fails in its task and the Earth survives.
 

Offline syhprum

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SETI: Fundamentally Flawed?
« Reply #11 on: 10/11/2007 22:06:41 »
I remember it well, the author certainly stretched the computer technology that was available at the time.
going further back two decades there was a wonderfull series on the wireless about the Establishment of a colony on Mars, does anyone else remember that?
 

lyner

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SETI: Fundamentally Flawed?
« Reply #12 on: 11/11/2007 00:40:03 »
'Journey into space; the Red Planet' by Charles Chiltern.
Andrew Faulds played Jet Morgan, the leader of the crew.
I was allowed to stay up for that one!
 

Offline Ophiolite

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SETI: Fundamentally Flawed?
« Reply #13 on: 13/11/2007 14:34:25 »
'Journey into space; the Red Planet' by Charles Chiltern.
Andrew Faulds played Jet Morgan, the leader of the crew.
I was allowed to stay up for that one!
Good God! You people are as old as me. They rebroadcast these in the early 90s (late 80s). Syphrum, the tapes of A for Andromeda were wiped, so you'll have to rely on your memory and a Dr. Zhivago DVD.
 

lyner

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SETI: Fundamentally Flawed?
« Reply #14 on: 13/11/2007 18:17:40 »
I heard some of J into S on Radio 7 this summer. AAAH
 

Offline JimBob

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SETI: Fundamentally Flawed?
« Reply #15 on: 13/11/2007 19:38:29 »
This is Geezer Corner, I'll appoint myself president!


 

Offline syhprum

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SETI: Fundamentally Flawed?
« Reply #16 on: 13/11/2007 19:51:23 »
Sophie

I was a little surprised that you could remember so much detail from the age of four but I note there has been a recent re broadcast also a CD is available.
I have clear recollections of the first serial broadcast on the wireless when I was five ( The count of Monti christo ), I hope they get round to repeating this but it was before the days of tape recording.


 

Offline gfellow

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SETI: Fundamentally Flawed?
« Reply #17 on: 17/12/2007 03:46:48 »
Hi,

Since this is a favorite subject of mine, I always have google notify me when it comes up. A possible absence of signals denoting intelligence may be for the simple reason that no creature that reaches sentience gets very far:
"Why is SETI not receiving ET signals?"
newbielink:http://www.goodfelloweb.com/nature/ideas/seti_faliure.htm [nonactive]

Best,

Stephen Goodfellow

 

Offline Pumblechook

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SETI: Fundamentally Flawed?
« Reply #18 on: 20/12/2007 22:54:13 »
Our transmitters are far too weak to reach very far at all. Even various SETI groups admit it. 

I have done a lot of calculations and it suggests we would need transmitters 1000's Millions and even billions of times more powerful that we have depending on the distance you want to cover.

The other problem is when you have highly direction antennas is knowing where to point them.  Even a 'smallish' dish with a one degree beam width can point at any azimuth 0 - 360 deg and 0 - 90 elevation.. So that is 360 x 90 possible directions.. = 32,400 possible directions.  The chance of two similar antennas aligning is 32,400 sqrd = over 1 billion to 1. 

I know we can see distant stars and pick up radio noise from them but like our Sun they are mind-bogglingly powerful.   
 

Offline Pumblechook

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SETI: Fundamentally Flawed?
« Reply #19 on: 20/12/2007 23:04:16 »
From SETI Institute...

"""If an extraterrestrial civilization has a SETI project similar to Project Phoenix, could they hear Earth?

In general, no. Most earthly transmitters are too weak to be detectable by Phoenix-type equipment at the distance of even the nearest star. To detect "leakage" radiation similar to our own will require instruments that are many times more sensitive than what we now have."""


http://www.seti.org/about-us/faq.php

 

Offline syhprum

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« Reply #20 on: 21/12/2007 10:49:03 »
I understand that SETI mainly concerns itself with bandwidths of about 1 Hz, if the aliens had a different concept of time 1 nHz might be what was needed which of course would lead to much greater range but would be pretty meaningless to we Earthlings
 

Offline Soul Surfer

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SETI: Fundamentally Flawed?
« Reply #21 on: 21/12/2007 14:03:44 »
It also depends whether the alien civilisation wants to be heard.  A lot of modern communications uses techniques called spread spectrum processing in which narrow band signals are sent down broad band channels using a correlation process and not a convetional carrier.  If you design transmitters like this they can be virtually indistinguishable from noise.

It has been said that if there were the deep space equivalent of pirates out there looking for life forms to plunder our radio and television signals would be a beacon to drag them in so the sooner we get into spread spectrum signalling for all high power applications the safer we are likely to be  :-)
« Last Edit: 21/12/2007 14:06:10 by Soul Surfer »
 

Offline Pumblechook

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SETI: Fundamentally Flawed?
« Reply #22 on: 21/12/2007 19:39:34 »
People say that radio waves go on forever and it is just a matter of the received signal being above the noise floor or not.  But there must be a limit where there are simply no electroncs being stimulated by an Earth transmitter in a distant bit of metal. 
« Last Edit: 21/12/2007 19:44:29 by Pumblechook »
 

Offline Soul Surfer

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SETI: Fundamentally Flawed?
« Reply #23 on: 22/12/2007 12:03:42 »
I am not quite sure what you are trying to say here.  There are always limits to them sensitivity of all types of receivers but with good technology and signal processing it is amazing how sensitive they can be.

When you get down to the quantum levels for radiation that it is possible to detect individual quanta there is no limit to the range of detection of the quanta but there could be too many interefering quanta to detect any sensible communication.
 

Offline Pumblechook

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SETI: Fundamentally Flawed?
« Reply #24 on: 22/12/2007 20:57:12 »
As I say at some distance from earth there will be no electrons being stimulated by a transmitter on Earth.  There is a finite limit.  Once you get to only one electron being stimulated the next step further out is zero.  Is my flea power 2.4 GHz router stimulating any electrons in a distant planet or on the Sydney Harbour Bridge?
 

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SETI: Fundamentally Flawed?
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