We are quite aware just how far it is "out there". With the speed of light being the fundamental limit for baryonic matter, it will be next to impossible to travel between the stars (at least under our current level of physics knowledge). So the universe may be populated with little isolated bits of intelligence all wondering if any other species are out there.
Just in the past few years we have advanced far enough in our technical prowess to both "announce" to the universe we are here (radio waves) and to receive the same from another species. With that in mind and the speed of light being a constant in a vacuum, the expanding sphere of radio noise heralding our presence has only gone about 60 light years or so. So there may be an entire galactic community out there but our "knock" hasn't yet hit the door so to speak.
(Note: Astronomers use another term for stellar distance that may be not so familiar called the Parsec. A Parsec (parallax-arcsecond) is the distance needed for one astronomical unit (AU) to subtend one second of arc. However for this discussion I will revert to the more familiar “Light Year”)
This also applies in the opposite direction. If there was a radio producing species only 70 light years away and they have had radio only for 50 years, we would have no possible way of detecting them for another 20 years. Expand that out to approximately 100,000 light years (diameter of just our little galaxy) and you begin to see the problem.
While SETI is indeed a long shot, we do have one example of a species that sends signals out into interstellar space: ourselves. This means that intelligent life in the universe is possible and proven. Further, it is possibly detectable if that intelligence uses any form of EM radiation to communicate as we have for years. It is therefore not without merit.
Moore's law has affected the Drake equation in ways we don't even know yet. I personally think the Fermi Paradox is pure BS and not well though out, however, the Drake equation seems to have stood up to scrutiny.
SETI (at least the current trend) is searching for extremely narrowband carrier signals that are Doppler shifted due to planetary rotation. The Doppler shift is extremely important since if it is not there, we know the signal is either terrestrial or an artifact of the equipment itself. The other thing that is very important is the two-antenna approach. If two antennas, separated by a thousand miles, were pointed at the same patch of sky, this would not allow a satellite to "spoof" the system. First, the likelihood of it being within the footprint of both antennas are exceedingly small, and the Doppler characteristics between the two antennas would rule it out if such a thing happened.
All that said, I think the advances in communications technology can cause a search to be futile for many types of broadcasts. Frequency hopping spread spectrum and the like will make it far harder to detect a tool building species that uses radio (EM).
To be fair to the other side there is another factor in this conjecture. A race is progressing along and figures out that the electromagnetic spectrum is the only real practical method of long-range communications. So high-powered transmitters are built as this technology is in its infancy. As the engineering and science of radio advances, they figure out that tight beam, spread spectrum, synthetic aperture, frequency hopping, etc. are a way of not only saving power, but also bandwidth. So for the first 50 years they have been "bleeding" EM into space across a huge range of frequencies into and ever-increasing sphere of radio noise. However, do to technological advances, this RF that is being bled into space quiets down dramatically.
Now, lets jump a few years. This race has expanded off its initial planet and is exploring the solar system it resides in. (IMHO, star travel still remains firmly in the realm of SiFi) Somehow they have to communicate. So again high power transmitters are employed to accomplish this. Light is not out of the question, however, microwave is easy, cheap, less pointing accuracy requirements, and wont be drowned out by the star. So suddenly this race again is radiating RF into the universe. So according to this scenario, a race can emit RF then grow silent for a time, and then restart emitting RF.
Why EM and not some other means I hear you ask?
There appears to be only four fundamental forces in all of nature; Strong Force, Weak Force, Gravity, and Electromagnetism EM. Both the strong force and Weak force are confined to the nucleus of the atom. Gravity requires prodigious amounts of energy to manipulate, so the only one that appears practical for long distance communication is EM. In an extremely short period of time, we are using EM across the entire spectrum from basically DC to light.
I personally believe for a race to become technologically advanced, it must eventually realize the need for the ability to store and convey information over long distances. Since radio waves (I am including any EM in this such as RADAR, TV, microwave, etc.) are still the best method for accomplishing this, any other race would use/do the same. For about the past 60 years we have been isotropically radiating EM across a huge RF spectrum into outer space. What many SETI systems are looking for is another species that is doing the exact same thing we are; unintentional radiation of EM into outer space.
Even the nearest star (Proxima Centauri), actually a member of a ternary star system, is 4.22 light years away. This is why radio and/or optics (I know some people who are contemplating optical SETI) are the best and at the moment the only way to find other civilizations. The advancing sphere of radio noise radiating from our own planet now encompasses an area more than 120 light years across. There are literally thousands of stars within that volume of space. As we measure the heavens with more precise instrumentation we are finding a plethora of planets orbiting other stars.
A few years ago there were many people who were quite skeptical about the possibility of extra solar planetary systems. Statements were made like "just because there is one known planetary system (ours), it doesn’t mean there are others". It appears now that planetary systems are the norm instead of the exception. I am now hearing the same argument against the possibility of ET. I personally do not "believe" ET is out there. I suspect ET is out there. We are finding the building blocks of life through out the heavens. I also think life is far more tenacious than most people believe. We even find life in the sulfur volcanic vents on this planet.
The other question that periodically comes up is “what about von Neumann probes”?
Two things. First, there may me thousands of races out there, but they are "stuck" just like we are by general relativity. Sigh! Second, the prodigious amount of time it would take to cross the galaxy at sub light speed would possibly prohibit even the most ambitious race from basically spending the money and wasting the precious resources of a local solar system to attempt that feat. Also how long can a machine function and replicate without error entering the picture. Not unlike evolution. :)
And just where in the heck do we look and at what frequency?
Lets start with a bit of a background:
Radio astronomers use temperature to describe the strength of detected radiation. Any body with a temperature above -273 deg C (approximately absolute 0) emits electromagnetic radiation (EM). This thermal radiation isn’t just in the infrared but is exhibited across the entire electromagnetic spectrum. (Note: it will have a greater intensity (peak) at a specific area of the EM spectrum depending on its temperature). For example, bodies at 2000 K (Kelvin), the radiation is primarily in the infrared region and at 10000 K, the radiation is primarily in the visible light region. There is also a direct correlation between temperature and the amount of energy emitted, which is described by Planck’s law.
When the temperature of a body is lowered, two things happen. First, the peak shifts in the direction towards the longer wavelengths and second, it emits less radiation at all wavelengths.
This turns out to be extremely useful. When a radio astronomer looks at a particular point of the sky and says that it has a noise temperature of 1500 K, he/she isn’t declaring how hot the body (nebulae, etc) really is, but is providing a measurement of the strength of the radiation from the source at the observed frequency. For example, radiation from an extra solar body may be heated from a nearby source such as a star. If this body is radiating at a temperature of 500 K, it exhibits the same emissions across all frequencies that a local test source does. The calculated noise figure will be the same across all frequencies. (Note: this does not take into account other sources of radiation such as synchrotron radiation).
So, here’s the rub. Not only does the source that is of interest to the radio astronomer emit thermal radiation but also both the local environment (ground, atmosphere, etc) and the equipment (antenna, amplifiers, cables, receiver, etc) being used to make the measurements. To accurately observe and measure the distant sources, the radio astronomer must subtract all of the local environment and detection equipment noise additions.
In 1963, Arno Penzias and Robert Wilson were working with a horn antenna trying to make it work with as high efficiency as possible for the Telstar project. This antenna was also going to be used for radio astronomy at a later date. They pointed it to a quiet part of the sky and took measurements. When they subtracted all of the known sources of noise, they found approximately 3 K left over. They worked very diligently to eliminate/describe this noise source and were unable to. This mysterious source of noise seemed to be there no matter where they pointed the antenna. What they had discovered was the microwave background produced from the Big Bang. This 3 (closer to 2.7) K microwave background originated approximately 300,000 years after the Big Bang itself had occurred. It has been determined that when these signals originated, the universe had already cooled down to around 3000 K.
So what frequencies do radio astronomers use and subsequently SETI?
There are two real sources of noise that limits the radio astronomer's ability to search for very weak signals. The galactic noise halo interferes with us below 1 GHz and noise due to earth's atmosphere interferes with us above about 10 GHz. This pretty much keeps all SETI searches (at least radio ones) between 1 and 10 GHz. Inside these two frequencies, from about 1.4 to 7 GHz the noise level drops off even further to near the 2.7 Kelvin Cosmic Microwave Background (CMB) that permeates all space. Hydrogen (H) molecules, the most abundant element in the universe, excite and emit (masers) at around the 1.4 GHz frequency (21 cm band) and the hydroxyl (OH) emits at around 1.65 GHz. This is where much of our radio astronomy and SETI research is concentrated. Since H + OH is water, the frequency gap between these two is often called the “Water Hole”.
Also SETI searches are not looking for intelligence riding on a signal itself. The scintillation of the interstellar medium will quickly make that unintelligible. What most current SETI searches are looking for, is the extremely narrowband signal (carrier) that the information rides on. Indeed as we evolve into more "spread spectrum" type signals, the carrier(s) will be harder to detect. However, I think that will be a temporary phenomena. As we spread out into the solar system, we again will require high power carriers to convey information from point to point. So there may be a naturally "quiet" period in many advanced races prior to then spreading through out their solar system.
(from: http://www.seds.org/~rme/seti.html)
"Given an effective radiated power of the transmitter (in watts), the effective area of the receiving antenna (in square meters), the excess receiver noise temperature of the receiver used (in K), the averaging time of the receiver (in seconds), and the accepted band-width of the signal (in Hz), the range at which we can detect a signal transmitted by an intelligent civilization, is:
R=8x10-6(PeA/T)1/2(t/B)1/4 light years.
Where the constant is calculated from 1/[9.4608x10 15(4”pi”k) ½]. Here the constant is the number of meters per one light year, and k is the boltzmann constant.
So to offset some of the limitations, we (SETI searches in general) are looking for extremely narrow band CW waves that have been Doppler shifted due to planetary motions.
However, this is not fraught with its own set of problems. Much of our own radio transmissions do not fall within this range. Also this is one of the coveted frequencies of radio astronomers, thusly we have international treaties to not broadcast at these frequencies since they would interfere with radio astronomers. So here we are looking for signs of a narrowband signal heralding the fact that intelligent life is not wholly constrained to our tiny little planet at these very frequencies.
Just imagine another tool building species that ends up developing radio and radio astronomy that may also recognizes the importance of this 21cm band. And they also may instigate a SETI search using these same bands such as we do. So here is the question. Would they hear us at those frequencies? They are the very ones that we are not transmitting on at all. I could just see 500 races all looking for each other at the very frequency band that none of them are transmitting on due to the very nature of its importance for the exploration of the universe.
Here is an excerpt from a paper I wrote a while back: (note: I cannot get the symbols for Pi or lambda to work )
With any link, there is parameter called a link margin. This the margin of degradation before the Bit Error Rate (BER) becomes unacceptable. This margin must take into account signal attenuation due to distance, atmospheric conditions antenna gain, transmitter power, frequency, etc.
The energy of an electromagnetic wave is directly proportional to its frequency. The Energy (E) equals Planck’s constant (h) times the speed of light (c) divided by the frequency of the wave (“lambda”): E = hc/”lambda” or in other words since c = “lambda”*v (v is frequency) then E = h v
Whereas Planck’s constant describes the nature of matter and energy at the atomic levels. Planck’s constant is; 6.626 x 10-34 Joule-second. A joule is the amount of energy exerted when a force of one (1) newton is applied over a displacement of one meter, which is also equivalent to one (1) watt of power radiated for one second.
All of these equations lead up to the simple fact that the shorter the wavelength, the higher the energy of the wave.,
The following are just a few of the things that affect link margin (being able to receive data):
1. The frequency of the wave
2. RF interference (local radio noise, solar RFI, another satellite, etc)
3. Bit rate of the data
4. Antenna elevation (such as a 5° contact with the satellite versus 85°)
5. Atmospherics (rain, clouds, snow and the like)
6. Solar affects (sunspots, geomagnetic storms, solar flares and storms, etc)
7. Antenna gain and size
8. Radiated power from the transmitter
9. Antenna type (omni, dish, yagi, etc)
10. Antenna efficiency (efficiency of the LNA and the like)
All of these items must be taken into account by the RF engineer whenever he/she is designing the link. I have defined a few of the terms you may run across that are used by the engineers when describing or computing link margins.
FSL (Free Space Loss)
Loss in free space is a function of frequency squared plus distance squared plus a constant. Free space means transmission without absorption or reflection of energy. Expressed in decibel form, the free space loss is:
(FSL)dB = 20log(4"pi"d/"lambda")
Where "lambda" is wavelength.
EIRP: (Effective Isotropically Radiated Power).
Dish Antennas are a very directional antenna. This allows most of the radiated power to be broadcast in a single direction. EIRP is the power received that the antenna appears to broadcast as if it was an isotropic radiator. Thusly it is the product of the gain of the antenna and the transmitter power.
EIRP can be calculated using the following formula: EIRPdBW = P0 + Lt + G1 where P0 is the power out of the transmitter, Lt is the transmission line loss, and G1 is the gain of the antenna.
Eb/N0: (Energy per Bit Noise Density Ratio)
This is the efficiency of the digital communications with respect to the noise on the link. N0 is commonly measured by the received bit energy to noise density ratio Eb/N0.
C/N0: (Carrier to Noise Ratio).
C equals Carrier power received and N equals the noise of the ground system.
G/T: (Gain-to-Noise Temperature Ratio)
Basically this is a ratio of the Gain of the ground station antenna to the Noise temperature of the ground station RF equipment.
Putting this all together gives us a “feel” for the link budget:
The link budget is a tabular method of calculating the space communications systems parameters. So the total equation would look something like this:
C/N0 = EIRP – FSLdB – (other losses) + G/TdB/K - k
Where FSL is the free space loss, k is Boltzmann’s constant (1.3806 x 10-23 joule/K) expressed in dBW or dBm, and the “other losses” may include:
· Polarization loss
· Pointing loss
· Off-contour loss
· Gaseous absorption losses
· Atmospheric effects (such as rainfall)
· Localized interference
Note: off contour loss refers to spacecraft antennas that are not earth coverage, such as spot beams, zone beams, or multiple beam antennas.
Thanks for the Ping and exposition of the parameters involved!
If we are ever visited by physical beings, they may have discovered the means to trans-dimensionally cross over from an alternate universe. Exploring alternate universes would take virtually no time at all and may be far more compelling to an explorer than wandering around in the vast emptiness of our own universe.
Seriously, a good post.. thanks..
It illustrates what I was trying to point out, that it is as difficult (if not impossible) for other intelligent life to find us, as it is for us to find them..
I suggest the most probable possibility of an actual, physical contact is the use of some sort of "Ark", a self-contained world, a multi-generational spacecraft, coming to our solar system with another life form...
In a sense, contact being Forced Upon Us..
Such an eventuality would be "interesting" in the extreme..
Would earthly humankind be willing to share our planet with another intelligent species ??
What if interbreeding were possible? (assimilation)
What if it were not? (competition)
What social, philosophical, religious ramifications??
Would we be willing (or able) to demand they "move on", subjecting their kind to possibly another multi-generational oddysey?
Could WE be that "inhuman", in face of the fate we would be condemning them to??
Are you gearing up to write the book on the search for ET?
Wow!
Nice post!
Are you getting a chance to look at Venus and Mars or any of the meteors? Good viewing out there.
The biggest problem with the Drake Equation is its first variable: The number of stars in our galaxy. We now understand that our galaxy has a relatively narrow "habitable zone" which is needed for the evolution of higher lifeforms. Move too far in towards the galactic core and gravitational disturbances caused by the reduced distances between the stars robs potential planets of the long term orbital stability they need to evolve lower lifeforms into higher ones. Move too far out and the increased rate of star formation in the outer bands will soak your planet in radiation, sterilizing it in minutes.
The problem is that these two regions are home to the bulk of the stars in our galaxy. Remove them from the picture and you have a far smaller starting number.
The most comprehensive analysis of the question that I've read put the number of intelligent civilizations existing today at no more than 5-7 per galaxy, with 2-4 being a more probable number. When you add in a second missing Drake Equation factor, the number of communicating civilizations that achieve interstellar spaceflight, the odds of us actually meeting any of them fall to practically zero. If mankind ever meets a single extraterrestrial civilization during its time of existence, we'll be lucky. Star Trek is fiction.
I have no doubt that our infinite universe is home to countless thousands of species, but the very fact that our universe is infinite means that we'll never get to meet them.
Wow. Post of the month! Great reading.
GReat post.
I don't think you are going to find humans bouncing around, but out in the universe we could find cells, microbes, maybe other things like missing Whitewater papers. You never know.
I personally think the Fermi Paradox is pure BS and not well thought outWe think alike. ;')