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New Telescope Array Goes Live For SETI
The Skinny writes "Today is a historic day for the SETI program. The New York Times reports that astronomers are flipping the switch today on the Allen Telescope Array — 350 antennas, each 20 feet in diameter — which will, among other things, extend the search for extraterrestrial life a thousandfold. From the article: ' There are some 200 billion stars in the galaxy, and a significant fraction of them have planets. Estimates of the number of intelligent civilizations in the galaxy have ranged from one (or none, if you are particularly discouraged about human affairs) into the millions. Dr. Shostak calculated that the full Allen array would be able to detect a signal from as far as 500 light years that is only a few times more powerful than what can now be sent by the Arecibo radio telescope, a 1,000-foot-diameter dish in Puerto Rico that is the world's largest (although it is in danger of being shut down to save money). That translates to about a million stars, which he said was getting into a promising number. Dr. Shostak described the expanded search as looking for the needle in the proverbial haystack with a shovel instead of a spoon.'"
I think the better metaphor would be "trying to move a mountain with a spoon instead of a pen cap." Seriously, taking into account the number of stars, the number of planets orbiting the stars, and the span of time that they're likely to be spewing radio waves, the task is monumental compared to any resources that SETI may get. The work is still important, but let's not underestimate the task.
I always find it amusing when people say money is "wasted". If I took a stack of bill and burned them, or buried them never to be seen again, that would be wasting them.
If they spent $100mill on a telescope array, where did the money go? It went to some firms who do that, who in turn paid their employees and their suppliers, who paid their employees, etc. Those employees bought groceries, sent their kid to the dentist, sent their kid to college, bought a new car.. the money flowed through the economy. Assuming a large percentage of the firms and suppliers are in this country, then the money stayed in the national economy.
When the economy is flowing actively, more of those people downstream will be willing to donate their time and money to what you'd probably classify as "good things". When it slows down, or the Government is taking a big chunk at every step as taxes, then they'll be less inclined to do so.
42. Why would they need more?
I keep tellin em but they never listen. Aliens gave up on radio eons ago. Poor range, prone to interference, and a host of other disadvantages. If you want to eavesdrop on what's being said about us in the universe, you gots to gets your hands on one of them newfangled SHF gravity wave radios.
If I didn't have absolutely NOTHING to do, I wouldn't be here.
Although I agree with the rest of your comment, I don't think burning money is wasting it. If you destroy currency you are removing it from circulation, which will cause prices to go down due to deflation.
If you truly want to waste money, you should buy something of value to others and destroy that thing. The grandfather post would be right, if one assumes that scientific research has no value. However, that is very seldom the case. Research is almost always valuable, even if it turns up nothing. Negative results are also knowledge. If we find no sign of extraterrestrial intelligence in our search we will know more than we did before about the abundance or scarcity of intelligence in our galaxy.
The first is that there is a concept of 'best-use'. That is, there are some projects (such as SETI) that some people feel are less worthwhile than other projects. Some people believe that the man-hours and capital used on SETI is wasted because nothing of value is produced by SETI (in their opinion) -- so yes, the money flows through the economy, but on a more worthwhile project, that money would flow through the economy while producing something of value. The money is in effect hoarded, which means that the opportunity to use it for growth is wasted.
The second point has to do with your remark about taxes.
Money paid as taxes also flows through the economy, for the same reason that money put into erstwhile "wasteful" projects flows through the economy. It's a bit of a double-standard to say that money that goes to taxes inhibits downstream spending, since that money is, in a very real way, redistributed to others, whether by government contract, to government employees, or otherwise. The exceptions would be foreign spending, which generally has benefit to the US as well, if less tangible.
If anything, with today's government, money taken out as taxes actually produces more money in circulation, since the US government runs a deficit budget with a cap on borrowing based loosely on government receipts. Every $1.00 given to the federal government returns $1.00 * [1 + (annual debt)/(annual receipts) -- of course, that's financed at an as-yet-undetermined final cost, since who knows what interest rate we'll have to pay on it when we refinance through new debt offerings...
"Trolls they were, but filled with the evil will of their master: a fell race..." -- J.R.R. Tolkien on Olog-hai
I dont mean to flame but...
I'm in the EE field, specifically wireless/radio communications.
The calculation for path loss is:
Loss dB = 32.44 + 20 log (dist in km) + 20 log (freq in MHz)
Lets take absolute optimal conditions..proxima centauri is roughly 4 light years away. This is roughly 3.78x10^13 km away. One of the most common frequencies monitored is the "hydrogen line" (1420.40575 MHz) since this is the resonant frequency of hydrogen and is more likely to be used by aliens since we'd most likely be looking there.
So, lets fill in the equation:
32.44+ 20log(3.78x10^13)+20log(1420.41)= 367.038 db of loss...
So lets say they are transmitting with a million watts(90dBm), and there is a 60db dish on both ends(huuge dish)...This gives us a receive level of -157.038dBm. This is a good bit below what any normal radio will receive at. The noise floor is certainly higher than this. Now keep in mind this is the very closest star, which I don't think even has any livable planets.
Our galaxy is 70-100 thousand light years across and we are right near the edge. So if you take a star not even close to that distance, say 500 light years (still somewhat close on a galactic scale) then the calculations work out to a receive signal of -198dBm. The equipment doesn't exist to pick the signal out of the noise at levels like that.
God forbid trying to pick the signal out of another galaxy, the nearest being Andromeda. some 2.5 million light years away. Giving Rx signal levels of ~ -273dBm. Safe to say the noise floor is MUCH MUCH higher than this.
I think SETI is a hopeless pipe dream. That being said, I DO think there is intelligent life out there, probably in our galaxy. There are just too many stars with too many planets to think otherwise.
It's easier to fight for one's principles than to live up to them.
Spoons, shovels? I always thought it would be easier to search for a needle in a haystack with a magnet, but what do I know?
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
"I think SETI is a hopeless pipe dream."
.211m. The brightness temperature of the galaxy as viewed from Earth's surface is around 5-10 Kelvin at that wavelength.
.211) = 4.63*10^18 meters
I assume you think your erroneous application of signal theory leads to that conclusion. More studious and clever people than you have already illustrated the viability of signal reception at these distances, and your analysis is quite simply wrong. Your "EE" expertise has led you astray: when you ask someone who only knows about whales a question about ducks, he talks about whales anyway. Radio astronomy has had these things down for more than 50 years, and you're a day late and a dollar short.
We're interested in obtaining a signal against a background. The antenna temperature, Ta, determines this:
Ta = [(pi^2)/16k] * (W/r^2) * (D1^2 * D2^2) / lambda^2
where
k is Boltzmann's constant
W is the power per unit of bandwidth of the source
D1 and D2 are the diameters of the receiving antenna and (hypothetical) transmitter antenna
lambda is the wavelength
The signal, per the common example, is 1420.4GHz => 21.1cm =
What about the noise temperature of the receiver? A receiver must have sufficiently low Tn, otherwise it's louder than the signal it tries to measure:
Tn-rms = Tn / sqrt(t * Bw)
where
Tn-rms is the root-mean-square value in question
Tn is the noise temperature of the receiver in question
t is the integration time (how long we keep the lid off the photon bucket)
Bw is the receiver's bandwidth
The noise temperature of modern low-noise amplifiers is much lower. A rule of thumb for present-day: 1 Kelvin per GHz, plus 1 Kelvin, so 2~3 Kelvin for this LNA, and there are lower noise devices available for a price, but only to a point. The cosmic background noise is larger than the receiver noise!
Let's combine them and rearrange, and see just what kinds of power and distance we need:
r = (pi/4) * sqrt(W / k*Tn) * (D1 * D2 / lambda) * (t * Bw)^.25
Suppose we have a 50kW transmitter, use the 300m Arecibo dish to transmit and receive, use a bandpass of 1Hz (this is reasonable), and an integration time of about 20 minutes (1,000s). Go ahead; do the math--
r = (pi/4) * sqrt(50000 / [(1.38e-16)*3] * (300 * 300 /
Which is 489 light years.
Yes, given currently manufactured technology, the Arecibo dish could communicate with an identical dish at exactly the distance in the article, given a modest 50kW transmitter. I picked numbers to contrive the distance in question, but all of them are available with current technology, and most of them are already installed and operational at Arecibo Observatory. What if we chose a MW transmitter (available), or halved the wavelength to 10cm, or used a bigger (perhaps virtual) dish, or a lower noise antenna? All of these things would MASSIVELY improve the resolvable range of the transmission. 5000 light years is well within our current technology-limited broadcast/reception range. The hard part, as discussed by others here, is justifying implementing this much hardware and employment (versus buying ONE SINGLE JET FIGHTER).
If you think the problem with SETI lies in its technical shortcomings, you're sorely mistaken. The SETI program is a long shot for other, more difficult scientific and borderline philosophical reasons, but close examination of the physical problem at hand (which you clearly have not done) illustrates that it's not as long as your cynicism would have you judge in lieu of actual thought. You're welcome to argue your opinions, but don't mis-apply one inapt little corner of signal theory as proof that your perception of the world is, in fact, reality.
+5 Insightful? The mods have been bamboozled by unfamiliar equations. As for my analysis? Go ahead-- verify it with your favorite relevant textbook, for a change; please.