They dropped photons off the roof of a building and measured their blue shift at the bottom, confirming general relativity. One description of the experiement is here.
Pound is an interesting guy. He experimented with using microwaves to heat people instead of wasting energy heating entire buildings. He tested it out by rigging his microwave oven to operate with the door open. He told me that he had to bypass three interlocks, but that he got it working: there was a nice warm glow, like standing in front of a campfire.
Needless to say, don't try this at home unless you're a damn competent physicist.
The capacitive sensor circuit described in here is easy and cheap to make, and is sensitive enough to be used as a proximity sensor.
We've been able to sense a finger from several inches away with one of these that has been adjusted correctly. If a person can move a finger up to an inch, even without being able to apply pressure with it, a sensor like this will have no problem detecting that.
(Yes, this is a tech report about the Mitsubishi Electric "Smart Drinking Glass" that was reported earlier on slashdot.)
Is it possible to use many smaller dishes to achieve the same effect as one big dish in picking up C-band transmissions?
I looked into doing exactly this about seven years ago and the prospects were dismal.
Building such a phased array is certainly possible, but the grief you'd have to go through to get it to work would be tremendous.
1. The total area of the smaller dishes would have to be at least the area of the big dish you're replacing, i.e. you'd need at least 45 18" dishes to equal the area of a single 10' dish.
2. You will need to steer your array of small dishes together to point at the desired satellite. The pointing accuracy of each would have to be on the order of a couple of degrees.
3. You'd need a phasing network to add the signals from each of those dishes together with the correct phasing. Note that the phasing will change as you steer the dish system. The network would have to have sufficient bandwidth to cover the spectrum of interest, which is not going to be easy. The design of such a monster would probably get you a PhD and a very good job at a major corporation.
4. The low noise amplifiers used (one per dish) would have to be very low noise indeed, since their contribution to the total noise of the phased signal goes as the square root of their number. If you've got 45 small dishes, each LNA would have to be only about 1/7 as noisy as would the amplifier for the single dish system.
I could go on, but realize what a horrible mess this would be. Arrays of dish antennas are used by radioastronomers for various reasons. The Very Large Array in New Mexico uses 27 25-meter telescopes to obtain very high angular resolution images. All of those antennas combine to become the equivalent of one 130-meter antenna.
A project of interest to those reading this is the Allen Telescope Array being built by the SETI Institute. It will use 350 6-meter TVRO dishes phased together to create one large radiotelescope. The engineering issues involved are extremely complicated.
Bottom line: it would be easier and cheaper to bribe your community's zoning board to give you a variance for a big dish, than it would be to build a phased array of smaller dishes. Even if you got prosecuted, the jail time would probably end up being less than the design time.
Autowatch by these guys has been on the market for a few years now. It plugs into the standard diagnostic port on your car and logs events past user settable thresholds.
Apparently the original prototype was called "Narc on Lisa", Lisa being the inventor's then 16-year-old daughter. Poor Lisa.
The instrument used was a spectrum analyzer. An oscilloscope looks at signals in the time domain and a spectrum analyzer looks at them in the frequency domain. Spectrum analyzers are much more complicated and much pricier than oscilloscopes.
If you go here you can read about Lego-style bricks with built-in microcontrollers. After you build a structure, the bricks talk to each other, figure out who their neighbors are and download the information to a host computer. Your structure can then be rendered in 3-D. A Prolog program can process the model and look for architectural feature (corners, roof, doors, windows) which can then be rendered in imaginative styles.
The coolest part is that you can download your model into Quake and frag your friends inside the structure you built.
There was a paper on this at Siggraph 2000 and a tech report is here.
The imager in the gameboy camera is a Mitsubishi Electric M64282FP CMOS image sensor (not a CCD). It is slightly more sensitive to near infrared than it is to visible light. The '282 has a resolution of 128x128 pixels, will do 30 frames per second and outputs the pixels in analog format.
in the Wall Street Journal? Maybe we could all chip in for something like this:
[a picture of federal marshalls carting computers away from from a business, horrified managers in the background]
Complicated licensing and expensive audits could land you in legal hot water and cost you your business. Linux will save you money and give you peace of mind. [Add examples of companies such as Amazon that have moved to Linux.]
SETI projects tend to look for deliberate beacons: signals designed to be easy to receive. UWB and other spread spectrum signals have far too many parameters, which make the search space larger and less tractable.
Deploying UWB signals here on earth will be really bad for SETI. It will cause interference in the protected bands where the various projects are looking for very weak signals.
I still miss the -analog flag to xcalc. Under the X window system, if you run "xclock -digital" you get a digital clock, while "xclock -analog" gives you an analog clock. The command "xcalc" gives you a calaculator. Long ago some sneaky individual programmed it so "xcalc -analog" would give you a working slide rule. This feature is not in current version, but I wish it would make a comeback.
GPS signals are weak and pretty line-of-sight, so hiding the antenna is nearly impossible. What happens if you cover the antenna with some alumunum foil? It can't rely on GPS all the time since the signal is often blocked by buildings, tunnels, etc. Maybe AirIQ will shut down the car if it doesn't get periodic GPS information.
Of course, you can always use a GPS simulator to fool the car's receiver, but that would only be cost effective if you speed a lot.
Except for the fact that this particular band already suffers from interference produced by electric motors at about the power level.
What "particular band" are you talking about? This stuff is "ultrawide", remember. Pulses have significant frequency components up to the reciprocal of the pulse width. Picosecond type pulse widths will cause significant interference well up through the microwave bands, well beyond where you see most motor interference. I don't know what propaganda you've been reading, but I thought this was pretty telling: But it means there could be no reasonable expectation of unusual interference to pre-existing services.
Listen to that lawyer-speak. No "reasonable" expectation of "unusual" interference to pre-exisiting services.
So, if a couple of people are pissing in a river it's OK to run a sewer line there because the people downstream have no "reasonable" expectation of "unusual" contamination to their current use of the water?
With all of the good medical care technology that we have now, those born with problem genes are not being weeded out by natural selection. We are no longer evolving. Since the problem genes are being passed on to future generatiosn instead of disappearing, the amount of medical care each person needs will rise until either:
1. The total cost becomes prohibitive, medical care is less available and people start dying in greater numbers before they reach breeding age.
or
2. The problem genes are replaced.
Our choice will be large scale genetic engineering vs. a large scale die off.
There's no free lunch with spread spectrum signals. They do not magically provide more information carrying capacity, lower probability of intercept or defense against intentional jamming.
All modulation techniques use a set of basis vectors to transmit information. The traditional non-spread sprectrum methods use the frequency, amplitude or phase of a sinusoid as a basis. Spread spectrum methods use "weirder" bases, such as pseudo-random codes. The only real differences between the SS methods and the traditional ones are that the SS bases are highly unlikely to look like "common" interfering signals (carriers, impulse noise, etc.) and that they tend to have a wider bandwidth as well.
"Ultra wideband" is just another spread spectrum technique that uses the time position of pulses as its basis set.
There is only so much bandwidth out there and the amount of data you can send through it is bounded by the Shannon limit which is a function of bandwidth and noise floor. Any signal you transmit, no matter what modulation technique it uses, will interfere with other signals, at the very least by raising the noise floor, and thus lowering the Shannon limit for that section of the spectrum. It may be possible to demonstrate that a few ultra-wideband signals don't interfere with exisitng transmissions, but that certainly won't be the case for a large number of ultra-wideband signals.
The one advantage of ultra-widband is that it has very good time resolution because of the short pulses, and since the speed of light is constant, this equates to very good spatial resolution. Lawrence Livermore Labs was demonstrating something called "micropower impulse radar" (MIR) based on these techniques a number of years ago. This was the gadget that lets you "see" through walls. The range was very short, but it did work. This looks like the best application of ultra-wideband.
I hope the FCC isn't fooled by snake-oil claims of non-interference and unlimited bandwidth. They should not approve ultra-wideband for normal communications use.
We have just barely become a technological civilization; we are arguably the youngest one in the galaxy. Sending out signals and waiting for a reply would take millenia. We need to start out by listening first, which is what we're doing.
Besides, do we really want to get a bad interstellar reputation by shooting our mouths off before we've even checked to see who's already talking?
Darren
Signal to noise is the first thing that SETI people think about. Actually there are some pretty good ways of getting sufficient SNR, if you are looking for a beacon and not just trying to peek at local comm traffic. SETI comes in two flavors:
1. Beacons
Some search projects are set up to look for deliberately transmitted beacons, i.e. signals designed to be received by faraway alien SETI systems. The signals can be constructed to be different enough from the noise that even a modestly powered transmitter can be seen across interstellar distances. One such designed signal is a pure sinusoid. There are good reasons to believe that nature cannot make a very pure sinusoidal signal, while it is easy to do with a radio transmitter. One nice thing about looking for beacons is that you can assume that the aliens have done the right things to make the signal easy to receive, and they may very well be sending it with "primitive" technology like radio instead of their own advanced "Q-rays".
2. Leakage radiation
Some SETI projects are more geared to eavesdropping on the aliens' local communication. This is a much harder prospect since the local stuff is not beamed in our direction or designed for us to understand. Personally, I think that intelligent alien civilizations will send their own traffic efficiently and not waste power. The upshot of this is that efficiently encoded information looks just like noise and we would not be able to distinguish these signals from the natural background. I'm not a big fan of leakage radiatiion searches, but others disagree with me.
The more technically minded out there might be able to get a little more insight from the reading the first chapter or so of my dissertation: http://seti.harvard.edu/grad/d-thes.html.
Slashdot Mirror
They dropped photons off the roof of a building and measured their blue shift at the bottom, confirming general relativity. One description of the experiement is here.
Pound is an interesting guy. He experimented with using microwaves to heat people instead of wasting energy heating entire buildings. He tested it out by rigging his microwave oven to operate with the door open. He told me that he had to bypass three interlocks, but that he got it working: there was a nice warm glow, like standing in front of a campfire.
Needless to say, don't try this at home unless you're a damn competent physicist.
We've been able to sense a finger from several inches away with one of these that has been adjusted correctly. If a person can move a finger up to an inch, even without being able to apply pressure with it, a sensor like this will have no problem detecting that.
(Yes, this is a tech report about the Mitsubishi Electric "Smart Drinking Glass" that was reported earlier on slashdot.)
I looked into doing exactly this about seven years ago and the prospects were dismal.
Building such a phased array is certainly possible, but the grief you'd have to go through to get it to work would be tremendous.
1. The total area of the smaller dishes would have to be at least the area of the big dish you're replacing, i.e. you'd need at least 45 18" dishes to equal the area of a single 10' dish.
2. You will need to steer your array of small dishes together to point at the desired satellite. The pointing accuracy of each would have to be on the order of a couple of degrees.
3. You'd need a phasing network to add the signals from each of those dishes together with the correct phasing. Note that the phasing will change as you steer the dish system. The network would have to have sufficient bandwidth to cover the spectrum of interest, which is not going to be easy. The design of such a monster would probably get you a PhD and a very good job at a major corporation.
4. The low noise amplifiers used (one per dish) would have to be very low noise indeed, since their contribution to the total noise of the phased signal goes as the square root of their number. If you've got 45 small dishes, each LNA would have to be only about 1/7 as noisy as would the amplifier for the single dish system.
I could go on, but realize what a horrible mess this would be. Arrays of dish antennas are used by radioastronomers for various reasons. The Very Large Array in New Mexico uses 27 25-meter telescopes to obtain very high angular resolution images. All of those antennas combine to become the equivalent of one 130-meter antenna.
A project of interest to those reading this is the Allen Telescope Array being built by the SETI Institute. It will use 350 6-meter TVRO dishes phased together to create one large radiotelescope. The engineering issues involved are extremely complicated.
Bottom line: it would be easier and cheaper to bribe your community's zoning board to give you a variance for a big dish, than it would be to build a phased array of smaller dishes. Even if you got prosecuted, the jail time would probably end up being less than the design time.
Autowatch by these guys has been on the market for a few years now. It plugs into the standard diagnostic port on your car and logs events past user settable thresholds. Apparently the original prototype was called "Narc on Lisa", Lisa being the inventor's then 16-year-old daughter. Poor Lisa.
The instrument used was a spectrum analyzer. An oscilloscope looks at signals in the time domain and a spectrum analyzer looks at them in the frequency domain. Spectrum analyzers are much more complicated and much pricier than oscilloscopes.
The coolest part is that you can download your model into Quake and frag your friends inside the structure you built.
There was a paper on this at Siggraph 2000 and a tech report is here.
The imager in the gameboy camera is a Mitsubishi Electric M64282FP CMOS image sensor (not a CCD). It is slightly more sensitive to near infrared than it is to visible light. The '282 has a resolution of 128x128 pixels, will do 30 frames per second and outputs the pixels in analog format.
You can find more information on hacking this chip and the gameboy camera at http://home.earthlink.net/~apendragn/gbcam/
in the Wall Street Journal? Maybe we could all chip in for something like this:
[a picture of federal marshalls carting computers away from from a business, horrified managers in the background]
Complicated licensing and expensive audits could land you in legal hot water and cost you your business. Linux will save you money and give you peace of mind. [Add examples of companies such as Amazon that have moved to Linux.]
SETI projects tend to look for deliberate beacons: signals designed to be easy to receive. UWB and other spread spectrum signals have far too many parameters, which make the search space larger and less tractable.
Deploying UWB signals here on earth will be really bad for SETI. It will cause interference in the protected bands where the various projects are looking for very weak signals.
I still miss the -analog flag to xcalc. Under the X window system, if you run "xclock -digital" you get a digital clock, while "xclock -analog" gives you an analog clock. The command "xcalc" gives you a calaculator. Long ago some sneaky individual programmed it so "xcalc -analog" would give you a working slide rule. This feature is not in current version, but I wish it would make a comeback.
GPS signals are weak and pretty line-of-sight, so hiding the antenna is nearly impossible. What happens if you cover the antenna with some alumunum foil? It can't rely on GPS all the time since the signal is often blocked by buildings, tunnels, etc. Maybe AirIQ will shut down the car if it doesn't get periodic GPS information.
Of course, you can always use a GPS simulator to fool the car's receiver, but that would only be cost effective if you speed a lot.
Except for the fact that this particular band already suffers from interference produced by electric motors at about the power level.
What "particular band" are you talking about? This stuff is "ultrawide", remember. Pulses have significant frequency components up to the reciprocal of the pulse width. Picosecond type pulse widths will cause significant interference well up through the microwave bands, well beyond where you see most motor interference. I don't know what propaganda you've been reading, but I thought this was pretty telling: But it means there could be no reasonable expectation of unusual interference to pre-existing services.
Listen to that lawyer-speak. No "reasonable" expectation of "unusual" interference to pre-exisiting services. So, if a couple of people are pissing in a river it's OK to run a sewer line there because the people downstream have no "reasonable" expectation of "unusual" contamination to their current use of the water?
Keep your trash out of other people's spectrum.
With all of the good medical care technology that we have now, those born with problem genes are not being weeded out by natural selection. We are no longer evolving. Since the problem genes are being passed on to future generatiosn instead of disappearing, the amount of medical care each person needs will rise until either:
1. The total cost becomes prohibitive, medical care is less available and people start dying in greater numbers before they reach breeding age.
or
2. The problem genes are replaced.
Our choice will be large scale genetic engineering vs. a large scale die off.
There's no free lunch with spread spectrum signals. They do not magically provide more information carrying capacity, lower probability of intercept or defense against intentional jamming.
All modulation techniques use a set of basis vectors to transmit information. The traditional non-spread sprectrum methods use the frequency, amplitude or phase of a sinusoid as a basis. Spread spectrum methods use "weirder" bases, such as pseudo-random codes. The only real differences between the SS methods and the traditional ones are that the SS bases are highly unlikely to look like "common" interfering signals (carriers, impulse noise, etc.) and that they tend to have a wider bandwidth as well.
"Ultra wideband" is just another spread spectrum technique that uses the time position of pulses as its basis set.
There is only so much bandwidth out there and the amount of data you can send through it is bounded by the Shannon limit which is a function of bandwidth and noise floor. Any signal you transmit, no matter what modulation technique it uses, will interfere with other signals, at the very least by raising the noise floor, and thus lowering the Shannon limit for that section of the spectrum. It may be possible to demonstrate that a few ultra-wideband signals don't interfere with exisitng transmissions, but that certainly won't be the case for a large number of ultra-wideband signals.
The one advantage of ultra-widband is that it has very good time resolution because of the short pulses, and since the speed of light is constant, this equates to very good spatial resolution. Lawrence Livermore Labs was demonstrating something called "micropower impulse radar" (MIR) based on these techniques a number of years ago. This was the gadget that lets you "see" through walls. The range was very short, but it did work. This looks like the best application of ultra-wideband.
I hope the FCC isn't fooled by snake-oil claims of non-interference and unlimited bandwidth. They should not approve ultra-wideband for normal communications use.
We have just barely become a technological civilization; we are arguably the youngest one in the galaxy. Sending out signals and waiting for a reply would take millenia. We need to start out by listening first, which is what we're doing.
Besides, do we really want to get a bad interstellar reputation by shooting our mouths off before we've even checked to see who's already talking? Darren
I knew I'd screw up the link. Here's the right one:
http://seti.harvard.edu/grad/d_thes.html
1. Beacons
Some search projects are set up to look for deliberately transmitted beacons, i.e. signals designed to be received by faraway alien SETI systems. The signals can be constructed to be different enough from the noise that even a modestly powered transmitter can be seen across interstellar distances. One such designed signal is a pure sinusoid. There are good reasons to believe that nature cannot make a very pure sinusoidal signal, while it is easy to do with a radio transmitter. One nice thing about looking for beacons is that you can assume that the aliens have done the right things to make the signal easy to receive, and they may very well be sending it with "primitive" technology like radio instead of their own advanced "Q-rays".
2. Leakage radiation
Some SETI projects are more geared to eavesdropping on the aliens' local communication. This is a much harder prospect since the local stuff is not beamed in our direction or designed for us to understand. Personally, I think that intelligent alien civilizations will send their own traffic efficiently and not waste power. The upshot of this is that efficiently encoded information looks just like noise and we would not be able to distinguish these signals from the natural background. I'm not a big fan of leakage radiatiion searches, but others disagree with me.
The more technically minded out there might be able to get a little more insight from the reading the first chapter or so of my dissertation: http://seti.harvard.edu/grad/d-thes.html.
Darren