Slashback: Iridium, Synthesis, Drives

Slashback tonight with word on the (groan) fate of Iridium, more Speak n' Spell modding, examples of Serial ATA oozing to market, the RIAA versus mandatory DRM, and more. Read on for the updates.

In this household, we obey the laws of physics! Tuesday before last, we mentioned that two scientists had announced what they claim is the first accurate measure of the speed of gravity.

Now, Emperor_Alikar writes "In an article on Space.com, many physicists have criticized the current work on the speed of gravity, calling it 'nonsense' and 'simply incorrect.' Many of them still doubt the claims made by Fomalont and Kopeikin even before the results were even announced. Many of the physicists still hold on to the idea that gravity works instantaneously no matter what the distance, an idea that originated by Newton, but that was argued against by Einstein."

Back from the back from the back from the dead. Checkers writes "Spacedaily.com posted the following two stories about Iridium today. The first story is about the DoD committing the first of three renewal options that will use Iridium through 2005. The second story related story is about an agreement inked between Iridium and Harris Corp. that allows Iridium the right to use Harris' OS/COMET satellite command and control system for the life of the Iridium satellite network."

E.T. was also into this scene. In re: matt simpson writes "Another fantastic Speak & Spell modder is Dave Wright of the band "not breathing". You can check his work out, among other modifications to toys, at www.carrionsound.com Dave has made speak & spell/math/read for Nine Inch Nails, Meat Beat Manifesto, and many other bands. Figured you might be interested in other neat synth hackers :)"

Further evidence, never a good time to buy. SpinnerBait writes "It's seems like Serial ATA Controllers have been on the market forever but where have all the Serial ATA Hard Drives been? The wait seems to finally be over, as HotHardware shows with this review and showcase on a pair of new Seagate Barracuda V Serial ATA drives. This article covers benchmarks with the product in single drive configurations, as well as RAID 0. In addition, they show performance on two different SATA controllers, from Promise and Silicon Image. And oh, those nice thin neat little SATA cables! Gotta love 'em."

We've had a few articles about Serial ATA; I hope it lives up to its reputation.

Just to add to the confusion ... probejockey writes "A current article in the Globe and Mail claims SCO will start collecting licensing fees from some Linux users, not all Linux vendors as previously reported here."

Birds of a feather, separate rooms. Finally, Declan McCullagh sent in a few interesting links yesterday regarding the RIAA and its announced opposition to mandated DRM technologies:

"First, here are the photos from today's press conference.

Second, the supposed news of today's announcement was that the RIAA would no longer pursue mandatory-DRM technologies like the Hollings bill. But it was the MPAA that was behind Hollings from the beginning (September 2001). And when Hollings finally introduced his bill in March 2002, it was the MPAA that endorsed it, while the RIAA pointedly did not."

Thanks to Declan for the links.

Wasn't smart enough to get in, either ... Finally, thanks to the several readers who alerted me by email and in comments that the school variously rendered Cal Tech, CalTech and other things even worse is in fact properly spelled "Caltech."

Comments

Iridium and GPS

[The Bungi]

1. Put satellites in orbit
2. ???
3. Profit!!

It seems they've filled in the '???' part - sell 'em to the DoD.

I couldn't help but think about the GPS system though. As the military shifts from laser guidance systems for bombs and cruise missiles to GPS-based ones, the GPS network becomes more and more critical and overloaded. Is the Iridium network being used only for simple voice/data communications or is there a dual-use capability (targeting, whatever) in the network as well?

Re:Iridium and GPS

[cristofer8]

About the GPS missiles, I recently took a tour of the Trident Missile facility in California (Moffet Field) with my school. The trident missiles, which are basically our doomsday machine, not only don't rely on GPS, but don't even really have any electronics. The gov is so worried about radiation and interference and such, that they use pressurized tubes to send signals, and orient themselves by actually looking for certain stars through a little hole in the side. Of course, they refused to explain how the "magic inertia" device worked.

Re:Iridium and GPS

[Wyatt Earp]

The problem with jamming GPS munitions is the fact that the aircraft dropping a GPS bomb has GPS up above the jamming.

The aircraft is connected to the bomb in flight with a databus. The plane gives the weapon updated location via the bus up to the point of release.

The bomb knows where it was, the bomb also has a ballistics computer updating the rate of decent and distance to target.

So when the weapon gets into the jamming region, it still knows where it was when it was dropped, and knows how fast/far is dropped and where the target was. The weapon still falls relativly close to the target, the CEP just increases.

I've read the CEP doubles when GPS is off/jammed. Which is still much better than a dumb iron bomb.

http://www.google.com/search?q=jdam+gps+jamming& ie =UTF-8&oe=UTF-8

http://www.darpa.mil/spo/programs/gpsguidancepac ka ge.htm

http://www.globalsecurity.org/military/systems/m un itions/jdam.htm

"Once released, the bomb's INS/GPS will take over and guide the bomb to its target regardless of weather. Guidance is accomplished via the tight coupling of an accurate Global Positioning System (GPS) with a 3-axis Inertial Navigation System (INS). The Guidance Control Unit (GCU) provides accurate guidance in both GPS-aided INS modes of operation (13 meter (m) Circular Error Probable (CEP)) and INS-only modes of operation (30 m CEP). INS only is defined as GPS quality hand-off from the aircraft with GPS unavailable to the weapon (e.g. GPS jammed). In the event JDAM is unable to receive GPS signals after launch for any reason, jamming or otherwise, the INS will provide rate and acceleration measurements which the weapon software will develop into a navigation solution."

http://www.boeing.com/news/releases/1998/news_re le ase_980423n.htm

"A new anti-jam Global Positioning System (GPS) developed by Boeing has successfully defeated jammed environments in two successive drop tests, allowing the test vehicles to strike well within their designated target areas."

"In the most recent test, the AGTFT test vehicle was dropped into a high-power GPS-jammer environment from 44,000 feet and achieved direct military code GPS acquisition within 8 seconds. While descending through wind shears of up to 110 mph, the test vehicle continued to track GPS satellites in the jammed environment and ultimately struck within 6 meters of the target.

In an earlier test, the AGTFT test vehicle was dropped from 44,000 feet into a low-power GPS-jammer environment and achieved direct military code GPS acquisition within 12 seconds. The test vehicle descended in the jammed environment through wind shears of up to 105 mph, continuously tracking GPS satellites and striking within 3 meters of the target."

Those tests were conducted in 1998.

Re:Iridium and GPS

[marcsiry]

Many GPS guided weapons have inertial guidance as a backup. If they lose guidance from the satellites, they remember where they where, and roughly what direction and how far they had to go to hit their target.

This article claims that GPS jamming reduces the accuracy of a 200 lb JDAM to +/- 100 feet; considering the destructive power of those weapons, the difference is academic against all but hardened targets.

The frequencies are fixed; they'll only change when the next generation of GPS satellites are launched, a prospect that hasn't even been planned yet. Anyhow, any sort of technological countermeasures deployed by Iraq against its much more powerful enemies are going to be a speed bump at best- they're hopelessly overmatched. Their best bet will be evasion, deceit, and propoganda- the only things that (barely) worked for them in Gulf War I.

Okay, answer me this:

[TClevenger]

If the Sun suddenly disappears (hypothetically), would the Earth continue to hold its orbit for 8 or so minutes, or would it go whizzing off into space instantly? Does this new "Speed of Gravity" research change that answer from what it was, say, a year ago?

Re:Okay, answer me this:

[Guppy06]

"would the Earth continue to hold its orbit for 8 or so minutes, or would it go whizzing off into space instantly?"

Yes and yes.

For an observer on Earth, the planet will start leaving the star system as soon as the sun vanishes.

For an observer equidistant from both the sun and the earth, the earth will start flying out of the star system ~8.5 minutes after the sun vanishes.

For an observer on/near the sun, the earth will start to leave its path ~17 minutes after the sun vanishes.

And they're all right. Ain't relativity grand?

Iridium Flares

[FrostedWheat]

If you haven't already seen one, Iridium Flares are really quite impressive.

Measuring the speed of gravity

[Anonymous Coward]

Okay, we can't make the sun disappear and watch what happens to the earth's orbit (and really, why would you want to?)

BUT - what if scientists create an amount of matter and anti-matter, and using very sensitive equipment measure the gravity effect it has on say a hanging weight (ala the two really heavy bags suspended next to each other). Then, all of a sudden combine the matter and anti-matter and measure how quickly the gravity "disappears". (BTW, the antimatter can be "held" in a magnetic field, as opposed to wearing really thick gloves)

Okay, there's a lot of work to be done before this could even be considered, let alone be done in the garage of /.'ers, but are there any arguments against this being possible?

I'm not sure if the energy released by the matter/anti-matter combination would interfere in any way (it probably would, for all I know). Also, it's probably not practical to generate a significant amount of anti-matter, and I believe it may have a very short half-life. Also, do we have equipment sensitive enough?

There we go - I've suggested a better experiment, shot it to bits, admitted my ignorance and also taken the piss out of my suggestion a bit! This is the ultimate /. post - no replies necessary!!! (But the replies will still come. So sayeth the spider)

Re:Infinite speed gravity?

[Doctor Fishboy]

What I was saying in my first comment was that the majority of physicists believe gravity has a finite propagation speed, whilst the /. tagline suggested that few physicists do. The experiment itself is being questioned by physicists thinking they're measuring the speed of light, not gravity. Apart from the Newton quote, none of the modern physicists thought that gravity propagated 'infinitely' fast - it's another usual /. not-quite-right headline.

> After all, GR certainly doesn't agree with quantum mechanics

Not sure if I agree with you there - I don't recall that QT is inconsistent with GR. The problem is that it is very, very hard to test a QT of gravity because the hypothesized quanta of gravity are 10^41 times smaller than those of electromagnetism and nuclear forces.

Anyway, they came up with a speed of gravity (if that is what they measured) of plus or minus 20 percent of the speed of light, so if they were measuring gravity, it is consistent with GR.

Dr Fish

The speed of gravity, a consequence

[Traa]

Hypothesis: The speed of gravity == infinite

If the above hypothesis where true then one could (theoretically) build the following device: At place A we have a measurement tool that measures the gravitational pull of an object at place B. At place B we move the object back and forth based on a coded pattern (sending information). At spot A the difference in gravitational pull allows us to decode the pattern (reading information). The time it takes to send this information is based on the time it takes for the gravity 'waves' to reach from point B to point A. Our hypothesis says that this time is 0 so it means that we can now build a device that can send information FASTER then the speed of light. Einstein allready proofed that there is nothing faster then the speed of light.

Conclusion: The hypothesis is FALSE.

(disclaimer: bah, I'm no physicist, so don't flame me for not writing the above proof in a perfect physicist lingo...I tried :-)

Re:The speed of gravity, a consequence

[kcbrown]

Well, you're thinking along the right lines...

Here's the experiment you really want to perform:

At place A, you place a massive object in front of a light, and move the object back and forth.

At place B, you set up a light detector and a gravity detector (the means by which one builds the gravity detector is left as an exercise to the reader).

You start off with points A and B really close to each other so you can calibrate your equipment (you need to be able to account for the difference between reading the gravity detector and the light detector). Once you do that, you move the points further apart.

Now, if the speed of gravity is instantaneous, then the phase difference between the signal received by the gravity detector and the signal received by the light detector should change as you move the points away from each other.

If the speed of gravity is the same as the speed of light, then the phase difference between the two signals should always be zero (after accounting for the equipment), no matter what the distance between points A and B.

The relationship between the phase difference and the distance between points A and B will give you a clue as to the speed of gravity versus the speed of light, if that of gravity is finite but different from that of light.

Re:The speed of gravity, a consequence

[Anonymous Coward]

"Einstein allready proofed that there is nothing faster then the speed of light."

In the paper "On the Electrodynamics of Moving Bodies" (1905), Einstein states that "We will raise this conjecture (the purport of which will hereafter be call the "Principle of Relativity") to the status of a postulate, and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body." [The first postulate is that "the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good."]

From this statement it is evident that Einstein did not prove that there is nothing faster than the speed of light, but rather he postulated that in the formulation of his theory. As a result, it is not surprising that any theory that allows for instantaneous information transfer is inconsistant with the Principle of Relativity, as it violates one of the postulates of Relativity theory.

Re:We wouldn't know it.

[Ramze]

Actually, if gravity is instantaneous, then you would percieve the sun as moving away from the earth instantaneously after it vanished due to the earth moving quickly out of orbit. The earth would fling off in a straight line from the sun as soon as it vanished at incredible speed, and the light from where the sun WAS would take longer to reach the earth as the earth moves away. From earth's perspective, it would be as if the sun were moving away from the earth at incredible speed instead (relativity). However, since gravity has supposedly been measured as being affected at the speed of light, then you would notice no change at all until 8 minutes after the sun was gone.

The argument itself is moot b/c it's impossible for a mass such as the sun to simply vanish & since gravity is influenced by mass and mass can only move at sub-light speeds, it would be impossible for any change in the sun to be noticed gravitationally by any object at any speed faster than light. :-)

Ahhh... Physics rocks... lol. No wait, that's geology. ;-)

Re:Hey Y'all

[Kaz Riprock]

Don't forget to click the "save" button at the bottom of the page once you've decided what bonus you want to give.

In the meantime, I was wondering what this will do to moderation. If I'm surfing with a karma bonus of 3 and there's a post (+1) from an excellent karma (+3) that's been modded insightful twice (+2)...will the post show up with a score of 6? If it still stops at 5 like it used to, then if I surf at bonus of 4, who would I mod up? They're all already at five, or do I mod up the good posts (as a good mod should) but then, that's a wasted mod if everyone mods the first few good posts and we end up with posts getting 16 mods, since you have to mod it up because its good and you don't know what threshold someone is surfing at to let everyone know it's good.

In the other meantime, I think the mod system needs a ton of work. The biggest problem is lazy mods that don't skim through at a lower browsing level. If you want to get modded up to the point that your posts hold more weight (more than 1 or 2 points above a SOVIET UNION or Stephen King is dead post) then you have to get to the discussion early and catch a modder's eye, instead of waiting until there are already 300 posts and you fall into that oblivion of post titles at the bottom of the discussion that nobody responds to or reads.

'kay. That is all.

Re:Okay, I'll try:

[glenebob]

"...would the Earth continue to hold its orbit for 8 or so minutes..."

There would be no clue that anything happened to the sun until 8 minutes after it happened. Or so the scientests are telling us. And if you think about it, it seems to make some sense when compared against other relativistic theories.

For one thing, if gravity was instananeous it could conceivably be used to send information anywhere in the universe with zero ping time. Imagine a gravity-wave wireless link that would enable us to communicate with civilizations in other galaxies. Imagine playing Q3 with an alien on a planet in M3 and still having a 20ms ping.

Now imagine sending energy via gravity waves. With the right technology you (in energy form) could be beamed, Star Trek style, to another galaxy. You could go visit your alien buddy for a lan party and be back in time for dinner.

Unfortunately, the notion of energy (and indirectly, matter) moving at infinite velocity seems to violate the entire theory of relativity. Moving you from here to another galaxy instantly certainly seems to violate the theory of relativity.

Speed of gravity paradox

[nebbian]

If the speed of gravity isn't infinite, then I think you get a paradox when two bodies are orbiting each other.

Let's say we have two bodies, body 1 and body 2, both orbiting a central point.

Both of them are getting pulled in towards the central point by the other one. Right?

But if the speed of gravity isn't infinite, each body will be pulled not exactly towards the center, but towards the point at which the other body used to be, a certain time ago.

Try this experiment: You will need:
1 friend
2 tennis balls
1 roundabout (the circular playground variety)

Stand on a point on the circumference of the roundabout, and get your friend to stand opposite you. Spin the roundabout so you are both orbiting the central point.

Now throw your tennis ball at your friend. Chances are you will miss, because your friend will have moved by the time the ball gets there. So now change your aim so that the ball actually hits your friend. Get your friend to do the same.

When you've got things sorted, you should get the tennis balls hitting you from slightly 'front-on' compared to the center of the roundabout.

So what this means is that if gravity has a speed, then each orbiting body will be pulled by the phantom ghost of the other one, which will appear to be slightly behind the center of rotation. Therefore, the two bodies will keep on accelerating, pulling themselves up by their shoelaces, until the orbits around the central point become so huge that the effect isn't very big at all.

In other words, orbits won't be stable if gravity has a speed.
If we assume that 2-body orbits are stable, then gravity must be instantaneous, but this introduces a communication paradox (as pointed out by many other posters).

So we have a paradox! If you were God, would you make gravity have a speed, or not? Or do you make it so friggin' hard to measure that people give up and argue over which physicist has the bigger reputation? :-)

Re:Speed of gravity paradox

[NanoProf]

I'm impressed. Very clever, but you've forgotten about the coordinate transformations of relativity. Assuming I remember my grad school E&M correctly, if one does a full calculation relativistically, the force arising from a body moving in a straight line at uniform speed does in fact appear to come from where the body would be predicted to be at the time that the signal is received, not the time that it is sent. Of course, if the body curves suddenly, this simple result breaks down (since own can't anticipate how it would curve). The situation with co-orbitting bodies is more complex, but the basic idea is the same: the full relativistic calculation with retardation effects (i.e. finite signal propagation) eliminates the naive nonphysical effects. One does, however, see things like precession of the perihelion from GR, which is absent in the Newtonian approximation.

Re:Can we turn gravity off?

[Guy Harris]

Couldn't you collide some matter and antimatter? If you had some mass and then it co-annihilates, it should be like turning gravity off.

No, it shouldn't. A matter-antimatter annihilation isn't really an "annihilation" in the sense that the "nihil" in "annihilation" might suggest; instead, if, for example, an electron and positron mutually annihilate, you get a pair of photons, and the total energy of the photons is equal to the total energy (rest energy, from rest mass, plus kinetic energy) of the incoming electron and positron.

The photons have a gravitational field just as the electron and positron did. (Mass isn't the source of gravity - energy and momentum, and the flow thereof, are.)

library licences are all you need

[boots@work]

Well, you're closer, but you're still not on the money.

It sounds like either Linux-ABI steps on SCO patents, or certain customers are shipping SCO libraries to run on top of Linux-ABI (which is outright copyright violation).

They don't *need* patents. They just need for the SCO C library licence to say that programs developed using it may only be run on genuine SCO Unix. In that case, anyone running such a program would be in trouble -- they wouldn't have to redistribute it.

I suspect the background for this story is that a few long-standing SCO customers with an eye to the future have had a bright young nerd look at how hard it would be to get their vertical application to run on Linux instead of SCO. (Perhaps it's a dental surgery management suite running on Ingres or something similar.) Probably in many cases the customer has a binary app without source access, but that can be fixed with Linux-ABI. It's probably not so hard in most cases.

It's a good deal for the customer: they cut out their SCO licence costs, they get a platform with a bright future, and they have much less trouble finding people who can support and enhance it.

This is a bit bad for SCO, though. Once word gets back to HQ that this is happening, they start to think about methods that can be used to keep their customers locked in. One technique is to exploit the licence that the customer's application vendor originally signed to get the SCO libraries. If SCO were smart enough to put in a "this can only be used on SCO" clause, then they're set!

Anybody who has the source for their applications should be easily able to move to Linux, and probably most of the commercial applications like Oracle already have native ports. Linux-ABI and this licensing strategy really just apply to people with legacy SCO apps who can't, or don't want, to port to Linux.

Microsoft could use such a clause in the Office (or DirectX or MSVC Runtime) licences to put an end to all this Wine, Crossover and Transgaming nonsense, if they wanted to. I think there are enough precedents for that kind of restriction in software licences that it would be possible. For example, lots of driver software comes with a licence saying it may only be used with the vendor's original software. I think this technique is a terrible abuse of customers, like most proprietary software licences. But it would probably work to shake down some more money.