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

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?

Iridium Flares

[FrostedWheat]

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

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: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.)

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.