I would like to turn to Principles of Optics (Born & Wolf), Chapter 1.3.3, (p. 19 in volume 7) for some clarification on this:
...The phase velocity may in certain cases be greater than c. for plane waves this will be so when n = sqrt(epsilon*mu) is smaller than unity, as in the case of dispersing media in regions of the so-called anomalous dispersion. Now according to the theory of relativity, signals can never travel faster than c. This implies that the phase velocity cannot travel faster than c. [...] the phase velocity cannot be determited experimentally and must therefore be considered to be void of any direct physical significance. For in order to measure this velocity, it would be necessary to affix a mark to the infinitely extended smooth wave and to measure the velocity of the mark. This would, however, mean the replacement of the infinite harmonic wave train by another function of space and time.
Ok, so I oversimplified by calling phase velocity the 'speed of light itself',
sorry, sorry. I should have been more careful, especially when calling myself
a terminology stickler. Your definition is more correct, but in my correction
of redtea, I wanted to show what was stated is the opposite of standard
operating procedure. Phase velocity is omega/k, temporal frequency over
spatial frequency, and in most approximations it matches the speed of light in the medium. Considering
information travel, information's not going to get there any sooner than the
phase velocity. You can have whatever group velocity you want, but the
information won't get there until the electromagnetic field changes: that is, until the
light arrives. It's limited by c, and causality; and pretty much physics as we
know it.
So let's move on to page 23, ch 1.3.4 on group velocity:
...If the medium is not strongly dispersive, a wave group will travel a
considerable distance without appreciable variation. In some circumstances,
the group velocity, which may be considered as the velocity of the propagation
of the group as a whole, will also represent the velocity at which energy is
propagated. This, however, is not true in general (emphasis mine). In
particular, in regions of anomalous dispersion the group velocity may exceed
[c] or become negative, but there is no conflict with the special theory of
relativity.
Redtea said "it is impossible to get group velocities faster than c". That
simply isn't true. I see everyone has already posted to a nice applet link, so
I won't belabor it any more.
I've been using NetworkManager for wireless on 10.0 for a few weeks. It's a huge improvement over dhcpcd (standard install on 10.0), at least for ndiswrapper-based card drivers. Before, I had to open kwifimanager to get a list of available networks, but I couldn't connect with kwifi. I had to go into YaST, change the network settings to whatever I found with kwifi, by hand, restart the Network with YaST, hope I typed everything in right, then maybe connect; I also sometimes had to do it from ifdown/ifup in the command line. It was enought to make me want to boot into windows.
Now with NetworkManager, I can wardrive again! Thank God for NetworkManager!
Just to be a terminology stickler, you've got group and phase velocity confused.
"Group velocity" refers to the speed of a pulse on the wave, it's usually defined as (d\omega)/dk, where \omega is the temporal frequency and k is wavenumber. This can be adjusted to all sorts of crazy values with the right material. It's done all the time. Technically, group velocity exceeds c when light travels into many metals.
"Phase velocity" is c, the speed of the light itself, and the information it carries. It's never gone faster than 3e8 m/s (not that we know of), and still hasn't after this experiment.
So yeah, like everyone else says, this is a grabbing headline for a not-so-revolutionary story. The group velocity data confirms previous theory, and it's been difficult to check on this before, but no one has called the laws of relativity into question. No need to philosophize or write a freshman-experience 'thought-provoking' one-act play just yet.
1. Please don't leave out high-fructose corn syrup. A lot of other posters have mentioned sugar, but there's something about HFCS that really messes with one's metabolism and overall health. It's a great low-cost sweetener/preservative for mass-production of foods, it helps burn off the U.S. economy's excess corn supply, but it will ruin you. This is more of a symptom, though, of the greater food-industrial-complex. Read
Fatland.
2. The whole infrastructure is designed around driving and cars. Try walking downtown in a U.S. city of less than 100,000 and doing any necessary economic activity (grocery shopping, clothes shopping, getting a haircut, finding jobs worth applying for). It might be possible, but not easy. All the activity has moved to the interstate beltways and monster parking lots. Those places are eyesores that rob you of your will to live. Now compare to western Europe: not perfect, but the town-centers still exist and work for the most part.
I can't add much to points 3 through 5. Most Americans care a lot about the environment and their own health, but the government is not on our side. As long as big business's current quarterly profits remain our government's top priority, we won't be able to address these problems seriously until after the negative effects take place (see terrorism, hurricane katrina, or gas prices). It's possible to eat healthy, buy green and exercise in the U.S., but we're lazy. So are Europeans, but a European can still ride a bike around town, but all organic groceries, and visit a hospital without going broke. It's easier in Europe.
So this is a fixed exchange rate, like the Chinese Renminbi. Is this like saying the virtual experience is always worth 1/10th of the actual one? Are there pricing fluctuations in the PED that would suggest it is under/over-valued?
On that note, another SD article mentioned how Flooz was put out of business by $300,000 worth of virutal credit charged to fake accounts. This PED virtual economy sounds a little more robust, but that doesn't seem to rule out the possibility of large-scale fraud from criminals in countries where the real-world rules won't get enforced. What's a Flooz worth now? And what will a PED be worth if someone rips them off, or someone else designs a better universe in a year or two?
Slashdot Mirror
Ok, so I oversimplified by calling phase velocity the 'speed of light itself', sorry, sorry. I should have been more careful, especially when calling myself a terminology stickler. Your definition is more correct, but in my correction of redtea, I wanted to show what was stated is the opposite of standard operating procedure. Phase velocity is omega/k, temporal frequency over spatial frequency, and in most approximations it matches the speed of light in the medium. Considering information travel, information's not going to get there any sooner than the phase velocity. You can have whatever group velocity you want, but the information won't get there until the electromagnetic field changes: that is, until the light arrives. It's limited by c, and causality; and pretty much physics as we know it.
So let's move on to page 23, ch 1.3.4 on group velocity:
Redtea said "it is impossible to get group velocities faster than c". That simply isn't true. I see everyone has already posted to a nice applet link, so I won't belabor it any more.
Now with NetworkManager, I can wardrive again! Thank God for NetworkManager!
"Group velocity" refers to the speed of a pulse on the wave, it's usually defined as (d\omega)/dk, where \omega is the temporal frequency and k is wavenumber. This can be adjusted to all sorts of crazy values with the right material. It's done all the time. Technically, group velocity exceeds c when light travels into many metals.
"Phase velocity" is c, the speed of the light itself, and the information it carries. It's never gone faster than 3e8 m/s (not that we know of), and still hasn't after this experiment.
So yeah, like everyone else says, this is a grabbing headline for a not-so-revolutionary story. The group velocity data confirms previous theory, and it's been difficult to check on this before, but no one has called the laws of relativity into question. No need to philosophize or write a freshman-experience 'thought-provoking' one-act play just yet.
2. The whole infrastructure is designed around driving and cars. Try walking downtown in a U.S. city of less than 100,000 and doing any necessary economic activity (grocery shopping, clothes shopping, getting a haircut, finding jobs worth applying for). It might be possible, but not easy. All the activity has moved to the interstate beltways and monster parking lots. Those places are eyesores that rob you of your will to live. Now compare to western Europe: not perfect, but the town-centers still exist and work for the most part.
I can't add much to points 3 through 5. Most Americans care a lot about the environment and their own health, but the government is not on our side. As long as big business's current quarterly profits remain our government's top priority, we won't be able to address these problems seriously until after the negative effects take place (see terrorism, hurricane katrina, or gas prices). It's possible to eat healthy, buy green and exercise in the U.S., but we're lazy. So are Europeans, but a European can still ride a bike around town, but all organic groceries, and visit a hospital without going broke. It's easier in Europe.
Ten PEDs are the equivalent to one US dollar.
So this is a fixed exchange rate, like the Chinese Renminbi. Is this like saying the virtual experience is always worth 1/10th of the actual one? Are there pricing fluctuations in the PED that would suggest it is under/over-valued?
On that note, another SD article mentioned how Flooz was put out of business by $300,000 worth of virutal credit charged to fake accounts. This PED virtual economy sounds a little more robust, but that doesn't seem to rule out the possibility of large-scale fraud from criminals in countries where the real-world rules won't get enforced. What's a Flooz worth now? And what will a PED be worth if someone rips them off, or someone else designs a better universe in a year or two?