This article had some information that astounded me. Apparently the University of Rochester has been playing around with fiber optics and pulses of light. Here's what the scientists found:

quote:

---

A pulse of light shot into the fiber departs before it enters.

Within the fiber, the pulse travels backward — and faster than the speed of light.

---

Light, traveling backwards, travels at a speed FASTER than the speed of light? And without violating the laws of physics?

quote:

---

For Dr. Boyd's trick, the scientists used an optical fiber of glass with small amounts of the metal erbium, which acts as an amplifier. In the experiment, a pulse of laser light was fired into the fiber. Even before the peak of the pulse entered the fiber, another pulse appeared, seemingly out of nowhere, at the far end of the fiber.

This new pulse then split in two. One, a twin of the original pulse, moved forward, while the other moved backward through the fiber.

The backward pulse, which traveled faster than the speed of light, and the original pulse met at the front end of the fiber, where they canceled each other.

Even though one pulse momentarily became three, the experiment did not violate the law mandating conservation of energy because the amplifying effect of the erbium added a temporary surge of energy.

---

The researcher, Dr. Robert W. Boyd, calls this a "nifty trick." I call it amazing.

I was actually as intrigued by the following quote from the piece:

quote:

---

In 1999, physicists led by Lene Vestergaard Hau of Harvard slowed the speed of light to a leisurely 38 miles per hour by shining it into an exotic ultracooled material known as Bose-Einstein condensate.

Two years later, Dr. Hau's group, as well as a second team of scientists at the Harvard-Smithsonian Center for Astrophysics, were able to bring light to a standstill — and then release it with its original properties intact.

---

Now, who was it whose SF stories had "slow glass" in them? Sounds like they were on the money...

quote:

---

The backward pulse, which traveled faster than the speed of light, and the original pulse met at the front end of the fiber, where they canceled each other.

---

quote:

---

Even before the peak of the pulse entered the fiber, another pulse appeared

---

note the word "peak." That's what lets this happen. It's not that the first pulse never entered the fiber, it's that only a certain percentage of the gaussian wave-packet was in the fiber, and something about the unsual properties of the erbium-filled optical fiber amplifies the part of the pulse that was already in the fiber.

As far as just sending a shorter pulse, the shortest pulse you can possible shoot is a single photon. But even a single photon is mathematically described by a Gaussian wave-packet. So theoretically, this effect would work regardless of the duration of the pulse.

quote:

---

News like this makes me wish I was writing sci-fi and not fantasy.

---

quote:

---

So what's stopping you?

---

I'm happily immersed in writing my fantasy novel. At 67,000+ words, I figure I'm nearly half way done.

I was also trying to prove, using wikipedia, that soda is bad for you and I came across an article on the Mpemba effect, wherein hot water freezes faster than cold water in some conditions. Of course, under some conditions really cold water never freezes at all, but anyway... it was originally observed by Sir Francis Bacon but I guess everyone just assumed he didn't know that he had some kind of faulty methodology. So it wound up being named for an African high school student who didn't wave it off as a fluke. Plus he has a cooler sounding name.

Maybe I can get the effect of cold water boiling faster named after me. Not that it has ever been observed. We just grew up using the cold tap instead of the warm tap because the water that comes out of the warm tap has hot water heater residue in it.

quote:

---

Now, who was it whose SF stories had "slow glass" in them? Sounds like they were on the money...

---

Actually, the NYT article kills Le Guin's example using Shaw's story. She wrote in The Norton Book of Science Fiction that "though science is the megatext, science-fiction stories cannot be judged according to their actual scientific content. Serious writers...take pride in careful research and fact-checking....But there are serious and beautiful science-fiction stories in which the science is completly imaginary and the technology not only implausible but impossible. A perfect example...is Robert Shaw's 'Light of Other Days.' Shaw imagines a kind of glass which slows the velocity of light....The beauty...is not in the scientific probability of the concept, but in its coherent development, its convincingness, its imaginative resonance...and its aesthetic function as 'the idea' of a moving and elegant story."

Another example of science catching up with science fiction?

quote:

---

It's not that the first pulse never entered the fiber, it's that only a certain percentage of the gaussian wave-packet was in the fiber. . .

Still a nifty trick, but not quite as causality-violatingly baffling as it appeared at first glance.

---

Why would it violate causality if a pulse exited the fiber before it entered? If the pulse were travelling backwards in time, causailty would actually demand it.

Basically, you have a fiber, and it has mild lasing qualities and some internal reflection at both ends. Like this

| + + + + + + + + |

Then you start shooting a pulse of light into it. The pulse increases in intensity as a function of time and peaks at some point.

1 2 3 4 5 4 3 2 1 > | + + + + + + + + + |

As the light begins to enter the fiber, the erbium particles begin lasing, releaseing photons in synch with the pulse of light. By the time the light reaches the other end, it has...let's say it's doubled the pulse. Note that the amplification builds across the length of the fiber, thus the image I create below is a bit...well, you could already tell that it's symbolic. But it symbolizes the values of light intensity that points in the pulse will have upon reaching the end of the fiber, not the values anywhere else in the fiber.

|2+4+6+8+A+8+6+4+2+>|

Then the light hits the end of the fiber. We'll say that half of it is transmitted and half reflected internally. Thus it splits into two pulses, one is traveling back through the fiber and the other is leaving the fiber. Again, the erbium lases to double the backwards moving pulse.

|<+2+4+6+8+A+8+6+4+2| 1 2 3 4 5 4 3 2 1 >

Okay, now let's pretend that we shoot another pulse of light into the fiber as the backwards pulse is again being divided in half, with half being reflected. However, this pulse is exactly out of phase with the pulse that has been reflected and is staring to move forwards again.

1 2 3 4 5 4 3 2 1 >|<+2+4+6+8+A+8+6+4+2| 1 2 3 4 5 4 3 2 1 >

Okay, it's hard to show the next step graphically with just static symbols, so...um, trust me The amplified backwards pulse is split in two again, half being transmitted out of the fiber and half being internally reflected. The new pulse, 180 degrees out of phase with the internally reflected pulse, cancels it out and the quantum energy of both pulses is reabsorbed by the erbium (at least some of it, the rest is pretty much lost as heat). The backwards transmitted pulse is unaffected, the pulse that has already left the fiber is also unaffected. We have something that looks a bit like this:

< 1 2 3 4 5 4 3 2 1 |0+0+0+0+0+0+0+0+0+>| ...1 2 3 4 5 4 3 2 1 >

The elipses represent a full pulse length, not drawn to scale. The zeros represent two pulses, the second pulse and the double reflected pulse, canceling each other out.

Okay, so we got all of that? Good (I know you're all just nodding because you're sleepy, but I'll pretend you're following me ). Okay, this is not what the guys did in this experiment. They used one pulse that took longer to build to a peak. The double internal reflection of the pulse begins to cancel the pulse before it peaks, thus creating the impression of a faux peak which propagates to the other end of the fiber.

The mathmatics of this dictates that the faux peak must appear at the other end of the fiber after light has traversed the length of the fiber three times. The backwards pulse has an advantage beacause the lasing effect allows it to appear to propagate faster than the speed of light (this can happen because photons are being added by erbium particles slightly sooner than the pulse reaches them, because of the chosen quantum properties of the lasing material relative to the length of the fiber and so forth), but the forward propagation can't recieve the same benefit, and it has to happen twice before the faux peak appears.

In other words, the signal ended up traveling much slower than it could have. Also, you're left with a lot of nasty reverberation in the fiber, because the system they use doesn't have two discrete pulses, with one being neatly cancelled by the double reflection. Thus the erbium keeps lasing incompletely canceled faux pulses which bounce off the ends of the fiber until it runs out of energy. I suppose that it is possible that you could control the die-off of the originating pulse in such a way as to help cancel all the faux pulses quickly, but that implies a degree of control that utterly obviates the necessity of using this lasing trick to create a steeper pulse build to the desired faux peak.

The article described this as some kind of breakthrough but really it's just a totally useless lab trick that let these guys seem to be saying that they were getting a signal to come out before it entered the fiber. But they didn't actually say that, they just tried to imply it. This trick can't increase communications speed or send messages back in time or anything like that. It is marginally possible that we could eventually create materials in which the speed of light would be higher than in a vacuum, but it would require additional energy input and create serious noise problems for information bearing signals.

As for Le Guin's article, I don't think that it destroys the literary significance of an imagined technology if that technology later comes into existance. Le Guin says that the literary role of a plot device is independent of its possibility in the lab. She was referring to plot devices that function in stories though they don't function in the lab, but that doesn't mean that when a plot device can be shown to function in the lab, it ceases to be meaningful in the story. The independence of a plot device's literary function from it's practical demonstration in the lab runs both ways, it doesn't matter to the story whether the effect is proved possible or impossible.

Indeed, that is because what is thought impossible today is often proved possible in the future. Just over a hundred years ago, it was impossible that heavier than air machines could ever fly. It was impossible that a human could survive the destruction of any vital organ, such as the heart or the liver. It was impossible that mathmatics could be proven unprovable. In the end, you don't really know what's impossible till you know everything that is possible.

Thanks for the physics lecture, but that is not the question I was asking. I was not asking anything about what happened in this experiment.

In AstroStewart's message he described something that was not in the article. He said it was ". . . not as causality-violatingly baffling as it appears at first glance."