The parent post is right: electrons themselves move too slowly for them to carry information all the way from one end of a cable field. Information is carried through cable via an electromagnetic wave, which can propagate much faster. In fact, the parent post is right again: the information propagates at the speed of light (in that medium). In fact, any given electron in the cable probably doesn't go anywhere. A simple example demonstrating this to be true of wave phenomena is that if you send a wave through a string, the end of the string you're holding onto doesn't magically find it's way to the other end of the string--you were holding onto it the whole time. The fact that the wave propagates and the medium doesn't is also why a beach ball out in the ocean beyond the breakers doesn't spontaneously return to shore.
I just read the paper, and I was right about the latency of CAT-5:
The least squares fit to these data yields a slope of 2.04 +/-.14 x 10^8 m/s , indicating that the speed of propagation in a cat-5 cable is some 2/3 the speed of light in the vacuum.(bottom of page 8 of the PDF)
Where does friction enter the picture? If you have the impression that electrons are flowing through CAT-5 to carry bits of information, you're horribly mistaken. You even more horribly mistaken if you think friction has anything to do with fiber-optic communication.
In general, the speed of light pulses sent through a fiber will be approximately 2/3's the speed of light in vacuum, since the refractive index (ratio speed of light in vacuum to speed of light in that medium) of glass is approximately 1.5. You get the latency by dividing the transmission distance by this speed. I haven't had a chance to read the paper yet, but I imagine that CAT-5 latency is probably similar.
SETI@home is a piss-poor benchmark, especially for multiprocessor machines, because it's not multithreaded and therefore will only use one processor to compute. Running a SPEC benchmark would probably be the only way to compare the two machines fairly, and even then the benchmark results may be due to better optimizations, not faster computation. In general, though, I have no doubt that an Octane 2 would kick the crap out of any PC (dual PIII/Athlon/G4) at rendering, but I wouldn't base that assessment on SETI@home.
I have never, ever seen an SGI machine crash. I cannot say the same for Macintoshes (and certainly not for Wintel). In fact, I've seen anecdotal evidence that MacOS X.0 had stability problems.
My guess is that it's a liquid crystal panel. It might also be possible to make a electrochromic material that turns light and opaque as well as dark and opaque.
Given that the story kinda veered off-topic by mentioning transparent aluminum, the abundance of semi-off-topic threads should not come as a surprise. I myself consider electrochromic materials to be way cooler than translucent/transparent concrete.
Any reasoning that classifies this mixture of "plastic and glass beads and transparent glue" as concrete would also classify fiberglass and carbon-fiber as concrete, and that definitely does not sit well with me.
That's nice, but I and most people prefer Outlook (I use Outlook 98, if you really care) to Outlook Express. Yes, it requires that you not be a dumbass and open unsolicited attachments, but integrated scheduling and email is _a good idea_ as many people schedule appointments and plan projects via email. (Scripting is a bad idea, but nothing an intelligent user can't work around) If my Palm weren't from the stone age (to give you an idea how old it is, it's a US Robotics model), I could synchronize my Palm schedule and address book with Outlook, which would also be very nice. The killer feature for me is Outlook's ability to export mailboxes to a single file. I have not seen an equivalent feature in Netscape (my previous mail client, last used about 4 years ago) or anything else. If there is a great mail client that does this that I don't know about, please tell me. The best hope I see is either Evolution or Mozilla, but neither of them are quite there yet.
Incidentally, am I the only person that thinks the whole OE / Outlook fork is dumb? A rational company would just write one mail client that worked, or maybe build one on top of the code base from the other, but OE / Outlook seem to be the product of Microsoft's right hand not communicating with it's left...
What you describe sounds like a photonic bandgap material. I have not heard of metal photonic bandgap or multilayer structures, and therefore, I am not sure whether there is a physical limitation that makes them either impossible or just very difficult to make. You are correct in stating that such a structure would be very frequency selective, and so to the naked eye it still wouldn't look transparent, , but I would also be very curious if something like this could operate at a specific wavelength.
I hate to dignify this with a response, but an obvious counterexample to this argument is wood. I have never seen shiny untreated wood, no matter how well polished.
In general, surface roughness does affect reflectivity, especially whether the reflection is diffuse or specular, but intrinsic material properties (e.g. metallic bonding [free electrons], band gaps, etc.) are a strong factor as well. The free-electron model also explains why you can't see through aluminum foil but you can see through mirrored sunglasses. The electromagnetic theory of light also generalizes to the microwave radiation that enables the culinarily-challenged like myself to cook, and to radio waves that enable radio, television, and wireless networks. Try patching your "shiny reflective surface" theory to explain all these phenomena...:-p
I have to agree here -- I don't think that crystalline structure alone will confer transparency on a material, especially metal. It has firstly to do with the properties of the atoms and molecules themselves, and maybe second the crystalline nature.
Why, then, would glass be transparent? Glass has a most uncrystalline structure!
Doh! Why didn't I think of that obvious counterexample?;-)
Some people (*cough*moderator*cough*) have no sense of humor and don't know anything about the subject they're moderating...:-p
Re:Transparent building materials
on
Transparent Concrete
·
· Score: 4, Informative
It's a shame that electrochromic windows haven't taken off. I first read about them in Popular Science, probably about 10-15 years ago, and if I recall correctly, they were used in a concept car by Ford (I could be mixing two Popular Science articles together), but they allow you to electrically darken and lighten windows, and they actually reflect light and heat (unlike liquid crystals, which just scatter light and heat but still let them through). I'm not sure, but they might also be wavelength-independent, i.e. reflecting all colors of light equally. The obvious barriers to their widespread adoption are probably cost and the ability to make panes large enough to use as windows.
Technically, concrete is simply a mixture of three ingredients: big lumps of material called the coarse aggregate (such as gravel), smaller lumps called the fine aggregate (such as sand) and a binding agent, or cement, to glue it all together into a solid. So translucent concrete, in theory, should be fairly easy to make using bits of plastic or glass of various sizes, with some kind of transparent glue to act as a binding agent.
A multiphase material formed from a combination of materials which differ in composition or form, remain bonded together, and retain their identities and properties. Composites maintain an interface between components and act in concert to provide improved specific or synergistic characteristics not obtainable by any of the original components acting alone. Composites include: (1) fibrous (composed of fibers, and usually in a matrix), (2) laminar (layers of materials), (3) particulate (composed of particles or flakes, usually in a matrix), and (4) hybrid (combinations of any of the above).
By this definition, "transparent concrete" is a particulate composite of plastic or glass, probably in a matrix of epoxy or resin. Concrete is also a composite by this definition, but despite what my civil engineering friends might try to tell me, that doesn't mean that all composites are concrete.;-)
The reason you will never see transparent aluminum is not because of a lack of crystalline structure--in fact, I think metals generally are crystalline or at least have a crystalline microstructure. The reason that aluminum, and basically all metals, are opaque is the same reason that metals tend to be shiny. Because there are a lot of free electrons in metals (which is why they conduct electricity well), the electric field of light expends energy driving these free electrons (therefore metals are opaque), which in turn reradiate light back in the direction of the incident light (therefore metals are shiny). The amount of light that gets through goes as e^-ax where a is a constant and x is the thickness of the metal, so in a very thin metal film (e.g. mirrored sunglasses) you can still get some light through, but for any measurable thickness of metal (e.g. aluminum foil and anything thicker), the amount of transmitted light is negligible.
I know this is a very hand-wavy explanation, but it's hard to explain without a pretty advanced background in electromagnetics. If you want an explanation of this from a rigorous electromagnetic point of view you can try wading through Chapter 14 of Principles of Optics by Max Born and Emil Wolf, but its mostly math with very little physical intuition or explanation.
Such a material already exists--in fact it predates human civilization. It's called Al2O3, or alumina, and more commonly known as sapphire (or it's chromium-doped cousin, ruby). It has a hardness of 9 out of 10 on the Mohs scale (the only harder material I know of is diamond) and is transparent in the absence of impurities. However, it is not an alloy--it's a crystalline oxide.
Metallic aluminum cannot be transparent except in thin films; this will be explained in a reply to the top-level post in this thread.
They're called windows, and they're usually made of a neat transparent material called glass...;-)
Seriously, though, any slurry-based material like concrete is most likely to be opaque because microscopic structures tend to scatter light. You only need to pour a glass of milk to see this in action.
That's why I qualified statement (a) with statement (b). Trust me, I want superluminal fiber-optic transmission as much as the next geek, maybe even more because that would improve my job outlook as a new graduate optical engineering tremendously, but based on having read the articles and taken quite a few optics classes, all the evidence suggests that this technique will break down upon trying to transmit data because it is basically a trick of wave superposition.
One of my professors last semester had a really good electrical engineering example of something that works in sort of the same way and also explained why this wouldn't work for data transmission, but unfortunately I can't remember what it was...
Since they're using a photonic bandgap fiber, the pulse is already traveling at or very near c. Also, you can't actually use this technique to send information because a) that would actually violate relativity, and b) modulating the pulse screws up the effect by adding or subtracting frequency components to the signal. It's a neat trick, but with no practical use that I can think of...
A math major buddy of mine has a saying: "I'm a mathematician, not an arithmetician."
Re:electrocution? I don't think so.
on
A Beautiful Mind
·
· Score: 3, Interesting
(one practical joke of Nash's involved filling a light fixture with water, which could have electrocuted a hapless victim when he turned on the light)
I have to say that, so far, one of my main annoyances with this book are these tiny one-line anecdotes that honestly could have been innocent, albeit stupid, pranks. If someone were to write a biography about me, I hope they wouldn't dig up stupid little things I did (and probably am still doing) in my youth and use it as evidence that I was insane, intrinsically cruel, etc.
Slashdot Mirror
The parent post is right: electrons themselves move too slowly for them to carry information all the way from one end of a cable field. Information is carried through cable via an electromagnetic wave, which can propagate much faster. In fact, the parent post is right again: the information propagates at the speed of light (in that medium). In fact, any given electron in the cable probably doesn't go anywhere. A simple example demonstrating this to be true of wave phenomena is that if you send a wave through a string, the end of the string you're holding onto doesn't magically find it's way to the other end of the string--you were holding onto it the whole time. The fact that the wave propagates and the medium doesn't is also why a beach ball out in the ocean beyond the breakers doesn't spontaneously return to shore.
Where does friction enter the picture? If you have the impression that electrons are flowing through CAT-5 to carry bits of information, you're horribly mistaken. You even more horribly mistaken if you think friction has anything to do with fiber-optic communication.
In general, the speed of light pulses sent through a fiber will be approximately 2/3's the speed of light in vacuum, since the refractive index (ratio speed of light in vacuum to speed of light in that medium) of glass is approximately 1.5. You get the latency by dividing the transmission distance by this speed. I haven't had a chance to read the paper yet, but I imagine that CAT-5 latency is probably similar.
[me@home log]# uptime
:-p
4:31pm up 9E99 days, 59:59, 1E50 users, load average: 99.65, 99.55, 99.95
Do you believe that? I thought so...
SETI@home is a piss-poor benchmark, especially for multiprocessor machines, because it's not multithreaded and therefore will only use one processor to compute. Running a SPEC benchmark would probably be the only way to compare the two machines fairly, and even then the benchmark results may be due to better optimizations, not faster computation. In general, though, I have no doubt that an Octane 2 would kick the crap out of any PC (dual PIII/Athlon/G4) at rendering, but I wouldn't base that assessment on SETI@home.
I have never, ever seen an SGI machine crash. I cannot say the same for Macintoshes (and certainly not for Wintel). In fact, I've seen anecdotal evidence that MacOS X.0 had stability problems.
My guess is that it's a liquid crystal panel. It might also be possible to make a electrochromic material that turns light and opaque as well as dark and opaque.
Given that the story kinda veered off-topic by mentioning transparent aluminum, the abundance of semi-off-topic threads should not come as a surprise. I myself consider electrochromic materials to be way cooler than translucent/transparent concrete.
Any reasoning that classifies this mixture of "plastic and glass beads and transparent glue" as concrete would also classify fiberglass and carbon-fiber as concrete, and that definitely does not sit well with me.
That's nice, but I and most people prefer Outlook (I use Outlook 98, if you really care) to Outlook Express. Yes, it requires that you not be a dumbass and open unsolicited attachments, but integrated scheduling and email is _a good idea_ as many people schedule appointments and plan projects via email. (Scripting is a bad idea, but nothing an intelligent user can't work around) If my Palm weren't from the stone age (to give you an idea how old it is, it's a US Robotics model), I could synchronize my Palm schedule and address book with Outlook, which would also be very nice. The killer feature for me is Outlook's ability to export mailboxes to a single file. I have not seen an equivalent feature in Netscape (my previous mail client, last used about 4 years ago) or anything else. If there is a great mail client that does this that I don't know about, please tell me. The best hope I see is either Evolution or Mozilla, but neither of them are quite there yet.
Incidentally, am I the only person that thinks the whole OE / Outlook fork is dumb? A rational company would just write one mail client that worked, or maybe build one on top of the code base from the other, but OE / Outlook seem to be the product of Microsoft's right hand not communicating with it's left...
I'm glad someone can explain this stuff a lot better than I can... ;-)
What you describe sounds like a photonic bandgap material. I have not heard of metal photonic bandgap or multilayer structures, and therefore, I am not sure whether there is a physical limitation that makes them either impossible or just very difficult to make. You are correct in stating that such a structure would be very frequency selective, and so to the naked eye it still wouldn't look transparent, , but I would also be very curious if something like this could operate at a specific wavelength.
I hate to dignify this with a response, but an obvious counterexample to this argument is wood. I have never seen shiny untreated wood, no matter how well polished.
:-p
In general, surface roughness does affect reflectivity, especially whether the reflection is diffuse or specular, but intrinsic material properties (e.g. metallic bonding [free electrons], band gaps, etc.) are a strong factor as well. The free-electron model also explains why you can't see through aluminum foil but you can see through mirrored sunglasses. The electromagnetic theory of light also generalizes to the microwave radiation that enables the culinarily-challenged like myself to cook, and to radio waves that enable radio, television, and wireless networks. Try patching your "shiny reflective surface" theory to explain all these phenomena...
Some people (*cough*moderator*cough*) have no sense of humor and don't know anything about the subject they're moderating... :-p
It's a shame that electrochromic windows haven't taken off. I first read about them in Popular Science, probably about 10-15 years ago, and if I recall correctly, they were used in a concept car by Ford (I could be mixing two Popular Science articles together), but they allow you to electrically darken and lighten windows, and they actually reflect light and heat (unlike liquid crystals, which just scatter light and heat but still let them through). I'm not sure, but they might also be wavelength-independent, i.e. reflecting all colors of light equally. The obvious barriers to their widespread adoption are probably cost and the ability to make panes large enough to use as windows.
The reason you will never see transparent aluminum is not because of a lack of crystalline structure--in fact, I think metals generally are crystalline or at least have a crystalline microstructure. The reason that aluminum, and basically all metals, are opaque is the same reason that metals tend to be shiny. Because there are a lot of free electrons in metals (which is why they conduct electricity well), the electric field of light expends energy driving these free electrons (therefore metals are opaque), which in turn reradiate light back in the direction of the incident light (therefore metals are shiny). The amount of light that gets through goes as e^-ax where a is a constant and x is the thickness of the metal, so in a very thin metal film (e.g. mirrored sunglasses) you can still get some light through, but for any measurable thickness of metal (e.g. aluminum foil and anything thicker), the amount of transmitted light is negligible.
I know this is a very hand-wavy explanation, but it's hard to explain without a pretty advanced background in electromagnetics. If you want an explanation of this from a rigorous electromagnetic point of view you can try wading through Chapter 14 of Principles of Optics by Max Born and Emil Wolf, but its mostly math with very little physical intuition or explanation.
Such a material already exists--in fact it predates human civilization. It's called Al2O3, or alumina, and more commonly known as sapphire (or it's chromium-doped cousin, ruby). It has a hardness of 9 out of 10 on the Mohs scale (the only harder material I know of is diamond) and is transparent in the absence of impurities. However, it is not an alloy--it's a crystalline oxide.
Metallic aluminum cannot be transparent except in thin films; this will be explained in a reply to the top-level post in this thread.
They're called windows, and they're usually made of a neat transparent material called glass... ;-)
Seriously, though, any slurry-based material like concrete is most likely to be opaque because microscopic structures tend to scatter light. You only need to pour a glass of milk to see this in action.
That's why I qualified statement (a) with statement (b). Trust me, I want superluminal fiber-optic transmission as much as the next geek, maybe even more because that would improve my job outlook as a new graduate optical engineering tremendously, but based on having read the articles and taken quite a few optics classes, all the evidence suggests that this technique will break down upon trying to transmit data because it is basically a trick of wave superposition.
One of my professors last semester had a really good electrical engineering example of something that works in sort of the same way and also explained why this wouldn't work for data transmission, but unfortunately I can't remember what it was...
Since they're using a photonic bandgap fiber, the pulse is already traveling at or very near c. Also, you can't actually use this technique to send information because a) that would actually violate relativity, and b) modulating the pulse screws up the effect by adding or subtracting frequency components to the signal. It's a neat trick, but with no practical use that I can think of...
A math major buddy of mine has a saying: "I'm a mathematician, not an arithmetician."