What? How can you link a paper like that and completely not understand its contents? No, they did not create matter out of light. The important thing from that paper is that the light was frozen in place while it was traveling through the material. It's a nice experiment, but has absolutely nothing whatsoever to do with photon-photon interactions and creating of particle-antiparticle pairs. The word "mass" doesn't even appear in the paper, for example. The photon energies are eV level in that paper, and photon-photon interactions require billions times more. Like, gamma rays, not visible light.
You might argue, pedantically, that while the light was trapped in the sodium in that paper, the kinetic energy of the sodium atoms increased. And due to relativity, increase the kinetic energy of something also increases its mass. Well, you would be right, and that happens every time the sun shines on something and warms it up. But when you talk about creating matter from photons, they mean making brand new particles-- that is, making even the *rest mass* portion of their energy out of the photons-- not just speeding up existing particles. And that just cannot be done with light near the visible spectrum.
There is no laser in the world that gets anywhere near close to pulsing 1 quadrillion = 10^15 times per second. That's just silly. But, femtosecond pulse length lasers (i.e. 10^-15 seconds wide) are common lab devices. They tend to pulse between 10^1-10^7 times per second.
So, the summary is only off by a factor of 10^8... but I can understand his confusion.
I've heard that the mass is right on the edge of what would make the vacuum state of the universe unstable. Are there hints to possible new physics here, or any interesting speculation as to a reason why? Do any GUT models predict this careful balancing?
the second close up focus only works when the light has a certain polarization
Not entirely accurate. It would be better to say that the contacts always focus one polarization of light so you can see things close up and the other polarization normally. Normal light has both polarizations, so only one of the two will be correctly focused, the other will be incorrectly focused, causing a diffuse blur in your field of vision (in one eye.) So, 1/2 of the light in 1/2 of your eyes will be blurry. So, 1/4 of the data your brain gets will be blurry. Maybe this isn't such a problem?
Maybe you combine it with polarizing (aka polaroid) sunglasses, so that the outside world only had the correct polarization?
Yes, a picowatt is HUGE compared to visible blackbody emission at normal temperatures. Even at room temperature (which is warmer, and therefore has *more* visible emission) the human body only emits a few photons per second. This is actually measureable, and there have been papers about (very tiny) anomalous increases in the human body's blackbody radiation from electrochemical processes. Anyway, go type "h * c / (500 nm) / (1 second)" into google, and you'll find that one photon per second in the visible is 10^-19 watts. So, this is some 6-7 orders of magnitude larger than a much bigger object's emission at a higher temperature. So, yes, claiming this is blackbody radiation is idiotic.
No, the worst case is much, much lower. The problem is that there are two different definitions of efficiency going on here. The 90-100% conversion to electricity means that 90-100% of the absorbed photons are turned into single electrons. This does *not* say that 90-100% of the energy in the original photons is converted to energy in the electrons. In fact, just as in all other solar cell devices, the photons initially create fast moving electrons, converting all of their energy. But most of that kinetic energy is lost to heat before the electrons can be extracted from the device and used to do work.
So, the take-home message is that efficiency can refer to number of converted photons, regardless of how much energy was lost to heat.
You can derive the Schwartzchild radius using newtonian physics like clone53421 is claiming, and if that was what people were basing the existence of black holes on, then clone would be right. But it is just an accident that this derivation works.
If you do the derivation properly, using general relativity, you get the same result for the Schwartzchild radius. Though there are some interesting differences in how "radius" is defined in general relativity.
So, I'm sorry that the only derivation you saw was the incorrect classical physics one (which is used to motivate the result using simple math), but the answer is still true. But honestly, if you really thought that you were the first person to realize this problem with the derivation-- that none of the thousands of physicists to learn it since it was derived had noticed this glaringly obvious problem, then you are a monumental fool.
Metamaterials don't need to be periodic. They are made up of small (compared to the wavelength of light they work with) nano-fabricated structures, but even if they are randomly distributed it will have the desired effect. Just like both periodic structures (crystals) and amorphous ones (glass) have "normal" dielectric constants, so can metamaterials.
Some people say "periodic" when they just mean "made up of small stuff". If that was your complaint, then I challenge you to find something with any index of refraction that isn't "made up of small stuff."
Assuming you weren't being snarky, he's just speaking in the language of physics. Don't take "observe" literally-- he just meant when the light reaches us. If you were being snarky, then when you close your eyes, you'd be likely to be eaten by a grue.
Yes, but that's meaningless, and moreover you don't have to speculate. If the light has not reached us yet, then the two events (here&now and the ka-boom) are not causally connected. That is, they are "space-like" separated. You can show that there exists a reference frame with any time duration between two space-like separated events. So, in some reference frame, I'm typing this post *after* the light from the supernova has occurred. In another frame, I'd have to wait a billion years for it to happen. And all choices are equally arbitrary, including yours.
No, he would never say the last line. Time travels at the speed of light. When we see it, it is the same instant of time when it exploded. Or more formally, the two events become causally connected the instant we see the light.
Don't read too much into that sentence. They're just saying that if they found a clump without stars inside it, then one can immediately rule out a star-based source of gamma radiation.
If they don't rule that out, then it will be hard to argue that the gamma rays are from dark matter, and not some other more mundane source.
AFAIK that isn't a requirement, though it does lead to some neat things to think about.
For example, imagine one string with both of its ends stuck on our 3D "plane", but with the bulk of it floating "above" the plane. The point at one end is an electron and the other end a positron. When they meet, the loop closes, forming a photon, which is a closed loop type of string.
You should read the abstracts of the articles, since it turns out you're right. From the abstract:
"This flow is difficult to explain by gravitational evolution within the framework of the concordance LCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities."
They would, at least, find it less plausible to describe it with a huge mass of dark matter.
Magnetic fields will bend light, which I believe is what this paper was based on.
That's not true. Maxwell's equations are linear, meaning that they obey superposition. So, the light you are trying to bend and any additional magnetic fields will just pass right through each other.
The most striking thing was how closely the developers copied Diablo. It really shows a lack of imagination, and that is reflected in the overall feel of the game.
You do realize that these were the guys that originally developed diablo? I think you can't fault them for copying their own game after leaving a company that they thought was taking their game in the wrong direction.
Actually, in Type-II (high temperature) superconductors there can be a small but finite resistance. From wikipedia:
In a class of superconductors known as Type II superconductors, including all known high-temperature superconductors, an extremely small amount of resistivity appears at temperatures not too far below the nominal superconducting transition when an electrical current is applied in conjunction with a strong magnetic field, which may be caused by the electrical current. This is due to the motion of vortices in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. However, as the temperature decreases far enough below the nominal superconducting transition, these vortices can become frozen into a disordered but stationary phase known as a "vortex glass". Below this vortex glass transition temperature, the resistance of the material becomes truly zero.
And isn't the atom round, so how come reflection works like the atoms are a plane. I think all your problems boil down to that one question. Because light is a wave, it does not feel the effects of things below its wavelength. It basically smears out their effects. So, the property of lenses and mirrors is that they are flat when smeared out to the particular wavelength of light.
Visible light is around 500 nm in size, while an atom is around 0.5 nm in size. So, the wavelength of light is smearing out the effects of hundreds or thousands of atoms into a single flat blob.
Getting the surface to be flat is an important quantity in optics, and in fact when you order lenses, they will typically say how flat they are in relation to the wavelength of light (e.g. wavelength/10, meaning it's flat within 1/10th of the wavelength.)
If you were to somehow hit the surface with very high energy photons with a wavelength around 1 nm, you would not see a flat surface, and things would bounce off the round atoms just like you want. In fact, this is how x-ray crystallography works.
Slashdot Mirror
What? How can you link a paper like that and completely not understand its contents? No, they did not create matter out of light. The important thing from that paper is that the light was frozen in place while it was traveling through the material. It's a nice experiment, but has absolutely nothing whatsoever to do with photon-photon interactions and creating of particle-antiparticle pairs. The word "mass" doesn't even appear in the paper, for example. The photon energies are eV level in that paper, and photon-photon interactions require billions times more. Like, gamma rays, not visible light.
You might argue, pedantically, that while the light was trapped in the sodium in that paper, the kinetic energy of the sodium atoms increased. And due to relativity, increase the kinetic energy of something also increases its mass. Well, you would be right, and that happens every time the sun shines on something and warms it up. But when you talk about creating matter from photons, they mean making brand new particles-- that is, making even the *rest mass* portion of their energy out of the photons-- not just speeding up existing particles. And that just cannot be done with light near the visible spectrum.
There is no laser in the world that gets anywhere near close to pulsing 1 quadrillion = 10^15 times per second. That's just silly. But, femtosecond pulse length lasers (i.e. 10^-15 seconds wide) are common lab devices. They tend to pulse between 10^1-10^7 times per second. So, the summary is only off by a factor of 10^8... but I can understand his confusion.
I've heard that the mass is right on the edge of what would make the vacuum state of the universe unstable. Are there hints to possible new physics here, or any interesting speculation as to a reason why? Do any GUT models predict this careful balancing?
the second close up focus only works when the light has a certain polarization
Not entirely accurate. It would be better to say that the contacts always focus one polarization of light so you can see things close up and the other polarization normally. Normal light has both polarizations, so only one of the two will be correctly focused, the other will be incorrectly focused, causing a diffuse blur in your field of vision (in one eye.) So, 1/2 of the light in 1/2 of your eyes will be blurry. So, 1/4 of the data your brain gets will be blurry. Maybe this isn't such a problem?
Maybe you combine it with polarizing (aka polaroid) sunglasses, so that the outside world only had the correct polarization?
Yes, a picowatt is HUGE compared to visible blackbody emission at normal temperatures. Even at room temperature (which is warmer, and therefore has *more* visible emission) the human body only emits a few photons per second. This is actually measureable, and there have been papers about (very tiny) anomalous increases in the human body's blackbody radiation from electrochemical processes. Anyway, go type "h * c / (500 nm) / (1 second)" into google, and you'll find that one photon per second in the visible is 10^-19 watts. So, this is some 6-7 orders of magnitude larger than a much bigger object's emission at a higher temperature. So, yes, claiming this is blackbody radiation is idiotic.
No, the worst case is much, much lower. The problem is that there are two different definitions of efficiency going on here. The 90-100% conversion to electricity means that 90-100% of the absorbed photons are turned into single electrons. This does *not* say that 90-100% of the energy in the original photons is converted to energy in the electrons. In fact, just as in all other solar cell devices, the photons initially create fast moving electrons, converting all of their energy. But most of that kinetic energy is lost to heat before the electrons can be extracted from the device and used to do work.
So, the take-home message is that efficiency can refer to number of converted photons, regardless of how much energy was lost to heat.
You can derive the Schwartzchild radius using newtonian physics like clone53421 is claiming, and if that was what people were basing the existence of black holes on, then clone would be right. But it is just an accident that this derivation works.
If you do the derivation properly, using general relativity, you get the same result for the Schwartzchild radius. Though there are some interesting differences in how "radius" is defined in general relativity.
So, I'm sorry that the only derivation you saw was the incorrect classical physics one (which is used to motivate the result using simple math), but the answer is still true. But honestly, if you really thought that you were the first person to realize this problem with the derivation-- that none of the thousands of physicists to learn it since it was derived had noticed this glaringly obvious problem, then you are a monumental fool.
Metamaterials don't need to be periodic. They are made up of small (compared to the wavelength of light they work with) nano-fabricated structures, but even if they are randomly distributed it will have the desired effect. Just like both periodic structures (crystals) and amorphous ones (glass) have "normal" dielectric constants, so can metamaterials.
Some people say "periodic" when they just mean "made up of small stuff". If that was your complaint, then I challenge you to find something with any index of refraction that isn't "made up of small stuff."
Assuming you weren't being snarky, he's just speaking in the language of physics. Don't take "observe" literally-- he just meant when the light reaches us. If you were being snarky, then when you close your eyes, you'd be likely to be eaten by a grue.
Yes, but that's meaningless, and moreover you don't have to speculate. If the light has not reached us yet, then the two events (here&now and the ka-boom) are not causally connected. That is, they are "space-like" separated. You can show that there exists a reference frame with any time duration between two space-like separated events. So, in some reference frame, I'm typing this post *after* the light from the supernova has occurred. In another frame, I'd have to wait a billion years for it to happen. And all choices are equally arbitrary, including yours.
Perhaps it would help if I logged in... we can all be glad that ACs cannot mod things up.
No, he would never say the last line. Time travels at the speed of light. When we see it, it is the same instant of time when it exploded. Or more formally, the two events become causally connected the instant we see the light.
Experimental data speculation + crackpot plasma theory = Slashdot science?
Don't read too much into that sentence. They're just saying that if they found a clump without stars inside it, then one can immediately rule out a star-based source of gamma radiation.
If they don't rule that out, then it will be hard to argue that the gamma rays are from dark matter, and not some other more mundane source.
AFAIK that isn't a requirement, though it does lead to some neat things to think about.
For example, imagine one string with both of its ends stuck on our 3D "plane", but with the bulk of it floating "above" the plane. The point at one end is an electron and the other end a positron. When they meet, the loop closes, forming a photon, which is a closed loop type of string.
You should read the abstracts of the articles, since it turns out you're right. From the abstract:
"This flow is difficult to explain by gravitational evolution within the framework of the concordance LCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities."
They would, at least, find it less plausible to describe it with a huge mass of dark matter.
Yes, mod him up. I was thoroughly confused before I read his post. Now there's an interpretation that seems plausible.
That's exactly what the parent was trying to say, as I read it.
Magnetic fields will bend light, which I believe is what this paper was based on.
That's not true. Maxwell's equations are linear, meaning that they obey superposition. So, the light you are trying to bend and any additional magnetic fields will just pass right through each other.
The most striking thing was how closely the developers copied Diablo. It really shows a lack of imagination, and that is reflected in the overall feel of the game.
You do realize that these were the guys that originally developed diablo? I think you can't fault them for copying their own game after leaving a company that they thought was taking their game in the wrong direction.
Actually, in Type-II (high temperature) superconductors there can be a small but finite resistance. From wikipedia:
In a class of superconductors known as Type II superconductors, including all known high-temperature superconductors, an extremely small amount of resistivity appears at temperatures not too far below the nominal superconducting transition when an electrical current is applied in conjunction with a strong magnetic field, which may be caused by the electrical current. This is due to the motion of vortices in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. However, as the temperature decreases far enough below the nominal superconducting transition, these vortices can become frozen into a disordered but stationary phase known as a "vortex glass". Below this vortex glass transition temperature, the resistance of the material becomes truly zero.