Follow Slashdot blog updates by subscribing to our blog RSS feed


Forgot your password?

Slashdot videos: Now with more Slashdot!

  • View

  • Discuss

  • Share

We've improved Slashdot's video section; now you can view our video interviews, product close-ups and site visits with all the usual Slashdot options to comment, share, etc. No more walled garden! It's a work in progress -- we hope you'll check it out (Learn more about the recent updates).


Comment: Re:This was already done back in 2001 (Score 5, Informative) 223

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.

Comment: Quadrillion Hz laser (Score 1) 231

by Karma Bandit (#44251825) Attached to: Data Storage That Could Outlast the Human Race
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.

Comment: Nearly unstable vacuum (Score 1) 170

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?

Comment: Re:NO THANK YOU. (Score 1) 41

by Karma Bandit (#39684029) Attached to: Pentagon Orders Dual-Focus Contact Lens Prototypes

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?

Comment: Re:Not breaking any laws (Score 2) 502

by Karma Bandit (#39299209) Attached to: LED's Efficiency Exceeds 100%
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.

Comment: Re:Absorbed not necessarily equal to electricity (Score 1) 439

by Karma Bandit (#31313842) Attached to: Caltech Makes Flexible, 86% Efficient Solar Arrays

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.

Comment: Re:Black holes are fiction (Score 1) 314

by Karma Bandit (#30097166) Attached to: Micro-Black Holes Make Poor Planet Killers

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.

Comment: Re:metamaterials are just periodic structures (Score 2, Interesting) 113

by Karma Bandit (#29162723) Attached to: Big Bang Could Be Recreated Inside a Metamaterial

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."

Comment: Re:Relitivity (Score 1) 383

by Karma Bandit (#28305867) Attached to: Could Betelgeuse Go Boom?
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.

Google Releases Chrome 2.0 Pre-Beta 326

Posted by ScuttleMonkey
from the what-is-too-fast-if-it's-pre-beta dept.
Nick Fletcher writes "Just a few short months after the initial release, Google has released a pre-beta version of Google Chrome 2.0. It sports a few new features including form auto-completion, full-page zoom, 'profiles,' and Greasemonkey support. It seems the only notable feature would be profiles, which allows users to separate out their homepage, history, and bookmarks on a per user or category basis. It seems Google is still playing catch-up but they're definitely moving at a pace unknown to some of their competition. The full list of new features is available in the release notes."

Adobe Releases C/C++ To Flash Compiler 216

Posted by samzenpus
from the transmutations dept.
SnT2k writes "Adobe recently released the beta version of Alchemy which compiles C/C++ code into AS3 bytecode (which runs on AVM2) that can run on the Flash or Flex platform and boasts increased performance for computationally-intensive tasks (but still slower than native C/C++). It was demonstrated last year during the Chicago MAX 2007 to run Quake. A few months later it has been demonstrated to run a Python interpreter and Nintendo Emulator. One interesting tidbit is that the thing is built upon the open source LLVM Compiler Infrastructure."

There are two major products that come out of Berkeley: LSD and UNIX. We don't believe this to be a coincidence. -- Jeremy S. Anderson