Why Empty Space Isn’t Empty

New Scientist has a nice little video explaining that vacuums, empty space, aren’t really empty. You, my dear reader, already know that from reading about the big laser that will tear apart virtual particles, and the recent experiment that materialized virtual photons, but you should check this short video out if you’re interested (can’t embed the video here, sadly). 

They also link to a full-length article discussing how the theory of the vacuum has evolved over time, which it looks like you’ll have to register (for free) to read. I won’t go into all of it, but in essence it portrays a somewhat philosophical struggle over the millennia about how emptiness could be empty, which led to and away from the idea of a luminiferous aether filling everything, and finally to quantum mechanics.

Now we know that because of the quantum uncertainty involved at the smallest scales, there are always fluctuations of fields and particles in a vacuum, meaning that any vacuum does indeed have energy in it. There’s never nothing. Is that reassuring? I think a constantly fluctuating space is much more interesting than a giant, vast emptiness. 

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New Material Emits Near-Infrared Light For Weeks

Researchers have created a material that can absorb one minute of sunlight and release that energy through near-infrared light for 360 hours, or over two weeks. It can also be charged by indoor lighting. The light it releases is invisible to the human eye, but can be seen with the right equipment. More from PhysOrg:

The material can be fabricated into nanoparticles that bind to cancer cells, for example, and doctors could visualize the location of small metastases that otherwise might go undetected. For military and law enforcement use, the material can be fashioned into ceramic discs that serve as a source of illumination that only those wearing night vision goggles can see. Similarly, the material can be turned into a powder and mixed into a paint whose luminescence is only visible to a select few…

In a process that Pan likens to perfecting a recipe, he and postdoctoral researcher Feng Liu and doctoral student Yi-Ying Lu spent three years developing the material. Initial versions emitted light for minutes, but through modifications to the chemical ingredients and the preparation—just the right amounts of sintering temperature and time—they were able to increase the afterglow from minutes to days and, ultimately, weeks.

“Even now, we don’t think we’ve found the best compound,” Pan said. “We will continuously tune the parameters so that we may find a much better one.”

The researchers spent an additional year testing the material—indoors and out, as well as on sunny days, cloudy days and rainy days—to prove its versatility. They placed it in freshwater, saltwater and even a corrosive bleach solution for three months and found no decrease in performance.

In addition to exploring biomedical applications, Pan’s team aims to use it to collect, store and convert solar energy. “This material has an extraordinary ability to capture and store energy,” Pan said, “so this means that it is a good candidate for making solar cells significantly more efficient.”

Very cool. It sounds like the kind of thing very clever people will find very clever things to do with. 

This material is phosphorescent, which basically means that it emits light like this: photons of light (ex. from the sun) hit electrons in the material. The electrons absorb that energy (generally one electron can absorb one photon) and as a result orbit farther from their atom’s nucleus, better resisting the positive pull of the protons. Eventually the electrons drop back to a less-energetic state that’s closer to the nucleus, and in the process emit their energy back as a photon. This photon is less energetic than the one they first absorbed, so where the sun’s photon was in the visible light range, the emitted photon is, at least in this case, in the near-infrared range.

If all of this happens in one rapid step then it’s called fluorescence, but if the energized electrons take a detour and take a while to emit a photon, it’s called phosphorescence. This is also what happens in fluorescent lightbulbs: electricity causes mercury in the bulbs to emit ultraviolet light, which is more energetic than visible light. This light is absorbed by fluorescent material in the bulbs, then emitted as visible light. In contrast, incandescent lightbulbs emit light because the filament wire inside is heated to a high temperature, causing it to glow. 

Yes, there are awesome things happening in your lightbulbs. Thanks science! Keep in mind though that mercury is toxic, so remember to take your CFLs to the appropriate recycling center instead of trashing them.

Creating Light From a Vacuum

Quantum theory predicts that in a vacuum, virtual particles are constantly being created in pairs and then quickly destroying each other. Up until now, outside of theory there hasn’t been any proof that they actually exist. Now, researchers have managed to make some of these particles materialize: by giving energy to virtual photons, they created “real”, measurable photons. Did they say “Let there be light!” as they did it? Let’s just pretend so. 

From ScienceDaily:

Chalmers scientist, Christopher Wilson and his co-workers have succeeded in getting photons to leave their virtual state and become real photons, i.e. measurable light. The physicist Moore predicted way back in 1970 that this should happen if the virtual photons are allowed to bounce off a mirror that is moving at a speed that is almost as high as the speed of light. The phenomenon, known as the dynamical Casimir effect, has now been observed for the first time in a brilliant experiment conducted by the Chalmers scientists.

“Since it’s not possible to get a mirror to move fast enough, we’ve developed another method for achieving the same effect,” explains Per Delsing, Professor of Experimental Physics at Chalmers…

The “mirror” consists of a quantum electronic component referred to as a SQUID (Superconducting quantum interference device), which is extremely sensitive to magnetic fields. By changing the direction of the magnetic field several billions of times a second the scientists were able to make the “mirror” vibrate at a speed of up to 25 percent of the speed of light.

“The result was that photons appeared in pairs from the vacuum, which we were able to measure in the form of microwave radiation,” says Per Delsing. “We were also able to establish that the radiation had precisely the same properties that quantum theory says it should have when photons appear in pairs in this way.”

What happens during the experiment is that the “mirror” transfers some of its kinetic energy to virtual photons, which helps them to materialise. According to quantum mechanics, there are many different types of virtual particles in vacuum, as mentioned earlier. Göran Johansson, Associate Professor of Theoretical Physics, explains that the reason why photons appear in the experiment is that they lack mass.

“Relatively little energy is therefore required in order to excite them out of their virtual state. In principle, one could also create other particles from vacuum, such as electrons or protons, but that would require a lot more energy.”

That’s crazy. What’s the wear and tear like on something vibrating at 25% the speed of light? It’s unimaginable. Whoever engineered that must’ve had an incredibly difficult time.

I was torn about posting this article since on the one hand it sounds awesome, but on the other hand it’s definitely over my head, so I can’t exactly help break it down for you any more than they already did. Anyway, it’s clear at least that this is a very cool experiment and very big news for physics, so let’s bask in this moment of awesome. Are you basking? Bask!

The World’s Lightest Material

Via PhysOrg: Researchers have created a material that’s about 100 times as light as styrofoam. 99.99% of it is composed of air, and the other 0.01% is composed very, very carefully.

“The trick is to fabricate a lattice of interconnected hollow tubes with a wall thickness 1,000 times thinner than a human hair,” said lead author Dr. Tobias Schaedler of HRL.

The material’s architecture allows unprecedented mechanical behavior for a metal, including complete recovery from compression exceeding 50 percent strain and extraordinarily high energy absorption.

“Materials actually get stronger as the dimensions are reduced to the nanoscale,” explained UCI mechanical and aerospace engineer Lorenzo Valdevit, UCI’s principal investigator on the project. “Combine this with the possibility of tailoring the architecture of the micro-lattice and you have a unique cellular material.”

Developed for the Defense Advanced Research Projects Agency, the novel material could be used for battery electrodes and acoustic, vibration or shock energy absorption.

This is very interesting. I’m curious about the ratio of lightness to energy absorption (which they pin at “extraordinarily high”) – simplistically, how proportionally strong is it? If you could make armour that weighed as much as a shirt but absorbed a bullet impact, well, that’d be just dandy. However, it seems like future experiments and applications would be limited by the difficulty of creating this material – mass-producing objects with specific features on the nanometre scale is not yet an easy task. The cost, of course, goes without saying. 

So what does that mean? What does it always mean? We wait and see! In 10 years I’ll want my Macbook 99.99% Air. 

Material Marvels with Ainissa Ramirez

Yale University has a new video series on its YouTube channel by Dr. Ainissa Ramirez explaining some of the materials used in modern engineering. Her first video, below, is on ceramics used in space shuttles and how they allow space shuttles to survive the incredible heat of atmospheric reentry. The videos are very short and accessible, although I’d like if they had a bit more details.

Her videos don’t have their own channel, unfortunately, but you can easily find them by searching for Material Marvels; there are four so far. I found these videos via the USA Science & Engineering Festival blog at Science Blogs.

An Explosive Material Based on Nanoparticles and DNA

Researchers have created an explosive composite material using nanoparticles and DNA. Aluminum and copper oxide put together are known to produce energy, but now by using nanoparticles of them their surface area can be increased, and by using DNA to link them together they can be made to self-assemble. DNA exists in organisms in two complementary strands tightly stuck together; these researchers took advantage of this by grafting individual DNA strands onto nanoparticles, mixing them up and letting the complementary DNA strands stick together.

From PhysOrg:

As a result, the complementary strands on each type of nanoparticle bind, turning the original aluminium and copper oxide powder into a compact, solid material which spontaneously ignites when heated to 410 °C (one of the lowest spontaneous ignition temperatures hitherto described in the literature).

If I’m not mistaken, spontaneous ignition here just means that it begins burning (combustion) without being “lit” by a flame or a spark. 

In addition to its low ignition temperature, this composite also offers the advantage of having a high energy density, similar to nitroglycerine: for the same quantity of material, it produces considerably more heat than aluminium and copper oxide taken separately, where a significant part of the energy is not released. In contrast, by using nanoparticles, with their large active surfaces, the researchers were able to approach the maximum theoretical energy for this exothermic chemical reaction.

The high energy density of this composite makes it an ideal fuel for nanosatellites, which weigh a handful of kilograms and are increasingly used. Such satellites are too light to be equipped with a conventional propulsion system once in orbit. However, a few hundred grams of this composite would give them sufficient energy to adjust their trajectory and orientation.

The composite could also have a host of terrestrial applications: ignitors for gas in internal combustion engines or for fuel in aircraft and rocket nozzles, miniature detonators, on-site welding tools, etc. Once its heat is turned into electrical energy, the composite could also be used as a back-up source for microsystems (such as pollution detectors scattered through the environment).

This article really caught my attention due, of course, to their use of DNA as a sort of glue. While the article explains why DNA works, and it seems like using DNA to bind nanoparticles is not a new idea, unfortunately it doesn’t explain why DNA is the best choice in this particular case. Double-stranded DNA normally comes apart at temperatures way below 410°C, which seems like it would be relevant here. 

In trying to find another article to explain the DNA thing, I found the one I just linked above (and here) about using DNA to form crystal lattices out of nanoparticles; you should check it out. Maybe this line of research will open up nanoparticles for wider use and greater self-assembly, which would probably be pretty revolutionary for all of us. 

Big Science and a Big Laser

Scientific research is generally rather expensive and requires specialized equipment and real estate, but some projects are bigger than others. Physics World has a pdf of a supplement to their magazine describing a few giant-sized physics facilities currently working (like the LHC at CERN) or in the works; it’s pretty interesting to look over and see the huge ambition at play, and the frontiers of science. 

One of the proposed projects, the Extreme Light Infrastructure Ultra-High Field Facility, is the subject of a Telegraph article today. It’s going to include the most powerful laser in the world by orders of magnitude, strong enough to tear apart the virtual particles that are theorized to appear and disappear in a vacuum, and thus be able to learn more about them.

From the Telegraph:

Contrary to popular belief, a vacuum is not devoid of material but in fact fizzles with tiny mysterious particles that pop in and out of existence, but at speeds so fast that no one has been able to prove they exist.

The Extreme Light Infrastructure Ultra-High Field Facility would produce a laser so intense that scientists say it would allow them to reveal these particles for the first time by pulling this vacuum “fabric” apart.

They also believe it could even allow them to prove whether extra-dimensions exist.

“This laser will be 200 times more powerful than the most powerful lasers that currently exist,” said Professor John Collier, a scientific leader for the ELI project and director of the Central Laser Facility at the Rutherford Appleton Laboratory in Didcot, Oxfordshire…

The ELI Ultra-High Field laser is due to be complete by the end of the decade and will cost an estimated £1 billion. Although the location for the facility will not be decided until next year, the UK is among several European countries in the running to host it…

The Ultra-High Field laser will be made up of 10 beams, each twice as powerful as the prototype lasers, allowing it to produce 200 petawatts of power – more than 100,000 times the power of the world’s combined electricity production – for less than a trillionth of a second…

It will cause the mysterious particles of matter and antimatter thought to make up a vacuum to be pulled apart, allowing scientists to detect the tiny electrical charges they produce.

These “ghost particles”, as they are known, normally annihilate one another as soon as they appear, but by using the laser to pull them apart, physicists believe they will be able to detect them.

Cool. It’s funny to think that the solution to the most subtle universal mysteries are solved by building giant crazy lasers and shooting stuff – it sounds like a solution from the mind of a 12-year-old boy. Or look at supercolliders like the LHC, where the solution instead is to smash particles together really really hard. Then again, those are descriptions tailored for mass consumption, so they leave out the 99.99% of the work that’s not quite so exciting – but still, at least parts of it are pretty exciting. 

If you looked at the supplement about “big science” from Physics World, you may have noticed that all of the projects they discuss are mainly or entirely European, which is kind of disappointing. It should be clear why science can be damn expensive, but if our continent doesn’t step its game up it looks like it’s going to fall behind, at least in this realm.

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