Monthly Archives: October 2012

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An entangled kitten.

(Admittedly, the cute kitten was added by my editor.)

Albert Einstein described quantum entanglement in 1935, along with colleagues Boris Podolsky and Nathan Rosen, and used it as an argument against quantum mechanics. Entanglement is the phenomenon by which two widely separated systems act as a single system, due to interactions in the past; a measurement on one system reveals the outcome of a similar experiment performed on the other, no matter how far they are separated in space. Since the 1980s, a wide variety of experiments have showed (contra Einstein) that entanglement is a real feature of quantum physics, though no information usable by an experimenter can be extracted—which preserves relativity and causality (that is, future events can’t cause past events).

A new theorem has showed even more that entanglement truly seems to be the result of separated systems actually being parts of a single unbroken system, however you end up interpreting that (and I don’t want to get into that today!).

However, one possible explanation for entanglement would allow for a faster-than-light exchange from one particle to the other. Odd as it might seem, this still doesn’t violate relativity, since the only thing exchanged is the internal quantum state—no external information is passed.

But a new analysis by J-D. Bancal, S. Pironio, A. Acín, Y-C. Liang, V. Scarani, and N. Gisin shows that any such explanation would inevitably open the door to faster-than-light communication. In other words, quantum entanglement cannot involve the passage of information—even hidden, internal information, inaccessible to experiment—at any velocity, without also allowing for other types of interactions that violate relativity. [Read more…]

Quantum entanglement, locality, and a cute kitten

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Pulsars are rapidly rotating neutron stars—the dense remnants of stars much more massive than the Sun. Some pulsars are in binary systems, and when they feed off their companion star, their rotation rate can increase until they’re spinning hundreds of times per second. Known as millisecond pulsars, these are often also strong emitters of gamma rays, but no one had identified one through gamma ray observation alone…until now.

Astronomers have now used the Fermi Gamma-Ray Space Telescope to identify a “black widow” pulsar that’s stripping mass off a close companion star while simultaneously evaporating it by emitting intense radiation. It’s having these dramatic effects because the pulsar and its companion orbit each other so closely that they complete an orbit once every 93 minutes, making this the tightest black widow binary yet discovered. [Read more….]

Pulsar eats companion star, burps gamma rays

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(Not fully alliterative, but it’s the best I can do after driving 6 hours today.)

The halos of galaxies are best known for harboring dark matter, but they also contain stars. Only a tiny fraction of the total stars in a galaxy are in the halo, so usually they’re hard to spot, but astronomers are realizing they can contribute a significant amount to the total light profile. In particular, a group of researchers using the Spitzer infrared space telescope has determined that much of the infrared haze in the sky is due to galaxies that formed in the early Universe—including their halo stars.

However, the earliest stars and galaxies should contribute to the total infrared glow of the Universe, known as the cosmic near-infrared background (CNIB). (“Near-infrared” refers to wavelengths closest to visible light in the electromagnetic spectrum; in this case, the study was in the 1 to 5 micron range.) Much of the haze in the CNIB is from the Milky Way and known galaxies, but a significant portion is not associated with any obvious sources. Astronomers have postulated it must originate in either to dwarf galaxies (which are too small to be seen at significant distances) or faint galaxies from the early Universe. [Read more….]

Halo star haze helps hidden galaxies look huge

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The business end of a Rocketdyne F-1 rocket engine, used in the first stage of the Saturn V rockets. Five of these engines were used to launch the Apollo missions into space. Note the picnic tables at left for scale comparison.

For the next two weeks, I am on the move, traveling to various observatories in the American south and southwest, as part of the research for my book-in-progress Back Roads, Dark Skies: A Cosmological Journey. This morning, I will be visiting the Laser Interferometer Gravitational-wave Observatory (LIGO) near Livingston, Louisiana, before heading west to other observatories in Texas, New Mexico, and Arizona. My full itinerary is over at Galileo’s Pendulum:

Being a travel book, though, I am also seeking a new way to see through travel and exploration. Cosmology is a very familiar field to me, but often the person closest to a subject is the worst to try to explain it to a lay audience. By going to particle physics labs and astronomical observatories, I am learning to see my own discipline in a new way, in hopes that it will help me bring it to my readers. As you can tell, this book is different from most cosmology books (A Brief History of Time is perhaps the best example), where the focus is on highly speculative ideas and Big Theories. While theory will always inform the research I discuss—and, being a theorist myself, I can’t help but discuss theory—the primary emphasis of Back Roads, Dark Skies is on experiment and observation. Without these things, theory is nothing but the ramblings of creative people, unconnected to reality. [Read more…]

While the scientific part of the agenda begins today, I haven’t been idly driving without keeping an eye out for interesting things. To wit: yesterday, I saw a wild alligator and one of the engines from the Saturn V rockets, which were used to launch the Apollo missions and the Skylab space station.

The Bowler Hat is on the move

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(In honor of Terry Pratchett, I almost wrote that “Twisted light? Onna chip?”, but that would probably confuse 90% of my readers.)

Light is used to carry data, but mostly we don’t use the properties of the photons themselves to convey information. Quantum communication, among other applications, could use the state of the photon to encode data. In particular, the orbital angular momentum (OAM) state of a photon, where the photon describes a helix as it travels, can carry a lot of bits. Now researchers have fabricated a silicon chip to make twisted light.

Photons possess a number of quantum properties that can be used to encode information. You can think of photon polarization as like the rotation of a planet on its axis. In this view, the helical shape of the light wave—known as its orbital angular momentum (OAM)—is akin to the planet’s orbit around the Sun. These properties are independent of each other, and of the wavelength of light, so they can be manipulated separately. Whereas polarization occurs as a combination of two possible orientations, the OAM theoretically can have infinite values, though in practice far fewer states are available. Nevertheless, exploiting OAM greatly expands the potentially exploitable quantum states of photons we could put to use.

The researchers created helical OAM states using a ring-shaped chamber fabricated from silicon and mounted on a chip. [Read more….]

Twisted light on a silicon chip

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(Yes, I’m inundating you all with writing. It’s a busy week, and I still have a few more things forthcoming to share with you.)

Supernova remnant SNR 1987a, what’s left after a bright blue star exploded in the Large Magellanic Cloud. [Credit: NASA/ESA/P. Challis and R. Kirshner (Harvard-Smithsonian Center for Astrophysics]

Supernova 1987a was the death of a massive blue star in the Large Magellanic Cloud, one of the satellite galaxies of our Milky Way. Because of its relative proximity and occurrence during the era of modern astronomy, the supernova remnant SNR 1987a (as it is known) is one of the best-studied of all. As a result, it provides a good testbed for the theory of star explosions. A new X-ray observation has measured the amount of radioactive titaniumcreated in the remnant, and showed it’s enough to power a lot of the light emission in the years following the supernova.

The decay of 44Ti produces high-energy X-ray photons at three distinct wavelengths. The researchers in the current study aimed the INTEGRAL (INTErnational Gamma-RAy Laboratory) satellite at SNR 1987a for about 4.5 million seconds (a total of over seven weeks) to obtain clear X-ray spectra. This process was complicated by the presence of a pulsar and a black hole binary system that, from our perspective, appear near SNR 1987a in the sky—these bodies also emit X-ray light. The astronomers identified the telltale spectral signature of titanium decay, and extrapolated from the number of photons (the flux) to determine the mass of the titanium before the decay process began. [Read more….]

Radioactive titanium powers a supernova afterglow

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Scanning electron micrograph of graphene. [Credit: Lawrence Berkeley National Laboratory]

In his science fiction novel The Diamond Age, Neal Stephenson describes a world filled with electronic paper, tiny flexible computers, and transparent displays. Graphene—a crystal comprised of a single layer of carbon atoms—is perhaps the most promising material to make that world real (though hopefully without the universal surveillance state and environmental collapse that are also part of the book). However, promises aren’t the same thing as practical technology, so it behooves us to take a critical look at what graphene can and can’t currently do.

…Nobel Laureate Konstantin Novoselov and colleagues have written a critical, yet optimistic, assessment of the state of graphene research and production.

As they point out, there is a big question that must be answered before widespread adoption of graphene technology is possible: are graphene’s advantages sufficient to use it in place of the materials we use in existing devices? The authors conclude that, to some extent, that’s the wrong question. Graphene’s biggest promise lies in novel applications, designed especially for the advantages that graphene offers. [Read more…]

Not quite ready for the Diamond Age

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Every exoplanet discovery seems to bring us closer to understanding the variety of planetary systems out there in our galaxy. The latest find is particularly exciting: an Earth-mass planet orbiting around Alpha Centauri B, one of three stars in the closest system to the Solar System. The planet isn’t very Earthlike in most respects, but it’s still an incredibly exciting discovery.

However, the discovery is still exciting for a number of reasons. First is the proximity of the star system to us: Alpha Centauri is 4.4 light years away, a tiny distance in cosmic terms. The stars Alpha Centauri A and B are some of the brightest in the sky in the Southern Hemisphere. (Sorry, fellow Northern Hemisphere-dwellers; we can’t see them from here.) We don’t have starship technology to travel there, but we could conceivably send a robotic probe that could arrive within my lifetime, and 4.4 years isn’t a terribly long time for data to travel back to Earth. No one has such a probe in the works yet, but the mere fact of discovery of a planet might encourage investment in that direction. [Read more…]

Alpha Centauri harbors an Earth-mass planet

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Ada Lovelace, 1815-1852 [Credit: Wikipedia]

For Ada Lovelace Day, I compiled a list of many of the best science writers I know:

Last year, I celebrated Emmy Noether, perhaps the greatest mathematician of the 20th century. This year (largely because I’m swamped with other work), I’m stealing a great idea from Ed Yong, and celebrating living writers who are my friends, colleagues, and influences. This list is in no particular order, isn’t anywhere close to complete, and has some overlap with Ed’s list. My main criteria are that these are writers I read regularly, so their interests mix with mine to some degree. (Writers marked with an asterisk* are people I have met in Real Life, whatever that signifies.) Leave your own favorites and influences in the comments! [Read more….]

Happy Ada Lovelace Day!

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Information in quantum physics is carried in a system’s quantum state, which is basically a list of all the important properties. An atom’s state, for example, contains the relative orientation of the nucleus and electrons, the energy levels the electrons occupy, and the like. Quantum computing manipulates these states in prescribed ways for calculation purposes, but to get the data from one place to another requires communication:

W. J. Munro, A. M. Stephens, S. J. Devitt, K. A. Harrison, and Kae Nemoto have designed a system where quantum bits (qubits) were transferred by individual photons, but interpreted using a special algorithm designed to contain a lot of redundancy and avoid data loss. Since the states of the transmitter and receiver were not entangled (or copied), they don’t need to remain coherent, obviating the need for quantum memory. The actual data transfer could take place over fiber optic cables, and the receiver could itself be used as a transmitter, forming a repeater for larger networks. [Read more….]

Quantum communication without entanglement