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Theoretized 80 years ago was Breit-Wheeler pair production in which two photons result in an electron-positron pair (via a virtual electron). It is a relatively simple Feynmann diagram, but the problem is/was how to produce in practice a high energy photon-photon collider... The collider experiment that the scientists have proposed involves two key steps. First, the scientists would use an extremely powerful high-intensity laser to speed up electrons to just below the speed of light. They would then fire these electrons into a slab of gold to create a beam of photons a billion times more energetic than visible light. The next stage of the experiment involves a tiny gold can called a hohlraum (German for 'empty room'). Scientists would fire a high-energy laser at the inner surface of this gold can, to create a thermal radiation field, generating light similar to the light emitted by stars. They would then direct the photon beam from the first stage of the experiment through the centre of the can, causing the photons from the two sources to collide and form electrons and positrons. It would then be possible to detect the formation of the electrons and positrons when they exited the can. Now this is a good experiment... :)

True, but isnt it E2=(pc)^2 + (m0c^2)^2 such that for photons E\propto{pc} and for mass E\propto{mc^2}. I agree it will take a lot of energy, but this assumes that that wont be the problem at least. The question therefore is whether the mass flow of the photon rocket (fuel consumed to create photons, eg fission/fusion) is higher/lower than the mass flow for e-p creation. You are probably right that the low e-p cross-section will favour direct use of photons to create low thrust for long periods of time, but with significant power available the ISP might be higher for e-p pair creation.

In essence the equation tells you that for photons with zero rest mass m0 all the energy will be converted to momentum of the particles. If you want to accelerate e-p then you first spend part of the energy on creating them (~511 keV each) and you can only use the remaining energy to accelerate them. In this case the equation gives you a lower particle momentum which leads to lower thrust (even when assuming 100% acceleration efficiency). ISP is a tricky concept in this case because there are different definitions which clash in the relativistic context (due to the concept of mass flow). R. Tinder gets to a I_SP = c (speed of light) for a photon rocket (using the relativistic mass of the photons) which is the maximum possible relativistic I_SP: http://goo.gl/Zz5gyC .

While my attitude to articles about interstellar travel is generally sceptical, this one seems to raise quite an interesting point... Physicists?

Also, remember never to dereference null pointers.

True, it's almost like installing accelerometers upside down...

The effect of gravity on virtual electron-positron pairs as they propagate through space could lead to a violation of Einstein's equivalence principle, according to calculations by James Franson at the University of Maryland. While the effect would be too tiny to be measured directly using current experimental techniques, it could explain a puzzling anomaly observed during the famous SN1987 supernova of 1987.

What would happen if you tried to hit a baseball pitched at 90% the speed of light? --not sure it is correct, but it would be a lot of fun :)

UK researchers say they have achieved data transmission speeds of 10Gbit/s via "li-fi" - wireless internet connectivity using light. The researchers used a micro-LED light bulb to transmit 3.5Gbit/s via each of the three primary colours - red, green, blue - that make up white light. This means over 10Gbit/s is possible.

:-)

Well, it's not yet confirmed... That error would be worse than the magnetic moment of the muon about 10 years ago. There, it was "at least" a conflict of conventions used in the computer codes!

In a statement based on an earlier press release from the OPERA collaboration, CERN said two possible "effects" may have influenced the anomalous measurements. One of them, due to a possible faulty connection between the fiber-optic cable bringing the GPS signals to OPERA and the detector's master clock, would have caused the experiment to underestimate the neutrinos' flight time, as described in the original story. The other effect concerns an oscillator, part of OPERA's particle detector that gives its readings time stamps synchronized to GPS signals. Researchers think correcting for an error in this device would actually increase the anomaly in neutrino velocity, making the particles even speedier than the earlier measurements seemed to show. CERN's statement says OPERA scientists are studying the "potential extent of these two effects" but doesn't indicate which source of error (if either) is likely to outweigh the other. However, Lucia Votano, director of the Gran Sasso laboratory, says the "main suspicion" focuses on the optical-fiber connection. She adds that OPERA researchers deserve credit for "having tenaciously followed this particular evidence via checks completed in the last few days." The two effects will get a new round of tests in May, when the two labs are scheduled to make velocity measurements with short-pulsed beams designed to give readings much more precise than scientists have achieved so far.

smart!

We propose a way of implementing an event cloaking device without the use of metamaterials. Rather than slowing down and speeding up light, we manipulate an obscurity gap by diverting the light through paths of appropriate length with an arrangement of switchable transreflective mirrors.

wonder if we can use that to power a moon base .... or on-board a SBSP satellite

I am not the physicist but I thought it might be interesting, from a space security point-of-view

Yes it seems really interesting and opens new possibilities. However this technology review article is not very good and the guy uses terms which have a precise meaning (like teleportation), which is different from the word we know... Quantum teleportation is what we use for designing quantum computers, but we are quite far from any practical applications. This energy teleportation will allow new scheme involving energy (if it is experimentally confirmed) which is very nice. However it seems this occurs in an entangled many-body system, which the only macroscopic one I know is a bose-eintein condensate (BEC). So it would mean infuse energy in the BEC by doing a measurement on one of the atom and extract it few millimeters away by doing a measurement on another atom. very far from any long distance power transmission...

essentially they made an experiment that does not prove or disprove anything -big deal-... what is the scientific value of "strongly disfavour"??? I also like the sentence "most models do not have exact predictions for the energy scale associated with this violation of Lorentz invariance" ... but if this is true WHAT IS THE POINT OF THE EXPERIMENT!!!! God, physics is in trouble ....

hum, null result experiments are not useless !!! there is always the hope of finding "something wrong", which would lead to a great discovery. For the state of theoretical physics (the "no exact predictions" quote), i totally agree that physics is in trouble... That's what happen when physicists don't care anymore about experiments...! All you can do now is drawing "nice"graph with upper bounds on some parameters of an all tunable weird theory !

Just getting a particle up to near the speed of light isn't good enough for today's physics. To properly unravel the fundamentals of the universe, particles have to be smashed together with enormous force. And two Stanford researchers have just devised a laser-based method that imparts ten times the power of traditional methods at a fraction of the cost.

I like this one "The kind of idle pastime that might amuse physicists is to imagine drafting Einstein's grant applications in 1905. "I propose to investigate the idea that light travels in little bits," one might say. "I will explore the possibility that time slows down as things speed up," goes another. Imagine what comments these would have elicited from reviewers for the German Science Funding Agency, had such a thing existed. Instead, Einstein just did the work anyway while drawing his wages as a technical expert third-class at the Bern patent office. And that is how he invented quantum physics and relativity." There is an even more pointer example of the Prussian academy of sciences reviewing the Dr. application of Hertz ...

Shocking. What is federal research funding for? No, wrong question. Instead maybe: What is federally funded review for?

Sante, Luzi have a look at this???!!!

Leo, you mean that they measured 3 years? That's not a point to criticize: since the only interaction of neutrinos with matter is the Weak Interaction (which is indeed very, very weak), it is extremely hard to get a reasonable statistic. By the same reason, it's essentially impossible to shield the experiment from the background. And this background (solar neutrinos, cosmic radiation neutrinos) is huge.

for sure a result to be taken seriously. It makes a buzz in my lab... but always be cautious with this kind of declaration, that hugely violates all physics we know and even most of the reasonable alternative theories... Remember the Pionneer anomaly for which it took almost ten years to set up that finally its a thermal effect.

Kip Thorne looks into the black hole he helped create and thinks, "Why, of course. That's what it would do." This particular black hole is a simulation of unprecedented accuracy. It appears to spin at nearly the speed of light, dragging bits of the universe along with it.

title is misleading, but the paper is interesting (and as obvious as ignored)

sure was a fun assignment ...

apart from the doppler shift the perspective also changes when you look at objects while traveling close to the speed of light: http://www.spacetimetravel.org/tompkins/node1.html