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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 .

By focusing our defense resources into a space-superiority platform and weapon system such as a Death Star, the government can spur job creation in the fields of construction, engineering, space exploration, and more, and strengthen our national defense.

Bad news from this frontier: https://petitions.whitehouse.gov/response/isnt-petition-response-youre-looking As the Americans are not going for it, it might be a good opportunity for Europeans to make a real difference in space.

Merkel seems anyway a bit short of ideas ...

what an interesting personality ... very symathetic Peter Higgs, the British physicist who gave his name to the Higgs boson, believes no university would employ him in today's academic system because he would not be considered "productive" enough.

The emeritus professor at Edinburgh University, who says he has never sent an email, browsed the internet or even made a mobile phone call, published fewer than 10 papers after his groundbreaking work, which identified the mechanism by which subatomic material acquires mass, was published in 1964.

He doubts a similar breakthrough could be achieved in today's academic culture, because of the expectations on academics to collaborate and keep churning out papers. He said: "It's difficult to imagine how I would ever have enough peace and quiet in the present sort of climate to do what I did in 1964."

Speaking to the Guardian en route to Stockholm to receive the 2013 Nobel prize for science, Higgs, 84, said he would almost certainly have been sacked had he not been nominated for the Nobel in 1980.

Edinburgh University's authorities then took the view, he later learned, that he "might get a Nobel prize - and if he doesn't we can always get rid of him".

Higgs said he became "an embarrassment to the department when they did research assessment exercises". A message would go around the department saying: "Please give a list of your recent publications." Higgs said: "I would send back a statement: 'None.' "

By the time he retired in 1996, he was uncomfortable with the new academic culture. "After I retired it was quite a long time before I went back to my department. I thought I was well out of it. It wasn't my way of doing things any more. Today I wouldn't get an academic job. It's as simple as that. I don't think I would be regarded as productive enough."

Higgs revealed that his career had also been jeopardised by his disagreements in the 1960s and 7

And the follow up by Nobel prize winner Randy Schekman http://www.theguardian.com/science/2013/dec/09/nobel-winner-boycott-science-journals

interesting one - Luzi will like it :-)

Interesting toolkit/resources page for actual creation of soft robots.

Pretty amazing Celestial Mechanics effects that could potentially help creation of life...

First time I heard about this relevant project. In brief: The mission of the Scientific and Technical Information Exchange (STIX) font creation project is the preparation of a comprehensive set of fonts that serve the scientific and engineering community

Let's all start up some crazy space companies together: harvest hydrogen on Jupiter, trap black holes as unlimited energy supplies, use high temperatures close to the sun to bake bread! Apparently it is really easy to do just about anything and Deep Space Industries is really good at it. Plus: in their video they show Mars One concepts while referring to ESA and NASA.

hmm aside from the technological feasibility, their approach still should be taken as an example, and deserve a little support. By tackling such difficult problems, they will devise innovative stuffs. Plus, even if this doom-to-fail endeavour may still seem you useless, it creates jobs and make people think... it is already a positive! Final word: how is that different from what Planetary Resources plan to do? It is founded by a bunch of so-called "nuts" ... (http://www.planetaryresources.com/team/) ! a little thought: "We must never be afraid to go too far, for success lies just beyond" - Proust

I don't think that this proposal is very different from the one by Planetary Resources. My scepticism is rooted in the fact that - at least to my knowledge - fully autonomous mining technology has not even been demonstrated on Earth. I am sure that their proposition is in principle (technically) feasible but at the same time I do not believe that a privately funded company will find enough people to finance a multi-billion dollar R&D project that may or may not lead to an economically sensible outcome, i.e. generate profit (not income - you have to pay back the R&D cost first) within the next 25 years. And on that timescale anything can happen - for all we know we will all be slaves to the singularity by the time they start mining. I do think that people who tackle difficult problems deserve support - and lots of it. It seems however that up till now they have only tackled making a promotional video... About job creation (sorry for the sarcasm): if usefulness is not so important my proposal would be to give shovels to two people - person A digs a hole and person B fills up the same hole at the same time. The good thing about this is that you can increase the number of jobs created simply by handing out more shovels.

good luck with this....

In 1996 Sokal hoaxed sociologists with his famous nonsense text on political implications of quantum gravity. Can one play a similar game with "researchers" on Boltzmann brains, multiverses, string landscapes or similar? I doubt, this is just reality satire that can't be topped.

Poor Boltzmann ...

A long read but very interesting and well written.

PS: Does this quote from the article not sound a lot like Inception? 'In any given situation, the brain will retrieve old memories to inform an organism's behavior. If the memory is relevant to the situation, the organism can act on the information; if it is not relevant, then the organism can learn from the situation and create a new memory. With reconsolidation, researchers argued, there seemed to be a brief window in between the retrieval of an old memory and the creation of a new memory in which the old memory is vulnerable to manipulation.'

High energy gamma rays are shown to be bent slightly by specialized lenses. The effect is likely due to pair-creation close to the atomic nuclei in the material.

Marc Stephens "ProtoSpace embodies agility," says Vincent Loubière. "We can move from concept to demonstrator quickly." The 'agility' method is modelled on proven successes in the computer industry but the ProtoSpace team also works with automotive and communications blue-chips, as well as start-ups whose creations could have applications in aerospace. Airbus's ACT :)

Atmospheric rivers, short-lived wind tunnels are created in the upper troposphere and carry vast amounts of water. They 'fuel' from the tropical Pacific reservoir and cause heavy precipitation events and even floods to mid-latitude land, as soon as they encounter the Sierra mountains. The new finding is that two inter-hemispheric climatic oscillation modes allow for their creation, as soon as they are found in a certain phase combination.

Could we conceivably control these like we're thinking to do with taifuns? :)) Would be geoengineering at its finest

another Zeilinger experiment ...

And what if the freedom-of-choice is corrupted due to yet another hidden variable in past lightcone of the whole experiment that triggers Alice and Bob's choice as well as the pair creation? Then we can design yet another experiment that will have yet another loophole. I guess this is experimentally interesting work, but the introduction rather reads like an article from the "Institut für Grenzgebiete der Psychologie und Psychohygiene"...

Withdrawing a paper 52 years after publication. Brave guy.

:-) a weekend post ...

smells like ariadnet for ariadna papers and researchers

I am on mendeley now and I like it so far ! You can check my page on http://www.mendeley.com/profiles/pacome-delva/

am also on Medelay since some time - think that Tobias has showed it to me. Nice but did not actually use it yet really ....

Astronomers have observed up to three newborn planets evolving from a disk of gas and dust particles circling a distant Sun-like star. While 1,900 planets have been discovered outside our solar system, these are the first to be seen that are still forming.

"Here we report the development of the computer algorithm Melvin which is able to find new experimental implementations for the creation and manipulation of complex quantum states." Published in Physical Review Letters. Researchers target future use more artificial intelligence algorithms, such as reinforcement learning techniques.