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Comment Re:Question for the Physicists. (Score 4, Interesting) 79

A permanent magnet is polarized by something called the exchange field. This is related to the Pauli exclusion principle and the Coulomb interaction and happens spontaneously. Energy is stored in the electronic state as kinetic, external and interaction (this includes the magnetic dipole field energy)

These two new magnets are unlikely to replace the current champion (neodymium-iron-boron), or be particularly useful as permanent magnets at all. The reason is that the researchers only calculated the moment and Curie temperature. A good permanent magnet should also have a high magnetic anisotropy energy (MAE) as well. The Heusler alloys are predominantly cubic and so have a very low MAE.

How do I know this? We just spent three years doing exactly the same thing: spending thousands of CPU hours trying to find a good magnet among the Heuslers. All to no avail.

Comment Ahead of his time (Score 4, Interesting) 187

He also wrote:

"Might not a bomb no bigger than an orange be found to possess a secret power to destroy a whole block of buildings -- nay, to concentrate the force of a thousand tons of cordite and blast a township at a stroke? Could not explosives even of the existing type be guided automatically in flying machines by wireless or other rays, without a human pilot, in ceaseless procession upon a hostile city, arsenal, camp or dockyard?"

in 1924.

Comment Re:Any idea how it works? (Score 5, Informative) 477

<quote>Now, does it work? No idea, frankly. I'm more inclined to believe the results of, you know, an actual test than someone who didn't do the test but insists it can't work in spite of the test....</quote>

It's difficult to convey to a non-physicist just how accurately and consistently quantum field theory describes nature. Physicists routinely make calculations which have lower uncertainly than the best experiments. For example the anomalous magnetic moment ( is in agreement with theory to ten significant figures.

Physicists tend to be fairly cautious describing results, but when it comes to basic theory at energies up to a few hundred GeV we are confident that we have *all* physical effects well and truly nailed. This doesn't mean that we can always solve the equations perfectly: quantum mechanics is hard, but the equations themselves are almost beyond reproach.

It's not undeserved hubris: it's trillions of independent experiments, billions of dollars and hundreds of thousands of man-years working on the theory by lots of very smart people. The theory, quantum field theory (QFT), is simple, consistent and universal. It describes everything we can see around us, with the exception of gravity.

If you ask an actual physicist what he or she thinks of the EM drive, they will overwhelmingly say that is is highly likely there is an unresolved source of error because violation of moment conservation has never been observed and is inconsistent with QFT.

Comment Re:Any idea how it works? (Score 5, Interesting) 477

IAATP working on quantum electrodynamics (QED) and other theories.

The fundamental problem with this experiment is that it appears to violate conservation of momentum. This violation is not something that can be discarded easily: it has been confirmed directly and indirectly in millions of experiments over decades.

Momentum conservation is also a cornerstone of quantum field theory (QFT) and it is a symmetry which survives quantization. The entire Standard Model (SM) is a momentum-conserving QFT. The SM has been confirmed to a high accuracy in particle accelerators for many years. Any violation of momentum conservation would have been quickly noticed. You cannot simply invoke 'quantum mechanics', 'zero point', 'vacuum fluctuations', etc. to explain excess thrust. Momentum conservation is fundamental, both classically and quantum mechanically.

So what about the EM drive results? There is a possibility that some new physics is at play, however it is vastly more likely that there is a systematic error which has not been eliminated. (If I had to guess I would imagine that because a large amount of RF energy is being pumped into large metal cavities, the apparatus is resting at the bottom of a standing wave potential.)

The way to finally confirm or refute this is to take the drive into space. In this case, it is almost certain that the net thrust would be equal to the momentum of the photon flux leaving the drive.

Comment Standardize one-time pads (Score 1) 210

Given the amount of data we can store on memory cards (now up to 512 GB), now would be a good time to standardize the one-time pad.

For example, Alice and Bob meet in person. They plug their credit-card-sized one-time pads into each other and exchange giga-Bytes of truely random numbers generated on-card. Then when Alice wishes to send Bob a message over an untrusted chanel (i.e. the internet), she adds a section of the random numbers to her message (modulo 256). Bob then decrypts with his matching set of numbers.

The used numbers are then deleted on both Alice and Bob's cards.

A single meeting between A & B would be enough to encrypt every text message they send for ever after. All that is needed is an international set of standards for doing this and the associated hardware. For example, you could take your OTPad to your bank and plug in into a socket and exchange random numbers, and use them for secure banking at home. No CA's required.

This is future-proof and unhackable (assuming A & B's computers are not compromised).

You could even exchange the random numbers over an untrusted chanel. Just make sure there's a huge number. If everyone does this, it would overwhelm the storage capacity of the NSA and friends.

Comment Re:Can't we clone them? (Score 5, Informative) 108

That's right: the RD-180 is based on the four chamber RD-170 which began development in the early 1970's.

These Soviet engines rocket were more efficient than their US counterparts. The reason is that they used an oxgen-rich preburner, as opposed to the US engines (including the space shuttle's) which were fuel rich.

Thus there was a flow of superheated oxygen passing through the preburner and then through the turbine to power the turbo pumps. It turned out that no existing steel could withstand this and so the engineers spent years finding a steel alloy which could. The US never did so, and went fuel-rich instead.

To clone this would take a lot of R&D into devloping these steels and learing to machine them. Although in the 1980's so-called 'superalloys' were developed which are not steel (nickel-cobalt for example) and could do the job. These are used in the extreme conditions of modern jet engines and also have to withstand superheated oxygen.

This is just one example of the problems involved in building and testing a cloned engine: it would take many years to get it into production. It's possible this information request is just to shake the Russians up a bit.

Comment Re:Q: Why Are Scientists Still Using FORTRAN in 20 (Score 5, Insightful) 634

My previous supervisor decided to fork our Fortran code for performing quantum mechanical calculations. We'd worked on it for more than half a decade and it was world-class.

He handed it over to a computer science graduate (i.e. a non-physicist) who really liked all the modern trends in CS. Now, five years later:

1. the tarball is an order of magnitude larger
2. the input files are now all impenetrable .xml
3. the code requires access to the outside (not possible on many superclusters)
4. he re-indented everything for no apparent reason
5. the variable names were changed, made into combined types and are much longer
6. as a result, the code is basically unreadable and nearly impossible to compare to the original formulae
7. code is duplicated all over the place
8. it now depends on unnecessary libraries (like the ones required to parse .xml), and it only compiles after a lot of work
9. it's about four times slower and crashes randomly
10. it generates wrong results in basic cases

To quote Linus Torvalds: "I've come to the conclusion that any programmer that would prefer the project to be in C++ over C is likely a programmer that I really *would* prefer to piss off, so that he doesn't come and screw up any project I'm involved with." ... and I feel the same way about CS graduates and Fortran. They have no idea about the physics or maths involved (which is the difficult part), so the do the only thing they know which is to 'modernize' everything, making it into an incomprehensible, ungodly mess.

Fortran, apart from being a brilliant language for numerical math, has the added benefit of keeping CS graduates at bay. I'd rather have a physicist who can't program, than a CS type who can.

(Apologies to any mathematically competent computer scientists out there)

Comment Re:Wrong interpretation of energy (Score 5, Informative) 135


This is the usual muddle up between energy and intensity.

There is no apparent upper limit to the energy of a photon. The galaxy Markarian 501 emits photons in the teraelectronvolt (TeV) range.

The question here is about intensity. The relativistic energy-moment dispersion, E^2=(mc^2)^2+(pc)^2, which applies to all on-shell particles, has a gap when m>0. This gap, which is about 1 MeV for electrons and positrons, can be overcome when the electric field (generated by a sufficient number of photons, irrespective of their energy) approaches the Schwinger limit of about 1.3 x 10^18 V/m. At this point, virtual electron-positron pairs can be created in abundance because the mass gap has been overcome, and electromagnetism then becomes non-linear. Pumping in more photons after this simply creates more virtual e-p pairs.

Hope that helps.

(IAAP working on this topic).

Comment Re:And what good would that have done? (Score 5, Insightful) 504

Quite agree.

Given that James Clapper was perfectly willing to lie to Congress, what would the NSA administration have done to a 29 year old system administrator, had he aired his views to them? He would have been sidelined, fired or arrested, that's what. And we would be none the wiser.

It is amusing that politicians will express the need for public discussion about NSA surveillance and then condemn Snowden in the next sentence. You can't have one without the other.

In my opinion, he is the definitive whistle-blower. He had only one way to reveal the NSA/GCHQ excesses and revealed them in the right way. Further, he gained nothing personally from all this: no money and he seems to dislike the attention. And spending a month in a Russian airport can't be much fun.

He has my gratitude and admiration, and I wish him well.

Comment Fortran works fine with MPI (Score 5, Informative) 157

...and has done for years.

We write a scientific code for solving quantum mechanics for solids and use both OpenMP and MPI in hybrid. Typically we run it on a few hundred processors across a cluster. A colleague extended our code to run on 260 000 cores sustaining 1.2 petaflops and won a supercomputer prize for this. All in Fortran -- and this is not unusual.

Fortran gets a lot of bad press, but when you have a set of highly complex equations that you have to codify, it's a good friend. The main reason is that (when well written) it's very easy to read. It also has lot's of libraries, it's damn fast, the numerics are great and the parallelism is all worked out. The bad press is largely due to the earlier versions of Fortran (66 and 77), which were limited and clunky.

In short, the MPI parallelism in Fortran90 is mature and used extensively for scientific codes.

Comment 1988 Toyota Olympic Ideas winner (Score 5, Informative) 104

This has already been turned into a personal vehicle some years ago. It won the 1988 Toyota Olympic Ideas competition and ran on perpetually spinning Chinese woks. The best link I can find is

Perhaps someone can find a better picture or video.

Comment Duplicitous encryption scheme (Score 1) 484

I had an idea for a duplicitous encryption scheme. Not sure if it's already been done.

It's very simple: you can use one of two keys A and B. If you use key A, then you get the plain-text you wish to keep private. If key B is used, then you get some diversionary data (something innocuous, but for which encryption is plausible). The encrypted files would be larger, but the scheme could be made so that you would never know if there are two sets of data or only one.

Thus if you encounter nosey border guards, you type in key B and show them your soft-core pron collection ("I didn't want the wife to see it, Officer...")

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