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Comment: My weird-o-meter needs recalibrating... (Score 1) 347

by Richard Kirk (#47313901) Attached to: Evidence of a Correction To the Speed of Light

This is a story about the speed of light being not what we thought it was, and involving general relativity, neutrinos, and its one data point from a unique astronomical event. Oh, yeaah, riiight. And yet, it is clearly explained, and stands a good chance of being right. I am definitely going to have my weird-o-meter recalibrated.

The speed of light is the same as it always was. Any given photon may, extremely rarely, split into an electron-positron pair, and then recombine. The electron and the positron are not travelling at the speed of light, so this event will stick in a small delay. If you measure the speed of light over most human experimental lengths, this event will be very rare - so the very occasional photon will show a tiny delay. If your light travels over such vast distances that the photon may have experienced so many of these delays that it spent whole hours as electrons and positrons.

Each photon will have a random number of these delay events, so you might expect the light pulse to get blurred out a bit by this randomness. There will be a slight blurring, but because the number of events is so huge, the fractional deviation from the mean is pretty tiny.

Cute, and neat. Some posters still try and argue for gravitational viscosity, or for faster-than-light neutrinos, or that this is a failure of science and only philosophers can help us now. Ho-hum. Too little fog, too late, chaps. Better luck with the next one, eh?

Comment: Re:Next in pipeline: Honking Humugous Telescope (Score 1) 76

The 'OWL' was the first telescope in this series of names as far as I know. I think all the others since have been given 'OWL' like names.

It's a bit unfair to say the 'OWL' project was cancelled because it was really only a feasibility study, and back in the 1980's rather a bonkers one at that. When people started working with computer-controlled segmented mirrors, it because clear that you could make a huge mirror from almost flat segments of glass. So the next step was to see whether you could make a moving and pointing telescope the size of the Great Pyramid. Over they years that 'OWL' wasn't built, the design was improved and it became clear that it was practical to make telescopes between 20m and 100m. Much bigger than 100m, and you probably have to go into space, to avoid the problems of weight, and atmosphere.

One day they may build the 'OWL' on the Antarctica dome, and you will have the finest seeing of all earth-bound telescopes, ever, and there is no point building any others unless you want to look North. The 'ELT' is a nice compromise: it's in Chile and not down by the South Pole which can be as hard to get to as space, and it's bloody big but it leaves something for our kids to do. Yay.

Comment: Re:What am I missing here? (Score 2) 223

Empty space isn't that empty. You can get virtual pairs of electrons and positrons appearing and disappearing. They pop into existence because they can, even in empty space, but the have negative energy and a virtual wavelength, so they are almost bound to re-coalesce, and the energy of their recombination will exactly equal the energy of their creation, so they pay back all the energy they 'borrowed' and disappear without trace. However, if a photon turns up at this critical moment and pumps in the energy, then they can get permanently separated. Needless to say, this is pretty rare for single photons or we would not be able to see distant galaxies. We need monster photon energy densities, hence the hohlraum (I used to work on these ages ago).

You can also measure a tiny force between two plates in a vacuum due to these virtual particles. This is called the Casmir effect or the Casmir-Polder force. See... for example. So they are real. Well, real-ish.

This is not the same as Compton scattering. That also makes electron-positron pairs from photons but it also requires some mass to be around. This is the dominant absorbtion mode above about 1.5 MeV. So, I can see how they might get a tiny bit of straight pair production in their hohlraum, but they will also have some high-Z gold plasma giving you lots of conventional Compton scattering, which will look pretty similar. I guess they have a plan for that.

Here's a fun site...

Comment: Re:Fragile (Score 1) 33

by Richard Kirk (#46733217) Attached to: AT Black Knight Transformer Hits the Road and Takes a Hop

This actually looks good to me. Most helicopters can be shot down with a rifle. They are huge engines with large fuel tanks and large, whirling blades, and it is not that difficult to get them to destroy themselves with their own momentum, height, or fuel. This thing has eight separate lifting units. I would imagine with the large body, it would not fall that fast, and even if you were missing several rotors it could land in a controlled fashion. The wheels make it look a bit like the chariot from "Lost In Space" but I imagine it could run over uneven ground with computers anticipating the uneven terrain.

I doubt if it is a fast or as powerful as a purpose designed helicopter. However, for something like mountain rescue it would work. You could drive most of the way with lots of first-aid kit, hop over the river where the bridge is down, get to where you are going, dump the supplies to lose weight, fly up the mountain to rescue people, then drive back fully loaded with everyone on board.

Lastly, if you have to use this in a warlike manner, this is a potential solution. You can use bombs, and drones and gas and napalm to clear the ground, but all skirmishes from the bronze age to today are still settled in the field by one lot of people with weapons going over to another lot of people with weapons on foot, and persuading them to give up. The art has always been to deliver your foot soldiers, fresh and well-equipped, in a short hop to the forward position, and get them back if things go bad. This may do it more safely or more cost-effectively than a helicopter if you avoid the temptation to turn it into a long-distance speed-flying helicopter gunship with frickin' lasers () and just stick to the job in hand. This particular beast may look a bit Jules Verne's Armada of the Skies, and it may turn out to be a dog, but IMHO the thinking behind it is sound.

Comment: Nostradamus redux (Score 2) 60

by Richard Kirk (#46472301) Attached to: First Mathematical Model of 13th Century 'Big Bang' Cosmology

I went to the presentation at the Royal Society last week given by this group on Grosseteste's colour theory. Grossteste's papers are very dense and very short, and this one fitted on a sheet of A4. He had a theory about colour that seems to have three clear axes and eight corners. However, he never tells us what the axes are called, or names a single colour, or even tells us where white and black come, which the presenters admitted was 'pretty strange'. There is no obvious algebra, which is correct for the age, but makes it very hard to interpret an unambiguous meaning. Aristotle's theory on colour, which Grossteste would have read in translation from Arabic at the time, has clear experimental models for generating infinitesimal shades between any two colours, and names seven colours - perhaps in an early attempt to see how many colours are needed to mix any colour. In contrast, it is difficult to be sure whether Grosseteste's work is philosophical (which colours should exist), experimental (which colours do exist), or mathematical (how can we model what we see).

Grosseteste was known to be one of the better mathematicians of his age. He is not Nostradamus, pumping out cryptic statements in the hopes that some of them will match something at random. What he said was respected in his day. We have some modern computer model that seems to match what he said to some extent, but only for some small subset of the parameter space. I suspect this tells us more about how we think then about how Grossteste did.

Comment: Re:is there an xkcd comic for this? (Score 2) 138

by Richard Kirk (#46407207) Attached to: The Rise and Fall of Supersymmetry

Experiments are real but the results aren't pretty. SUSY is pretty but the results aren't real.

When we look at the tables of known particles, it is tempting to think of the periodic table. We might hope to see patterns in the particles, and then guess at the missing parts of the grid. Unfortunately, we don't have nice families of halogens, alkaline earths, and so on. We started off with electrons, protons, and neutrons which all had sensible masses even if the electron was less than a thousandth of the mass of the others, and photons which had no rest mass at all. Then we have a very irregular family of subatomic particles including things like mesons, and neutrinos, with finite but stupidly tiny mass. They don't seem to form a family at all, but a lot of clever people invented new sub-particles called quarks, and in the end managed to come up with a plausible theory that seemed to fit a lot of these weirder particles into families. But not everything.

The periodic table was backed up by quantum calculations, which showed why the should be two elements per row, then eight, and then all the transition elements. Unfortunately, we don't seem to be able to finish off the table of the subatomic elements in the same way. We can come up with neat SUSY theories that would work if there are lots of symmetric particles that we do not ordinarily see, but might be more common at higher energies, and bend the various graphs into fitting at some point. However, as the guy neatly tabulated, all plausible versions of the SUSY theory seem to come up with things that we ought to be able to see with the LHC and other things, and we don't. So, right now, and after a lot of people had spent most of their lives fooling with this model, it is beginning to look like we may have gone down a dead end.

Comment: Comments from shipping experts? (Score 2) 216

by Richard Kirk (#46355717) Attached to: Rolls Royce Developing Drone Cargo Ships
So far we have had 100% negative comments in the direct replies, unless one slips past me while writing this. Many of these raise issues that were raised in the original article. Many others just say it won't be safe if computers are in charge. I am not convinced by any of these.

The Rolls-Royce calculations show that there is a measurable saving in pollution by leaving off most of the crew support features. Fine - a potential saving exists. Now let's explore whether the saving is practical

Large ships do not turn suddenly - it can take miles and tens of minutes to turn a large tanker. You do not have to provide the captain with a real-time 360-degree virtual environment. You have to provide some sort of autonomous fail-safe in case communications are lost. You can have a one-time pad encryption for sending instructions, so remote hacking without a copy of the pad should be difficult if not impossible.

What if the ship gets into difficulties? We know the problems that conventional ships get into. It should be possible to calculate what fraction of these could be fixed by the crew at see, and factored into the potential saving. This is what the analysis should do. If you are in a storm, and a conventional container ship starts spilling its load, there is probably not much the crew can do other than hang on and wait for the storm to pass. It seems entirely reasonable to me that a small number of faults at sea could be fixed by flying out personnel to the ship and landing on the flat top of the containers, if nowhere else. So, you factor in the costs of a call-out.

Might work. Won't ever work if no-one's prepared to think about it, though.

Comment: Re:Sounds like they're trying to hard (Score 1) 170

by Richard Kirk (#45712795) Attached to: Polynesians May Have Invented Binary Math
Going to make that point myself. There is 'four score' in English, and an old Northumbrian counting scheme that used to count in multiples of 20 ('chiggit'). Weirdly enough, 'quatre vingts' seems a compartively recent invention: I am told 'ottante' was used in Belgium around WW1. This counting style may not have been ancient.

Comment: Peter Pan & Doctor Who... (Score 1) 216

The UK laws granted a sole case of perpetual rights to 'Peter Pan', which J.M.Barrie had given to the Great Ormond Children's hospital. This isn't quite copyright that 'never grows up' ( see ), but it comes pretty close. I think the UK legislation could be a bit flexible to a time traveller too.

Comment: Re:Unfortunately, you need real molecules to do th (Score 3, Informative) 175

by Richard Kirk (#44969091) Attached to: Scientists Create New "Lightsaber-Like" Form of Matter

This is happening in a non-linear medium where photons interact: it can't happen in free air. Photons hardly interact on most transparent media, but there are materials with non-linear electric properties that can be used to generate harmonics ( see for example ). This is used to convert red light into green in some green laser light pointers. At high power levels, the refractive index increases in more normal materials, which is a nuisance in high-power lasers as light in NdYg glass laser elements can self-focus and damaage the apparatus if the power gets too great.

Hardly "contrary to decades of accepted wisdom about the nature of light" if you can find it in a green laser pointer. Meh.

Comment: Use pictures (Score 1) 385

I do not think the original article was a success for various reasons. It is not easy to explain quantum mechanics convincingly, and I don't think the lack of equations was a main weakness. Those of us who are happy with equations with Hamiltonian operators and eigensolutions probably understand the uncertainty principle too. Those of us who have not touched serious maths, or have done it too long ago will be made to feel stupid rather than being helped.

I think what the article needs was good pictures. How about...

A picture of the Young's slit experiment. A light wave goes through two slits, and interferes with itself. You get fringe patterns. You can calculate the fringe patterns using classical physics.

A picture of the Stern-Gerlach experiment. An electron beam is split into two and interferes with itself. You get similar fringe patterns. What, what? This works with electrons? Yes, it even works with substantial molecules such as buckyballs. In fact, if you did your Young's Slit experiment with a very dim light source and a long integration time, you would be passing photons, one at a time, through the apparatus.

So, when a particle interferes with itself, does it go through the left slit or the right one? Some people say it goes through both, but it doesn't, really. The wave function, which we can calculate but we can't measure, may go through both slits in some senses, and determine the fringe pattern. If we install a detector that can tell us the electron is going through the left slit, or going through the right slit, then the electron goes through one slit, and we do not get the interference pattern. We can know which slit the electron goes through, or we can predict the interference pattern, but we can't do both.

A picture of a wave packet plotted in ordinary space, and in frequency space.

There is nothing magical about the observation, itself. The idea that being observed changes the states dates back to an old and rather unhelpful thing called the Copenhagen model. A better approach is to say that we can measure some property of a particle wavefunction such as the position, or the momentum of the particle; but in measuring the position we lose the ability to also measure the momentum, and vice-versa. In this case, the width of the wave packet determines how accurately we know where the particle is at the time of measurement, while the width in frequency space determines how accurately we know the momentum. Our measurement will tell us what the wavefunction was like at the point of the experiment, but nothing else. This is one form of the Uncertainty principle, but it can be applied to other measurements too.

See, it can be done. If you don't get it, don't worry: small things and quantum stuff are pretty weird.

Comment: James Bond did not like the Walther PPK... (Score 1) 38

by Richard Kirk (#44326135) Attached to: James Bond's Creator, and the Real Spy Gadgets He Inspired
He was supposed to use the Walther PPK it. It was the standard MoD handgun. The AWE guards used to have them. I expect it still is. But he thought it was too bulky, and preferred a Beretta 418. I am not a big fan of the books, but I picked up 'Dr No' years ago, thinking I ought to see what a Bond book was like, and that bit stuck. The films get that wrong too.

Comment: Nice design... (Score 1) 51

by Richard Kirk (#44295355) Attached to: Oldest Lunar Calendar Found In Scotland
I have always wondered why people build stone circles for astronomical measurements. You could do a lot better by picking some distant landmark - the pass in this case - and moving sideways until the sun or moon appears aligned. Better still, pick something that is above you, so you are looking slightly upwards - if you were trying to mark the position where the sun sets over the sea, there is a lot of atmosphere that may contain clouds and stop the reading, and a lot of distortion. This uses a valley, and a set of sticks in the ground: more accuracy for less effort than stone circles.

The person who makes no mistakes does not usually make anything.