Negative moon
Wesson has to go to the fifth dimension to look for negative mass. Or, more easily, he can look up an article in the American Journal of Physics (vol 63, p 853) in which I show that the well-known object called a hole in condensed matter, which represents an energy band with one missing electron but otherwise full, has negative mass 鈥� m, where m is the electron mass.
Negative moon
If negative mass was created in the big bang, and there is indeed negative mass scattered about in our known universe, could it account for the apparent acceleration of the expansion rate of the universe? Of course, we would expect that ultimately, all negative mass would go off and isolate itself away from all positive mass.
Gypsum plus carbon
Having read with interest the article on creating “new land” by treating limestone with sulphuric acid to convert it to gypsum (20 November, p 38), I wonder if any of the proposed projects have taken into account the carbon tax that will be attracted by all the carbon dioxide produced.
Gypsum plus carbon
Your article reports on an acidic reaction turning porous limestone solid. Does this mean that acid rain could tend to create an impermeable layer which would prevent water replenishing a limestone aquifer?
Rudders in flight
Your report on the fatal Airbus A300 crash in 2001, in which the plane’s tail fin and rudder parted company with the plane in flight, stated that the “main purpose” of the rudder on an aircraft “is to steer the plane while taxiing” (6 November, p 26). That is not the case.
The rudder is primarily used to balance the adverse lateral motion (yawing) that affects an aircraft as it banks and turns, although this effect is less significant in commercial jets. It can also be used to “trim” the aircraft in flight to maintain a straight line. And, as correctly stated in the article, it can also be used to counteract adverse yaw in asymmetric flight such as that caused by an engine failure.
The editor replies:
鈥� Though what Paul Summers writes is true, the fact remains that commercial pilots rarely use the rudder pedals except on or near the ground, during crosswind take-offs and landings, and when taxiing. The rudder is almost never used at the speeds involved in the flight AA 587 accident.
The US air crash investigator, the NTSB, made this clear in its final hearing when its investigator, himself an experienced commercial pilot, David Ivey said: “Pilots seldom use rudders at high airspeeds, and therefore may not have experienced the airplane’s response characteristics…and could be surprised and confused by the airplane’s response to those inputs.”
Fake degrees
Feedback may find the Michigan list of non-accredited universities amusing (20 November). However, they are a serious problem for those concerned with maintaining the reputation of bona fide institutions.
Examples here in the UK include “universities” bearing the names of towns which have no such university. There are also many local colleges offering degrees from supposed universities in the US, Ireland and elsewhere. Often they award qualifications only for the holder to discover that they are not recognised. Worse still, some employers fail to check credentials properly and people end up holding positions of authority and trust with no real qualifications. This has led to considerable criticism of the UK and the relatively weak controls provided by the Education Reform Act.
If readers want to find out more about the problems posed by degree mills they should join the prolonged discussion forums on .
Pendulum test
In your excellent article discussing the Allais eclipse effect and the work of those of us who are investigating such anomalies further, there is a minor mistake (27 November, p 28). The URL is not Maurice Allais’s website; it is our own group’s internet base. A full description of our development and “dry-run” experiments in Malaysia has been recently uploaded, and details of further work will be posted regularly.
For the solar eclipse of 8 April next year, members of our group are currently on track to make simultaneous observations in Colombia, Australia, New Zealand, Malaysia, Portugal, and Iowa, using several “English-style” paraconical pendulums of virtually identical specification at each location.
The Colombia and New Zealand locations are very close to the eclipse track. We hope to be able to report something of interest.
Google still top
Your article on the new Microsoft MSN search service strongly suggests it is now a worthy adversary for Google, even outstripping it in the quality of some of its returns (20 November, p 23). As a web developer I have to say I have not been that impressed.
About three months ago, I re-coded all of our Powerwatch website, including changing the file extensions from .htm to .asp. Within two days, Google had re-indexed the site on its searches, and was returning the .asp pages just as successfully as the old pages. However, three months on, MSN has still not managed to pick up any of the new pages, which means its cache must be a good three months old.
This in itself is not a problem, but it does make one wonder how many of their 5 billion pages are up-to-date. This is not easy to find out, because the MSN search does not allow users to look at the cached pages themselves, nor does it allow users to see when the page was cached 鈥� a very useful feature of Google.
I am not saying that the new MSN search is not an improvement, but from my experience, it has a long way to go to achieve the same feature-rich functionality and credibility that Google can claim.
Keeping a clear head
Ben Heller would like to know “whether and how the science we are doing differs from the science we would do without caffeine” (27 November, p 27). I came off caffeine about four years ago. Since then my head has felt clearer, I seem to be more in charge of my intellectual faculties, and I am publishing more papers per year than I did before. This might just be coincidence, of course, so I would be curious to know what experiences others have had.
Robo cup
Alan Lindsay suggests that football would be a good test of man versus machine, and says he will only start worrying when 11 robot footballers can beat Celtic (20 November, p 29).
He might like to know that the goal of the RoboCup challenge () is to develop a team of fully autonomous humanoid robots that can win against the human world champion team in soccer, and to accomplish this by 2050. Robot football teams now battle it out with each other, originally using wheeled robots but now including four-legged and humanoid robots. International championships have been held since 1997, and are hotly contested.
Very likely the robot teams of 2050 will be designed and built by the generation who are now at school, so RoboCupJunior is taking the football and other challenges, such as robot rescue and robot dance, into schools.
So Alan Lindsay may want to start worrying now 鈥� or perhaps he would prefer to join the fun, excitement and creativity generated by teams of kids faced with these challenging problems.
Forced labour
Your 13 November Feedback about a baby clearly showed you were desperate for baby stories, so here is another one.
When my wife was near term with our first baby, we were sitting around waiting for something to happen and getting thoroughly cheesed off with the process. Both of us are GPs and have done a fair bit of obstetrics. So I had a brainwave, and hired a video of Three Men and a Baby. Admittedly it has a weak story line, but does include a lot of hungry-baby noises. My rationale was that the crying baby would prompt my wife to release oxytocin and stimulate her milk let-down reflex. The oxytocin would also stimulate her uterus to contract, thus inducing labour.
My wife was sceptical.
Ten minutes before the end of the movie, she went into labour.
Negative moon
I was very surprised by Paul Wesson’s statement that if the moon had negative mass it would be driven away from us instead of orbiting the Earth (20 November, p 30). Assuming (as experiment tells us) that gravitational mass and inertial mass are equivalent, then the repulsive gravitational force on a negative-mass moon would cause the moon to accelerate towards us (because of the negative m in F = ma). Hence a negative-mass moon would orbit the Earth.
However, there are some complications, because this negative-mass moon would in turn gravitationally repel the Earth, so we would accelerate slightly away from it. The consequences of this can be understood by thinking about the normal situation of two orbiting bodies in space: they actually orbit about their centre of mass, which lies on the line joining their centres, but closer to the centre of the heavier mass (in this case the Earth). For the Earth and a negative-mass moon, the centre of mass would lie on the extrapolation of the line joining the centres of the two masses, just past the centre of the Earth. Both Earth and negative-mass moon would orbit around this point, and the repulsive force from the moon would keep the Earth on its much smaller orbit about the centre of mass.
Since a negative-mass moon could be orbiting us, how can we decide whether our moon actually has positive or negative mass? In fact, there would be observable consequences of a negative-mass moon: for instance, the lunar tides would have the opposite phase from those you get from a positive-mass moon. Also, any astronauts walking on the moon would find that the forces between their boots and the lunar surface (which are electrical, not gravitational in origin) would have very interesting consequences, which I leave your readers to imagine.
Flask warning
For the sake of safety, please inform your readers not to use domestic vacuum flasks, especially glass-lined ones, to collect liquid nitrogen from a laboratory, as suggested in the item “Home lab: make liquid nitrogen ice cream” in your book 100 things to do before you die. I hope laboratories would refuse to dispense the nitrogen into such flasks, in any case.
The explosion of an unmodified flask containing liquid nitrogen was the most shocking incident in my career. I still have the scars from it.