In search of the greatest ever equations
E = mc2? F = ma? Or maybe nƒÜƒn= 2d sinƒá? Physics World columnist Robert Crease is asking physicists to vote for their greatest equations of all time. As the German physicist Heinrich Hertz once said, great equations are "wiser even than their discoverers [for] we get more out of them than was originally put into them". Crease's own view is that the greatest equations tend to be those dealing with fundamental properties like space, time and energy. The results of his readers' poll will be reported later in the year.
Results will be issued in an embargoed news release later this year — for more information contact David Reid, Press Officer, Institute of Physics, Tel: 020 7470 4815, E-mail: david.reid@iop.org.
Can you turn a tyre's inner tube inside out through a hole in its wall?
This question, first posed by physicist Eric Voice in January, had many Physics World readers stumped. But what made the question harder was that readers were asked to find the solution using only their minds - without writing or drawing anything down. Voice reveals the answer in this month's issue, which includes photos of what happens when you try it for real. The question serves to show just how hard many people find it to visualize in three dimensions.
Redefining the kilogram
In a vault on the outskirts of Paris sits a small platinum-iridium cylinder that has the unique property that its mass can neither rise nor fall. What makes this lump of metal so special is that it is the "official" kilogram. So whether the cylinder gets "heavier" by picking up dust or "lighter" as a result of being cleaned, it always has a mass of 1 kg. Ian Robinson describes two new experiments that aim to sweep away this unsatisfactory state of affairs - by redefining the kilogram so that its value cannot change with time. One experiment defines it in terms of a certain number of carbon atoms, while the other involves matching the pull of gravity on an object with the electromagnetic force on it from a current-carrying wire. Unfortunately, agreeing upon a new definition is still "many years" away and would also mean having to redefine the units of energy (the Joule) and force (the Newton).
Also in this issue:
Gravity hunt goes underground
US science adviser takes on his critics
Hubble successor shifts to the red
Challenges for a new Europe
US threat to European journals
Beating the diffraction limit
Tales from the transneptunian sea
Atoms and light get intimate
Lasers feel the Z pinch
Dark energy: the latest findings
Please mention Physics World as the source of all these items and, if publishing online, please carry a hyperlink to: http://www.physicsweb.org
Notes for editors:
For interviews, copies of Physics World, and advance copies of the articles reviewed here contact: David Reid, Press Officer, The Institute of Physics, Tel: 44-207-470-4815 or 44-773-425-6729, email: david.reid@iop.org
Physics World is the international monthly magazine published by the Institute of Physics. For further information or details of its editorial programme please contact the editor, Dr Peter Rodgers on 44-117-930-1007. The magazine's Website physicsweb.org is updated regularly and contains physics news, jobs and resources. Visit http://www.physicsweb.org.
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