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Massive Update on Strings Theory in Wikipedia
S3D writes "There is a massive update on Strings Theory in Wikipedia :
AdS/CFT
, Andrew Strominger
, Cumrun Vafa, Ashoke Sen, Juan Maldacena,
Mirror symmetry,
String field theory,
Holonomy,
Heterotic string,
Closed string
, Open string,
F-theory,
Background independence,
Higgs mechanism,
Conifold,
Tachyon_condensation,
Einsteinian_manifold,
Second superstring_revolution
Now you can easyly tell Open string from Closed string
at last."
Flat Earth
As far as I know, anyone who talks about tachyons as physical particles which we might use to construct warp drives or build a better mousetrap, is venturing into crackpot domain. The word does have a useful meaning in particle theory, which is indicated by the last paragraph of the entry. I'll give it a go, but this may not be helpful - it's unfortunately rather technical and abstract. Imagine you're trying to see how some particle (field) behaves. You can sum up a lot of the field's properties by a potential energy function. This can be a crazy function with lots of peaks and valleys in it, and what it tells you is how much energy it costs for the field to be in a given state. Usually, the field chooses to sit in the minimum energy state possible - the "ground state", the deepest of the valleys. If you "kick" the field with some kind of interaction, it will go into oscillations rolling around the bottom of the valley. These excitations are what we call particles. (Sorry, I said it was technical and abstract). A tachyon occurs when you made a mistake of sorts in your work - you picked the ground state to be at a peak rather than a valley. So the field value is such that you are perched atop one of these peaks. It turns out this would seem to correspond to a bizzare particle called a tachyon - a particle for which the square of its mass is negative (since the potential function is curving down instead of up). This isn't a real particle, though - if you "kick" the field when it's in that state, it won't oscillate normally to give particle states - it will roll off the peak and into a valley. This often happens when you spontaneously break a symmetry of your theory. Imagine your potential function looked like the letter "W". You might choose your ground state to be the one with left/right symmetry, but then you'd be on the peak of the W - you'd eventually roll off to the left or right and break the symmetry. The take-home message is that the tachyon state isn't a real particle, it's an unstable situation that is an indication that you picked the wrong ground state. I think that in the early days of particle physics people didn't understand this kind of thing so well and thought tachyon particles might actually exist. Sorry if I can't figure out how to make that much clearer.