The nature of mass is one of the great enduring puzzles of science. What is mass and where does it come from are questions that have puzzled scientists and philosophers for centuries.
So the suggestion that mass can be created inside carbon nanotubes will produce some significant head scratching.
The idea comes from Abdulaziz Alhaidari at the Saudi Center for Theoretical Physics in Saudi Arabia and a few pals who begin with a review of the exotic properties of graphene, a 2-dimensional sheet of carbon “chickenwire”.
One of the most exciting new ideas in solid state physics is that graphene can act as a laboratory for studying exotic relativistic physics. It turns out that the electronic properties of graphene can be tuned so that the movement of electrons and holes through the structure at speeds of 10^6 m/s is mathematically equivalent to the behaviour of electrons travelling in a vacuum close to the speed of light.
In the language of physics, their behaviour is governed not by the conventional Schrodinger equation that ordinary electrons obey, but by the massless Dirac equation than describes relativistic physics. These equations take no account of mass (as the name implies)–so the electrons and holes behave as if they have no mass.
That’s important because, in the past, the relativistic behaviour of electrons was only accessible to physicists with a high energy particle accelerator in their yard. Now any laboratory equipped with carbon, electricity and wires can do it.
This has led to massive interest: one idea is that a new generation of graphene-based electronic devices will be able to exploit the effects possible in relativistic physics rather than using plain old vanilla effects (although exactly how isn’t yet clear).
Now let’s jump to the antics that theoretical physicists sometimes get up to when thinking about mass. One idea is that mass arises because the universe has extra, space-like dimensions that exist only on the tiniest scales. Physicists say these dimensions are compactified.
Compactified dimensions have an important effect in quantum mechanics, changing the equations that describe the universe so that they include a term for mass. In these theories, that’s how mass arises.
Alhaidari and co’s idea is that a similar effect can occur in graphene if the space-like dimensions in graphene can be compactified. In other words, if you reduce the number of space-like dimensions in graphene from two to one, the massless equations that describe the behaviour of electrons and holes will change to include a term for mass. In effect, compactifying dimensions creates mass.
So how do you compactify space-like dimensions in graphene? Simple, you roll it up. This changes the sheet into a tube that is effectively 1-dimensional, at least as far as the electrons and holes are concerned.
There are some important mathematical differences between the mass that can be generated this way and the stuff you can rap your knuckles on. But now physicists have the chance to compare the effects in an ordinary lab.
The ability to generate or destroy mass simply by changing the geometry of graphene is a powerful idea. The first challenge will be to reproduce the effect in the lab. Expect to find solid state physicists burning the midnight oil in coming weeks.
Beyond that, the question is how to exploit our newfound power over mass. Suggestions in the comments section please.
Ref: arxiv.org/abs/1010.3437: Dynamical M ass Generation Via Space Compactification In Graphene
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