As bond yields come up, they compete for investment dollars from other yield-heavy investments, so the theory goes.

FORBES: Pump Up Yields In Master Limited Partnerships

Malcolm Dome, presenter of British heavy metal radio station TotalRock has a theory.

CNN: Iron Maiden to rock Brazil ... again

In theory, employers pay a tax exactly as heavy as that levied on their workers.

CNN: A Debt-Threatened Dream

Steering and braking could also be controlled electronically and operated by tiny electric motors, in theory at least, so cutting the need for heavy metal brakes and pedals.

ECONOMIST: Clean machine

The most popular theory holds that dark matter is made up of relatively heavy particles which, when they encounter one another, "annihilate" with a flash of light that the Fermi telescope can see.

BBC: Fermi telescope may change to dark matter hunting

The same device could also play video that is streamed over an airport network and could, in theory, surf the Web and retrieve e-mail easily, with all the heavy lifting done by the Powermac or iMac it's connected to.

FORBES: Apple Gooses IBook Speeds