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This is a highly speculative half-baked imaginative conjecture to be taken with a grain of Kosher salt based on the Nobel Prize in physics 2010 for graphene sheets given to the two Russians now in UK and from my synchronistic discussions with James Woodward.

PS - Jim's radiative gedankenexperiment below looks like a heat engine. But again, this would be a very tiny effect in actual experiments so far. However, it would be a good idea to design experiments specifically to look for such an effect.

On Oct 5, 2010, at 10:37 AM, JACK SARFATTI wrote:
The practical reason why there is no reason to believe that metamaterials transform the energy densities of electromagnetic waves propagating through them from positive to negative is that were that the case, serious violations of the law of local energy conservation would ensue.  Consider an electromagnetic wave as it makes the transition from propagation in free space to propagation in a metamaterial.  If the energy density of the wave propagating in the metamaterial is negative, the wave must divest itself of enough energy to change its state from positive to negative as it enters the metamaterial.  That energy must go somewhere – presumably into the physical structure of the metamaterial.  So, where the wave enters the metamaterial we should expect to see strong heating.  And where the wave exits the metamaterial, we should expect to see the reverse process – strong cooling.  No reports of this behavior, which could hardly be missed as it would be a pronounced effect, are to be found in the literature. - JW

I think "strong heating" is quantitatively false in every experiment done in meta-materials so far. "Hardly be missed"? On the contrary, very easily missed in the actual experiments done so far. First of all the frequency region of electromagnetic radiation in which conditions for negative EM energy density to obtain needs to be identified. The power levels in those bands are probably quite small and the anomalous heating hard to detect. Also |n| ~ 1 still in the meta-materials that actually exist today. So my point here is that unless extraordinary measures are taken to measure the heat produced it will not even be noticed in actual meta-materials used today.

Certainly if we succeed in making a super-conducting meta-material with |n| >> 1 and negative permittivity and permeability, the heating effect needs to be taken into account and in that case could be strong. Also, for application to wormhole/warp metric engineering we do not want to use incident radiation at all! Woodward's premises above are the wrong ones to use! It's a Red Herring.

Imagine, maybe a 2D graphene sheet doped and nano-engineered to be an ultra-high Tc superconducting metamaterial. Now place equal and opposite static charges Q & - Q on the two boundaries of the sheet - a capacitor. The generated non-radiating electrostatic near field energy density will be ab-initio negative. There is no transformation of positive to negative energy real photons in this gedankenexperiment.