Subject: PS Hal’s explanation below is really not correct.
The blue shift from the Tic Tac in Alcubierre metric is only seen in the tail of Tic Tac running away from you, or in another case, hovering above you causing harmful ionizing plasmas in some cases. The nose of Tic Tac coming toward you is redshifted - this opposes motional Doppler shifts.
Jack: John Hogan made a good point that these anomalous shifts may not be detectable by bouncing signal off the Tic Tac because the effect is symmetrical and will cancel out in the return signal. The reverse effect only seen in signals created from the Tic Tac.
JH: Actually I had a more practical consideration in mind. I suggested to Jack that the easiest way to measure the existence of either a gravitational or an antigravitational warp field surrounding a piece of active (energized) metamaterial is to measure the frequency shift of light emitted from a laser diode embedded in the metamaterial relative to the frequency of light emitted from the same laser diode when the electrical input to the metamaterial is shut off.
Jack: Yes, good suggestion.
JH: Since photons climbing out of a gravity well are red-shifted, then presumably photons climbing out of an antigravity well (antiwell?) are going to be blue-shifted. If, however, you bounce photons off of a piece of active metamaterial and then detect them with a detector located in the same piece of equipment housing the laser emitter (external to the metamaterial), then the frequency shift that the photons experience on entering the warp field will be exactly counteracted by the frequency shift that they experience on leaving the warp field after being reflected from the metamaterial. In this case no net frequency shift will be observed. This makes laser-Doppler-interferometer-type devices useless for measuring the existence of a static gravitational/antigravitational warp field generated by an active piece of metamaterial.
Jack: Yes, that seems correct.
JH: I wasn’t really suggesting measuring a Doppler effect here. In fact it would be best if both the metamaterial and the diode-array detector or spectrophotometer measuring device are bolted down to an optical table to avoid movement/vibration during measurements. I apologize for any confusion that I may have caused here. I was merely trying to offer a helpful suggestion to Jack to enable him to develop a simple method to measure his progress as he crafts his metamaterials. I believe that if Jack simply incorporates a laser diode into each slab of metamaterial that he produces, that this objective can be achieved with a minimum amount of difficulty.
Jack: Yes, that seems correct.
JH: In my opinion before Jack develops materials which vary a warp field switchable from being gravitational to antigravitational on demand as a function of time and location in the material he will have to optimize the technology he develops for generating and testing static gravitational and antigravitational warp fields in metamaterials (one step at a time). I believe that the suggestion that I have made above will help him to achieve this.
LSU Dept. of Chemistry
That is the easy problem solved already by Alcubierre. The hard problem is how is the warp field generated with small amounts of energy and that’s where the meta-materials come in. Hal has no plausible explanation consistent with battle-tested physics for that apart from my explanation.
Hal: Check righthand side of Table 1. As you see, from afar a powered-up craft and its characteristics all look blue-shifted. That means that inside clocks run fast, etc., etc. Therefore, to one inside the craft, outside events appear to be in slow motion (i.e., red-shifted). Therefore, to what appears from the outside to be an impossibly high-g acceleration at right angles, say, from the inside it's experienced as a slow lazy turn.