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In the episode Identity Crisis of Star Trek TNG, wouldn't Geordi have been able to see the heat signature of the "invisible" aliens?

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From the transcript

OGAWA: Sorry to disturb you, Doctor.

CRUSHER: That's all right. What's happened?

OGAWA: I thought you should see this. (Alyssa shines a torch on Susanna)

CRUSHER: Her skin is simulating light. A radiant reaction. Some sort of mimetic ability?

OGAWA: That's not all. Her body temperature is dropping.

CRUSHER: It's as if she's generating a disruptive field. I can barely get any readings off her now. What's her rate of transformation?

OGAWA: It's increasing.

The aliens were not only mimicking the visible light spectrum (causing most of the crew to be unable to see them), but were also matching their body temperatures to accomplish the same sort of mimicry in the infrared spectrum, and (since we know he can't see them) presumably in the other spectrums in which Geordi can see as well.

  • Except for the UV spectrum (if I remember the episode correctly). – Xantec Aug 6 '12 at 16:59
  • ahh, I didn't recall Ogawa saying that about her temperature. – Audrey Aug 6 '12 at 17:04
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That would depend entirely on the process which was causing the aliens to be invisible. Geordi can't see everything, but he does have a much broader range of "vision" than normal humans do. If the process is similar in concept to a cloaking device, for example, the rays of energy that Geordi can see would be bent around the invisible person and Geordi would not see them. Or if it were similar to the camoflage technologies portrayed in some movies like GIJoe or James Bond, where an outer layer hides what's behind that layer by superimposing an image from the opposite side. Again, even Geordi's advanced vision could easily miss what was being hidden. Yet another option is if the hidden alien is hidden due to something taking them slightly out of phase (a trick used in other Star Trek episodes). There too he would likely miss what was there.

So there are quite a few ways for an alien to hide themselves from being seen, even to Geordi's advanced vision abilities.

3

The aliens emitted a electromagnetic field that redirected all wavelengths of light including the infrared and ultraviolet light that Geordi is able to see in using the VISOR. This redirection worked for their own personal radiations.

  • Geordi's VISOR is able to detect ambient as well as emitted radiation.
  • The field emitted by the aliens redirected ambient radiation making the creatures literally invisible to every sensing mechanism including the VISOR.

As usual, the Enterprise crew creates/modifies a technology to solve the problem:

  • The device emitted a strong ultraviolet beam of light and then highlighted the regions of ABSORPTION artificially.
  • The creatures preferred ultraviolet radiation, likely seeing in a PORTION of that spectrum. Otherwise they would be completely blind.
  • This made the aliens veins-like organs which emitted the absorptive field stand out.

The show had a technical error:

  • It allowing one of the aliens to display a shadow during Geordi's analysis.
  • That shadow should not have existed since the information gathered was only in the visible spectrum.
  • The shadow could have been a creature still developing its cloaking field, and thus was partially visible for key frames and extrapolated by the computer but managed to remain invisible to normal vision.
  • Regarding the ultraviolet part, the episode specifically mentions that ultraviolet is "beyond their visual spectrum", which is the reason they wouldn't run away from it. – NominSim Aug 6 '12 at 17:32
  • UV is a range of electromagnetic phenomenon. The doctor could have isolated just a part that was invisible to the aliens for her patient's comfort. The aliens were able to utilize at least a tiny segment of it, because otherwise they would not have any vision at all... Their field blocked all other forms of light. – Thaddeus Howze Aug 6 '12 at 17:35
  • I didn't get the impression that their field blocked the other forms of light, but that it mimicked it by radiating the correct wavelengths. – NominSim Aug 6 '12 at 17:43
  • The language used in the show is ineffective. They aliens did not emit light to mimic their surroundings, that would be VERY difficult, they bent light around them, their energy field acting as a metamaterial might, moving light around their body so they appeared to NOT be there in the first place. Much easier to accomplish. – Thaddeus Howze Aug 6 '12 at 17:46
  • I don't know that it is much easier to accomplish bending of light than it is to accomplish projection of light, the concepts are relatively easy to grasp in and of themselves, its when you add the scale and complexity of bending/projecting in the large number of directions where both get complicated. In any case the language used in the show indicates the radiation/projection reasoning, not a bending. Either way there are technical errors, so there is no real way to say with certainty what was actually happening. – NominSim Aug 6 '12 at 17:58

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