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Lots of sci-fi franchises (Stargate, Eureka, Transformers to name a few) love to throw around the term "energy signature" when they want to indicate that something can be magically identified, measured, located, tracked, or otherwise observed without resorting to technical details. From what I can tell "energy signature" doesn't seem to mean anything in any scientific field but it's near-ubiquitous in fiction. Where did it come from?

Some Googling doesn't reveal any meta-discussion about the term except for a lone blogger comparing it to Applied Phlebotinum (TV Tropes warning). It doesn't seem to be a well-defined trope itself. Outside of sci-fi, most mentions come from the new age pseudoscience realm.

So what's the story? Was it derived from any legitimate science? Is it a running gag among sci fi writers? A backhanded reference to the new age stuff? Do we have an Ur example? (TV Tropes again)

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    Probably related to EM spectra (the real-world fact that things that give out EM radiation, including light, do so with different intensities at different frequencies, and this can enable us to determine their composition. We use it all the time on stars, for example) – Darael Jan 25 '14 at 10:07
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    The Google Ngram Viewer shows the expression starts appearing in around 1968. Searching Google Books for the expression in the 60s shows a bunch of scientific-looking articles, of which the Adelphi Papers of 63 seem to be the earliest, saying: "More precisely, sensors enable POM to home on the target's energy 'signature'." It seems to talk about heat-seeking and laser-guided missiles. – SáT Jan 25 '14 at 11:56
  • @SáT - oups. Sorry, didn't notice your comment till I posted my answer. – DVK-on-Ahch-To Jan 26 '14 at 3:25
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UPDATE

Izkata's guess was right. Star Trek: TNG usage of the term predates any printed SciFi works. The earliest episode I could find was:

"A Matter of Perspective" (aired 1990, script final draft 1989)

DATA:
The energy signature would seem to indicate a phaser-like blast...


ORIGINAL ANSWER:

Google N-Gram gives us 1969-1970 as the first year it was used in quantity.

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Delving deeper into N-gram results:

  • The term was clearly a valid scientific and technical term, if not widely used (~10 mentions total before 1972). It was used in several books/papers in 1960-1972; both dealing with nuclear energy and others. The first one I found was "Adelpi Papers" from International Institute for Strategic Studies in 1963.

  • It started being mentioned more in 1970s-80s; with ~100 or so mentions. More emphasis on scientific publications (especially nuclear and particle physics - we see some CERN stuff), but still some engineering/tech.

  • The very earliest mention I can find in SciFi work is early 1990s, both by David Weber ("Mutineer's Moon" in 1991 and "Crusade" in 1992); followed by 1993 ST:TNG book "Descent" and Ben Bova's 1994 "To Fear The Light". 1994 also saw the first mention in a fantasy(ish) book - "Curse of the mistwraith". Then 1995/1996 had Dr. Who book "The Also People"; and a couple Star Trek books (Voyager, TNG and Crispin's "STAR TREK VI" sequel "Sarek".

    This (TNG book) lends credence to Izkata's theory in comments that TNG may have pioneered it - presumably, the show used the phrase before the book though I can't find firm evidence of it yet. The earliest use I could confirm 100% was that samesuch 1993, in transcripts to episode 'Timescape':

    DATA: It appears to be a highly focused aperture in the space-time continuum. Its energy signature matches that of the temporal fragments we observed earlier. However, it is approximately one point two million times as intense. I believe this may be the origin of the temporal fragmentation.

  • I posted it as off-hand comment earlier, but just noticed that you actually asked about New Age. Ngram shows that New Age use of the term started AFTER it was picked up in SciFi (first ones were ~1995/1996).

  • Could it be Star Trek TOS? Google searches seem to indicate it wasn't used until TNG, but that lines up so well... – Izkata Jan 26 '14 at 3:01
  • Ah, if it was used in 1963, then the origin is not Star Trek (1966), although it could still have brought the term to the general public – Izkata Jan 26 '14 at 3:02
  • Runner-up: 1994 Tom Clancy's "Sum of all fears". Frankly, given the nuke stuff in the book, I'd motion it to be classified SciFi and not just a technothriller. – DVK-on-Ahch-To Jan 26 '14 at 3:16
  • Another fun fact: around 1994/95 the term was picked up by biology/ecology publications. – DVK-on-Ahch-To Jan 26 '14 at 3:23
  • I'm pretty sure TNG used "energy signature" in a transporter episode in one of the first few seasons, which places it in the late 80s, since you're expanding the answer like that – Izkata Jan 26 '14 at 3:25
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This is actually a scientific concept. It would be possible to identify the source of power for (some) ships because an antimatter reaction would produce radiation at very specific energy levels. For electron-positron annihilation this is gamma at 511kev (kilo-electron volts). More plausible for a ship would be something based on proton-antiproton annihilation, but I can't remember what value that's supposed to be.

Fission reactors would also certainly be emitting something specific depending on their reactor design and fuel cycle, and I would think most fusion fuel cycles would also be detectable (not all, since p-boron emits primarily beta radiation and a few others are like that as well).

The funny thing is you should be able to detect these technologies even if you don't yet have the science and engineering yourself to make them. If a ship showed up in orbit around Earth today and it was using one of these power technologies, we'd be able to determine just which it was.

[edit] DavidZ corrected me on the value for electron-positron annihilation.

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    Matter-antimatter annihilation produces photons with energy equivalent to the mass of the annihilating particles, i.e. 511 keV for electron-positron or 938 MeV for proton-antiproton. Of course, these photons get blocked by things like warp core containment fields, deflector shields, or even just walls. – David Z Jan 26 '14 at 9:08
  • @DavidZ - Walls in Space! </Mel_Brooks> – DVK-on-Ahch-To Jan 26 '14 at 12:12
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ACOUSTIC SIGNATURES

I suspect this was (at least in part) derived from acoustic signatures which are used in both military and civilian applications to identify unknown objects. Tom Clancy's "Red October" -- the book, not the movie -- is an excellent semi-fictional/semi-factual read which wonderfully describes submarine sonar operators using advanced acoustic signature analysis to track enemy ships.

OPTICAL SIGNATURES

While doing research for this answer I just stumbled upon this nineteenth-century journal describing the chemical sulfur as having an "optical and acoustic signature". This reminded me that we have been using optical signatures via spectroscopy for about 200 years and today we can identify the chemical composition of stars millions of light years away by their spectral lines.

IMHO, these were early forms of the still advancing science of energy signatures, for after all what are light and sound but forms of energy?

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