Song Of The Day - 20th October 2008: Speed of Light


Out 20 2008, 14h54

Joe Satriani / "Speed of Light" / Time Machine (7) / Oct 1993

Artist: Joe Satriani
Original Album: Time Machine
Track: Speed of Light

Einstein's two axioms for special relativity:

- The laws of physics are identical in all inertial frames
- There exists an inertial frame in which light signals in vacuum always travel rectilinearly at constant speed c*, in all directions, independently of the motion of the source.

* c is 2.9979245...x 10^8 m/s, that's roughly 300,000,000 metres per second.

Between the two of these axioms we are given Einstein's law of light propagation:

-Light signals in vacuum are propagated rectilinearly, with the same speed c, at all times, in all directions, in all inertial frames.

This essentially means that if you are standing still (in relation to the inertial frame of the planet Earth), light travels away from you and towards you and in every direction at the same speed. However, if you are moving at a constant speed in relation to the Earth and then consider yourself to be at the origin of an inertial frame, light still travels away from you, towards you and in all directions at the same speed. If you think about it, that's actually quite bizarre.

Because of this, if you consider an observer onboard a moving train's carriage and equidistant from each end of the carriage, who then shines two torches to either end of the carriage simultaneously, both light signals reach their respective ends of the carriage at the same time. However, if you consider another observer on the ground outside the train, who is not moving, and who witnesses the original observer perform his experiment, then the beam of light travelling toward the rear of the train's carriage shall reach it's destination before the beam travelling toward the front of the train**. This is known as the relativity of simultaneity.

** I think it is, in fact, also helpful to specify that the observer outside the train should, with the observer on the train form a tangent to the train at the moment in time where in the observer on the train's inertial frame both hit their marks at the ends of the carriage.

I think that's right anyway. Anyone who can follow that well enough to spot a mistake, please do correct me before January.

Anyway, this track is from Joe Satriani's 1993 outtakes and leftovers album Time Machine. It has something of a resemblance to Motorcycle Driver, so it's no surprise to learn that it is in fact a leftover specifically from 1992's The Extremist album. In checking the release month for the header at the top of the journal, I also learned that the 26th will be the 15th anniversary of this album's release, and that this song features in the 1993 movie adaptation of Nintendo's Super Mario game series - haha, didn't expect that! Existing Satriani fans should pick up Time Machine as it's got a lot of material that's actually better than many of his later album tracks, as well as a decent recording of a live performance. Non-fans would be well advised to start elsewhere though.


  • saronix

    I did not know of the Mario movie connection -- which blows my mind.

    Out 23 2008, 22h03
  • GrantRS

    Yeah, it was a surprise for me as well. It's a better known fact that One Big Rush was written for a movie, but I can't remember which for the life of me. Satriani also appeared in a Christopher Guest (of Spinal Tap fame) movie, I believe, though I can't remember which and haven't seen it. On the other hand, Vai's had absolutely loads of movie connections.

    Out 24 2008, 9h33
  • saronix

    I know Christopher Guest appeared in the ''Satch Tapes'' which I own on DVD, but aside from that I'm not sure.

    Nov 3 2008, 20h28
  • GrantRS

    ...and Joe played on Break Like The Wind. I've had the Satch Tapes DVD for ages, it's a really good DVD, but I've not made the time to go back and re-watch it for a while. Guest/Tufnel says some really funny stuff in that. ...Ok, I've looked Satch up on IMDb and the flim he appeared in was 2006's For Your Consideration.

    Nov 3 2008, 21h16
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