No, really, it does. Apparently, when we humans use planetary fly-bys to speed up spacecraft headed for distant parts, there is a source of energy that bumps up the acceleration just a teeny bit more than the scientists have calculated it should. These events are known as “fly-by anomalys” and no one knows what causes them.
Universe Today has a nifty article on the issue here. From the piece:
A recent study by Magic McCulloch suggests that “Unruh radiation” may be the culprit. The Unruh effect, put simply, suggests that accelerating bodies experience a type of electromagnetic radiation. At very low acceleration, the wavelength emitted will be so large that a whole wavelength will be longer than the dimensions of the Universe (otherwise known as the Hubble Distance). Low acceleration would therefore generate waves that have no effect on the body. However, should the accelerating body (i.e. Galileo getting accelerated by Earth’s gravity during the 1990 flyby) slowly exceed an acceleration threshold, the Unruh radiation will decrease in wavelength (smaller than the Hubble Distance), causing a tiny, but measurable “boost” to its increasing velocity.
That’s so cool!