With the help of a gravity assist from a black hole, can light travel faster than its natural light speed??

Satellites use gravity assistance. In a similar way can light traveling near black hole accelerate as well?

  • $\begingroup$ When speaking of speed, you should provide a frame of reference. For probes, the frame of reference in which speed is increased is heliocentric. I suggest you read this xkcd - what if (Stop Jupiter) $\endgroup$ – Manu H Jul 12 '19 at 8:00
  • $\begingroup$ Light cannot move faster than "light speed". The speed of light in vacuum is a hard limit and no matter what you do, nothing can move faster. Not even light itself. $\endgroup$ – DarkDust Jul 12 '19 at 9:05
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    $\begingroup$ I don't think you can get any answer besides "no" using science. The speed of light is assumed to be constant in all workable theories of black holes and general relativity. $\endgroup$ – uhoh Jul 12 '19 at 9:10
  • $\begingroup$ Hey people, this is not unclear what you're asking! It's off-topic perhaps (rather belongs to physics.SE), but since a gravity assist is a perfectly well-known maneuver it's clear how it would naïvely generalise to “accelerating light”. $\endgroup$ – leftaroundabout Jul 12 '19 at 15:42
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    $\begingroup$ I'm voting to close this question as off-topic because it probably belongs on Physics instead. $\endgroup$ – Michael Seifert Jul 12 '19 at 17:35

No, nothing can move faster than the speed of light in a vacuum. There are no tricks around it (that we know of), for example if you fly around with speed v in a spaceship and mount a lamp at the front, the speed of the light will not be v+c. It will still be c. That is actually why time passes at a different speed on fast-moving objects such as spaceships.

That being said, when talking about gravity assist you always need to talk about the frame of reference. From the view of the object you are doing a gravity assist with, you'll always have the same outgoing speed as incoming speed - that is basically how gravity assists work: From the frame of reference of the object you're swinging by, your speed does not change. But when viewed from a different frame of reference, your speed changes depending on the speed and direction of the object.


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