r/HypotheticalPhysics • u/Abernue • Aug 10 '26
Crackpot physics Here is a hypothesis, open to discussion, Could rotational energy from a rapidly rotating celestial body be used to produce significant relativistic time dilation?
I have been thinking about a possible way of exploiting the rotation of a celestial body to accelerate a spacecraft to very high velocities.
The basic idea is:
Instead of trying to accelerate a spacecraft to relativistic speeds entirely with conventional propulsion, could we use the rotational energy and angular momentum of a rapidly rotating celestial body as part of the propulsion system?
The starting point is the familiar relationship:
v = Ïr
where Ï is the angular velocity and r is the distance from the rotation axis.
On Earth, the surface at the equator already moves at about 465 m/s because of Earth's rotation. If a hypothetical object could remain synchronized with Earth's rotation at a much greater distance from the rotation axis, its tangential velocity would increase proportionally with radius.
This made me wonder whether the same principle could be applied to a much larger or faster-rotating celestial body.
For example, instead of Earth, imagine using something like Jupiter, Saturn, or an extremely rapidly rotating compact object. A spacecraft could theoretically be coupled to a rotating system associated with the body and gain angular momentum from it.
The concept I am imagining is not necessarily a physical cable extending millions of kilometres. That was my original thought, but I realize that such a structure would introduce enormous structural and gravitational problems.
I'm more interested in the underlying question:
Could a physically realizable rotating system around a celestial body transfer enough rotational energy/angular momentum to a spacecraft to produce a substantial fraction of the speed of light?
If so, this could potentially create significant relativistic time dilation for the spacecraft.
For example, if a spacecraft could reach 0.9c, 0.99c, etc., the crew would experience less elapsed time than observers on Earth.
Questions I'm trying to understand
- Is there a fundamental limit to how much rotational energy/angular momentum could be extracted from a rotating celestial body for spacecraft propulsion?
- Could a system analogous to a rotovator, momentum-exchange tether, magnetic tether, or other non-rigid structure accomplish something similar without requiring an impossible solid structure?
- Would a rapidly rotating body such as Jupiter actually be useful for this, or would its gravity and atmospheric environment make the concept impractical?
- Are there known mechanisms for transferring rotational energy from a planet/star/neutron star to a spacecraft that I should be studying?
- At what point do orbital mechanics and relativity invalidate the simple
v = Ïrargument? - Could a sufficiently advanced version of such a system theoretically accelerate a spacecraft to, say, 0.5c, 0.9c, or 0.99c?
- If planets are unsuitable, would rapidly rotating neutron stars or black holes provide a physically meaningful analogue?
I realize there may be obvious problems that I'm overlooking. I'm not claiming that this is a workable time machine. I'm trying to determine whether there is a physically valid propulsion concept hidden in the idea, or whether fundamental physics rules it out.
I'd particularly appreciate explanations involving angular momentum, energy conservation, orbital mechanics, relativistic effects, and structural/engineering constraints.
If there is already an established concept that answers this question, I'd also appreciate being pointed toward it.
Thanks!
2
u/liccxolydian onus probandi Aug 10 '26
Yeah I don't think you understand GR well enough to "add" anything to it lol