Would it be possible to ride a gravitational wave?
I'd like to travel really really fast, and I've got some scientists proposing a novel new way of doing so.
They've developed the technology to generate extremely powerful controlled gravitational waves. Based on my knowledge of these things, I understand that they propagate at the speed of light as a ripple in the time-space continuum. My scientists tell me that I can ride in a patch of distorted space in which I don't actually need to exceed $c$ locally in order to effectively travel faster than the speed of light relative to a destination. Of course, a single gravitational wave travels the speed of light, so I know I can't go any faster by riding one of those, but my scientists are proposing that I ride the moving interference pattern between two sets of waves, since a local maxima caused by wave interference can effectively move significantly faster than $c$, based on the angle of the intersecting wave patterns.
If we image the blue sections of this image to be peaks in which the fabric of space is streched, we can travel in one of the blue bubbles, which should "move" faster than c, since they don't represent an actual moving wave, but rather the intersection point between two waves.
The effective propagation speed of one of the intersection points is based on the angle at which the two waves intersect. Specifically, propagation speed s can be given by the equation $s=u/\sin{\theta}$, where $u$ is the speed of the wave front and $\theta$ is the half-angle between two otherwise symmetric waves.
My scientists tell me that, if we line a potential space lane with gravitational wave emitters, we can create a route that can be traveled at what are effectively superluminal velocities. However, they're asking me for a very large sum of money to do this. Should I fund their project or rescind their grant money and feed them to my pet sharks?
This post was sourced from https://worldbuilding.stackexchange.com/q/36113. It is licensed under CC BY-SA 3.0.
1 answer
No can do.
I was able to find the answer here, written by LIGO scientist Dr. Amber Stuver:
How valid is the wave-like-in-water analogy? Can we "surf" these waves? Are there gravity "peaks" like there are "wells"?
Stuver: Because gravitational waves can travel through matter unchanged, there isn't a way to surf them or use them for another kind of propulsion. So no gravitational-wave surfing.
The "peaks" and "wells" is an excellent point. Gravity is always attractive because there is no negative mass. We don't know why but it has never been observed in a lab or any evidence found elsewhere in the universe. So gravity is usually represented on spacetime graphics as being a downward curvature, or your "well." A mass traveling by the "well" will tend to bend inward toward it; this is gravitational attraction. If you had negative mass, you would have repulsion, which would be represented by a "peak." A mass moving by a "peak" would tend to bend away from it. So there are"wells" but no "peaks."
The water analogy is very good at talking about how the strength of the wave decreases as it travels away from its source. A water wave will get smaller and smaller just like a gravitational wave will get weaker and weaker.
Slightly simplified, this means that you can't use gravitational waves for propulsion because they don't transfer energy quite in the same way that water waves do. The analogy breaks down further because gravitational waves are plane waves, not sinusoidal waves - so you shouldn't try to visualize them as being anything like water waves.
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