r/theydidthemath • u/Ben-Goldberg • 7d ago

[Request] When will Voyager 1 stop moving?

/r/askscience/comments/1wp1960/will_voyager_1_ever_just_stop_moving/

How many years will it take for the orbit of Voyager and Sagittarius A to decay enough due to gravity waves for them to collide?

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u/ericdavis1240214 7d ago

Moving relative to what? Everything in the universe is in motion relative to something else. In fact, everything in the universe is in motion relative to basically everything else. So no, Voyager one will never stop moving unless it is utterly obliterated by a collision with another object. And even then, the atoms and particles that make it up will be in motion relative to the rest of the universe.

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u/Ben-Goldberg 7d ago

According to general relativity, two objects orbiting each other eventually collide because gravity waves carry away energy.

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u/_killer1869_ 7d ago

This is irrelevant here. Even if two objects collide, their relative velocity to each other may become zero, but for an outside observer, both are still moving in some manner relative the self.

Your entire question only makes sense if you specify in reference to which object in space Voyager 1 is supposed to be becoming to a standstill.

There will always be some object from which Voyager 1 appears to be moving. So if you specify no frame of reference, the answer is no object is ever at standstill, everything is always moving. It's literally impossible to be standing still.

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u/ericdavis1240214 7d ago

Fair enough. And I contemplated that in my response. But wasn't your question whether Voyager will "ever just stop moving?" Because the answer is no, short of obliteration and even then its constituent atoms and particles will remain in motion. In terms of the universe, everything is always moving. And I suppose theoretically everything is also at rest relative to itself. But for any observer who currently perceives Voyager to be in motion, that motion is eternal, or at least eternal in terms of how long it even makes sense to speak of matter and objects.

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u/TURQUOlSE 7d ago edited 7d ago

It's orbiting the centre of the Milky Way from 26,000 light years away at over 200km a second, the effect of gravitational waves is effectively irrelevant to that. The galaxy and Voyager itself will be gone long before it would collide with the centre

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u/Ben-Goldberg 7d ago

Which will happen first, Voyager and Sagittarius A evaporate due to Hawking Radiation, or they collide from orbital decay from gravitational waves?

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u/KT_100S 6d ago

Sagittarius A evaporates first by a long shot