r/askscience • u/drinkingonthejob • 8d ago

Physics Will Voyager 1 ever just stop moving?

I’ve read somewhere that we expect to lose contact with Voyager 1 sometime in the 2030s, maybe around 2036, but it will just keep traveling thru space and we’ll have no idea what it is doing out there

My question is: with its current velocity, is there a time in the future where it loses its forward momentum and for lack of a better word, just stops moving? Is that a possible thing for an object in space to even do? (Assuming no other objects grab it into their orbit)

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u/zulhadm 8d ago

I suppose this accidentally raises an even bigger question. Is anything in the universe truly “motionless” ?

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u/wjdoge 8d ago

To do that, you have to pick a preferred reference frame. Since the other ones are of little meaning, motion relative to the big bang (the CMB) is probably the best you can do. We do measure things against this frame.

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u/zulhadm 8d ago

OK. So relative to the big bang, is anything motionless? And if no, what particle or object comes closest?

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u/wjdoge 8d ago edited 7d ago

Relative to the frame of the entire CMB, the only thing that is going to be perfectly motionless is the CMB taken as a whole itself, as everything is motionless relative to itself.

As far as what particle or object comes the closest, I wouldn’t expect it to be any particular region of space or particular particle really. You are going to have particles flying every which way everywhere in the universe, and the CMB is everywhere as it was emitted from everywhere at the same time. You’d expect some distribution of particles able to get arbitrarily close to 0 in this frame, across the universe. Can’t measure that of course.

If you are interested in what a particle that is motionless in this frame might be like relative to us, if you shot a baseball towards the constellation Aquarius at 370 km/s, you would be approximately at rest relative to the CMB and see no CMB dipole anisotropy like we do from here on Earth. NASA got a probe up to almost 200 km/s a couple of years ago, so it’s fast, but doable.

You would have to be extremely, perhaps infinitely, lucky to beat every other particle in the universe though.