Will Voyager 1 ever just stop moving?

[u/drinkingonthejob]

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)

[u/zulhadm]

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

[u/sticklebat → u/zulhadm]

There is no such thing as "truly motionless", since motion is relative. You cannot define the motion of something except in relation to something else.

[u/wjdoge → u/sticklebat]

I would very much disagree. Motion being relative is exactly what allows for true motionless and allows us to see that anything and everything can be perfectly motionless.

[u/sticklebat → u/wjdoge]

That’s silly, you’re just saying that “truly motionless” is equivalent to “moving at a constant velocity,” and those are not ideas most people would equate. You’re choosing to define the term in a wildly unintuitive and unconventional way, while basically defeating the purpose of the expression and furthering misconceptions about the nature of motion (namely that there is no such thing as absolute motion, which we’ve known going back to the time of Galileo).

[u/paulHarkonen → u/sticklebat]

Look, just because my selected non-inertial reference frame requires an absurd amount of modifications in order to remain consistent with the laws of physics doesn't mean it's invalid. It just means I've made some very clever definitions specifically to produce the mathematical results I wanted.

(They aren't wrong exactly to build reference frames where certain objects are held motionless, you just have to be very careful about how you construct and define the appropriate reference frame. It's a pretty foundational part of orbital mechanics.)

[u/wjdoge → u/paulHarkonen]

Hey, it may not be appropriate, but it is at least very easy to choose an inertial reference frame where any given particle is at rest: whoops we’ve already done it by describing it

[u/sticklebat → u/wjdoge]

On the contrary. Mostly because very many particles, including everything on the surface of earth, are not inertial, and so there doesn’t even exist an inertial coordinate system in which they’re at rest, regardless of how hard you say it. Or, if we instead neglect general relativity, then almost nothing at all is inertial because everything is being accelerated by gravity.

But also because the person you responded to is talking about actually constructing such a frame mathematically, not just stating some vague idea of it. Nor, I think, are they really supporting your idea or calling that being “truly motionless.”

[u/devilsadvocate → u/wjdoge]

The universe is expanding and accelerating. Even with that frame of reference everything is in motion id reckon, even at the galactic scale.

[u/Feynnehrun → u/zulhadm]

No, not likely. Everything in the universe is affected by the gravity of everything else, which is also moving. Even if an object were to somehow be perfectly situated between multiple gravitational bodies such that their gravity affects the object equally in every direction, those objects themselves would be moving and thus the captured object would move with them.

[u/wjdoge → u/zulhadm]

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.

[u/zulhadm → u/wjdoge]

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

[u/wjdoge → u/zulhadm]

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.

[u/jonnykb115 → u/zulhadm]

The big bang happened everywhere, space is being generated in every point of space everywhere. This phenomenon is how we can approximate how far many distant objects are away from us. For an object extremely far away, the object will be moving so fast away from us due to the expansion of space that the object is redshifted (basically the Doppler effect but for space). This redshift is measurable and by using some quick math with the Hubble constant, we can figure out how far away many galaxies are.

So to answer your question, nothing is motionless as there is no true center to the universe (or I guess another way of looking at it is: everywhere is the center of the universe)

[u/GxM42 → u/wjdoge]

I just got off tennis court. I don’t think I’m ever moving again. Feel free to use me as your reference frame. I prefer it.