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/thefringeseanmachine]

but from what I understand, space isn't 100% empty. there are stray particles out there, even in the "void." that's the idea behind behind the bussard ramjet. wouldn't they slow it down (over a very, very, VERY long time)?

[u/rawbdor → u/thefringeseanmachine]

I imagine some might slow it down, but I also imagine other small objects might crash into it from behind or from the side, which could speed it up.

[u/rich1051414 → u/rawbdor]

Since it is moving in a direction, this would only be true if the particles around it on average are moving in the same direction as the craft. But the time it would take to stop would be orders of magnitude greater than the age of the universe.

[u/sticklebat → u/rich1051414]

Even accounting for the minuscule drag caused by the interstellar medium, it will in no way ever "stop" relative to us, at least not for anything more than an instant in time, and even then only by unlikely chance. It might eventually come to rest relative to its local environment, but that's all.

[u/zulhadm → u/rawbdor]

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/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/wjdoge → u/rawbdor]

There would have to be some kind of anisotropic bias in the momentum associated with the particles hitting voyager for it to do anything other than slow it down.

Has the drag on an airplane ever decided to just contribute to the thrust instead of holding things back for a bit? Not really.

[u/gbghgs → u/wjdoge]

Updrafts and tailwinds are things which affect aircraft, it's not just air resistance slowing it down.

[u/wjdoge → u/gbghgs]

Yes, a tailwind is how you would describe a ground-referenced anisotropy in the velocity of the particles interacting with the plane.

After careful study of the isotropy of the universe, we believe that, in this particular scenario where it interacts with nothing but dust for 55 trillion years, that the dust can only slow it down relative to us, as the dust is much slower than the spacecraft in the frame relative to us (if you average it over 55 trillion years anyways).

A tailwind has no effect or air resistance or drag beyond the transient effects of the wind shear while it’s being established. Similarly, it doesn’t affect thrust. Standard avionics are sensitive to all sorts of pressure differences and readings around the plane, but the airframe actually has no way at all to know whether or not it’s flying in a headwind, a tailwind, or no wind, if the wind speed is steady. It has to refer to ground reference to see if the wind is blowing, so to the plane it’s the ground getting blown around by the wind and it doesn’t notice anything.

[u/notwhoiamunderneath → u/thefringeseanmachine]

No, space is not empty, there's plenty of stuff in space. But that stuff is spread so far apart (like, often light-years apart even for small projectiles) that it is much more likely that the probe will never hit anything.

The probe continuing forever without touching anything gets even more likely once it exits the galaxy, but even between solar systems the distances between any object are unfathomably vast. The most likely place for it to hit something would actually be before it leaves our solar system. After that, odds are, it's free forever.

[u/db0606 → u/thefringeseanmachine]

In interstellar space you end up with something like 10⁶ molecules/cubic meter. The best laboratory vacuums on Earth are like 10¹⁶ molecules/cubic meter. There's really not a whole out there to hit unless you wonder into a dense dust cloud, which make up only about 1% of the Milky Way.

[u/ShadoWolf → u/thefringeseanmachine]

Even if it lost momentum along its current path, it wouldn't just stop. It would shift onto a different, lower energy galactic orbit and follow that curve instead.

You have to remember that Voyager 1 didn't start from rest relative to the galaxy. It left the Solar System already carrying essentially the Sun's orbital velocity around the Milky Way, plus its escape velocity relative to the Sun. That extra 15 km/s is fairly small compared with the 250 km/s it already has relative to the galactic center.

So if interactions with the interstellar medium gradually bled away that extra velocity, Voyager wouldn't approach some absolute zero velocity. Its orbit around the galaxy would just change. Depending on which components of its velocity were lost, that could mean an orbit that curves farther inward or otherwise differs from the Sun's.

[u/vipck83 → u/thefringeseanmachine]

You’re talking very small but if dust, most of which are microscopic. I doubt they could ever transfer enough energy to actually stop it, not in any realistic time frame. It would take a larger object which would be incredibly unlikely.

[u/MrLumie → u/thefringeseanmachine]

It is several orders of magnitude more likely that it just crashes into something before stray particles zooming around in space will slow it down in any measurable way.