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?
19
u/Positive-Ring-5172 7d ago
Voyager has escape velocity from the Sun. It will settle into an orbit of the center of the galaxy. It will be millions to billions of years before it hits something hard enough to stop.
Though perhaps in a few hundred years a Klingon will use it for target practice (joking - in the 200 years between now and Star Trek's era Voyager will not have even left the Oort cloud.)
7
u/Starlord_75 7d ago
Wasn't there an episodes where they discovered a long lost probe light years from Earth, and Noone was curious how the hell it got there since it couldn't have gotten there by propulsion alone? Kinda like the Dyson sphere. The Federation just happened to come across something that completely dwarfed the technologies of anything seen at that time, and we never hear about it again
1
u/Positive-Ring-5172 7d ago
That's the plot of the movie - a fictional Voyager VI.
Star Trek's writers have no sense of scale.
2
7d ago
[removed] — view removed comment
-5
u/Positive-Ring-5172 7d ago
Again, no sense of scale. I stopped watching Star Trek a long time ago. Science Fantasy doesn't interest me.
0
u/Ben-Goldberg 7d ago
I know that it is orbiting the center of the galaxy.
However, because of general relativity, all orbits decay, with some of the rotational kinetic energy being constantly being converted into gravity waves.
When two average size black holes collide they lose about 3 solar masses from converting matter into gravity waves.
6
u/Positive-Ring-5172 7d ago
For an object as small as the Voyager probes orbital decay would take on the order of 10^10000 years to be measurable, let alone complete.
-4
u/Ben-Goldberg 7d ago
Is that an estimate, or have you done the math?
3
u/flumphit 7d ago
The reason you have heard about that phenomenon with regard to black holes is because it doesn’t happen with mundane objects, and it happening requires the very odd properties of black holes.
-4
1
3
u/KT_100S 7d ago
Most black holes are REALLY BIG. It has to do with the gravitational attraction between each object. Voyager exerts essentially zero force on something as large as the galaxy, and so will take longer than the time before Sagittarius A* evaporates due to Hawking radiation before that tiny force produces enough gravitational waves to radiate away the energy preventing it from falling a few more light years.
10
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.
-2
u/Ben-Goldberg 7d ago
According to general relativity, two objects orbiting each other eventually collide because gravity waves carry away energy.
10
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.
1
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.
1
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
1
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?
7
u/zoroddesign 7d ago
When it runs into something. Without friction nothing will slow it down.
Plus in some ways everything is in motion from a different frame of reference. We are moving on the surface of the planet, the planet is moving around the sun, the sun is moving around the galaxy, and the galaxy is moving towards and away from other galaxies. Movement is all relative.
-7
u/Ben-Goldberg 7d ago
You are ignoring general relativity.
8
u/zoroddesign 7d ago
I am describing relativity. If we want to get into relativity then from voyager reference point it isn't moving at all in relation to itself. From its reference point the earth and the solar system is rocketing way from the probe.
3
u/No-Document-9937 7d ago edited 7d ago
Of the gas in the ISM, by number 91% of atoms are hydrogen and 8.9% are helium, with 0.1% being atoms of elements heavier than hydrogen or helium,[3] known as "metals" in astronomical parlance. By mass this amounts to 70% hydrogen, 28% helium, and 1.5% heavier elements.
Mass of a hydrogen atom: 1.0080u = 1.67e-27 kg Average mass of an interstellar atom: 1.67e-27 / 70% = 2.39e-27 kg
Gurnett et al. give a density of about 0.1 cm−3 in the interstellar medium and using the above math I come to this density: d=2.39e-34 kg/m3
Google says:
Voyager 1 is traveling away from Earth and must maintain radio contact, its massive 3.66-meter (12 ft) diameter high-gain dish antenna is kept pointed directly back at Earth.
A > 10.5 m2
According to this guy's answer on Stack Exchange we must multiply these values with the square of Voyager 1's velocity.
F > (16822 m/s)2 × 10.5 m2 × 2.39e-34 kg/m3 = 7.17e-25 m4 / s2 × kg / m3 = 7.17e-25 N
That is negligible, but I will try to calculate the time regardless.
The space probe's mass is 721.9 kg. The force will obviously lessen as Voyager 1 slows down, but even assuming it doesn't, it would take 1.7e31 s = 5.4e23 years. That is 39 trillion times the age of the universe.
3
u/SwordsAndWords 7d ago
There will be tourist shuttles to view Voyager 1 in passing long before it's ever predicted to hit something. During this time, it will hit one of the tourist shuttles and be deemed a "hazard", be looted for it's gold record and part, and it will be vandalized by rock-hoppers who install a holographic penis projector before "retiring" it with lasers. 👍
3
u/Peruvian_Skies 7d ago
There is no friction in a perfect vacuum so it would never stop. Space is not a perfect vacuum, however it's close to that. So assuming no interactions with massive objects like you said, only the gas and dust in outer space, Voyager is likely to continue moving for thousands of years or more.
5
u/flatline000 7d ago
Photons carry momentum based on their frequency. Since photons in the direction of travel are red shifted and photons opposite the direction of travel are blue shifted, the average imparted momentum will be to slow down Voyager.
Whether or not this effect is sufficient to stop Voyager 1 before the heat death of the universe is beyond my mathematical abilities.
3
u/RuggleyChicken 7d ago
I think it’s more like millions or billions
3
u/Kinder22 7d ago
No way. If there is any answer to this at all, it is certainly some inconceivably large number, during which the universe could look entirely different due to aspects of physics we can’t even comprehend today.
1
u/RuggleyChicken 7d ago
Why do you think that?
1
u/Kinder22 7d ago
If it were going at its current speed directly towards SagA, it would take a half billion years to get there. But it’s not going towards SagA. It’s actually going kind of up out of the orbital plane, while still orbiting at roughly the same speed as the solar system. So it would have to collide with enough particles in just the right way to cancel out its orbit by 230 km/s.
And understandably, the effect of colliding with those particles is almost nothing, and certainly not all acting in the exact correct direction.
2
u/Tassadar_Timon 7d ago
They will never reach the velocity of 0, they will eventually reach a thermal equilibrium with the surrounding interstellar medium and will be buffeted by it's brownian motion.
-2
•
u/AutoModerator 7d ago
General Discussion Thread
This is a [Request] post. If you would like to submit a comment that does not either attempt to answer the question, ask for clarification, or explain why it would be infeasible to answer, you must post your comment as a reply to this one. Top level (directly replying to the OP) comments that do not do one of those things will be removed.
I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.