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Old 03-17-2017, 10:42 PM
tullsterx tullsterx is offline
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What if our solar system were isolated?

If the rest of the universe. . . disappeared FOR SOME UNKNOWN REASON. Would we feel the effects? If there were no more stars, how would it affect our solar system?
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Old 03-17-2017, 10:44 PM
Little Nemo Little Nemo is offline
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We'd lose a lot of our ability to navigate without instruments.
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Old 03-17-2017, 10:51 PM
Debillw3 Debillw3 is offline
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It'd ultimately depend on what "disappeared" means.

Put simply, if the rest of the galaxy disappeared, leaving just our solar system, the effect would be comparable to what would happen if the rest of the solar system (including the Earth) disappeared, leaving just the Moon.

Just as the Moon orbits the Earth and the Earth orbits the Sun, the Sun orbits within the galaxy.

It's an oversimplification, but I'm sure you can understand the havoc that would play with regard to the orbital mechanics. The extent of that havoc would be determined by where it went and how it got there.
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Old 03-17-2017, 11:06 PM
tullsterx tullsterx is offline
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Originally Posted by Debillw3 View Post
It'd ultimately depend on what "disappeared" means.

Put simply, if the rest of the galaxy disappeared, leaving just our solar system, the effect would be comparable to what would happen if the rest of the solar system (including the Earth) disappeared, leaving just the Moon.

Just as the Moon orbits the Earth and the Earth orbits the Sun, the Sun orbits within the galaxy.

It's an oversimplification, but I'm sure you can understand the havoc that would play with regard to the orbital mechanics. The extent of that havoc would be determined by where it went and how it got there.
Well, yeah, but how would that take? I mean, we're currently on the long highway-to-hell with our Sun. Seems like it could take a while to feel those effects. In my scenario we still have mass and gravity and physics and all of the principals that make our solar system "function."
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Old 03-17-2017, 11:15 PM
Debillw3 Debillw3 is offline
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Well, yeah, but how would that take? I mean, we're currently on the long highway-to-hell with our Sun. Seems like it could take a while to feel those effects. In my scenario we still have mass and gravity and physics and all of the principals that make our solar system "function."
But from your post, we aren't talking about a gradual thing--we're talking about something that just suddenly disappears.

The Sun (and, likewise, the solar system in general) orbits a center of gravity within the galaxy.

If that were to suddenly disappear, it can be comparable to the Earth disappearing on the Moon.

The solar system, though a system in & of itself, is also part of a larger system within the galaxy, which is, itself, part of a larger system.

While the solar system would likely continue to function within itself, the larger systems that the solar system is part of would cease to exist, which wouldn't be good.

As I said, this is an oversimplification, but I think it works for the purposes of discussion.
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Old 03-17-2017, 11:50 PM
Dr. Strangelove Dr. Strangelove is online now
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If Mach's principle is correct, losing the rest of the universe might really screw up inertia. As in, it might take on a really small coupling constant or disappear completely.

Mach's principle is the idea that inertia (linear and rotational) only come about because of the global distribution of matter--that somehow they influence spacetime in a way that gives us inertia. Take away the matter and this influence goes away, along with inertia itself (there might be some left over from local influences, but not a lot).

Mach's principle is probably wrong, and certainly unproven. But it also hasn't been ruled out completely.
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Old 03-17-2017, 11:57 PM
buddha_david buddha_david is offline
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When it comes time to evacuate the solar system in 4½ billion years as the sun goes nova, our options will be severely limited.
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Old 03-18-2017, 12:00 AM
eschereal eschereal is offline
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The earth would have a lot less boron.
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Old 03-18-2017, 12:54 AM
markn+ markn+ is offline
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Originally Posted by Debillw3 View Post
Just as the Moon orbits the Earth and the Earth orbits the Sun, the Sun orbits within the galaxy.

It's an oversimplification, but I'm sure you can understand the havoc that would play with regard to the orbital mechanics.
You're suggesting that the orbital mechanics of the solar system are affected by the gravitation of the rest of the galaxy? This seems very unlikely to me. I don't think the orbits of the planets would be affected at all if the rest of the galaxy disappeared.

As a first order approximation, based on the fact that the solar system orbits the galactic center every 230 million years, and is 27,000 light years from the center, I use Kepler's Third Law to calculate that the galaxy as a whole exerts a gravitational force equivalent to a mass of 3x1040 kilograms at the distance of the galactic center. (Details of calculation on request.) This is equivalent to a mass of 1x1022 kg at one astronomical unit. In other words, it's the same as the pull of a body 1/7 the size of the moon at the distance of the sun. This is very small. Furthermore, it's essentially uniform across the whole solar system. I don't think it affects the planets' orbits in any significant way.
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Old 03-18-2017, 01:11 AM
Debillw3 Debillw3 is offline
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You're suggesting that the orbital mechanics of the solar system are affected by the gravitation of the rest of the galaxy? This seems very unlikely to me. I don't think the orbits of the planets would be affected at all if the rest of the galaxy disappeared.
No, I'm suggesting that the orbital mechanics of the solar system as a system (not the individual entities that make it up themselves) are affected by the gravitation of the galaxy--which is why it orbits in the first place.

I'm then further suggesting that a sudden cessation of those forces would have an effect on the solar system as a system.

The extent of that effect, as I further suggested, would have a great deal to do with the reason for that cessation. Obviously something like a black hole would have a greater impact than a sudden "poof" (which could well be negligible).

As I acknowledged, my analogy was an oversimplification, as I didn't feel like doing the math (kudos to you on that, by the way) or getting into the nitty gritty of how orbits actually work, but I felt it worked as a sample what type of thing we're talking about.

I never intended to discuss the effect (which, again, could be negligible) on the Earth itself, as that would depend on a number of factors not specified, but, rather, the solar system as a systematic whole.
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Old 03-18-2017, 01:32 AM
mikecurtis mikecurtis is online now
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Originally Posted by tullsterx View Post
Well, yeah, but how would that take? I mean, we're currently on the long highway-to-hell with our Sun. Seems like it could take a while to feel those effects. In my scenario we still have mass and gravity and physics and all of the principals that make our solar system "function."
well, if you still had the entire space/time of the universe, since gravity "travels" at c; we probably wouldnt even notice for over 4 yrs, as thats how far the closest object of any significance is. and it would take another 27,000 yrs for all of the gravitational effects of our own galaxy to disappear. then another 2.5 million yrs for the gravity from andromeda to start to disappear...etc. i'm not sure what the effects would be, but it would happen very slowly (in human terms)

mc
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Old 03-18-2017, 02:10 AM
watchwolf49 watchwolf49 is offline
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well, if you still had the entire space/time of the universe, since gravity "travels" at c; we probably wouldnt even notice for over 4 yrs, as thats how far the closest object of any significance is. and it would take another 27,000 yrs for all of the gravitational effects of our own galaxy to disappear. then another 2.5 million yrs for the gravity from andromeda to start to disappear...etc. i'm not sure what the effects would be, but it would happen very slowly (in human terms)

mc
Stars would wink out one-by-one ... that would be cool ...
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Old 03-18-2017, 03:14 AM
Derleth Derleth is online now
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Originally Posted by Dr. Strangelove View Post
If Mach's principle is correct, losing the rest of the universe might really screw up inertia. As in, it might take on a really small coupling constant or disappear completely.

Mach's principle is the idea that inertia (linear and rotational) only come about because of the global distribution of matter--that somehow they influence spacetime in a way that gives us inertia. Take away the matter and this influence goes away, along with inertia itself (there might be some left over from local influences, but not a lot).

Mach's principle is probably wrong, and certainly unproven. But it also hasn't been ruled out completely.
Here's a more mathematical development of the concept, with some interesting analogies to electromagnetism not in the sense of unifying EM and gravity, but in the sense of applying the same concepts and machinery to both:
Quote:
Now if gravity behaves like electromagnetism, we can simply hijack the mathematical formalism of electromagnetism in order to calculate gravitational effects. This isn't always true. But for the simple case we're going to consider it is. We look at a "test particle", a massive object that's so small that it doesn't disturb any of the stuff it finds itself in. It's located in a universe much like ours, but to keep things simple we assume that everything in the universe, other than the test particle, is smeared out smoothly throughout space. We now let our test particle move along a straight line in this stuff and ask: What is the force of gravity on the test particle due to the rest of the stuff? In general, both "gravito-electric" and "gravito-magnetic" fields, the gravitational counterparts of electric and magnetic fields, may act. In this case, however, the gravito-magnetic field itself doesn't act, so we can ignore it. The reason why is that the rest of the stuff out there doesn't "circulate", so the "curl" of the vector potential vanishes.

[snip]

Well, all of this is fine, but maybe we don't have to take the effects of gravito-magnetism and the vector potential seriously. Perhaps they're so minute they can be ignored. Turns out that that's not true. As Ken Nordtvedt pointed out in 1988 [International Journal of Theoretical Physics, 27, 1395-1404], gravito-magnetic effects must be taken into account in even the simplest planetary orbit calculations. Only a moment's reflection is needed to see that this must be right. From Newtonian mechanics we know that the gravitational force acting on a planet must act along the instantaneous line of centers of the planet and the Sun if an elliptical orbit is to be recovered. (That is, the force exerted by the Sun must propagate to the planet instantaneously. This fact is the reason why Newtonian gravitation is called an "action-at-a-distance" force. Newton privately thought this preposterous; but he never found a way around it.) If relativity is right, then the gravito-electric field (i.e., Newtonian gravity) must propagate at the speed of light, and the corresponding gravitational force on the planet wouldn't point along the instantaneous line of centers. So, if the gravito-magnetic contribution to the total force weren't included, the force of the Sun on the Earth, for example, would point in the wrong direction and its orbit wouldn't be elliptical. (Nordtvedt arrives at this conclusion by a variant of this argument. He shows that the motion of a test particle around the Sun is elliptical for an observer at rest with respect to the Sun. In this frame of reference the field is stationary and everywhere points toward the Sun at all times, so the force is always along the instantaneous line of centers. If the observer moves with respect to the Sun [for example, with the planet], however, and doesn't take into account the gravito-magnetic vector potential, the predicted orbit "blows up". [This example is a neat illustration of the fact that "coordinate transformations" in general relativity theory are equivalent to "gauge" transformations in electrodynamics. The observer at rest with respect to the Sun is effectively in the Coulomb gauge, and the one moving with the planet in the Lorentz gauge.])
This web page is from the Stupid Age of Text Encoding, so all the inline equations are images, and sometimes hard to read. I can transcribe into a PDF form if anyone really has a problem with them.
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Old 03-18-2017, 06:49 AM
Quartz Quartz is offline
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Something similar might actually happen in a billion years or so. The Andromeda galaxy will collide with the Milky Way and the Sun with the solar system could be ejected as a result.
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Old 03-18-2017, 07:56 AM
John DiFool John DiFool is online now
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I heard something similar will happen in 40-50 billion years, thanks to expansion (all other stars and objects will recede beyond our visual horizon).
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Old 03-18-2017, 08:47 AM
Quartz Quartz is offline
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I heard something similar will happen in 40-50 billion years, thanks to expansion (all other stars and objects will recede beyond our visual horizon).
You may be thinking of Wikipedia's Timeline of the Far Future, wherein that figure refers to galaxies beyond the Local Group. The timescale for that particular event is given as 100 billion years, and the Local Group will coalesce into a single galaxy in around 450 billion years.
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Old 03-18-2017, 08:51 AM
Chronos Chronos is offline
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The rest of the Galaxy disappearing would wreak havoc with the orbital mechanics of the Galaxy. It would have almost no effect on the orbital mechanics of the Solar System. The Sun with its entourage of planets would fly off on a tangent to its current path, but there's no reason we would care about that.

Quote:
Quoth John DiFool:

I heard something similar will happen in 40-50 billion years, thanks to expansion (all other stars and objects will recede beyond our visual horizon).
Not under most models of cosmological expansion. Objects as small as galaxies or even galaxy clusters have more than enough gravity to hold themselves together against the cosmological expansion. The only way to rip apart a galaxy would be if the dark energy dramatically increases in strength. While there are some plausible models that predict that, they usually go much further: Not long after the point where galaxies would be dispersed, so would solar systems, planets, and individual atoms.
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Old 03-18-2017, 09:43 AM
rbroome rbroome is offline
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Here's a more mathematical development of the concept, with some interesting analogies to electromagnetism not in the sense of unifying EM and gravity, but in the sense of applying the same concepts and machinery to both:This web page is from the Stupid Age of Text Encoding, so all the inline equations are images, and sometimes hard to read. I can transcribe into a PDF form if anyone really has a problem with them.
Thanks for the link!
fascinating read.
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Old 03-18-2017, 02:00 PM
Hari Seldon Hari Seldon is offline
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A lot of speculation for GQ, but my first (and last impression) is Chronos's. I cannot see why the gravity of the rest of the universe would have any discernible influence on the solar system. Unless Mach's principle is correct.
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Old 03-18-2017, 03:36 PM
joema joema is offline
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No, I'm suggesting that the orbital mechanics of the solar system as a system (not the individual entities that make it up themselves) are affected by the gravitation of the galaxy--which is why it orbits in the first place....
If the rest of the universe vanished, the practical effect on our solar system would be microscopic. We know this for two reasons:

(1) Even though gravity has infinite range, it drops off in inverse proportion to the square of distance. E.g, double the distance and gravity is 1/4 as much, triple the distance and it's 1/9th as much quadruple the distance and it's 1/16th as much, etc.

The inverse square law coupled with the gigantic interstellar and intergalactic distances means the gravitational effect of the rest of the universe on our solar system is very small.

We can easily calculate this using the sun which contains 99.86% of the mass of the entire solar system. The sun's mass is 1.99E30 kg. The combined mass of the closest star system, Alpha Centauri, is 2.1 times this, or 4.18E30 kg.

The physical force between the entire Alpha Centauri star system and the sun is given from the equation for gravitational attraction. Fortunately there's an on-line calculator which allows entry in solar masses and light years: http://www.ajdesigner.com/phpgravity...e.php#ajscroll

The resultant force is 6.45E17 newtons or 6.58E13 metric tons of force. This sounds like a lot but it's roughly the water mass of the Caspian Sea: https://goo.gl/maps/aMazWBGeoX12

Relative to the mass of the sun (99.86% of the solar system), this is microscopic. We can even calculate how much the presence or absence of this force would accelerate the sun from F=ma. The sun's mass is 1.99E30 kg. This would accelerate the sun (or our solar system) at 3.24E-13 meters per sec^2, or less than the diameter of a single hydrogen atom per second. The effect would be so slight it could not be measured with the most sensitive instruments. And that is from the *closest* star system. Due to the gravitational inverse square law, more distant bodies (even if far more massive) would have even less effect.

(2) Gravity moves at the speed of light. Most of the mass of our galaxy (much less the universe) is vastly far away. Even if it vanished instantly, it would take eons of time for most of that tiny force difference to reach earth.
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Old 03-18-2017, 07:08 PM
dtilque dtilque is online now
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Stars would wink out one-by-one ... that would be cool ...
All right! Who wrote down the 9 billionth name? Was that you, Watchwolf?

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Originally Posted by Quartz View Post
Something similar might actually happen in a billion years or so. The Andromeda galaxy will collide with the Milky Way and the Sun with the solar system could be ejected as a result.
The merger with Andromeda is going to be more like 3 billion years from now. And even if the Sun is ejected, it'll take something like a million1 years before it's far enough away that we can't see the merged galaxies with the naked eye. They'll still be very visible with a telescope, of course.

AFAIK, the only significant gravitational effect from the galaxy as a whole on the orbital dynamics of the solar system is that Oort Cloud objects had their orbits circularized by it after being ejected from the inner parts of the system. If that hadn't happened, all them would have returned to the inner system over and over again long ago and we would no longer have any long period comets.


1 Rectally-extracted number, but it should be within an order of magnitude of being correct. The actual number will depend on the speed of ejection, of course.
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Old 03-20-2017, 04:09 AM
UY Scuti UY Scuti is offline
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If the rest of the universe disappeared leaving the solar system on its own, it would be catastrophic.

The Sun doesn't just float in void. It is part of a galaxy, which behaves like disk rather than a bunch of random celestial bodies. The disk behavior has probably a lot to do with dark matter. Dark matter and dark energy account for over 90% of what the universe includes.

Does the question refer to the disappearance of dark matter and dark energy? If so, the rules of physics would change completely. They would change radically even if the solar system existed on its own, retaining a small fraction of the existing dark energy and dark matter as well. Either way, I don't think the solar system would function as the solar system anymore, which is why I said it would be catastrophic. But from a non-human perspective it might be interesting, who knows?
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Old 03-20-2017, 06:51 AM
joema joema is offline
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Originally Posted by UY Scuti View Post
If the rest of the universe disappeared leaving the solar system on its own, it would be catastrophic....Does the question refer to the disappearance of dark matter and dark energy? If so, the rules of physics would change completely. They would change radically even if the solar system existed on its own, retaining a small fraction of the existing dark energy and dark matter as well. Either way, I don't think the solar system would function as the solar system anymore...
As I showed two posts above yours, basic gravity equations seem to indicate there would be no significant effect on our solar system if the rest of the universe vanished.

Since gravity travels at the speed of light it would take eons of time for most of that difference to reach our solar system. For this same reason you wouldn't see large numbers of stars or galaxies immediately wink out of existence.

After several years went by and the light from the first vanished star had time to reach earth, it is unlikely anybody except an astronomer would notice this. There are only about 26 stars within 12 light years of earth. As decade after decade passed, a few more would gradually vanish from view but most of the stars would still appear in the heavens for millennia -- even if they no longer existed in the universe. Likewise their gravitational effect -- moving at the speed of light -- would still exist from earth's standpoint.

If all galaxies suddenly vanished it would take 2.5 million years for the light and gravity effect of the *closest* spiral galaxy Andromeda to reach earth. Maybe an advanced alien race disintegrated Andromeda a million years ago and it's no longer there. If so we won't know it or detect any tiny gravity effects for another 1.5 million years.

When that gravitational difference finally arrived, the effect would be microscopically small relative to the mass of the solar system. Planets would not leap from their orbits. This has nothing to do with dark matter, which is thought to only effect galactic structure on a large scale, not a solar system scale.
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Old 03-20-2017, 10:55 AM
Mr. Bill Mr. Bill is offline
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You're suggesting that the orbital mechanics of the solar system are affected by the gravitation of the rest of the galaxy? This seems very unlikely to me. I don't think the orbits of the planets would be affected at all if the rest of the galaxy disappeared.

As a first order approximation, based on the fact that the solar system orbits the galactic center every 230 million years, and is 27,000 light years from the center, I use Kepler's Third Law to calculate that the galaxy as a whole exerts a gravitational force equivalent to a mass of 3x1040 kilograms at the distance of the galactic center. (Details of calculation on request.) This is equivalent to a mass of 1x1022 kg at one astronomical unit. In other words, it's the same as the pull of a body 1/7 the size of the moon at the distance of the sun. This is very small. Furthermore, it's essentially uniform across the whole solar system. I don't think it affects the planets' orbits in any significant way.
I read a while back in a newspaper article about comets that it is believed that comets are first nudged out of the Oort Cloud and into their typical extremely eccentric orbits by the gravitational influence of nearby galaxies.

I think that when we consider astronomical phenomena, in addition to the vast distances involved, we also have to factor in the vast time scales. A very small influence can have a large effect over a long period of time.
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Old 03-20-2017, 12:03 PM
Lemur866 Lemur866 is online now
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Originally Posted by UY Scuti View Post
If the rest of the universe disappeared leaving the solar system on its own, it would be catastrophic.

The Sun doesn't just float in void. It is part of a galaxy, which behaves like disk rather than a bunch of random celestial bodies. The disk behavior has probably a lot to do with dark matter. Dark matter and dark energy account for over 90% of what the universe includes.

Does the question refer to the disappearance of dark matter and dark energy? If so, the rules of physics would change completely. They would change radically even if the solar system existed on its own, retaining a small fraction of the existing dark energy and dark matter as well. Either way, I don't think the solar system would function as the solar system anymore, which is why I said it would be catastrophic. But from a non-human perspective it might be interesting, who knows?
But as best we can tell, dark matter doesn't have any significant influence on regular matter, besides gravity. That's what makes it dark. If dark matter were constantly interacting with normal matter it wouldn't be dark matter it would be normal matter.

And our solar system doesn't seem to be particularly concentrated with dark matter compared to interstellar space.

So the only difference we'd notice is that we're no longer gravitationally bound to the galaxy, whether that gravitation is caused by dark matter or normal matter or a mix of both would be irrelevant.
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Old 03-20-2017, 12:24 PM
LSLGuy LSLGuy is online now
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Originally Posted by UY Scuti View Post
If the rest of the universe disappeared leaving the solar system on its own, it would be catastrophic.

The Sun doesn't just float in void. It is part of a galaxy, which behaves like disk rather than a bunch of random celestial bodies. The disk behavior has probably a lot to do with dark matter. Dark matter and dark energy account for over 90% of what the universe includes.

Does the question refer to the disappearance of dark matter and dark energy? If so, the rules of physics would change completely. They would change radically even if the solar system existed on its own, retaining a small fraction of the existing dark energy and dark matter as well. Either way, I don't think the solar system would function as the solar system anymore, which is why I said it would be catastrophic. But from a non-human perspective it might be interesting, who knows?
IANA professional scientist, but AFAIK there is no practical or theoretical basis for anything you've said here.

Care to elaborate on why you think all this stuff will change absent the rest of the universe?
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Old 03-20-2017, 12:27 PM
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Cosmic rays would go away.

Some effects:

Production of Carbon-14 would go way down. This would mess with future Carbon-14 dating except that atmospheric testing of nukes already did a number on this.

Fewer electronics would be damaged by cosmic rays. Esp. random flipping of bits in computer memory.

Fewer cases of cancer. Not a lot, but some.

There might be a climate effect. And the ozone layer would suffer less damage. There might be an effect on lightning strikes.

Manned space travel would get safer. Etc.

The dark matter thing is interesting. I wonder if the removal of dark matter outside of our Solar system would create a temporary gravitational effect as the large (but basically uniform) dark matter is our area dispersed. Which wouldn't take long. I.e., if going from uniform to a gradient to uniform would be noticeable.

I checked on if the removal of the heliopause might have an effect, eventually, on the local distribution of the Solar wind. Doesn't seem like it would do much.

As to the Oort cloud. Some pair of objects that were/were not going to collide might now collide or not, then what objects later end up becoming comets could change. But the net effect should still be the same. And we certainly wouldn't be able to tell.
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Old 03-20-2017, 12:41 PM
Darren Garrison Darren Garrison is offline
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I would think that the rest of the universe disappearing would have no noticeable effect at all for almost everyone (other than the night sky becoming more boring.) It would make the chances of long long-term survival much better--no more passing stars nudging comets out of the Oort cloud, no worry about nearby supernovas. Interplanetary travel would become safer--there would still be the solar wind to worry about, but no more concern about cosmic rays. It would make the telescopic search for objects in our own solar system much easier. (I don't know if any of our scientific instruments would have to be recalibrated--does GPS or anything have to take into account the slight relativistic effects of the solar system's 800,000 kph / 138 mile per second orbit around the center of the galaxy? I've never heard that mentioned, and it never crossed my mind to wonder before.)
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Old 03-20-2017, 12:43 PM
LSLGuy LSLGuy is online now
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I thought a bit about the slightly different idea of what would happen if not only did the entire rest of the Universe disappear but also all the consequences of the disappearance arrived here at the same instant.

I thought about Chronos' words from post #17: "The Sun with its entourage of planets would fly off on a tangent to its current path, but there's no reason we would care about that."

I got to wondering just how much centripetal acceleration the solar system currently experiences in its orbit about the galaxy. If that was a big number and it changed suddenly, that might provoke quite a jolt. Which might indeed be something to care about.

So I did the math using data from wiki. The centripetal acceleration of the solar system in its galactic orbit is about 2E-10ms-1. For comparison, Earth's surface gravity is about 1E1ms-1. So the galaxy's collective influence is 2 ten-billionths as strong as Earth gravity. Not a big force.

It's pretty obvious Chronos was right to be unconcerned about any meaningful jolt if this entire minuscule force was suddenly removed. And even more right to be even more unconcerned if it slowly declined over a couple hundred centuries as the gravity changes from distant disappearances eventually propagate their way to us at c.
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Old 03-20-2017, 04:49 PM
Chronos Chronos is offline
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What's more, even if there were a big jolt, it's gravitational. We still wouldn't feel it.
  #31  
Old 03-20-2017, 05:33 PM
dtilque dtilque is online now
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I read a while back in a newspaper article about comets that it is believed that comets are first nudged out of the Oort Cloud and into their typical extremely eccentric orbits by the gravitational influence of nearby galaxies.
If you read that, then whoever wrote it was mixed up. Oort Cloud objects are thought to be nudged by passing stars, not galaxies. Stars come within about 1 light year fairly often, in astronomic terms. The last one happened about 70,000 years ago; the next certain one will be 1.35 million years from now. There's another one which may pass by before that, but more astrometry work needs to be done to be sure.
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Old 03-20-2017, 10:16 PM
LSLGuy LSLGuy is online now
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What's more, even if there were a big jolt, it's gravitational. We still wouldn't feel it.
I was noodling on that idea but couldn't convince myself whether the nature of gravity mattered or didn't. And I don't know enough specific terminology to search up more relevant reading. Physics 202 isn't helpful.

I was speculating that any change in acceleration regardless of cause is still perceptible at least in principle. And if the time of change is short, the jerk goes towards infinity. So if the delta-a is nontrivial ISTM you'd expect to notice something.

Care to throw me a bone here?
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Old 03-21-2017, 04:00 AM
UY Scuti UY Scuti is offline
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But as best we can tell, dark matter doesn't have any significant influence on regular matter, besides gravity. That's what makes it dark. If dark matter were constantly interacting with normal matter it wouldn't be dark matter it would be normal matter.

And our solar system doesn't seem to be particularly concentrated with dark matter compared to interstellar space.

So the only difference we'd notice is that we're no longer gravitationally bound to the galaxy, whether that gravitation is caused by dark matter or normal matter or a mix of both would be irrelevant.
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IANA professional scientist, but AFAIK there is no practical or theoretical basis for anything you've said here.

Care to elaborate on why you think all this stuff will change absent the rest of the universe?
If the information laymen can find in mass media does not come from Laputa, dark matter does influence how systems of regular matter behave. They say "the universe contains roughly five times more dark matter than regular matter, and the gargantuan gravitational force created by all that dark matter influences how galaxies form and evolve. […] its presence greatly influences the motion of regular matter." This is the reason why I predict the solar system would become unstable in the absence of dark matter and its heat death would occur a lot sooner.

Dark energy, on the other hand, plays a much more important role in the fate of the universe. When the solar system is isolated, the universe is suddenly reduced to an infinitezimal crumb. There are various theories, but nobody knows exactly what dark energy consists of, or its mechanism. My opinion is that both its absence and its presence within a tiny portion of the universe will significantly change the parameters of the remaining physical system to such an extent that the solar system will not manage to last for long.

Plus, the solar system would suddenly find itself within a pocket universe, whose physical laws cannot be the same as those of our current universe.
  #34  
Old 03-21-2017, 04:58 AM
LSLGuy LSLGuy is online now
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Originally Posted by LSLGuy View Post
I was noodling on that idea but couldn't convince myself whether the nature of gravity mattered or didn't. And I don't know enough specific terminology to search up more relevant reading. Physics 202 isn't helpful.

I was speculating that any change in acceleration regardless of cause is still perceptible at least in principle. And if the time of change is short, the jerk goes towards infinity. So if the delta-a is nontrivial ISTM you'd expect to notice something.

Care to throw me a bone here?
Never mind the above. I'd intended not to post this after I'd realized it was stupid.

For a bit I was mixing being in a gravitational field which is per Einstein indistinguishable from accelerated motion versus being in "freefall" orbit which is indistinguishable from unaccelerated motion. Once I got the 4 cases connected on the diagonal instead of correctly the rest of the confusion follows. All better now.
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Old 03-21-2017, 06:48 AM
Chronos Chronos is offline
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Quoth UY Scuti:

If the information laymen can find in mass media does not come from Laputa, dark matter does influence how systems of regular matter behave.
More relevantly, most of the information we have comes from Liliput. On a galactic scale, dark matter is hugely significant. On a tiny scale like the Solar System, however, it's nearly irrelevant. And it's the solar system scale that the OP is asking about.
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Old 03-21-2017, 11:49 AM
Lemur866 Lemur866 is online now
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Yes, dark matter does influence normal matter--gravitiationally. It is extremely important for how galaxies or systems of galaxies form and interact, because as far as we can tell galaxies are much more massive than we would expect based on the stars and dust in those galaxies.

That's because, as I said, dark matter appears to interact gravitationally with normal matter, but not in any other way. Dark matter is concentrated in galaxies, but it isn't particularly concentrated in solar systems. So stars and black holes and dust clouds and dark matter orbit around the center of the galaxy. The dark matter passes through our solar system without interacting with it.

So remove the galactic dark matter and what happens? Exactly the same thing that happens when we remove the normal matter from the galaxy. We just lose the gravitational effect. And as was shown above, that gravitational effect is very small. Sure, the galaxy (include all the dark matter) is very large and very massive. It's also very far away and very diffuse.

So yeah, dark matter affects us via gravity, but in no other way. The reason we know that is because if dark matter interacted in other ways, we could detect those ways. Since we can't, we know it doesn't. Or rather, if it does, it interacts so very weakly and rarely that we haven't managed to detect any of those interactions yet, which puts an upper bound on how strong those interactions could be. We know they can't be strong or common, because if they were we'd see them. So the interactions have to happen so rarely and/or so weakly that we haven't managed to detect them over the last 200 years of experimental physics.

Again, we've detected gravitational interaction, but nothing else. And we know our solar system isn't particularly concentrated in dark matter compared to interstellar space because if it were we'd find that every object in orbit around the sun would act differently. Since dark matter doesn't seem to interact with normal matter except via gravity, it doesn't clump into planets or stars. A normal matter particle falling into a planet gets stopped by the electromagnetic forces--it hits the ground and is stuck on the planet. A dark matter particle just falls through the planet and swings on out the other side in a hyperbolic orbit, just as if the planet's surface doesn't exist.

Obviously, if we have alien space bats that can ping the entire rest of the universe out of existence, we have no way of saying what the laws of physics in the remaining universe that consists only of our solar system will be, they will be whatever the alien space bats say. But as far as we can tell, what we call dark matter is only an important influence on galactic scales, and what we call dark energy is only important on intergalactic scales. Since those won't exist anymore after the universe goes "ping", they won't matter. Unless the alien space bats say they do.
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Old 03-21-2017, 05:28 PM
UY Scuti UY Scuti is offline
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More relevantly, most of the information we have comes from Liliput. On a galactic scale, dark matter is hugely significant. On a tiny scale like the Solar System, however, it's nearly irrelevant. And it's the solar system scale that the OP is asking about.
A system is a group of elements, between which there is a well-defined and constant relation.

The existence, nature and characteristics of the solar system are utterly dependent on the Sun's movement as part of the Milky Way. If the solar system were to find itself detached from the rest of the galaxy and the entire universe, (supposing it would survive the initial shock as the Sun came to a screeching halt) the Sun's current voyage would cease and its movement would become rather chaotic and destabilizing, like a top spinning on a table. It wouldn't take long for the Sun to swallow all the planets.

What about the other two aspects I mentioned: dark energy and pocket universe?
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Old 03-21-2017, 05:50 PM
Chronos Chronos is offline
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I'm not sure what you were trying to prove by linking to that site, but whatever it was, you didn't, because that site is a load of nonsense.
  #39  
Old 03-21-2017, 07:06 PM
enalzi enalzi is online now
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Originally Posted by UY Scuti View Post

The existence, nature and characteristics of the solar system are utterly dependent on the Sun's movement as part of the Milky Way. If the solar system were to find itself detached from the rest of the galaxy and the entire universe, (supposing it would survive the initial shock as the Sun came to a screeching halt) the Sun's current voyage would cease and its movement would become rather chaotic and destabilizing, like a top spinning on a table. It wouldn't take long for the Sun to swallow all the planets.
Your own link disputes this:
Quote:
There’s absolutely no reason the planetary speeds have to be constant as they move around the galaxy — the massive gravitational pull of the Sun is keeping them firmly in its orbit, regardless of how those orbits are inclined.
  #40  
Old 03-21-2017, 07:15 PM
LSLGuy LSLGuy is online now
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Sounds like this thread just got easier.

One can believe bunk or one can accept the slightly simplified explanations of a more complex reality on offer here. Further discussion / debate about bunk is IMO pointless.
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Old 03-22-2017, 03:46 AM
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I'm not sure what you were trying to prove by linking to that site, but whatever it was, you didn't, because that site is a load of nonsense.
I don’t have to prove anything. That the Sun is traveling around the center of the Milky Way Galaxy at a very high speed as the planets revolve around the Sun in helices is a fact. I can’t find a site that can show this movement more accurately, but if anyone can I’d be grateful.

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Originally Posted by enalzi View Post
Your own link disputes this:
The idea in my statement is that the stability of the solar system depends on the Sun’s stability. Let’s try to visualize the Sun traveling around the center of the galaxy at 230 km/s as the planets revolve around it in helices. When the galaxy and the rest of the universe suddenly disappear, the following things will happen:

1. The gravitational forces that keep the Sun on a fixed and stable orbit are canceled. These forces are even bigger when considering dark matter. Their absence will cause the Sun to behave like a top whose spinning motion becomes more and more irregular due to its gas composition and internal activity. In time, the changes in the Sun’s motion can become so sudden and irregular that the entire solar system will collapse.
2. With the dark matter gone and so little mass left, dark energy (which is extremely powerful, accelerating and homogeneously spread across the space) will rip the system apart. If we hypothesize the absence of dark energy, we’re left with the possibility of a quick Small Crunch (that will mirror the Big Crunch scenario).
3. With the entire universe gone, the solar system will abruptly turn into a pocket universe, a completely different system whose parameters may not support the physical laws that we experience in our current universe. Due to a different vacuum energy, matter will reorganize differently from what we can see today.
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Old 03-22-2017, 05:07 AM
eburacum45 eburacum45 is offline
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I'm not sure what you were trying to prove by linking to that site, but whatever it was, you didn't, because that site is a load of nonsense.
To be fair, that link is actually a debunking of the 'Solar System vortex' nonsense by Jason Major of the Universe Today website, which is definitely not a 'woo' site.

Sure, the planets in our Solar System move in complex helices round the galaxy; but this gives us no real insight into what would happen if the rest of the universe disappeared.
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Old 03-22-2017, 05:25 AM
UY Scuti UY Scuti is offline
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Sure, the planets in our Solar System move in complex helices round the galaxy; but this gives us no real insight into what would happen if the rest of the universe disappeared.
I've already stated that the key to what may happen to the solar system in the absence of the rest of the universe is the Sun's movement. The video can simply enable one to visualize the Sun speeding along its orbit as opposed to a stationary Sun, whose spinning motion will be entirely influenced by the differences in density of its layers & regions and by the violent reactions occurring in its core. My opinion is that the stability of the solar system depends greatly on the Sun's 'membership' to the Milky Way Galaxy.

Last edited by UY Scuti; 03-22-2017 at 05:26 AM.
  #44  
Old 03-22-2017, 06:51 AM
Darren Garrison Darren Garrison is offline
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I don’t have to prove anything. That the Sun is traveling around the center of the Milky Way Galaxy at a very high speed as the planets revolve around the Sun in helices is a fact.
No, it is a steaming pile of ignorant bullshit.
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Old 03-22-2017, 07:17 AM
LSLGuy LSLGuy is online now
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The Sun is now traveling in a path caused by the collective gravity of the rest of the galaxy, both ordinary and dark matter. If all that matter and hence all it's gravity simultaneously went poof the Sun would not suddenly stop. It would continue on just as it was. And would drag all its planets along with it just as it does today.

The thing that seems to be hard for you to visualize is that a curved orbit in the presence of gravity and straight-line motion in the absence of gravity are exactly the same thing from the POV of the object in motion.

That was part of the wonder of Einstein's work. Gravity bends space and an object moving "straight" through bent space is actually traveling a curve. The technical term is "geodesic" which wiki can explain further.

If net gravity increases someplace then space bends more and the curvature of anything orbiting in that gravity increases too.
If net gravity decreases someplace then space bends less and the curvature of anything orbiting in that gravity lessens too.
If net gravity decreases to zero someplace then space bends zero and the curvature of anything orbiting in that gravity lessens to zero too. So now it goes straight.


In addition to the above, until and unless you can understand that the same motion looks different depending on where you're standing when you take a movie of it you're not going to make progress understanding this stuff.

As an unrelated example: While you drive your car the ground isn't moving. And while you drive your car your tires are rolling, not sliding, across the ground. So how is it possible that a moving tire and a non-moving ground are touching but aren't sliding? How can that be? Does each part of the tire stop when it gets to the bottom? If so, then what about the preceding or following parts of the tire; they're moving, but the part touching the ground isn't? How can that be?

The answer is simple: motion is not absolute. The situation looks totally different depending on whether you concentrate on the ground or the tire. Also whether you concentrate on the linear motion of the car and ground or the rotary motion of the tire. In technical terms which "frame of reference" you choose determines how the exact same situation appears. The underlying reality is constant. What it looks like changes completely.


Your idea that the planets are traveling in helices as they follow the Sun moving through space is correct if and only if you choose a "reference frame", a point of view, that isn't following along with the Sun. And doing so is artificial ignorant BS carefully designed to fool people who don't / won't understand the fundamental truth about any motion, even that of prosaic car tires: What you see depends on where you stand.

Last edited by LSLGuy; 03-22-2017 at 07:21 AM.
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Old 03-22-2017, 07:21 AM
UY Scuti UY Scuti is offline
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I'm sorry, but I think you're mistaken. Please see the statement you quote again: "That the Sun is traveling around the center of the Milky Way Galaxy at a very high speed as the planets revolve around the Sun in helices is a fact." Do you dispute this statement? Do you think I need to prove it?

Or do you find the video to be inaccurate? I have already admitted to it, but it is the only one I've found showing the solar system in motion. If you could produce a better one, it would actually help the discussion in this thread, thank you.
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Old 03-22-2017, 07:37 AM
Darren Garrison Darren Garrison is offline
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What would help the discussion in this thread is if you knew what the hell you were talking about. You are spewing ignorance, not fighting it. Read the (former Doper, I hear) Phil Plait link. The video is a worthless pile of garbage.

(And yes, I would love for you to "prove" that the planets orbit the sun in helixes. It could be entertaining to watch.)

Last edited by Darren Garrison; 03-22-2017 at 07:39 AM.
  #48  
Old 03-22-2017, 02:29 PM
Derleth Derleth is online now
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The thing that seems to be hard for you to visualize is that a curved orbit in the presence of gravity and straight-line motion in the absence of gravity are exactly the same thing from the POV of the object in motion.
To a very good first-order approximation. In fact, to a very good umpty-order approximation, which only breaks down when you're close to extremely dense objects.

The spanner in the works here is the tidal force, which is a lot more important in GR because it's how we define how curved the spacetime is in a given region: The more deformed a body wants to become due to tides, the greater the curvature.

We formalize this mathematically with the notion of parallel transport and express it in terms of the Riemann curvature tensor.

Anyway, if you're in a reasonably reasonable gravity field, the amount of curvature over the volume inhabited by a human being is minimal. Tidal forces can be neglected, which is exactly analogous to taking a straight-line tangent to a curve and using that straight line as a good approximation of the curve over a small region. The fact this works so well over quantum scales makes physicists happy, because our field theories only account for special relativity, which is the flat spacetime special case (hence the name) of general relativity. It makes physicists doubly happy because we can stand up without out feet getting pulled away from our heads.

So, dragging it back to your point: The only way you're going to see a "pure" example of things following a geodesic, utterly unaffected by tidal forces, is to look at objects which are essentially not extensive; that is, point particles, and things we can model as point particles with a negligible loss of accuracy. Photons are a prime example, because they can have long lifetimes and we can see them. That's why being able to correctly predict the quantitative amount of gravitational lensing caused by massive objects is such an important experimental test of GR: It allows us to look at one specific part of the theory.
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Old 03-22-2017, 07:47 PM
Chronos Chronos is offline
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Yes, the Sun's orbit is stable. But a straight-line uniform-speed motion is even more stable, and that's what the Sun would be doing if the rest of the Universe disappeared. What do you think would happen, it would crash into something?
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Old 03-22-2017, 08:41 PM
dtilque dtilque is online now
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Yes, the Sun's orbit is stable. But a straight-line uniform-speed motion is even more stable, and that's what the Sun would be doing if the rest of the Universe disappeared. What do you think would happen, it would crash into something?
If the rest of the universe disappeared, we could treat the sun as motionless or nearly so. There'd still be its orbital motion around1 Jupiter and the other planets, but other than that, we couldn't detect any other motion. So we may as well assume that the sun has stopped moving.

The question in the OP, like many other similar questions2, is poorly specified. I can think of two things that need to be specified. First, when you say the "rest of the universe", does that include the photons and gravitons and other forms of energy, or just the matter? Several upthread assumed that the energy would not go away, so we wouldn't know about this for 4 years. I think it's equally likely, perhaps even more likely, that the energy would go away at the same time and we'd find out within at most a couple years, depending on what you call the solar system.

That brings up the second underspecified part: what exactly is the Solar System? Well, there's lots of definitions, but perhaps the best is "everything gravitationally bound to the Sun". But that definition doesn't specify a region. (Oort Cloud objects could be up to two lightyears away, but there are almost certainly objects within that distance that aren't bound. And not just the five space probes that are leaving the system.) So if photons are disappeared along with matter, the question should specify how far away that happens.


1 not quite the right preposition, but I can't think of a better one.

2 questions where alien space bats perform some magical action and we're asked about the consequences.
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