What if our solar system were isolated?

Factual Questions
21

All right! Who wrote down the 9 billionth name? Was that you, Watchwolf?

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 million[sup]1[/sup] 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.
[sup]1[/sup] 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.

22

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?

23

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.

24

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.

25

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.

26

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?

27

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.

28

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.)

29

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[sup]-1[/sup]. For comparison, Earth’s surface gravity is about 1E1ms[sup]-1[/sup]. 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.

30

What’s more, even if there were a big jolt, it’s gravitational. We still wouldn’t feel it.

31

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.

32

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?

33

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

Never mind the above. I’d intended not to post this after I’d realized it was stupid. :smack:

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. :smack: All better now. :slight_smile: :smack:

35

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.

36

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.

37

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?

38

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

Your own link disputes this:

40

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.