# What if the rest of the universe disappeared?

Thought experiment: imagine if everything in the universe disappeared, except for our solar system including the sun, the major planets, the minor planets and the asteroid belt. Aside from not seeing any stars at night, would our existence be affected by the absence of the other stars and galaxies? Or would life on earth continue as before? I suspect that humans might be psychologically affected and of course celestial navigation would no longer be possible. But would any other species be affected? Any birds that rely on the stars to navigate?

Are you asking if the entire universe (space) disappeared or just the stuff in it?

My understanding is that if the universe(space) remained but the stuff in it disappeared except for our solar system, the solar system would be distorted and shredded to bits by the gravitational “whiplash” of all the stuff suddenly disappearing. I’m assuming you mean vanishing from existence all at once.

Someone more knowledgeable than me will be along shortly to correct and expand on this I’m sure.

ETA; there might also be weird temporal effects, reversal of cause and effect due to the power and magnitude of the gravitational waves from the rebounding of space from the sudden loss of all the stuff in it.

I’m not at all certain that that’s correct. Gravity is by far the weakest of the fundamental forces. And the force of gravity falls off by the square of the distance.
https://www.physicsclassroom.com/class/circles/Lesson-3/Newton-s-Law-of-Universal-Gravitation

Let’s calculate: Jupiter is 318 times more massive than Earth and 410 million miles away. According to Newton’s Law of Universal Gravitation, Jupiter pulls you up 34 million times less than Earth pulls you down. Jupiter’s “pull” is utterly feeble.

https://science.nasa.gov/science-news/science-at-nasa/2006/04may_jupiter

Let’s assume the rest of the universe disappears by some magical method that means no gravitational whiplash caused by the disappearance.

As to the question of whether the rest of the universe disappears or just the stuff in it, is there a difference?

Well with all that dark matter gone and probably other quanta space stuffs we know little about, I’m thinking one of those things might mean our doom.

Like maybe the outer planets go flinging off into the void.

Well, if the space remains but the stuff in it all vanishes in a wink, that’s a lot of stuff that has a gravitational affect on space itself.

Just the milkyway galaxy alone blinking out of existence leaving the solar system by itself would have some pretty disruptive effects as the very fabric of space rebounds from the sudden loss of that mass and the gravity it generates.

Yes, gravity is the weakest force, but it is also the farthest reaching. Visible matter, and dark matter might not make up the majority of “stuff” in the universe, but there is still enough of it that we can discern gravity waves from sources very far away and we don’t (can’t) know what’s beyond our light horizon and if gravitational waves might or might not constructively interfere with each other.

OTOH Bootb could also be correct and LIGO would register something and all the scientists would be asking where did everything go and that would be about the extent of it.

I’m honestly not sure that there is a fully factual answer or even can be one for something like that. I’ve wondered that myself and gone looking for answers but my first response was what I found that I thought was best.

Yes, many animals navigate by the stars, including birds. Dung beetles, for example, use the Milky Way, and some seals use individual stars.

The fundamental properties of our universe are intrinsically related to its contents. So it’s impossible to answer your question in any exact and definitive way without specifying the “rules” of the magic by which everything disappears.

But setting aside the details, it’s a very interesting question that relates to the deep unanswered question in physics and cosmology about where inertia “comes from”. Velocity is relative, but acceleration appears to be absolute. For example, something that is rotating experiences centrifugal force, but why? Rotating relative to what? It appears that the background stars define a frame (or set of inertial frames) that are non-rotating and experience no such force. How does this work? What if the entire universe were rotating?

Mach’s principle (or more accurately Mach’s conjecture) is that the large-scale distribution of matter gives rise to inertia. It’s controversial exactly what Mach’s principle entails, or whether General Relativity (which undoubtedly works) is Machian. So it’s certainly possible that the few remaining objects in your hypothesized almost-empty universe would have negligible inertia. That’s a rather more drastic state of affairs than just the absence of navigation reference.

The Forgotten Mystery of Inertia | American Scientist

We have a working theory of gravity, one that has been tested more precisely than any other theory ever devised. It accounts for the expansion of the universe; it describes the behavior of black holes; and it has successfully predicted the existence of gravitational waves. It should tell us why gyroscopes point at the stars.

Thank you for that and for the other replies. I know that the heavier elements in the Earth came from earlier stars but I guess I was kind of wondering about what importance the nearby stars, the rest of the galaxy and other, more distant galaxies have for life on Earth today.

Eventually, after millions if not billions of years, we will not be able to see other galaxies. After enough time there will be nothing visible outside of our solar system. A consequence of universal expansion.

It would free up six inches of newspaper space between the word jumble and dry cleaning coupons.

Of those two scenarios, I think the first one is more interesting. Imagine a world in which the edge of the universe was located just past the orbit of Pluto. At the very least, assuming we aren’t destroyed immediately by some kind of unknown effects, we would be able to find out what happens when we reach the edge of the universe. Is space 4 dimensional? If so, does that mean that sunlight, after a few hours, would start returning from the edge and back to. the middle, making endless circuits until the whole sky is filled with increasing amounts of solar radiation until some new equilibrium is reached?

Despite having thought about it on numerous occasions, I still have trouble picturing what the edge of our actual universe looks like. The explanation I’ve seen most often is that it is “curved.” To me that implies that there is some kind of edge or surface, unless one is also proposing a fourth spatial dimension. AFAIK. something like that doesn’t have any basis in relativity or quantum physics, and only appears in stuff like string theory. I suppose the alternative is that at the edges, time acquires some sort of space like characteristic, but that is also very difficult (actually impossible ) for me to picture.

It would be several years before anyone would notice. About 4 years from now the light from the Alpha Centauri system would blink out, eventually followed one by one by stars that are closest. Some of the stars we can now see (or more accurately the light they produced long ago) would be visible for at least as long as the human race exists.

Maybe. But if read the OP correctly, the light that is already on the way would also disappear. Presumably that means the only light that would still be visible from those stars would only last a few hours, as it makes its way from the edge of the solar system to Earth.

You just banished the Oort cloud and the solar system no longer has comets. I’m not sure if I appreciate that.

Reminds me of Stephen Kings short story “The Life of Chuck”. He gives a very melancholy take on the winking out of stars, one by one.

I was thinking of It’s A Good Life and The Nine Billion Names of God.

S. P. Somtow wrote a series of short works about aliens that cut humanity off from everything outside Pluto - it was all still there, but not visible.

Greg Egan wrote a novel in which as far as humans could tell everything outside of Pluto was just gone.

Cosmic rays would vanish, leaving only solar radiation. Cosmic rays are part of the evolution of life on Earth, affecting things like the climate and the mutation rate of species.