If our current universe only had one star and one planet:
How far out could the planet orbit? Would it be possible for them to be in intergalactic distance and still orbit?
Is there a speed of gravity which I assume is the speed of light? In such a long distance orbit would such a limit get in the way of a stable orbit?
Given that galaxies in clusters essentially orbit one another there are existence proofs of very long distance orbits.
What you might have to ask in such a simple universe is more interesting.
What does it mean for there to be a universe containing only that pair of objects? Mach’s principle makes things very odd to think about. It isn’t clear that such a universe would work in the same manner as ours, and that momentum and its preservation would made as much sense. How your two object even got to where they are isn’t going to be easy to understand and will have an influence on the answer.
The idea that the speed of gravity might lead to instabilities is interesting. As the distance get bigger however things will become more stable. Orbital period squared is proportional to the cube of the radius. So as the period increases the radius goes up less and less. So the delay due to the distance as a proportion of the period reduces. Instabilities are more likely at small radii.
One suspects that worrying about a pair of orbiting black holes might lead to the need to worry about propagation time of gravity. However the geometry of this makes my brain hurt just to contemplate.
AFAIK, there are plenty of gravitationally bound galaxies (including our own!) in our current universe.
Leaving out all celestial bodies except two would only make the motion of those two more predictable; not affect their distance of attraction, which, to the best of my knowledge, is infinite.
(Maybe you could come up with some strange geometry of the universe though, like in Clarke’s The Wall of Darkness?)
Several years ago I started a thread about a hypothetical universe in which existed only two particles, billions of light years apart. Turns out that they would slowly move toward each other, on a collision course… but would decay before meeting.
Does that mean that our present familiar universe is dependent on those questions, too? Such as: Why is the universe here, and not someplace else?
Such a pity Italo Calvino is dead. This reads like one of his Cosmicomics. All it needs is a reference to Mrs. Vhd Vhd.
Actually, it used to be 3 feet to the left, but they had to move it to comply with fire codes.
But, we have the expansion of the universe, at least in this one.
Light can not travel a infinite distance due to the expansion of the universe (there is a limit of how far out we can see due to this), gravity may have also such a limit IDK. If your particles, or in this case the planet/star is further apart than that and we assume a similar expansion they would not only never feel the attraction, but would be moving away from each other due to the extra space between them that is coming into existence.
No, that’s a completely different question. Researchers on our present familiar universe are however concerned with the question of “why is the substance in our universe distributed they way it is?” and have made a lot of interesting and significant discoveries therefrom.
re the “speed of gravity,” it seems – by mathematical theory and by observation – to be the speed of light.
There is a minority view, bordering on the crackpot, but just serious enough to be worth engaging and debating, that the speed of gravity is infinite. This, however, would appear to violate actual observations, and also violates a couple of tons of mathematical models. It would totally trashcan Relativity.
(Google Tom Van Flandern for fun: was he a kook, or a serious physicist? Darn hard to tell.)
Not so sure. If a fly buzes by me and I swat at it, my hand didn’t need to first transmit its starting location to my brain – my consciousness remembered where my hand was, and kept track of it for ready reference. Could it be that the Universe has a central consciousness that remembers where everything is, and they are all kept coordinated by a response that we perceive to be Gravity? But Earth doesn’t have to transmit gravitation to Sun to stay in position,since the singular consciousness remembers where the Earth and Sun are, with with no need to keep sending signals to each other to constantly reaffirm those locations. And if the Earth collides with an asteroid, the universe-consciousness already knew it was going to, and made the necessary adjustments to preserve parity.
Sure. There could also an infinite number of angels pushing the celestial orbs around and around. You’d have about as much evidence either way.
Actually, although the speed of gravity (to the best of our ability to determine) is finite and exactly equal to the speed of light, in any system of objects that interact only gravitationally, in the small-potential limit (so no close flybys of black holes), the motions are exactly what you would expect if gravity were Newtonian and infinite in speed. Which isn’t too terribly different from what jtur88 is describing, there.
The catch, of course, is that gravity is not Newtonian.
Of course, now the speed of gravity has the possibility of being empirically measurable–if we happen to pick up a gravity wave from a neutron star collision that is also close enough to be seen in some wavelength or another.
I started a thread asking pretty much the same question 9 years ago. Here
It applies to any field, really. If there were only a proton and electron in the whole universe, what does it even mean to rotate? Or to be closer or further away? What are you measuring in relation to?
And once you add things back into your universe to make it more realistic, you run into the noise floor again. That is, technically, the electric field extends forever, throughout the entire universe. But practically, you don’t have to go too far before the field strength (the portion you can assign to the original, distant source, at least) drops below the level distinguishable from closer sources. It’s just more noticeable with gravity, because gravity doesn’t cancel out like positive and negative electric fields do. But still, I assure you, the electric field from a molecule in my nose extends all the way to Andromeda, it’s just really hard to measure once you’re there.
One problem with this is that it would require information to be transmitted, not only faster than light, but absolutely instantaneously, and this would violate the laws of physics as they are currently understood.
Also, you would have to describe the mechanism by which all of this information was stored. Where is the central consciousness? How does it store and retrieve information? It’s a model that has vast complications, and a model that would be monstrously difficult to describe in hard mathematical terms.
Is gravitation force continuous or quantified? i. e. if I measure the attraction between 2 masses, as they get further away from each other, would the attraction change in discontinuous steps
?
You do have the inflationary period of the big bang, while not instantaneous, was much faster than the SoL.
That doesn’t involve the flow of information that action by a consciousness would require. The consciousness would have to perceive, consider then act over billions of light years, constantly.
Nor does it involve anything moving FTL; that’s space itself expanding.