Actually, no it doesn’t. The propagation speed of gravity as being c is an assumption in special relativity, and in general relativity it falls out of the metric tensor as a constant. We assume (and there are [POST=6060775]some very good reasons to justify this assumption[/POST]) that the propagation speed of gravity is very close to c, but it is an assumption, not a falsifiable prediction from GR itself.
There is also the issue of what the medium via which gravity works; we can talk about the “fabric of spacetime” until we’re blue in the face, but that doesn’t explain what spacetime is or what its underlying properties are except as some kind of applied phlebotinum that responds as predicted to a self-consistent set of rules. However, part of the assumption is that mass-energy concentrations, and thus, the energy stored in gravitational couplings, is conserved and continuous. If you suddenly remove a piece of mass completely from the “fabric of spacetime” without radiating it away as some other form of energy (which still has momentum), the mathematics get nasty and unworkable; hence, why all reputable physicists insist that things like naked singularities and open time-like curves just can’t exist.
Except it isn’t a fact; it is an assumption based upon our interaction with the world on everyday scales. Causality is an expectation, not an incontrovertible fact, and we’ve performed many experiments that interact at the quantum level which clearly violate local causality. The “weirdness going on at the quantum level” can’t just be conveniently swept aside as irrelevant; while the effects may not be perceivable at the level of large systems of particles where decoherence masks the individual stochastic nature of fundamental particles, the fact–such as we understand it today–is that the behavior we clearly and repeatably experience with individual particles is at odds with established classical and relativistic theory, and indicates that we still don’t understand the basic unified principles on which the universe functions.
It’s less than the difference in perceived weight difference from centrifugal force between a person at the equator and one at the South Pole.
Ok, it’s an assumption supported by a theory that models gravitational interactions with spectacular accuracy. How is that not good enough? Anyway the larger point is that if the sun vanished and the gravitational disturbance was felt before any radiation disturbances, that would be “faster than light information travel”, thus it’s an impossibility.
As far as I know, every experiment ever made, quantum or not, weird or not, does not allow faster than light information travel, including quantum entanglement. So I feel justified in calling it a fact. Note I didn’t say a causal universe was a fact, and although that point might be argued, I don’t disagree with the gist of your position about that.
Isn’t the premise of the OP inherently flawed due to the fact that stars don’t just “wink out” while on the main sequence without some kind of observable warning signs? And even once a star starts approaching the end of its hydrogen burning days, isn’t that condition generally observable too (“Oh My God, the Sun is becoming a red giant!”)?
I suppose we are operating under the presumption that the Sun could in fact just “turn off” like a light, which is impossible… isn’t it?
You’re pre-defining “faster than light information travel” as an impossibility, which is tautological. While the tenants of special and general relativity are certainly predicated on this assumption, and it accords with our everyday conception of the world, that does not necessarily make it so. Agent K: “Fifteen hundred years ago everybody knew the Earth was the center of the universe. Five hundred years ago, everybody knew the Earth was flat, and fifteen minutes ago, you knew that humans were alone on this planet. Imagine what you’ll know tomorrow.”
At one time, the universally accepted theory is that there was an underlying plenum of “luminiferous aether” which conveyed electromagnetic energy, and it was established to the point that several reputable and first rate physicists devoted years to attempting to measure the directionality of the field, and concocted various theories of how it was being dragged along with the Earth, et cetera, to explain why the experiments would not turn out as anticipated. The reality was that the then-extant theory was badly wrong despite that it gave great answers in a limited set of circumstances. Similarly, general relativity works to the limits of our ability to measure it…but not in areas with discontinuities in spacetime, such as within the surface of a gravitational singularity, or when mass-energy spontaneously disappears.
It isn’t true that entanglement doesn’t permit the transmission of information faster than light could travel between the two particles on a geodesic curve. Indeed, it is well-established that it can, in fact, transmit information. It is merely the the case that the users at each end cannot interpret the information thus transmitted without communicating (via causal channels like radio waves) about the relative states of the particles at the respective times of communication. So it is like receiving a coded transmission, but having to wait for someone to deliver the cypher key before decrypting it. This may seem like a back door to causality–that we can violate causality, but not in an applicable way–but it still violates the principle that two points cannot be connected in a non-local fashion. Similarly, it may be that two masses that are gravitationally coupled cannot be severed without a significant rewriting of physics, or instantaneous interaction. Since all masses that we deal with can only be broken up and separated in ways that are conservative (i.e. the energy loss or gain can be accounted for in other aspects of the process) we have no way to directly measure this, nor is such a prediction workable within the framework of general relativity except by introducing discontinuities into the theory that make physicists crawl under the Christmas tree and cry themselves to sleep.
The OP is not asking about a real-universe possibility. HubZilla is asking an impossible hypothetical question for the sake of an intellectual exercise (I would not call that “flawed,” I would call it deliberately fantastic). Not just what if the light went out, but what if “One day, it just disappears.” All of the sun’s matter simply vanishes (are you listening, David Copperfield?).
If you read the entire thread you will see various objections to the scenario, but pointing out the impossibility of the situation spoils the fun.
It’s entirely plausible that at some point between 1370 and 2008, Betelgeuse went supernova – and the light, shock waves, etc., from the explosion simply have not reached us yet.
This is an outstanding reason why ‘simultaneity’ is a moot concept when talking astronomical distances. What we see when we look at Alpha Centauri is what it looked like in 2005; at Vega, what it looked like when Reagan was president; and at Rigel, what it looked like in 4000 BC. When the light we now see from the Andromeda Galaxy was first emitted, th transition from the Pliocene Epoch to the Pleistocene was just in the process of happening. And when the light we see left the Virgo Cluster, dinosaurs roamed the Earth.
My question was more along the lines of: “The sun’s light travel’s 8 minutes to earth. If there was no sun, would we know anything before that 8 minutes? Would there be a giant shockwave, would the Earth start wobbling, would tehre be a sudden cool breeze, would anything happen before the speed of light tells us ‘no more sun’”.
I was imagining a Watchmen-type scenario:
Villian: I will destroy the sun.
Heroes: Oh yeah, we’ll see about that. When do you expect to do this?
Villian: Eight minutes ago.
I’m not entirely sure that bit is correct - tidal forces act so as to elongate a body along their axis - so under normal circumstances the sun’s gravity causes a tidal bulge on both the near and far sides of the Earth.
I think the people on the far side would get heavier too - because they are, under normal circumstances, part of that tidal bulge, or maybe to look at it another way - yes, when you’re on the dark side, the sun is pulling you toward the earth, but it’s also pulling the earth away from you, a bit more than it’s pulling you.
After initially agreeing with your “mischievous aliens” scenario, I’ve given the matter some more thought, and I’m closer to my original assertion that “anything” might happen.
If these aliens are capable of doing something that, to us, seems to defy natural laws . . . then they may be capable of doing ***other ***things that seem to defy natural laws. So if they are capable of plucking the sun away, they may also be capable of leaving the rest of the solar system intact, without a central source of gravity, heat and light. They may also be capable of extinguising all the stars and gallaxies . . . everything except earth . . . and turning us into our own little self-sustaining universe.
In short, it’s the “any sufficiently-advanced technology” thing. To us, it would appear to be “magic,” and if the disappearance of the sun is magical, anything else might be, as well. If the aliens can appear to be violating any and all natural laws, then for all practical purposes anything is possible.
There is no principle that two points can’t be connected non-locally - indeed they can, surprisingly. That still doesn’t violate any known physical law. What we can say is that if the sun could vanish, it would have to do so within the confines of physical law in general and special/general relativity in particular (and obviously it can’t since that would be inherently non-conservative). Otherwise the question becomes meaningless.