I’m pretty sure astrologers would be upset.
Well it’ll completely screw with my sun sign.
What would happen if the Sun just… disappeared?
Attached Video has deeper explanations and accompanying graphical descriptions. Very interesting thought experiment.
This may read like a general complaint or an absurd nitpick (coming from me a nitpick in this field has to be absurd), but maybe it’s not… :: :eek: *spooky organ music in background *:: In that respect I speak generally and seriously about all sorts of science questions. So please take this in the sprit in which it is offered.
And that it took me a long time to write and format on an iPad with my thumbs and required two re-logins because I timed-out.
I’ve thought of this before, sometimes in the context of silly questions–like (to choose personal OPs), how much light bends around me, or Lorentz contraction of my arm reaching to shake hands–where physicists here played along with the joke up to a certain point, showing in principle that it could be worked out, given certain stated or unstated conditions, out if you put your mind to it. Besides the fun, I always learned more things than before, in layman’s terms, when feasible, about the issues I was up against and unsurprisingly never even considered.
OTOH, sometimes, equivalently silly posts–IIRC, one of mine on solar pressure on back during a sun tan–are more or less answered with “incredibly small,” or “unmeasurable.” Fair enough. I’m butthurt [Go SD!], but I’ll live. Hell, the very fact that someone with a brain even responded is a gift.
OTO-OH, a question in quantum physics may be correctly answered as “unmeasurable.” Right? Which brings me to this Chronos post, from someone well-known here as one of the Smartest Guys in the Room, particularly in GR, I think.
I believe I understand the plain meaning of the post. You’re not sure between yes and no. And if yes, teeny. But then your last sentence is a qualification that, *in the context of my preparatory remarks * puzzles me. Not a lot, but.
I read it as a hedge, even though I know a) you have just said the matter is an either/or one and b) you are not one to really think that by saying “just a little” she’s not really pregnant. Ever, as a scientist or man.
But that’s my confusion when physicists talk in my presence about these, to me (and maybe in a way to them) bizarre-o realms of physical reality.
Sometimes I read “unmeasurable” as meaning
A look Jack, forget about it,
B it’s in principle unmeasurable
C no-one will measure now because instruments/methods are lacking, but it’s doable, or
D it ain’t gonna happen, ever, because/or
d.1 intrinsic to the concept (eg quantum measurement)
d.2 the question/demand is as it is currently framed is impossibly wrongheaded (eg OK, you know the mass of the star, but has anyone put a scale underneath to weigh one?), which would be a response to a question/demand implying that the proposition (weight != mass) is completely wrongheaded (NB: not “you couldn’t get a spring balance big enough”) or is in fact
[indent]d.2.1 merely an instance of response A.[/indent]
What would we see if the Earth deorbits?
Cx: B is equivalent to d.1. Sorry about that.
Eta: to post #44.
What about climate?
How quickly could we expect wild fluctuations in temperatures? Would we just turn into a big ice-ball?
If the Sun just vanished, we’d see the night sky like we’ve always seen it. The Earth continues to rotate as it always has, so the moon and stars rise and set like always, although the Moon’s orbit is going to be a bit different now, different enough to measure although it will probably look exactly the same to the naked eye. And of course the Moon will now be dark. Even darker than the new moon we’re used to, since the new moon is light by reflected light from Earth.
The planets will no longer be visible, since they are no longer reflecting light from the Sun. Note that the planets will stop reflecting sunlight a bit after the Sun since light from the Sun has to travel to the planets and then bounce back to Earth. So for instance, Jupiter is about 33 light minutes from the Sun, while Earth is 8. So depending on where Jupiter and Earth are lined up, Jupiter would stop shining from reflected sunlight somewhere between 50 and 82 minutes after the Sun stopped being visible from Earth. The other planets would stop being visible at other times depending on the length of the path the reflected sunlight takes from the sun to the planet to the Earth.
Also the planets and asteroids and comets and other bodies in the solar system would now be headed off into space at different tangents. But we wouldn’t be able to see them anyway since they’d now be dark.
Other than that we’d see no change, except now the Earth is getting colder and colder and colder, pretty soon the oceans freeze, the plants die, human beings resort to cannibalism to stay alive, and eventually the last humans die as the air starts to freeze.
I think you’re probably right as far it is possible to be right, as asking what the speed of GW in a medium means answering a few other questions first: e.g. what is the background metric,? how do you define the speed of a perturbation? of the background metric, etc, etc.
Leo Bloom, I didn’t mean to suggest that it was absolutely unmeasurable in the quantum mechanical sense. I mean, maybe it is, but it would take quantum gravity to say one way or the other. I’m just saying that it would be unmeasurable as a practical matter.
And I’d like to calculate just how small it is, but I don’t know how. As a back-of-the envelope estimate, though… Let’s say that the decrease in speed of gravity, compared to the decrease in speed of light, would be comparable to the mass-to-charge ratio of a typical particle, so maybe one part in 10[sup]20[/sup] for typical solid matter.
To me the real problem is some kind of nice behaviour (e.g. smoothness, global hyperbolicity, etc) of the spacetime must be violated, which would make it inherently unpredictable in some way. Not that that is necessarily a total barrier.
Conservation of energy isn’t a massive problem as global conservation of energy and momentum aren’t universal laws in GR, the Sun-Earth system does radiate energy away in the form of gravitational waves, GPE doesn’t always mean anything in GR, so I wouldn’t be too concerned about these things.
Conservation of energy might not be global in GR, but it’s still obeyed locally, which the Sun instantly disappearing would still violate. I suppose you could convert the entire mass of the Sun into gravitational waves and let them radiate away, or something crazy like that, though.
It’d be interesting to see exactly what happened if the entire mass of the Sun were converted into gravitational wave energy. I expect doing that on any short timescale (like less than the 8 minutes we’re from the sun) would destroy the Earth when the waves got to us. I also expect there’d be a small black hole leftover, since there’d be no electromagnetic or nuclear forces to keep some fraction of the gravitational energy from self-interacting itself into a singularity.
You’d think so, wouldn’t you? But the coupling of gravity to matter is a lot weaker than you expect. The collision of two stellar black holes can, in fact, release multiple solar masses worth of gravitational waves, and yet matter more than a few tens of radii away would be largely unaffected.
This question has come up from time to time:
[THREAD=411531]What Would Happen If The Sun Burned Out?[/THREAD]
[THREAD=544823]Poof goes the sun. Can humans survive?[/THREAD]
[THREAD=611731]How long could humanity survive if Earth were flung out of its orbit?[/THREAD]
[THREAD=427700]How long do humans survive if sun stops producing light?[/THREAD]
Stranger
I’d love to see an animation of that, as everything in the solar system flies out, in order of their distance from the sun, plus local gravitation.
I wouldn’t know how to calculate the chance of colliding with another planet, but I’m confident that it’s miniscule.
The inner planets would leave their orbits first, continuing tangentially from their orbits. Inner planets are moving faster, so they’d eventually catch pass the outer planets, should they happen to be headed in the same general direction. But um … space is kinda big, even within the Solar system. Well, more thank kinda big, more like really really big, compared to the size of the planets and the reach of their gravitation. I just don’t think collisions between planets are likely at all.
But I wonder whether we’d have to worry about asteroids? There sure are a lot more of them. But, well, back to the earlier point about space being big!
If I’m bored this weekend, I can at least try to calculate the time period where collisions with asteroids might occur. Given that, and if I can find any figures for asteroids per unit area, I could calculate the density in the collision zone (of course, it would be a range of densities, getting thinner as the Earth moves out).
But not being an orbital mechanic, I’m not quite sure what I’d do with that info! Given the relative speeds, I’m not sure to figure out how close we’d need to be for there to be danger. (We’d also want to know the density for different sizes.)
And then the next step would be trying to calculate some kind of probability, but I’m not even quite sure how to pose the question.
In any case, just knowing the time period would help. If it’s fairly soon (if it would happen fairly near to the original Sun), I think the probability might be significant. If we wouldn’t reach the interception zone for many years, say out in the Oort cloud, then I wouldn’t worry.
In any case, we’d have bigger issues to worry about. Like our bucket for getting a bucket of air gets so cold it’s starting to fracture everywhere. We’re gonna need a new bucket soon.
Well, humans as a species could persist a lot longer than that. We arguably have the technology / resources to enable a small population to live for thousands of years underground.
Given a certain amount of planning and preparation we could probably use geothermal energy to persist on a frozen planet more-or-less indefinitely. Geothermal hotspots would continue to put out heat even after the atmosphere was frozen, and we could use the heat to power greenhouses and grow crops. There would be plenty of CHON on such a planet. Even if humans don’t get their act together and survive, then thermotrophic ecologies might persist around black smokers.
In fact frozen, rogue planets of this sort might turn out to be acceptable locations for interstellar colonisation, since planets like this could be numerous in the galaxy, either in the Oort clouts of stars or floating free in space. If the colonists have access to cheap fusion then even better. Perhaps the most difficult problem would be finding these small, dark objects in the first place.
Wouldn’t the atmosphere have a) been flung or b) “left” before the temp dropped enough to freeze?