PDA

View Full Version : Poof goes the sun. Do we know before 8 minutes?

HubZilla
12-21-2009, 07:32 PM
It take 8 minutes for light from the sun to reach Earth. One day, it just disappears Goes dark suddenly, but not a nova.

What would it be like for those 8 minutes? Or would we know sooner? Anything the instant the sun goes out?

Superfluous Parentheses
12-21-2009, 07:33 PM
If it "just disappears"; the same as usual, no and no.

JWT Kottekoe
12-21-2009, 07:41 PM
No information can travel faster than the speed of light, so there would be no physical effect at the Earth until the light hits us, along with anything else (like gravity) that is traveling at or near that speed.

12-21-2009, 07:41 PM
To know sooner than 8 minutes, information would have to be communicated to us at a speed faster than that of light. So far, no method for that has been found.

Lobohan
12-21-2009, 07:53 PM
I'd like to join in the no way of knowing before eight minutes club.

I have an question if I can hijack just a tad. The Sun goes dark. How long does life on Earth go on? We'd have to radiate away our heat before the atmosphere pooled into puddles at our feet, but how fast do we lose heat to the cosmos?

Also, how deep are those puddles? :D

panache45
12-21-2009, 08:01 PM
Here's an answer based as much on epistemology as physics:

The situation described in the OP is only possible if several immutable laws of nature are violated. Once that happens, anything is possible . . . including information traveling faster than light.

CookingWithGas
12-21-2009, 08:02 PM
As many times as I've seen this question answered, it never occurred me what an independent observer would see. Suppose you are located a long distance from our solar system at right angles to the plane, somewhere near the line projecting out of the sun perpendicular to the plane. Your distance is large compared to Earth's distance from the sun, but close enough to be able to see both Earth and the sun, and light from concurrent events on each reaches you at more or less the same time (let's not get into relativity of concurrent events for the purpose of this idea). You see the sun blink out, and continue to watch for 8 minutes when suddenly the Earth shoots off its orbit on a tangent. That would be a weird thing to see.
I have an question if I can hijack just a tad. The Sun goes dark. How long does life on Earth go on? We'd have to radiate away our heat before the atmosphere pooled into puddles at our feet, but how fast do we lose heat to the cosmos?I don't know the complete answer but overnight I know that temps can drop dramatically during a very clear night, like in the desert. So I would imagine things would get damn cold in a few days. The food chain would take a while to collapse but it would happen faster and more thoroughly than the mass extinction 65M years ago (I don't know how fast that happened).

HubZilla
12-21-2009, 08:20 PM
So any shockwaves or jarring would be slower than the speed of light? Interesting.

kunilou
12-21-2009, 08:29 PM
One day, it just disappears Goes dark suddenly, but not a nova.

By "just disappears" do you mean it clicks off, like a light bulb, leaving a big, dark ball ? Or do you mean poof, and there's a big empty space where the sun used to be?

And if, poof, suddenly there's a big empty space, would the earth suddenly shoot out of orbit and continue in a straight line at +/- 67,000 mph? Would it happen instantly, or would it take 8 minutes for gravity to stop, as well as light?

Chief Pedant
12-21-2009, 08:33 PM
By "just disappears" do you mean it clicks off, like a light bulb, leaving a big, dark ball ? Or do you mean poof, and there's a big empty space where the sun used to be?

And if, poof, suddenly there's a big empty space, would the earth suddenly shoot out of orbit and continue in a straight line at +/- 67,000 mph? Would it happen instantly, or would it take 8 minutes for gravity to stop, as well as light?
Gravitational waves are thought to travel at the speed of light. It would take a bit over 8 minutes for the effect of the loss of the sun's gravity to reach the earth.

TimeWinder
12-21-2009, 08:33 PM
Here's an answer based as much on epistemology as physics:

The situation described in the OP is only possible if several immutable laws of nature are violated. Once that happens, anything is possible . . . including information traveling faster than light.

This answer comes up a lot, and it always seems a bit of a cop-out. What the OP is asking is pretty clearly "...and everything else stays the same." Otherwise, you're almost saying you can't ever answer a hypothetical ("but it didn't!"), which might be epistemologically true, but isn't very useful as a producer of knowledge.

Assume a race of aliens with much better technology than us come along and wrap the sun in a radiation-proof (maybe gravity-wave/graviton-proof) bag before hauling it off to replace a light bulb in some other galaxy. No laws violated, except for an intersteller misdemeanor about stealing suns from planets without leaving the standard crop-circle warning ahead of time.

Keeve
12-21-2009, 08:48 PM
Gravitational waves are thought to travel at the speed of light. It would take a bit over 8 minutes for the effect of the loss of the sun's gravity to reach the earth.The critical words here are "are thought".

Unless I'm mistaken, this is a presumption based on the oft-quoted "information can't move faster than light". But it is only a presumption. The truth is that the scientists don't yet really understand how gravity works, or whether it is limited to the speed of light.

If I am mistaken, please enlighten me.

CookingWithGas
12-21-2009, 08:53 PM
The critical words here are "are thought".

Unless I'm mistaken, this is a presumption based on the oft-quoted "information can't move faster than light". But it is only a presumption. The truth is that the scientists don't yet really understand how gravity works, or whether it is limited to the speed of light.

If I am mistaken, please enlighten me.Well, somewhat true, but we can only answer a question using the best facts and theories available at the time. Otherwise the answer to the OP would be, "Who the fuck knows?"

OldGuy
12-21-2009, 09:48 PM
This answer comes up a lot, and it always seems a bit of a cop-out. What the OP is asking is pretty clearly "...and everything else stays the same." Otherwise, you're almost saying you can't ever answer a hypothetical ("but it didn't!"), which might be epistemologically true, but isn't very useful as a producer of knowledge.

Assume a race of aliens with much better technology than us come along and wrap the sun in a radiation-proof (maybe gravity-wave/graviton-proof) bag before hauling it off to replace a light bulb in some other galaxy. No laws violated, except for an intersteller misdemeanor about stealing suns from planets without leaving the standard crop-circle warning ahead of time.

But as far as we know there is nothing that is gravity-wave/graviton proof. That is we know of no way to create a gravity shield. So either that law is violated or we Earthlings don't know enough to answer the question of what happens.

Elendil's Heir
12-21-2009, 09:51 PM
...No laws violated, except for an intersteller misdemeanor about stealing suns from planets without leaving the standard crop-circle warning ahead of time.

If you ask me, it oughta be a felony.

Der Trihs
12-21-2009, 10:05 PM
I have an question if I can hijack just a tad. The Sun goes dark. How long does life on Earth go on?Millions of years I expect, at least for bacteria. Some of them live deep in the Earth's crust, eat rock and don't depend on the Sun for energy. Tidal and radioactive heating will keep the interior of the Earth from freezing, I think.

Pedro
12-21-2009, 10:19 PM
The critical words here are "are thought".

Unless I'm mistaken, this is a presumption based on the oft-quoted "information can't move faster than light". But it is only a presumption. The truth is that the scientists don't yet really understand how gravity works, or whether it is limited to the speed of light.

If I am mistaken, please enlighten me.

That's not the truth at all. Not having experimental evidence of a graviton particle does not translate to "not understanding how gravity works". General relativity is a theory that describes gravity very accurately. Also it's well established that faster than light travel breaks causality, and most people believe in a causal universe.

Silophant
12-21-2009, 11:40 PM
Not me. I believe in a formal universe.

JWT Kottekoe
12-22-2009, 12:02 AM
... scientists don't yet really understand how gravity works, or whether it is limited to the speed of light.

If I am mistaken, please enlighten me.

General relativity has been a remarkably successful theory. It predicts the speed of gravity to be precisely the same as the speed of light. There are no compelling alternative theories and all viable alternatives also predict the same speed for gravity. There is still no quantum field theory that properly unifies quantum mechanics and relativity in the strong gravity limit, but this is irrelevant to the OP's hypothetical situation, which involves weak gravity.

Chipacabra
12-22-2009, 01:22 AM
As far as I've been able to find, we haven't observed any 'gravity particles' or 'gravity waves' or whatever, but we have observed interactions between bodies in space that are consistent with gravity propagating at the speed of light.

In particular, measuring the orbital decay rate of a pair of pulsars orbiting each other will tell you that gravity propagates at a non-instantaneous speed. (The exact speed you calculate depends on the theory you're using, so it doesn't prove GR by itself.)

In 2002, some guys indirectly measured the speed of gravity by watching Jupiter pass in front of a quasar, but the interpretation of their results is disputed. I don't understand the math of that argument, so you're on your own there.

The fun thing about "slow" gravity is that the earth experiences a force toward where the sun is <i>now</i>, not where it was 8 minutes ago. Gravity has error prediction.

Mosier
12-22-2009, 02:37 AM
The fun thing about "slow" gravity is that the earth experiences a force toward where the sun is <i>now</i>, not where it was 8 minutes ago. Gravity has error prediction.

Can anyone else confirm the truth of this statement? If so, how could any model of physics honestly predict it? If a model can just answer the questions of "why does the effect of gravity appear to be instantaneous?" with "because gravity knows where the sun will be in the future and exerts a force based on it's future location, not it's present one" I call bullshit.

The Urban Spaceman
12-22-2009, 03:19 AM
...

The Urban Spaceman
12-22-2009, 04:23 AM
Can anyone else confirm the truth of this statement?

The statement is a misunderstanding.

The idea that a body, whilst in orbit, should act according to the time-retarded gravity position of a second body is superficially plausible. However, this neglects a significant amount of canceling out required to preserve the total angular momentum of the system, due to the mechanical instability introduced by the time-retarded gravity. Since a body in orbit under constant acceleration cannot radiate gravity, this additional compensation is in terms of the gravitational focus.

In reality, and demonstrated experimentally, this means that a body acts according to the interpolated time-retarded gravity position of a second body. This phenomenon is why instantaneous Newtonian gravity and speed-of-light General Relativity gravity are in such close agreement.

UncleFred
12-22-2009, 06:26 AM
To know sooner than 8 minutes, information would have to be communicated to us at a speed faster than that of light. So far, no method for that has been found.

While there is no *practical* method for transmitting information faster than the speed of light, I have read of experiments indicating it may be possible.

I'm going by Bill Bryson's "Short History of ..." wherein he relates an experiment with particle pairs having opposing spin. Apparently when you 'flip' one of them the partner reacts instaneously.

I don't know how valid this is, but if true it does imply that some form of information can be transferred faster than the speed of light.

12-22-2009, 09:21 AM
I don't know how valid this is, but if true it does imply that some form of information can be transferred faster than the speed of light.
I've read about that hypothesis in the past, but as of yet it remains highly suppositional, and thus far we lack even a theory of how to transmit information faster than light, much less an actual method.

Kiber
12-22-2009, 10:08 AM
I think the phenomenon your refering to is called Quantum Entanglement. I won't pretend to be able to describe it - but note the following from the Wik (http://en.wikipedia.org/wiki/Quantum_entanglement)i link:

A 2008 quantum physics experiment performed in Geneva, Switzerland has determined that the "speed" of the quantum non-local connection (what Einstein called spooky action at a distance) has a minimum lower bound of 10,000 times the speed of light.

The Urban Spaceman
12-22-2009, 10:51 AM
Nice try, but no-communication theorem (http://lesswrong.com/lw/q2/spooky_action_at_a_distance_the_nocommunication/) probably throws a spanner in the works. Long story short, no meaningful transfer of information can occur at faster than light speeds.

Dandmb50
12-22-2009, 11:08 AM
I guess we'll never KNOW until/when it happens. One question that comes to mind is if the sun disappears and it takes 8 minutes for us to know, what is allowing us to revolve around the sun/unsun? And is it true that light travels at 186,000 miles per second? What's that in metric? Kilometers?

Please PHONE ME (http://i78.photobucket.com/albums/j83/dandmb50/DSC_0035-2-1.jpg) before it happens.

CookingWithGas
12-22-2009, 12:51 PM
I guess we'll never KNOW until/when it happens. One question that comes to mind is if the sun disappears and it takes 8 minutes for us to know, what is allowing us to revolve around the sun/unsun? If you read the thread above you will learn the answer.And is it true that light travels at 186,000 miles per second? What's that in metric? Kilometers?You can look it up (http://www.google.com/search?hl=en&rlz=1T4GWYF_enUS321US241&ei=whQxS_nRAoeXtgfN0-mOCQ&sa=X&oi=spell&resnum=0&ct=result&cd=1&ved=0CA0QBSgA&q=186000+miles+per+second+in+kilometers+per+second&spell=1).

12-22-2009, 12:56 PM
300,000 km/sec is a very good approximation, once again proving that metric is the superior unit system ;)

(Need more proof? 1 lightyear = 10 trillion kilometers)

The Hamster King
12-22-2009, 01:04 PM
I don't know how valid this is, but if true it does imply that some form of information can be transferred faster than the speed of light.It is indeed quantum entanglement, it has been observed in the lab, but it doesn't allow faster-than-light transmission of information.

It's not that you "flip" the particle and the other one responds. Rather you measure the spin of one particle and discover that the other one matches.

What's so weird about that you might ask? Obviously the two particles had their spins synched when they were together so of course it should match when you measure it when they're apart. This is called the "hidden variable" explanation.

However, an experiment can be set up to prove that no hidden variables exist. Unfortunately, it's difficult to provide a simple explanation of how the experiment works. Basically you create a situation where you gradually vary how you take one of the measurements. If the correlation were the result the two particles being synched when they were together, then it should drop off linearly as you gradually change how you measure. However, it doesn't work out that way. Instead of a linear decrease you get a curve -- they stay correlated longer than they should, then there's an abrupt drop off. Somehow both particles "know" what technique will be used to measure them at each end of the experiment and that affects their spin.

But you can't use the technique to transmit information. At both ends of the experiment all you see are a random sequence of spin measurements. It's only when you put them next to each other and compare them that you can see that what you did at one end of the apparatus instantly altered what happened at the other end.

Boyo Jim
12-22-2009, 01:05 PM
But as far as we know there is nothing that is gravity-wave/graviton proof. That is we know of no way to create a gravity shield. So either that law is violated or we Earthlings don't know enough to answer the question of what happens.

As the universe's expansion is accelerating, there is something acting against gravity. Perhaps it can be collected and put to use, maybe for a gravity shield.

Stranger On A Train
12-22-2009, 01:05 PM
That's not the truth at all. Not having experimental evidence of a graviton particle does not translate to "not understanding how gravity works". General relativity is a theory that describes gravity very accurately. Also it's well established that faster than light travel breaks causality, and most people believe in a causal universe.General relativity is a theory that explains the effects that gravity has on masses. In no way does it explain how gravity really "works", except that the manifestation of it is a property an underlying plenum (which we can't measure or see) that is influenced by the presence and relative velocity of local mass. Charles Misner, Kip Thorne, and John Archibald Wheeler wrote a book quite simply titled Gravitation which explains the tenants of general relativity and is widely considered the primary reference text on gravitation, and Thorne himself admits that we don't really understand what the underlying mechanic is, just that we can describe it (in most regimes) in very accurate detail. General relativity is like most non-computer engineers conception of a computer; they can describe it, they can use it for a multitude of tasks, if they're clever they can even program it, but from the processor down it may as well be all little green men with abacuses as far as they can tell.

Whether we "believe" in an underlying causal mechanic in the physics of the universe or not is immaterial; the universe will continue to do whatever it pleases. A study of quantum mechanics indicates that while an assumption of causality is at least a valid approximation at most scales in which quantum behavior is decoherent (not distinguishable from normal mechanics with expected classical uncertainty of measurement and perturbation), on the quantum level behavior such as that found in the famous double slit experiment is explained only by non-local connection (entanglement, de Broglie–Bohm and other explicitly non-local hidden variable interpretations), predetermined mechanics (consistent histories), the intersection of multiple consistent permutations (Everrett-DeWitt many worlds), solipsism (Consciousness Causes Collapse), "it all just works at the boundaries" (pilot wave theory), or any other number of theories all of which violate classical causality either in locality or explicit determinism.

However, for mass-energy to suddenly and completely disappear would be a violation of conservation of mass, and this would cause a complete breakdown of physics. The coupling between two masses at any distance is more than just an exchange of information; it actually controls their binding properties to each other and the other masses around them, and for one of those to change with an infinite time rate of change is just outside of the ability of current physical theory to address.

While there is no *practical* method for transmitting information faster than the speed of light, I have read of experiments indicating it may be possible.

I'm going by Bill Bryson's "Short History of ..." wherein he relates an experiment with particle pairs having opposing spin. Apparently when you 'flip' one of them the partner reacts instaneously.

I don't know how valid this is, but if true it does imply that some form of information can be transferred faster than the speed of light.I implore you to please, please, please don't treat anything that Bryson offers in this book to be anything other than ill-informed regurgitation of vaguely understood factoids.

Stranger

Projammer
12-22-2009, 01:22 PM
It's been a year so I have no supporting links at the moment, hopefully another Doper can fill in or at least add to the info so I can research it properly.

I was watching a show about string theory and alternates, mathematical proofs of extra dimensions, general geek stuff. One of the issues they brought up is that gravity isn't as strong as is should be. Then one of the brainiacs that thinks about these things realized that the numbers for gravity work out if gravity is actually native to a different dimension and all we're getting is the leakage. This was suggested by a woman researcher if that helps anyone looking it up.

I hadn't considered until now, but that's a perfectly valid reason why we wouldn't be able to block gravity. We would have to erect our barrier in another dimension to keep it from leaking into here. I could also concede that the speed of light isn't an absolute barrier in the gravity-0 dimension. So removing the local gravity component could mean that the effects don't have to propogate.

msmith537
12-22-2009, 01:55 PM
I was watching a show about string theory and alternates, mathematical proofs of extra dimensions, general geek stuff. One of the issues they brought up is that gravity isn't as strong as is should be. Then one of the brainiacs that thinks about these things realized that the numbers for gravity work out if gravity is actually native to a different dimension and all we're getting is the leakage. This was suggested by a woman researcher if that helps anyone looking it up.

If I'm not mistaken, you might be talking about a couple of things here:
Dark matter - From observing the motion of stars in a galaxy, it appears that the galaxies are spinning faster than the observable amount of mass would allow. Therefore, there must be a significant amount of non-observable mass (75% of the mass in the universe IIRC) whose gravity is holding it together.

Dark energy - By some calculations, the stars and whatnot are continuing to accelerate away from each other faster than their mass should allow. This implies that there is some form of unobserved energy pushing them along.

IIRC there have been some theories around these observations and I believe one of them includes multiple universes or the additional dimensions inherent to string theory.

Projammer
12-22-2009, 02:26 PM
Dark matter/energy were mentioned, but the primary focus of this episode were the theories of extra dimensions and the possible ramifications. I'm thinking they were talking about something like 11 or 14 total. One interesting note was the disagreement between the string theorists and a new idea that was being pushed.

And then someone pointed out that one of the shortcomings of string theory meshed nicely with the new school. Suddenly everyone is all buddy-buddy again.

Which is a good thing. Theoretical physicists feuding is not something for the squeamish.

Pedro
12-22-2009, 02:29 PM
General relativity is a theory that explains the effects that gravity has on masses. In no way does it explain how gravity really "works", except that the manifestation of it is a property an underlying plenum (which we can't measure or see) that is influenced by the presence and relative velocity of local mass.

If by "works" it is meant works on a sub atomic level then fair enough. For the purposes of the original question (about the speed of propagation of gravitational effects) general relativity suffices.

Whether we "believe" in an underlying causal mechanic in the physics of the universe or not is immaterial; the universe will continue to do whatever it pleases.

It is material as the first example that popped into my head about why information (energy) can't travel faster than light. This is scientific fact regardless of all the weirdness going on at the quantum level.

Projammer
12-22-2009, 02:46 PM

If you just mean to flip off the lights and leave the mass of the sun in place, I can't imagine that we would have any warning before things went dark.

If, on the other hand, you want the sun to completely vanish taking its gravity well with it, then you have two possible paths.

If gravity travels at the speed of light, then you're still going to wait 8 minutes to get the bad news.

If gravity isn't bound by the speed of light and is indeed faster, then you would have up to 8 minutes warning. What would happen in that time is anybody's guess.

Googling speed of propagation of gravity (http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4GGIH_enUS211US211&q=speed+of+propagation+of+gravity) as to the speed of light, the concensus seems to be , "maybe".

The Hamster King
12-22-2009, 03:42 PM
If gravity isn't bound by the speed of light and is indeed faster, then you would have up to 8 minutes warning. What would happen in that time is anybody's guess.Very little. Earth's orbital velocity is about 30 km/sec. That means in 8 minutes it only travels about 14,000 km. For comparison, Earth itself is about 12,500 km wide. So the deviation from our normal orbital path during those first 8 minutes would be TINY. I'm not sure we could even detect it if we were trying to.

Boyo Jim
12-22-2009, 03:51 PM
Hmmm, I would assume the people on the sun side of the earth would be slightly heavier, as the sun's gravity had been tugging them ever so slightly away from the earth. And correspondingly the people on the dark side should be lighter as the gravity of the two bodies would no longer be additive.

Anybody have the knowledge to calculate the magnitude of the effect? I can't imagine it would be large enough to notice.

Stranger On A Train
12-22-2009, 05:33 PM
If by "works" it is meant works on a sub atomic level then fair enough. For the purposes of the original question (about the speed of propagation of gravitational effects) general relativity suffices.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 some very good reasons to justify this assumption) 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.

It is material as the first example that popped into my head about why information (energy) can't travel faster than light. This is scientific fact regardless of all the weirdness going on at the quantum level.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.

Hmmm, I would assume the people on the sun side of the earth would be slightly heavier, as the sun's gravity had been tugging them ever so slightly away from the earth. And correspondingly the people on the dark side should be lighter as the gravity of the two bodies would no longer be additive.

Anybody have the knowledge to calculate the magnitude of the effect? I can't imagine it would be large enough to notice.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.

Stranger

Pedro
12-22-2009, 08:12 PM
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 some very good reasons to justify this assumption) that the propagation speed of gravity is very close to c, but it is an assumption, not a falsifiable prediction from GR itself.

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.

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.

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.

Xema
12-22-2009, 10:14 PM
I would assume the people on the sun side of the earth would be slightly heavier, as the sun's gravity had been tugging them ever so slightly away from the earth.
IOW, the Sun's tidal effects would cease.

FoieGrasIsEvil
12-22-2009, 11:38 PM
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?

Stranger On A Train
12-23-2009, 12:13 AM
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.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.

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.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.

Stranger

CookingWithGas
12-23-2009, 06:15 AM
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?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.

Nars Glinley
12-23-2009, 11:13 AM

Polycarp
12-23-2009, 11:28 AM
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.

HubZilla
12-23-2009, 12:41 PM
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.

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.

CurtC
12-23-2009, 01:05 PM
But as far as we know there is nothing that is gravity-wave/graviton proof. That is we know of no way to create a gravity shield. So either that law is violated or we Earthlings don't know enough to answer the question of what happens.
I think the OP was just imagining that the Sun suddenly went dark, not that it ceased to be there.

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.
Rigel's not that far away. We're seeing it as it looked in maybe 1200 CE.

Merijeek
12-23-2009, 01:32 PM
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?).

Given that God is infinite, and given that the universe is infinite...

Why the hell is Claudia Schiffer having sex with David Copperfield?

-Joe

Mangetout
12-23-2009, 05:34 PM
Hmmm, I would assume the people on the sun side of the earth would be slightly heavier, as the sun's gravity had been tugging them ever so slightly away from the earth. And correspondingly the people on the dark side should be lighter as the gravity of the two bodies would no longer be additive.

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.

panache45
12-24-2009, 05:53 PM
This answer comes up a lot, and it always seems a bit of a cop-out. What the OP is asking is pretty clearly "...and everything else stays the same." Otherwise, you're almost saying you can't ever answer a hypothetical ("but it didn't!"), which might be epistemologically true, but isn't very useful as a producer of knowledge.

Assume a race of aliens with much better technology than us come along and wrap the sun in a radiation-proof (maybe gravity-wave/graviton-proof) bag before hauling it off to replace a light bulb in some other galaxy. No laws violated, except for an intersteller misdemeanor about stealing suns from planets without leaving the standard crop-circle warning ahead of time.

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.

Pedro
12-25-2009, 03:41 AM
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.

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.