How long would daylight last on Earth if the sun disappeared?

[adjkgh]

what are the consequences of Earth if our sun had somehow disappeared?
can someone prove how long daylight on Earth would evaporate if the sun disappeared?

I think it'd be equivalent to the speed of light, which is 8.3 minutes because that is how fast light travels from the sun to the Earth but i'd like some derivations and explanations on how and why it is 8.3 minutes?

plus would there be any orbital changes amonst our solar system?

thank you ^^

 

[SpaceTiger]

I think it'd be equivalent to the speed of light, which is 8.3 minutes because that is how fast light travels from the sun to the Earth but i'd like some derivations and explanations on how and why it is 8.3 minutes?

Distance from the Earth to the sun: 1.5e8 km

Speed of light: 3e5 km/s

Time for changes in the sun to be communicated to Earth ->

Distance/Speed of light = (1.5e8 km)/(3e5 km/s) = 499 seconds = 8.3 minutes

plus would there be any orbital changes amonst our solar system?

Without the sun, the Earth wouldn't orbit at all. It would continue moving in a straight line with whatever speed and direction it had prior to the sun's disappearance.

 

[Chessguy]

Without the sun, the Earth wouldn't orbit at all. It would continue moving in a straight line with whatever speed and direction it had prior to the sun's disappearance.

SpaceTiger,
Would the Earth break orbit the instant the sun disappears or would it continue to orbit normally for another 8 minutes before breaking off at a tangent?
I guess if gravity propagates at the speed of light then it would have to be the latter but it doesn't make intuitive sense to me. I don't think I understand how gravity works well enough to get it.

 

[SpaceTiger]

SpaceTiger,
Would the Earth break orbit the instant the sun disappears or would it continue to orbit normally for another 8 minutes before breaking off at a tangent?

I guess if gravity propagates at the speed of light then it would have to be the latter but it doesn't make intuitive sense to me.

In the relativistic limit, we probably shouldn't take this question too far because it's really unphysical. The nearest physical situation I can think of would involve a detonation (like a supernova). In that case, it would take more than eight minutes for the matter and energy to leave the system anyhow.

 

[adjkgh]

thank you for your responses =)

earth orbits the sun...and so does other planets as well, but is it true that other planets' gravity places Earth at where it is? meaning that...if the sun disappears, it's gravitational pull is gone so would Jupiter (or any other planets) alter our Earth's tangent motion once the sun disappeared?

 

[EP]

I'd imagine the other planets would affect Earths path, I don't believe anyone has ever calculated exactly how but I would think it would move out towards the larger planets. Also if the Sun instantly disappeared the Earth would move out tangentially immediatly not 8.3 minutes later. Atleast to my understanding of relativity. Basically the curvature of space will change instantly. Gravity is not a force pulling on something like a rope would, its an effect of curvature of space. Therefore it wouldn't take 8.3 minutes for the force to disappear.

In response to SpaceTiger these types of questions are the ones that Einstien asked him self in his famous thought experiments. They are very important to Theoretical Physicist.

 

[adjkgh]

I'd imagine the other planets would affect Earths path, I don't believe anyone has ever calculated exactly how but I would think it would move out towards the larger planets. Also if the Sun instantly disappeared the Earth would move out tangentially immediatly not 8.3 minutes later. Atleast to my understanding of relativity. Basically the curvature of space will change instantly. Gravity is not a force pulling on something like a rope would, its an effect of curvature of space. Therefore it wouldn't take 8.3 minutes for the force to disappear.

In response to SpaceTiger these types of questions are the ones that Einstien asked him self in his famous thought experiments. They are very important to Theoretical Physicist.

but gravity has speed and i think i heard that it was almost equal to the speed of light which means it would take 8.3 minutes before it changes path?

side note: if the sun suddenly disappears, would Earth crash into another planet then? consider jupiter's great mass and gravitational pull, wouldn't Earth me traveling towards that way? because the sun isn't there to restrain it anymore.

 

[EP]

I'm sorry your right the gravity does act at the speed of light. I got confused on the einstiens experiment. It was if Newtons law was correct the Earth would fly off immediatly. This sight briefly descibes the experiment. So It would take 8 min.
http://www.perimeterinstitute.ca/explore/einstein1.php It might crash into Jupiter. That has many variables. How far away it is, the velocities, direction the Earth is heading at time loss of gravity. You would have to calculate that.

 

[SpaceTiger]

I'd imagine the other planets would affect Earths path, I don't believe anyone has ever calculated exactly how but I would think it would move out towards the larger planets.

These forces are extremely tiny. Yes, they have been calculated and yes, you would see slight deviations from a straight-line path, but you won't learn anything physical from it.

Also if the Sun instantly disappeared the Earth would move out tangentially immediatly not 8.3 minutes later. Atleast to my understanding of relativity. Basically the curvature of space will change instantly. Gravity is not a force pulling on something like a rope would, its an effect of curvature of space. Therefore it wouldn't take 8.3 minutes for the force to disappear.

No, this is incorrect. The changes cannot be propagated at faster than the speed of light. Otherwise, casuality would be violated.

In response to SpaceTiger these types of questions are the ones that Einstien asked him self in his famous thought experiments. They are very important to Theoretical Physicist.

Name one thought experiment that Einstein did that was unphysical. In fact, he did the opposite. He took the theories of the time and stretched them to their limits to see whether or not the results made physical sense.

 

[adjkgh]

and eistein's ideas DID make physical senses.

 

[Janus]

side note: if the sun suddenly disappears, would Earth crash into another planet then? consider jupiter's great mass and gravitational pull, wouldn't Earth me traveling towards that way? because the sun isn't there to restrain it anymore.

The Earth would have to been pretty much on a intersection course with Jupiter already for them to collide.

 

[EP]

In the relativistic limit, we probably shouldn't take this question too far because it's really unphysical. The nearest physical situation I can think of would involve a detonation (like a supernova). In that case, it would take more than eight minutes for the matter and energy to leave the system anyhow.

I'm not the one that said this idea was unphysical. You did. Or maybe I interpeted it wrong.

 

[adjkgh]

The Earth would have to been pretty much on a intersection course with Jupiter already for them to collide.

sorry, could you please explain that more? =)

 

[SpaceTiger]

I'm not the one that said this idea was unphysical. You did. Or maybe I interpeted it wrong.

Yes, I did say it was unphysical -- and it is. Then you responded with:

In response to SpaceTiger these types of questions are the ones that Einstien asked him self in his famous thought experiments.

I'm saying it's nothing like those thought experiments because Einstein wouldn't have started by thinking about a situation that none of the theories of the time predicted could occur (including his own).

 

[SpaceTiger]

sorry, could you please explain that more? =)

I'm pretty sure he means that the two could collide if the paths that they leave on intersect one another. This could happen, but it would be pretty improbable. The main point here is that the planets would not be bound to one another (i.e. in orbits about one another) after the sun disappears. Their relative velocities would be much too large.

 

[EP]

What I interpeted as you saying was unphysical was having the Sun disappear. So there was no point in discussing the implications of this happening. Which is why I put that link up explaining the experiment that I was referring to. Einstein did imagine what would happen if the Sun just disappeared.

 

[tony873004]

Even though it's unrealistic, It's still worth considering if it helps you understand something about the Sun's role in the solar system. It's unrealistic that humans could exist on an Earth with no atmosphere, but lots of beginning Physics problems tell you to ignore air resistance to help you better understand momentum.

Here's a pic of what would happen if the Sun just vanished. Watch how fast Mercury leaves!

 

[SpaceTiger]

What I interpeted as you saying was unphysical was having the Sun disappear. So there was no point in discussing the implications of this happening. Which is why I put that link up explaining the experiment that I was referring to. Einstein did imagine what would happen if the Sun just disappeared.

If anyone has a link that indicates this particular thought experiment really originated with Einstein, I'd be curious to see it. The article just uses it as an example, so it may be one of those crude popularizations (like the "warped space" analogy) that surfaced after the formulation of relativity. If Einstein had presented this as his reason for not believing Newtonian gravity, the naysayers could respond that it violated the conservation of energy. Matter simply cannot disappear. It would have been silly to use this thought experiment when there are countless other physically valid ones that can be formulated.

For example, if the sun were to suddenly explode and eject matter in an asymmetric fashion, its center of gravity would change before the news of the event could reach earth. Thus, Newtonian gravity would predict an instantaneous change in the Earth's orbit. Why is this a problem? Well, it's not obvious from the article that you linked:

http://www.perimeterinstitute.ca/explore/einstein1.php]So[/PLAIN] if the Sun were to suddenly disappear, the universal speed limit forbids us any means of knowing of this catastrophe until 8 minutes later. Light itself respects this required time delay: the Sun would continue to blaze in our sky during the whole 8 minutes it takes the last ray of light from the Sun to make its journey to the Earth. Only then would the Earth be plunged into darkness. Newton’s model of gravity does not respect this required time delay: it predicts that at the same instant the Sun disappears, the “gravitational force” it exerts on the Earth would also disappear, causing the Earth to immediately break out of its usual orbit. Observers on night side of the Earth could be immediately aware of this catastrophe by noticing a change in the apparent motion of the distant stars produced by the change in Earth’s motion. General relativity resolved this problem.

Why should it matter that observers can still see light from the sun after its gravitational influence disappears? Wouldn't the light just be delayed relative to the gravity?

The reason that it matters is that it violates causality, as I said. If the two events are simultaneous in one frame, you can boost to another frame in which the Earth goes off course before the sun explodes. That is a real physical problem and it doesn't require invoking an impossible thought experiment.

 

[adjkgh]

alright, i feel an argument coming up so i just like to clarify that i started this thread because i needed help on my physics project. my purpose is to derive and explain how the greek used geometry and algebra to calculate how far the sun is from earth. after that, i plan to explain further the consequences if the sun has suddenly disappeared. also along with more mathematical proofs on how 8.3 minutes (speed of light)was derived.
i was curious about this in the first place and that's why i chose this topic as my research project.

 

[SpaceTiger]

alright, i feel an argument coming up so i just like to clarify that i started this thread because i needed help on my physics project. my purpose is to derive and explain how the greek used geometry and algebra to calculate how far the sun is from earth. after that, i plan to explain further the consequences if the sun has suddenly disappeared.

Okay, but I'm not seeing the relationship between these two topics. The Greeks used trigonometry to estimate the earth-sun distance when the moon was in an exact quarter phase (explained http://www.astro.washington.edu/labs/eratosthenes/rung3.html").

In the Newtonian limit, the consequences of the sun disappearing have already been explained and can be understood simply in the context of Newton's laws. If you're interested in the consequences of the sun disappearing in the relativistic limit, then you shouldn't dismiss what's said above as simply argumentative -- it addresses some of the fundamental reasons that Einstein thought general relativity was necessary in the first place!

also along with more mathematical proofs on how 8.3 minutes (speed of light)was derived.

The speed of light has been measured by many experiments, but again, this is only distantly related to the two things above. The speed of light measurement with the most relevance to astronomy was performed by Ole Romer in 1676 by timing the eclipses of Jupiter with its moons (more information http://www.wonderquest.com/calculate-speed-of-light.htm"). Once you have the speed of light and distance to the sun, deriving the "8.3 minutes" is just a matter of doing what I did in my first post.

 

[adjkgh]

well they DO relate in a way. you would need the distance to the sun and the speed of light to know how long it would take before the sunrays disappear from earth.

anyways, i don't want to argue, i just want to clear up a few questions i had. thanks who everyone to contriubuted. big help.

 

[vincentm]

well they DO relate in a way. you would need the distance to the sun and the speed of light to know how long it would take before the sunrays disappear from earth.
anyways, i don't want to argue, i just want to clear up a few questions i had. thanks who everyone to contriubuted. big help.

Since the lgiht from the sun takes about 8 minutes to travel to Earth, wouldn't it be the same for them to disappear?

 

[pervect]

I thought there was a FAQ on the topic of "what happens if the sun suddenly disappears" but I can't find it. There is of course the FAQ about the "speed of gravity", which shows that attempting to find the speed of gravity by the direction of gravity is just as wrongheaded as finding the speed of light by the direction of the columb electrostatic force. This approach does not give the correct speed of light - nor does it give the correct speed of gravity. (You may read some popularizations that indicate otherwise. These are mostly the work of one person, Tom Flanderen. These popularizations are wrong).

Details on the "speed of gravity" can be found at

http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html

But back to the original question. There is no solution to Einstein's equations which correspond to the sun suddenly disappearing. The reason why there is no solution can be stated simply, though the deatails are complex: the differential form of the conservation of energy is "built into" Einstein's equations.

Thus you cannot find the solution for what happens when the sun suddenly disappears according to Einstein's equations, because these equations have built into them the assumption that the sun can't suddenly disappear.

Fortunately, there is no reason why it's actually _necessary_ to have the sun suddenly disappear to talk about the idea of the "speed of gravity". One can, in theory, "blow it up", instead of having it disappear. This gives a situation where the equations are soluble.

So the idea is this: one blows up the sun, then, sitting with a stopwatch, one looks for the amount of time it takes for the Earth's orbit to change from it's old predicted value.

There are a few additional wrinkles here. It turns out that in order to measure the speed of gravity, it is necessary to blow up the sun in a manner that is spherically assymetrical. If one blew the sun up symmetrically, the disturbance in gravity would propagate only as fast as the debris traveled - the Earth would not experience any effect in its orbit until the debris actually reached it. (How long this would be would depend on how fast the debris were moving. If they were moving at .1c, it would take about 80 minutes or so for the first of them to reach Earth).

With an assymetrical explosion, one can notice an effect on the orbit much earlier, one that travels at the speed of light. The magnitude of this effect will be small though - it would be determined by the amount of gravity waves emitted by the sun. It would be hard to blow up the sun vigorously enough to generate any significant gravity waves. It would probably be better to make the sun _implode_ rather than to explode it. The fact that the sun is rotating would generate the necessary assymetries, and the gravity wave production would be much higher.

People don't usually actually write out, much less solve, the equations that would be needed to describe these situations, with a few exceptions. The general characteristics of the extremely comlex differential equations that represent GR are already known, and one of the properties that the solutions to these equations have is the property that disturbances in them always propagate at 'c' or less.

Here is the exception - with the development of LIGO, people actually _have_ done the necessary modelling to try and understand what the expected gravitational radiation signals would be from a supernova, or from a binary neutron star inspiral. This is not exactly equivalent to "blowing up" the sun, and is much closer to the case of imploding the sun.

 

[Danger]

Pervect, I don't have time to search, but that other stuff about the sun disappearing was right here in one of the physics threads. It was one where someone was thinking that gravity was instantaneous. There might have been a FAQ about it as well, but this is where I saw it.

 

[Chronos]

Humbug. The sun cannot just magically disappear. It's an unphysical and useless exercise in 'logic'. It is, however, a great excuse to look for ways to confirm a pet 'aha, Einstein was wrong' theory. Pardon my petulance.

 

[SpaceTiger]

It is, however, a great excuse to look for ways to confirm a pet 'aha, Einstein was wrong' theory.

So this really appears in his writings? Do you know which ones?

 

[adjkgh]

of course the sun cannot magically disappear, I'm saying "IF" it did, what would happen. IF it blew up, IF it was abducted by the aliens etc etc etc. what would happen IF there was no sun. there is no such way we can find out for sure what would happen but any logical ideas according to what we have found out so far (such as gravity traveling at the speed of light) would be great.

 

[SpaceTiger]

of course the sun cannot magically disappear, I'm saying "IF" it did, what would happen.

The fact that the sun cannot disappear means that we don't have a theory to describe such an event. The conservation laws are built into general relativity and, since GR is the best theory of gravity that we have, there is no answer to your question other than "it cannot happen."

If we instead think in purely Newtonian terms (technically wrong, but instructive for understanding classical physics), you can ask what happens when an orbiting body is no longer subject to the force that was holding it in its orbit. The answer, as we've said, is that the body flies off in an approximately straight line (with small perturbations from the planets). This is simply a consequence of Newton's First Law -- a body in motion stays in motion at a constant velocity unless acted upon by an unbalanced force.

IF it blew up

This is a fair question. I hope it was answered to your satisfaction.

IF it was abducted by the aliens

In addition to the planets heading off on straight line paths, you would probably also see FOX do an hour-long special on it.

 

[heldervelez]

The fact that the sun cannot disappear means that we don't have a theory to describe such an event. The conservation laws are built into general relativity and, since GR is the best theory of gravity that we have, there is no answer to your question other than "it cannot happen."

There is a situation where mass/gravity can vanish and the underlying problem still needs an answer.
When we have matter/antimatter colision (ex. electron/positron pair) there is a gravitational field associated to the masses before 'colision'.
As they annihilate in photons with no rest-mass 'something' as to happen to the gravitational fields associated to that pair.
As a real physical world can not stand with 'instant action at distance' because it would became a 'magic world' with not a single physical law (lack of predictability), it is better to choose a limiting speed. There exists some consensus around the value 'c'.
And I think that GR still stands.
If somehow sun could suddenly disappear then, making the calculations, only 8.3 minutes later the Earth will leave orbit.

 

[ramsremedies]

Ok. I ask the question the otherway.
What if the sun's mass is doubled? whether Earth will spiral into collide with it OR it's orbit will be shortened OR will continue the same orbit but at a increased velocity? what is its effect on the already distorted spacetime around it? will it be further distorted and to what extend?

Earth is both rotating itself and revolving around sun. Will the there any effect of angular momentums of these two processes in determining where Earth should go when sun disappears suddenly? What about conservation of angular momentum here?

My opinion into the question "What if sun disappears suddenly?" is the Earth will not leave in straight path instantly and even after 8.3 min. Earth will start traveling in a curved path existing around the milky way centre at a velocity of its then velocity around sun + velocity of sun about milky way centre. The distortion by sun will merge with distortion by milky way to give a new distortion and the path of Earth in this distortion is depends on its momentum.

Can anyone clarify more? Many thanks in advance.

 

[D H]

It's the same old question, and the same old answer: "It can't happen."

This thread is six years old. It is very bad form to dredge up old threads, and it is also bad form to ask questions of the form "what do the laws of physics say will happen if something that violates the laws of physics occurs?"

Thread locked.