Speed of light and gravity..confused

Hey all, A few months ago, I brought up a question to my wife's attention, and after that looked for answers, even writing to Michio Kaku (Leading Scientist) to get an answer, yet haven't been able to find an explanation....

I was wondering that if the sun was to suddenly dissapear (ie just vanish, not turn to supernova etc..), what would happen to the earths' orbit. I mean it takes roughly 8 minutes for the light from the sun to reach earth, yet if the sun suddenly dissapeared, what would happen first... would the earth break its orbit first and 8 minutes later see the sun dissapear or what? If thats the case, doesn't that mean that gravity has a greater force over such distances than the speed of light can travel? Does that mean that gravity works in some sort of 'sub space' that connects to objects immediately, rather than 'travel' such as light does.

Appreciate responses to this.

Thx

The simple answer is that it is unknown at what speed the force of gravity travels. It has not been measured in the lab because the force of gravity is so weak.

Effectively, for weak gravitational fields, Relativity suggests the effect of gravity is instantaneous.

See here for more info: math.ucr.edu...

well if matter could disappear suddenly it would be interesting. I would say sense gravitation is looked on as a force, if the cause of the force where to suddenly vanish the body in motion (earth) would continue on an fairly linear path. same concept if your spinning a bucket and suddenly let go. but there is quantum mechanics to deal with saying its a field so the shape and properties of the field will effect it. then there is background independence and it just gets theoretical from there. so i guess i have lead you around in a circle because we have never experienced a large mass suddenly disappearing and its effects on space.

Hi Marty,
These are good questions. So, according to General Relativity, gravitational effects propagate at the speed of light (since gravity waves move at the speed of light). So if the sun were to be suddenly removed, we wouldn't notice anything for eight minutes (since we are eight light mins from the sun) after that, the Earth would fly off at a tangent to it's orbit in accordance with Newton's laws of motion.

Since both the sun, and it's gravity are travelling at the same speed, then Sun and it's gravity would dissapear at the same time from our view point here.

Hope this helps,

-Paul.



[edit on 18-1-2008 by timelike]

I would suggest that gravity works on the Quantum level, that is to say you couldn't apply relative theory to explain it (when are we gonna pull or fingers out and unify physics?? )

I got no real argument for this right now - I am you stereotypical armchair physicist.... But something along the lines of quantum entanglement could hold possibilities.

So if the sun were to suddenly disappear with out trace I think the effects would be immediately felt throughout the solar system (and beyond)... ergo we would already be spinning off on a tangent into space many minutes before the lights went out.

Hypothetically speaking by what method would the sun disappear? I'm thinking a startreck transporter of truly mammoth proportions!!


[edit on 18/1/2008 by Now_Then]

reply to post by Im a Marty


That is a good question, and Timelike has explained the answer currently accepted by most scientists. One reason it's not so obvious basd on certain predicted behaviors of orbits that aren't observed, leading some to say it's instantaneous, is that the equations for motion, which include warping of space time, affect the perceived propagation.

One thing that led people to agree with Einstein on the speed of light for gravity is that GR accurately predicted the anomalous behavior of Mercury's orbit, where no other known theory did.

There really is a lot of confusion about this issue, and there is still a debate in the scientific community. One really interesting theory that you might look into, which could be related, is Wheeler Feynman Absorber theory. That is also very related to quantum effects. Some people believe that the advanced waves, referred to in the Wheeler Feynman theory, which actually travel backwards in time, are, in fact the force of gravity. This is genuine scientific theory with backing via sound math (given certain models of the universe), but is not generally accepted in the scientific community.

Originally posted by Im a Marty
Hey all, A few months ago, I brought up a question to my wife's attention, and after that looked for answers, even writing to Michio Kaku (Leading Scientist) to get an answer, yet haven't been able to find an explanation....

I was wondering that if the sun was to suddenly dissapear (ie just vanish, not turn to supernova etc..), what would happen to the earths' orbit. I mean it takes roughly 8 minutes for the light from the sun to reach earth, yet if the sun suddenly dissapeared, what would happen first... would the earth break its orbit first and 8 minutes later see the sun dissapear or what? If thats the case, doesn't that mean that gravity has a greater force over such distances than the speed of light can travel? Does that mean that gravity works in some sort of 'sub space' that connects to objects immediately, rather than 'travel' such as light does.

Appreciate responses to this.

Thx

Interesting.

But no....the earth would remain in orbit for 8 more minutes.
Nothing can go faster than light (generally believed)(right?)

it was first supposed that the earth,along with the other planets,would stop orbiting the sun and go off in their own direction RIGHT when(if rather)the sun would all of a sudden dissapear.

but I believe it was Einstein that proved this wrong.
We now know that the planets (earth) would stay in orbit for roughly 8 more minutes.

Cheers

Hi Now_Then,

Forgive me, but I don't really see what Quantum Entanglement has to do with it. If we think of Gravity at the quantum level, then I guess we would use the Standard Model of Particle Physics, which states that the Gravitational force's gauge boson is the Graviton. Thus, gravity if transmitted by the Graviton is limited to a maximum interaction speed of c, the speed of light.

But your right, since we don't have a complete picture of Quantum Gravity (my money's on Loop Quantum Gravity rather than String Theory), we cannot be certain.

-Paul.