Conflict with special relativity

[Kewell]

If the sun were suddenly to explode, the earth would instantaneously suffer a departure from its usual eliptical orbit. Even though it would take light from the explosion eight minutes to travel from the sun to the earth. Wouldnt this conflict with special relativity since information can't be transmitted faster than the speed of light? Why is this so, I do not understand why that is possible!

 

[BoJangles2]

Hi,

Relativity suggests the earth would continue in its orbit for 8 minutes or so; its Newtonian mechanics that dictates it would lose its orbit instantly, which is the old way of looking at things. It’s a benign thing to understand, though apparently it has been observationally proven with effects like the orbit of mercury.

I hope this helps.

 

[vogon13]

.

In fact, until some solar material exceeds earth's orbit (and the center of mass of the explosion remains essentially unchanged) earth's orbit hangs tight.

Just remember to lather on 8 inches of lead sunblock.



.

 

[Saiph]

Gravitational information is also believed to travel at C, so we wouldn't have any change in orbit until we see the lights go out.

Vogon also has a point, in that there will be no change in the orbit until any material in the sun expands past the earths orbit. Until that happens, all the mass is still considered. You may think this is strange, but I'll pose a little question to you: When we consider the gravity due to the sun, acting on the earth, do we ever ask how wide the sun is? Or just the distance to the sun?

By exploding, the sun has just gotten larger...the center of the sun is still the same distance, and of the sun is, for a while at least, closer to that center than the earth is...so it's gravitational affects all add together. Once the mass moves beyond earth's orbit, the gravitational pull begins to lessen.

 

[Mee_n_Mac]

Gravitational information is also believed to travel at C, so we wouldn't have any change in orbit until we see the lights go out.

Vogon also has a point, in that there will be no change in the orbit until any material in the sun expands past the earths orbit. Until that happens, all the mass is still considered. You may think this is strange, but I'll pose a little question to you: When we consider the gravity due to the sun, acting on the earth, do we ever ask how wide the sun is? Or just the distance to the sun?

By exploding, the sun has just gotten larger...the center of the sun is still the same distance, and of the sun is, for a while at least, closer to that center than the earth is...so it's gravitational affects all add together. Once the mass moves beyond earth's orbit, the gravitational pull begins to lessen.

Oooo oooo {squirms in chair} can I be pedantic now !?! :mrgreen:

Given the Earth's orbit is elliptic would a large expansion of the Sun (but retaining all it's mass) have some effect on the orbit ? Puff the Sun out to Mercury's orbit and now the differential between the nearest portion of the Sun and the furthest portion of the Sun is no longer negligible. (R !>> rsun) Furthermore would the difference in gravity at perihelion and aphelion due to this change the orbit ? Anyway I've not done the math as I've not finished my AM OJ but given the OP's question has been answered correctly I'd thought I take the time to probe the minutiae of the issue.

{then again perhaps I shouldn't begin posting until afternoon ... )

 

[Saiph]

Won't matter, regardless of how big it gets.

Unless...

(yes, there's always an unless!)

The new distribution of mass isn't uniform. If it's lumpy..then things get weird. An example is how the moon, due to the tides it creates on earth, is moving away from us due to the uneven distribution of the oceans.