If the sun were to approach the earth

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Discussion Overview

The discussion explores the hypothetical scenario of the Sun approaching the Earth and the resulting gravitational effects on objects on the Earth's surface. Participants consider various aspects of gravitational interaction, tidal forces, and the implications of such an event on both the Earth and its inhabitants.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that as the Sun approaches, objects on the Earth's surface would gradually start to pull away from the Earth and gravitate towards the Sun's surface.
  • Others argue that any force pulling objects off the Earth's surface would also act on the Earth itself, suggesting that everything would fall towards the Sun simultaneously without noticeable change for those on Earth.
  • A participant mentions the concept of tidal forces, stating that for these forces to be strong enough to pull objects off the Earth's surface, one would need to be within the Roche Limit, which is dependent on the masses and densities of the bodies involved.
  • It is noted that the Roche Limit for Earth would be below the surface of the Sun, implying that the Earth would collide with the Sun before tidal forces could pull objects away from its surface.
  • Concerns are raised about the unrealistic nature of the scenario, particularly regarding the vaporization of objects on Earth as the Sun approaches.

Areas of Agreement / Disagreement

Participants express differing views on the nature of gravitational effects during the Sun's approach, with no consensus reached on how objects would behave. Some agree on the role of tidal forces and the Roche Limit, while others emphasize the simultaneous gravitational pull on both the Earth and objects on its surface.

Contextual Notes

The discussion includes assumptions about the nature of gravitational interactions and the hypothetical scenario's feasibility, which may not align with real-world physics.

pentazoid
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... as the sun was traveleing at a closer distance towards the Earth , would Earth bound objects start to fly away from the Earth surface and head towards the sun's surface , or would everything on Earth surface fly towards the sun's surface as the same time the Earth itself flew towards the sun's surface?
 
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Hi pentazoid! :smile:
pentazoid said:
... as the sun was traveleing at a closer distance towards the Earth , would Earth bound objects start to fly away from the Earth surface and head towards the sun's surface , or would everything on Earth surface fly towards the sun's surface as the same time the Earth itself flew towards the sun's surface?

The second one …

except that the surface of the ocean would get very slightly further away from the ocean floor (it's an inverse-cube ratio, I think) towards the centres of the hemispheres of the Earth facing and opposite to the Sun. :smile:
 
tiny-tim said:
Hi pentazoid! :smile:


The second one …

except that the surface of the ocean would get very slightly further away from the ocean floor (it's an inverse-cube ratio, I think) towards the centres of the hemispheres of the Earth facing and opposite to the Sun. :smile:

Assuming unrealistically, that everything on the Earth's surface doesn't vaporize, I find it hard to imagine that everything on the Earth's surface and the Earth itself will simultaneosly gravitiate itself towards the surface of the sun. It seems more of a realistic scenario to me that as the sun travels towards the earth, objects on the Earth's surface gradually start to pull away from the Earth surface and start to gravitate toward the sun's surface.. Its not like the Earth bound objects are attched to the surface. Well we are attached to the Earth surface but that's because there not an object around that is larger than the Earth surface.
 
pentazoid said:
Assuming unrealistically, that everything on the Earth's surface doesn't vaporize, I find it hard to imagine that everything on the Earth's surface and the Earth itself will simultaneosly gravitiate itself towards the surface of the sun. It seems more of a realistic scenario to me that as the sun travels towards the earth, objects on the Earth's surface gradually start to pull away from the Earth surface and start to gravitate toward the sun's surface.. Its not like the Earth bound objects are attched to the surface. Well we are attached to the Earth surface but that's because there not an object around that is larger than the Earth surface.

Any force pulling objects off the surface of the Earth would be due to the difference between the Sun gravity pulling on the center of the Earth and at the Earth's surface. This difference is called tidal force. For this tidal force to be strong enough to actually be stronger than the force of gravity holding objects to the surface of the Earth, you have to be close enough to be within the what is called the "Roche Limit". The Roche limit any two bodies depends on their masses and densities.

Because the Sun is much less dense than the Earth, it turns out the Roche limit for the Earth would be below the surface of the Sun. IOW, the Earth would hit the Sun before the Sun's tidal force could ever pull an object off the surface of the Earth.
 
pentazoid said:
Assuming unrealistically, that everything on the Earth's surface doesn't vaporize, I find it hard to imagine that ...
That's the trouble with imagining. Imagining is based on common sense, and common senese is based on things we've experienced before in the course of our natural lives. And I'm faaairly certain you haven't experienced the tidal effects of a close approach of the Earth and Sun. :smile:

Janus' explanation is brilliantly concise.

I'll add just one other aspect to it:

Any force that would pull an object off the Earth's surface is just as much going to act on the Earth as on the object. i.e. if the sun's pull could suck the object into it, then it's going to suck the Earth into it. We on the Earth won't notice any change, the Earth - and everything on it - will fall normally toward the sun.
 
Last edited:
DaveC426913 said:
Janus' explanation is brilliantly concise.

Seconded! :approve:

Janus, how about a PF Library entry on "Roche limit", or "tidal force"? :wink:​
 

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