Gravity: Sun Moves 10 Miles - Effects on Earth?

  • Context: Undergrad 
  • Thread starter Thread starter jefswat
  • Start date Start date
  • Tags Tags
    Gravity
Click For Summary

Discussion Overview

The discussion centers around the effects of a hypothetical scenario where the Sun moves 10 miles farther away from Earth in one second, specifically focusing on the implications for gravitational attraction and the propagation of changes in gravity. Participants explore the timing of gravitational effects and the nature of gravity itself, touching on theoretical aspects and implications for understanding gravitational interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that changes in gravity propagate at the speed of light, suggesting that if the Sun were to disappear, Earth would not notice the change for approximately 8 minutes.
  • Others argue that gravity is a property of local spacetime and does not take time to exist, but changes in gravitational fields do propagate at light speed.
  • A participant notes the difficulty of creating a gravitational "surprise" due to conservation of energy and momentum, indicating that significant changes in gravitational effects require substantial separation of mass.
  • There is a discussion about the theoretical ability to detect changes in gravity at a distance, with a humorous suggestion about using such changes to influence interplanetary horse races.
  • Some participants express confusion regarding the nature of gravity and its propagation, clarifying that while gravity itself does not travel, changes in gravity do propagate at the speed of light.
  • One participant raises a question about whether all four fundamental forces propagate at the speed of light, introducing the concept of the Higgs field as a potential unifying element.

Areas of Agreement / Disagreement

Participants generally agree that changes in gravity propagate at the speed of light, but there is disagreement regarding the implications of this for gravitational effects and the nature of gravity itself. The discussion remains unresolved with multiple competing views on the nuances of gravitational propagation.

Contextual Notes

Participants express uncertainty about the specifics of gravitational propagation and the conditions under which gravitational effects can be observed. There are unresolved questions regarding the theoretical frameworks and assumptions underlying their claims.

Who May Find This Useful

This discussion may be of interest to those exploring concepts in gravitational physics, theoretical physics, and the nature of fundamental forces, as well as individuals curious about the implications of hypothetical scenarios in astrophysics.

jefswat
Messages
92
Reaction score
0
So suppose we are on Earth and the sun moves 10 miles farther away in one second. When do we feel the changed effects of the gravitational attraction here on earth. Is it immediately or after at least ~8 minutes(time it takes light to get here)?
 
Physics news on Phys.org
Gravity as such doesn't take any time - it's a property of the local space time around you.
Changes in gravity (like you describe) propagate at the speed of light - they must since you can use them to send information.
So if the sun disappeared we wouldn't notice any change in our orbit for 8mins.
 
Ok, that's what I figured but I don't remember reading anywhere that explicitly said that
thanks
 
Note that it's very difficult to create a gravitational "surprise" because of conservation of energy and momentum. The most sudden thing the sun could do gravitationally, even in theory, is explode into two parts which separate in opposite directions. Even then, the gravitational field at the Earth would not change until the parts had separated far enough for the sum of the potential due to the two parts to be noticeably different from the original total effect.
 
mgb_phys said:
Changes in gravity (like you describe) propagate at the speed of light - they must since you can use them to send information.

How do you do that?
 
Well there is the information that the Sun is still there!
In theory you could move a large mass and detect the change in gravity at a distance (I didn't say it was easy) if you could measure the gravitational effect instantly on say Pluto you could use it to rig interplanetary horse races before the TV pictures of the winner arrived.
 
mgb_phys said:
Changes in gravity (like you describe) propagate at the speed of light
What changes in gravity propagate faster than the speed of light? I think you answered my original question though
 
mgb_phys said:
Well there is the information that the Sun is still there!
In theory you could move a large mass and detect the change in gravity at a distance (I didn't say it was easy) if you could measure the gravitational effect instantly on say Pluto you could use it to rig interplanetary horse races before the TV pictures of the winner arrived.

I was thinking that the gravitational response would be slower than c. If the sun disappeared instantly then we would see that it had gone a short while before the Earth headed off at a tangent. It must be reasonably easy to test with a torsion balance, or, hopefully, a more sophisticated equivalent, a large block of lead and an interferometer and away you go.
 
jefswat said:
What changes in gravity propagate faster than the speed of light? I think you answered my original question though
No changes propagate faster than light - what I meant to say was.
1, gravity doesn't travel - it's already there
2, changes in gravity do travel - at c
 
  • #10
mgb_phys said:
No changes propagate faster than light - what I meant to say was.
1, gravity doesn't travel - it's already there
2, changes in gravity do travel - at c

ok, you had me confused for a minute there
 
  • #11
Don't all four forces propagate at the speed of light...and how about the theoretical Higgs ocean..that too?? It seems to be a hint at least that they were all unified at some point...
 

Similar threads

High School Can we measure absolute motion of Earth and Sun?
  • · Replies 57 ·
2
Replies
57
Views
4K
High School How quickly does the Earth feel the effects of a halved Sun's mass?
  • · Replies 38 ·
2
Replies
38
Views
3K
Undergrad Disappearing Sun: A Thought Experiment on the Effects of Gravity and Light
  • · Replies 20 ·
Replies
20
Views
2K
High School Does the fact that gravity moves at the speed of light affect how planets move?
  • · Replies 9 ·
Replies
9
Views
2K
High School Gravitational Orbits: How the Earth Knows Where to Go
  • · Replies 29 ·
Replies
29
Views
2K
Undergrad Sun Disappearance: Impact on Earth's Path
  • · Replies 20 ·
Replies
20
Views
6K
Undergrad The Derivative Nature of Time and Its Relation to Earth's Rotation and Speed
  • · Replies 38 ·
2
Replies
38
Views
5K
Undergrad Effects of time dilation for near-speed-of-light travel
  • · Replies 65 ·
3
Replies
65
Views
13K
High School A thought experiment about the Sun vanishing
  • · Replies 12 ·
Replies
12
Views
2K
Undergrad Observation of the effect of gravity on the motion of antimatter
  • · Replies 1 ·
Replies
1
Views
1K