If the sun suddenly dissapeared.

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Discussion Overview

The discussion revolves around a hypothetical scenario in which the sun suddenly disappears, exploring the implications for gravitational effects and the propagation of light. Participants examine the theoretical consequences of such an event, including the timing of gravitational waves and the potential for other forces acting on Earth.

Discussion Character

  • Hypothetical situation, Thought experiment, Debate/contested, Conceptual clarification

Main Points Raised

  • Some participants reference Einstein's assertion that light from the sun would take approximately 8 minutes to reach Earth, while gravitational effects would be felt almost simultaneously.
  • One participant questions whether experiments have been conducted to confirm that a smaller object would not move until the light from a larger object has disappeared.
  • Another participant argues that the sun cannot simply "disappear" due to conservation laws, suggesting that moving it would require speeds close to that of light.
  • Some participants express uncertainty about the existence of other forces holding Earth with the sun, with one stating that gravity is the only significant force.
  • There is a discussion about the relationship between micro and macro scales, with one participant suggesting that demonstrating any movement of a planet could provide insights into the differences in governing laws.
  • One participant draws an analogy involving a pebble dropped into water to illustrate concepts of influence and propagation of effects, while others challenge the relevance of this analogy to the original question.

Areas of Agreement / Disagreement

Participants do not reach a consensus, with multiple competing views on the implications of the hypothetical scenario and the nature of forces acting on Earth. There is ongoing debate about the validity of the assumptions made and the relevance of certain analogies.

Contextual Notes

Participants express uncertainty regarding the propagation of gravitational effects and the potential for other forces beyond gravity, highlighting limitations in the current understanding of these concepts.

Willowz
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I have a question about this known hypothetical situation. Einstein asserts that once the sun vanishes we would still receive light for 8 min. Then at almost/same time when the sky goes dark, the gravitational wave hits Earth and we would fall out of the earlier orbit around the sun.

Some questions about the situation above.

Have any experiments of this type been done? Confirming that a smaller object would not move, until the light from the bigger object had dissapeared?

And would it be possible that once the sun disappeared the Earth could move, even though the gravitational wave did not reach the Earth?
 
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The Sun can't just "disappear". Conservation of energy and momentum prevents that. We can't even move it "out of the way" fast enough, it would have to be accelerated close to the speed of light, we don't know how to do that.
 
Some relevant material here: http://www.lightandmatter.com/html_books/genrel/ch08/ch08.html#Section8.1

The basic answer is that we have excellent evidence that gravitational waves exist, and that they carry energy, but we don't have any direct, model-independent evidence that disturbances in the gravitational field travel at c.
 
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It's a hypothetical situation or a thought experiment if you will.
bcrowell said:
The basic answer is that we have excellent evidence that gravitational waves exist, and that they carry energy, but we don't have any direct, model-independent evidence that disturbances in the gravitational field travel at c.
I believe they do exist. But what I have in mind is if there are any other force holding the Earth with the Sun? If there is another force, then it would be noticable in such a situation.
 
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Willowz said:
But what I have in mind is if there any other force holding the Earth with the Sun?

No, the only significant force on the Earth is gravity.
 
Willowz said:
It's a hypothetical situation or a thought experiment if you will.
Well, you did ask if any experiments had been done...

Willowz said:
I believe they do exist. But what I have in mind is if there are any other force holding the Earth with the Sun? If there is another force, then it would be noticable in such a situation.
I'm almost afraid to ask but what makes you think there might be another force than gravity?
 
DaveC426913 said:
Well, you did ask if any experiments had been done...
My quote:
Willowz said:
Have any experiments of this type been done?
"This type" in my lingo means something similar, something like the Gravity Probe B experiment. But I think it should be better be called a "thought experiment". Since such a situation is not possible.
I'm almost afraid to ask but what makes you think there might be another force than gravity?
I don't know. I'm not good at sci-fi at the moment.
 
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Willowz said:
I don't know. I'm not good at sci-fi at the moment.
but something made you ask the question.

Anyway, no. There are no other attractive forces known or hypothesized (though there are some repulsive ones, such as the solar wind).
 
I don't know if I should be concentrating on the micro world with this logic or in the macro. But if it can be shown that a planet would move(even the smallest movement), then that could be a stepping stone for some further explanation between the difference of laws governing the micro and macro scale.
 
  • #10
Willowz said:
I don't know if I should be concentrating on the micro world with this logic or in the macro. But if it can be shown that a planet would move(even the smallest movement), then that could be a stepping stone for some further explanation between the difference of laws governing the micro and macro scale.

I completely don't follow.

I'm not sure what micro vs. macro has to do with anything, but more importantly, it sounds like you're trying to invent a phenomenon out of whole cloth.

Since there are no attractive forces acting between Sun and Earth other than gravity, nor is there any reason to think so, nor is there any reason to think the Earth does or would move ...

... what is the origin of the question?


In the same sense (taken to a slightly more absurd level):
Q: It is possible that Neptune is a unicorn? If it were, it should have a horn. Has anyone looked to see if it has a horn? Because of it did, that would be evidence that it was a unicorn.

A: Um, why do you think Nepture might be a unicorn in the first place?
 
  • #11
Wait. In re-reading your post, I realize that the whole Earth-Sun thing is not the crux of your question. This is the crux of your question:
Willowz said:
...some further explanation between the difference of laws governing the micro and macro scale.

You're trying to sort out the quantum world versus the marco world.


There's no real difference. Quantum effects (such as wavefunction frequency) manifest as inversely proportional to the size/mass of the object. A 100kg human has a wavefunction just like a proton does, it's just that the frequency is so high as to be irrelevant at the macro scale.

A human can tunnel through a wall "just" like an electron can, but the probability is inversely proportional to the number of particles in the human.
 
  • #12
Ok, so I will try in other words. If I drop a pebble into the water, I will see waves forming. If I am in the water and a pebble falls. I can hear the sound of the pebble falling into the water sooner than the waves reach me, furthermore because I am in the water the pebble minimally affected me. Because there was a displacement of water.
 
  • #13
No, I think it would be wrong to say that the pebble directly affects me while in the water. I think the pebble might affect the space-time around me. Though I do think if it can somehow indirectly have an influence on me.
 
  • #14
DaveC426913 said:
Wait. In re-reading your post, I realize that the whole Earth-Sun thing is not the crux of your question. This is the crux of your question:


You're trying to sort out the quantum world versus the marco world.


Yes, I think you are right. But I don't know where now.
 

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