Physics, Astronomy & Cosmology / Re: Problems with PopSci articles in GR. Should we stop using one example?« on: Yesterday at 21:32:42 »
In contrast, GR is frequently associated with a finite speed for the propagation of gravity through space.Gravity is a field and is ‘already there’ so to speak, so it seems wrong to say it propagates at all. Changes to the field do propagate, and do so at the speed of light, which has been repeatedly verified, but changes to the field (conveyed with gravitons which have not been verified) is different that the field itself which does ‘radiate away’ in any way.
This may be called the "speed of gravity" in many PopSci articles and it is also frequently claimed to be identical to the speed of light.I agree that it is wrong for any article to say this. The speed of change to the field is the only thing that has a speed.
ii. If the Sun suddenly disappeared… Astronomy magazine, 2012As you mention later, it is meaningless to posit what would happen given an impossible scenario. You might as well talk about your infinitely stiff string, and sending signals at faster than light by pulling on it, or fishing out an object lowered into a black hole. You can make up any story you like and it is ‘not even wrong’ since the theory does not make predictions about impossible physics.
iii. Here's what would happen if the sun disappeared right now, Business insider, 2015.
Google will bring a list of such instances involving well known Q&A sites like Quora, Physics Stack ExchangeStack Exchange is an excellent source of decent answers because they propagate the best answers to the top and don’t allow fools to promote pet theories. Quora on the other hand seems to be the opposite, and I rarely find accurate information there.
1. Have you encountered a similar example being used in your own learning?Of course. Sometimes I even look for it. Go to a biased site like conspiracyoflight.com as a useful exercise in ‘find the fallacy’ in each of their assertions, especially those bent on debunking Einstein, a favorite target, perhaps because relativity, not being entirely intuitive, is easily misrepresented by hucksters, or perhaps only due to antisemitism.
How long would it take the earth's orbit to be affected by a sudden disappearance of the sun?You tell me. It’s like asking what happens if the Tardis materializes inside a ‘prior’ incarnation of itself. It’s your story and you can make any answer you want since the physics in your scenario is different than reality. You are free to make up new rules.
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