On 9/7/2025 6:46 PM, Alan Grayson wrote:
You seemed to have missed GR 101 where it is explained that gravity is NOT a force.On Sunday, September 7, 2025 at 7:36:32 PM UTC-6 Brent Meeker wrote: On 9/7/2025 5:52 PM, Alan Grayson wrote:On Sunday, September 7, 2025 at 2:29:11 PM UTC-6 Brent Meeker wrote: On 9/7/2025 12:12 PM, Alan Grayson wrote:*In reality, there surely IS acceleration, even though it might not be necessary to use it to solve the problem. Can the traveling twin return without acceleration? Of course not! AG*Actually he can. All he has to do it slingshot around a distant planet in order to head back to Earth: * * *But that's NOT how the TP is defined! AG *What is this "defined"? It's not /*defined*/ anywhere.*That's how it's described in almost any text one can find. You have a private definition. AG*It's just a thought experiment that was paradoxical in Newtonian mechanics. Every version I've shown you is paradoxical in Newtonian mechanics /*in exactly the same way*/. If you'd open you eyes and mind, you'd see that they give an intuitive grasp on why they all give the same answer in relativity and so resolve the same paradoxYou may object that he accelerated in turning around. */But general relativity teaches us that force free motion in a gravitational field is geodesic and there is no acceleration./* *So the traveling twin turns around without acceleration? AG *Read my last sentence above over again a few times. Brent * **I did, initially. During the turnaround the motion is NOT force free, which GR allows, and one can apply the Equivalence Principle, and then time dilation. AG *
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