Gravity is not a force – free-fall parabolas are straight lines in spacetime
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Gravity is not a force – free-fall parabolas are straight lines in spacetime
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Re: Gravity is not a force – free-fall parabolas are straight lines in spacetime
#2The video for this page provides great context https://youtu.be/XRr1kaXKBsU
Re: Gravity is not a force – free-fall parabolas are straight lines in spacetime
#3The video for this page provides great context https://youtu.be/XRr1kaXKBsU
Great Veritasium video.
So some flat earth arguments are actually correct if general relativity is correct, namely that gravity is an illusion and that the real reason we are stuck to the earth is that the earth is accelerating toward us at 9.8 m/s^2
Re: Gravity is not a force – free-fall parabolas are straight lines in spacetime
#4The video for this page provides great context https://youtu.be/XRr1kaXKBsU
Great Veritasium video. So some flat earth arguments are actually correct if general relativity is correct, namely that gravity is an illusion and that the real reason we are stuck to the earth is that the earth is accelerating toward us at 9.8 m/s^2
I don't understand it. How can it accelerate towards anyone on its surface? Where does it get energy to accelerate? We generally need to burn fuel to accelerate something in the space.
Re: Gravity is not a force – free-fall parabolas are straight lines in spacetime
#5How would periodic “free-fall” motion look in this setup? E.g. a point mass orbiting around a body, or a point mass oscillating back and forth in a 1D gravity well.
Re: Gravity is not a force – free-fall parabolas are straight lines in spacetime
#6True gravitational force is something that can’t be transformed away by an arbitrary choice of frame (even an accelerating one).
As a brief example, consider two objects in downwards free fall toward the centre of some massive object. Since they head towards the centre, in a free falling frame the two objects actually get closer to each other until they collide as they reach the centre.
This is known as the tidal effect of gravity and is the actual physical content of general relativity. This effect can be shown to be obtained by an appropriate curvature of spacetime which itself can be shown to be related to the stress-energy of matter inhabiting spacetime.
Re: Gravity is not a force – free-fall parabolas are straight lines in spacetime
#7Earlier quoted context omitted.
Great Veritasium video. So some flat earth arguments are actually correct if general relativity is correct, namely that gravity is an illusion and that the real reason we are stuck to the earth is that the earth is accelerating toward us at 9.8 m/s^2
I don't understand it. How can it accelerate towards anyone on its surface? Where does it get energy to accelerate? We generally need to burn fuel to accelerate something in the space.
"in curved spacetime, an object needs to accelerate just to stay still"
I don't really understand why, that was just the explanation Derek gave.
Re: Gravity is not a force – free-fall parabolas are straight lines in spacetime
#8I saw this and the related Veritasium video, but am still scratching my head about something. Does this mean that away from all gravity a body does not experience any time? ie a person on a spacecraft stopped in intergalactic space would not age relative to persons on planets?
Re: Gravity is not a force – free-fall parabolas are straight lines in spacetime
#9I saw this and the related Veritasium video, but am still scratching my head about something. Does this mean that away from all gravity a body does not experience any time? ie a person on a spacecraft stopped in intergalactic space would not age relative to persons on planets?
How do you get away from all gravity? Aren't you subject to gravity from all other matter in the universe at all times?
Re: Gravity is not a force – free-fall parabolas are straight lines in spacetime
#10I saw this and the related Veritasium video, but am still scratching my head about something. Does this mean that away from all gravity a body does not experience any time? ie a person on a spacecraft stopped in intergalactic space would not age relative to persons on planets?
I believe (from my limited knowledge from Interstellar) that it’s the opposite: higher gravity environments move slower relative to lower gravity environments, which enabled the “go down to high gravity planet for a couple hours and come back and it’s ten years later” plot point in the movie. So if you’re in intergalactic space, time is actually passing very quickly in the higher gravity environment of a galaxy.
But a person’s experience should always be the same, no matter what reference they are in. They will perceive time as passing at the same rate in all environments, but it will be different from people in other environments.
Caveat: IANA physicist, and this is not physics advice.