PBS Space Time
1 HN recommender · recommended in 3 months, 2021–2023
11:51 · 3M views · Feb 24, 2021
PBS Space Time explores whether time causes gravity, explaining that gravity does not truly warp the flow of time but arises from time gradients. It revisits how gravitational time dilation works in general relativity.
Recommended as a good explanation of what happens when gravity acts on an object.
3 comments from Hacker News
One problem is that a lot of simplifications get layered on in pop science explanations of relativity, or actually deep science of any kind. We often talk about the force of gravity, but the thing is it's actually not a force, or even a field, in the same way as other forces and fields in physics. This is why Einstein is so revered in Physics. He didn't just explain a force, otherwise why would he be given pre-eminence over Maxwell who explained electromagnetism? Relativity is something else completely. Here's a really good explanation of what's actually going on when gravity influences an object. Hold on to your chair. this video
Well maybe not literally, just in practical terms. If it's a time gradient that causes an object to accelerate, then if you can apply a reverse gradient that would just cancel out the forces. But yes, one would need to first figure out how to do that without an equivalent amount of mass on the other side, if it's even physically possible. Here's a stupid idea that's based on my definitely flawed understanding of relativity: If having high relative velocity causes time dilation, then wouldn't spinning a disc at relativistic speeds cause that same time gradient? Maybe we just need 99.9% c rad/s fidget spinners to float in the air just like bricks don't. Found the video on this theory: this video
It's space time curvature. This is an important distinction, because although you can zero out the spatial component of your 4-vector you can't also zero out the time component. Apparently you can think of the gravitational force as arising from time gradients [1]. Time flows slower closer to the planet, so if your arm is pointing towards the planet then your arm is advancing slightly slower in a particular way and this creates a situation where your arm wants to pull away from you; an apparent force. 1: this video