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Comment by SavantIdiot | Hacker News Reader

I read that whole article and all I came away with was, "Gravitational waves bend space time a little in a phenomenon called gravitational memory." I still have no idea by what mechanism though, other than guesses at some deeper super symmetry.

Can anyone dumb this down a little more for me? What holds on to the deformation? If spacetime can be deformed by a gravitational wave, then how can its original be entirely decided by the amount of and the arrangement of matter nearby. Meaning: if a wave passes by, unless it impacts the arrangement of matter in the locality, then what "holds" the deformation?

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Here's another (better, I think) attempt to explain it in plain language, from a few years ago:

https://nautil.us/issue/69/patterns/how-the-universe-remembe...

Spacetime is just 4D array: [x,y,z;t]. "Bending of spacetime" means that you need to apply a shader to this array.

If you want to talk about physics of the process, then you need to pick up a physical medium first, not an array of measurements.

I don't get in many depictions they show this planet/ball over a grid that's deforming downwards. I can understand how another mass would want to "fall" into that but is it actually that shape (has up/down) or it some kind of sphere. I also believe with regard to mass clumping, gravity is strongest near the surface of the Earth vs. inside where you could say it's equal/0 except the oblique part.

The rubber sheet analogy is criticised for this exact reason. Here’s a different visualisation that starts with what’s wrong with the rubber sheet: https://youtu.be/wrwgIjBUYVc

Oh yeah I can see the 3D sinking inwards

that's a neat video haven't seen that slicing idea before

That’s the best visualization of gravitation I’ve ever seen. Well done. I recommend it to anyone who’s been misled by the ubiquitous rubber sheet picture.

That's a great video. 7:50 is the important twist for me, and 10:25 really drives it home. I'll never forget that video now and it explains so much.

THere's still one "flaw" with this video: explaining that the grid "moves" is a little confusing. It doesn't move per-se, it .. evolves? ... over time. That's weird. I keep wanting to think the curves are static, but from t0->tn the grid pinches up. Yes, that's why they call it spacetime, but I have to stop and reset myself because how can the grid keep pinching up indefinitely but it doesn't it is just a concept. That is a stumbling block. 35 years after my last physics class...lol.

That's an amazing little video. thanks for posting. (Maybe that should go on to the main page, at some point)

Great video. Another one I like is "Why Gravity is NOT a Force" from Veritasium https://www.youtube.com/watch?v=XRr1kaXKBsU

It uses gravity force to demonstrate that gravity force is not a force. ;-)

That's clever. I'd suggest an improvement. When a sat has initial speed, show its small local reference frame, so we'd see that it always moves forward in its own reference frame, but the frame happens to be pulled to Earth.

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