I Gravity: A Fun Look - Any Bloopers?

[sophiecentaur]

TL;DR Summary

A guy with a loud voice gives an entertaining presentation

I don't know what the general opinion will be of this presentation. It seems ok to me but are there any enormous bloopers in it? (If there are, then the level is wrong and I apologise)

 

[PeterDonis]

If there are, then the level is wrong

There aren't necessarily any obvious "bloopers", but that doesn't mean the presentation is "A" level. At best it's "I" level. The thread level has been changed accordingly.

 

[PeterDonis]

It seems ok to me

As a rough heuristic, the idea of a "flow gradient" due to gravitational time dilation is not too bad. However, it's just a rough heuristic and it leaves out a lot.

The latter part of the video where it talks about point particles is not so good.

 

[Ibix]

The latter part of the video where it talks about point particles is not so good.

Yes - that felt to me like he'd realized that point particles were an obvious line of criticism and bunged in "this is too complicated to explain, just trust me" in an effort to cover it. Whether point particles exist or not, GR let's you consider them and says they fall.

I'm not keen on "flow" models. They feel like pandering to the notion that everything must really secretly be Euclidean and there's a flow of... something... pushing things around. That's not very GR-esque (I don't think it's even gauge gravity-esque). I like A.T.'s video better.

The "curvature of time" thing is pretty much true, though. Neglecting everything except the time-time component of the Einstein field equations and considering the limit of low speed causes them to simplify to Poisson's equation - so Newtonian gravity does genuinely drop out of the "curvature of time".

 

[PAllen]

Here is some info on the video producer:

https://www.aldacenter.org/flame-challenge-what-sound-0

He apparently has written a book:

http://www.scienceasylum.com/projects.php#book

 

[shjacks45]

I needed "a fun look at gravity". Gravity gets me down.

 

[sophiecentaur]

Here is some info on the video producer:

https://www.aldacenter.org/flame-challenge-what-sound-0

He apparently has written a book:

http://www.scienceasylum.com/projects.php#book

To quote Rod Steiger (No way to treat a lady) "Doesn't mean you're a bad person". One of my favourite movie quotes of all time.
His Gravity movie at least introduces an idea which everyone should think about. It's along the same lines as the Relativitistic explanation of the Magnetism force - perhaps more understandable.

 

[Sagittarius A-Star]

The latter part of the video where it talks about point particles is not so good.

To my understanding it is not experimentally verified, that classical point particles without interaction force would follow a geodesic, because classical point particles do not exist in reality. And de Broglie matter waves have a spartial size greater Zero, so that the model with the 2 clocks in the video would work for them.

 

[sophiecentaur]

Bearing in mind that this approach is a serious source of brain ache and remembering all our struggles with Newtonian, I would say it’s really not a bad stab at the topi. Of course, no single source can do it all.

 

[PeterDonis]

To my understanding it is not experimentally verified, that classical point particles without interaction force would follow a geodesic, because classical point particles do not exist in reality.

It is experimentally verified to high precision that ordinary objects like rocks, baseballs, and spaceships in free motion follow geodesics. So treating them as point particles in the math for cases where we don't care about their actual size or internal structure is perfectly justified.

In fact, it's even experimentally verified to high precision that large objects, like planets and stars, whose size, internal structure, and self-gravity are not negligible, in free motion follow geodesics. Demonstrating theoretically why this is expected to be the case to the precision of our current best measurements is actually quite complicated. There was a PF thread on this some time back, but I can't find it right now.

See further comments below.

de Broglie matter waves

Are quantum things, not classical, so they are out of scope for this thread.

have a spartial size greater Zero

This is way, way, way oversimplified, but again, it's out of scope for this thread anyway. If you want to discuss how the concept of "spatial size" is used in QM, please start a separate thread in the QM forum.

the model with the 2 clocks in the video would work for them

The model with the 2 clocks in the video is, at best, a very rough heuristic. The obvious problem with it is that GR predicts that point particles will follow geodesics. The fact that there are no point particles in the real world is irrelevant, since the video claims to be explaining why GR predicts what it predicts, and GR as a theory makes predictions about point particles, so the video should be explaining why those predictions are the way they are. The model with the 2 clocks fails to do that.

 

[MikeeMiracle]

I follow this channel along with PBS Spacetime to learn about spacetime as a layman. I have learned from this forum though to take all these pop-sci channels with a pinch of salt.

 

[phinds]

I follow this channel along with PBS Spacetime to learn about spacetime as a layman. I have learned from this forum though to take all these pop-sci channels with a pinch of salt.

More like a truckload