The River Model of General Relativity

Does space "flow" like a river? There's an analogy in General Relativity positing exactly that, and which, astonishingly enough, conveys the sophistication of Einstein's theory via a few simple intuitions. But how truthful is such a view, and what would it imply about the most infamous of massive objects to inhabit our universe -- that of the black hole? Climb aboard our river-boat and find out! Plus -- Curious Edgar finds himself in more than one vertiginous predicament.

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Content:
00:00 - Intro
01:05 - The Set-Up
01:54 - Accelerated Frames & "Flowing" Space
04:24 - Acceleration at the Surface of the Earth
06:10 - Reinterpreting Gravity
07:36 - Riverine Analogies
11:12 - Constructing the River of Space
12:43 - Phenomena on the River
16:05 - A Black Hole is a Waterfall of Space
18:09 - Conclusion

[ScienceClicEN]

I'm astonished by how good the visuals are! Great video as always!

[ibrahimsaleh]

I’ve honestly been trying to learn and visualize general relativity for years on YouTube and altho this “earth surface accelerating up in all directions” is the breaking point for all other videos, you’ve done a spectacular job with the explanation and the animation. I hope you reach a million subs. Uou just got one sub closer :)

[Benlucky]

I think the analogy is also useful to explain why information can't be sent out of a black hole. In subcritical water flow waves can move upstream against the current, even a low amount of energy tossing a small pebble in can still make upstream waves. But in super critical flow even the largest rock thrown overboard can't make a wave that moves upstream

[zedred]

Beginning to feel sorry for the gravity Monkey.

Another uniquely interesting and thoughtful take on this topic. Many thanks!

[notatakennick]

Your animations are getting ridiculously good. You absolutely deserve a million subs!

Also this flowing space model is how I've visioned gravity for a while now but damn does it raise even more questions...

[jack.d]

How did I miss the release of this a month ago? This analogy, along with the visuals, creates powerful intuition. Brilliant communication 👏

[jp-hhxq]

MSEE here and lifelong physics enthusiast. I have been thinking about this video since you put it out and watched it about once a week since. I showed it to others. I'm fully won over by the river model based on this and other videos of yours. I never thought I would reject the standard warped spacetime explanation, yet here I am. I am especially taken by the formation of massive objects with the analogy plugging up the hole. Brilliant. Your explanation of, and even daring to cover, an alternative to the status quo is a brave, but I'm very glad you did it. After the first 5 mins of the first video of yours I watched, I was ready to leave an angry comment, but waited until the end and had to watch again to punch any hole in the logic, but it was flawless. I deleted the comment. And have become a zealot for this theory now. Looking forward to more videos.

[czmzppn]

This is the best physics explanation channel on YouTube!

[SmashXano]

Love it! You always predict the questions which come to the viewers minds and guide them step by step through the argument. This helps me a lot to visualize the pricipals of GR and therefor keep them in mind permanently. Thank you very much!

[thetenrings]

I literally thought out the space time like a fluid all my life like a river. FINALLY someone addressed this.

[wafflepotato]

genuine questions for my confusion abt the analogy

1. where does the space go. Into the fourth (spacial?) dimension? Seems like a pretty big ontological burden for general relativity.

2. Is “space” destroyed when it reaches the center of earth? Is space generated elsewhere? Is space even that kind of thing?

3. Why does matter get stuck in the sinkhole? Why not just get sucked into wherever space is going?

Excellent videos as always! One of the few physics channels i actually trust 😅

[LucGendrot]

To me this feels so much more intuitive than the "stretched sheet" model used in so many science classrooms

[gabrielragum]

This video has answered all the pending questions I had about the equivalence principle and given me a tool to visualize GR like never before. Cheers.

[dmarckos]

You've very brilliantly explained the science gravity without the math.
I now understand it.

[ivocanevo]

Thank you for making this intuition detailed and concrete. I feel like we may have the Grant Sanderson of physics here.

On the edge of my seat for the next one... Subscribing!

[jmcsquared]

This might be your best video. You address the paradoxical question of what "the Earth is accelerating upwards" could mean. Though I still don't care for that language, your illustration of the river model as an explanation for this observation is beautiful.

I'm still curious how the river model connects to the block model, which is what I usually employ. I think the block model is the most realistic with how relativity works, but I might have to admit that the river model is be exponentially easier to visualize haha.

[-_Nuke_-]

I like that this channel sticks with special and general relativity. This is the reason I subscribed and you guys are the ONLY ONES addressing that river model.

I won't claim that I understand everything but I have the feeling that more are coming to the for.

[RalphEllis]

The river analogy.
…err - you have just reinvented the aether…..!
R

[VernAfterReading]

Wow! I would love to see this applied to orbital mechanics. I think I get it: the "flow" inward gives you the centripetal acceleration you need to move in a circle/ellipse, and you only have to have constant velocity laterally for your given orbit (so no need for an engine, once you have the right lateral velocity). Things like Oberth Effect make sense too.

[davidkeane]

Ive heard the ‘ground rushing up’ story before but this is a great way to understand how we stay neutral on the earth…well done for explaining it this way - thank you