Why Gravity is NOT a Force

  • 🎬 Video
  • ℹ️ Description


Amazing VFX, compositing, and editing by Jonny Hyman
2D animations by Ivàn Tello
Filmed by Steven Warren and Raquel Nuno
Special thanks to Petr Lebedev for reviews and script consultation

Rocket made by Goodnight and Co.
Screen images in rocket by Geoff Barrett

Slow motion rocket exhaust footage from Joe Barnard at BPS.Space

💬 Comments on the video
Author

Here's a question I've seen a lot in comments: OK, I'm accelerating up but then shouldn't someone on the other side of the globe fall off? No, here's why:
Either watch again from 8:28 or read what I've written below...

Spacetime is curved - it curves the opposite direction on the other side of the Earth. 

Neither us on this side of the Earth nor they on the other side are changing our spacial coordinates - we're not moving up, they're not moving down - Earth isn't flying into one of us.

BUT we both ARE accelerating. In curved spacetime you have to accelerate just to remain stationary.

The traditional definition of acceleration is something changing its velocity.

In general relativity you have to embrace a new definition of acceleration: it means deviating from a geodesic - not going on a straight line path through spacetime. Near the Earth a geodesic is a parabola so unless you're moving in a parabolic arc (like on a zero-g plane) you are accelerating.

This definition is the same as the old one  so if you're accelerating in deep space then your velocity is changing.

*BUT*... if you are near a large mass you are in curved spacetime, now acceleration  your velocity is changing. You can stay stationary relative to Earth's surface and still be accelerating. This is because your acceleration should be measured not relative to the Earth's surface but relative to free-falling objects - they are inertial observers.

Imagine this - I'm in deep space and I make horizontal rows and rows of stationary golf balls. Then I hop in my rocket and accelerate up through them. Just think about what that looks like. Now my rocket is back on Earth just sitting there. I freeze time for a sec and make horizontal rows and rows of golf balls up into the atmosphere. Now unfreeze time. What do you see? If you just look at the golf balls and the rocket ship it looks the same as the situation in space where the golf balls were stationary and the rocket was accelerating. Einstein's point was the golf balls have the better claim as the "stationary" thing since their experience is just like the golf balls in deep space - no forces experienced. The rocket on Earth is just like the rocket in space. It feels a force and hence an acceleration.

Author — Veritasium

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This video is a masterpiece. The best explanation of gravity on the internet currently.

Author — The Action Lab

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"Do you feel weightless?"
ISS astronauts watching your video: "Yes..."

Author — Pu Du

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As a Harvard Neuroscientist, here's another mind-bending gravity-related thought. When you rotate your head, you are NOT in control of the primary directionality of your eye movements under most circumstances. Try this. Keep your head still and look at your finger while you shake your finger left and right; your finger will look blurry due to motion blur. Now, instead, keep your finger still and look at it while you simultaneously shake your head left and right, which will demonstrate - in this situation - that you are still able to maintain a stable image of your finger. This is because your gravitationally-influenced sense of your head in space - your vestibular system - has a hardwired reflex to move your eyes in the opposite direction of your rotational head movements. This vestibular-ocular reflex (VOR) ensures automatic dynamic stabilization of images during head movements. You are not consciously doing this, and you can not consciously override it. The VOR is truly a reflex and, interestingly, does not depend on vision. During head movements, you will still have a strong VOR if you are in the dark or if you have your eyes closed. Your VOR originates from your vestibular system, which is located in your inner ear right next to your cochlea - your organ of hearing. Your vestibular system for rotational head movements consists of a series of three fluid-filled semicircular canals that have little "hair" cells inside the canals. When your head moves up-down (pitch), left-right (yaw), or shoulder-to-shoulder (roll), fluid inside the corresponding semicircular canal flows. This head motion-induced flow bends the hair cells within the canal to ultimately send electrical impulses to your hindbrain. These electrical impulses - encoding head movement - then talk to parts of your brain controlling eye movements, which connect to your eye muscles to reflexively move your eyes in the opposite direction of your head movement. So be thankful that your sense of your head in space - your vestibular system - takes care of maintaining a stable image of the world even when your head bobs around as you walk. Otherwise, walking would be a blurry journey of craziness. Videos coming soon.

Author — Flame P

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Einstein also said:

If you can't explain it simply, you don't understand it.

Author — L. W

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"Don't even get me started on Gravity" - Phoebe was right all along the way.

Author — MAYUR KALYAN CHHORIYA be15b017

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As long as I've known Derek he's consistently asked the difficult questions. This video challenged me, and taught me many things. I want to try the eclipse photo now. Impressed Eddington did it in 1919.

Author — SmarterEveryDay

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11:00 “My dear, here we must run as fast as we can, just to stay in place. And if you wish to go anywhere you must run twice as fast as that.”
― Lewis Carroll, Alice in Wonderland

Author — Chris B Kirov

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"The Earth is actually accelerating up..."

Flat Earthers: "Checkmate, science"

Author — Jordon

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Einstein: That's it. Gravity is not a force

Newton: Wait. Do I know you?

Author — Tahsin Maria

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Me: learning in physics class for the past three weeks about gravity.
Vertasium: there is no gravity
Me: then what the f$uck my teacher was blabbing for the past three weeks?!!

Author — hi

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Man falling off roof: "I'm going to die in a few seconds, but at least I don't feel my own weight."

Author — Toughen Up, Fluffy

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"It's not flying, it's falling, with style." 😂

Author — Louise B

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The reason Einstein and others like him are geniuses is because they imagine things the rest of us need help to imagine.

Author — Andrew Heagwood

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Me: Falling from a building feeling weightless Them: You are not an inertial observer Me: You lied to me.

Author — vbddfy euuyt

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Officer I can't walk in a straight line because we all walk in geodesics.

Author — Benjamin Tollison

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The only problem here is that he is talking about theoretical physics as if it were fact as click bait

Author — Bryson Raile

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"Gravity schmavity. What we need is some levity!"—Alberta Eisenstein.

Author — Toughen Up, Fluffy

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I was doing OK until the formulas showed their ugly heads then my brain hit a space time curve resulting in a super nova of neuronic proportions.

Author — audiotron1003

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"in curved spacetime you need to accelerate just to stand still". For everyone who can't follow, accept gravity as a simplified explanation ;)

Author — Jingles Khan Audio Productions