The REAL source of Gravity might SURPRISE you...

Einstein's general relativity says gravity is spacetime curvature, but what does that mean? Let's take a look at how gravitational time dilation results in an effect that looks a lot like gravity. The flow of time brings mass together.
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VIDEO ANNOTATIONS/CARDS

What the HECK is Time?!

Why Does Stuff Happen? Gradients!

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PBS Space Time on Building Clock:

Eugene on Gravitational Time Dilation:
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LINKS TO COMMENTS

[ScienceAsylum]

*1. Why does the motion arrow turn?*
Well... we're imagining that the squirrel is in some kind of fluid flow. It's not but it's a useful picture, so just imagine he is. If a real squirrel was in a real fluid flow like that, what would happen? The squirrel would turn. In a spacetime diagram, a rotation is a change in speed... also known as an acceleration. You're welcome 🙇‍♂️

*2. Wouldn't that mean that taller things would accelerate more because the gradient is bigger?*
No. While the total difference between the top and bottom of something like a building is bigger than it is for a squirrel, that doesn't actually matter. Curvature isn't a global phenomenon. It's a local one. Imagine both the building and the squirrel are giant stacks of infinitesimally-separated clocks. It's the gradient between _adjacent_ clocks that matters. Although, that does pose a different problem: spaghettification. Different parts of an object can experience different time gradients if they're tall enough. That means different parts of them will fall at different rates and be torn to shreds. This is a common event near stellar-mass black holes.

*EDIT on 6/29/2020:*

*3. Isn't this a circular argument? Doesn't gravity cause the time dilation?*
It only seems circular because of a common misconception you picked up along the way. At 2:40, I state that gravity is _not_ the cause of the time dilation. It is the result of it. The cause of the time dilation is the Earth (or whatever source mass). The Earth causes the dilation _directly._ That's the connection between energy/mass and spacetime described by Einstein's field equation. We don't have a mechanism for that because it _IS_ the mechanism that causes gravity. Note: When I say "gravity" in this video, I mean "gravitational attraction." That attraction is observed behavior, not a force.

*4. Isn't time dilation caused by motion?*
Yes, that is one type of time dilation called kinetic time dilation. Gravitational time dilation is a completely separate effect. They're two different types. How much there is of each depends on the circumstances. Tall buildings and GPS satellites are predominantly affected by the gravitational kind. Astronauts on the ISS are predominantly affected by the kinetic kind.

[jacqualinesalb]

I think I understand, I might not, but because of this video, I believe I’m much closer to understanding time-space. I’m 75 years old, and I’ve got a lot of un-learning to do. Thank you

[simoncook]

I'm now lying down to ensure my body ages at the same rate.

[jorgepiresjunior]

At the beginning It was confuse, but at the end it seemed like the beginning.

[walabter]

I would have never imagine a 7 seven minute video as mindblowing as this one thank you so much for all your effort

[IIVVBlues]

My bathroom scale is actually measuring time dilation. So, I'm not overweight, I'm just behind my time.

[samiverstine]

I’m a physicist and I never knew how to correlate time with gravity. You are a great teacher!

[murilovsilva]

This crazy looking man who speaks in hand waves and eye rolls has taught me more about gravity in 7 minutes than all other videos on the internet that I have ever watched. Great work!

[TimpBizkit]

I was trying to work out why the squirrel didn't just start to spin, or why a stationary squirrel still falls.

[bustedshark]

I just watched this with my 5-year-old great-grandaughter. She proceeded to walk up to my wife and declare that gravity was caused by a squirrel and two clocks. I'll try again in about 5 years!
Excellent analogy though!

[Icewind]

I think this is the first time "might SURPRISE you" in a youtube title actually guessed right.

[grahamecampbell]

My physics teacher once told me that time is immaterial, so I gave him my work assignment three days late.

[rondesantis]

Time Doesnt Wait For Me, It keeps on going. Well, I'm Taking My Time, I'm Just Moving Along, You'll Forget About Me, After I've Been Gone. It's Been Such A Long Time, I Think I Should Be Going. -- 1976 Boston

[Viperzka]

This is the first analogy that has actually made the "gravity isn't a force, it's curvature" make sense.

[randybarnhill]

Great video. This explains why people on the top floor have to leave earlier than people on the bottom floor to catch the same bus to get to work.

[wojo]

I'm reading a book on anti-gravity and just can't put it down.

[TheRealReVeLaTioN]

“What happens when there’s a gradient? Stuff.” 😄😆🤣

[runninginthebackground]

That explains why my beard turned white but not my pubic hair!

[JZainbear]

This explains why I got left back in the 10th grade for being too high.

[ryanedgerton]

Just realized that this means an hourglass is both the perfect symbol and a cognitive paradox. It's the influence of time measuring the passage of time, which means it's basically time measuring itself...