What Teachers Get Wrong About Equivalence

The Equivalence Principle is considered the major turning point in our understanding of gravity (General Relativity). But, if you think about it for more than a second, it doesn't hold up. Why is it so important if it isn't true?

Nick Lucid - Host, Writer
Em Lucid - Producer
Viki Lewis - Editor
Mikaila Blackburn - Animator
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TIME CODES

00:00 Cold Open
00:23 What is the Equivalence Principle?
02:01 What if weight doesn't exist?
03:01 Thought Experiment 1
03:36 Thought Experiment 2
04:11 Thought Experiment 3
04:37 Uniform Gravitational Fields
05:34 Why does the Equivalence Principle exist?
06:21 Solar Eclipse Experiment
07:28 Summary
08:03 Nebula Ad
09:21 Featured Comments

[xyzabc]

Today, I said "Fast, Fast!" at exactly the same time and cadence as you did. I'm gonna count this as a win.

[shantanusapru]

"Without air resistance..." 😱😱😱Physicist said the quiet part aloud!😱😱😱😱

[LuneLovehearn]

this also reminds me of when we used to talk about gravity, acceleration and perspective on the physics class on high-school. we used to have fun doing the math and experiments to prove and test the theory.

[Mysoi]

Great video as always, Nick!
I have consistently employed the equivalence principle to elucidate phenomena in classical physics that may not intuitively make sense, such as the less dense air above and the occasional perception of weightlessness in certain objects. However, when explaining this concept to individuals unfamiliar with the equivalence principle, comprehension is often elusive. Nevertheless, it provides a personal sense of satisfaction.

In positive news, recent experiments substantiate that antimatter falls down just like ordinary matter. This finding serves as compelling evidence that the equivalence principle remains valid even in the realm of matter-antimatter interactions, thereby demonstrating that all objects follow the same geodesics in curved spacetime.

General relativity for the win!

[kwezicanca]

Nick I really wish you already had a million subscribers. Man I love your channel, all the way from South Africa!!

[batlrar]

I really like all the minutiae you go into in this video, which probably covers a lot of questions or qualms people had with the previous one! Another part I usually don't see addressed is that the rocket would have to be pressurized to 1 atmosphere for it to feel like Earth (at sea level, at least), although I guess that part's usually just assumed. I've always found the part about light bending interesting as well, because light is considered massless, so it shouldn't technically be affected by gravity! The reasoning behind it is that gravity warps the space-time around the massive object, so it's not that the light is getting bent, but rather that the light is traveling in a straight line on a curved path, if that makes more sense.

[Emordiola]

Nick, I know you’re a physicist but can you make a video on math concepts, like calculus with real life examples, its history etc? Because you make people understand hard concepts easily and I want to understand advanced math, too!

[cortster]

Gravity being acceleration through time suddenly makes sense now. This is where the 'missing time' comes from when objects age slower in a gravitational field. They age slower in time, but move faster in space by an equivalent acceleration to compensate. It's conservation of energy in action.

[nathancampbell]

Can you do a video on how laser rust removal works scientifically? I find it fascinating how light can interact with the physical environment without being in a sense a physical thing.

[gaylord]

Another brilliant video from science, asylum, and Nick
Thanks for all the work and dedication you put into your videos

[favesongslist]

TY so much for this, I tried to present the same points online, admittedly not as eloquent as you just did, Without exception I was shot down and told I didn't understand the equiveillance principle.

[person]

4:14 in rindler coordinates (uniformly accelerating reference frame, what a rocket would experience), proper acceleration is inversely proportional to distance from the rindler horizon rather than constant (although the weight as a function of height would be different with that and gravity)

[mandelbraught]

As always, more great nuttiness from the asylum! Another excellent video, thanks! I have had one question about this for a while now and I honestly can't tell if you answered it, or not. The only way I can think to phrase it is: *IF* they worked out a theory of quantum gravity, would that theory also need to adhere to the equivalence principle? In other words, are they truly, deep-down equivalent? Like, wouldn't regular acceleration necessarily be different than the interactions of gravitons (if they existed)? Or is it just at the level of thought-experiment and description?

[gerryshacter]

You said the sun will bend the light's path. Would it be better to say that the light be will follow the curve of space caused by the sun's mass. When we say the sun did it, well it did, but that begs the question how. Not as confusing as continuing to talk about the sun 'coming up' in the morning? Your program is a gift. Helps clear out a lot of fog of subjects I'm so intrigued by.

[dgram]

I enjoyed chatting during the Patreon supporter stream on Saturday. Keep up the great work!

[RudivanderWalt]

I only upvote on videos where you either say "fastfast" or "it's ok to be a little crazy" 😊 great video as always, thank you!

[simi]

I noticed Nick's name among the winners in an old challenge from PBS Space Time.
Nick is smart! Smart, smart!

[bryandraughn]

I would like to understand how space is curved because of a nearby object.
Why does it curve?
Why doesn't it just move out of the way?
Does the object "pull" on the space surrounding it?
What's really confusing is that nobody ever explains this.
It's like everyone just says "Yeah, space curves because of the tensor" or whatever, but is there a mechanism?
How does ANYTHING affect space?
Space doesn't get hot or cold.
It doesn't move. It just sits there and when there's an object nearby, it "curves".
I seriously wish someone would clarify this thing.

[classifiedveteran]

So at 3:01 this only works if you just started accelerating. If you have been accelerating for a hour you'd be hitting a squirrel _(not the squirrel hitting you, remember you're the moving object)_ at approximately mach 102.857 or twice the speed of Voyager 1 probe. 🤯

The only way I could find out that I'm in a rocket I think is time. I just ran the numbers and you be aproaching lightspeed after 354 days of accelerating at 9.8 meters every second. _(Although this would probably feel much longer to me since I'd be undergoing the effects of time dialation.)_ But eventually the rocket couldn't accelerate more since the energy requirements would be infinity at that point. Then you'd become weightless.

I'm not sure how long it would take from the perspective of the passenger inside the rocket. But I'd have to guess it'd be a *long* time...

[jensphiliphohmann]

The equivalence principle is just the beginning of GR. Note that in a uniformly accelerating spaceship in free space, you experience a kind of*) perfectly uniform gravity because spacetime is still geometrically flat.
"Real" gravity caused by objects is a different situation because spacetime is curved there, leading to inhomogeneous gravity fields and tidal forces.

*) kind of because if you have 2 accelerating spaceships which are supposed to stay the same proper distance over time, the rear one must accelerate a bit stronger because their world lines are concentric RINDLER hyperbolas where "concentric" means that the intersection point of their asymptotes are the same. The closer the cusp of the hyperbola is to this point, the more it must be bent there which means stronger acceleration.