What Teachers Get Wrong About Equivalence
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- čas přidán 11. 05. 2024
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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
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Great video as always! But I'm concerned for that squirrel... How long had the rocket been accelerating before it collected the squirrel? Maybe the squirrel hit that floor at tens of thousands of kilometers per second!
Very good presentation sir but in the rocket model the light bending can be experienced by the observer in the rocket but not for the third observer which outside in space, when comes to the gravity light bending can be experienced by third observer
fast fast
Acceleration case - is it linear or circular acceleration? Circular acceleration is detectable through deflection of vertical beam of light. Linear acceleration goes eventually to speed close to c-speed, that is detectable too.
Squirrels falling to ground with the distance not changing between them doesn't prove that equivalence principle is not universal law because uniform gravity means gravity has same magnitude and direction at every point in space because acceleration is vector quantity therefore equivalence principle is universal law.
Today, I said "Fast, Fast!" at exactly the same time and cadence as you did. I'm gonna count this as a win.
I also count this as a win.
@@ScienceAsylum hi, want to see video about thermodynamics of Alqubierre drive 😊 if possible of course
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.
hmm, but dont objects close to event horizons appear to stop moving alltogether? Or is that just time stopping?
@havardsommerfeldt2437 They appear to stop moving from a distant outside perspective because they are travelling at a different angle through the dimension of time. From their perspective, they are still moving through time at a normal rate and it is you that has stopped moving.
@@AverageAlien im getting dizzy
@@havardsommerfeldt2437 Think of it like driving alongside someone else. You are both travelling at the same speed. Then, the driver beside you veers off away from you. They appear to fall behind you. But they have not changed their speed, only their direction of travel.
The same thing happens around massive objects. Spacetime is bent by the massive object. A black hole bends space and time so much that they swap places. As the person falls into the black hole, they're travelling at a different angle through time than you are. So they appear to move more slowly through time. From their perspective however, nothing is different. It is you that appears to be travelling more slowly through time.
@@havardsommerfeldt2437Things/ objects appearing to stop moving as they hit the event horizon is a purely us seeing it,, visual effect, not actual time slowing/ stopping for it.. The object would "feel" as if time is "normal" & is moving as normal, but the light coming off it ( that allows us to see it ) is being ”pulled” or falling back down at the speed of light due to the mondo gravity ( very simplified ), so the object appears to have stopped still..
Though in reality the object would just appear static & start to "redden" as it fades out of the visual spectrum due to "red shift" ( very simplified, again ) ..
😁☮️🌏
Another brilliant video from science, asylum, and Nick
Thanks for all the work and dedication you put into your videos
All the Nicks. Lol not including me tho cuz I don’t help. Wish I could tho! Love to learn
Agreed! This is such an important video. Thank you SO much for straightening this one out; the tidal effect 'anomaly' in the equivalence principle bothered me for years. I now understand how the strict wording stands....but it's still problematic; uniform gravitational fields at astronomical scales do not exist - gravity makes spherical objects which in turn create radial field lines. After about 6'25" the video gets all 'normative'.
So technically the gravitational acceleration is accelerating to compensate for diminishing acceleration over time?
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.
Hopefully now you can just share the video when you get into the next argument 👍
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!
i'm so used to your videos that when this one has no music i cant stop "looking" at it. kind of makes me realize how good the use of music is your videos
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...
The rocket can accelerate indefinitely with the same force(assuming infinite fuel).
Only to outside observers does it appear to have diminishing returns as they observe time in the rocket slow down.
So they would not see the rocket approach the speed of light in a year, rather they would see its acceleration slowly dwindle.
In more technical terms constant "proper" acceleration does not lead to constant "relative" acceleration.
@@narfwhals7843 🥴 I think insane asylum needs to explain this.
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.
what is with the nigerian caricatures. have some darn pride
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)
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.
That's exactly what happens to light when it bends towards Earth it's heading in a straight line but space is bent so the line isn't exactly straight from our perspective.
wrong, the massive object warps the space-time, gravity is the warping itself
I once saw a video that explained a lot of things about black holes by saying that gravity actually bends time so that "the future" points "down". That totally blew my mind but it makes perfect sense! You can't escape from a black hole not because it's sucking you in like a cosmic vacuum cleaner - rather, it bent all possible futures for you to point in its direction!
Great to see you pop up within my algorithm Nick.... Brilliant video as usual 👍
I wonder if you're on "The tiktok" Nick?.... 🤔
@@biblical-events I did TikTok for about a year (mid-2021 to mid-2022). I wasn't enjoying it though and it wasn't making any money either, so why continue?
I'm really psyched you brought up the example of how a really long ship wouldn't have the same gravitational expression as a planet. This is something been wondering about for awhile and how you could use it show if you were accelerating or in a gravitational field. I figured there would be some science-y mumbo jumbo to explain it away like how we can't measure the one-way speed of light (like if you were to synchronize the clocks but then move one there would be time dilation which would invalidate the experiment). There are also more pragmatic solutions like how no ship could keep accelerating forever because it would (probably pretty quickly) run out of fuel and gravity would "switch off" which would never happen to a planet. Good video!
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!
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?
Any model of quantum gravity would need to make every single prediction that general relativity does (plus at least one extra prediction to test it against general relativity).
I don't think that the "graviton" particle has ever been detected.
My belief is there is something like strings that repel matter and the more matter the stronger the repulsion and an isolated object floating in space has minor force applied equally all around maybe dark matter
Nick, I personally like to state a little phrase that is similar to being ok to be a little crazy. I don't suffer from insanity; I enjoy every minute of it.
That's a great saying. 10/10
Thank you for mentioning the experiments. Chears from Brazil
This is perfect, we're just now learning relativity in physics, thank you!
Excellent. I hope the video helped!
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.
I really missed this kind of videos from Science Asylum.
Nick I really wish you already had a million subscribers. Man I love your channel, all the way from South Africa!!
Thanks! I'm not sure my work is the kind that gets a million subs though. (which is fine by me)
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!
Nice vid Nick, I missed the experiment with the watter bottle with holes that stop leacking during fall time, it make sense of the postulate to begin with.
Crazy Nick has come back!
BTW, is expendable clone still flying through space?
Another great video Nick
Thanks! 🤓
Have you ever talked about the eclipse experiment ? I would love to see exactly what they compared to find the delta.
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.
I noticed Nick's name among the winners in an old challenge from PBS Space Time.
Nick is smart! Smart, smart!
Ah yes, that brings back some memories. Those were the Gabe days.
Talking FAST, FAST Days.
I live very close to Sobral, Brazil... amd there is a status for this experiment! Its a major stuff there! :D
Thx I understood this principle, like properly understood it for the first time
I enjoyed chatting during the Patreon supporter stream on Saturday. Keep up the great work!
It was good to have you! 🙂
"Without air resistance..." 😱😱😱Physicist said the quiet part aloud!😱😱😱😱
Great videos!! What about time dialation in both situations?
In both scenarios, you are within a room with no other point of reference. This means your frame of reference is always the room you are in, and you would not experience time dilation as there is no other frame to be relative to within the thought experiment.
If you're in a rocket that stands on the ground vertically, in gravitational field, then clocks at its tail are ticking slower than at the head, due to gravitational time dilation.
If you're in a rocket in space, accelerating at 1g, then from special relativity perspective you keep changing your frame of reference (because your speed changes), and you need to apply Lorentz transformation to keep track of relative coordinates around, this leads to an effect where if you're at rocket's head, an earlier moment in the history of rocket's tail is now simultaneous to you, and as you keep accelerating this rotation in 4D of plane of simultaneity makes it so that earlier moments of tail's history become "now" to you, which means for you it looks like clocks at the tail are ticking slower than at the head. And you should observe the same time rate difference as in case of gravitational time dilation!
If instead of constantly changing our frame of reference we want to describe astronaut's view as a single non-inertial frame of reference, we need to use the math of general relativity, and the result will look as if the rocket is inside a gravitational field.
Thank you for such a detailed reply. For a satellite in geosynchronous orbit around the Earth. Is the time dilation experienced caused by the gravity differential alone or is the centrifugal acceleration contributing to this effect? After all, the satellite is constantly accelerating. @@thedeemon
@@johnspathonis1078 A satellite is in free fall, its proper acceleration is zero, and it experiences two kinds of time dilation: from Earth's gravity and from motion. Relative to us there's less gravity so satellite's clocks go faster. Relative to us it's moving, so there's some clocks slow down due to motion. Two effects oppose each other. In case of geosynchronous orbit gravitational time dilation wins, so overall clocks on such satellite tick faster than ours.
long time no see, it's always a pleasure!
I always try to wrap my head around my hypothesis that gravity is an acceleration through time more so than space...but I haven't came up with a clear method to convey that yet.
I have an older video about that: czcams.com/video/F5PfjsPdBzg/video.html It's my most viewed video.
I disagree that "gravity is an acceleration through time", the reason being is that, if true, then everything would fall at the same rate, be it on the moon, on Earth or on Jupiter. This would also mean that matter warps time. It also implies Newton to be completely wrong (gravitational force is a 2-body problem) and energy is transferred towards the future, in perpetuity. Since Newton's formulas are the foundation of all relativity calculations, how could this be true? I don't see relativity being disproven any time soon.
Gravity is caused by time. Without time there is no gravity. A stationary apple above earth will not fall to earth if it isn't moving forward in time. Spacetime is bent into the earth by earths mass. The dimension of time means that spacetime will endlessly contract into the earth, dragging objects like an apple with it. Or rather, the earth will resist this contraction of spacetime, and will accelerate outwards at 9.81ms-^2, so that earth constantly expands into an ever contracting space.
@@AverageAlien That is a circular argument, for starters (correlation vs causation). Time doesn't exist as anything tangible, it's merely a function for the rate of change in a mathematical expression. It is merely a description for motion of anything. The Newtonian notion that an object in motion will remain in motion unless acted on by a force. Any object that is moving at a constant velocity would, as per what you are saying, will be frozen in time, if not accelerating (and shouldn't be moving at all). I challenge this notion and the other one that claims a temporal gradient (also circular logic) for objects approaching a gravitational well. A temporal gradient, if such a thing exists, would not make stuff "stick" together, but only spin/orbit. This requires an external force of attraction (and requires the counter centripetal force that is equal to keep it in orbit). With a simple thruster attached, as energy is lost to the field, you can maintain orbit indefinitely. Or, from your explanation, stop time. Like all the models of gravity being a warp in a "fabric", they still require an additional force to fall in, so to speak. This means you don't need warped space or "space-time" to describe gravity nor motion in general, just forces. You can just as easily explain a force gradient as you can a time gradient and still explain relativistic effects without any time function at all since it's merely an integral of distance at human-defined intervals. The idea of the passage of time is arbitrarily defined so we can make predictions of the next location of an object and uses units (also arbitrarily defined). Regarding rest frames and objects within them, they don't actually slow down when the frame is moving at or near c, they are simply moving as fast as they can against the impedance of space - which means that even atomic motion will effectively slow down and stop. It's a differential, not time slowing down and stopping. Einstein was basically correct, but the interpretations of relativity, especially later, and what it means, is completely off. Time travel, wormholes, expansion, etc, are the problem since the invention of "space-time", which, in and of itself, is merely a coordinate system in the mathematical realm to describe the Universe. There is no "space-time" and the speed of light is only a limit for transverse electromagnetic waves and limited, not by time, but by a counter part to EM (an impedance). Now you don't need exotic descriptions of quantum entanglement or other apparent instantaneous effects (which, as per current explanations, require time reversal, and is a bit of a stretch). The tethering of time with light speed is the greatest mistake of the 20th century.
@@davestorm6718 There is no force of attraction. General relativity perfectly explains orbits and everything else. There is no such thing as a gravitational field. Doesn't exist. Time is a dimension, like the spatial dimensions. It is a real and tangible thing.
There is no impedence through space for light either. Light travels at the speed it does because everything travels at that same constant speed. The only difference is massive objects share that speed through time and space. General relativity provides a much more complete explanation of reality than newtonian gravity.
I would say if you could measure length contraction (some sort of interferometer or very sensitive wavelength measurement), as apparently if gravity is strong enough things are stretched (falling into a black hole).
Edit: oops, not a uniform field if the stretching is happening. Maybe relative wavelength measurement could be used for some other measurement though? Like how 'flexible' space-time is?
Assuming current technology levels, can one even accelerate uniformly, though.
There's always some kind of inconsistency, that might not register on the testing equipment, depending on what it's trying to measure, but will still be noticable to the observer.
Things like turbulence from an atmosphere or the fluctuations of thrust from the physical processes involved in generating said propulsion.
The thing is, standing on the surface of a planet, you're not feeling gravity... You're feeling the planet pushing up on you, constantly accelerating you away from the path your body wants to take -- a _straight line through spacetime._ But since spacetime curves, that straight path appears to bend toward the planet as you progress forward in time. If the ground suddenly disappears from underneath you -- perhaps a trap door opened, or you stepped out of an aircraft to go skydiving -- then you go into a weightless freefall, and experience that curved-looking straight line. Jump straight up, and you briefly divert that path away from the planet, "falling" upward, until the curvature brings you to a halt relative to the surface and then sends you back toward it.
Bingo. Someone finally gets it. The earth expands outwards at 9.81ms^-2. The reason we don't see planets growing larger is because they are expanding into a contracting space.
@@AverageAlienThat does not make much sense to me and seems like an absurd conclusion. I understand how thinking of gravity as acceleration seems to match up but then there is the problem of how a planet accelerating outwards in all directions just goes against common understanding of things. "You don't notice it because [insert hypothetical here]" it just seems like an insufficient explanation. "Contracting space" may as well be fairies.
@@elio7610 No, that's the reality of what the model of relativity shows. Its not that difficult to understand. Earth has to grow outwards otherwise it would collapse in on itself. Not that hard to grasp. This is simply a basic fact. Gravity is quite literally the contraction of space into a massive objects. If earth didn't grow outwards, it would contract with the space into itself. The pressure exerted by the atoms that make the earth up resist this contraction.
@@AverageAlien Does not seem so obvious to me. "otherwise earth would collapse in on itself" that is exactly what gravity is doing, though, everything is being crushed into a point, it just hasn't gone all the way into being a black hole.
@@elio7610 what's your point?
Les go another science asylum upload
* I opened the CZcams app,
* One of my favourite channels had released a video about gravity.
* I clicked the video before the thumbnail even loaded😂
As expected, the video didn't disappoint.
Thank You Very Much!
It's not equivalence implying the inability to tell the difference.
It is the inability to tell the difference is what makes things equivalent.
In an constant accelerating box the force you experience is constant from all points in the box. If you are in a gravity well, the forces are less above you and more below and on an exponential curve. And centripetal force would also be less above than below but would be linear. I always wonder why no one points this out. And I mean no one, I had to figure this out myself.
This is pointed out in this very video. At around 4:37
You would notice differences between gravity and rotation if you were in a rotating cylindrical spaceship about 50' in diameter (like the one in _2001: A Space Odyssey_ ). For instance, when throwing a ball toward the centre you might be surprised by where it lands -- it would seem to accelerate oddly. You could even float in the centre if you could find a way to get there.
On a rotating ring the size of those in the _Halo_ games these differences wouldn't be noticeable unless you had a spaceship.
_"I always wonder why no one points this out"_ - maybe because it is only partly correct. Even in a constant accelerating box, the acceleration higher up in the box (and hence your weight) is less than the acceleration lower in the box. The gradient is different from a normal gravitational field, though. And indeed, the video is not fully correct about this.
@@renedekker9806 Do you have some kind of mathematical justification for this idea or does it just seem correct to you? Because if the room is rigid, or at least in a steady state, the entire room accelerates at the same rate, and measuring from any part of the room is equivalent to measuring from any other part, i.e. acceleration would have no gradient within the room. And if the room is not rigid and not in a steady state, it wouldn't be the uniformly accelerating room as required for the equivalence principle.
We can always count on science asylum to build a rocket and accellerate it to 9.8m/s squared just to troll a expendable clone
Real nice like always... but where is the classical background musics?
I've brought the volume down so much over the last year or so that most people could barely hear it, so I stopped using it a few videos ago. Apparently, my content doesn't need it anymore.
Thank you! I've been annoyed by so many CZcams videos getting this wrong.
6:03 Is the bending of light the same in the rocket and on earth? Does time dilation play a role here?
Why I am asking: The measured bending of light in a gravitational field is twice as much as when calculating it with free fall. The difference is due to gravitational time dilation (something I have not understood yet).
On a small scale like the inside of a rocket, the bending of the light would look the same.
I can think of five ways that the gravity on Earth is detectably nonuniform, and therefore can be used to determine if an expendable clone has been moved to a location with 1G that isn't sufficiently Earthlike.
1. It is not a uniform sphere. Gravity is higher over the denser parts. Although from within a sealed room, it would only be possible to measure a tiny part of the geoid.
2. It is (approximately) a sphere of a finite radius. The radius can be measured a few ways from within a hypothetical sealed room. An occupant can measure the strength of gravity at two different heights and use those two readings along with the difference in elevation to calculate the radius. That requires a lot of math. Method two is to measure which direction is down at two points and use the distance between them and some geometry or trig and calculate the distance to the center.
3. Measure the length of a day with a foucault pendulum.
4. Measure the length of a day by looking for the daily cycle in the strength of gravity. Gravity is stronger at night when the Sun's gravity adds to Earth's.
5. Measure the length of a month by looking for the lunar cycle in gravity strength.
It’s the gravity anomaly, not the geoid.
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.
Einstein's general relativity doesn't answer this at all, unfortunately. Only says "how much", "how strongly" but not "how the hell" it does. Some modern physicists hope to find the answer in properties of quantum entanglement and structure of quantum mechanics itself.
Haven't watched it yet, but I'm fairly certain that gravitation and constant acceleration are only equivalent in "UNIFORM GRAVITATION FIELDS."
The existence of tidal acceleration and inhomogeneous gravitational fields can't be explained in _Special_ relativity and flat spacetime.
The gravitational tidal forces in _Newtonian_ gravity are the result of spacetime curvature in _General_ relativity.
I don't think I have ever seen a squirrel fall on earth. They are particularly good at not falling. So if did see a squirrel falling from the sky, I would assume something is out of the ordinary.
I was driving along a few years ago and noticed a squirrel running along a telephone line ahead of me. I thought to myself that I've never seen a squirrel fall and just at that moment it fell.
A plumb bob will hang at a slightly different angle from one side of the room than the other if you are on a round body whereas in an accelerating rocket, there is no “down” for the plumb bob to point towards, so the plumb bob will point perpendicular to the floor at any point in the “room”. Same principle as when the circumference of the earth was calculated by measuring shadow angles.
Another great video! Well explained.
Thanks!
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.
The top down movement of the squirrel in the rocket even though motionless from the squirrels frame of reference would appear to have been moving from the observer inside the room in the rocket.
Thank you for talking about Brazil. Every time I see people mentioning this experiment they never remember to bring up my country. 😊
You're welcome! I try to be thorough.
My pet theory about why the equivalence principle is true is all about time, and what time IS. In our universe according to the laws of thermodynamics, any gradient has the capacity to do work. If you think about the paths of the virtual photons within atoms communicating the EM force in an accelerating reference frame, then you realize that under constant acceleration, light travelling in the same direction of the rockets motion will always need to “catch up” to the matter moving ahead of it, as that matter itself travels through the EM field ahead of the light, moving forward. We understand that mass warps spacetime, causing a gradient in the flow of time, which blurs the line between the cause and effect of gravity itself. Well to me, what I think that time gradient IS, in both a gravitational field and an accelerating reference frame, is a backlog on the transmission speed of quantum information. Causality literally has to slow down to “process” everything communicating to everything else where it is in space and when. But it’s a decentralized process, in situ. With gravity, it happens because matter is literally filling space, adding greater and greater “loads” to the network of quantized fields, whereas with acceleration, energy is compounding a fixed load at a greater and greater pace within a localized reference frame. The effect is the same from two different causes, but one is linear (acceleration) while the other follows the inverse square law, which gives us the slight discrepancies in the equivalence principle itself… There is no graviton with this explanation. Motion warps the flow of information, or information itself warps the flow of motion. Gravity effectively emerges from the relationships between matter in an already quantized universe.
Brilliant , thanks Nick 🙂 is there not also a further breakdown of the literal equivalence in that it is duration limited ? After 8.5 hrs at this constant acceleration C would be approached and the experiment becomes physically impossible ? If you wait 8.5 hours it would prove you were on earth or equivalent ?
I suspect relativistic time dilation might get in the way. Good question though.
I have exactly this question since childhood but no CZcamsr answered my question to date, thank you
C? If you mean c aka speed of light then you need about a year.
@@XtreeM_FaiL true, but still - what happens when we approach c?
@@christiankiss1736 Then you need to ditch Newton's laws and start using Einstein's special relativity or was it the general relativity. Idk, maybe both.
Finaly a channel that uses mks at least as secondary, when i see a video only expresing units in imperial y close the video and dislike, imperial units are very stupid. You earned my respect.
I often hear that not only is being in an accelerated frame indistinguishable from a uniform gravitational field, but they are the same thing. The thing I have trouble visualizing is how the surface of the earth could be accelerating. As a sphere, this could only happen if the earth were expanding at an accelerated rate, which, it doesn't seem to be. I think maybe the idea is that due to the curvature of spacetime, the surface is accelerating outward which is preventing the collapse of the earth into a singularity, but I have trouble visualizing that, and I'm not sure it's correct. I'd love to see a video examining this idea more thoroughly
I think he pointed it out. When you go up in a building you get further from the earth and thus get lighter. This would mean we are not experiencing gravity due to acceleration. Instead you are experiencing gravity due to mass from the Earth. You get lighter because you aren't near as much mass.
*"The thing I have trouble visualizing is how the surface of the earth could be accelerating."*
I'm hoping to go into this more deeply in a future video.
Thank you for this video.
You're welcome!
Hmm.. Good point. There are no uniform gravitational fields in nature. (Are there?) The squirrel will always fall a teeny, tiny bit faster in the rocket than on Earth. Since on Earth it will always fall from a location where the gravitational field is a teeny, tiny bit less than at ground level.
Which description best describes the scenareo, and which scenareo does it attempt to describe?
A. "The accelleration of a surface pushing you trough a stationary space."
B. "The accelleration of space pushing you against a stationary surface."
They're both _technically_ accurate, but they're both misleading to someone who hasn't worked with relativity before.
Technically accurate, the best kind of accurate.
I had a lightbulb moment when he said "Gravity is acceleration we just can't see". I think unravelling gravity/quantum gravity is going to be crazy difficult to work out, kind of like the actual mechanism of light "slowing down" in a transparent medium (glass or water for example). I wish I could thumbs-up this video multiple times :)
Gravitaty is the acceleration caused by the bending of of spacetime and that some objects doesn't move in straight line through the spacetime. An stone on the surface of the earth move in a curve throw the spacetime and this causes the acceleration we call gravity. If the stone is in a free fall, it moves in a straight line and there is no acceleration and no gravity.
Hello. I do not like this principle very much, not because I think it is wrong but because a lot of people misunderstand how limited it actually is. It is a neat comparison, a though experiment to make people think and nothing more. And yet people push the "equivalent" far further saying "it is the same" which it is not in many ways.
Still, I think your video was very clear and to the point. I hope more people will now understand what Einstein was talking about. Thx. Nick.
Exactly what happened to me, I was shot down and told I didn't understand the equiveillance principle.
Ok tell us about those many ways
If there was a way it wasn't the same then surely you could test that?
In the real world I'm not sure you ever get a uniform gravitational field so there may be real world differences between gravity and acceleration but that isn't what the principal is talking about
In this episode , no clone wasn't harmed.
Since inertial mass and gravitational charge cancel out when using Newton's Law of gravity to calculate the acceleration of a particle (all objects fall at the same rate), massless particles of light should bend in a gravitational field in Newtonian gravity as well. However, the amount light bends is different than in Einsteinian Gravity, I think mainly due to the fact that in the Newtonian case the particles of light can speed up and slow down, while in the Einsteinian case light always moves at the same speed.
Any object on the surface of the earth is moving due east at around 1000 miles per hour and also curving downward at the same time because it's path is circular . There is a angular momentum aspect to this movement that applies a force upwards due to centrifugal force trying to fling off anything that might be on the surface of a spinning ball . Any object on the surface of the earth has one force acting on it downward and at the same time another force acting on it in the opposite direction . Gravity's real strength must be hard to figure because you would have to subtract the upward force from the downward force .
I nitpick for a living. 1. The acceleration of that rocket cannot persist logically. Eventually the air around you receives so much radiation that it glows in visible light. If you somehow prevent that you're still gonna see stars move. If you close yourself off from the outside view then you still reach relativistic speeds and your mass weighs more the faster you go.
2. The hypothetical engine/drive forced into existence by the simulacrum/thought-experiment has two possible routes: the warp bubble where it relinquishes internal gravity making it a non-viable engine for the thought-experiment, or it picks combustion/photonic drive. This last route is equal in its inability to achieve constant acceleration of notable quantities.
So, there's a relation between gravity and time as well! The clock on top is just a teeny tiny fraction faster then the one on the bottom. Time dilation AND gravity dilation! Cool!
Is gravity = time… ?
@MePeterNicholls, the connection is there. It's subtle, intense, and I want to one day understand it.
@@MePeterNichollsbending of Spacetime
There is sn excellent video here on this very channel that explains that the reason why you are pulled down by gravity is because in the gravitational field of a massive object, time ticks more slowly at your feet than at your head.
So yeah, since gravity is nothing more then the bending of spaceTIME there is a very close relationship between time and gravity.
Or if you follow Erik Verlinde's reasoning entropy is what creates time, entanglement creates entropy and spacetime emerges from entanglement and entropy.
I once saw a video about black holes that explains it by saying that gravity doesn't suck you in or even bend space - rather, it bends time itself so that the future points ever so slightly down! Or straight down if you're inside a black hole...
Woah, nice new animation budget! =D
Thanks! 😄 To be honest, it was rather expensive. I can't afford it on the regular (even though I'd like to).
Wish you had explained the solar eclipse image in detail and how that confirmed the prediction of general relativity.
Amazing explanation of the equivalence principle!!! I can't help but wonder what the acceleration into the centre of a mass is caused from though. Are we falling into a dimension we can't observe or is something coming out at us we can't oberserve?
They say that falling towards the center of a mass is due to objects moving along paths in spacetime curved by that mass, not a force acting through space or an interaction with unseen dimensions.
It is pretty strange. As if the gravitational field is about changing the properties of space-time in such a way that being stationary means moving towards the centre of mass from the perspective of outside observer. The very nature of space-time changes so that the future leads any object to the centre of mass, it is mostly bending time, not space. In our case on the surface of the Earth the Earth is moving towards us preventing us from being stationaty, exactly like the rocket moves the clone, just not in a single direction but in all directions from the centre.
P.S. You cannot even feel the gravitational pull itself, it is not like any other acceleration: you can be accelerated at any rate without trouble of G force aside from the situation when different parts of your body experience different gravitational acceleration like near small black holes. So, it is a fictional force. It can be viewed as if the space is the water and it is moving towards the hole and we are moving with the water, so it is more like space moving than us moving. However it is not a proper analogy, space is not really moving, it is time that bends from time axis to space axis, moving through time becomes partially moving through space and time slows down as a result.
@@dmitriy4708 why do you think "gravitational pull is not like any other acceleration" ?
This exception has no basis in reality, gravitational pull is exactly like any other acceleration.
G forces are "caused" by reaction forces not by acceleration itself.
@@YounesLayachiacceleration is something that affects the object like some force, so it can deform the object by this force. Gravity is not a force, it does not affect the object, it affects the space-time in a way that the natural behavior of objects is to move to the centre from outsider's perspective. So, it is different. G force appears only when something prevents gravitational pull's effects, not caused by the force itself.
Like you can be accelerated by gravity without any G force, however it is not possible by any other force aside from electro-magnetism in case you are charged.
@@dmitriy9053 acceleration is not a force, nor is it "something that affects the object like some force".
You'd need to be way more specific in your wording, but acceleration is not an action
The movie "Einstein et Eddington" (2008) starring David Tennant (as Eddington) and Andy Serkis (as Einstein) talks about one of those solar eclipse experiences. I recommend watching it.
2:51 : well spoken.
Apparently, acceleration in a rocket makes your clone get a pretty dark tan in the process.
If I understand this hypothetical, assuming the rocket never runs out of fuel, and other hypotheticals, but as it approached the speed of light, it could not maintain the acceleration indefinitely... so the experience would eventually end and then you'd know that the you were in the rocket, that's how you'd know... what am I missing here? The fact that gravity causes things to accelerate and that you can simulate gravity through acceleration gives us no more insight or understanding about what gravity is, other than this is it's property. As pointed out by the weight decreasing at different heights. I find this fascinating to listen to and think about... Great Video as always!
In theoretical physics, mathematics is the leader. We can map out an accelerated rocket somewhere on the Rindler coordinate, where variables like fuel are unrelated because we focus on the underlying physics in that state. As the rocket runs out of fuel, it will decelerate, but we can add more fuel to maintain the same situation. The choice from an engineering perspective is to keep the rocket in the same state. However, it's not a solid conclusion to distinguish, as we don't need fuel in the math, just like always assuming no air resistance.
Edit : You can accelerate in a rocket in such a way that you float on the surface of the Earth. So, if something is falling from a high building, it will look like that because your rocket is accelerating forward to pass the object. As your rocket runs out of fuel, it will fall at the same rate as the object, and the object will appear to be moving at a constant velocity relative to the rocket.
In the space shuttle and the squirrel you're representing the space shuttle as having a constant speed and not accelerating therefore the ark to the floor was not understandable for a little bit of time
The Equivalence principle is defined, more precisely, locally, for an infinitesimal region around a "test particle", or around a point of an extended object..
So the "tidal forces" that objectively differentiate the "real" gravitational field ( with non zero curvature) from acceleration/ "homogeneous gravitational field" for extended regions, affect finite sized objects/ regions, not test particles / mathematical points.
By this definition, the Equivalence principle is universal for all events ( singularities are not considered parts of the Manifold in General Relativity).
Thank you for finally addressing one of my pet peeves in science explanations... the equivalence principle requires a uniform gravitational field to make sense... For you next mission, please explain where in the universe a uniform gravitational fields exists, or could exist...
We don't need physical uniform gravitational fields to apply the equivalence principle to thought experiments. We can define "local" infinitesimally and extrapolate to real physical effects.
The equivalence principle does not preclude tidal effects.
It's funny, because I seem to recall reading how Einstein found this principle to apply to much more than just acceleration and gravity. When he was trying to find a suitable geometry to describe spacetime. Euclidian wouldn't cut it. It's planar, not curvy. This led him to apply the principle of equivalence to both planar geometry and non-Euclidean and how each can approximate the same measurements. After all, we use Euclidean to great extent, on a spheroid. We also use raycasting, straight lines, to approximate curvature to great degree. Scale matters.
Newton's of force comes in to play, "weight" as we use it is just an easy reference for people to understand for when on earth
Light at solar system scales, even galactic scales are hardly noticeable when a gravitational field bends them. But at universal scales, very noticeable. The slight bend of light from a galaxy tens of billions of light years passing by another galaxy bend is very noticeable when it travels those distances and reach us. Is why we can get light from the same galaxy in different spots of the sky from gravitational lensing.
The only problem I have with that imagery is, gravity is more appropriately like deceleration. It's the matter that causes time dilation, aka, deceleration of time space.
Instead of saying gravity is like an accelerating ship, you should say it's like a decelerating ship because that is what matter is causing time space to slow. It's like the force that pushes you forward against your seatbelt in a car when you slam the brakes.
A good analogy would be , a human falling to the earth would be like rear-ending a sports car traveling 100 mph into the back of a loaded semi traveling only 10mph in the same direction.
0:16 "Hey, Vsauce! Michael here!"
Hi Nick! I have always wondered, is there a definitive answer to the question of the origin of inertia? And will we ever get that answer?
I don't have a physics background, but I always think of inertia as a lack of action. So when you're moving with a car, but the car stops, there's a lack of action on you that stops you. You are independent of the car but have the same velocity giving the illusion of togetherness, but when you act on the car to stop it, the action isn't applied to you causing you to continue moving (until friction/collision stops you that is).
Your feet are in a more intense gravity than your head.
Small difference, but it's there.
Near black holes, matter gets torn apart because the part nearer the black hole is pulled millions of times more strongly than the farther part.
Read "neutron star" by Larry niven.
I've always wondered this, if the curvature of space equals acceleration, do I eventually get a parabola out of those pesky space/time curvy equations if I rearrange the terms enough?
Never thought about trying. But Einsteins field equations give you giant matrices that stretch and pull lines of spacetime to create the curves. I'm sure there's some way to pull some parabolic curves out in there somewhere 😅
Video idea!! Use the formulas for Gravitational force to find the mass of Earth, then compare it to the density of Earth to prove that the Earth isn't flat!
What would happen if you jump?
Assuming there is a constant force accelerating the rocket: Wouldn't the force acting in the opposite direction slow down the rocket's acceleration (and increase it once you leave the ground)? Could this lead to a different acceleration profile of the jump in comparison to gravity?
Or would the force causing the acceleration need to be variable?
I'm having trouble wrapping my head around this.
We are specifying that the _acceleration_ is constant, not the force. The force would need to compensate for slight mass variations, as we are also ignoring what happens to the earth when you jump.
But constant acceleration requires constant energy and increases the energy of the mass as it approaches the speed of light. So does the energy difference between objects in a uniform gravitational field reflect the length of time they have been in the gravitational field? Does light going through a gravitational field get red shifted as the light "falls"?
Kinetic energy is relative. Inside the rocket its energy does not increase. And we are saying that you can't tell from inside the rocket.
Neither does a person standing still in a gravitational field notice a change in their own energy.
Light gets _blue_ shifted as it falls in a gravitational field as it gains energy by falling. Meaning an observer on the ground will see it have more energy than the observer on the plain that emitted it. It gained energy relative to them.
Similarly light gets red shifted as it moves "up" in a gravitational field.
And both these effects can be observed in the rocket as it accelerates towards or away from the light.
假設光被物體的重力場彎曲每光秒偏折一公尺，反光鏡直徑1公分正圓，鏡外設置光感應器，光束自反光鏡中心偏移到鏡外，有0.5公分，則光源至少必須有照射c * (5/1000)距離的功率。功率越高，光束發散越小，則可測得越細微的光線偏折。
愛因斯坦星光經過太陽偏折計算式
(4GM/Rc^2)*(180/π)*3600=1.760638516172007弧秒
每光秒偏折距離tanθ*c=2558.973380039165932公尺。
把太陽的數據換成地球則
=0.000574137836393弧秒，每光秒偏折距離tanθ*c=0.834471939140272公尺。
從而光線經過重力場是否會偏折？可在地球做實驗驗證。
Isnt the equivalence principle how Albert calibrated "G". The word gravity refers to the "free-fall" part. I.e, in free-fall you are accelerating inertially. If you accelerte in a rocket it's non-intertial. If you are standing on Earth, you are also accelerating non-inertially.
Your simple and entertaining explanation has changed my understanding of gravity forever. Thanks, Nick!
I have a feeling you could tell the difference, as the earth pulls in all directions, while in space, if you had only acceleration pulling upon you, it would be unidirectional.
I could be mistaken, but I feel this is how it works for some odd reason, and the gravity would not affect side to side movements the same as on earth, as its gravity would be far less uniform due to the sheer scale.
That's mostly correct. It's *not* in conflict with either the _Equivalence_ _Principle_ or any topics covered in this video.
The quality of you videos is craaazy (hehe)
...I find myself out
Why do we consider our relative speed to light in orthogonal direction directly but in the same direction we have to use Lorentz transformation?
5:15 iv been trying to do this expiriment on my desk with a ball and it appears that the Squirrels would be further apart from each other?
I have never understood, why would taking measurements during a solar eclipse prove that Light is affected by gravity?
What was the actual experiment analyzing?
Is it measuring the effect of the moon’s gravity on the light? If so, why would this need to happen during an eclipse? Or
Is it measuring star position and how it differs between day and night? ( bedside we normally can’t see their position during the day? )
Or something else?
Sun's gravity affects path of light from a distant star. To notice it you need to see the star when it's visibly very close to the sun. It's hard to do when sun is shining, but easier when it's occluded.
Lightspeed is 299.792.458 meter per second, meaning your rocked accelerating at 1G should reach that in 346.98 days. Shortly before you hit lightspeed, the energy requirement to continue to accelerate will reach infinity, hence your rocket will no longer accelerate at 1G. Instead you will creep closer to lightspeed in smaller and smaller increment reflecting the max engine output of your rocket. in any case, no more 1G acceleration. Then you will know you are in a rocket. Should you have a magical infinite energy rocket which can hit actual lightspeed, you will be frozen in time from your perspective. One day maybe the expansion of the universe will be fast enough to tear you to shreds in an instant, because ain't nobody got time to hit the breaks on such a vessel.
That decreased acceleration is what an outside observer will see. Not what the astronaut will feel, thanks to time dilation. The astronaut can still feel 1G of "gravity".
reminds me of project hail mary, where the main character uses his knowledge of physics and the flaws of the equivalence principle in the real world to determine why gravity feels weird in the room he wakes up in.
*YES!!* That was my first thought as well. I'm super stoked to see what Lord & Miller do with adapting the book to the big screen.