That was a tough one! The quiz for this video is here: quizwithit.com/start_thequiz/1702972458163x675901602454850000

@smlanka4u

4 ай бұрын

Gravity is a force, and space doesn't bend due to gravity. The density of space increases near massive object due to the gravitational force. The existence of Dark Matter shows that space is material. General relativity is not a quantum theory, and it doesn't explain the high gravitational force that make Black Holes during the supernova explosion. Neutrinos can be the cause of gravity because stars emit neutrinos from their 99% of energy of the supernova explosion, making pressure to make a small Black Hole.

@javahaxxor

4 ай бұрын

​@@smlanka4uinteresting statements care to explain that to us chimps?

@_John_P

4 ай бұрын

You left out tidal forces, which break the premise in the video's title.

@emifro

4 ай бұрын

Quizwithit asks for registration to see the correct answers :/

@davidmaxwaterman

4 ай бұрын

You should have given the correct answers 😜

I tried to tell my wife this the other day... she just pretended to care and nodded her head in approval. The life of a physicist :-/

@user-hk8yp7cw1v

4 ай бұрын

I tell this to both family and friends and they tend to do the same so don't feel alone 😅

@nicklacelle

4 ай бұрын

That's just the life of a husband.

@dtibor5903

4 ай бұрын

Well, don't try to explain this to regular people. For regular people and for practical purposes gravity is a force.

@TransdermalCelebrate

4 ай бұрын

Very Funny, I’d wished to of been there 😄👍

@josir1994

4 ай бұрын

She cared enough to pretend to care, that's a good start

"9.8 m/s/s as you were probably taught in kindergarten" Maybe in Germany but I grew up in Canada and was still figuring out that plasticene wasn't a food group. I think you're right though: never too young to learn that thing that holds you down is not holding you down.

@MrKotBonifacy

4 ай бұрын

"PLASTICINE", perhaps...? ;-)

@hooked4215

4 ай бұрын

Say pleistocene better@@MrKotBonifacy

@milanstevic8424

4 ай бұрын

@@MrKotBonifacy no he likely means Plasticene, as an informal "geological" epoch nomenclature, as the last part of the current age called Holocene, which is further subdivided to Anthropocene, an epoch in which all humans tend to be terminally guilty for existing. Needless to say these are all unofficial addendums, and are mostly there for rhetorical and socioeconomical purposes, of which Canada is a prime consumer.

@AlexAnteroLammikko

4 ай бұрын

@@milanstevic8424 Wonderful, but definitely wrong. OP obviously meant Plasticine because thats putty and thats what children tend to eat, and its not a food group. So your Chat GPT/wikipedia blurb doesn't add much to that.

@c.augustin

4 ай бұрын

Well, it was a joke. As Sabine likes to do. I can assure you that we don't have physics in Kindergarten here in Germany.

you comparison between newtons law and how we applied it up to now and general relativity point of view is amazing. First time I understand this difference and I have seen many videos on that...

@peterturner6497

24 күн бұрын

Yeah she certainly proved beyond doubt that Einstein was indeed a fraud and his "theory" is a worthless hunk of junk didn't she? Garbage is garbage no matter whey you try to spin it.

As a layperson in physics, I consider myself to be fairly educated. But this was a wild ride. I went from "Wait, what?!" to "That can't be right but Sabine wouldn't tell us something incorrect." to "Oh, now I get it!" to "I'm just slightly confused but I get it but I'm not trying to explain it to my friends." Thank you Sabine for expanding our understanding and knowledge with every video! 🎉

@dmariehatch8825

10 күн бұрын

By C300

@BlackistedGod

19 сағат бұрын

Veritasium has a video on the same topic years ago, I think he did a pretty good explanation

@rayRay-pw6gz

49 минут бұрын

As a Star Trek fan , this is very disturbing. How can we travel without gravity, our bodies were designed to work with gravity. I can not accept the ability to create artificial gravity. ✌️

Perhaps Sabine didn't want to introduce reference frames, and there are good reasons for that, but for some people it might help to think about this by talking about different types of reference frames. The whole thing can be summarized by saying that the usual reference frame, where the floor is not moving, is not inertial. The force of gravity is then a 'pseudo-force', an illusion that appears because we chose a non-inertial reference frame, similar to the centrifugal force or the Coriolis effect in a rotating reference frame. In general relativity, inertial reference frames follow geodesics of space-time, which implies that the origin must be in free fall.

@Earthstein

4 ай бұрын

So much of a construct; right?

@Matthew-by2xx

4 ай бұрын

@@kleinerprinz99 Statements that start with “It’s vert simple,” and then simply miss the nuances are always fun.

@NewNecro

4 ай бұрын

This so much. I think it'd have been much more helpful to better explain the spacetime model with geodesics, worldline and gravity's role within it rather than vaguely affirm what gravity is not. For most layman Newtonian gravity is the standard which makes special and general relativity particularly unintuitive. The fundamental differences between inertial and non-inertial reference frames are very important distinctions to explain Fictitious Forces you mentioned.

@ObjectsInMotion

4 ай бұрын

There’s no reason to not consider pseudo-forces to be as “real” as a “real” force. “Real” forces are mediated by virtual particles, which are themselves not “real”, so why do those forces get special consideration? They shouldn’t. A pseudo-vector is just as “real” as a normal vector. This entire video is just pedantry.

@gramail2009

4 ай бұрын

I have a vague sense you might be able to explain this better than Sabine does. It makes no sense to me yet. Maybe it is just a matter of language. Seems to work quite well for me (and most of the world's scientists too!|) to think in terms of the 'force of gravity 'pulling me onto this chair! Will I really benefit by pretending there is no such force??! Or calling it something else. First I guess I will have to find out what people mean by an inertial frame of reference as opposed to any other kind...

The fact that you use several examples makes room for different brain wirings to link in. At each step in this video, I felt a little closer to getting this right. It was extremely satisfying and educative. Well done and thank you!

@chrisstevens-xq2vb

4 ай бұрын

Pffft this is beyond stupid. If gravity wasn’t a force it wouldn’t do anything.

@andrewjoliver82

4 ай бұрын

​@@chrisstevens-xq2vb just because you're incapable of understanding does not make a complex set of ideas stupid. The stupid is you 🤷

@bartsanders1553

4 ай бұрын

​@@chrisstevens-xq2vbIt's just another lie from big globe. Stay strong, brother.

@CSpottsGaming

4 ай бұрын

​@@chrisstevens-xq2vbIf you don't understand, you can say that instead of being rude.

@thenonsequitur

4 ай бұрын

@@chrisstevens-xq2vb Gravity isn't "doing anything". Gravity is the natural fall of mass toward other mass due to the curvature of space-time. It's a description of the structure of space-time, not "doing something".

Okay but the gag at 3:47 had absolutely perfect delivery

wow! your explanation is the clearest I heard so far and I checked a lot of videos on you tube. thank you!

Every time she says "Gravity is not a Force!" I feel like she got me. Its like a punchline that doesnt grownold and messes you up no matter how often you hear it, just because most of our lives weve been learning something different that we adapted into our Framework of reality

@andrew3203

2 ай бұрын

Not something different, simply wrong. If you teach wrong things in school, you shouldn't be surprised when people say those things.

@biopsiesbeanieboos55

2 ай бұрын

I agree. It’s like an unripe plum. No matter which direction you approach it from, it doesn’t become any more palatable.

@robert-wr9xt

Ай бұрын

Thankfully the phone didn’t ring.

@Slitter_the_Dubstep

29 күн бұрын

@@robert-wr9xt huh :D

@robert-wr9xt

29 күн бұрын

@@Slitter_the_Dubstep New to the channel? Sometimes she has a red phone on a desk. It rings and she answers it. Charlie Brown adult voice talks on other end. She makes comments and hangs up. You’ll laugh. Have a nice week.

I usually can at least grasp the content of your videos. But... I gotta say, this had my head spinning. I eventually got it, but it was difficult. Thanks for the mental gymnastics!

Love the lesson with the quizwithit! added level of fun~

The problem that people have with this is that they have a hard time accepting that there is positive net acceleration when there is no apparent movement. We're trained to think that if an object appears to be at rest, then all of the forces are balanced and there is no net acceleration. The key is to understand what Sabine is trying to explain is that gravity interacts in 4D SPACETIME, not just 3D space. In 3D space, gravity appears to be a force pulling massive objects together, but in the 4D spacetime equations the objects are simply at "rest" (no acceleration). In the 4D General Relativity equations, gravity never accelerates any object--they will always move at a constant "4D velocity" until they interact with an outside force. A rock that appears to be at rest on the 3D surface of the earth is actually accelerating in 4D spacetime. 🤯

@onedaya_martian1238

9 күн бұрын

You lost me at " In the 4D General Relativity equations, gravity never accelerates any object--they will always move at a constant "4D velocity" ..... until they interact with an outside force." How do objects interact with an "outside force" ? The ball rolling around on a rubber sheet, "captured" by a mass sitting on the sheet is NOT interacting with an outside force but it is changing its relative velocity and is therefore being accelerated. Or is that the wrong way to understand this ?

@jeremypearson9019

9 күн бұрын

@@onedaya_martian1238 A ball rolling on a rubber sheet is touching the rubber sheet. The atoms in the rubber and the atoms in the ball are repelling each other by the electromagnetic force. The ball travels in a circle because the sheet is pushing it that way. If the sheet (and the air) weren't there, then General Relativity would say that the ball would travel in a non-accelerating trajectory through spacetime, which is curved by the strong gravitational influence of the nearby Earth. To our perception, the ball would seem to accelerate because it increases its speed with respect to the dimension of altitude. But, in General Relativity, it's not accelerating when you analyze it in the spacetime equations. Space and spacetime are not the same thing. I had a hard time with this concept when I was younger. People would usually describe relativistic gravity by explaining that an object in orbit travels on a "straight line in curved spacetime". That kind of made sense to me, but what about if a metal ball were to fall straight down, starting at rest, from 1000 kilometers above the earth? That doesn't seem like a "constant spacetime curve". The ball starts at rest, then is accelerated to hundreds or even thousands of km/hour before it hits the atmosphere. Well, I had a breakthrough in understanding when I studied the General Relativity equations and realized that their definition of "non-accelerating" is in 4 dimensions. An object can accelerate in 3 spatial dimensions but be non-accelerating in the 4D spacetime equations. I get a little irritated when people use the rubber sheet analogy to explain Relativity. The only way to really understand it is in the 4D equations. Gravity doesn't curve space, it curves spacetime, which is a mathematical concept.

@jeremypearson9019

7 күн бұрын

@@onedaya_martian1238 The rubber ball contacts the rubber sheet. The atoms in the rubber and the atoms in the ball repel each other with the electromagnetic force. The point I was trying to make is that General Relativity uses 4 dimensional math. People say that gravity "curves" space like a rubber sheet. It's much more than that. Gravity curves *spacetime* (there's a difference between spacetime and space). If gravity only curved 3D space, not 4D spacetime, then I think that it could explain how moving objects could orbit the planet, but I don't think that it would explain why stationary objects fall straight down. The fact that they are 4D equations enables gravity to actively morph 3D space over time. The altitude dimension of 3D space around a planet is constantly shrinking. According to General Relativity, a ball dropped from a tower doesn't fall because of gravitational "acceleration", it falls because the space underneath them is actively contracting. That morphing of space isn't considered to be acceleration. In spacetime coordinates, the object isn't moving. Once the ball contacts the ground, it does accelerate due to the contact force. After bouncing for a while, the ball settles on the ground. Gravity is contracting the space under the ball, but the earth is accelerating the ball upward. To us, the ball seems like it is at rest, but it's actually under constant upward acceleration that counteracts the shrinkage of the altitude dimension.

@kylebelle246

7 күн бұрын

​@@jeremypearson9019Interesting. It kind of reminds me of a flat earth theory which states that gravity is just the earth moving/accelerating upwards at 9.8m/s/s. But what i wanted to actually ask was about the seemingly perceived acceleration of free fall, or rather in this case according to your explanation, the increase of rate contraction over time. Like it's possible I'm missing something really simple which explains it but i dont really see why it should be the case that we "accelerate" in free fall

@jeremypearson9019

6 күн бұрын

The flat earthers seem to have borrowed the acceleration/gravitation equivalence to make their ideas seem more scientific. But Relativity actually matches with observation and is mathematically sound and the flat earth theory fails miserably. Your comment got me thinking: imagine you had two balls. You drop one of them from the top of the Tower of Pisa, then, when that ball reaches the middle of the tower, you drop the second one alongside it. The first ball will have a much higher velocity because it has already had time to accelerate, so it will speed past the second ball and strike the ground first. However, the two balls travel along the same path at the same time--straight down. If their motion is explained solely by the curvature of spacetime and not by acceleration due to gravity, then how could they move differently while occupying nearly the same space? Well, the short answer is that 1. the math is very complicated and 2. I don't actually have a sound enough understanding of this particular case to give a satisfactory explanation. It just goes to show that when we talk about Relativity in layman's terms, the analogies that we use don't adequately explain straight, vertical falling. It's been a long time since I studied it. The bottom line is that the 4D math is complicated and the analogies we use (like the ball rolling on the rubber sheet) don't really do it justice.

Absolutely fascinating as always - most accessible explanation I've ever heard!

@schweinehundbullshit9176

4 ай бұрын

As Absolutely fascinating as absolutely meaningless.

On the question of whether you're "accelerating" while in free fall vs. resting on the Earth's surface- Too many people say "space" is curved by gravity. That's wrong. If it were just space being curved it wouldn't take any more energy to move away from a gravitational field than to move into it - any more so than it requires more energy to move north on the earth than to move south. Nor would there be gravitational time dilation. Spacetime is what's curved by gravity in the GR model. The time part of that is what makes the model work. It therefore doesn't make sense to directly compare GR's four dimensional "spacetime" model of motion with Newtonian mechanics' 3D model where time is absolute and acceleration is *defined* as the second derivative of distance with respect to absolute time. In GR, the Newtonian definition of acceleration doesn't even make sense because the absolute magnitude of any object's 4D velocity vector is a constant (spoiler alert - it's always c); only the direction can change, which is of course not a constraint of 3D velocity vectors in classical mechanics. So any statement that you "are" or "are not" accelerating in GR has to be heavily qualified as to whether you're talking about a 4D velocity vector or a 3D classical velocity. When you are being acted upon by no non-gravitational influences, it is true that your 4D velocity vector doesn't change as you follow a 4D geodesic - because that vector is *defined* relative to a 4D geodesic! If it makes you happy, you can say you are not "accelerating in 4 dimensions." When you are being acted upon by a non-gravitational influence, on the other hand, your 4D velocity components DO change relative to a geodesic, for as long as that influence is acting on you. If it makes you happy, you can say that you are "accelerating in 4 dimensions". When you're standing on Earth's surface, the electromagnetic repulsion from the surface is pushing you away from the 4D geodesic you would otherwise be following, and therefore, if it makes you happy, you can likewise say you are "accelerating in 4 dimensions". But if you drop the "in 4 dimensions" part, then you're mixing apples and oranges - taking a statement that's true for a particular model and applying it to concepts from the prior model, which have no applicability in the new model, as if they prove the prior model wrong. The ugly truth is that all models are wrong, especially when it comes to spacetime. Some just make better predictions than others. No one has any clue what space or time even are. And the fact that GR doesn't work at the quantum level, and vice versa, ought to make us even more humble about making sweeping claims such as "gravity is not a force." The most common sin physicists commit in my opinion is confusing models for reality. This video, I think, is such an example.

@OldZoZo

10 күн бұрын

"The most common sin physicists commit in my opinion is confusing models for reality." is probably the truest statement to be said about modern science.

Thanks for teaching us the Spring Theory! 🙂

@mejseln

20 сағат бұрын

😄

One of my favorite explanations of gravity is a quote from John Wheeler, which interestingly, doesn't include the word "gravity" at all: "Space-time tells matter how to move; matter tells space-time how to curve."

@Nocholas

4 ай бұрын

yes, but maybe not.

@samibraheem1579

4 ай бұрын

I think this ia why we haven't and will not see a subatomic particle for gravity since it's a force like nuclear and electromagnetic

@juliavixen176

4 ай бұрын

The thing about General Relativity, is that this _is_ all that it says about gravity. It exactly describes how gravity works... but not _why_ Why does mass and energy curve space? Yeah, it just does, and we can calculate exactly how much and stuff... but what's the actual mechanism? Why should geodesic worldlines converge towards the largest pile of confined energy, and curve away from a vacuum. What is the mass (or vacuum) actually *doing* ? General Relativity just says that the spatial distance between two points shrinks as the time distance increases... that's it, that's all it says. It's not very satisfying. It really is just pure geometry.

@magicmulder

4 ай бұрын

Nobody puts gravity in a corner! 😂

@patinho5589

4 ай бұрын

So the matter matters. It makes a curvature within which lifeforms like us do our stuff. This mean planets matter.

Fantastic video! Please do a video covering Mark Kasevich's experiment demonstrating the Aharonov Bohm effect for gravity. I don't know why this is never mentioned in physics when it seems to be one of the greatest findings in decades. Your take would help naive science hobbyists like me who don't know if this finding is significant or why nobody covers it.

@ChaoticNeutralMatt

4 ай бұрын

Effect.. for gravity? I'm not familiar with that effect in that context.

this is my favorite thing to teach about relativity because you can get people to really think about what gravity feels like, which is nothing. i always start with the question, "can you actually FEEL gravity?" basically same as sabine's accelerometer example

@rosewood1

10 күн бұрын

That's a false analysis. No you cannot feel gravity. But that doesn't mean it's not there. You don't feel air around you when it's still. If your submerged in the sea you don't feel the sea around you. But in fact as you decend to deeper depths your body is compressed. Equally on the moon where gravity is much this has an effect.

Oh I love knowing new things I listen to you a lot and your smarts makes me wish that when I was younger I could have learned from you. Thank You fo promoting understanding in science!

Thanks for the awesome video about the matter (or the space-time curvature in this case). As much as we study it, having a graphical and very well done explanations is good to cement the ideas, and this one was a blast to watch.

@undercoveragent9889

4 ай бұрын

If 'mass' does not exert a force on spacetime then why should spacetime experience any warping?

Thanks for drilling in the phrase "because gravity is not a force", it really does beg for repetition haha. I love this topic. I originally came across it while watching a simulation of the universe expanding, through the perspective of what our solar system looks like as its moving away from the center of the galaxy. Coincidentally, the planets' orbits in tandem with the whole system moving across space time simultaneously follow the shape of a 4D spring. Thought that was a fun little fractal coincidence when you used a spring as a measuring unit for acceleration.

@silvercloud1641

10 сағат бұрын

It's more like water then? A calm still ocean until something acts on it, then it can become something that has an effect on other things like a wave?

I absolutely love your videos. I am interacting in the comments section specifically so that it gets pushed out to more people.

Thanks you so much for this Sabine. One of your earlier videos about this topic, which had a simple "gravity is not a force" and the raw explanation has been used by flat earthers as evidence of their position. This fully qualifies what you meant, and removes one more "justification" they can pull out of the bag

This seems profound. Still wrapping my head around it. Great way to launch the New Year. Heartfelt thanks Sabine, brilliant food for thought as always :)

@davidmudry5622

4 ай бұрын

NIST FAQ 31 - "the top of the WTC north tower came down essentially in free fall" - "as the floors fell more and more weight fell on each floor below" - in free fall? www.nist.gov/world-trade-center-investigation/study-faqs/wtc-towers-investigation

@ivoryas1696

4 ай бұрын

klauswassermann8054 It is, and back in 1915 it was a _such_ a big deal for a reason. 🧠

@davidmudry5622

4 ай бұрын

Things on earth fall only when Nothing Is Pushing Them Up... As we speak, do you feel a force on top of your head and shoulders, or do you feel a force under your feet and butt? The only way you can fall is when the force you can feel...underneath you...is removed. When sitting in a car that is accelerating forward you will feel a force of being pushed on your back, not on your chest. You will always feel the pushing force of acceleration on the opposite side of your body to the direction of the force causing the acceleration. When a force pushes on your body your body pushes back on the force, what you feel is a resistance to being pushed. In free fall there is no pushing back, you feel no forces on your body, therefore there is no force in free fall. Einstein would call the acceleration one sees in free fall apparent acceleration. Velocity is the speed that is relative to your surroundings, whereas acceleration is not relative to your surroundings. Acceleration is absolute. F = ma...and real acceleration gives mass weight, where weight is the mass resisting the acceleration.

@RobertStCyr-zh1tw

4 ай бұрын

Is gravity a force? Now my answer will depend on why you want to know. Lol.

@davidmudry5622

4 ай бұрын

@@RobertStCyr-zh1tw Gravity is not a force unless it's the year is 2001, especially September, and especially in NYC.

Nice video Sabine! It's so interesting that completely different views can describe facts from different perspectives. I like the beauty of the underlying mathematics and its symmetries. A paradox glimpse what space and time really are. Some facts always connecting and some doesn't fit together. So sad we will never completely understand a fractal universe.

@-danR

4 ай бұрын

Here's another perspective. I turn a teeter-totter on its side and apply pressure on one end and someone is resisting on the other end. Am I applying a force? Does the resisting party experience a force? The commonplace language of levers would say "yes". They are forces and can demonstrate acceleration, if the resistance is removed. Put the teeter-totter in its proper configuration and put a fat kid half way down and a little kid on the other end. And hold up the fat kid's end. Is the fat kid causing a force against my hands? No. Because of the Sabine youtube video effect: I'm accelerating the fat kid. I get tired of the Sabine effect and let go of the fat kid's end. Does the light kid accelerate upward? No he doesn't. Because there are no forces involved here; gravity is not a force You sit and scratch your head and say, but wait a minute... . But I've gone from the park to watch a Veritassium video: "Energy doesn't flow in wires", or something equally confusing.

I missed 2 out of 12. I LOVE the quiz after the “lecture” because I often wonder how much I retained and this is a good way to gauge that. Thanks Sabine. Only one suggestion: We don’t know which ones we got wrong, or am I missing something?

Das war der erste Beitrag, den ich von Ihnen gehört habe. Ich bin auf unterschiedlichsten Ebenen beeindruckt. Danke für das Video.

This is brilliantly explained! Very lucid; however, for a layman like me this is mind shattering!! I can appreciate that you have done your best to make it clear but I am just so confused now!! I will have to rework my ideas in my head and find some answers!! Thanks!! I can't believe the ease of access to the privilege of these things being explained by a physicist of your caliber!! Love you, and love KZread!! ❤

@Markielee72

4 ай бұрын

I feel the same. I am beyond grateful to people like Sabine, who attempt to convey complex physics to the layperson. But videos like this just remind me how little I know. 🤯

@VolodymyrLisivka

4 ай бұрын

I like how gravitational force is used to demonstrate that gravitational force is not a force because of geomethry of nothing. It's like 1 apple and 1 bannana: 1 = 1.

@BooksRebound

4 ай бұрын

Just wait until you realize that the reason things fall is because your head is moving throught time slightly (like 0.00001 nanoseconds or something ridiculously small) faster than your feet, which basically takes your flat horizontal floating line and starts curving it downward (falling) to the ground. Time passes at different speeds depending on the curvature of space time, so that's further away from the planet move through time slightly faster.

@antonystringfellow5152

4 ай бұрын

I find it helps to think of space and time as part of the same thing... spacetime. After all, that's how causality works (faster through space = slower through time and vice versa). When you take time into account, everything travels at the same speed, the speed of causality (cause and effect). From there, understand that time passes slower nearer a massive object, such as the Earth. Therefore, in order to maintain the same speed through spacetime, your path must be in the direction of the slower time... towards the object (or down). An object in orbit is not travelling a curve, it is travelling a straight path through spacetime. The difficulty comes from starting off with simple analogies that are very different from the reality. At the heart of space, time, speed and the gravitational effect is one single thing; causality. It is constant everywhere and for eveything.

@ChristopherCurtis

4 ай бұрын

I'm not a physicist and I've seen too many videos to recommend one, but a moment that "clicked" for me was the realization that if you see someone throw a basketball and watch it curve up and back down into a net, you are not observing gravity, but are watching the ball travel in a straight line through a curvature in time (mostly in time; space itself is "flat"). For more related videos/channels, check out PBS Spacetime, especially "Does time cause gravity". Sabine has another video titled "You move through time at the speed of light". Science Asylum has "The REAL source of Gravity may surprise you". And then, to confuse everything, Fermilab has "Is gravity a force?". Have fun!

It would be helpful to explain why charge interactions are driven by a force and the differences with gravity.

@drgetwrekt869

4 ай бұрын

Maxwell equations are linear, and thats why they can be represented as a field of vector """particles""" (photons) that interacts with electrons and so on. Gravity apparently doesn't fit in this formalism because it is inherently non-linear and defines the same coordinates that are used for the calculations. Edit: actually even "non-linear" fields can be quantized without issues, for example Higgs or phi^4 terms. But as far as I know that's it ? Not sure tho

@josefpharma4714

4 ай бұрын

@@drgetwrekt869 I'd say linearity (none-linearity) should not make any difference. But AFAIK: If gravitation is not a force, electro magnetic interactions are no force, too. (But this is a kind of definition only?)

@dannydetonator

4 ай бұрын

@josefpharma57.. Difference is in the origins: electro/magnetic forces have quantised matter-energy as a direct cause for forces exerted. Gravity is causing forces, but itself it's just a constant of spacetime bending per general relativity. The latter have no particles or known fields carrying or causing the forces created. It's like acceleration without an engine doing the work, while still carrying the accumulated potential energy.

@PrivateSi

4 ай бұрын

Spacetime is not a technically not a force, but gravity could be, and the cause/bits of space time could/SHOULD exert a force. Unless you believe space is empty or some nonsense like that..

@Dom-Nom-Nom

4 ай бұрын

⁠​⁠@@dannydetonatorbut if EM forces require work, like an engine, why don't I quickly run out of energy from all the EM acceleration from sitting on top of the Earth?

My daughter and I like to share interesting facts with each other every day. I will send her the link to this video because I never knew that I was accelerating upward. 🤓 Thanks, Sabine! New subscriber.

In the video, the question about a = dv/dt is quickly discarded "because it's another referential", which doesn't help if you don't know about general relativity. The spatial position of a free-falling object doesn't change in freefall because it's not simply dv/dt = a in space. There's an additional term cancelling out the acceleration upward, which comes from spacetime distortion. That's what explains that Earth's surface is accelerating upward without Earth expanding. The geodesic equation shows that d²z/dt²=a - Γ (dz/dt)². If a, which is F/m, equals the gamma term, the position remains constant: the ground pushes the object upward but spacetime distortion compensates it. Anyway, it's only one theory, so saying gravity's not a force is only true in that theory. Don't try to give it any meaning.

@kylelochlann5053

Ай бұрын

Gravity is not a force by direct measurement, and has nothing necessarily to do with relativity.

Wonderful Channel, Incredible Host, Makes learning fun again. Thank you Sabine for a wonderful channel. Wishing you and yours a wonderful Holiday Season.

Great indeed. Now the famous "Black square" by K. Malevich could be surely considered as illustration of the scientific equivalence principle in Fine Arts. The part about pressure from inside the Earth is my favorite.😂.

This was so much clearer to me than Veritasium's attempt on the same subject which left me confused and with a reduced will to live.

Wonderfully spoken and difficult to comprehend. Merry Christmas Sabina and everyone else!

This concept is one that I still can't get my head around. As always, love your stuff, Sabine.

@vibaj16

4 ай бұрын

Everything moves in a straight line when under no force. Since gravity is not a force, the Earth is under no force. So why does it orbit the Sun? That's not a straight line, right? Actually, it is. The sun's mass warps spacetime's geometry such that a straight line gets bent around the sun. Geometry itself is warped.

@rockovahsacralonte570

4 ай бұрын

I can't get my head around 1+1=3, mainly because it's not true!

@fewwiggle

4 ай бұрын

@@vibaj16 OK, but why does the floor push on me?

@D1N02

4 ай бұрын

Think of it as deceleration instead of acceleration and the quarter will fall (decelerate :p)

@D1N02

4 ай бұрын

@@fewwiggleit doesn't you push on it because you want to free fall the the center of the earth, but the floor is in your way. Your atoms do not want to be in the same spot as the floor atoms, so you are stuck in the cosmic water slide because a fat kid called "the floor" is blocking it.

But Sabine isn't acceleration also defined as rate of change of velocity (I know that velocity is relative to something)? Can one separate acceleration from force? If you're in a black box and it accelerates then you can't tell the difference between gravity & acceleration? Which means that gravity is equivalent to a force?

This is a great video as you see gravitational force everywhere in science media all the time. I think people just have a hard time wrapping there head around the fact that normal space is not curved but space near earth is and how that would actually look like. The marble on rubber is a good visual aid for 2d space but then trying to translate that into 3d space can give people trouble. Another interesting thing is when you think about when spacecraft use a planet's gravity well for slingshot maneuvers. Where does the energy come from if gravity is not a force that can give the spacecraft more energy then when it started with? I know the answer to that one but curious if others here do :)

Another highly inspired video. Thank you for teaching us how to think scientifically :) peace and love

As a programmer making a hard sci fi game and not a physicist, it's a little scary trying to advance a theory of gravity without knowing what I'm talking about. A character in the game says that if you only perceived in 2D but approached a 3D hill, you would experience it's effects as a mysterious pull (or push as the case may be). I was especially concerned that I was only moving the goal posts on this one. Nice to see I might not be so far off. Thanks for the great explanation!

@juliavixen176

4 ай бұрын

Well in the case of a two (space-like) dimensional manifold with intrinsic curvature... or extrinsic curvature as a hill in a three dimensional embedding space (with no time-like coordinate) What happens to two 2D creatures walking in straight parallel lines a constant distance apart from each other, when they encounter the hill, is that even as they continue to walk straight, the distance between them will change. The 2D creatures might interpret this as a mysterious force that is moving them either closer or further away from each other... but there is no force... they are not actually accelerating... they are still on straight line inertial paths and feel no force... but the distance between them is changing because the space between them is curved. This is General Relativity... it's just like this except in a 4D Spacetime (so the time interval between events can also stretch and shrink, and it will look like things are mysteriously changing velocity without accelerating, but it's actually just spacetime curving).

@dougdupont6134

4 ай бұрын

@@juliavixen176 Yeah, I'm a programmer and writer of fiction trained academically as a philosopher, so I want to write stories and craft games with a meaningful and accurate portrayal of science on characters that are digestible to regular people. My limited understanding of physics can be frustrating in that endeavor, especially since I know enough to know that I don't know anything (as Plato would say). It seems like what you wrote essentially confirms that my example might be a meaningful and accurate portrayal. I appreciate you taking the time to explain it better than I can. I hope you don't mind that I might borrow some of it.

@MrGemaxos

4 ай бұрын

@@dougdupont6134 Dont be frustrated, if you go down the rabbithole its like a Hydra. Every answer makes a few new questions and in the end you are rarely understanding, but you are still just realizing that there is more and more that you dont understand. (youd still be in platos place) In my Opinion its a good thing, it leaves more room for the fiction :3 if not, wouldnt it be just science? I have read so many good books with physic that dont work out. But without the "wrong" physics you couldnt tell the story. Jules Verne for example. With correct physics as Dogma most of his storys dont work out and you would have a very hard time to find a possibility to tell a similar story.

@eVill420

4 ай бұрын

That's really cool! So it can be imagined as falling into a Whirlpool and streching like spaghetti

@voltydequa845

22 күн бұрын

@@juliavixen176 I liked you other comment (though I do not remember what it was about). you say «when they encounter the hill, is that even as they continue to walk straight,» It is a hill for you, looking from outside, from a superior dimension, their "walk straight" from from 3d pov is not "walk straight" from their 2d pov. Their "walk straight" would put them to walk with constant distance between them, but could present some other "irregularities", like the impossibility to maintain the same distance while walking at the same speed. I usually use the example of 2d to try to show that there's no way 2d's can imagine seeing them from a 3d, or that they should be that conformist to buy into an abstruse 3d model if they already have some another explanation that is simpler. The main point being "Man is a measure of all things". What "exists" is the representation of the "reality". While the abstruse and overcomplicated curvature of the "reality" should be left to parrots.

Dr Rohin Francis demonstrates a very good point here - it would be extremely difficult to administer CPR to a patient in zero-G. Best not to take any risks whilst you're in zero-G, like doing flips or somersaults...oh, dear...

The equivalence principle only applies locally, its actually possible to see the difference between a person standing in a gravitational field and a person standing in a box with a rocket because when you look at the 2nd derivative and compare the fact that the person in a gravitational field will experience differing ("non-uniform") accelerations at their feet vs. their head while a person standing in a box with a rocket accelerating will experience uniform acceleration, you can see that the gravitational field can be distinguished. So while the two are close, they actually are very different and cannot be said to be physically the same. One could be treated as essentially a uniform field, while the other is non uniform when you compare it at different regions of spacetime.

This was great, Sabine. Another thing that would be interesting to address would be, why does curved space time cause objects to move?

@soyosunset

4 ай бұрын

Same problem. The bowling ball on the trampoline illustration is used to explain the reality behind our naive notions of how gravity works. But the illustration makes sense to this naive person only because it implicitly shows a world with an up and a down and a bowling ball that goes down, just like our naive ideas about gravity say it should. This seems circular and evasive. I am very willing to accept that there is no way of explaining physics to ordinary naive people such as me. You can't teach even Aristotelian physics to dogs or goldfish -- why should we imagine that all people can understand Einstein? If something can't be explained, that's the end of it -- a pretense of explanation accomplishes nothing.

@Gingnose

4 ай бұрын

Because mass also causes the time of curvature not only space curvature. Every object in this universe is moving with 'a speed of light' as GR says and that makes the object move towards mass as if there's a force but this is just a visual illusion. Since we can only visualize 3D space, we cannot recognize the axis of time dimension. But it is still there although we can't see. The Earth causes the time curvature and time moves slowly as you get closer to the Earth. Since we're all moving in the time dimension with a 'speed of light', the delay of time which is closer to the Earth side causes you to move towards Earth. Space curvature works likewise but it is only relevant when the two objects have the motion vector that is different from the axis between the two objects (if two objects aren't just free falling to each other but moving to other direction as well).

@ValeriePallaoro

4 ай бұрын

it doesn't. I think is the answer. f=ma is the math to explain the movement, gravity is the explanation for how they move.

@douginorlando6260

4 ай бұрын

Maybe the only thing moving is space, not the object …🤯

@calinculianu

4 ай бұрын

Something something rotates you with respect to time but not space or something. The Science Asylum guy did a good video on this.

Great video Sabine! Two comments. First, I’m with you on the whole gravity is not a force. BUT, then there are really only 3 fundamental “forces” (interactions if that is the preferred term), and then there is no need to quantize gravity, because gravity is not a force. This would explain also why it has been so hard to do. Second comment, it would be very good to get your take on the time causes gravity (or visa versa) discussion in many KZread videos. There have been counter videos on this as well, which is why I think you weighing in would be a great arbiter. Thanks!

@S.L.S-407

4 ай бұрын

@hu5116-Sabine already did a video on does time cause gravity.

@dhruvvikrant

4 ай бұрын

Does time cause gravity? Need a video on this pls!😅

@hu5116

4 ай бұрын

@@S.L.S-407ok thanks! I guess missed that one so need to track it down.

@michele3900

11 күн бұрын

Floatheadphysics channel has a video to help visualise this rather neatly, he uses paper cutouts to show how it's the bending of time that causes gravity

brilliant. thank yo Sabine. They say that satellites are always "falling toward the earth" but are "moving too fast to hit the earth". I'm gonna rewatch this and try to map out a more correct and precise explanation.

I have ordered your book ... Lost in Math.... Looking forward to read it . I'm so happy to discover you.

Here is my favorite analogy which helped me understand the concept: Imagine you and your friend are standing at the equator, and start walking towards north, parallel to each other. But as you walk, you notice that you start to get closer to each other, and would collide by the time you reach north pole. Some mysterious “force” is pulling you together. You have to physically accelerate to keep your paths parallel. Is it a force pulling you together? Of course not. The Earth’s surface is curved.

@Markielee72

4 ай бұрын

I like that. 👌🏻

@audience2

4 ай бұрын

​@@harmless6813Lines that intersect are not parallel by definition.

@acebulletman7389

4 ай бұрын

It seems that latitude lines are parallel, but longitude lines are not since they intersect.

@TBJ1118

4 ай бұрын

Nah it's the force of love 'cause we gay for each other

@ak74udieby

4 ай бұрын

@@acebulletman7389a latitude doesnt have a "line" besides the equator

1:00 These graphs only show that all three sensors are not calibrated to '0' (have offsets typical of electronics). Sorry, this is not theoretical physics, it's engineering.

@declanwk1

Ай бұрын

if you allowed the accelerometer sensors to freely fall, then they would read zero during the free fall, so they are calibrated.

Very interresting, could u explain about the recherch on the graviton?

Fantastic explanation!

Thank you for making such great videos about Important and debated Topics!

Finally, I was always wondering the acceleration i felt on this earth, without things moving. Thanks.

@Sabine I wish you would have used geodesics as part of your explanation to show how the object existing across converging spacetime geodesics must flow in the direction that the parallel lines get closer together

Such a nice explanation of a complicated (well not anymore) concept. I remember seeing Veritasium's video on this topic but I remember I understood much less.

Thank you so much for finally making this clear to me! I've spent years trying to understand why the upward acceleration of the Earth did not allow me to spring into the air and fly!

Fabulous explanation, you´re an extraordinary teacher. Peace and love for you.

@SabineHossenfelder

4 ай бұрын

Thanks! Wish you happy holidays 🎄🎅

@keithscott1957

4 ай бұрын

Yes, Sabine is quite a … um … force.

@Thomas-gk42

4 ай бұрын

@@keithscott1957😉

@VolodymyrLisivka

4 ай бұрын

She make me a lot of laugh this time..

@danielstan2301

4 ай бұрын

Although a nice explanation I feel it is incomplete. For example it doesn't explain why gravity still accelerates mass while is not a force, what happens with the body once the whole earth suddenly disappears(will it continue moving towards where it was the center of the mass, stay still or will it go towards the direction where it was pushed by the force of the surface and why is that) and a few more questions that really makes gravity seem to behave like a force. On another note, can we consider gravity as a "force" that pushed against spacetime fabric causing its curvature? 😊

Thank you Sabine for bringing science into youtube so we can try to become smarter.

Great video as always. I thought the definition of force was anything that can cause acceleration (which is ultimately also acceleration but atomic scale). By this definition anything that causes you to accelerate is a force and so is gravity. I am now wondering so how force is actually defined.

This is the most useful 15 minutes I have spent on KZread. Thanks, Sabine.

Wonderful analogy and presentation. As a fan of physics I may please ask whether the illustrated example of falling into a blackhole without noticing anything, may apply specifically to smaller objects and maybe in context of bigger blackholes in order to limit the tidal effects, as spacetime curvature may vary between adjacent points. Thanks. 🙏

Hello, greetings from a layman here who admires you and your videos, thank you for your work!

Great video! I have one question. In the example of the person jumping from the top of a building, around 12:00, why does the person suffer an impact, a larger acceleration or something, if it wasnt accelerating in the first place. In general, how can free falls cause collisions with consequences if the bodies did not gain velocity or energy (if energy or velocity even matter in this context) ?

@user-np7ic2dh3n

3 ай бұрын

And I would have thought his speed relative to the building would change ie he would be experiencing accelerations ... ?!?

Sabine…one of a kind. Another great tutorial.

General Relativity was such a breakthrough, it's quite amazing after all these years

@pholdway5801

4 ай бұрын

General Relativity is much more fun than Corporal Punishment

@kabongpope

4 ай бұрын

@@pholdway5801 both can lead to Major Issues!

@petergroves3153

3 ай бұрын

@@pholdway5801 Chacun à son goût.

@silvergreylion

Ай бұрын

None of the theories of relativity define an absolute rest frame. WIthout that, how do you apply the light speed limit to any inertial frame?

Merry Christmas Sabine! 🎄🎅🌌🌟

@SabineHossenfelder

4 ай бұрын

Merry Christmas to you too!

Fascinating, thank you.

It seems like a semantics argument. As a human observer, we usually experience a "force" transmitted through the electromagnetic force, which keeps up from passing through other objects, as you point out. Hopefully physics will come up with a better description of gravity, but it appears to me that the "force" of gravity is caused by entities with mass tend to want to go towards each other such that "time" (another nebulous concept not fully explained by physics) passes at a slower rate compared to space further away from other entities with mass. The ultimate goal of any mass is to move towards the event horizon of a black hole, where time appears to stop in this universe. The Cavendish experiment does measure something that appears to be a force.

I think I undestood pretty much everything Sabine said in this video, but I still don't get the most important part: The space is curved because of mass, but why would you follow the path of that curvature (towards the center of Earth) instead of remaining on the spot you are? Why follow that direction of the curve specifically? Is it because you have to assume a pre-existing movement of the object relative to (towards) the other bodies (eg. the Earth)?

@streettrialsandstuff

4 ай бұрын

It's not the space alone that is curved, but the space-time. As time passes, you are moved in space in a direction of a nearby object with a large mass.

@lorscarbonferrite6964

4 ай бұрын

It's because that apparently curved path is actually a straight line (or sort of one, the search term you want to look up is a geodesic) in 4d space. Imagine a 2d being walking around on a 3d curved object, like a sphere. If they plot their coordinates in a 2d grid and move around, they'll notice some really weird things about their movements. For instance, if they were to try to walk in an equiangular triangle by moving in a straight line for a fixed distance then turning 60 degrees (both measured according to their 2d grid) 3 times in a row, they won't end up where they started, as on a curved surface the angles of a triangle don't add up to 180. But to the being that only knows 2d space, there will appear to be something weird deflecting their path. Similarly, assume two of these beings standing at the equator of a sphere. They move in opposite directions along the equator at the same speed, and then, at the same time, both turn 90 degrees towards the north and starting moving north at the same speed. In flat 2d space, their lines are parallel, so they should never meet, and yet they both meet at the north pole. To them, it looks like something is dragging them towards the north pole.

Sabine forced me to have an interaction with something or another relative to something else. The gravity of her excellent discourse about the myth of the force of gravity has left me wanting a half gallon of chocolate ice cream and another look at the video! And she’s one of the few reasons the internet and KZread are worthwhile. ❤

@undercoveragent9889

4 ай бұрын

A word salad is not the same as an explanation. And Sabine is very good at producing word salads that explain nothing.

@tcl5853

4 ай бұрын

@@Benevezzioficial Relax! Did you read the entire post, the last sentence?

I think a good follow up video would be an explanation of gravitation tidal effects and black hole 'spaghettification' in terms of space time paths.

Thanks for this. I think I finally get it.

I concentrated very hard and still have so many questions. It seems more like a semantic trap than an actual Physics problem.

@vix86

4 ай бұрын

Glad I'm not the only one that feels that way. It also feels like this whole video would fall apart when discussed in the sphere of quantum mechanics.

@garymarkowitz5059

4 ай бұрын

"Don't ask what is holding down the ball in the middle of the trampoline. It's too confusing."

@garymarkowitz5059

4 ай бұрын

Irene is great but this is ridiculous dogma period it's a mathematical analogy. Her tortured attempts to avoid using the words push or pull. Gravity is a pushing force. Force. See LeSage theory of gravity and think about how that relates to dark matter

@voltydequa845

22 күн бұрын

It is not a semantic trap, it is just "instilling cognitive confusion". All this mess doesn't have to do with basic logic, let's not talk about Physics. It is implicit that Physics is about representing and understanding our world / reality. A thoughtful person cannot be but relativistic. But being relativistic such a person discards the Relativity Model because he/she would apply the Occam's Razor - choosing the simplest from the possible models (of "reality"). Between "when down to earth we are in reality accelerating" and "we are down to earth due to a gravitational force", we choose the second one since it is the simpler representation of (whatever could be) reality. Reality is what/how we perceive it, and we perceive it in a way that is easier to think about and infer laws and rules. Try to ask her to explain the acceleration and curving of space when it comes to tide moving due to the influence of the moon. Even if she / they succeed in giving an inevitable abstruse relativity curving-space explanation, they will implicitly give a proof that their relativistic model is counterproductive because excessively abstruse. The curvature of space is utter nonsense. Curved compared to what? Anyway you cannot perceive the eventual curvature. Immagine beings living in two dimensions. For them it is flat. They can live on a curved bidimensional surface seen from a 3d, but for them that curvature cannot be pertinent in any way. The same holds for the so called "curvature of spacetime" - it can eventually be seen from extraterrestrials that live in superior dimensions, but for us it is just a sophistry nonsense.

This is one of those shows about things I already know, but after watching I understand more than before. Thanks again, Sabine (and hidden team!).

great talk! One of the pitfalls is to think all the time relative to our earth. Just imagine being "in space", far from a reference object like earth. It would be hard to measure your velocity. Velocity relative to what? Earth? But earth itself is running fast around the sun. And our solar system is in orbit through the Milky Way, etc. This way I am starting to get the picture of relativity

thank you very much. Because I had an excellent professor, I received 12/12 on that quiz🙂

Very informational, I'll need to watch this one a couple of times for it to sink in and I've had undergraduate level Physics, although I was not that good at it.

@briancrowther3272

4 ай бұрын

Me too. I ended up teaching it at high school pre uni level when earth science is my natural go to ( a geology, physics, physical geography comboned hons degree). All high schools find it hard to get physics teachers. I eneded up doing it for 35 years and got better and better at it. It is a great topic am still learning, both the earth science and physics (a politics BA as well).

I watched the Veritasium episode on gravity is not a force and it was really good. This one is even better. I love this channel.

@governmentis-watching3303

4 ай бұрын

Yes, but Sabine said Acceleration is Absolut, but I dispute it is vodka.

I've had a lot of exposure to Einstein's work but this particular one violates my physical experience and teachings. At 73 I've had a lot of experience with being in touch with mother earth and this view requires a significant adjustment to ones thinking. Thanks for this interesting lesson.

My kinematic picture gets confused. Isn't acceleration the second derivative of the position coordinates w.r.t. time anymore?

@random_Person347

2 ай бұрын

Yes, but only in flat space-time, not curved. Also there is no fixed point in space that you can measure your position from anyway.

Thanks, Sabine! You know, I've seen a bunch of intro GR videos and I got everything that's explained. However I still miss a graphical exemple showing how the curved spacetime causes mass to fall. I know non accelerated matter follows geodesic paths but how geodesics can be free-falling ones?

@Gunni1972

4 ай бұрын

The "Gravity is not a force" theorem(eme). Acelleration is only absolute to it's starting point. NOT TO CURVED SPACETIME EITHER.

Thank you so much for this video and explanation. Many times I told people that gravity isn't a force, but a consequence. I just never could explain what gravity is a consequence of. I'm not a scientist, there's more that I don't understand than that I do understand, I try to understand things though. People said to me that I didn't understand gravity and I simply replied that maybe I didn't, but that the other person didn't understand gravity as well and I was laughed about. Now I can address them to your video 🙏

@jarirepo1172

4 ай бұрын

We have dark matter to explain how galaxies stay together, dark matter to explain why galaxies move apart from each other on large scale.... does anyone REALLY understand gravity?

Hi Sabine, great video as always. I have some questions that are bugging me. 1) you say Einstein said an elevator in a box with you and a spring on Earth is the same as in a rocket and indistinguishable. But how can this be true? If we actually do this on Earth you will feel nothing and the spring will not stretch. However in an accelerating rocket you will feel being pushed down and you will see the spring stretch. So this analogy make no sense to me ? 2) Not sure if Einstein explained how the curvature of space-time works. For example is it the case that somehow there are 'magically' lots of sheets or rail tracks holding up massed objects ? This is what the analogy of rubber sheet suggests, but how? Whete does this cone from? Eg is it a field of some sort (like magnetic fields create a force, is this series of 'rubber sheets' the gravitational field or something? It just seems to me that we went from unexplained action at a distance from Newton to more unexplained actions with Einstein. Is this being researched currently? 3) If an apple is falling off a tree I have seen some explanations say it is not the apple necessarily falling but the Earth accelerating upwards to meet the apple. I dont understand this. For example this explanation may work for a single apple but whete we have multiple same experiments all over the world at same time then which way is Earth accelerating now to meet every apple? Seems like we are causing the Earth to stretch in all directions? 4) if gravity truly is not a force then why does Newtons gravitational equation even work at all ? If Newton was so completely and utterly wrong then his equation has no right to work at all. It should be completely wrong. However it does work and extremely well, exceot in some cases. His equation concept is based on a force and on interacting masses. ? Are Einsteins equations very different eg do not involve mass and distance or fairly similar to Newton? 5) how can acceleration be absolute ? Acceleration is defined as the rate of change of velocity. Velocity is relative, time is relative, but somehow acceleration which is the derivative of velocity is absolute, just dont see why mathematically? Or conceptually ? For example we talk abot inertial frames in Special Relatively, and say velocity is relative. However if you accelerate within an accelerating frames at a different rate to the frame itself, why is it conceptually any different to the relative concept in an inertial frame ? Ie why wouldnt acceleration also be relative?

Physicists still don't understand the difference between space and surface. A spherical surface is curved, but the space inside is not, nor is the space around it. Gravity and electrical charges are determined using the Heaviside torsion balance. The torsional force of a wire is used. Coulomb determined this power. Consequently, gravity and electric charge have the same origin in atoms.

I liked this before I even got past 4:18. This is one of the most interesting short presentations on gravity that I've ever listened too. Like many, I always thought of gravity as a "Force" pushing down on things, rather than simply as a curvature of space time. Thanks so much for this simple, effective, and mind-boggling explanation of gravity for lay persons, like myself!

@vibaj16

4 ай бұрын

Vsauce's video "Which way is down?" includes the best explanation of gravity I've ever seen.

@Technotranceism

4 ай бұрын

Who says gravity has to apply a force downward? Maybe it applies a force by pulling! After all, gravity can also repel.

@vibaj16

4 ай бұрын

@@Technotranceism as far as we know, gravity can't repel

@gregorysagegreene

4 ай бұрын

But it's the mass that curves spacetime because, well, *within* spacetime mass has to be generating some kind of 'curving force' ? 🤔

Just wanted to say that the quizz was really fun! It's a super cool idea to make the contents of the video stick in our minds. People (me included) usually watch a video and immediately jump to the next one about a different topic, not giving our brains the time to fully process all the information. Those quizzes are a great addition. Thanks Sabine! Good quality as slways.

@titerado

4 ай бұрын

I unfortunately disagree. This comment took me to the quiz, but by not getting the results without paying then I've learnt nothing from the mistakes. Having a quiz is a great idea but I do hope Sabine can consider a better platform to make it actually useful

@kevincleary627

4 ай бұрын

Confucius say "Don't let KZread stardom go to your head and cause you to charge for access."

As an eager physics undergraduate 50 years ago I struggled more than I ever expected with the explanations of relativity theory I was given, and this was the final straw that convinced me I did not want to ever be a physicist after all. I kind of understand it now, but I still can't quite get my head around the idea that the earth is making me accelerate upwards even though I'm motionless and the earth is not visibly expanding. The explanation, so I understand, is that the earth, due to its internal pressure, is expanding into space at the same rate at which space-time is collapsing inwards due to gravity, but why are these two things happening at the same rate? Why should there be an equivalence between the earth's internal pressure and the curvature of space-time?

@narfwhals7843

2 ай бұрын

Because the earth's pressure and the "infalling space" have an equilibrium. That equilibrium defines the earth's size. If gravity were stronger, the earth would shrink until the pressure increases enough to balance it again. If it were weaker, the earth would grow until the pressure decreases enough.

Its amazing how parts of your anatomy stay perfectly still and firm whilst you accelerate other nearby parts with considerable force, if that sounds rude well I must be a bit like you but male version. Anyway I am impressed with your knowledge and educational videos. Keep them up, ... and the videos.

@user-cl1jn2qe4y

Ай бұрын

After all we don't want gravity having an effect on you!

4:57 Unless the spring itself has zero mass. It would be a clearer illustration if a weight is attached to the other end of the spring, and the spring's mass is assumed to be zero.

@HughCStevenson1

4 ай бұрын

And for a non-massless spring the extension proportion (strain) of the spring is not uniform. The end that is attached extends more and the free end extends 0, proportionally, right at the end, because there is no mass attached to the end. It seems to be shown as uniform in the animation...

@andrewm9425

4 ай бұрын

Why would you assume a massless spring for this discussion?

@alexneigh7089

4 ай бұрын

@@HughCStevenson1 Yes. In effect, it measures (the manifestation of) weight, and it would be more intuitively clear if weight is attached to the spring rather than the non-uniformly distributed weight of the spring is measured with an additional complication of changing distribution when the spring extends/contracts. In simple terms, when you use scales, you do not determine the weight of the scales, but the weight of the item whose weight you try to determine.

Nice video! I teach this material to undergraduate students, and must admit i sometimes use the wrong terminology in the moment. I would say that I think your black hole animation may confuse some viewers who have heard of spaghettification - though i understand why you might have wanted to avoid the complication that two ends of the same object can be travelling along diverging spacetime paths and get stretched. Perhaps that's another video for another time!

@oddarneroll

4 ай бұрын

Good point, idk if i understand your point about spagettification, maby you can help me underastand this betterr? What about equliliance principle in a box resting on a massive small object, in my head you chould measure a change in direction of accelleration across your box? And what about the theorised graviton particle, can you have a graviton particle but no force? All suggest gravity being a force, no? If quantum gravity theorems look at gravity as a force, is not quantum theroy really more fundamental (and therefore, closser to truth) than general relativity? If gravity is a force in quantum gravity, is it correct to say we know gravity to not be a force? im confused.

@KaiVieira-jj7di

4 ай бұрын

@@oddarneroll Gravity is not force by direct measurement and measurements of other parameters that determine if the gravitational field cannot/(can) exert a force (the Local Lorentz violating parameter, β, for example). To date all measurement confirms that absence of a gravitational force, and this is independent of any theory. The graviton further demonstrates that the gravitational field cannot produce a force as the massless spin-2 field we associate with it reproduces the Einstein-Hilbert action and the Einstein field equations in the appropriate limits. What the virtual graviton field does (assuming it exists for the moment) is communicate the curvature, the curvature over which particles would travel along their geodesic paths.

@raymondlines5404

4 ай бұрын

What book do you use for undergraduates? And does it go into simple dynamics examples like Sabine did in this video?

@MrClivesinger

4 ай бұрын

@@raymondlines5404 It's quite a surface level introduction in a UK University 2nd year module called "Fundamental Forces" (and yes I do stress the irony regarding gravity not being a force!), where the majority of the year long module is spent on electromagnetism and the nuclear fundamental interactions. On the quick intro to gravity I go through a number of thought experiments involving a little doll of Einstein in a little elevator flying through space. My favourite part is explaining gravitational redshift :)

@darkpheonix77

4 ай бұрын

What is the definition of "force" then? Its never stated in the video. I was actually thinking about spaghettification, or conversely an object long enough to mesure the difference in "gravitational interaction" on each end. Would that not show an acceleration?

If you are accelerated , isn't any object held in your hand also subject to acceleration? Why then do we feel the weight of the object? Are we being accelerated at a greater rate? I watched this video last night and am watching again.Very interesting. Thank you for sharing your knowledge. I love science.

@sabine if an object is in free fall and if we track its motion at 1sec, 2sec etc. then how is the position of the object explained without acceleration?

I think when we imagine (or even physically hold) a spring or slinky it becomes easy to see. We just have to change our perspective of what is acting our applying force. When the slinky sits in a pile on my hand with no gaps between the coils, because my hand is applying acceleration pushing it up. If I hold it from the top coil and it opens up into loose coils, it's because of my hand applying acceleration holding it up. If I drop it (and we imagine wind resistance and air turbulence having no effect) it will go to a position where it's neither fully compressed, nor under tension being stretched out. Additionally, it would be straight, the coils would all be in line, whereas if I went back to holding it, with one end in each hand, the middle coils would sag, because of the acceleration applied by my hands. If I apply more acceleration by lifting it above my head, the sag would be greater while I moved it. And if I suddenly pushed it towards the ground, the bend would be upwards rather than downwards. Simply put, the sag/bend in the coils is opposite to the direction of acceleration.

@rustyspygoat4089

2 ай бұрын

I love my wife, but she is so bored of this. She rather watch tick tock and facebook shorts .. women ☕

Here's what I don't get: If the argument is that a spring in free fall does not experience acceleration because it doesn't change shape, then would the same not also be true if we swapped the gravitational field for a magnetic one? Since magnetism also works on the entire spring at once (rather than just on contact area), the observed effect would be the same: The spring keeps its shape and therefore is not accelerated. So therefore magnetism should also not be considered a force? Same with an electric field.

@pasqgrasso

4 ай бұрын

@thisuserhasaname, yes your argument is valid. Electric and electromagnetic forces are recognised as forces, but due to a lack of understanding, gravity is not seen as a force by some (which it is of course, sorry Sabine). The wider community of Physicists STILL haven't got a clue what gravity is. They must discard Einstein's theory in order to move forward. He was very good at describing effects, but he was not good at identifying causes. This is a major issue with General Relativity and Quantum Mechanics - cause and effect are divorced, which has led to misunderstanding. We will never make leaps forward if we do not get past this paralysis.

@187nemesis3

4 ай бұрын

Who says a spring has to be made of a material that can be affected by magentism?

@DanielSamaniego-of5xl

4 ай бұрын

Gravity is the bending of spacetime in a 4th conceptual medium per Albert Einstein it's an effect not a force. (Pseudo math formula for a conceptual medium) This replaced Newton for mass does not attract mass i.e. 🎈 ☁ Not 1 single scientific (natural phenomenon independent variable and dependent variable) experiment has even been conducted to prove Gravity!

@jasonsutton4415

4 ай бұрын

If you were to experience being pulled by a magnetic field (say you were wearing a suit of steel armour) you would feel the force, when in free fall you feel nothing. Oh and electric and magnetic fields are the same thing.

@QuasiRandomViewer

4 ай бұрын

@@187nemesis3 Who says Dr. Hossenfelder's spring has to be made of a material that can be affected by gravitation? ;^)

A true genius is one who can make you laugh while sharing knowledge/understanding. Thank you so much for this ❤

Doesn’t the box and spring stretch when they enter the black hole as space is getting bigger one end in comparison to the other ? Or does this depend on the frame of reference you observe it from ?

Although this explanation is perfectly valid, I always have trouble visualizing how all of us standing on different points of a sphere feel a similar acceleration in different directions.

@briancrowther3272

4 ай бұрын

From my understanding since retiring from teaching physics high school pre uni level, is this. Read a great book, why e equals m c squared by brian cox and a mate, I think that is where I got this. IN general relatively, the clocks run slower (ill need to check, faster or slower the point is the same though) as you move further away from a mass. With big ones like Earth. That gives the illusion of acceration as the relative velocity at the mass is different than away from it. So this is a bit like say travelling from the equator to the north pole (in my case south as I am in Australia), but you want to go in a straight line (no warped sapce time due to no mass), but space time is curved due to the mass and that bends the line to the pole, as on a globe. The effect is you are made to conintually change direction (or it feels like it) as your path is being constantly corrected or resisted by the curved line between the pole and the equator. This gives the effect of acceleration but is not a force, it is like centripetal or centrifugal force by analogy. This makes the clocks run at different speeds at different disatnces from the mass. SO cool. I really want to re read all that but cant find the book in a local bookstore ie Sydney CBD rats. Ill need to try harder, it has disappeared from my library.

@heisag

4 ай бұрын

@@briancrowther3272 I guess one can use a clock inside "Einsteins elevator" to tell wether one is beeing at rest on a planetary surface or accelrated in space then? If it ticks differently when at the bottom compared to ceiling, one is at rest on a planet, and if there is no difference, one is beeing accelrated somewhere in space?

@gcewing

4 ай бұрын

@@heisag You're right, if you can detect a non-uniformity in the acceleration then you must be in a gravitational field. This doesn't contradict the equivalence principle, because the equivalence principle is only talking about a uniform gravitational field. BTW, you don't need a clock to detect non-uniformity, just make measurements with the accelerometer in different places.

@JerehmiaBoaz

4 ай бұрын

You could try imagining a rocket hovering 1 meter above earth's surface. It's rather obvious that the rocket needs 1g of thrust to keep hovering above the surface and avoid falling down. If the rocket needs 1g of acceleration to maintain the same distance to earth's surface then earth's surface must be experiencing exactly the same acceleration as the rocket does.

@JT-sv9bi

4 ай бұрын

@@JerehmiaBoaz Okay, except the rocket isn't accelerating. It's hovering, like you said. Now I get that's what this entire video is about, but if we're going to change the definition of something so fundamental, we should really lead with that, and replace the old meaning with something else. If the earth was accelerating upwards in all directions in a Newtonian sense, it would constantly expand. That's why people, myself included, still don't understand this. Pressure -> force -> acceleration, sure, if there is movement. If I press my hand on the wall, I'm exerting a force, but nothing is moving. No kinetic energy, no motion, no acceleration.

Amazing video, it is not stressed enough in divulgative physics that acceleration is absolute

@paulmichaelfreedman8334

4 ай бұрын

The irony being that absolute as it is, acceleration relies on time to be accurate, and guess what time is? Yup, relative.

Hi Sabine Could you tell me where I have gone wrong….Let’s say you take the case of the train and flashing lights and put the flashing lights one up high and one on the floor in a rocket ship with Alice. Have the rocket ship accelerate upwards constantly the light basically blue shifts from bottom to top which is opposite of what the gravitational potential does. Now as the rocket ship comes into a landing back on earth it now shifts as the gravitational potential does. Would this not indicate a difference to be noticed between acceleration and gravity thus a flaw in the equivalence principle in this scenario? Try drawing the different scenarios out as I did one just considering acceleration up and down and another scenario of just using gravitational potential (which would not matter if going up or down as it is always red shifted upwards) curious where I have gone wrong. Love your videos

@narfwhals7843

2 ай бұрын

"the light basically blue shifts from bottom to top" That is not correct. Light sent from the bottom to the top will arrive red shifted as the rocket accelerates away from it while light sent from the top to the bottom will arrive blue shifted as the rocket accelerates into it. Just like in a gravitational potential.

Thank you, no one taught this including my Professor in Physics. we paid them but they only teach us how to pass the exam.