Hold on! Let's not be so quick to judge the cognitive ability of flatlanders and flat earthers. According to the Force Concept inventory, the average high school student's thinking about the physical world is full of common sense misconceptions about the physical world. I applaud Dr. Hossenfelder's approach to the proposed gedanken experiment and relevant experimental evidence. I would have also liked to have seen her mention Dr. Mendel Sach's ideas about STR in a universe with mass and the Mach principle. This is a learning moment.
Fighting the flat earth troll is a waste of time. I was hoping for a good video, but instead I get flat earth debunking. I love this channel, but there is no heroism in debunking something that is obviously a troll to an audience full of people who already know better.
@@cougar2013 I think it depends on the viewer's level of scientific literacy. I know enough science to know that FE is fraudulent. But I still learned something from her explanation of the equivalence principle.
I wonder how many brain cells Sabine had to sacrifice just to read the flat earth website and think about what they wrote. Hope the hurt's gone away by now.
oiSnowy , my thoughts exactly! While good people 👼 are spending time debunking the intentional deception of evil people 👹, the latter use the diversion to continue to do evil...
I tried to read a PDF with 200 "proofs of Flat Earth", but I decided not to read it, because I need those brain cells for more important stuff like sleeping and farting.
chem.tufts.edu/answersinscience/relativityofwrong.htm My answer to him was, "John, when people thought the earth was flat, they were wrong. When people thought the earth was spherical, they were wrong. But if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together."
@@PMA65537 Brilliant Peter! I've kept that link handy for 30 years, thinking it such a clear and powerful retort to attacks against science. A superb contribution here. Your excerpt is even tweetable, should it find its way into a certain momentous 'debate'. thx
@@SabineHossenfelder Please answer very simple question. I am at 198m elevation spot and i can see mountains in full that are 201km away - the highest peak is 1750 m above sea level and can see full mountain also peaks that are 700 m above with full shape. Why is it possible if Earth curvature makes it impossible - 1850 m should be hidden I can provide 100% legit evidence of this observation - it is a serious problem for Globe model.
@@bastardosss Sounds weird, I'm curious about that evidence! Meanwhile here's my evidence of flat eath, a beautiful lunar eclipse, clearly everyone has seen this hundreds of times: i.pinimg.com/236x/2e/1e/13/2e1e13ca6943764c4f6f015f034d0f47--funniest-memes-funny-memes.jpg
It's 4:14 a.m. here, but I'm glad I'm investing my time into the things I love, and I'm good at it. Physics is the best, and I'm happy channels like this exist in these moments.
I just found your channel today, i am literally binge watching every video of you and also sharing it with my colleagues of my university. Thanks for this great videos
WHY ELECTROMAGNETISM/ENERGY IS GRAVITY: Gravity/acceleration involves balanced inertia/inertial resistance, as ELECTROMAGNETISM/energy is gravity. This is consistent WITH F=ma AND E=mc2, as gravity IS ELECTROMAGNETISM/energy. So, inertia/inertial resistance is proportional to (or balanced with/as) gravitational force/energy; as this balances AND unifies ELECTROMAGNETISM/energy AND gravity; as this balances gravity AND inertia. In other words, GRAVITATIONAL force/energy is proportional to (or balanced with/as) inertia/inertial resistance; as ELECTROMAGNETISM/energy IS gravity. Accordingly, gravity/acceleration involves balanced inertia/inertial resistance; as gravity IS ELECTROMAGNETISM/energy. It is proven. Energy has/involves gravity, AND energy has/involves inertia/inertial resistance. "Mass"/energy involves balanced inertia/inertial resistance consistent with/as what is balanced ELECTROMAGNETIC/GRAVITATIONAL force/energy, as ELECTROMAGNETISM/ENERGY IS GRAVITY. By Frank DiMeglio
I never cease to be impressed by the graphic design of these videos. The costume + background combo is always super-effective at keeping my focus long enough to digest the concept.
Another excellent video. Thanks for not showing the classic curved space diagram that is often somewhat misleadingly used in explanations involving general relativity - the one where a planet is resting on a rubber-like sheet and thereby curving the formerly flat sheet.
Thanks, great video and Merry Christmas to you. At 5:52 you stated "all kinds of energy densities (....) gravitate". Did you mean ALL kinds? Does gravitational potential energy count as a form of energy that gravitates? Do we need to calculate and include gravitational binding energies as a contribution to the stress-energy tensor? Can we calculate that binding energy BEFORE you have the stress-energy tensor to tell you how spacetime curves?
The Equivalence Principle is one way you can tell that relativity is incomplete! Yes when one is in free fall in a closed and sealed elevator, the experience seems indistinguishable from one floating in a spaceship in deep space. However, the one in free fall does experience tides; his feet being closer to the Earth than his head. Whoever can resolve this mathematically and experimentally should be awarded the Nobel Prize!
The flat earth society is a troll. It has to be. It’s annoying when scientists feel the need to debunk it, as if anyone watching this channel thinks the earth is flat. The only way to deal with a troll is to ignore it.
@@cougar2013 It's worse than that though. There's a lot of con artists who make bucks peddling pseudoscience to ignorant people or those vulnerable to conspiracy theories. It contributes to the overall anti-science movement (especially in the U.S.) and feeds into politics as well.
This reminds my of Velikofsky’s “When Worlds Collide”. He was ridiculed for his theories. Carl Sagan thought that the rebuttal should have been scientific (as Velikofsky was erroneous on many points), instead of just ignoring his hypothesis, regardless of how outlandish it seemed. After all, Wegener was ridiculed for the theory of continental drift, but accumulated evidence eventual proved his hypothesis was substantiated. Darwin seems to have erred in assuming evolution was gradual, whereas punctuated evolution is now gaining traction. Asimov’s essay “The Relativity if Wrong” address this basic scientific issue. Real scientists never assume they know an absolute truth, only that each successive hypothesis/theory is more correct than the last one. They knew over 2,000 years ago the earth was not flat.
Professor Dave has disproved Velikofsky's ideas, scientifically. Darwin and Huxley and teachers of evolutionary biology were ridiculed and insulted and attacked initially, and still until this day, for stating the reality of evolution & proving it and teaching. Karl Marx & Friedrich Engels & revolutionary communists were insulted, ridiculed, imprisoned, tortured, murdered by fascist nationalists & religionists (e.g. catholic church in Spanish Civil War of the 1930s against the secular & pro-Marxist Republicans) for their new revolutionary ideas about economics, and for fighting extreme inequalities in wealth. Most of their ideas are still true today.
Dear Sabine, every time I watch your videos I’m more convinced that you’re very good explaining difficult physics concepts to ignorants like me. Now I think that it would be very beneficial to have you explaining difficult biology concepts, which everyday seem to be more numerous, given the avalanche of publications about discoveries coming out of research. Biology seems to be the most exciting branch of science these days and it shows undeniable signs of becoming the de facto source of the most fascinating discoveries in the days ahead. Math and physics are gradually (maybe inadvertently?) turning subservient to Biology. Your strong pedagogical skills would be very efficient in explaining things like the promoter/enhancer TF binding site nucleotide sequences related to GRN and cell fate. That’s just one of gazillion examples that we could provide. Hopefully somebody with your clear eloquence will appear in biology too.
Sabine is looking so beautiful. And 174 likes/0 dislikes. Everybody likes her. One of the best physics channel. And the way she roasts the idiots in a cold way.
I do not understand how the "earth is flat" theory can hold up. Anyone can get on a plane and fly around the planet. A more obvious proof that the theory of the flat earth is wrong can hardly be given.
More simply by looking at the time table of the flight companies. But flat earth is not about earth, it is about the lost of trust to the scientists. Calling it nonsense won't cure anything.
@@manoo422 Indeed, they will come up with bizarre convoluted explanations to explain this...however one simple observation that I have yet to see a flat earth explanation for, that I've made, is that of the stars. So in the Northern hemisphere one constellation that is familiar to many is Orion. However, when I went to Australia, lo, it was "upside down" in the night sky (sword sticking up!) I suppose they would have to argue that there is some sort of amazing interation in the atmosphere in a band across part of their disc that perfectly inverts the starlight to give that result...or perhaps there are no stars, only satellites put -up by NASA, cunningly arranged to give everyone the impression that we are standing on a sphere ;-)
Small note on the lift experiment. It is very possible to find out whether the lift is moving upwards. On the one hand, the movement can be detected by means of a barometer, on the other hand, after a certain distance up or down, a pressure difference should be felt in the ears.
If earth has been accelerating at 9,8 m/s2 for the last 6000 years (flat earthers are great friends of the creationists, who believe the universe was created some 6000 years ago) then it must have reached by now 6180 times the speed of light, assuming Newtonian mechanics. I am sure Einstein wouldn't have liked that either!
You'd be wrong to assume newtonian mechanics. In special relativity, it's perfectly possible to have something with a constant proper acceleration that doesn't ever move faster than the speed of light.
@@Nickesponja of course you are right but I was just giving a back of the envelope calculation. If you are good in special relativity can you find out the apparent mass of the earth after 6000 years of constant acceleration starting from rest with a rest mass of Me 6 10^24 kg? I can't do it.
@@royk.466 Well if you mean 6000 years of proper time, I'm afraid I haven't found a calculator with enough precision to do so. All of them are unable to calculate which speed would an external observer measure for the Earth, instead they give the speed of light because the actual speed is so close they just don't have enough precision to calculate it. Effectively this means that the apparent mass that an external observer would see is almost infinite. If, however you mean after 6000 years of time measured by an external observer, then the calculation is doable: the apparent speed would be 2.999999961*10^8 m/s (which is very close to the speed of light). If you calculate the apparent mass you get 3.72*10^28 kg. For the record, 6000 years of proper time correspond to ~10^2683 years, which is absurdly large (far larger than the age of the universe). Meanwhile, 6000 years of external time correspond to only about 9 years of proper time, which is equally ridiculous.
@@Graeme_Lastname I can hardly manage with high school physics but I think it is clear that a steady acceleration for 6000 years in earth's proper time means that we must be all travelling now very very close to the speed of light with an apparent mass that probably exceeds the total energy of the universe. And of course needless to ask where our energy came from and who was pushing us all these years!
This is the best video of equivalence principles so far that is accurate and explain correctly Most of the youtubers describe object fall because the time and space is in our future yeah that’s make sense. but we do not know if we our falling or not that’s the rule of equivalence principles in short distances so it is a misleading to say object fall because our time and space is in future because we do not know if really the object falling or not in a small region space Acceleration flat space and time is only to discribe the curvature of gravity since acceleration is indistinguishable to gravity
Thank you! I’ve been saying this for a while. I hate it when people feed the troll and waste their time debunking this obvious nonsense. The only way to deal with the obvious troll that is the flat earth society is to ignore it. I was hoping for a great video, but instead I get flat earth debunking :/
I agreed with that until November 2016. I believe some people can be that dense, and the consequences can be extreme. ...whether or not there's some degree of trolling going on, it's a worthy context for a discussion.
Thank you for this video! I was confused since a time when some of my physicist friends told me about the elevator illustration of the equivalence principle and I devised two thought experiments that could distinguish gravity from acceleration in a closed box. That can’t be done with a localized point particle, however. Your videos always help!
Say what you want about flat earthers, but they are the greatest marketeers of the world. For every one of them, they get a few million mentions on the internet every year.
I'm profoundly impressed by this approach, more so even than Sabine's charcteristically clear and succinct explanation. Typically, explanations for a general audience over-simplify things and therefore can become subject to abuse as pseudo-science. IMO, "one step deeper" in almost all cases adds valuable scientific perspective. Sabine found a way to start with the over-simplified abuse, motivate us to understand it and the next level, AND simultaneously show how it disproves the pseudo-scientific position. All in less time than I can write these five sentences.
Quite apart from the flat Earth discussion: People tend to talk about time seconds and minutes after the Big-Bang as if it could be measured in the conventional way, where you have a standard against which you can calibrate clocks. It would be most interesting if you made a video explaining what physicists really mean by time at that stage.
Thank you for pointing out that it is measurable differences in g that kill this flat earth "model" and not the earth reaching the speed of light as is often claimed by debunkers. This notion of an accelerating earth is actually a good thought experiment for reference frames, time dilation, and length contraction.
My mistake: Dear Sabine, I'm not really qualified to correct you but I think I heard you saying relating to gravity not being a force but actually representing the longest path between points on a curved space - I think it should be the shortest path... at 7:15 you worded it a bit differently about longest path in proper time so maybe there's something I am missing
Nice video ! Good to know that a serious scientist like Sabine also visits sites like flat-earth just to see what kind of argumentation they use. We all agree I guess that Earth is round, but sometimes it can't hurt to seriously re-think stuff we 'know for sure' but is not as easily fact-checked as a round Earth (satellite optical footage should convince anyone). Take for instance the 'equivalence principe'. Albert Einstein derived a few brilliant gems from this principle, but there are limits we may not have recognized. Take the 'equivalence relation of: E=MC2. Everyone knows that this means energy and mass are 'equivalent'. Or does it? Mathematically sure, the terms left and right of the '=' sign equal out. But does that physically mean energy and mass are 'interchangeable'. Really? Let's look at the formula Distance (space) = Time * speed. Does this mean that given a certain speed, time and distance are equivalent? After all, if we take more time, then obviously we get more distance. Now, we humans living in spacetime have a much better feel with the terms like distance and time instead of mass and energy. And so no, we would be inclined to say space and time are not 'equivalent'. But fundamentally both formula's are not different. Now lets for a moment assume mass is not physically equivalent to Energy, anymore then Space is to time. Let's in stead assume for a moment Energy is equivalent to the inverse of Space. Application: look at our big bang universe. Before the big bang there was infinite Energy now there is little energy left and infinite Space. That sounds like a lot more logical 'equivalence relation does not it? If we take the in-product of our cosmos' energy and space (as in inversed energy) we get a constant of 1 , which only would be 0 (zero) at the time of inflection at the big crunch. Digital...entropy expressed in information terms that is...hmm. And what about mass being the inverse of time? Application: If we say a particle A has 4x more mass than particle B , that would mean it has 4x more inversed time (as a particle property), which would lead to the logical conclusion it would take as 4x more time to yet change its speed. Make sense? See how we can make the 'spacetime alien' terms Energy and Mass more accessible this way? So now, lets take this a step further and combine the two; suppose in the subatomic realm distance is expressed in ENERGY and the clock is expressed in MASS. Lets take our spacetime formula of distance (space)= time * Speed. What do we get if we replace space with energy and time with mass ?? the formula becomes E=M*speed . Speed is now expressed in Energy/Time= Joules/kg or in spacetime terms Nm/kg= s2/m2 or C2. So the entire speed formula becomes; E=MC2 at the subatomic scale. Evidence? well there are 2 instances where we know we cross the subatomic (sub Planck) scale, namely during nuclear fusion or fission. During the very short moment right before nuclei merge (or separate) they must cross the sub-Planck region. So if there is a separate speed formula as described above it needs to be eminent right here. And we KNOW that at these instance E=MC2 arrises. Case proven! Just as we thought we knew every thing..... So no, we all need to be careful with 'equivalence principle' . this one got us fooled for 100 years...And the community is still NOT ready to accept failure...
I have to say watching your videos is a highlight of my week. You have a remarkable ability to take a complex topic, break it down and explain the concepts in 8 - 10 minutes. It is a talent that many do not have, well done and please keep it up.
The comment at the 5:30 minute mark gave me a great idea: Would a disc be stable if it was large enough? or would the pull at the edges be too strong? Is there a mass distribution at the edges that allows for a solid disc that is way beyond (many orders of magnitude, think something bigger than a galaxy) the hill sphere?
Equivalent Exchange is my favorite law of physics. It comes from the fruit of the Locacaca tree follows the same principles of "equivalent exchange" as the grounds of the Higashikata estate; they are capable of granting anyone who eats it "something" by taking "something else" from them. The most faithful example of this concept is when the old man uses the Locacaca fruit to regrow his lost leg in exchange for his eyesight, both of his eyes transforming into stone and breaking apart soon thereafter. Apparently this process can be repeated as long as someone has a fruit, continuously sacrificing random parts of their own bodies in order to gain back what they had given in the previous instance.
Whether or not a leg and eyesight are equivalent is not an objective thing that you could determine by doing an experiment, so that's not a law of physics at all.
Constant acceleration is an exponential curve (speed), while rotation is a goniometric. But cos(x) + i sin(x) = e^ix. Does this relation show an equivalence between linear accelleration and centrifugal accellaration?
Re Einstein’s silly elevator/chest gedanken for supposed equivalence. 1. Hanging wts will hang parallel in accel, but will converge if in gravity. 2. Clocks will tick at same rate in accel, but will tick differently if at different altitudes if in gravity. 3. Photons crossing the room will all remain horizontal in accel, even tho the ray of light curves down, but photons will not remain horizontal in gravity, they will have a slope parallel to the curved traject if in gravity. Re 3. Einstein’s elevator/chest gedanken for the equivalence of a curving ray of light in accel & in gravity ignores this lack of equivalence. If we apply Einstein’s gedanken to the bending of light passing a star then no photon passing a star would ever fall below the mid-line of the star. Hence there would never be a focus, hence there could never be an einstein ring, or even a part-ring. Every one of Einstein’s gedankens is wrong. His prediction of the doubled bending of light passing the Sun is a lucky guess. Likewise his prediction of rings. Likewise his prediction of Shapiro Delay. None of these are a legitimate prediction of any of his gedankens. The only remnant of his GTR is the slowing of light near mass, confirmed by Shapiro Delay. We need to find the real cause of Shapiro Delay. If i am kind i can give Einstein credit re the doubled bending of light passing the Sun. But we know that a mysterious half of it is due to Shapiro Delay (Dicke). Hence we need to find the cause of the other mysterious half (hint)(it is due to a psuedo-ballistic bending). Re 2. I should add that all kinds of clocks must be affected differently by altitude & by velocity. Tests show that some atomic clocks behave nearnuff as per GTR. But we will find that GTR does not apply for most kinds of clocks, eg tuning fork & balance wheel clocks.
I want to ask a question related to the equivalence principle that has been bothering me for a while. I understand that inside an elevator that is accelerating upward in gravity-free space, the situation is equivalent to a uniform gravitational field directed downward. But how about the space-time inside the elevator? Is it flat? Then how is the bending of a light ray explained? Is it curved? Then how does its curvature differ from the curvature of an actual gravitational field that is always non-uniform?
7:13 But why? Shouldn't the point particle with mass also curve spacetime around it dependant on the mass of it? Why should 2 point particles with different masses then take the same spacetime path?
Because of isostatic compensation (mountains are typically made of lighter material than other areas, and have deep roots of this lighter material), the local gravity vector actually typically is deflected _away_ from mountain ranges. (In other words, mountain ranges typically have less mass than would be there if they weren't there, and thus slightly repel a plumb-bob.) I believe the British first found this out when they were surveying India and the Himalayas.
I'd like to hear a psychologist explain this phenomenon. Understanding this thought process might help explain why the world's political systems are flat.
I think you ommited a much better, and much more easily demonstrated piece of evidence: gravitational pull works towards the center of the Earth, and that's how we can show the locality of the equivalence principle. That fact is best seen on long bridges, where two distand pylons are not parallel to each other, with the tops farther apart than the bottoms. On flat Earth, it would make no sense to construct pylons that don't stand up straigh, and yet engineers do that all the time.
Would you please comment on the assumption, referred to by Einstein, that the speed of light is the same in all directions? Is this related to the equivalence principle? Calculations of the speed of light have always been made from the time taken for a round trip, and would yield the same result whether the speed is c in both directions or, in the extreme case, c/2 in one direction and infinite in the other, or any intermediate combination?
We've all experienced equivalence when we sit side by side to another train at a terminus station. When one train moves, we're not sure if it's us moving or the adjacent train. We can also see why this doesn't work if we're on platform 1 and a train moves on platform 12.
@Sabine Hossenfelder Quite bad example of Equivalence principle w/ elevator on planet because if you say locally in flat space-time, you contradict yourself. If you say planet, then there is central force, and therefore if you take two point masses next to each other in elevator, it will seem to us as some magical force between them, they would "attract" because of central force and you can definitely say it's due to gravity not acceleration (therefore 2:24 till 2:40 is wrong). You can fix this by saying that by "Locally in flat space-time" you mean in a small region and for small amount of time (preferably infinitesimal), or mention Eötvös' experiment. Also I have a question, we know that inertial and gravitational mass are mutually proportional (under right system of units are equal). We can assign mass (corresponding to energy) and therefore gravitational effect to E&M field, what do you think about that?
The observation that gravitational field strength varies also explains why atomic clocks tick at observably disparate rates from one location to another (gravitational time dilation). Doesn't this mean that John Stewart Bell should have employed a gravitational path integral to account for the inevitable decoherence of otherwise entangled particles as they speed apart in the presence of arbitrary gravitational gradients? Had he done so, doesn't it follow that the presumptive hidden variable would not have vanished, but would have yielded a non-vanishing "beat frequency" term arising from any time-varying term in the presumptive hidden variable. Or to put it another way, isn't time itself at the root of any hidden variable?
I think the best way to put it is: one cannot build an accelerometer that isn’t at the same time affected by gravity. Thus, we have to accept whatever an accelerometer ascribes 0 acceleration to as true inertial frame, while someone standing on the Earth is clearly accelerated. However, we’re not being accelerated upward, but outward, and this only makes sense if space is contracting at the same time. In a way, flat Earthers are on to something, they just don’t realize that one can make sense of outward acceleration without the planet blowing up.
4:12 "The Acceleration also differs between the equator and the poles. This can and has been measured..." It must be a very small effect compared to other differences between the equator and poles. Has this affect really been measured? Can you provide your source?
Sabine, there's a we2 trendy channel called Dialect which tries to reintroduce notions like the Ether. I know you're an extremely busy person, but I think it would be amazing (and educational) if you addressed those ideas in minutiae.
What astounds me is despite evidence people profess an actual believe in the Earth being flat, I often wonder if they actually believe that or are they posturing for effect and shock value, and that some how its fashionable.
In 3:20 you mention that general relativity is locally flat, which means it can not describe the singularity inside a black hole and it doesn't. My question is, is this shortage in GR caused by principle of equivalence not being true any more or is it caused by quantum mechanics becoming significant in the singularity? My point is, to make a theory of quantum gravity, shouldn't we first fix our theory of gravity to work in a singularity?
Thank you Sabine, As clear as mud but covers the subject, makes sense to me, I once told a flat earthen that they were misinterpreting or misusing the science, there’s an old saying , if you can’t dazzle someone with brilliance, baffle them with BS.....I love your lessons, and your beautiful...stay well !!
I like what Einstein said about curvature of space and Time but I always go back to Boyd Bushman on his experiment where he slowed down the electrons and caused time and gravity to slow down.
I am wondering if the equivalence principle also applies to the magnetic force - if my body was made of iron and I was near a big magnet of negligible mass I would feel a force indisdinguishable from gravity unless I was accelerating towards the magnet when I would feel "weightless".
Dear Sabi, weak equivalence principle equalizes between geometrical entity and gravitation. Therefore gravity is expressed as curvature in space time and GR established. That's okay but that don't mean gravity can not be expressed as a force. So if gravity is a force then a mediator has to be found. Physics called it graviton. Physicists collide with the principle "you get what you are expected". Is that interesting?
Sabine, if you throw an apple with your right hand away at the speed of light and another apple with your left hand away at the speed of light, what is the speed these 2 apples are moving away from one another?
I have great respect for you for even bothering to read any of the flat earth nonsense. I hope that the flat earth proponents get to see this video. It amazes me that contemporary people can hang on to such things.
Well, look at the hundreds of years it took to accept the globe theory and changing the POV from being the center of the universe. They killed people over that heresy. crazy
One can say energy and gravity have equivalence, since gravity is still present during a gravitational collapse and all that mass is converted to energy. To say that energy warps space/time is true in its waveform. It also warps space/time outside the waveform of the radiation itself. This seems to be the production of space itself, the gravity field given off by light energy.
I remember watching this a while back. Then most recently I stumbled on Andre Fuzfa and I'm about to read his paper. He talks about Einstein's Equivalence Principle so I came back here as a refresher. Now I'm wondering if I should respect the flat earthers more based on what Dr. Sabine Hossenfelder is saying if flat earthers is using say the Universe as a reference, wouldn't the Earth be a localized area in that respect, so wouldn't they be right? Lol, sorry I've been out of school for a couple years now.
Nice video and presentation. An observer’s perception to his situation do not and cannot use to define how the universe operates or behave in the way it is. Especially not for observers who perform more mind experiments than apparatus based research.
But can you accelerate forever? Once you get close to the speed of light and your acceleration slows down, do you still experience the same acceleration because of time dilation?
This is so good. Thank you, you're the best explainer. I've read a whole stack of general-reader-level physics books, and I never understood about the elevator thought experiment being the logical leap between SR and GR. I really need more maths so I can read real physics books. I did sign up for Brilliant in hopes of getting some, but it seems to be mostly comprised of various brain-teaser puzzles. Anyway, cheers and stay safe. You are superb and I'm a big fan.
Hey Chief! Just wondering if you've gotten around to reading more physics books! I hope so! You should go ahead and read Einstein's work on GR and SR if you've haven't-even if you don't quite understand the maths yet. It is still very valuable! He gives an incredible train example for explaining...well essentially causality now that I think about it and really breaks down how and why he came to the conclusions he did and explaining it in a way that can be (mostly) understood by a lay-man. Also no one ever mentions his amazing sense of self-deprecating humor. Trust me pick up the 50th anniversary copy, you won't be sorry.
these guys, are pulling off the longest trolling scheme thus far in the modern world. These, alongside those other spaggetti-monster worshipers. Love them both.
Mass inertia is a mutual holding of those units which - according to Ernst Mach - are dynamic phenomena that extend into the entire cosmos. Well observe the short term super inertia, this is the basis of the Overuniti principle of Rotoverter and was first discovered by Max Planck. "It takes a certain amount of energy to move anything at all." He stressed that this finding is far from being fully understood and can only be considered provisional. Planck did not find any evidence of a parcel nature to be inferred from this. However, if harder blows are applied, the mass is temporarily inert, ionized and evaporates. See A-bomb. A glaring gap in knowledge is, not to register asymmetry of any inertia-bond. See Lorenz contraction, low inertia in the direction of travel, increased at right angles. Next glaring mistake is not to recognize, gravity is only a small compression of inertia-mediating structures, but just that?s why clocks tick slower near mass-concentrations.
The problem of "locally" is that it's theoretically an almost infinitely small volume of space. Space is always curved, everywhere, so this principle never actually applies. It's kind of how thermodynamics talks about "isolated systems", even though the only truly isolated system is the universe itself (which we can only observe a tiny part of, anyway). The example of the elevator, for example, is false. Within an elevator, the gradient of gravity means you can measure whether you're being accelerated or whether it's the presence of gravity. Your feet will be more strongly accelerated towards the Earth than your head, and you could theoretically measure this difference.
I was a Flat Earther for 4 years.... and then I turned 5..
You're lucky. I know people who are still Theoretical Physicists after 40 years, ...
@@ianalanneilgrant4626
Ha ha ha ha ha ha ha ha ha ha ha ha ...
Nitpick: if you'd always been a flat earther until you turned 5, then you've been a flat earther for 5 years, not 4 :-)
@@rv706 It'd still work if they became a flat Earther at 1 year old.
@@Laff700 actually, I think your nit has nits. 😂
"The flat-earthers think........." - There is already a paradox in that incomplete sentence.
Hold on! Let's not be so quick to judge the cognitive ability of flatlanders and flat earthers. According to the Force Concept inventory, the average high school student's thinking about the physical world is full of common sense misconceptions about the physical world. I applaud Dr. Hossenfelder's approach to the proposed gedanken experiment and relevant experimental evidence. I would have also liked to have seen her mention Dr. Mendel Sach's ideas about STR in a universe with mass and the Mach principle. This is a learning moment.
@@BlueGiant69202 He was just virtue signalling.
Oxy-Morron.
Well to believe a misconception about reality you first need the capacity to have thoughts, so yes they do think
It must be quite exhausting being a heroine fighting the demons of ignorance and intentional deception. But you do it beautifully! ❤️👼👍🏻👌✨🇮🇪☘️
Even from within the science community, it seems.
I do heroine everyday
Fighting the flat earth troll is a waste of time. I was hoping for a good video, but instead I get flat earth debunking. I love this channel, but there is no heroism in debunking something that is obviously a troll to an audience full of people who already know better.
@@cougar2013 I think it depends on the viewer's level of scientific literacy. I know enough science to know that FE is fraudulent. But I still learned something from her explanation of the equivalence principle.
Philly Philly you’re right. That’s why she didn’t need to waste any time debunking flat earth.
I wonder how many brain cells Sabine had to sacrifice just to read the flat earth website and think about what they wrote. Hope the hurt's gone away by now.
oiSnowy , my thoughts exactly! While good people 👼 are spending time debunking the intentional deception of evil people 👹, the latter use the diversion to continue to do evil...
The fiat earth website boasts that "we have members all around the globe." :|
@@T.H.W.O.T.H No, seriously, does it really??
I tried to read a PDF with 200 "proofs of Flat Earth", but I decided not to read it, because I need those brain cells for more important stuff like sleeping and farting.
@@T.H.W.O.T.H Wow, that broke my irony meter.
6:41 "which is, excuse me, a sphere"
Nicely summed up Sabine!
chem.tufts.edu/answersinscience/relativityofwrong.htm My answer to him was, "John, when people thought the earth was flat, they were wrong. When people thought the earth was spherical, they were wrong. But if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together."
@@PMA65537 Brilliant Peter! I've kept that link handy for 30 years, thinking it such a clear and powerful retort to attacks against science. A superb contribution here. Your excerpt is even tweetable, should it find its way into a certain momentous 'debate'. thx
She explains and throw shades with casual sassiness. I love it!
Really looking forward to your live stream on PBS Space Time next week, Sabine!
Me too!
That's going to be great. PBS Spacetime is an amazing show.
When is that? What will it be about?
@@SabineHossenfelder Please answer very simple question. I am at 198m elevation spot
and i can see mountains in full that are 201km
away - the highest peak is 1750 m above sea level and can see full mountain also peaks that are 700 m above with full shape. Why is it possible if Earth curvature makes it impossible - 1850 m should be hidden
I can provide 100% legit evidence of this observation - it is a serious problem for Globe model.
@@bastardosss Sounds weird, I'm curious about that evidence!
Meanwhile here's my evidence of flat eath, a beautiful lunar eclipse, clearly everyone has seen this hundreds of times: i.pinimg.com/236x/2e/1e/13/2e1e13ca6943764c4f6f015f034d0f47--funniest-memes-funny-memes.jpg
Sabine makes Saturdays extra special
It's 4:14 a.m. here, but I'm glad I'm investing my time into the things I love, and I'm good at it. Physics is the best, and I'm happy channels like this exist in these moments.
I think I'm in the same timezone as you.
For me it is 3:30 am. West coast USA. Be well CM.
Lol. It's 3:52 am here Pacific time. California
@@pspicer777 Same for you, my friend.
I just found your channel today, i am literally binge watching every video of you and also sharing it with my colleagues of my university.
Thanks for this great videos
Happy that you find them useful!
Same, I'm really surprised I didn't find this channel earlier.
@@SabineHossenfelder Honesty and integrity matter Hossenfelder.
" the Earth is, excuse me, a sphere. " LoL, love it.
"The Flat Earth Society has members all around the globe." 😎
Hhhhhhhhh
😂🤣
absolutely, idiots are equally distributed around the entire human race...
Whereas there are genuine physicists all over the disk
WHY ELECTROMAGNETISM/ENERGY IS GRAVITY:
Gravity/acceleration involves balanced inertia/inertial resistance, as ELECTROMAGNETISM/energy is gravity. This is consistent WITH F=ma AND E=mc2, as gravity IS ELECTROMAGNETISM/energy. So, inertia/inertial resistance is proportional to (or balanced with/as) gravitational force/energy; as this balances AND unifies ELECTROMAGNETISM/energy AND gravity; as this balances gravity AND inertia. In other words, GRAVITATIONAL force/energy is proportional to (or balanced with/as) inertia/inertial resistance; as ELECTROMAGNETISM/energy IS gravity. Accordingly, gravity/acceleration involves balanced inertia/inertial resistance; as gravity IS ELECTROMAGNETISM/energy. It is proven. Energy has/involves gravity, AND energy has/involves inertia/inertial resistance. "Mass"/energy involves balanced inertia/inertial resistance consistent with/as what is balanced ELECTROMAGNETIC/GRAVITATIONAL force/energy, as ELECTROMAGNETISM/ENERGY IS GRAVITY.
By Frank DiMeglio
If Sabine says it... THAT'S IT.
Amazing, that she can turn wasted time (flat earth theory) into valuable information. fabulous.
I never cease to be impressed by the graphic design of these videos. The costume + background combo is always super-effective at keeping my focus long enough to digest the concept.
Best communicator of science as far as I am concerned, should be mandatory in schools and universities.
And English is not her primary language.
Another excellent video. Thanks for not showing the classic curved space diagram that is often somewhat misleadingly used in explanations involving general relativity - the one where a planet is resting on a rubber-like sheet and thereby curving the formerly flat sheet.
These channel is just great😍🔥
I'm in love with popular science for long. Your style is refreshing. Keen and precise. No fantasy, just facts. Refreshing.
Thanks, great video and Merry Christmas to you.
At 5:52 you stated "all kinds of energy densities (....) gravitate". Did you mean ALL kinds?
Does gravitational potential energy count as a form of energy that gravitates? Do we need to calculate and include gravitational binding energies as a contribution to the stress-energy tensor? Can we calculate that binding energy BEFORE you have the stress-energy tensor to tell you how spacetime curves?
The Equivalence Principle is one way you can tell that relativity is incomplete! Yes when one is in free fall in a closed and sealed elevator, the experience seems indistinguishable from one floating in a spaceship in deep space. However, the one in free fall does experience tides; his feet being closer to the Earth than his head. Whoever can resolve this mathematically and experimentally should be awarded the Nobel Prize!
most remarkable collection of nonsense xD
4chan love their jokes :P.
That quote is a perfect and accurate description of the flat earth soicity tbh
The flat earth society is a troll. It has to be. It’s annoying when scientists feel the need to debunk it, as if anyone watching this channel thinks the earth is flat. The only way to deal with a troll is to ignore it.
I laugh in this part
@@cougar2013 It's worse than that though. There's a lot of con artists who make bucks peddling pseudoscience to ignorant people or those vulnerable to conspiracy theories. It contributes to the overall anti-science movement (especially in the U.S.) and feeds into politics as well.
Sabine’s accent and voice is just 😍😍😍😍
This reminds my of Velikofsky’s “When Worlds Collide”. He was ridiculed for his theories. Carl Sagan thought that the rebuttal should have been scientific (as Velikofsky was erroneous on many points), instead of just ignoring his hypothesis, regardless of how outlandish it seemed. After all, Wegener was ridiculed for the theory of continental drift, but accumulated evidence eventual proved his hypothesis was substantiated. Darwin seems to have erred in assuming evolution was gradual, whereas punctuated evolution is now gaining traction. Asimov’s essay “The Relativity if Wrong” address this basic scientific issue. Real scientists never assume they know an absolute truth, only that each successive hypothesis/theory is more correct than the last one. They knew over 2,000 years ago the earth was not flat.
Professor Dave has disproved Velikofsky's ideas, scientifically. Darwin and Huxley and teachers of evolutionary biology were ridiculed and insulted and attacked initially, and still until this day, for stating the reality of evolution & proving it and teaching. Karl Marx & Friedrich Engels & revolutionary communists were insulted, ridiculed, imprisoned, tortured, murdered by fascist nationalists & religionists (e.g. catholic church in Spanish Civil War of the 1930s against the secular & pro-Marxist Republicans) for their new revolutionary ideas about economics, and for fighting extreme inequalities in wealth. Most of their ideas are still true today.
Dear Sabine, every time I watch your videos I’m more convinced that you’re very good explaining difficult physics concepts to ignorants like me.
Now I think that it would be very beneficial to have you explaining difficult biology concepts, which everyday seem to be more numerous, given the avalanche of publications about discoveries coming out of research.
Biology seems to be the most exciting branch of science these days and it shows undeniable signs of becoming the de facto source of the most fascinating discoveries in the days ahead.
Math and physics are gradually (maybe inadvertently?) turning subservient to Biology.
Your strong pedagogical skills would be very efficient in explaining things like the promoter/enhancer TF binding site nucleotide sequences related to GRN and cell fate. That’s just one of gazillion examples that we could provide.
Hopefully somebody with your clear eloquence will appear in biology too.
She isn't a biologist but there are plenty who do actually do as you ask. Go find them.
Sabine is looking so beautiful. And 174 likes/0 dislikes. Everybody likes her. One of the best physics channel. And the way she roasts the idiots in a cold way.
Love your European, strict, sarcastic, precise, right to the point teaching of physics concepts! Miss that from teachers these days!
I do not understand how the "earth is flat" theory can hold up. Anyone can get on a plane and fly around the planet.
A more obvious proof that the theory of the flat earth is wrong can hardly be given.
More simply by looking at the time table of the flight companies. But flat earth is not about earth, it is about the lost of trust to the scientists. Calling it nonsense won't cure anything.
Are you flying around a spherical planet or flying around a flat disc...? Yes I know its stupid but they have a stupid answer for everything!!
@@manoo422 Not anymore stupid than the round earther revengers.
Add to that that everyone knows the Earth is hollow. 🤪
@@manoo422 Indeed, they will come up with bizarre convoluted explanations to explain this...however one simple observation that I have yet to see a flat earth explanation for, that I've made, is that of the stars. So in the Northern hemisphere one constellation that is familiar to many is Orion. However, when I went to Australia, lo, it was "upside down" in the night sky (sword sticking up!)
I suppose they would have to argue that there is some sort of amazing interation in the atmosphere in a band across part of their disc that perfectly inverts the starlight to give that result...or perhaps there are no stars, only satellites put -up by NASA, cunningly arranged to give everyone the impression that we are standing on a sphere ;-)
Small note on the lift experiment. It is very possible to find out whether the lift is moving upwards. On the one hand, the movement can be detected by means of a barometer, on the other hand, after a certain distance up or down, a pressure difference should be felt in the ears.
I am at the moment working on my Einstein Elevator that accelerates me at 1 g for however far I want to go. Take that Space X. 😋
It's like a class being taught by someone who can speak directly to your mind.
If earth has been accelerating at 9,8 m/s2 for the last 6000 years (flat earthers are great friends of the creationists, who believe the universe was created some 6000 years ago) then it must have reached by now 6180 times the speed of light, assuming Newtonian mechanics. I am sure Einstein wouldn't have liked that either!
You'd be wrong to assume newtonian mechanics. In special relativity, it's perfectly possible to have something with a constant proper acceleration that doesn't ever move faster than the speed of light.
@@Nickesponja of course you are right but I was just giving a back of the envelope calculation. If you are good in special relativity can you find out the apparent mass of the earth after 6000 years of constant acceleration starting from rest with a rest mass of Me 6 10^24 kg? I can't do it.
@@royk.466 Well if you mean 6000 years of proper time, I'm afraid I haven't found a calculator with enough precision to do so. All of them are unable to calculate which speed would an external observer measure for the Earth, instead they give the speed of light because the actual speed is so close they just don't have enough precision to calculate it. Effectively this means that the apparent mass that an external observer would see is almost infinite.
If, however you mean after 6000 years of time measured by an external observer, then the calculation is doable: the apparent speed would be 2.999999961*10^8 m/s (which is very close to the speed of light). If you calculate the apparent mass you get 3.72*10^28 kg.
For the record, 6000 years of proper time correspond to ~10^2683 years, which is absurdly large (far larger than the age of the universe). Meanwhile, 6000 years of external time correspond to only about 9 years of proper time, which is equally ridiculous.
@@royk.466 Try speedcrunch or Qalculate. ;)
@@Graeme_Lastname I can hardly manage with high school physics but I think it is clear that a steady acceleration for 6000 years in earth's proper time means that we must be all travelling now very very close to the speed of light with an apparent mass that probably exceeds the total energy of the universe. And of course needless to ask where our energy came from and who was pushing us all these years!
i doht understand much of you videos but watching them anyway makes me feel smarter
Flat earth is nonsense. Well, I have learnt something this week.
This is the best video of equivalence principles so far that is accurate and explain correctly
Most of the youtubers describe object fall because the time and space is in our future yeah that’s make sense.
but we do not know if we our falling or not that’s the rule of equivalence principles in short distances
so it is a misleading to say object fall because our time and space is in future because we do not know if really the object falling or not in a small region space
Acceleration flat space and time is only to discribe the curvature of gravity since acceleration is indistinguishable to gravity
Oops, she missed out on a million clicks by leaving "flat earth" out of the title.
It comes up in a search for "flat earth", so she still might get some visits from Flerfdumb.
@@govshill4557 Thank you for doing Flat Earth searches so we don't have to. I guess?
I read your book. I’ve recommended it to others. Frak. I think I’m in love.
The Flat Earthers are most likely just having fun to see who believes their mind poop. I’d not take them seriously at all. 😀
Thank you! I’ve been saying this for a while. I hate it when people feed the troll and waste their time debunking this obvious nonsense. The only way to deal with the obvious troll that is the flat earth society is to ignore it. I was hoping for a great video, but instead I get flat earth debunking :/
Agreed. They simply want attention.
Nothing like shadow boxing is there?
I agreed with that until November 2016. I believe some people can be that dense, and the consequences can be extreme. ...whether or not there's some degree of trolling going on, it's a worthy context for a discussion.
@@YayComity Take the many, sad, historical cults as an example of what many, many folk can believe with absolute certainty, no matter how ridiculous.
sabine you have at least 1 subscriber who has learned all he know about physics from your youtube channel frankly it's interesting.
Never argue with the flat earth society.
As soon as you start arguing with them it looks like if they have something
serious.
Anyway, most 'serious' FE'rs think that the FE Society is a NASA/Elite front organisation. Really.
Almost at 100k for this channel . Let’s get it !!
Oh puhlease. Everyone around the globe knows the Earth is flat.
I fell down my steps. The steps did not come up to meet me. 10 weeks in a boot. Thank you Dr Sabine.
So. "Gravity" requires concepts to curve. Got it. Sounds like a warped concept to me.
You made my day in under 12 seconds.
congrats on 100.000 subscribers!
Thank you for this video! I was confused since a time when some of my physicist friends told me about the elevator illustration of the equivalence principle and I devised two thought experiments that could distinguish gravity from acceleration in a closed box. That can’t be done with a localized point particle, however. Your videos always help!
I do try watching other channels, but there isn't anyone else as cool as Sabine.
Lucas Boninsegna Try professor dave.
Say what you want about flat earthers, but they are the greatest marketeers of the world. For every one of them, they get a few million mentions on the internet every year.
I'm profoundly impressed by this approach, more so even than Sabine's charcteristically clear and succinct explanation. Typically, explanations for a general audience over-simplify things and therefore can become subject to abuse as pseudo-science. IMO, "one step deeper" in almost all cases adds valuable scientific perspective. Sabine found a way to start with the over-simplified abuse, motivate us to understand it and the next level, AND simultaneously show how it disproves the pseudo-scientific position. All in less time than I can write these five sentences.
Quite apart from the flat Earth discussion: People tend to talk about time seconds and minutes after the Big-Bang as if it could be measured in the conventional way, where you have a standard against which you can calibrate clocks. It would be most interesting if you made a video explaining what physicists really mean by time at that stage.
Thank you for pointing out that it is measurable differences in g that kill this flat earth "model" and not the earth reaching the speed of light as is often claimed by debunkers.
This notion of an accelerating earth is actually a good thought experiment for reference frames, time dilation, and length contraction.
My mistake: Dear Sabine, I'm not really qualified to correct you but I think I heard you saying relating to gravity not being a force but actually representing the longest path between points on a curved space - I think it should be the shortest path... at 7:15 you worded it a bit differently about longest path in proper time so maybe there's something I am missing
No, what Sabine said is correct. Free falling particles in GR follow the path with the greatest proper time.
@@Nickesponja thanks. That indeed was above my level. I misunderstood what she was talking about
Could you explain in a further video what gravititional time diletation has to do with objects falling down?
They are linked by the constancy of the speed of light to all observers. Try some gedankenexperiments!
Nice video ! Good to know that a serious scientist like Sabine also visits sites like flat-earth just to see what kind of argumentation they use. We all agree I guess that Earth is round, but sometimes it can't hurt to seriously re-think stuff we 'know for sure' but is not as easily fact-checked as a round Earth (satellite optical footage should convince anyone). Take for instance the 'equivalence principe'. Albert Einstein derived a few brilliant gems from this principle, but there are limits we may not have recognized. Take the 'equivalence relation of: E=MC2. Everyone knows that this means energy and mass are 'equivalent'. Or does it? Mathematically sure, the terms left and right of the '=' sign equal out. But does that physically mean energy and mass are 'interchangeable'. Really? Let's look at the formula Distance (space) = Time * speed. Does this mean that given a certain speed, time and distance are equivalent? After all, if we take more time, then obviously we get more distance. Now, we humans living in spacetime have a much better feel with the terms like distance and time instead of mass and energy. And so no, we would be inclined to say space and time are not 'equivalent'. But fundamentally both formula's are not different.
Now lets for a moment assume mass is not physically equivalent to Energy, anymore then Space is to time. Let's in stead assume for a moment Energy is equivalent to the inverse of Space. Application: look at our big bang universe. Before the big bang there was infinite Energy now there is little energy left and infinite Space. That sounds like a lot more logical 'equivalence relation does not it? If we take the in-product of our cosmos' energy and space (as in inversed energy) we get a constant of 1 , which only would be 0 (zero) at the time of inflection at the big crunch. Digital...entropy expressed in information terms that is...hmm. And what about mass being the inverse of time? Application: If we say a particle A has 4x more mass than particle B , that would mean it has 4x more inversed time (as a particle property), which would lead to the logical conclusion it would take as 4x more time to yet change its speed. Make sense? See how we can make the 'spacetime alien' terms Energy and Mass more accessible this way?
So now, lets take this a step further and combine the two; suppose in the subatomic realm distance is expressed in ENERGY and the clock is expressed in MASS. Lets take our spacetime formula of distance (space)= time * Speed. What do we get if we replace space with energy and time with mass ?? the formula becomes E=M*speed . Speed is now expressed in Energy/Time= Joules/kg or in spacetime terms Nm/kg= s2/m2 or C2. So the entire speed formula becomes; E=MC2 at the subatomic scale. Evidence? well there are 2 instances where we know we cross the subatomic (sub Planck) scale, namely during nuclear fusion or fission. During the very short moment right before nuclei merge (or separate) they must cross the sub-Planck region. So if there is a separate speed formula as described above it needs to be eminent right here. And we KNOW that at these instance E=MC2 arrises. Case proven! Just as we thought we knew every thing.....
So no, we all need to be careful with 'equivalence principle' . this one got us fooled for 100 years...And the community is still NOT ready to accept failure...
I have to say watching your videos is a highlight of my week. You have a remarkable ability to take a complex topic, break it down and explain the concepts in 8 - 10 minutes. It is a talent that many do not have, well done and please keep it up.
A fabulous explanation of Einstein's thoughts between special and general relativity....great job!!!
The comment at the 5:30 minute mark gave me a great idea: Would a disc be stable if it was large enough? or would the pull at the edges be too strong? Is there a mass distribution at the edges that allows for a solid disc that is way beyond (many orders of magnitude, think something bigger than a galaxy) the hill sphere?
Equivalent Exchange
is my favorite law of physics.
It comes from the fruit of the Locacaca tree follows the same principles of "equivalent exchange" as the grounds of the Higashikata estate; they are capable of granting anyone who eats it "something" by taking "something else" from them. The most faithful example of this concept is when the old man uses the Locacaca fruit to regrow his lost leg in exchange for his eyesight, both of his eyes transforming into stone and breaking apart soon thereafter. Apparently this process can be repeated as long as someone has a fruit, continuously sacrificing random parts of their own bodies in order to gain back what they had given in the previous instance.
Whether or not a leg and eyesight are equivalent is not an objective thing that you could determine by doing an experiment, so that's not a law of physics at all.
Nickesponja it is objective that’s why he has 4 testicles
Constant acceleration is an exponential curve (speed), while rotation is a goniometric. But cos(x) + i sin(x) = e^ix. Does this relation show an equivalence between linear accelleration and centrifugal accellaration?
At about 7:15, did you not mean to say the "shortest path"?
Re Einstein’s silly elevator/chest gedanken for supposed equivalence.
1. Hanging wts will hang parallel in accel, but will converge if in gravity.
2. Clocks will tick at same rate in accel, but will tick differently if at different altitudes if in gravity.
3. Photons crossing the room will all remain horizontal in accel, even tho the ray of light curves down, but photons will not remain horizontal in gravity, they will have a slope parallel to the curved traject if in gravity.
Re 3. Einstein’s elevator/chest gedanken for the equivalence of a curving ray of light in accel & in gravity ignores this lack of equivalence. If we apply Einstein’s gedanken to the bending of light passing a star then no photon passing a star would ever fall below the mid-line of the star. Hence there would never be a focus, hence there could never be an einstein ring, or even a part-ring.
Every one of Einstein’s gedankens is wrong. His prediction of the doubled bending of light passing the Sun is a lucky guess. Likewise his prediction of rings. Likewise his prediction of Shapiro Delay. None of these are a legitimate prediction of any of his gedankens.
The only remnant of his GTR is the slowing of light near mass, confirmed by Shapiro Delay. We need to find the real cause of Shapiro Delay.
If i am kind i can give Einstein credit re the doubled bending of light passing the Sun. But we know that a mysterious half of it is due to Shapiro Delay (Dicke). Hence we need to find the cause of the other mysterious half (hint)(it is due to a psuedo-ballistic bending).
Re 2. I should add that all kinds of clocks must be affected differently by altitude & by velocity. Tests show that some atomic clocks behave nearnuff as per GTR. But we will find that GTR does not apply for most kinds of clocks, eg tuning fork & balance wheel clocks.
I want to ask a question related to the equivalence principle that has been bothering me for a while. I understand that inside an elevator that is accelerating upward in gravity-free space, the situation is equivalent to a uniform gravitational field directed downward. But how about the space-time inside the elevator? Is it flat? Then how is the bending of a light ray explained? Is it curved? Then how does its curvature differ from the curvature of an actual gravitational field that is always non-uniform?
7:13 But why? Shouldn't the point particle with mass also curve spacetime around it dependant on the mass of it? Why should 2 point particles with different masses then take the same spacetime path?
Because of isostatic compensation (mountains are typically made of lighter material than other areas, and have deep roots of this lighter material), the local gravity vector actually typically is deflected _away_ from mountain ranges. (In other words, mountain ranges typically have less mass than would be there if they weren't there, and thus slightly repel a plumb-bob.) I believe the British first found this out when they were surveying India and the Himalayas.
I'd like to hear a psychologist explain this phenomenon. Understanding this thought process might help explain why the world's political systems are flat.
It should be listed as a mental illness. And also religion.
I think you ommited a much better, and much more easily demonstrated piece of evidence: gravitational pull works towards the center of the Earth, and that's how we can show the locality of the equivalence principle. That fact is best seen on long bridges, where two distand pylons are not parallel to each other, with the tops farther apart than the bottoms. On flat Earth, it would make no sense to construct pylons that don't stand up straigh, and yet engineers do that all the time.
Would you please comment on the assumption, referred to by Einstein, that the speed of light is the same in all directions? Is this related to the equivalence principle? Calculations of the speed of light have always been made from the time taken for a round trip, and would yield the same result whether the speed is c in both directions or, in the extreme case, c/2 in one direction and infinite in the other, or any intermediate combination?
We've all experienced equivalence when we sit side by side to another train at a terminus station. When one train moves, we're not sure if it's us moving or the adjacent train. We can also see why this doesn't work if we're on platform 1 and a train moves on platform 12.
@Sabine Hossenfelder Quite bad example of Equivalence principle w/ elevator on planet because if you say locally in flat space-time, you contradict yourself. If you say planet, then there is central force, and therefore if you take two point masses next to each other in elevator, it will seem to us as some magical force between them, they would "attract" because of central force and you can definitely say it's due to gravity not acceleration (therefore 2:24 till 2:40 is wrong). You can fix this by saying that by "Locally in flat space-time" you mean in a small region and for small amount of time (preferably infinitesimal), or mention Eötvös' experiment. Also I have a question, we know that inertial and gravitational mass are mutually proportional (under right system of units are equal). We can assign mass (corresponding to energy) and therefore gravitational effect to E&M field, what do you think about that?
The observation that gravitational field strength varies also explains why atomic clocks tick at observably disparate rates from one location to another (gravitational time dilation). Doesn't this mean that John Stewart Bell should have employed a gravitational path integral to account for the inevitable decoherence of otherwise entangled particles as they speed apart in the presence of arbitrary gravitational gradients? Had he done so, doesn't it follow that the presumptive hidden variable would not have vanished, but would have yielded a non-vanishing "beat frequency" term arising from any time-varying term in the presumptive hidden variable. Or to put it another way, isn't time itself at the root of any hidden variable?
I think the best way to put it is: one cannot build an accelerometer that isn’t at the same time affected by gravity. Thus, we have to accept whatever an accelerometer ascribes 0 acceleration to as true inertial frame, while someone standing on the Earth is clearly accelerated. However, we’re not being accelerated upward, but outward, and this only makes sense if space is contracting at the same time. In a way, flat Earthers are on to something, they just don’t realize that one can make sense of outward acceleration without the planet blowing up.
4:12 "The Acceleration also differs between the equator and the poles. This can and has been measured..." It must be a very small effect compared to other differences between the equator and poles. Has this affect really been measured? Can you provide your source?
Sabine, there's a we2 trendy channel called Dialect which tries to reintroduce notions like the Ether. I know you're an extremely busy person, but I think it would be amazing (and educational) if you addressed those ideas in minutiae.
What astounds me is despite evidence people profess an actual believe in the Earth being flat, I often wonder if they actually believe that or are they posturing for effect and shock value, and that some how its fashionable.
In 3:20 you mention that general relativity is locally flat, which means it can not describe the singularity inside a black hole and it doesn't. My question is, is this shortage in GR caused by principle of equivalence not being true any more or is it caused by quantum mechanics becoming significant in the singularity? My point is, to make a theory of quantum gravity, shouldn't we first fix our theory of gravity to work in a singularity?
Thank you Sabine, As clear as mud but covers the subject, makes sense to me, I once told a flat earthen that they were misinterpreting or misusing the science, there’s an old saying , if you can’t dazzle someone with brilliance, baffle them with BS.....I love your lessons, and your beautiful...stay well !!
Thanks lady, It's a good and easy explanation of a such complicated subject.
I like what Einstein said about curvature of space and Time but I always go back to Boyd Bushman on his experiment where he slowed down the electrons and caused time and gravity to slow down.
I am wondering if the equivalence principle also applies to the magnetic force - if my body was made of iron
and I was near a big magnet of negligible mass I would feel a force indisdinguishable from gravity unless
I was accelerating towards the magnet when I would feel "weightless".
I don't give a shit about what flat earthers are saying, I'm here for the equivalence principle
Dear Sabi, weak equivalence principle equalizes between geometrical entity and gravitation. Therefore gravity is expressed as curvature in space time and GR established. That's okay but that don't mean gravity can not be expressed as a force. So if gravity is a force then a mediator has to be found. Physics called it graviton. Physicists collide with the principle "you get what you are expected". Is that interesting?
Sabine, if you throw an apple with your right hand away at the speed of light and another apple with your left hand away at the speed of light, what is the speed these 2 apples are moving away from one another?
So so good. I will be watching this many times over
I really like all your explanation ma'am, love from one your one of the fans/students
I like your teaching style mam .
You are great
I have great respect for you for even bothering to read any of the flat earth nonsense. I hope that the flat earth proponents get to see this video. It amazes me that contemporary people can hang on to such things.
Well, look at the hundreds of years it took to accept the globe theory and changing the POV from being the center of the universe. They killed people over that heresy. crazy
One can say energy and gravity have equivalence, since gravity is still present during a gravitational collapse and all that mass is converted to energy. To say that energy warps space/time is true in its waveform. It also warps space/time outside the waveform of the radiation itself. This seems to be the production of space itself, the gravity field given off by light energy.
I remember watching this a while back. Then most recently I stumbled on Andre Fuzfa and I'm about to read his paper. He talks about Einstein's Equivalence Principle so I came back here as a refresher. Now I'm wondering if I should respect the flat earthers more based on what Dr. Sabine Hossenfelder is saying if flat earthers is using say the Universe as a reference, wouldn't the Earth be a localized area in that respect, so wouldn't they be right? Lol, sorry I've been out of school for a couple years now.
Nice video and presentation.
An observer’s perception to his situation do not and cannot use to define how the universe operates or behave in the way it is. Especially not for observers who perform more mind experiments than apparatus based research.
But can you accelerate forever?
Once you get close to the speed of light and your acceleration slows down, do you still experience the same acceleration because of time dilation?
Can you do a video on your Master's thesis?
"Particle Production in Time Dependent Gravitational Fields"
This is so good. Thank you, you're the best explainer. I've read a whole stack of general-reader-level physics books, and I never understood about the elevator thought experiment being the logical leap between SR and GR. I really need more maths so I can read real physics books. I did sign up for Brilliant in hopes of getting some, but it seems to be mostly comprised of various brain-teaser puzzles. Anyway, cheers and stay safe. You are superb and I'm a big fan.
Hey Chief! Just wondering if you've gotten around to reading more physics books! I hope so! You should go ahead and read Einstein's work on GR and SR if you've haven't-even if you don't quite understand the maths yet. It is still very valuable! He gives an incredible train example for explaining...well essentially causality now that I think about it and really breaks down how and why he came to the conclusions he did and explaining it in a way that can be (mostly) understood by a lay-man. Also no one ever mentions his amazing sense of self-deprecating humor. Trust me pick up the 50th anniversary copy, you won't be sorry.
Always a joy to watch.
these guys, are pulling off the longest trolling scheme thus far in the modern world. These, alongside those other spaggetti-monster worshipers. Love them both.
Sabine always stunning the audience with her awesome fashion and immense knowledge!
Go get 'em Sabine, but this is one very tough windmill to tilt at.
Many videos say gravitational force is an illusion quoting Einstein, but you come with that term for explaining.so is there a force involved?
Mass inertia is a mutual holding of those units which - according to Ernst Mach - are dynamic phenomena that extend into the entire cosmos. Well observe the short term super inertia, this is the basis of the Overuniti principle of Rotoverter and was first discovered by Max Planck. "It takes a certain amount of energy to move anything at all." He stressed that this finding is far from being fully understood and can only be considered provisional. Planck did not find any evidence of a parcel nature to be inferred from this. However, if harder blows are applied, the mass is temporarily inert, ionized and evaporates. See A-bomb.
A glaring gap in knowledge is, not to register asymmetry of any inertia-bond. See Lorenz contraction, low inertia in the direction of travel, increased at right angles.
Next glaring mistake is not to recognize, gravity is only a small compression of inertia-mediating structures, but just that?s why clocks tick slower near mass-concentrations.
Nice handling of the topic :)
The problem of "locally" is that it's theoretically an almost infinitely small volume of space. Space is always curved, everywhere, so this principle never actually applies.
It's kind of how thermodynamics talks about "isolated systems", even though the only truly isolated system is the universe itself (which we can only observe a tiny part of, anyway).
The example of the elevator, for example, is false. Within an elevator, the gradient of gravity means you can measure whether you're being accelerated or whether it's the presence of gravity.
Your feet will be more strongly accelerated towards the Earth than your head, and you could theoretically measure this difference.