3 ms·

Same. The only path I see is to really learn GR (and the requisite differential geometry) and do lots of examples. I never got far enough to grok it.

FrenchAmerican 5y ago
I feel that I sort of get it - after listening to many many podcasts by scientists trying to make it understandable. It took me years. And still I may be wrong, so please consider what follows as an essay. My first major step was to really understand that gravity is a law and not a force. This is totally counterintuitive since we feel gravity as if it were a force, and because many people use the expression "force of gravity". So a mass should be viewed as a "tag" that an object has - and the higher the number on the tag, the higher it deforms the space-time around it. My second major step was to understand that all objects, for example planets, always go straight along a line. They appear to have an orbit because they move in a space-time that is deformed by other planets and mainly stars or black holes. The moon goes along a straight line in its space-time. But the latter is deformed by the mass of Earth so it looks to us living in Earth's space-time that the moon is orbiting around Earth. The third major step is to understand that the two space-times mentioned (the Moon's and Earth's) are not "related". Someone on the moon lives in a different space-time than someone on Earth. So the duration of time that person lives on the Moon as measured by an atomic clock he/she brought will diverge with an atomic clock on Earth. The difference won't be huge, in truce very very small - but measurable. Everyone of us lives in its own space-time. Because the gravity is not equal on the point of Earth surface. Because of mountains, and because the Earth itself is not homogeneous, and because we move around and up and down all the time. In final, this means to get rid of two related notions that appear so self-evident that it is almost impossible to really get over with: - there is a common 3D space that we all share ; - there is such a thing called time that is totally independent and flows continuously. What really exists - for each person or object or planet - is its own space-time. And all these space-times are unrelated to each other. The proof of it is that there is a maximum speed limit to any existing thing. That maximum speed does not vary whatever are the speeds of two considered space-times. The only thing we know that reach that maximum speed happens to be the light in space. If the two space-times were related, then the speed of light would vary if one space-time is moving in a different direction and/or speed relatively to the second considered space-time. But it doesn't. So you and me don't share the same space-time. So, between two encounters, we won't have lived exactly the same duration of time. Our personal atomic clock, if synchronized at the first meeting will have diverged when we meet again. Of course, the difference will be so super small that it's unnoticeable to us (but measurable with today's technology). GPS satellites orbite at around 36,000 kms from Earth. That's far enough to make GPS calculations quite wrong if Einsten's relativity is not taken into account (by around 50 meters). That is noticeable. By the way, Einstein deeply regretted his poor choice of words. Because its theories of "relativity" precisely demonstrate that the different space-times are NOT related. We need to understand that space and time don't exist. Only unrelated space-times co-exist, within which time as we feel it flows at a different pace than in other space-times. But there is only one "Reality", right? Well... that really depends what we mean by that. The only common point among space-times is the respect of causality. That sort of reinstates time as we feel it. If A causes B, then B can not precede A. In a sense, events creates time as we know it. After all, we are all very often surprised by the time it is on our watch. So this "unstoppable Time that flows no matter what" that we think as self-evident in our representations ... just doesn't match our very variable perception of time in our lives. Isn't it weird that we commonly consider obvious a notion that contradicts directly our daily experience of it? Maybe it is time to reconsider the way we teach physics at school ; we learn Newton's laws and then we are supposed - much later if ever - to unlearn it in order to grasp Einstein's relativity. Some will argue that Newton's laws are good enough for our daily lives. Well... not anymore since we use GPS all the time. And Newton's law can't explain Mercury's orbit either so why are we taught Newton to explain the orbital system when 1 planet among 9 contradicts what we are taught? Science is by principle a work on ourselves to deconstruct reality as we perceive it spontaneously, through our senses, our biases and also the inherited paradigms from the established Science. It is super difficult to unlearn. If you play tennis for years without taking lessons, it is super difficult to train our body to unlearn the bad habit and learn the proper way taught by a professional. So maybe let's stop calculating where will land a cannonball without even taking into account the effect of the air! This is not even a practical teaching of everyday life since the major effect of air on the cannonball is obliterated to teach us Newton's laws that are not totally true either. Let's learn Einstein first. That the nucleus of an atom is 100 000 times smaller that the atom ; that no graphical representation of a nucleus composed of neutrons and protons is possible ; all these illustrations with agglomerated spheres of different colors are ... just wrong. Phycists don't know how to represent a nucleus, which is not a static thing but rather something that is animated by opposite forces but kept close by a vastly superior force. Physics is like History. We keep on learning at school things that we know to be at best approximate and very often just plain oversimplification that leads to misrepresentations that are super difficult to correct. Hence the so many Russians, including Putin himself, considering that Ukraine and Russia are historically one nation. Totally ungrounded but war nonetheless.
- MathMonkeyMan 5y ago
  Fascinating essay, thanks for putting all of that down. You have thought about this plenty. The only thing I'll add is that all objects live in the same spacetime. The metric of that spacetime is a mathematical object that obeys known laws under coordinate transformations, and the parameters of those transformations depends on the energy momentum tensor (likewise an object that transforms...). Trouble with GR is that the "trivial" solutions are heavy shit. So it goes.
- kristov 5y ago
  Teaching anything when the student doesn't want to learn is a bit futile. I was taught physics at school. I am actually interested in physics now, and I am finding the historical progression, the story behind the move from an older model to a newer one to be very enlightening. I was taught this way at school but I just didn't understand it and wasn't interested enough to pay full attention. I think there is value in telling the historical story of physics, just only to interested students.
- edmcnulty101 5y ago
  Yes! That's fascinating and thank you for writing that. It expanded my knowledge. You should put that in some sort of linkable format. However, think about insane it sounds. Like if we didn't have the subject physics or if you had to explain it to a medieval king in the 1300's. They would think we are totally insane. Because it is different than what our everyday hairless monkey lizard brain sensory organs are reporting to our brains. That's why I struggle with it. Cool example of satellites. That actually grounds it in an understandable example. Also does relativity discount Newton? Or can it be viewed as an extension? > Physics is like History. We keep on learning at school things that we know to be at best approximate and very often just plain oversimplification that leads to misrepresentations that are super difficult to correct. I think all of science is like that. It's continually advancing and changing our views of the universe which is beautiful. Im going to tell my boss next time I'm late that I'm not late it's just that our space times are subjective and aren't currently synchronized.

FrenchAmerican 5y ago

I feel that I sort of get it - after listening to many many podcasts by scientists trying to make it understandable. It took me years. And still I may be wrong, so please consider what follows as an essay. My first major step was to really understand that gravity is a law and not a force. This is totally counterintuitive since we feel gravity as if it were a force, and because many people use the expression "force of gravity". So a mass should be viewed as a "tag" that an object has - and the higher the number on the tag, the higher it deforms the space-time around it. My second major step was to understand that all objects, for example planets, always go straight along a line. They appear to have an orbit because they move in a space-time that is deformed by other planets and mainly stars or black holes. The moon goes along a straight line in its space-time. But the latter is deformed by the mass of Earth so it looks to us living in Earth's space-time that the moon is orbiting around Earth. The third major step is to understand that the two space-times mentioned (the Moon's and Earth's) are not "related". Someone on the moon lives in a different space-time than someone on Earth. So the duration of time that person lives on the Moon as measured by an atomic clock he/she brought will diverge with an atomic clock on Earth. The difference won't be huge, in truce very very small - but measurable. Everyone of us lives in its own space-time. Because the gravity is not equal on the point of Earth surface. Because of mountains, and because the Earth itself is not homogeneous, and because we move around and up and down all the time. In final, this means to get rid of two related notions that appear so self-evident that it is almost impossible to really get over with: - there is a common 3D space that we all share ; - there is such a thing called time that is totally independent and flows continuously. What really exists - for each person or object or planet - is its own space-time. And all these space-times are unrelated to each other. The proof of it is that there is a maximum speed limit to any existing thing. That maximum speed does not vary whatever are the speeds of two considered space-times. The only thing we know that reach that maximum speed happens to be the light in space. If the two space-times were related, then the speed of light would vary if one space-time is moving in a different direction and/or speed relatively to the second considered space-time. But it doesn't. So you and me don't share the same space-time. So, between two encounters, we won't have lived exactly the same duration of time. Our personal atomic clock, if synchronized at the first meeting will have diverged when we meet again. Of course, the difference will be so super small that it's unnoticeable to us (but measurable with today's technology). GPS satellites orbite at around 36,000 kms from Earth. That's far enough to make GPS calculations quite wrong if Einsten's relativity is not taken into account (by around 50 meters). That is noticeable. By the way, Einstein deeply regretted his poor choice of words. Because its theories of "relativity" precisely demonstrate that the different space-times are NOT related. We need to understand that space and time don't exist. Only unrelated space-times co-exist, within which time as we feel it flows at a different pace than in other space-times. But there is only one "Reality", right? Well... that really depends what we mean by that. The only common point among space-times is the respect of causality. That sort of reinstates time as we feel it. If A causes B, then B can not precede A. In a sense, events creates time as we know it. After all, we are all very often surprised by the time it is on our watch. So this "unstoppable Time that flows no matter what" that we think as self-evident in our representations ... just doesn't match our very variable perception of time in our lives. Isn't it weird that we commonly consider obvious a notion that contradicts directly our daily experience of it? Maybe it is time to reconsider the way we teach physics at school ; we learn Newton's laws and then we are supposed - much later if ever - to unlearn it in order to grasp Einstein's relativity. Some will argue that Newton's laws are good enough for our daily lives. Well... not anymore since we use GPS all the time. And Newton's law can't explain Mercury's orbit either so why are we taught Newton to explain the orbital system when 1 planet among 9 contradicts what we are taught? Science is by principle a work on ourselves to deconstruct reality as we perceive it spontaneously, through our senses, our biases and also the inherited paradigms from the established Science. It is super difficult to unlearn. If you play tennis for years without taking lessons, it is super difficult to train our body to unlearn the bad habit and learn the proper way taught by a professional. So maybe let's stop calculating where will land a cannonball without even taking into account the effect of the air! This is not even a practical teaching of everyday life since the major effect of air on the cannonball is obliterated to teach us Newton's laws that are not totally true either. Let's learn Einstein first. That the nucleus of an atom is 100 000 times smaller that the atom ; that no graphical representation of a nucleus composed of neutrons and protons is possible ; all these illustrations with agglomerated spheres of different colors are ... just wrong. Phycists don't know how to represent a nucleus, which is not a static thing but rather something that is animated by opposite forces but kept close by a vastly superior force. Physics is like History. We keep on learning at school things that we know to be at best approximate and very often just plain oversimplification that leads to misrepresentations that are super difficult to correct. Hence the so many Russians, including Putin himself, considering that Ukraine and Russia are historically one nation. Totally ungrounded but war nonetheless.

MathMonkeyMan 5y ago
Fascinating essay, thanks for putting all of that down. You have thought about this plenty. The only thing I'll add is that all objects live in the same spacetime. The metric of that spacetime is a mathematical object that obeys known laws under coordinate transformations, and the parameters of those transformations depends on the energy momentum tensor (likewise an object that transforms...). Trouble with GR is that the "trivial" solutions are heavy shit. So it goes.
kristov 5y ago
Teaching anything when the student doesn't want to learn is a bit futile. I was taught physics at school. I am actually interested in physics now, and I am finding the historical progression, the story behind the move from an older model to a newer one to be very enlightening. I was taught this way at school but I just didn't understand it and wasn't interested enough to pay full attention. I think there is value in telling the historical story of physics, just only to interested students.
edmcnulty101 5y ago
Yes! That's fascinating and thank you for writing that. It expanded my knowledge. You should put that in some sort of linkable format. However, think about insane it sounds. Like if we didn't have the subject physics or if you had to explain it to a medieval king in the 1300's. They would think we are totally insane. Because it is different than what our everyday hairless monkey lizard brain sensory organs are reporting to our brains. That's why I struggle with it. Cool example of satellites. That actually grounds it in an understandable example. Also does relativity discount Newton? Or can it be viewed as an extension? > Physics is like History. We keep on learning at school things that we know to be at best approximate and very often just plain oversimplification that leads to misrepresentations that are super difficult to correct. I think all of science is like that. It's continually advancing and changing our views of the universe which is beautiful. Im going to tell my boss next time I'm late that I'm not late it's just that our space times are subjective and aren't currently synchronized.