5 ms·

Sure, I can explain how to visualise it (I think :) ) First off, a note: lots of people think they know how to visualise GR, but actually don't. For example,

Sure, I can explain how to visualise it (I think :) ) First off, a note: lots of people think they know how to visualise GR, but actually don't. For example, explaining with marbles falling down curved rubber sheets doesn't help, because you're using gravity (the marble being pulled down) to explain gravity. And if you think you can just explain it with geodesics along a curved rubber sheet with a heavy weight in the middle, then think about how to explain why a stationary object falls towards the heavy weight. Anyway, here is how to visualise it: Imagine you are driving a car along some surface. We require that each wheel rotates at exactly the same speed with respect to the surface. Now imagine there is a decreasing curvature gradient from left to right across the path of your car - in other words the surface below the left wheel is curving faster than under the right wheel. Seen from above, the left wheel has extra distance to travel in the vertical direction than the right wheel, to achieve a given horizontal distance. This causes the direction of the car to turn slowly to the left - in other words the car is 'gravitationally attracted' to the left - i.e. towards the region of greater curvature, i.e. towards the attracting mass. To explain why static objects are gravitationally attracted to a mass, you just have to realise that according to Einstein, there are no such things as stationary objects (in some sense). Rather, even a 'stationary' object is travelling rapidly through spacetime. To go back to the car metaphor - the car is not stationary, rather it is always driving forwards (through spacetime). Some notes on this - think about what a bizarre, weirdly-shaped surface the car must be driving over. You can also think of the car front axle as being a wavefront of light. And finally - if you think this explanation is too bizarre, don't blame me, blame Einstein. Personally I don't actually like GR as a theory due to how weird it is.

vagab0nd 6y ago
> For example, explaining with marbles falling down curved rubber sheets doesn't help, because you're using gravity (the marble being pulled down) to explain gravity. Exactly, and it drives me nuts. There are many similar examples in SR and GR that maybe help a layperson intuitively, but creates confusion and frustration when you actually try to learn the theory. I can think of 2: The "escape velocity" explanation of black hole event horizon. Yes, the number comes out correct. No, it does not make sense and does not help me understand how black hole works. "Mass increases when object moves". No it doesn't. And no it doesn't explain why massive particles can't reach speed of light, because in the frame of the object, its speed is zero. I can't tell you how much time I've spent searching for the answers, and drowned by these answers that seemingly make sense.
- ISL 6y ago
  For the latter concern, you may find this Physics Today article from Okun helpful: http://www.hysafe.org/science/KareemChin/PhysicsToday_v42_p31to36.pdf http://www.hysafe.org/science/KareemChin/PhysicsToday_v42_p3...
steve76 6y ago
Special Relativity: It's easier to win a race with a slow stopwatch. You run a 5 minute mile. Other person's fast watch shows 7. Nature doesn't care about your watch. Like a hot water tank it's going to press out everywhere. Nature efficiently takes some energy, slows down it's own watch because it's the easiest way to move. With heat being transferred through the vacuum of empty space between the sun and the earth, it will be really nice to say changing clocks is it's own thermal medium alongside conduction and convention. Now you just need to make it a general principle. Einstein and Brownian Motion: Brownian motion reverses the second law. A bath of particles causing each one to move instead of each particle having it's own little internal thermodynamic engine, like dust in the sunlight. That allows you to apply subatomic principles outside the atom. Nature doesn't care about what we call an atom. Atoms exist because all of the light and heat being radiated already sees them that way. Boltzmann and the Kinetic Theory of Gasses: Modeling an atom, focusing a lens, connecting conductive surfaces, I think of as little soup cans. Ideally, two particles either collide with each other, the walls of the soup can, or nothing else. That way you can just talk in probabilities, 99%, 10%, and put an end for a building block collect-a-thon. Planck and Photons: If you just had thermal transfer on temperature difference alone, closing the door on cupboard full of cast iron pots and pans causes on to be white hot and all the other ones turn as dark as they could be. Planck calculated if it exists, it needs to increase energy before it radiates higher energy. Einstein said you have a start, you have an end, you have a particle. That particle isn't a little cannonball shot out of the atom. More a photo of the entire object at once. Regardless of the intensity focused on one spot, the photon exchange, using time as it's medium, hits the entire photoelectric conductive surface at once, so frequency, the weight of the photon matters, not the intensity or amount per second. Gravity: I think of a film project strip at two different frame rates. Since nature is in the terms of photons and photoelectric effects, I can have one really long frame rate, and one really short frame rate. The Earth's on the slow one. It has to tick, so it orbits. Sun's on the long one, one tick for every 365 of the Earth.
chadlavi 6y ago
isn't it still gravity that keeps the car in contact with the road in your example, meaning it's also using gravity as part of its explanation of gravity?
- gizmo686 6y ago
  In this case, the mechanism holding the car to the road is not relevant. The important part of the visualization is the implication of all wheel rotating at the same speed on a curved surface. Any visualization on Earth would have this problem, because gravity effects the possible configurations you can think of. If it makes you feel better, move the car and road into space and hold them together via magnatism.

vagab0nd 6y ago

> For example, explaining with marbles falling down curved rubber sheets doesn't help, because you're using gravity (the marble being pulled down) to explain gravity. Exactly, and it drives me nuts. There are many similar examples in SR and GR that maybe help a layperson intuitively, but creates confusion and frustration when you actually try to learn the theory. I can think of 2: The "escape velocity" explanation of black hole event horizon. Yes, the number comes out correct. No, it does not make sense and does not help me understand how black hole works. "Mass increases when object moves". No it doesn't. And no it doesn't explain why massive particles can't reach speed of light, because in the frame of the object, its speed is zero. I can't tell you how much time I've spent searching for the answers, and drowned by these answers that seemingly make sense.

ISL 6y ago
For the latter concern, you may find this Physics Today article from Okun helpful: http://www.hysafe.org/science/KareemChin/PhysicsToday_v42_p31to36.pdf http://www.hysafe.org/science/KareemChin/PhysicsToday_v42_p3...

steve76 6y ago

Special Relativity: It's easier to win a race with a slow stopwatch. You run a 5 minute mile. Other person's fast watch shows 7. Nature doesn't care about your watch. Like a hot water tank it's going to press out everywhere. Nature efficiently takes some energy, slows down it's own watch because it's the easiest way to move. With heat being transferred through the vacuum of empty space between the sun and the earth, it will be really nice to say changing clocks is it's own thermal medium alongside conduction and convention. Now you just need to make it a general principle. Einstein and Brownian Motion: Brownian motion reverses the second law. A bath of particles causing each one to move instead of each particle having it's own little internal thermodynamic engine, like dust in the sunlight. That allows you to apply subatomic principles outside the atom. Nature doesn't care about what we call an atom. Atoms exist because all of the light and heat being radiated already sees them that way. Boltzmann and the Kinetic Theory of Gasses: Modeling an atom, focusing a lens, connecting conductive surfaces, I think of as little soup cans. Ideally, two particles either collide with each other, the walls of the soup can, or nothing else. That way you can just talk in probabilities, 99%, 10%, and put an end for a building block collect-a-thon. Planck and Photons: If you just had thermal transfer on temperature difference alone, closing the door on cupboard full of cast iron pots and pans causes on to be white hot and all the other ones turn as dark as they could be. Planck calculated if it exists, it needs to increase energy before it radiates higher energy. Einstein said you have a start, you have an end, you have a particle. That particle isn't a little cannonball shot out of the atom. More a photo of the entire object at once. Regardless of the intensity focused on one spot, the photon exchange, using time as it's medium, hits the entire photoelectric conductive surface at once, so frequency, the weight of the photon matters, not the intensity or amount per second. Gravity: I think of a film project strip at two different frame rates. Since nature is in the terms of photons and photoelectric effects, I can have one really long frame rate, and one really short frame rate. The Earth's on the slow one. It has to tick, so it orbits. Sun's on the long one, one tick for every 365 of the Earth.

chadlavi 6y ago

isn't it still gravity that keeps the car in contact with the road in your example, meaning it's also using gravity as part of its explanation of gravity?

gizmo686 6y ago
In this case, the mechanism holding the car to the road is not relevant. The important part of the visualization is the implication of all wheel rotating at the same speed on a curved surface. Any visualization on Earth would have this problem, because gravity effects the possible configurations you can think of. If it makes you feel better, move the car and road into space and hold them together via magnatism.