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Gaussian97
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I particularly like the following video:
Have you studied Newton’s laws? Objects do not need a push to move. They need a push to change their velocity. No force is required for an object to continue at constant velocity.paradisePhysicist said:Anyway, I have heard the explanations of how mass bends spacetime, creating a geodesic path for objects to move through, but what I don't get is how this actually creates gravity. What is actually pushing the object to move through the path in the first place?
Gaussian97 said:I particularly like the following video:
Oh. So far I have watched Flatland, but the movie Sphereland seems elusive, website is down. I see a physical copy of it for $24.95 on Amazon but maybe there is someway to rent it.jbriggs444 said:I was actually thinking of the book. It has been so long since I read it that I do not remember whether it was Flatland or Sphereland. But it got me to the point where I could wrap my head around curved space and higher dimensional geometries.
Hmm it won't let me access without a login.ergospherical said:If you have access through your college / other, familiarise yourself with the geodesic hypothesis.
https://aip.scitation.org/doi/10.1063/1.522416
Ibix said:It is tautological. This by @A.T. is much better:
Gaussian97 said:I particularly like the following video:
My original statement was implying that time is the result of location.stevendaryl said:Orbiting means that its location changes as a function of time.
I read some of that but I will try to read it again more in detail later.Dale said:If spacetime were flat, then yes. It is the curvature of spacetime that allows different parts of the Earth to be continually accelerating away from each other without getting further away from each other. Did you read the link I cited earlier? I really tried to walk through the origin of these concepts. No math is involved, but it is a verbal description of the actual theory and not a handwaving “rubber sheet” thing.
I don't have the energy for that right now but maybe later when I have more free time. Was hoping for also an easier explanation that didn't require hundreds of pages...ergospherical said:mate my advice would be to go buy/borrow/steal yourself a nice general relativity textbook, or if that's not possible then read through the notes of tong/carroll/blau/etc. (i.e. you've got the enthusiasm, but at some point you've got to back it up with a solid understanding of the basic principles )
No. Consciousness has nothing to do with it. (Nor do I understand how you could get the idea that it does from that video.)paradisePhysicist said:Assuming this video is true, my hypothesis is that consciousness is what causes gravity. The object deciding to accelerate is caused by consciousness going forward.
It's not time that is curved, it's spacetime. Spacetime has 4 dimensions.paradisePhysicist said:If time is 1 dimensional, how can it be curved?
Your basic intuition here is correct, but you need to change your definition of what constitutes a "turn". In GR, a "turn" is non-geodesic motion, i.e., non-freely-falling motion (motion in which the object feels weight), which is the correct generalization to the spacetime case of the intuitive notion of "moving in a straight line" that you are using here. So what requires a "push" on the object is non-geodesic motion through spacetime.paradisePhysicist said:lso, in order to turn an object (like a car on a turn) you need fuel. A turn is simply when motion in one dimension is converted to motion in a different dimension.
If what is pushing on the object is a rocket engine or something like that, then yes. But in the case of the Earth, what is pushing on the object is a huge static configuration of matter in hydrostatic equilibrium. Such a configuration can push on an object on its surface without having to expend any fuel.paradisePhysicist said:So in order for an object to convert its time momentum to spatial momentum, there seems like fuel is required.
paradisePhysicist said:Assuming this video is true, my hypothesis is that consciousness is what causes gravity.
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My original statement was implying that time is the result of location.
paradisePhysicist said:Seen that. Seems tautological, it just replaces space movement with time movement, but doesn't explain what is causing the forward momentum in time in the first place.
It takes at least two dimensions for curvature. But it isn’t time that is curved, it is spacetime that is curved. Spacetime can curve in the time direction, but it is still 4D spacetime that is curvingparadisePhysicist said:If time is 1 dimensional, how can it be curved?
Try my explanation then. It is only a few pages. In the meantime please don’t speculate. The whole consciousness thing is silly.paradisePhysicist said:Was hoping for also an easier explanation that didn't require hundreds of pages.
Not one way, reverse process is possible. Say you throw a ball upward, it goes slower, stops at the top, goes down faster and comes back to your hand. All through the trajectory is geodesic and called free fall even when it is going upward, or called, more properly I think, in free motion.sawer said:but I imagine even it is geodesic, it is line, why does it have to be just one way on the geodesic, even my free falling stopped?
mitochan said:Not one way, reverse process is possible.
My original understanding (or lack thereof) was that the object was moving on the geodesic, through space time, then when it collides with the Earth most of the object is still moving or at least trying to move, except for the parts of the object touching Earth.PeterDonis said:Second: Objects that are not being pushed on by something (the Earth's surface, a rocket engine, etc.) move through spacetime on geodesics, i.e., freely falling worldlines. Such objects feel no weight; they are weightless, like astronauts (and all other objects) on the International Space Station. (This, btw, shows that not all geodesics near the Earth are falling towards the Earth; there are others that are orbits around the Earth.) Note that such objects are not "accelerating" in the sense in which that term is used in GR (the more precise term is "proper acceleration").
Third: Objects sitting at rest on the Earth's surface are being pushed on by something: the Earth. That's why such objects feel weight--because they aren't moving through spacetime on geodesics.
A curve is produced when a function uses x input to change the y output. Are you saying that some dimension of space, let's say z, changes the t output of time? Or maybe that t changes the output of z? Z refers to the vertical dimension of earth, the surface normal pointing up.PeterDonis said:It's not time that is curved, it's spacetime. Spacetime has 4 dimensions.
"Time curvature" is just a way of saying that the effects of spacetime curvature for an object sitting at rest on the Earth are the result of moving through spacetime in the time direction, not one of the spatial directions.
A plane follows a geodesic to save on fuel. I guess what's confusing is when a plane chooses not to follow a geodesic, the plane doesn't automatically experience a force compelling it to follow the most geodesic trajectory, which would rubberband it back to the most optimized trajectory. Or at least that's of my current understanding of how planes operate.PeterDonis said:Your basic intuition here is correct, but you need to change your definition of what constitutes a "turn". In GR, a "turn" is non-geodesic motion, i.e., non-freely-falling motion (motion in which the object feels weight), which is the correct generalization to the spacetime case of the intuitive notion of "moving in a straight line" that you are using here. So what requires a "push" on the object is non-geodesic motion through spacetime.
It was merely a hypothesis I said. The hypothesis I said, that consciousness caused time momentum, was meant to support the Einstein gravity theory.stevendaryl said:Are you trying to understand General Relativity, or had you rather just make up your own theory? Physics Forums is not the place for the latter.
Perhaps this did muddy the waters, but I was only trying to offer a suggestion as to why time moves forward. I was not trying to contradict the Einstein theory but offer an explanation of why it works. My first statement, that time was simply the result of location, was meant to merely offer a new perspective of time, not to be presented as a proper theory. But in the future I shall not post any more speculations on here about such matters, if that's what you desire.stevendaryl said:If you are trying to ask questions about how a theory works, then don't interject your own theory. That's just muddying the waters. And a general rule of thumb is that you try to understand existing theories before you venture to make up your own. You don't make up your own theory because you can't be bothered to understand what people have already learned.
I plan on reading this explanation of yours today. I shall also not post any more speculations on here about such matters.Dale said:It takes at least two dimensions for curvature. But it isn’t time that is curved, it is spacetime that is curved. Spacetime can curve in the time direction, but it is still 4D spacetime that is curving
Try my explanation then. It is only a few pages. In the meantime please don’t speculate. The whole consciousness thing is silly.
paradisePhysicist said:I was not trying to contradict the Einstein theory but offer an explanation of why it works.
I am going to look into reading Dave's theory on the matter, then watch all of the Flatland movies, then maybe read one of the chapters of the books mentioned, after that if I still don't get it I plan on maybe giving up on this for a few weeks.weirdoguy said:How can you offer any meaningfull explanation if you don't even know and understand this subject on a technical level? What for? It's a waste of time - primarily yours. You could use this time to try to learn technical details.
During the collision, yes, the object will in general not be rigid; its shape will deform. If the collision is hard enough, the object's shape when it comes to rest on the Earth will still be deformed, but once it has come to rest its motion in the new shape will again be rigid; it won't deform any further once it has reached its new equilibrium shape resting on the Earth's surface.paradisePhysicist said:when it collides with the Earth most of the object is still moving or at least trying to move, except for the parts of the object touching Earth.
Yes; the closer you are to the center of a large massive body like the Earth, the slower time flows for you. Or, to be more precise, the slower your proper time (the time according to the clock you carry with you) "ticks" as compared with the proper time of someone very, very far away from Earth. (I am assuming here that both observers are at rest relative to the Earth.)paradisePhysicist said:A curve is produced when a function uses x input to change the y output. Are you saying that some dimension of space, let's say z, changes the t output of time?
Neither does an object in spacetime. Gravity is not a force in GR.paradisePhysicist said:when a plane chooses not to follow a geodesic, the plane doesn't automatically experience a force compelling it to follow the most geodesic trajectory
You should not try to do this with a theory you don't understand. Before you even try to explain why a theory works, you first need to understand how it works.paradisePhysicist said:I was not trying to contradict the Einstein theory but offer an explanation of why it works
paradisePhysicist said:I watched this video again, the animation seems to show gravity causing gravity, like the Earth is using free energy and pulling the fabric of space inwards.
Unfortunately I don't think this video's final representation, the one it claims is new and improved, is useful; rather, it is misleading. The best representation the video actually gives is in the middle, the one with the grid all around the Earth and clocks at each point of the grid. It does not, however, show the clocks closer to the Earth ticking slower than the clocks further away, which is the crucial point of looking at things that way. All you would need to add to that is a rule that the worldlines of objects in free fall bend towards the region where the clocks tick slower.paradisePhysicist said:this video
Say a ball falls and bounce back from the floor to make a reverse motion. Falling ball is along a geodesic and the going up ball is along another geodesic because momentum is given from the floor and free motion is interrupted then. This shows that reverse motion is not going backward along the geodesic, from future to past, but transfer to another geodesic starting with reversed velocity.weirdoguy said:Still, even in that case - geodesic is a curve in spacetime, not space, and everything is "moving" only one way along it.
Gaussian97 said:I particularly like the following video:
So basically the 2D sheet with a dent or hill is actually a better representation of the spatial geometry than those distorted grids, because it has more surface area than a flat sheet would have. But spatial geometry doesn't explain gravity.A.T. said:You cannot correctly show the curved 3D space around a mass with a distorted 3D-grid that is embedded in non-curved 3D space (the illustration). The shown distorted 3D-grid still encompasses the same total volume as would a non-distorted 3D-grid with the same outer boundary. But in actual curved 3D-space around a mass there is more spatial volume enclosed than in flat space of the same outer boundary.
Movies... *pffft*. Kids these days.paradisePhysicist said:Oh. So far I have watched Flatland, but the movie Sphereland seems elusive, website is down. I see a physical copy of it for $24.95 on Amazon but maybe there is someway to rent it.
A.T. said:It's good that they point out the issues with the rubber sheet analogy. But I have issues with this video too:
- The animation at 7:00 makes it look like the spatial geometry is changing with time, which is wrong.
jbriggs444 said:Movies... *pffft*. Kids these days.
Understanding is the goal. A visual understanding is not.paradisePhysicist said:On a more serious note though, I think the movie will be easier to visualize since its already visual. On the other hand, the book may be so well written that it is easy to visualize also.