# The Earth warps the space around it but... **URL:** \ **Category:** Factual Questions\ **Created:** [January 11, 2018, 7:29pm UTC](https://boards.straightdope.com/t/the-earth-warps-the-space-around-it-but/806417 "2018-01-11T19:29:34Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 12, 2018, 3:12pm UTC](https://boards.straightdope.com/t/the-earth-warps-the-space-around-it-but/806417/21 "2018-01-12T15:12:00Z")
If you’re looking for an easy-to-visualize picture which incorporates both the curvature and spacetime, in a way that your brain has evolved to be able to grasp, then I’m afraid you’re out of luck. Most humans are only easily able to visualize three dimensions: It is possible to visualize more, but it’s very difficult to train yourself to do it, and it might be necessary to start the training when you’re very young and your mind is still flexible. So to start with, you need at least two dimensions of space for the orbit itself. You could get away with one, but that means you’re going to need to find some other way of representing an orbit, and you’ll have to train yourself on that, too (though this is probably a bit easier than training yourself to visualize more dimensions, it’s still likely to take a few years before it’s really intuitive). Then, the way that we usually think of curvature is extrinsically, which means we need another dimension to show that. We could instead think of curvature intrinsically, but now you need some other way to represent curvature on our visualization. And then you need some way to represent time, and we’re out of dimensions to do it with. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [January 12, 2018, 9:12pm UTC](https://boards.straightdope.com/t/the-earth-warps-the-space-around-it-but/806417/22 "2018-01-12T21:12:53Z")
> [@blood63](#): > > Ok, I get that. > I cannot get how light can move against the fabric of space. If the road is curved, the car can only follow the road no matter how fast it is going. There is no “off road” in space. A car has tires and steering and friction. Instead, imagine rolling a frictionless bolling ball at high speed along a [banked, circular track](http://dynref.engr.illinois.edu/avb_3886159972_71e0dc52d8_o_600.jpg). If you get the speed just right, the ball will follow the curved track thanks to the banked surface. If you roll the ball too fast, it will travel off the outer edge of the track. If you roll the ball too slow, it will follow the bank down and end up crashing on the inner edge of the circular track. If you didn’t roll it at all and instead just set it down on the track, it would start rolling down the banked surface straight toward the center of curvature. All of this holds for an object in orbit around a planet. (1) Stationary: fall straight down to the planet. (2) Moving too slow: follow a curved path that crashes into the planet. (3) Moving at just the right speed\*: follow a curved path that meets itself after a full circuit around. (4) Moving too fast: follow a curved path that never bends enough to actually loop back around; escape the planet. Light is in category (4) for earth. [sub]\*or range of speeds in the case of elliptical orbits[/sub] ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [January 12, 2018, 11:05pm UTC](https://boards.straightdope.com/t/the-earth-warps-the-space-around-it-but/806417/23 "2018-01-12T23:05:15Z")
> [@Pasta](#): > > A car has tires and steering and friction. Instead, imagine rolling a frictionless bolling ball at high speed along a [banked, circular track](http://dynref.engr.illinois.edu/avb_3886159972_71e0dc52d8_o_600.jpg). If you get the speed just right, the ball will follow the curved track thanks to the banked surface. If you roll the ball too fast, it will travel off the outer edge of the track. If you roll the ball too slow, it will follow the bank down and end up crashing on the inner edge of the circular track. If you didn’t roll it at all and instead just set it down on the track, it would start rolling down the banked surface straight toward the center of curvature. > > All of this holds for an object in orbit around a planet. > (1) Stationary: fall straight down to the planet. > (2) Moving too slow: follow a curved path that crashes into the planet. > (3) Moving at just the right speed\*: follow a curved path that meets itself after a full circuit around. > (4) Moving too fast: follow a curved path that never bends enough to actually loop back around; escape the planet. > > Light is in category (4) for earth. > [sub]\*or range of speeds in the case of elliptical orbits[/sub] Whilst this is correct, I feel it muddies the water as in this example it is gravity and not the curvature of the banked track (modelling gravity) that causes the difference in trajectories for balls with the same initial position, parallel velocities, but different speeds. The point is that the rubber sheet analogy is actually quite a superficial one. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [January 12, 2018, 11:26pm UTC](https://boards.straightdope.com/t/the-earth-warps-the-space-around-it-but/806417/24 "2018-01-12T23:26:45Z")
> [@PlaceboTarget](#): > > I’m back to clarify my befuddlement. I really miss Isaac Asimov and his ability to explain complex concepts in simple statements. > > In Newton’s model, space is distinct from body and time passes uniformly, where space and time are flat dimensions. > > In Einstein’s model, space and time become intertwined, and spacetime gets pushed, pulled, stretched and warped by matter: “matter tells spacetime how to curve, and curved spacetime tells matter how to move.” > > Visual explanations in nowadays mass media do not use the idea of gravitational force but that of ‘tracks’ in spacetime caused by large objects: light seems to bend near the sun due to the curbs and twists in the fabric of spacetime. > > Of course these visual representations only show the space. How does time change things? When we use [Minkowski’s diagram](http://www.elektromania.net/default.asp?tid=622), a satellite’s trajectory around Earth turns from an ellipse into an elliptical spiral. > > But when Earth wraps the spacetime frame around it, this spacetime wrapping is constant in time no matter how minute. Either the ‘tracks’ one can see in visual explanations of nowadays mass media are real and light has to follow them when passing by our planet or these ‘tracks’ is just a way of putting things and in fact the force of gravity and the speed of light are all that matters. The reason it works in spacetime but not space is an object’s orientation in spacetime is dependent on its speed (through space), whereas an object’s orientation in space is not dependent on its speed. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [January 12, 2018, 11:32pm UTC](https://boards.straightdope.com/t/the-earth-warps-the-space-around-it-but/806417/25 "2018-01-12T23:32:25Z")
> [@blood63](#): > > Ok, I get that. > I cannot get how light can move against the fabric of **space**. If the road is curved, the car can only follow the road no matter how fast it is going. There is no “off road” in **space**. Bolding mine. To add to the above, I’ll reiterate a core point that is lost in many explanations that is also missed here. The problem is that all of the simple visualisations - either rubber sheets, or diagrams of space that is distorted implicitly (or sometimes explicitly) imply that the geodesics are curved **space** , and thus there is a “road” to follow in **space**. As noted a few times above this is not so. The geodesics are in space and time - **spacetime**. The idea of following a curved **spacetime** geodesic does not get you a single road in space. You can _perhaps_ think of the curvature in space as depending upon how long it takes you to traverse that part of space. In the limiting case - something travelling at the speed of light - you get one extreme of the paths to be taken in space, but at slower speeds the curvature of space and time means the path in space seen is different, and we can do things like go into orbit. The path in _spacetime_ is the same for all objects. Perhaps remembering that all objects traverse spacetime at the same speed - c - the speed of causality - would help. Light travels at c, it does not travel in time, all of its speed is only in space, and so it doesn’t see any curvature in time, only space. A still object in space travels at c as well, but since it is not travelling in space it must travel at c in time. So it only sees curvature in time. (Which is why gravity affects the passage of time). Anything travelling at slower speeds than c in space is travelling in time as well as space, and they see a mix of the curvatures in time and space that depends upon their speed. There is no one curvature of space, only spacetime. [Previous page](https://boards.straightdope.com/t/the-earth-warps-the-space-around-it-but/806417.md?page=1)