Why does Space-Time curve and more importantly, why and how does Space and Time come together to form a “fabric”?
In: Physics
We find that everyone agrees on a certain measurement between two events, the spacetime interval, ie the time between them squared minus the square of the distance between the two events. (c^2 T ^2 = c^2 t^2 – x^2 – y^2 – z^2)
What does this imply?
Think in two dimensions, say on a square sheet. That sheet has to be somewhat special in that if you stretch it in some direction, it has to squeeze in the other in such a way that the surface remains the same. It sounds like I’m describing a piece of fabric.
Be it tight pants or spacetime, it behaves the same. Stretching it in one direction (space or time) makes the other direction (time or space) squeeze to preserve the overall surface. This is why you can say spacetime has a nature similar to that of fabric
There is an awesome Netflix special on Einstein that explains a lot of his theories and how he arrived at them in eli5 terms. I think they go over this in the first episode….
Everything you can touch is called matter. That matter stuff has mass, which creates gravity. The more mass the more gravity. Big massive things can pull on other things with gravity, and hold them in orbit like the moon orbits the earth. The moon follows a curved path in space. If the Earth were replaced instantaneously with the Sun, the moon would curve even more and crash into the Sun. So gravity curves space.
Time is only realized and measured when things move, like a pendulum clock or atomic orbitals.
If you and a friend set your watches to the exact same time, and you travelled really fast away from them and came back, your watches would have different readings. Time is something you take with you when you move in space. So when you move in space and in time, you are moving in spacetime.
How the fabric is woven is determined by relativity and the speed limit the universe has set upon matter.
Why ? You would have to ask Steven Hawking.
Time is more of an illusion. All it is, is the process of things travelling from point A to B… If there was no universal speed limit, essentially the universe would happen all at once in an instant. But since there is mysteriously a speed limit (the speed of light) in which information can move through space, it has created the illusion of time.
This is why space and time are tied together, because time requires space to exist.
Two questions. I’ll answer the second one first.
You always move through time, but if you move through space then you move through time more slowly. If you move as fast as you can (the speed of light) then you stop moving through time.
Photons don’t age.
Time is different for different things because they move through space differently.
Space is curved because a straight line isn’t what you would think of as straight if there’s an object big enough to mess up the curvature of space in your path.
Let’s say you shoot two beams of light in the same direction, but a meter apart. If space were flat they’d stay a meter apart. But space isn’t flat, so as the beams of light travel, they get closer to each other, or farther away.
Why does it work this way? We don’t really know. But it does.
Reading about these things makes me sad because I used to dream about being an astrophysicist. Then I found out most of them spend all day doing math, not brainstorming about the nature of the universe. Idk why I didn’t consider that this all comes from math and that I would need to be an incredible mathematician to just be an average physicist capable of partaking in the discussion. I’m about to go to school for IT because I like computers and there’s practical job opportunities in that, but I hope I never stop thinking about the big questions and I hope those of you smart enough to do this will answer them some day.
Lots of technical stuff in this thread, which is great, but doesn’t explain like you’re 5. Simplest explanation of space-time is to imagine cutting time into increments, then laying the 3D space on top of itself so it forms a block. As if you take all the individual frames of a film and stacking them, so you get a big pile of individual spatial snapshots that move forward and backward through time as you look up and down the pile. As the aforementioned Einstein Nova said, we are all spaghetti strands moving through both space and time simultaneously.
Curvature is just mass warping this field. Our inability to differentiate between inertia and gravity (is the ground moving us up or is gravity holding us down?) breaks our lizard brains so leave this to the theoretical physisists lol.
FWIW Hawking’s Brief History of Time is surprisingly understandable (at least some of it) to the non-genius out there, recommended.
Note: Sorry if this is already posted, didn’t feel like reading “billions and billions” of posts (RIP Sagan).
The Space-Time Fabric is a **metaphor** used to explain to the space-time curvature and why things get funky around around super-massive objects like black holes.
Imagine space as a 2d plane, in this case a well made checker quilt. You and your friends each grab a corner and stretch it taut. Another friend rolls some marbles across the quilt’s surface. The marble are fairly small and don’t distort the surface as they move across in a straight lines. Now, the friend drops a bowling ball onto the quilt. It’s big and heavy enough that it does distort the surface of the fabric, causing it to bend and curve under the weight of the bowling ball. Some more marbles are rolled across and instead of moving in straight lines, they curve following the shape of the fabric underneath them. You can physically see the distortions in the surface as the straight lines of the checker’s grid are pulled down and twisted.
At this point, things still make sense, as the gravity of super-massive objects like black holes as the same effect on space-time as the bowling ball has on the fabric of the quilt. Where the metaphor sheers is that since space is 3d, the curvature doesn’t appear in a spatial dimension, it appears it time. What that physically means, I am not entirely sure, but it makes the math work out and what little observations we have match the math. I’m not a physicist, so I am out of depth, but hopeful this answers your question.
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