I need help with an analogy here because I simply don’t know/can’t visualise the true physics here.
Many people use an analogy for gravity acting on space-time as a sheet of material stretched across a plane and a heavy object in its center acting as a celestial body.
This is great for envisioning orbits, the curvature of spacetime and so on.
Now this is a “2D” sheet/plane that deforms “downward” in the 3rd dimension, I get it… But how does it translate to the actual universe? The universe is always 3D in all directions, isn’t it?
I’m stuck here guys, science help me!
In: 81
Our perception of the universe is always 3D, but that doesn’t mean the universe only exists in those 3 dimensions.
I suppose one way to help visualize the difference is to imagine what the 2-dimensional perspective the ball will have as it moves in the sheet example. As far as the ball cares, its momentum and movement is trying to carry it through a straight line in its 2D space and plane of existence. If limited to only 2 dimensions, it can’t visually observe the 3rd-dimensional feature that’s affecting its movement (the indention in the sheet), its possible to measure and record the effects, it can even write laws and predict on how it will move around that point in its 2nd-dimensional space. It can do plenty of things, even when limited to 2 dimensions. But, as long as you are confining it to a 2D existence, it will never be able to observe the 3D feature that is affecting its 2D motion in its 2D existence.
That’s what’s going on here with gravity and spacetime. Our observations are limited to the scope of our dimensions. Spacetime in itself is a dimension we can only experience and measure in only singular points at a time. When we say something is bending spacetime, what we are really saying is “at this specific point in space, at this specific time of existence, this particular point in our dimension is bent.”
Once a single moment passes, that point in space is a different point in the dimension that is spacetime. If there happens to be a large mass near your point of spacetime, that mass can distort your spacetime in the form of gravity. In fact, if there’s enough mass and enough gravity, your sense of space and time can be distorted. You can’t observe the distortion of spacetime affecting your 3rd-dimensional existence, but it is possible to measure and record how you are affected. We even write laws and can predict how your 3rd-dimensional movement through spacetime will be affected by such distortion. We can do plenty of things, even when limited to 3 dimensions. But, as long as we are confined it to a 3D existence, we will never be able to *observe* observe the 4D feature that is affecting your 3D motion in your 3D existence.
Latest Answers