I was looking at how our solar system works and see that essentially the curvature from space and gravity or, lack of creates the movement of our planetary systems. I couldn’t seem to make sense of the details of how space is similar to a fabric and can be shaped in some way.
The example used was the age old blanket with a bowling ball in the center creating a wide curvature leading to the edges of the blanket.
How is this possible but can’t be seen, nor does it cause friction?
In: 2411
We can see the curvature of space time, but not directly. We can see it clearly relative to other things we *can* see with our eyes. Our eyes evolved as a light sensor, not a gravity sensor.
A great example is gravitational lensing. Which is a a phenomenon that occurs when we look at stars *very, very* far away. [In this, we see a star captured multiple times in a single photo](https://earthsky.org/upl/2021/08/2M1310-1714-gravitational-lensing-ESAHubble-NASA-T.-Treu-Acknowledgment-J.-Schmidt-sq-e1630463741865.jpg). But how is that possible…? Because the light from that star has fallen into the well of other massive bodies and has become distorted. In this case, the light that hits the lenses of the telescope was split four ways. This can only happen if the fabric of spacetime can bend. And we see pretty clearly that the massive bodies in space are the ones responsible for that bending.
You can identify lots and lots of things that are useful to us in our environment using light as the data. But even within the light spectrum, our view is incredibly narrow. Ultra-violet, infra-red, gamma-rays are all waves of light that we cannot see. So even though our eyes have evolved especially to process information given to us by light, it can’t even pick up anywhere close to the entire spectrum. Which means that even in an arena where we assume our eyes are pretty good, it turns out our eyes are pretty under powered…
So what do we do when we encounter things that light itself doesn’t really interact with in a way that our minds can perceive? Usually, light is emitted from a source, bounces off a surface, and the wavelengths not absorbed by that surface bounce into our eyes giving us an idea of the shape, depth, colour, etc. But what happens when the thing you’re trying to observe quite literally has no surface for light to bounce off of? Well, you’re not going to see it that’s for sure.
Well, now you have to find *other* ways of presenting what we see. Curvature of space time is something that we can observe in terms of things we *can* see interacting with it, but we can’t see the curve directly. We only know its there because of other things we can see. If planets are all swirling around around a single point, it’s probably safe to say that there is something going on with that point. We can’t see it, but we know its there, because it’s interacting with the universe around it.
Spacetime, or the curvature of space is not a “thing” per se. So it can’t be seen. With ultra-violet light we can detect it and portray it in a medium we as humans understand, but when it comes to spacetime, we have to resort to somewhat clunky analogues (like your big ol’ blanket with a bowling ball in the centre). It is just a fundamental rule of our universe that anything with mass bends space time, and other things with mass and particles *fall into* the well created by that bend. That is how we know the universe has a sort of “fabric” and that fabric can bend. We have a few ideas of what forces are involved in this, and what its actually made of, but ultimately those questions are far from being comprehensively answered.
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