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
Blankets reflect light which enters your eye and is absorbed by your retina.
Space can transmit light, but doesn’t reflect it.
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.
It also doesn’t help, our understanding could be wrong. The idea of curving spacetime isn’t compatible with quantized gravity. Until we further understand what’s going on, GR in it’s current form is the best we can do. Both theory and experiment have stalled.
I think what happens is that our brains want us to see things as we expect them to be, flat and static in the way we assume the universe operates. It’s like natives of New Guinea calling airplanes “birds”. The mind turns one thing into another in order to understand it. So we do see curved space, but we understand it only by seeing it the way we already understand things. A planet moving back and forth must actually be moving forward, then backward, which of course cannot happen, but there it is up there right in front of our eyes.
What explains the pull of gravity on planets not causing the planets to continue moving towards the object crating the gravitational force?
Basically why isn’t everything pulling into the sun…even if the gravitational force of the sun isn’t powerful enough to automatically draw everything to it shouldn’t the lack of friction or opposing force cause objects to continue on due to the force of the motion they’re experiencing?
I’ve never understood the explanations of gravity and I have always loathed the ball in the sheet theory/explanation.
I don’t think we understand gravity at all. I think we figured out how to manipulate it but I don’t think we actually understand it.
Imagine you’re an ant and you’re walking around on a globe. You walk long the equator, following the straight line. You’re fairly happy that this is a straight line. You then turn 90 degrees and follow a line of longitude. You’re also fairly happy this is a straight line (other than the bit at the poles where you needed to go round the stick that the globe rotates about, of course).
Your mate is also an ant, and he decides to take a walk on this globe as well. You both agree to start on the equator and walk north but on different lines of longitude. You’re happy that you’re both walking in straight line that are parallel, and therefore you’ll stay exactly the same distance apart forever. This is why you and your mate get *very* confused when you bump into each other at the North Pole. You give it another go. You even swap lines. Both of you are *adamant* that you’re walking in straight lines, and that your lines should be parallel, yet they’re always meeting at the pole.
So this is what *curvature* is. An object moving through a curved space thinks it’s moving in a straight line — and in a way, it really is — but the way in which the space is curved causes it to behave *weirdly* and you get effects that you can’t explain. In the case of our ants, they’re walking in straight parallel lines yet the curvature of the Earth means they meet at the pole. In the case of our universe, light travels in straight lines but the intense gravity of black holes curves space so much that we can actually see stars *behind* them and the light appears to be curved. In both cases, we’re not really observing the curvature itself — that’s like our ant being able to step off the globe and view the entire thing as a whole, which it can’t really do — but we can definitely observe the evidence (the weird things that don’t make sense) that curvature is happening.
Take a entheogen. You’ll see the fabric of space time bending. LSD or the right mushroom will do the trick.
Magnetic fields are invisible, too, but they can also be bent. One way to demonstrate that is by holding a compass close to an electrical circuit carrying charge. The needle of the compass will stop pointing north and realign with the wire so long as the power is turned on. It’s important to remember that when we talk about “fields”, “bonds”, and “the fabric of spacetime” those words don’t refer to material objects, they are analogies that describe how objects interact with each other
Find a star in the sky, but make sure when the sun comes around that it comes in front of it blocking your view. Then wait for a total solar eclipse, go to totality where the sky will be completely dark. Now the star that would have been blocked by the sun’s presence, and not just its light since it’s dark, that star might be visible. It’s light will visibly curve around the sun.
Gotta say I don’t really like all these posts saying that you can see it. Effects, sure. Yes, light shows it pretty well, but you are still looking at light, not spacetime.
I think its worth to point out that the idea of space, or in the more modern thinking of it, spacetime, is our creation. Its not just any random creation, yes, its one that works really really well. General relativity has been tested to hell and back. But its just our depiction of reality. Its what we think is going on.
Anyway. Its not the only thing we cannot see. Infrared for example. Sure we can see it with the equipment. We evolved to see certain stuff and without the help we are oblivious of everything else.
But yeah, I think it also comes down to the fact that spacetime is special in a way, different from everything else we interact with.
Latest Answers