In the case of black holes, lights are pulled into by great gravitational force exerted by the dying stars (which forms into a black hole). If light has no mass, how is light affected by gravity?
In: 784
Gravity doesn’t bend light. Gravity bends the space that the light is traveling through. The light goes “straight”, but the space is bent so that “straight” appears “curved”.
I’ll try a eli actually 5. Draw a straight line on a piece of paper, end to end. This is the straight line that light, and mass, and everything will take. Now pick up the paper and bend it into a curve. The line is still straight on the paper, the paper has just changed shape. If you curl the paper into a loop so the lines touch at each end, now you have an orbit. But the line is still straight. Believe it or not, the earth itself is traveling in a “straight” line, but the space it’s traveling through is curved around the sun.
Gravity bends “spacetime”
This means that the light is following a straight path through curved space.
When we are outside of that “curved space” the apparent bending of light lets us know that the space it travelled through is curved.
It’s because gravity is generally very misunderstood, we still don’t *really* know all there is to know about gravity.
But for why it bends light, that’s because gravity is less a force the way other forces are. For this application specifically, the understanding of gravity as a “force” fails to tell the whole picture. Gravity is instead the curvature of spacetime itself.
If you think of light as a straight line you draw along a sheet of paper, Gravity would be bending that sheet of paper. That straight line is now curved. A black hole would be like a well in that sheet of paper that is infinitely deep, so any straight line drawn on the pieces of paper that line a black hole would all converge into the black hole.
A popular analogy for this would be to think of spacetime as a trampoline. And heavy objects as balls you place on that trampoline. It warps the surface of the trampoline, making it curved. A black hole would be a heavy object that drags down the trampoline infinitely deep.
We thought gravity was like a magnet. Two magnets pull each other closer. In this example, mass would be what makes a “magnet” work. But actually, gravity changes the shape of space, like a ball on a stretched out sheet. Two balls sitting on a sturdy flat surface won’t “pull” each other in. Two balls on an outstretch sheet however, will change the shape of the sheet, causing them to roll towards each other.
Light is a ball that doesn’t change the shape of the sheet, but it still follows the shape of the sheet.
The presence of mass changes the meaning of distance around an object.
All objects follow the shortest path between two points, (known as a “geodesic”).
Because distances between points are now “warped” near the mass, the shortest path between two points is no longer a straight line.
Imagine a piece of paper and draw a horizontal line on it.
Now shape that paper into a cylinder but vertically.
The line itself is still straight but the way you see the line is not straight anymore.
Welcome to the world of spacetime curvature 🙂
gravity isn’t a force. so there is no gravitational pull on mass. This is a teaching lie taught to kids. Granted it is a very useful lie in that gravity as a force is actually applicable in most scenarios. Even a moon landing can be done with just newtonian physics (gravity as a force).
But a slightly more advanced educational lie is that mass distorts space-time and makes everything pass through it bend towards it slightly (depending on the size of the mass and the distance).
this covers the fact that light also is affected by gravity. It also solves the problem of ‘how does gravity affect an object at a distance’
I think the last explanation I saw was that time is distorted a little bit more closer to the mass than it is further away which makes an object that is going straight (even at standstill you have speed since the earth rotates and the entire solar reference frame is moving at speed). the small difference in time means your head has a different trajectory from your feed, causing all of you to experience ‘gravity’.
[this seems to explain it](https://www.youtube.com/watch?v=UKxQTvqcpSg)
Imagine an ant walking on a piece of paper and always moving straight ahead.
If we leave the paper flat it will trace a straight line.
Now bend the paper. The ant still moves straight ahead but “straight ahead” is a different direction then when the paper was lying flat and so it traces a different trajectory. The geometry of what the ant is moving on (or more precisely *within*) influences how the ant moves on it (through it).
Gravity is analogous in the sense that it’s not a force pulling the light in a different direction but a change in the geometry of what light is moving through.
Imagine you have a white piece of paper, a marker and a ruler.
Use your pen to draw a line up against the ruler, when the pen gets half way up the page start moving the page in a direction while keeping the ruler in the same place. Continue drawing up the rest of the ruler length.
From your view you followed the ruler line perfectly straight, but when you check the line on the page it bends half way up and isn’t straight.
Gravity bends space (the page) so if a light passes, it follows the bend in the page.
Latest Answers