Eli5: How does gravity affect time, dumb it down for me as much as possible
In: 286
TL;DR Gravity pulls EVERYTHING, and Time is a thing.
Sun’s gravity pulls Earth, Earth’s gravity pulls Moon, Moon’s gravity pulls ocean, you know this already.
Gravity also pulls the space BETWEEN stuff, and because space and time are connected just like anything else in the universe, that means it also pulls time. Let’s use an analogy (and yeah, this isn’t really how it actually works, but this is ELI5, not askScience):
Draw two Xs on a trampoline, we’ll call those points “start” and “end”. Now find the shortest path between them, we’ll call that the “race track”. Measure the length of the race track (which is a straight line), let’s call that the “race length”.
The speed of light is a constant, no matter what. It doesn’t matter what you do to light, light will ALWAYS go the same amount of fast if it’s traveling through the same stuff.
Speed = distance / time, you also know this. Let’s call that formula the “fast formula”.
Let’s make light run a race along our race track from Start to End. It’s going to take time – not a lot of time, but time.
Now put a bowling ball in the middle of the trampoline. Start and End didn’t move, because we didn’t erase them and the draw them again: they’re still exactly where they were, but the space they were on is getting pulled by the bowling ball now. Measure the race length along the trampoline’s surface again. It’s a little bit longer now, because even though we could draw a straight line between Start and End, that line wouldn’t be touching the trampoline anymore (it would be going through a different dimension). We can’t go that way (or if we can, we haven’t figured out how yet), we have to stay on the trampoline.
Let’s make light run the race again. It’s still going from Start to End, and it’s running along the same race track. How long will it take now?
Remember, light is ALWAYS the same amount of fast. That means that light’s speed without the bowling ball is the same as light’s speed with the bowling ball.
So, speed (no ball) = speed (yes ball).
Remember our fast formula: Speed (no ball) = distance (no ball) / time (no ball). Easy math, you know how to do this.
Let’s look at the fast formula for the second race.
Speed (yes ball) = distance (yes ball) / time (yes ball).
We know that the speed from each race is the same and that the race length got bigger when we added the ball, so let’s rewrite the fast formula.
Speed (no ball) = Speed (yes ball) = “distance (no ball) + gravity pull” / time (yes ball)
If the top of the fraction got bigger and the result stayed the same, that means the bottom of the fraction had to also get bigger, right? Let’s rewrite the fast formula again.
Speed = “distance + gravity pull” / “time + something”
We know that something had to make the bottom bigger, but the only “something” we changed between the two races was adding the bowling ball. We didn’t change the stuff light was running through to get from Start to Finish, we just pulled the race track a little and made it longer.
Let’s assume that gravity DOESN’T affect time. If the ball’s gravity didn’t pull on time, the speed of light would have changed, because it ran a longer race in the same time. But that can’t happen because light is always the same amount of fast, so the ball’s gravity must have also pulled on time.
Speed = “distance + gravity pull” : “time + gravity pull”
Everything in the universe is constantly moving at c (The speed of light) through spacetime.
This speed is split between movement through space and movement through time, but it always adds up to c. (Movement through space + Movement through time = c)
The more of this total speed you allot to move through space, the less you are using to move through time.
Photons (light particles) move at the speed of light through space, and so do not move through time at all, 100% of their speed is allotted to movement through space.
Gravity warps space in such a way that it takes light longer to traverse it.
The speed of light is a universal constant, so if it takes light longer to traverse that warped space, then time has to move slower.
Here’s an example:
We have a 50ft hallway and it takes you 10 seconds to walk across it.
I press a button which increases the gravity in that hallway enough to warp the space inside of it substantially(Ignoring the fact that you would be crushed by said gravity).
When you walk across the now spatially warped hallway, something weird happens. From my point of view outside the warped space, instead of taking 10 seconds it takes 20.
The hallway is still only 50ft long, and you went at the same speed, but it took you longer to come out the other end.
When I ask you what happened you say “What do you mean? it still only took 10 seconds.”
If it took you longer to traverse the same distance at the same speed the only explanation is that time was moving slower for you(You were effectively moving in slow motion).
You had to allot more of your total speed(c) towards movement through space than you normally would to traverse the warped space, and due to the tradeoff between movement through space and movement through time, in order to do so you had to take that speed from your movement through time.
EDIT: This is also why it’s impossible to move faster than the speed of light(c), your total speed through spacetime can only ever equal c.
Think of…putting a tarp over several rows of boxes. If something falls onto the tarp as it extends between the rows, the tarp will sag into the space between the rows, and it will cover a smaller area relative to its overall size.
However, the tarp’s overall size has not changed. You would just have to expend a greater amount of energy to travel between any two points on the tarp (because you would have to climb up the other side to complete your journey).
Expending that extra energy means that you’re slower getting up the other side of the slope, because you have to work that much harder to climb.
Thus, it takes longer to travel between two points in the intervening space, *despite* covering the same relative distance.
(this may not be entirely accurate, so feel free to *politely* correct me if I make an error.)
As simple as possible im gonna try!
Need to know what gravity is and what time is.
Gravity
A word used to simplify bending of spacetime.
Time
A metric used to explain different points, like on a line graph.
Gravity can move the points closer together or further apart, like a slinky.
Or
Spacetime can be stretched or pulled closer together, kinda like how plastic wrap can be stretch or squished together.
As far as we know there is no limit on how much it can be squished or pulled apart. We do not possess the technology to do bend spacetime we can only observe it.
Space and time are the same thing called spacetime. So you can’t impact one without impacting the other. So gravity is not just distorting space, it’s distorting spacetime which affects time as well because space and time are not independent things.
Why are they linked? It seems that everything moves through spacetime at the same speed, which is the speed of light. Yes, that includes you, too.
How is that possible? Think of two glasses of water where one represents time and the other represents space. The total amount of water from the two glasses is your speed through spacetime. If you want to go faster through space you have to pour some of the water from the time glass into the space glass and so now you’re going through time more slowly.
What happens when your time glass is empty and all of the water is in the space glass? Now you’re going through space at light speed and so you experience 0 time. You also can’t go any faster through space because you have no more water from time to re-assign.
This is why there’s a universal speed limit (light speed). It’s really just the speed that everything moves at and there’s not really any difference to speed except for how it’s perceived in dimensions of space vs time which appear to be distinct things but actually aren’t.
The easiest way to understand it all is this: In areas where time runs slower, mass tends to gather. You can substitute my use of ‘mass’ for ‘matter’ if it is easier for you.
Space is like, “Time you and I are bros forever”
Time is like, “bro, no cap”
Gravity comes along straight buggin and stresses Space out.
Time is like “hey Gravity! You’re stressing Space out and me and Space are like two sides of the same coin so you’re stressing me”
For those struggling with the idea of space-time, you encounter it more than you think. Imagine you have a meeting at a coffee shop. It’s not enough to know which coffee shop or what time – you need to know how both time and space will be intersecting in order for you to arrive at the meeting. Objects always exist in both time and space.
Think of space and time as a blanket of the two interwoven together.
Now imagine dropping a ball on that blanket, that blanket is going to weighed down and the fabric bent – the ball bent space and time, effectively causing gravity.
[Here is a video to demonstrate](https://youtu.be/MTY1Kje0yLg)
The closer you are to the center of gravity of a massive object, the slower time passes with respect to distant points. So time passes at a slower rate at the center of earth w.r.t. its surface. General relativity exactly describe how to calculate this difference.
Latest Answers