It’s a bit hard to understand if you don’t know the math but there are lots of explainer youtube videos that you can look for. The first thing to try to understand is the Special Theory of relativity which will explain time dilation. Then once you understand that, understand that standing in a gravity well is exactly the same as accelerating at 1g somewhere in space, and that the time dilation will be the same. Therefore, if you have a clock in a gravity well that is synchronized with a clock outside of the gravity well, your clock will move slower relative to the deep space one. That’s why GPS satellites which are high in geosynchronous orbit need to have the General Theory involved in the calculations.

I realize that’s not an answer to your question. But the key thing to understand is that gravity not only is just like being in an accelerated frame of reference in deep space, it is EXACTLY the same.

Is it kind of like how gravity makes astronauts move slower?

@MakeItSo1701 No. Gravity doesn’t make astronauts move slower. I’m not sure what you mean by that.

Here is a decent video by a guy I trust
https://www.youtube.com/watch?v=XRr1kaXKBsU&t=15s&ab_channel=Veritasium

I watched The Martian and they seem to be move slower in zero gravity. Like things don’t zip around unless they accelerate themselves.

It’s speed that also affects time. If you had twins and one managed to fly a plane at Mach 17,486 (about 2% of the speed of light) for a year without stopping, they’d be about 1 minute younger than their sibling who was hanging out on terra firma.

@MakeItSo1701 It’s not that you can’t move as quickly in lower gravity. It’s that there’s no(t as much) gravity keeping you down, so you might want to be more careful how you move so you don’t bound up in the air. And if you’re in zero-gravity, you probably want to move quite carefully so to not lose control and start floating and bumping into things. Also if you’re an astronaut in a space suit with no breathable atmosphere and your survival may depend on not breaking something, you might just tend to move more deliberately.

Very basically, the time axis is longer (more stretched) around objects with mass (like planets and stars) because the curvature of spacetime is greater.

If you’re far out in space, the curvature is less, and the time you experience is travelling along a straighter (less curved) path.

As you’re in space, the clock on Earth would appear to be ticking slower. Observers on Earth would look at the clock in space and find it is ticking faster.

Were you to be in space and return to Earth, your clock would be slightly out of synch with those on Earth.

Time itself is a constant from your frame of reference and you will always see your clock ticking at 1 second per second no matter where you are.

Trying to explain this in text isn’t the best. There’s lots of good visualisations of general relativity on YouTube.

The space-time continuum is “bent” by the distortion that the mass of an object (star, planet, comet, asteroid, etc) on it.

Gravity is the result (not the cause) of the distortion that mass has on the space-time continuum.

Why is time different for moving objects? What is time?

“The distinction between the past, present and future is only a stubbornly persistent illusion.”
-Einstein

Imagine spacetime as a fabric, and massive objects like planets or stars are like heavy weights placed on that fabric, causing it to sag and curve.
Because of this curvature, time itself is affected, meaning a clock closer to a massive object will tick slower than a clock further away.

@Kropotkin “As you’re in space, the clock on Earth would appear to be ticking slower. Observers on Earth would look at the clock in space and find it is ticking faster.”
– It might appear that way to sensitive equipment, that can measure the very small difference, and that can read clocks from that distance.

Speed causes time to slow, gravity/acceleration causes time to slow. A GPS satellite has a lot of speed relative to a receiver on Earth (add a negative bias factor to its clock relative to the receiver) but it is exposed to slightly less gravity while in its orbit (adds a positive bias factor to its clock). So part of the time calculation in a GPS satellite contains compensation for relativity. The first GPS satellites had a way to turn off that compensation, in case it wasn’t real. It was counterintuitive and had not been proven on Earth by the time those satellites were built. They never needed to turn off compensation. Later GPS satellites did not have the feature to turn off compensation since it was not needed. => relativity works as predicted.

OOOOOO! I get to correct @RocketGuy which doesn’t come up often as he is smarter than me. Speed doesn’t cause time to slow. If you have a clock that is ticking away on your fast moving space ship, that clock is going at exactly one second per second. Same as the clock at rest. But the observer at rest looking at the one at speed it will be going slower.

@Caravanfan – counterintuitive! But the equations actually work.

@RocketGuy Of course they work. But I’m still correct. We will debate this further on our next backpacking trip and we will be smarter than everybody else.

I’m an Engineer. Just give the right equations and I’ll make something useful out of it. For our satellites I’m fascinated that we use the Lorenz equation in two completely different systems to get amazing results – RF amps that generate no noise and ion thrusters.

@RocketGuy According to BBT physicyst, Sheldumb Cooper, @Caravanfan is smarter because he’s a doctor, and you’re “only” an engineer. ;-0

lol! That’s telling him!

Bazinga!