why time moves differently while closer to a massive body?
In: 50
A few people have referenced the rubber sheet. I prefer to think of space-time as a sponge. Picture a decent-sized sponge. Like the size of a coffee table. This is a representation of space-time. Cut a hole and put a grain of sand in there. Doesn’t do much. Now squeeze a bowling ball into the middle of it. All the sponge surrounding it gets squished. This is space-time getting compressed – it’s displaced by the mass of the bowling ball (or, in real size, space-time is displaced by the mass of the earth). That’s how I visualize space-time getting squished in 3D.
Now, picture a big 3D grid in the sponge. The distance from one space on the grid to the next is a unit – let’s call that one light-year. Based on Einstein’s theories, *the speed of light* is the constant. No matter how squished those boxes of the grid are, nor how stretched they might get – regardless of how far apart they might seem, it *ALWAYS* takes a beam of light one year to cross a unit. That’s the key to why time slows down. But let’s get one more example to visualize this.
Let’s just say that one unit is the width of the entire United States. Light going across that one unit moves pretty fast to get across it. And remember time changes, so we can’t really use units of real time, and we can call it whatever we want, but for now let’s call that distance across our reference year. Now, let’s squish that one unit that crosses the entire United States down so that it’s the distance to your neighbor’s house. Because it’s still one unit, just squished, it’s STILL one light-year across – *it will take light the same amount of time to cross the original US unit as it does to cross to the next-door unit*. That’s one unit of space-time, just squished – even though it’s just to your neighbor’s house, *it’s still one year*. *Light still travels at the same speed in both*. *So light still travels the same distance in both*. Light needs to cross both of those distances *in the same amount of time, because they’re both one unit across*. How can light possibly go “one unit” which are both different “sizes” (just one is squished) in the same amount of time? One way would be for light to speed up – but that’s not possible – *the speed of light is a constant*. The other way, as impossible as it may seem, is that light slows down. It’s harder for light (really, time) to travel, because the “sponge” here is so dense, it’s been compressed. So the time moves more slowly in this compressed area of space-time – the “next door year” has to move slower than our “reference year” to end up in the same place at the same “time”.
Hope this helps!
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