Confusing things are easier to understand with an analogy, and time is no exception. We tend to think of time as a road. This way, moving through time (which we don’t understand) is just like moving through space (which we do understand). Just look at how we talk about time: stuff can be in the “far” or “near” future, we look “forward” to things and put the past “behind” us, Friday is “approaching” and June “follows” May.
It wasn’t until this one pretty smart dude came along that we realized this was more than just analogy. Albert Einstein came up with the theory of relativity, which tells us that it doesn’t really make sense to think of space without time or time without space. We’re not moving through space and moving through time—we’re moving through spacetime.
What does that mean? Well, right now you’re moving through spacetime super-duper fast. It just happens that pretty much all of that movement is in the time direction. If you got in a spaceship and rocketed away at half the speed of light, you’d be going so fast in the space direction that you’d be slower in the time direction. When you made it back to Earth, you’d have aged less than the rest of us! (So, if you can’t wait to see who wins the 2018 World Cup, zoom around the galaxy at near-lightspeed for a couple weeks.)
You’re always moving at the same speed through spacetime, it’s just the direction that changes.
But wait a minute. Time is different than space, right? You can move right and left, no problem. But you can only move from the past toward the future, not back. Why?
Well, this is embarrassing. We’re not sure.
Believe it or not, the laws of physics work just as well backwards as they do forwards. The same way you can watch the world through a mirror and everything makes sense, you could watch the world in rewind and all the rules would still work.
Don’t buy it? Imagine throwing a ball up in the air and catching it. Now rewind. Still works. Imagine dribbling a ball. Now rewind. Still works! You could even drop a glass and shatter it and rewind that—if all those shards of glass were thrown together just right, they’d lock together and shoot up into your hand. (Just because it follows the rules doesn’t mean it’s particularly likely.)
It’s actually even crazier than that. We’ve run some experiments where things in the future seem to affect things in the past. We’ve even caught some tiny particles that seem to be traveling backwards in time. The one thing we know for sure only goes forward through time is this thing called “entropy”.
Sort: Trending