How does time dilation work?
Just rewatched Christopher Nolan’s masterpiece **Interstellar** for the umpteenth time, and I still fail to understand the concept of time dilation, can anyone explain it to me like I’m 5? Or like I’m a recent high school graduate who made a B in AP Physics?
In: Physics
Okay, first of all, the most fundamental thing you have to accept in order to grasp this:
Your everyday perceptions and intuitions of “time” are wrong.
You are accustomed to the idea that there is a steady, consistent, and universally equal flow of events. Event A happens, then event B happens ten seconds later, then event C happens ten seconds after that, etc.
It turns out – based on a very large number of observations that we’ve made – that the universe doesn’t actually work that way. It is close enough *at our scales* that the “linear, consistent, constant” model works just fine for humans almost all the time, and works for animals literally all the time – so that is the intuition that we’ve evolved to have.
But at other scales – notably, when things are *extremely* “big” or “fast” or “energetic” by our standards – things don’t work like that.
The *sequence of events* is different for different “observers”. These don’t have to be literal observers, by the way – you can designate a rock as an “observer” here.
One observer might say: event A happens – 10 seconds pass – event B happens – 10 seconds pass – event C happens.
Another observer might say: event A happens – 5 seconds pass – event B happens – 5 seconds pass – event C happens.
Even the *order* of events can be different. Yet another observer might say: event C happens – 10 seconds pass – event B happens – 10 seconds pass – event A happens. Another observer might say “events A, B, C happen simultaneously.”
And there is no “true timeline” – these observers are all exactly equally *correct*. It’s not just an optical illusion or something like that (those certainly exist but are a different matter). In those people’s reference frames – in a certain sense, in their *realities* – each is correctly observing and recording the sequence of events.
Time dilation is one specific – and “common” – example of this. It’s when different observers measure the “times between” the same events as being different.
Let’s say you stay at home and your friend leaves and comes back. You look at the clock and find they’ve been gone for 1 hour. They believe they’ve been gone for only 5 minutes. And this isn’t just them being mistaken. Their watch has only measured 5 minutes. Even if you look at their cells, at their very atoms – every part of them has only experienced 5 minutes. Because in their frame of reference, only 5 minutes have passed. That’s what we call “time dilation” – there’s a mismatch in experienced duration.
This doesn’t mean time has no rules, of course, or that just anything can happen. For example, if two observers are at the same point in space and time, they will always agree on any observations made *right there*. It just means the rules are a lot more complicated than your intuition might tell you.
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