I vaguely understand that, according to the theory of relativity, because the speed of light is constant, it stays the same regardless of how bent the space is, so time has to pass slower when there is a bend in space – but I cannot apply that understanding to time actually slowing down. All the examples on youtube seem to be understanding something I’m not. I cannot wrap my head around time dilation.
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I do really well with real world examples/visualisations.
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This is something very difficult to explain to most adults, let alone a five year old, but I’ll try!
The truth is, time never “slows down,” but different observers may experience what seems like time passing at different rates. The way you described it is essentially correct: since time and space are linked, at very high speeds the amount of time passing will be very low compared to objects which are relatively stationary. This point is important, since NOTHING is truly stationary in any real sense, except for an observer at any given point. But even to an observer traveling near the speed of light, time will appear to be passing normally. It’s only when they return to a point that has remained relatively still that the discrepancy would be notable.
There actually is a correct yet fairly intuitive explanation.
Everything moves through spacetime at the same rate, it’s called the “spacetime interval”. It has a space component and a time component, but overall a fixed value.
Massless things, like photons, travel at the maximum speed through space, c, and therefore don’t experience time at all (from a photon’s point of view it is emitted and absorbed in the same instant).
Massive things cannot travel through space at c, therefore they have a non-zero time speed. The less space speed they have, the more time speed they have (i.e. “age faster”)
Now to explain WHY that is and to understand the math behind it basically requires a phd.
So Einstein’s explanation in his book ‘Relativity: a Simple Explanation that Anyone can Understand’ was that we only measure time or distance using objects, and if you use objects with relative velocities approaching the speed of light to measure time then they will report time and distance as doing weird things.
This is because the speed of light is determined by the relative electric permittivity and magnetic permeability of a vacuum, which are *laws of physics*, and the special postulate of relativity says that you don’t observe things as obeying different laws of physics just because their velocity is large relative to yours – so they *must* be measuring the velocity of a photon moving away from them as the same as you’d measure it even though this makes them look to you as if time is slowed down for them.
Imagine you’re in a box accelerating through space. Shine a light and observe the path of the light curve because you are accelerating and the light is unaffected by that acceleration, meaning that you observe the moving on a curved path, and an outside observer observes the light moving on a straight path. The two path lengths (they have the same start and end point, but the path changed) are different, and therefore they need to take different amounts of time so that both observers measure the same speed of light. Therefore, the accelerating person experience time slower.
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