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Time dilation analogy. Please tell me if this is accurate.

  1. Mar 20, 2012 #1
    I'm trying to wrap my head around how C could be constant and time can change depending on perspective. I wasn't getting anywhere until I starting thinking of light as water and then I started feeling like I understood it a little better but tell me if this is accurate at all.

    If running water represents light then suppose the universe is like a lake. The lake is full of varying currents running this way and that. There are rocks in some areas causing the water to move faster and areas where the banks narrow causing the water to speed up. Some inlets where the water swirls in and then seems to stagnate. Big open bodies where the water flows at the same speed for long stretches and some whirlpools swirling around. Then there are other forces like wind and undercurrents etc.
    We're like fish. While swimming around we encounter differen't currents but we adapt. If we're swimming along in a stagnant pool and then find ourselves suddenly in a swirling current beside a boulder we have to exert more energy to keep up the same speed. So our heart beats faster and metabolism speeds up along with our brain activity but this actually makes it seem as though the same amount of time is going by since our biological functions have sped up. The water is going twice as fast but our body and mind have sped up to meet the challenge. By our perspective the same amount of time has passed. Once we get out of the fast moving water everything slows down in perfect symetry to meet the new speed speed of the current. If I'm swimming in slow moving water there could be a fish beside me caught in a faster current but he's moving faster and seems to be swimming alongside me.

    Does that make any sense?
  2. jcsd
  3. Mar 20, 2012 #2


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    No. The best analogy to water with regard to light is an absolutely still and very large body of water. The waves on the surface all travel at the same speed. If you drop a pebble in the water, you will see a concentric circle of waves propagating outward from the point of impact. This is a two-dimensional analogy to how light propagates in any Frame of Reference according to Einstein's convention. The only thing you have to remember is that if you put yourself in the analogy, you can't observe the waves with light--you have to bounce the waves off of an object and wait until some of them return to you to have any awareness of the propagation of the waves.
  4. Mar 20, 2012 #3
    Yes, that's why sound is a better analogy than water, because we don't usually directly measure the effects of air (except in the case of wind). Before the Michelson-Morley experiment, many people believed that light waves behaved just like sound waves, meaning their speed was independent of the motion of the source but dependent on the motion of the medium. (Although before Maxwell there was a lot of belief in emitter theories in which light depended on the motion of the source as well.) But then the Michelson-Morley experiment revealed that unlike sound, the speed of light was the same in all inertial reference frames.
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