# Beginners Virtual Dilation

1. Dec 10, 2004

### Bruninho

Say 2 observers are moving with a constant non-zero velocity with respect to one another. Each sees the others clock running slow but since they both know about relativity they know that the other is infact aging at the same rate as they are. They just observe otherwise. To the layman this begs the question is the time dilation virtual?

For example, say they pass each other and zero clocks at that point. After an hour they both drink a beer. Intuitively, each observer could imagine the other drinking the beer at the same time but they see the other lag behind. Could they then say well, I know he's drinking it, I just can't see it yet? Likewise, couldn't an observer at CERN say well I know that particle has decayed it's just that I can't see it yet?

Once you can accept that both observers see the others clock run slow, an understanding of the twins or any other paradox immediately follows. It seems to me that this is the true "paradox" and the sticking point for many. I'm sure that simultaneity is the key but would appreaciate some help.

2. Dec 10, 2004

### chronon

There is some confusion over this point because time dilation is often presented as being due to the time it takes for the light from an object to reach the observer i.e. I see the clock in a fast moving rocket slowing down because the light takes longer and longer to reach me. This is not a correct explanation of special relativity.

Rather think of observer A, and her friend A' who is 0.8 light-hours away from A, but stationary with respect to her. Because they are not moving with repect to each other, they will be able to agree on the time of events. However, A will see A' s clock as being 48 minutes slow because of the time light takes to travel between them. No one should see anything paradoxical in this.

Suppose now that B comes speeding at 0.8c passing A at 6pm, travelling towards A'. They synchronise their clocks and agree to drink a beer in an hours time. Then when A drinks her beer, B will be passing A' (A and A' agree on simultaneity) who will see that only 36 minutes have passed on B's clock, and so B will still have to wait some time before his beer. Thus it's hard to say that A and B drink their beer at the same time.

A gets to see B passing A', and B's clock saying 6.36pm, at 7:48 pm. Thus what you see depends both on the light travel time and on time dilation.

3. Dec 10, 2004

### Bruninho

Reality

If I was Homer Simpson I'd say what about orange juice but that is the best explanation I've had yet. The use of a third observer really attaches 'reality' to the effect of time dilation. Thanks a million!

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