# Time dilation difficulties

1. Sep 15, 2006

### QuantumKing

Ive been wondering about time dilation, and how it effects different observers.
If an observer1 is in motion, in a frame of reference relative to an other observer2 at rest, observers1 and 2's measurements of time will differ from one another, observer1 will experience a slower time than observer2. would you agree with me that observer1 perceives to be at rest, and perceives observer2 to be in motion, but doesnt that mean observer2 should have a slower time then observer1? as well?....and another question i have is, when the clock tics slower, for an observer in a frame of reference, moving uniformly, nearing the velocity of light, does the observer experience a "slow motion" feeling? like if he were to move, would he feal as if he is a state of sluggish movement?

thanks

2. Sep 15, 2006

Last edited by a moderator: Apr 22, 2017
3. Sep 15, 2006

### Galileo

This point is exactly why they say time is relative, i.e. it depends on your point of view, or more precisely, it depends on the inertial reference frame you are in.
If you say observer1 is at rest, then you are saying we are looking at things from the inertial frame in which observer1 is at rest. Thus we are measuring length and time with rods and clocks that exist in this frame. Form that viewpoint, observer2's clock indeed goes slower than our own.
However, the same argument holds for observer2 and observer1's clock goes slower, but this is when we measure things from the inertial frame in which observer2 is standing still.

So there is no contradiction here. Whether observer1's clock is going slower than observer2's or the other way around depends on your frame of reference. You can even choose a frame of reference in which they both have the same speed (going in opposite directions). Then they will both go at the same rate (but slower than the clock in your system).

Ofcourse, if they want to compare their clocks, they have to come together and stand next to eachother. For this, at least one of them has to accelerate (and change his inertial system). This will eventually make the real time difference between their clocks. The one who accelerated will have exerienced less time going by than the one who did not accelerate (this can be shown).

Ofcourse no-one ever experiences a slow-motion feeling. You are always at rest wrt yourself, so you experience no time dilation.

4. Sep 15, 2006

### QuantumKing

thanks, that clears things up...i ran into this "difficulty" when i thought of two observers with identical stopwatches, one observer is in motion relative to an observer at rest...the observer in motion will have a shorter time, for a certain event ,then the observer at rest when they compare their times...if both observers appear to be moving with the same velocities..why is one specific time shorter? i couldnt figure that out..lol