time dilation and the paradox thingy (1 Viewer)

[serge]

The second last line is wrong. Yes, earth observer is stationary but not because Earth rotates at a constant speed. The Earth is always accelerating due to it's gravitational pull from the sun.

you're right, but the fact is the spaceman's observations are wrong because
he's been accelerating more, or something like that?

 

[Abtari]

The paradox doesn't really exist if you introduce acceleration into it. A better example might be as follows: Imagine two twins, James and Mary, who are in deep space, each in their own space ship. They are both at the sampe point in space and then suddenly, without any noticeable acceleration, the begin to move away from each other at relativistic speeds. In James' frame he sees himself as stationary and believes that Mary's frame is becoming time dilated as she moves away from him. Likewise, Mary believes that she is stationary and that James is becoming time dilated as he moves away from her. This is the important part, that it is impossible tell whether James or Mary is the one who is really experiencing the physical effects of time dilation - it could be either of them. Suddenly, without any apparent acceleration they start to return towards each other (which doesn't imply that they are both moving) and then suddenly 'stop' in the same place. It is only once they meet up with each other and compare their clocks that they can know who was really travelling at the relativistic speed. It turns out that James has measured less time, hence it was he who sped off away from Mary and then travelled back towards her.

Now, if you consider the various effects that James experiences in travelling at a relativistic speed relative to Mary and then returning to her frame:

- Mass dilates (relative to the observer's frame) and then returns to 'normal' once you return to the observer's frame.

- Length contracts (relative to the observer's frame) parallel to the direction of motion and then returns to 'normal' once you return to the observer's frame.

- Time dilates (relative to the observer's frame) and then returns to 'normal' once you return to the observer's frame.


Note that none of the effects actually remain. Time dilation, as with the others, ceases to 'affect' James once he has returned to Mary's frame of reference. I don't know this for sure, but theoretically one doesn't actually notice all these effects as they occur. Within your frame, provided it is inertial, you notice no difference. This is why I emphasise the relative, observational nature of these effects - because it is only when measured by an observer in a different frame of reference that they become apparent.

This post is long enough as is but I'll finally get to the 'time dilation lingering' thing. If you replace James and Mary with twins and have their trips apart made quite long then we'll get that situation where one of them is middle aged but the other is looking grandpa-esque. Consider the following: if you have two things that are identical and, at a later time, you find that something is different about one of them. Why is it that you have noticed a difference? - it is because one of them has changed. Time is the agent of change. The rate at which time flows dictates, in part, the rate at which change can take place. As one twin travels at relativistic speeds then, relative to the stationary twin, the particles makign up their atoms slow down in their oscillations, their cells slow down accordingly and, as a result, their entire body system ages at a slower rate than the other twin. That time then has a lasting effect can be attributed to time being an agent of change which allows change/difference to occur/exist in the first place.

I hope that helps in some way.

thanks, that clears a lot of things up.

does that mean that the earth twin sees from his inertial frame of reference, a kind of slow motion movement taking place withing the ship travelling at relativistic speeds?...i mean would that mean time dilation or?

 

[spank_meh]

well now that some1 taught me how to use quotes PROPERLY hehe...

u confused me on that one:

does that mean that the earth twin sees from his inertial frame of reference, a kind of slow motion movement taking place withing the ship travelling at relativistic speeds?...i mean would that mean time dilation or?

 

[KFunk]

does that mean that the earth twin sees from his inertial frame of reference, a kind of slow motion movement taking place withing the ship travelling at relativistic speeds?

If they were able to observe events in the ship somehow (using some super telescope or something?) then technically yes, but because the earth also looks time dilated relative to the space ship then the people on the earth would appear to be in slow motion, as observed by the people on the space ship. Therein lies the paradox. I chose to use two space ships in deep space because in that situation you become less attached to the earth as a reference point.

 

[Abtari]

ok then, thanks

that clears things up a bit

 

[spank_meh]

yeah for sure hahah thanx dude

hmm i think im becoming adicted to this site dam

 

[sicarphime]

em... i dont whether this is actually argued over already.....


from the space twin's frame of reference... didnt the earth twin accelerate and deccelerate? or am i confusing myself...?

 

[NightShadow]

heres a question extension... if the person on the ship sees the guy on earth older than he is... and the guy on earth sees the guy on the ship older than he is due to frames of reference... but in reality the guy on the ship undergoes time dilation and thus ages slower as his clocks run slow... BUT upon slowing down to land on earth what happens? sure the guy on the ship is younger... BUT what will he see....though since he thinks that the guy on earth is older?

 

[Wackedupwacko]

no he will not .... he will feel that the same amount of the time has passed... whether the guy on earth will have aged more than him physically (ie look like an old man) or not is something we wont ever find out.... (due to the fact theres no way to prove this). relatively he is younger but i dont think he will be any younger physically... reason? if u take a 3rd point of reference lets say planet x . now the spaceship dude will have time dialation in relation to u on planet x but none to guy on earth so what now?

 

[Halfasian89]

One thing clear. The spaceship twin will be physically younger. Say, the earth twin thinks that the trip of the spacecraft is 4 years, and the spacecraft twin thinks the trip was only 1 year. They dont feel that time has slowed, for everything in time dilation is slowed (including processes in the brain that provide conscienceness, everything on an atomic level is 'slowed') as observed by an inertial frame of reference. So the spaceship twin feels that time has passed as it would on Earth.

relatively he is younger but i dont think he will be any younger physically... reason? if u take a 3rd point of reference lets say planet x . now the spaceship dude will have time dialation in relation to u on planet x but none to guy on earth so what now?

That made no sense, to me totally illogical (no mean to offend), because say planet x would be an inertial frame of reference, and thus would observe the same effects of the spaceship twin if he had instead went to planet x (without considering other factors, such as the larger distances he may have to travel.

To state the obvious, what makes an inertial frame of reference is that the net force applied upon the frame of reference is zero (F=ma, so therefore zero acceleration). Earth is considered an inertial frame of reference because the force applied upon our frame of reference is near to zero, for im sure none of us humans can feel earth's accelerations in rotation and revolution around the sun (disregarding accelerations experienced beyond our solar system). Technically, earth isn't an inertial frame of reference, but if we were to assume so (without considering the minute effects of its accelerations) it wouldn't hurt, and so it happens.

Any further argument?