time dilation and the paradox thingy (1 Viewer)

[Abtari]

dunno if this has been asked before but im asking anyhow. slight confusion.

a rocket that is travelling at say 0.8c towards a star, away from earth and there is a guy in the rocket. from earth, we see his clock run slower than our own, according to special relativity. But because for the guy, it seems that the earth is moving 0.8c away from HIM, then he would see the watch of an observer on earth run slow too....

so why the hell when the guy comes back to earth (which is like earth moving towards the rocket - motion is relative), then he has aged less, time has run slower for him...blablabla

thanks!

 

[serge]

so why the hell when the guy comes back to earth (which is like earth moving towards the rocket - motion is relative), then he has aged less, time has run slower for him...blablabla

thanks!

he HAS aged less because he has not been in an inertial frame of reference

to reach 0.8c he has to accelerate, and to turn around and come back to
earth he has to accelerate as well, whereas the earth rotates with
a constant speed, thats why the earth observer is in an inertial
frame of reference, while the spaceman is not

 

[Abtari]

he HAS aged less because he has not been in an inertial frame of reference

i agree with wot uve said but i dont understand ur reasoning as above^

how does him not being in an inertial frame of reference make him age less..

thanks

 

[serge]

i agree with wot uve said but i dont understand ur reasoning as above^

how does him not being in an inertial frame of reference make him age less..

thanks

lol

it doesnt really make him age less physically

its just his arguement that earth time is wrong is incorrect

 

[Captain Gh3y]

If anyone on this forum happens to have completed post graduate level mathematics and physics at university, I'm sure they'd be more than willing to show you the general relativity calculations that could clearly show why the space twin aged slower.

But for now we have to accept that it's only a paradox in terms of Special relativity, that is resolved by general relativity because the spaceship is a non-intertial reference frame (it accelerates to leave, turn around and come back) and the fact is that the space twin is younger.

 

[KFunk]

If you want to get a better understanding and to look at the paradox in more depth then search google for the "twin paradox". Here's something to start with:

http://en.wikipedia.org/wiki/Twin_paradox

 

[05er]

I don't get a word of what this is about
I do Modern History instead
Trotsky was Russian

 

[Abtari]

ok

you said that the space twin is younger or whatever, basically time runs slower for him than on earth and when he returns like the clocks would be slower...so like there would be time discrepancies in their clocks.


so why doesnt the same thing happen with mass and length...like the earth guy would observe mass dilation and length contraction on the spaceship at 0.8c but when the spaceship actually returns, everything is back to 'normal'...the spacecraft isnt squished up or the guy hasnt become heavier or nething...

why is it with just time that the effect 'lingers'???

 

[KFunk]

ok

you said that the space twin is younger or whatever, basically time runs slower for him than on earth and when he returns like the clocks would be slower...so like there would be time discrepancies in their clocks.


so why doesnt the same thing happen with mass and length...like the earth guy would observe mass dilation and length contraction on the spaceship at 0.8c but when the spaceship actually returns, everything is back to 'normal'...the spacecraft isnt squished up or the guy hasnt become heavier or nething...

why is it with just time that the effect 'lingers'???

It's because of the nature of time. When they return to earth the space twin's clock starts to run at the same speed again but upon comparison they would discover that the earth clock has measured a greater length of time than the space clock. Time dilation itself doesn't linger but its effects are more noticeable because it is only through the passage through time that we can experience change - without time there is no rate of change.

The effect itself (of time slowing down relative to the earth clock) ceases once the space clock is in the same frame of reference in the same way mass and length return to 'normal'. The changes experienced while in this dilated frame cannot suddenly fast forward and catch up to those of earth and the lingering effect you're noticing is the discrepency in the amount of change experienced in each of the two frames of reference. In summary, what we are noticing is a difference in the amount of change where the amount of change experienced is a direct consequence of the rate at which time flows.

 

[LostAuzzie]

The 'paradox' is that the twin travelling in the spaceship is seen by the earth twin to have aged less, yet from the perspective of the travelling twin the Earth twin has aged less because from his perspective the Earth took the journey at close to light speed.

However, this was solved simply because the traveller is not in an inertial frame of reference, in turning around he changes velocity (accelerates) and thus the effects of time dilation are removed

 

[serge]

ok

you said that the space twin is younger or whatever, basically time runs slower for him than on earth and when he returns like the clocks would be slower...so like there would be time discrepancies in their clocks.


so why doesnt the same thing happen with mass and length...like the earth guy would observe mass dilation and length contraction on the spaceship at 0.8c but when the spaceship actually returns, everything is back to 'normal'...the spacecraft isnt squished up or the guy hasnt become heavier or nething...

why is it with just time that the effect 'lingers'???

it doesnt really linger because he begins 'aging'
exactly the same as the other twin when he gets back
remember this isnt a physical thing its just an observation
that less time has passed for the space-twin

ie. he only ages-less while he's travelling and accelerating

 

[KFunk]

remember this isnt a physical thing its just an observation

But it's a real physical thing in that once the twins meet the space twin will in fact be physically younger. Taking the example of muons travelling from the upper atmosphere at relativistic speeds, I think time dilation does lead to real physical effects - i.e. the oscillations of particles slowing down and stuff - which are indeed physical but are relative in that they're only really noticeable through relative observation.

 

[serge]

But it's a real physical thing in that once the twins meet the space twin will in fact be physically younger. Taking the example of muons travelling from the upper atmosphere at relativistic speeds, I think time dilation does lead to real physical effects - i.e. the oscillations of particles slowing down and stuff - which are indeed physical but are relative in that they're only really noticeable through relative observation.

so you mean one will have less wrinkly skin and stuff?

After accelerating to 0.8c I think the space-twin will come
back as a younger looking twin in pancake-form

 

[KFunk]

so you mean one will have less wrinkly skin and stuff?

yes

After accelerating to 0.8c I think the space-twin will come
back as a younger looking twin in pancake-form

and yes . It's quite possible that the latter would also contribute to the former.

 

[spank_meh]

Trotsky was Russian

yeah y "was" but nd wat does the russian guy have to do with all this?
are you russian?

 

[Abtari]

kfunk - i sorta get what u are trying to say, but the part about 'relative observation' doesn't really click...

lets do it this way. lol. i found this from physics contexts...

it says the paradox lies, as lostauzzie mentioned, in the fact that both twins are seeing the other twin moving away from them at the speed of light or whatever. And each twin sees the time pass slower for the other twin... but both cannot be right.

it mentions that because the rocket is not an inertial frame of reference, special relativity cannot be used to predict... and general theory of relativity should be used instead. the prediction of the earth twin is valid... and the travellling twin returns having aged less than the one on earth...

fair enough. i sorta get that. but why doesn't that happen to length and mass as well...why doesn't the effect 'linger'...i hope im making sense when i use this term loosely... because the effect of time dilatoin has caused the twin on earth to become a frail grandpa and the spacetwin is still young...why don't we get to 'see' things like mass dilation and length contraction 'accumulate'...


AAAAAAAARGH

 

[Original_Angel]

dunno if this has been asked before but im asking anyhow. slight confusion.

a rocket that is travelling at say 0.8c towards a star, away from earth and there is a guy in the rocket. from earth, we see his clock run slower than our own, according to special relativity. But because for the guy, it seems that the earth is moving 0.8c away from HIM, then he would see the watch of an observer on earth run slow too....

so why the hell when the guy comes back to earth (which is like earth moving towards the rocket - motion is relative), then he has aged less, time has run slower for him...blablabla

thanks!

the dude who goes away in the rocketship or whatever he goes away in - travelling at o.8c - well due to the fact that he is travelling at such high speeds, his "time" slows down hence he doesnt age as quickly from the point of view (frame of ref.) from someone on earth - i.e. the earth dude would age quicker because to us - our time is set as is and blah blah we're moving at this speed and blah blah - so anyway by the time the rocketship guy comes back, there would be a significant age difference
..

hmm - i can write a better response in the exam
lol

it's all relative

 

[spank_meh]

why doesn't the effect 'linger'...i hope im making sense

some good point there lol nd u r making sence but yeah something is really missing in here.. but we dun have to kno the answer on that one its not in the syllabus or is it? hahah

 

[wanton-wonton]

he HAS aged less because he has not been in an inertial frame of reference

to reach 0.8c he has to accelerate, and to turn around and come back to
earth he has to accelerate as well, whereas the earth rotates with
a constant speed, thats why the earth observer is in an inertial
frame of reference, while the spaceman is not

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.

 

[KFunk]

kfunk - i sorta get what u are trying to say, but the part about 'relative observation' doesn't really click...

lets do it this way. lol. i found this from physics contexts...

it says the paradox lies, as lostauzzie mentioned, in the fact that both twins are seeing the other twin moving away from them at the speed of light or whatever. And each twin sees the time pass slower for the other twin... but both cannot be right.

it mentions that because the rocket is not an inertial frame of reference, special relativity cannot be used to predict... and general theory of relativity should be used instead. the prediction of the earth twin is valid... and the travellling twin returns having aged less than the one on earth...

fair enough. i sorta get that. but why doesn't that happen to length and mass as well...why doesn't the effect 'linger'...i hope im making sense when i use this term loosely... because the effect of time dilatoin has caused the twin on earth to become a frail grandpa and the spacetwin is still young...why don't we get to 'see' things like mass dilation and length contraction 'accumulate'...


AAAAAAAARGH

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.