Question about twin paradox

On July 22 2011 01:03 iNSiPiD1 wrote:
If you assumed that they were actually able to keep in touch in real-time, which as others have pointed out is not possible with a cell phone, then yes, the twin on the spaceship would simply listen to the twin on earth die way before he dies.

On July 22 2011 01:07 skunk_works wrote:
how does traveling at the speed of light keep you from getting old?

On July 22 2011 01:06 nam nam wrote:


What if the twin on earth get hit by a car?

On July 22 2011 01:02 Nawyria wrote:
The Lorentz transformation in flat space-time is a continuous transformation, so the signal will not be discrete; however, the signal will be distorted due to the relativistic doppler-effect.
Name the twin that stays on earth twin A and the travelling one twin B; assume further that they communicate by way of a continuous stream of light that varies mildly in wavelength around 550 nanometres (yellow).

1B) As twin B moves away from the earth at high speed, the relativistic doppler-effect redshifts the light signal, the signals he receives are in the red or infrared. He will also receive the signals at a lower pace due to the fact the light signals have to catch up to him, and thus the intensity will be much lower and the transmitted message plays very slowly.
2B) Just after twin B reverses his direction of travel (which we will assume he does instantly), all the signals he has been travelling ahead of will catch up to him in a very short amount of time. Since twin B is now travelling towards earth, the signals will be blueshifted and the signals he receives are in the blue, ultraviolet or beyond. He will now receive the signals at a much much higher pace, so the intensity will be much higher and the transmitted message plays extremely fast.
3B) After this short burst has passed and twin B is travelling back towards the earth, we are in the inverse of situation 1B. The light signals are blueshifted (as in 2B), the intensity is higher (though not as high in 2B) and the message players faster (though not as fast as in 2B).

1A) After twin A says his farewell to twin B, he will receive messages at a very slow pace, with the same redshift, intensity and message speed as in 1B.
2A) As twin B nears earth, all the messages that he has sent since turning around will reach earth in a very short fashion, much like what happens in 2B, only the intensity will be even higher.

Edit: Assuming the distances are vast enough for twin A to die as twin B is travelling, it depends on the speed of twin B whether he receives words of twin A's death as he is travelling or soon after he turns around. The faster twin B travels, the less messages he will receive before turning around, thus increasing the chance he will hear of it after he turns around.

On July 22 2011 01:29 KimJongChill wrote:


Wow, are you an astrophysicist?

On July 22 2011 01:15 AmericanUmlaut wrote:

Serves him right if he's talking on his cell phone instead of paying attention...

On July 22 2011 01:47 proberecall wrote:
Nawria, thank you

So I understand that cell phone wouldn't work. Does your explanation also apply for any other radio signal or any other way of keeping in communication ?

On July 22 2011 01:47 proberecall wrote:
Nawria, thank you

So I understand that cell phone wouldn't work. Does your explanation also apply for any other radio signal or any other way of keeping in communication ?

Also. Now that I see the signals are continued, if they keep talking at all times... at what point does the time difference start to notice ? meaning when does travelling twin start noticing Earth twin is growing older?

On July 22 2011 01:58 Blazinghand wrote:
They won't be able to keep talking due to the relatavistic "bend/stretch."

Imagine, if you would, a train or car going past. It goes "wweeeeeeeee-ooooooooh", with the sound being high pitched as it approaches and low pitched as it passes away. This is because of the frequency of the sound being emitted sounding different to you due to the motion of the car.

A similar, but somewhat different effect happens with "time dilation" where if I communicate, say, through a series of pulses, each pulse and the gap between each pulse becomes shorter and shorter as my reference frame moves faster and faster. This would make the establishment of some sort of communications standard very difficult, since anything using frequency would be out the window, or extremely hard to calculate.