Special Relativity Time Dilation Q (1 Viewer)

[milton]

from 2003 HSC Physics q5

An astronaut set out in a spaceship from Earth orbit to travel to a distant star in our galaxy. The spaceship travelled at a speed of 0.8 c. When the spaceship reached the star the on-board clock showed the astronaut that the journey took 10 years.
An identical clock remained on Earth. What time in years had elapsed on this clock when seen from the astronaut's spaceship?
(A) 3.6
(B) 6.0
(C) 10.0
(D) 16.7

From the astronaut's point of view, it is the Earth that is receding away and thus time should dilate for clocks on Earth, so the answer should be B. The official answer is indeed B.
However a textbook says there is NO ANSWER. If 6 years had indeed passed on Earth, ppl on Earth can claim time dilates for the astronaut, so 3.6 years should pass on for the astronaut. So 10 yrs = 3.6 yrs!

This is kinda like a symmetrical part of the Twin Paradox. But it isn't really a paradox since Einstein said there's no such thing as absolute time and its relativity of simultaneity so the time on Earth is undefineable.
As far as the astronaut's concerned, time on Earth doesnt exist.
Not only is space and time relative, i've read in NewScientiest magazine that even EXISTENCE is relative. There are these hypothesised Rindler particles that observers in some inertial frames of reference will detect, but others can't

just goes to show how freaky and weird relativity really is.

 

[nounderscore]

However a textbook says there is NO ANSWER. If 6 years had indeed passed on Earth, ppl on Earth can claim time dilates for the astronaut, so 3.6 years should pass on for the astronaut. So 10 yrs = 3.6 yrs!

This isnt true. You have the formula tv = to/(1-v2/c2)^1/2. From the reference from the astronaut, 10 years would pass though only 6 years would pass on earth. Though from the reference from the person on earth, to= 6 and tv would need to be calculated as to is time in the reference point.
So from earth's point of view the formula would look something like
tv = 6/(1-0.64)^1/2
tv= 10 which satisfys the HSC answer

correct me if im wrong but the textbook is a bit suss. In the study of time dilation, the person that is travelling at the speed of light or close to it, will experience no difference, though the people from an external point of reference would see the person travelling going faster than they normally would. This is always the case. In youre text book example, it states that 6 years is 3.6 years in a spacecraft which cannot be true.

 

[fwong]

from 2003 HSC Physics q5

An astronaut set out in a spaceship from Earth orbit to travel to a distant star in our galaxy. The spaceship travelled at a speed of 0.8 c. When the spaceship reached the star the on-board clock showed the astronaut that the journey took 10 years.
An identical clock remained on Earth. What time in years had elapsed on this clock when seen from the astronaut's spaceship?
(A) 3.6
(B) 6.0
(C) 10.0
(D) 16.7

From the astronaut's point of view, it is the Earth that is receding away and thus time should dilate for clocks on Earth, so the answer should be B. The official answer is indeed B.
However a textbook says there is NO ANSWER. If 6 years had indeed passed on Earth, ppl on Earth can claim time dilates for the astronaut, so 3.6 years should pass on for the astronaut. So 10 yrs = 3.6 yrs!

This is kinda like a symmetrical part of the Twin Paradox. But it isn't really a paradox since Einstein said there's no such thing as absolute time and its relativity of simultaneity so the time on Earth is undefineable.
As far as the astronaut's concerned, time on Earth doesnt exist.
Not only is space and time relative, i've read in NewScientiest magazine that even EXISTENCE is relative. There are these hypothesised Rindler particles that observers in some inertial frames of reference will detect, but others can't

just goes to show how freaky and weird relativity really is.

The HSC question from BoS was wrong. The person who set this question didn't know what he was saying. Some students a few years back said that this question was cancelled in the HSC marking.

Trust me. I am a teacher. I have confirmed that this question does not make sense with Dr Joe Wolfe from the Phys Dept, UNSW. He holds a HSC Phy forum, BTW.