Special relatvity help.?

Question

In the twin paradox the person traveling near the speed of light appears to age slower than the twin on Earth and vice versa.

I don't get the whole vice versa part. Who actually ages more slowly?

Regular fockin comedians around here.

Answer 1

Time is relative to the frame it is measured in. When someone moves out at close to light speed, that traveler sees time go by normally...at a rest-time rate. But outside, another person sees time dilate on board the traveler's ship. That is T' = T + deltaT; where T is rest time for the person on Earth, deltaT is the lengthening (dilation) of time, and T' is the longer interval of time as seen by the outside observer.

For example, suppose T = 1 sec on Earth, but due to very fast velocity on a spaceship, T' = 2T = 2 sec to the outside observer on Earth. In other words, for each click of the second hand on the ship, two clicks of the second hand went by on Earth. To the outside observer, time on the ship slowed down.

The spaceman travels one year out and one year back, according to his own calendar. But when he lands on Earth, he discovers that four years, not two, have passed on the planet. To the spaceman, time on Earth sped up to twice the rate he experienced on the ship.

And that's the vice versa part. To the Earthman time slowed down on the ship. To spaceman, time sped up on Earth.

Answer 2

The twin paradox is a paradox in the way the proposition is put. As stated the situation sounds symmetric - the twins move with respect to one another and so each sees the other age more slowly. Hence it is paradoxical that the one who returns ages less.

The key to understanding this is NOT general relativity. Potentially acceleration could have an effect, but it would not of itself account for all the difference and in any case you can phrase the problem so it does not arise.

The solution is that while the problems seems to involve two reference frames - that of the twin at home and that of the twin on a trip - it in fact involves three frames. These are that of the twin at home, that of the twin leaving earth and that of the twin returning. Only ONE twin spends time in two frames, and this accounts for the lack of symmetry.

Answer 3

rijim200... got it as wrong as anyone could.

The twin which ACCELERATES comes back younger. This answers the question what the difference between the observer on Earth and the observer on a spaceship is. One is stationary and the other one experiences an acceleration which changes his velocity relative to ANY other rest frame. Physics AND nature can very well tell the difference between the two.

Having said that, it is NOT the acceleration which makes the ultimate difference. It is also NOT the relative velocity as discussed naively by special relativity. One has to take into account the whole world line of the accelerating observer. Which general relativity and well formulated special relativity do. The formula for the "proper time" of a moving observer is given here:

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

One can show that by accelerating infinitely hard at the beginning and end of the journey, the result found by Einstein by comparing rest frames is recovered. There is no additional penalty term for transient acceleration. But this is a COINCIDENCE which only holds for time dilation. A similar analysis for spacial contraction results in a completely different physical effect which is a spacial ROTATION of the object rather than a skewing along the axis of motion.

The twin paradox is called a paradox for good reason: it violates OUR naive image of how nature works. That makes us idiots and it makes nature .... well... nature.

And, by the way... both twins age equally fast. They just age equally fast in different reference systems. The resting twin perceives the universe in one way, the moving twin in another. But the rate of aging is exactly the same. I bet that nine out of ten people have a real problem telling the difference between time dilation between TWO clocks and the rate of aging of ONE individual. Which is exactly what makes SR and GR so much fun: unlike a Rubick's Cube they are actually intellectually challenging.

Answer 4

In reality there is no Twin Paradox. There are problems with General Relativity effecting the Twin Paradox that most people do not consider when explaining it. The twin in the spaceship must slow down and turn around and accelerate back toward earth and this violates Special Relativities inertial rules. The GR effects tend to cancel the SR effects. See source below for more inormation on that.
What the teachers want you to realize is that time is a measured quatity that is relative to the inertial frame of reference in which it's measured.

I just solved a problem for another yahoo question. Perhaps the example will help. Here it is:

The period of an oscillating weight on a spring measured in a laboratory is 1.80s. A moving observer measures its period as 2.20 s. what is his speed?
The answer is 1.72x10^8 m/s


Here is my solution:
t' ... time indicated by the moving observer clock
t ... time indicated by the laboratory clocks
v ... speed of the observer
c ... speed of light
Einstein's Time Dilation equation is as follows:

t = t' sqrt (1-v^2/c^2)
Substituting in the known values and solving for v

1.80 = 2.20 sqrt[1-v^2/(3x10^8)^2]

1.80/2.20 = sqrt[1-v^2/9x10^16]

0.818181818 = sqrt[1-v^2/9x10^16]

0.669421487= 1- v^2/9x10^16

-0.330578513 = -v^2/9x10^16

-2.97520662 x 10^8 = - v^2

1.72487873 x 10^8 m/s = v

1.72x10^8 m/s = v

You could change the problem and state "The period of an oscillating weight on a spring measured in a laboratory is 1.80s. How long a period does an observer moving at a speed of 1.72x10^8 m/s measure the period of the oscillating weight on the spring?"
The answer of course would work out to be 2.20 seconds.

So it looks like someone's clock is slower than than the other's. But that is NOT the case. They are both correct. Time and time intervals are relative.

Answer 5

The one moving near the speed of light gets to age more slowly when compared to the twin on earth.

Answer 6

Only the one who is moving at the high speed is affected by the time dilation.

Answer 7

The person who went out into space and came back was younger than the people who stayed on Earth.

Answer 8

The one that moves. The real question is: WHO REALLY MOVES? - If I move then I age slower than the person WHO SEEM TO ME that stands. Vice versa: If I stand, then the person who SEEM TO ME that moves, age slower than me.(The word "seem", here means observe, see, hear, percept....)

Answer 9

the one with Oil of Olay