Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum Twin paradox?

It is customary to construct a twin paradox, using the fact that 'time' between events depends on the velocity of observer, according to the special relativity.

What is being missed, is the fact that time between clock ticks depends on the velocity of observer the same way.

The number of clock ticks ovserved will not depend on the velocity of observer at all.

The taveller and the coach potato will age equally.


e s

extraNONsense wrote:
"It is customary to construct a twin paradox, using the fact that 'time' between events depends on the velocity of observer, according to the special relativity."

Customary where? In your mind perhaps ... but where else?

Your statement has all of the authority of an invisible purple rhinoceros. And an equal value.
This is a science forum you might recall. Point to something that supports your propositions.

Lets not have another endless thread of nonsense where you weave, waffle, and bob but never address anything of substance.

Difference is in the Time experienced with respect to each other. For individual frames the time is perfect scale.

What? Were you trying to respond to my question?

Time, as experienced by different observers, in different frames-of-reference, may be be different.

In what way is that relevant to your original statement: "the fact that 'time' between events depends on the velocity of observer"?

The thing is that we measure times and distances, using light beams and clocks.
It works, since all the times seen from every observer platform are changing proportionally, as the theory says.

ES

The twin paradox, when only using special relativity, is really just baloney. According to the twin on earth the clock of his twin travelling away at a constant speed v is ticking slower; BUT according to the twin on the spaceship the clock on earth is ticking slower. On the other hand the clock rate each experiences, as measured relative to the reference frame within which the clock is at rest, is the proper time which is an invariant parameter; it must thus be the same in both reference frames.
In order to determine which twin aged more than the other, the reference frames must be brought into coincidence so that their relative speed becomes zero. This requires acceleration/deceleration, which then changes the time according to Einstein's general theory of relativity. If the twin in the spaceship returns to earth, it implies that he had to be accelerated away and decelerated back. He thus suffered more acceleration/deceleration than his brother who stayed behind; therefore he will be younger. If, on the other hand his borther on earth decides at a later date to chase his brother in another spaceship and to catch up with him before he decelerates back to earth, then the chasing brother would suffer more acceleration, so that he will be younger than his brother who preceeded him into space.

The acceleration in fact has nothing to do with twin paradox.
Let's say, that both twins travel VERY fast for 10 years in opposite directions, and then both turn around and return home.

Each one would claim that his brother must be younger because of his relative motion.
But they obviously have made the same trip!

e s

The difference in time rates when the relative motion is with a constant velocity is purely a relativistic "illusion". It manifests because you observe the other twin's time relative to your time frame and then conclude that his time is slower; however he reaches the same conclusion about your time relative to his reference frame. A similar situation arises when you look at a ball being thrown up directly into the air on a train passing you. You will observe a parabolic trajectory and conclude that the ball was thrown at an angle; i.e. there was also a horisontal force component. A passenger on the train looking at you throwing a ball straight into the air will also conclude that you have thrown the ball at an angle. In both cases the forces are illusions; there are no horisontal forces involved. The twin's perceptions that each other's times are running slower is also such an illusion while they are moving with a constant speed relative to each other. You can only compare what has really transpired by comparing their ages after they again share the same reference frame. Time only flows slower within a reference frame when gravity increases; i.e. when there is acceleration involved . Thus if two twins leave the earth in opposite directions and accelerate and decelerate by the same amount to again get back to earth, they will be the same age; but younger than the other people who stayed behind on earth.

You are throwing the logic out of the window.

What am I supposed to say?

e s

How! you can only compare time relative to the same reference frame. The twins have to get back to the same reference frame in order to compare their ages. What each perceive of the other while they are travelling with a constant speed relative to each other might seem like a paradox while they are moving, but it is not one once thy are comparing when both are within the same reference frame.

I don't think its the acceleration. The twin on earth could take a short trip and be accelerated and decelerated as much. It's the speed, relative to earth, over a duration of time that makes the twin who travelled younger. I don't know if it makes any difference that the twin whose speeding would see everything in the universe going slower, while the one on earth would only see the time and movement within the rocket going slower.

extraNONsense wrote:
"You are throwing the logic out of the window."

Pot = Kettle = Black

You're a fine one to talk.

Look on the ground around your chair. Perhaps you can find a few synapses.

Speed is relative. This is the point of relativity theory since the time of Galileo. He said that there is no mechanical experiment possible to determine whether it is the spaceship moving relative to earth or vice versa. Einstein expanded it to say that one cannot even use light speed to determine which body is moving and which one not. Thus all movement is relative. Thus according to the twin on the earth the time of the twin on the spaceship ticks slower, while according to the twin on the spaceship the time on earth is ticking slower. What is really happening is that the time on the spaceship as measured relative to the spaceship is ticking at the proper rate which (neglecting earth's gravity) is the same on earth relative to earth's reference frame. The different perceptions of each twin that the other's time is ticking slower is only valid while they are moving at a constant velocity relative to each other. Only when a reference frame accelerate or is attached to a gravity field does the time actually tick slower that on a freely moving reference frame without gravity.
The only way to compare the ages of the twins is to do it relative to the same reference frame; i.e. the twins have to be brought together again. This requires acceleration. Acceleration is an invariant parameter, so that the twin that undergoes the most acceleration will be the youngest.

Is 'extrasense' is too young to remember the two atomic clocks, set to count Radio active decay?
One stayed here on Earth, the other was flown around the world in a standard Aircraft (not a jet)about 30 years ago.
Wonder if he can guess which clock had the fewer tics (radio active decays)? Q.E.D

Too young or too ignorant.

I'm flying into Heathrow on the 16th of May in another vain attempt to live longer by travelling faster. Hope to see you if you are in town.

You have just stated the theory of relativity (more or less).

Which states there is no unique abosulte time; instead each individual has his own personal measure on time.

When thinking about the twins paradox you must have in your mind the idea of absolute time.

You are missing the point. Relative to the inertial reference frame within which you are, time ticks away at the proper rate. The same is valid for another person within another reference frame travelling with a speed v relative to yours. It is only when you look "outside" your reference frame and are able to see a clock within the reference frame travelling relative to you that you conclude that the other person's clock is running slower, and vice versa. It is an "illusion" generated by the relative movement. You and the other person can only agree on time when you are sharing the same inertial reference frame. To do so while travelling relative to each other is futile; for example, when a muon is generated by cosmic rays and it moves down to earth, the decay time within its frame of reference is still the same as it would be within a laboratory on earth. We on earth, however, experience it to be longer because the muon generated by the cosmic rays is moving very fast relative to us. The muon DOES NOT LIVE LONGER AT ALL WITHIN ITS OWN REFERENCE FRAME. The only circumstances under which a clock really ticks slower is when it is accelerated or within a gravitaTional field. Thus while the airplane is accelerating and decelerating DA will gain a bit in youth. I hope it also makes him less grumpy!

This I agree with.
I doubt about the "accelerated" clause. But even if so, it is not going to produce twin paradox, as calculated based on relative time speed while not accelerating at all.

ES

Extrasense, regardless of your unsubstantiated claims regarding your background, I'm convinced you've never taken a single course in modern physics. Eliza knows more about the subject than you do.

I posted a topic about this subject not too long ago extrasense. If you want to better understand this, I suggest you read A Brief History of Time by Stephen Hawking.

otherwise... I'm sure you can get help from the responses here:

http://www.scienceagogo.com/ubb/ultimatebb.php?/topic/2/50.html