#### Posers and Puzzles

darkdirk1
Posers and Puzzles 10 May '06 02:59
1. 10 May '06 02:59
Two perfectly identical twins - clones even are split up at birth.
The first to be raised in a spaceship travelling near the speed of light.
The other raised here on earth.

One may postulate that based on special relativity if after 10 years here on earth the twin on the spaceship returned to earth she would be considerably younger than the twin who stayed on earth.

Perkier tits, no grey hair, less cellulite?

Or would the space of ten earth years only feel like a shorter period of time from the point of view of someone travelling near the speed of light?
Or phrased another way is time a measurement between events such as cellular breakdown, tooth decay, organic entropy (events we use to determine aging) or is time strictly an abstract concept which exists only as a mental device for humans and therefore only relevant in regards to our own awareness of events around us?

Frankly i have no idea.
2. AThousandYoung
All My Soldiers...
10 May '06 05:212 edits
Originally posted by darkdirk1
Two perfectly identical twins - clones even are split up at birth.
The first to be raised in a spaceship travelling near the speed of light.
The other raised here on earth.

One may postulate that based on special relativity if after 10 years here on earth the twin on the spaceship returned to earth she would be considerably younger than the twin who ...[text shortened]... re only relevant in regards to our own awareness of events around us?

Frankly i have no idea.
The Twins "Paradox" has bothered me for a long time. Since motion is relative to the observer, how can one twin be going faster than the other in an absolute sense such that one ages faster? It makes no sense.

EDIT - After skimming the article in Wikipedia, I think it has something to do with acceleration and not speed. Anyway, the time dilation applies to everything; so the "younger" one would have perkier tits etc. If the "older" one could watch the "younger" one's voyage, she'd appear to actually age slower. She'd also talk slower, think slower, etc.

Actually now I am confused again. I still haven't managed to comprehend how relativity works.
3. TheMaster37
Kupikupopo!
10 May '06 08:56

The one in space IS younger. That includes appearances.
4. Suzianne
Misfit Queen
10 May '06 13:19
Originally posted by AThousandYoung
The Twins "Paradox" has bothered me for a long time. Since motion is relative to the observer, how can one twin be going faster than the other in an absolute sense such that one ages faster? It makes no sense.

EDIT - After skimming the article in Wikipedia, I think it has something to do with acceleration and not speed. Anyway, the time dila ...[text shortened]... now I am confused again. I still haven't managed to comprehend how relativity works.

The reason the one in space would be younger is simple. The one on Earth, after 10 Earth years, would be 10 years older. The twin in space would see Earth time speeded up. If the twin in space could keep track of the time by watching a calendar in the background while watchin gthe Earth twin, when 10 years had passed on Earth, due to the relativistic effects, she would only have aged maybe 2 years, and it would have seemed as if only 2 years had passed for her. Of course, I'm hypothesizing her speed to come up with a number... the amount of time that passed for her in the 10 Earth years would be a function of her speed (the faster she is travelling, the stronger the effects and the faster (for her) the 10 years passes on Earth). This effect is called Time Dilation, and is a proven relativistic effect. (Identical atomic clocks have been placed in a stationary spot and in a moving vehicle and after a lengthy time, the time difference was measurable.)

And yes, as you researched, the effect IS due to acceleration, and not speed, but in a relatively (hah!) gravity-free environment, a ship travelling at any constant speed has a constant acceleration. Thus, the faster the speed, the faster the acceleration.
5. 10 May '06 15:221 edit
Originally posted by Suzianne
...., a ship travelling at any constant speed has a constant acceleration. Thus, the faster the speed, the faster the acceleration.[/b]
Errr...you are correct but...

Acceleration is the rate of change of speed (actually velocity) with time ie. a = dv/dt

But if velocity is constant: dv/dt = 0

So a constant speed DOES have a constant acceleration .... of zero.
6. 10 May '06 22:23
Wouldn't they be the same age because one got older faster as the ship flew away and then at a slower rate when the ship turned around and came home. After all, which one is travelling at the speed of light (or near the speed of light)? It is all relative.
7. 11 May '06 01:19
Another twist i like to consider is if i could be a third party who has closed circuit cameras on both twins - now I am just watching 2 girls who to me seem to be moving and aging at the same speed.

I postulate that the twin on earth watching the spaceship twin could not detect anything unusual.
I mean the twin relative to the spaceship is moving at the same speed that the earth twin is moving (relative to earth) they gesturing is at the same rate - a glass of water would fall of a table at the same accelleration.
However the twin in the spaceship would reach the same place in TIME-SPACE as the earth twin just in a fraction of the earth years.

Its inexplicable in a way - but this is how i struggle to grasp it.
8. sonhouse
Fast and Curious
11 May '06 02:281 edit
Errr...you are correct but...

Acceleration is the rate of change of speed (actually velocity) with time ie. a = dv/dt

But if velocity is constant: dv/dt = 0

So a constant speed DOES have a constant acceleration .... of zero.
Its not the delta that causes time flow to change, its the constant velocity. Think of it as being in this infinite matrix where the faster you go the more matrix lines get pused together, the matrix lines being duration. So you are squashing the matrix like a supersonic jet pushes air into a compressed state ahead of the jet. So as you go through the matrix, each time hack takes less time and thats on a fundamental basis, every electron orbit, every reaction, all slowing down in relation to earth time. Even in orbit around the earth the astronauts age a few microseconds less, practically unmeasureable but it is measurable.
Its a real effect, measureable by counting cosmic rays hitting the earth, particles going so close to C they last longer and reach the earth's surface which they couldn't do if they were going slower in a relativistic sense.
9. AThousandYoung
All My Soldiers...
11 May '06 06:101 edit
Originally posted by sonhouse
Its not the delta that causes time flow to change, its the constant velocity. Think of it as being in this infinite matrix where the faster you go the more matrix lines get pused together, the matrix lines being duration. So you are squashing the matrix like a supersonic jet pushes air into a compressed state ahead of the jet. So as you go through the matri ...[text shortened]... the earth's surface which they couldn't do if they were going slower in a relativistic sense.
But velocity is relative. You could just as easily say the space ship is motionless and the Earth is moving away. Then the Earthbound twin would be the one to stay young. That's why I don't understand all this.

EDIT - Even if it were acceleration, you could just as easily say the Earth accelerates away from the ship as saying the ship accelerates away from the Earth.
10. AThousandYoung
All My Soldiers...
11 May '06 06:11
Originally posted by darkdirk1
Another twist i like to consider is if i could be a third party who has closed circuit cameras on both twins - now I am just watching 2 girls who to me seem to be moving and aging at the same speed.

I postulate that the twin on earth watching the spaceship twin could not detect anything unusual.
I mean the twin r ...[text shortened]... ction of the earth years.

Its inexplicable in a way - but this is how i struggle to grasp it.
Well, it would depend on your motion relative to those of the girls.
11. 11 May '06 10:47
Originally posted by AThousandYoung

EDIT - Even if it were acceleration, you could just as easily say the Earth accelerates away from the ship as saying the ship accelerates away from the Earth.
You're right - velocities are relative. However accelerations are not.
The twin on the ship would know she was accelerating (and not the Earth) becasue she could feel it - she would be pinned against the rear bulkhead of the ship say. This is what is meant by the term "inertial frames".

The "paradox" occurs because the twin on the ship changes her inertial frame - when she does the U-turn (which necessarily involves an acceleration) in order to return to earth.
12. sonhouse
Fast and Curious
11 May '06 19:14
You're right - velocities are relative. However accelerations are not.
The twin on the ship would know she was accelerating (and not the Earth) becasue she could feel it - she would be pinned against the rear bulkhead of the ship say. This is what is meant by the term "inertial frames".

The "paradox" occurs because the twin on the ship changes ...[text shortened]... e does the U-turn (which necessarily involves an acceleration) in order to return to earth.
Thats not quite true. Its true if you are accelerated by a rocket but not true if you are accelerated by being in the gravitational well of a star or big planet, you would gain velocity without knowing you were gaining speed unless you had instrumentation to measure it, say by doppler measurement or parallax.
13. 11 May '06 20:40
Originally posted by sonhouse
Thats not quite true. Its true if you are accelerated by a rocket but not true if you are accelerated by being in the gravitational well of a star or big planet, you would gain velocity without knowing you were gaining speed unless you had instrumentation to measure it, say by doppler measurement or parallax.
I take your point but the Twin Paradox is essentially a problem of Special Relativity and not one of gravitation and General Relativity. Furthermore, given the set up of the problem - the travelling twin visits a nearby star and comes back - it is clear that she didn't use gravitation to power her space ship.
14. Bowmann
Non-Subscriber
15 May '06 21:44
Originally posted by Suzianne