Einstein's paradox

From wikipedia on the twin paradox, you can find the same on more academic sites.

from pbs nova special on einstein and relativity, use the internet and stick to physics sites or reliable academic sites.

Hi Prothero,

Excuse my interuption, but, If Al is travelling at 99.99% the speed of light and the system he is travelling to and from is 25 light years away, won't he take 25 years to get there and 25 years to return - Therefore aging by 50 years?

Thank you, and best wishes.

Mark...

I'm fairly certain that is precisely what relativity does not imply, because that information is wholly dependent on reference frame. There is no other data about which object is "actually" moving. If you take away all outside reference frames (thus isolating the actual motion of the two objects without any other aesthetic confusions), it can't be known which object is moving away from the other. Each particle or twin (at least in an otherwise objectless universe) would see the other as younger. And each would be correct from his perspective.

Well you see it is that problem with the way we typically think about time again. It is best to think of time as the rate at which certain processes occur, radioactive decay, aging, crystal oscillation, orbital emissions. Once you view time as process, the rate at which processes occur varies with acceleration and gravitational fields, so the "25years" is only from the frame of reference of the non traveling twin. For the traveling twin all these processes slowed (thus time slowed) and so the traveling twin does not age at the same rate as the stay at home twin. It is counterintuitive to our experience of the world and the notion we have of the constant unit of time but time is variable not fixed, and so is space and and other physical measurements. That is what is revolutionary about special and particulary general relativity notions of spacetime. Yes for us here on earth 50 years worth of process will have passed but for the accelerating twin much less.
Atomic clocks in orbit at high speeds keep time differently than those here on earth, GPS satellites have to account for relativistic effects, particles with certain 1/2 lives find there lives extended at high speeds in particle accelerators. Time (which funadmentally is the rate at which certain processes occur, not some independent fixed entity) is variable hence all the confusion in the various time threads in the forum. This is not my opinion. It is physics.

Yogi DMT;147717 wrote:

What if the box contains two inertial systems (which i'm not quite sure what this means). All i'm saying is if you look at the huge picture, why would time be any different in any particular place.

Bu the box could not contain two inertial systems. Einstein is discussing physics, and physics need not be commonsense. You really would have to look this matter up. Why not try Googling "the twin paradox"?

Yogi DMT;147723 wrote:

Okay, i probably don't know enough about this then. I just had discussion in English that's really all.

Well, discussions in ignorance usually don't lead anywhere much.

No, that is not it. There are some Time Life explanations of how relativity works that might help you. It would be easier with a diagram but here goes. Two spaceships, right? You're on one and George is on the other. Relative to you, George goes by at quite a few million miles an hour. Woosh.

Now in each spaceship, there is a clock. The clock works by firing a beam of light at the mirror on the floor once a second. This is how it keeps time. The clock on George's spaceship does this too. But, relative to you, the mirror in George's spaceship has actually travelled quite a few thousand miles between the time the beam left the roof, and hit the mirror on the floor, and then another few thousand miles on the return trip.

From where George is standing, the light has just made a standard round trip of a few meters. From where you are standing, the light has travelled a few thousand miles. Light always travels at the same speed.

Therefore the time taken for the light beam on George's spaceship has taken longer relative to you than it does, relative to George.

So the clock is actually running slower on George's spaceship.

hope that helps.

moving matter makes it vibrate faster. we call this an increase in temperature. it would be just as likely that temperature slows down the clock as does the speed. temperature expands metal which would make more friction.

wayne;147809 wrote:

Does a mechanical clock actually run slower, or does this only affect the light clock?

TIME actually slows down on George's ship. If he goes far enough, fast enough, 30 years for him will be 150 years on earth. But it is all theoretical. We don't have the technology, or the energy, to actually realise this effect, but the principle is clear. Time slows down the faster you go, relative to a stationary observer.

Not exactly. In the time it takes the light to travel two meters on your ship, it has travelled thousands of meters on George's ship. Visualize George's ship going past you - you're both in space, you can see it coming from 10,000 kilometers away. Lightbeam leaves origin point on George's ship, by the time it hits the mirror on the floor, the ship has moved several hundred thousand meters. And even though light moves pretty quickly, that difference is measurable.

So again, if George's ship is moving at millions of kilometers an hour, relative to you:

• From George's viewpoint, he sees the beam go straight down and straight back up
  
• From your viewpoint, if you could see the lightbeam in George's ship, you would see it travel obliquely for several hundred thousand meters in each direction, to 'keep up' with the motion of the ship
  
• So the distance the light beam has to travel, according to your frame of reference, is not two meters, but two hundred thousand meters (say)
  

And even though light is fast, the speed is finite, so it takes longer, from your frame of reference, for the beam on George's ship to make its return journey.

So time is actually moving slower on George's ship. it is not an illusion, an appearance, or the way the clocks work. The faster you go, the slower time is for you, relative to a stationary observer.

once again. all you are saying is two people can perceive the passage of time differently. that is not a claim about the physical aspect of time or light it is a claim fit for Optics or biology