Time dilation and speed being relative

[Liokault]

Ok, I can buy into the idea that the faster you go the slower time passes in relation to an (slower moving) observer.

I can buy into the idea that speed is relative and that there is no universal speed. Hence if you get into your rocket and fly away from Earth at near light speed, it’s just as true to view the Earth moving away from the stationary rocket as it is to view the rocket as moving away from the stationary Earth.

What I'm having trouble with is that if both the above are true, for which one relative to the other is time slowing for?

The book (that put this idea into my head and just left me confused)suggested that it’s not a paradox as when you decelerate the moving body to match the stationary one (either Earth or rocket), the vast deceleration from near light speed causes time to speed up just as much as the acceleration caused it to slow down.
Ok, what if there is no deceleration? What if we get two clocks, put one on the rocket and leave one on Earth, the one on the rocket travels at near light speed (or indeed the earth travels away from it at near light speed) in a large circle that laps near the clock on earth. A photo is taken of the two clocks together (one is still in motion, no deceleration has happened), which has been slowed down by travelling fast?

[Gene Vincent]

Liokault said:

I can buy into the idea that speed is relative and that there is no universal speed.

Speed or velocity is not relative, it is a meter, what you may be confusing is that the time taken to cover a given distance at a given velocity.

Liokault said:

Hence if you get into your rocket and fly away from Earth at near light speed, it’s just as true to view the Earth moving away from the stationary rocket as it is to view the rocket as moving away from the stationary Earth.

Yes, your time frame separates from those you leave behind and each party sees the other receeding whilst they themselves seem to not move (inertia omitted)

Liokault said:

What I'm having trouble with is that if both the above are true, for which one relative to the other is time slowing for?

To move your reference frame from the Earths you have to accelerate away, it is not the velocity that does this but acceleration.

You accelerate, you take your time frame with you.

Liokault said:

The book (that put this idea into my head and just left me confused)suggested that it’s not a paradox as when you decelerate the moving body to match the stationary one (either Earth or rocket), the vast deceleration from near light speed causes time to speed up just as much as the acceleration caused it to slow down.
Ok, what if there is no deceleration? What if we get two clocks, put one on the rocket and leave one on Earth, the one on the rocket travels at near light speed (or indeed the earth travels away from it at near light speed) in a large circle that laps near the clock on earth. A photo is taken of the two clocks together (one is still in motion, no deceleration has happened), which has been slowed down by travelling fast?

The frame is dragged with you and changed relative to the Earth, deceleration back to Earth still means you are travelling faster than the Earth and although acceleration will detach a time frame from its surrounding time frame the continuance of your mass/energy moving very quickly is that the amount expended in travelling along times arrow is still less than the one you left here on Earth.

[Liokault]

Gene Vincent said:

The frame is dragged with you and changed relative to the Earth, deceleration back to Earth still means you are travelling faster than the Earth and although acceleration will detach a time frame from its surrounding time frame the continuance of your mass/energy moving very quickly is that the amount expended in travelling along times arrow is still less than the one you left here on Earth.

Ok,so you get a photo of both clocks, one is (and has been for a long time (time?))moving near light speed, but the picture is of them side by side. Which has slowed and why?

[Sonic]

You might find this interesting

http://www.metaresearch.org/cosmology/gps-relativi...

[Kenzle]

Liokault said:

... stuff

Ok, what if there is no deceleration? What if we get two clocks, put one on the rocket and leave one on Earth, the one on the rocket travels at near light speed (or indeed the earth travels away from it at near light speed) in a large circle that laps near the clock on earth. A photo is taken of the two clocks together (one is still in motion, no deceleration has happened), which has been slowed down by travelling fast?

Hi Liokault, the problem is what you have written above. The two bits I have highlighted in bold are contradictory. Moving in a large circle means (even if your speed is constant) that you have experienced an acceleration (a force) because your velocity has changed. Velocity is defined as both a speed and a direction.

The answer to your question is that the clock which has been moving at near light speed will be slower than the clock on earth.

In fact this experiment was done in 1971 on airliners (nowhere near the speed of light obviously, but all the same the effect is measurable with atomic clocks).

See a reference here.

Hope that helps.