# Stupid Twins Question.

Al68

## Main Question or Discussion Point

If we add a third observer to the twins paradox at the turnaround point (at rest with earth), and with a clock that was synched with the other two when the ship left earth, what will that clock read when this third observer sees the ship turn around?

Assuming v= 0.8c, distance = 8 ly.

Also, since this third observer and the ship's twin could look at each other's clocks (locally), what would each observe the other's clock to read?

Thanks,
Al

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Hurkyl
Staff Emeritus
Gold Member
If we add a third observer to the twins paradox at the turnaround point (at rest with earth), and with a clock that was synched with the other two when the ship left earth,
Do you mean... the third observer and the Earthbound twin have synchronized their clocks according to Einstein's convention? Or equivalently, measuring simultaneity relative to an inertial coordinate chart where both the third observer and Earthbound twin are stationary, their clocks read the same value at the same (coordinate) time?

what will that clock read when this third observer sees the ship turn around?
Just choose a coordinate chart and compute! (An inertial coordinate chart centered on Earth is probably the simplest)

Assuming v= 0.8c, distance = 8 ly.
As measured by what coordinate chart?

Also, since this third observer and the ship's twin could look at each other's clocks (locally), what would each observe the other's clock to read?
Again, just select coordinates and compute!

In what way are you having trouble making the calculations?

Al68
Do you mean... the third observer and the Earthbound twin have synchronized their clocks according to Einstein's convention? Or equivalently, measuring simultaneity relative to an inertial coordinate chart where both the third observer and Earthbound twin are stationary, their clocks read the same value at the same (coordinate) time?

Just choose a coordinate chart and compute! (An inertial coordinate chart centered on Earth is probably the simplest)

As measured by what coordinate chart?

Again, just select coordinates and compute!

In what way are you having trouble making the calculations?

Al

Hurkyl
Staff Emeritus
Gold Member