observers in free fall

[michel123456]

This is from another (closed) topic, dear Moderators will judge if it goes against the rules or not.

 

Michel posted

You are on an airplane with a parachute.

A guy before you jumps in free fall.

After a second you jump in free fall

The next second a 3rd guy jumps in free fall.

 

Looking in front of you you will observe the first guy receding from you.

Looking back you will observe the 3rd guy receding from you.

 

All 3 observers will observe each other receding.

 

 

ACG52 answered

And when you look at the guy who jumped out of the plane next to you at the same time you did, you see he's relatively motionless.

 

Which is not what you see when you look at the universe.

 

And when you look at the ground, you see it is approaching you.

 

Which is not what you see when you look at the universe.

 

Pretty poor example trying to support an unsupportable position.

 

Which is absolutely correct.

 

But if you look closely to the analogy of the observers in free fall and compare to the Universe, you obtain the following.

 

_In the analogy, the "receding" is caused by 3 phenomas

a. the same and constant acceleration of the 3 jumpers

b. the same direction and same path (or parallel path)

c. the delay of 1 sec at the starting point between the jumpers.

 

_in the Universe

c. the delay is caused by the speed of light, not by a delay at the starting point. So in the universe there is no "guy who jumped out of the plane next to you". All are delayed.

b. in the universe there is no indication that all objects (galaxies or galaxy clusters) have the same direction or are actually on a parallel path. So indeed that would be a very bold statement, with only fragile support the famous "dark flow".

a. the same and constant acceleration could be caused either by gravity, either by some other phenomena (dark energy) since IIRC it is observed as being not constant.

 

Then you have the big objection:

And when you look at the ground, you see it is approaching you.

 

 

In order to counter this objection, one has to imagine a truly immense earth-object, infinitely big and infinitely far away, so that all objects from the observable universe are on a parallel path, like the sun rays reaching the Earth parallel to each other .