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Then the acceleration due to that planet would be 9.8m/s2

the gravitational attraction between the planet and the space ship would be G x (5.972 x 1024 x 2x 103)/((5X1010)2) = 0.000318860846 m3 kg-1 s-2 .

If the ship were being accelerated at 9.8m/s2 then the force exerted on the space ship would be equal to F = 2000 Kg x 0.00003 m/s1 = 0.62 N

Let’s just suppose (as a special case) that in interstellar space there is a planet exactly like earth about 50 billion miles away from the space ship, which weighs 2 tons or 2000 Kg. Then the acceleration due to that planet would be 9.8m/s2 and the gravitational attraction between the planet and the space ship would be G x (5.972 x 1024 x 2x 103)/((5X1010)2) = 0.000318860846 m3 kg-1 s-2 .

It is now possible to see that the gravity exerted on the space ship is very small, therefore if the mass of the spaceship were to be multiplied by the force of gravity a total force of 0.00031 N which is an extremely small force would be exerted by gravity. If the ship were being accelerated at 9.8m/s2 then the force exerted on the space ship would be equal to F = 2000 Kg x 0.00003 m/s1 = 0.62 N which is a ridiculously small force and certainly would not have the effect of pushing anyone in spaceship back against their seats.

Where am I going with this? I am trying to show that the equivalence principle of Einstein’s has absolutely no real meaning, it is just using gravitation as an explanation of itself. Here we have an object in space being accelerated to an equivalent acceleration of the acceleration due to the gravity on earth (i.e., 9.8 m/s2 ) yet it has no effect, some gravitational mass is needed close by to make it work.

Your reply seems to imply that in your opinion there is no difference for a passenger in a space ship accelerating away from the vicinity of the earth, say at a distance of 1000 m and a passenger in a space ship 50 billion kilometres away from an earth like planet.

The space ship that is one kilometre away from the earth is experiencing a force of 8.9 x 10^{20} kgm/s2 .

Whereas on the spaceship that is 50 billion kilometres from the earth like planet the force exerted by gravity is only 0.00003kgm/s2 , surely this makes some difference as to what the passenger on the spaceship 50 billion kilometres away from the earth like planet is experiencing?

Kryptid: The point I was trying to make is that an acceleration of 9.8m/s^{2}, 50 billion kilometres from earth or other gravitational influences,is in no way representative of the gravitational force on earth. Instead as Janus points out the force that would be experienced by the spaceship would be the same force that it would experience if it were on an earth that possessed a radius of 50 billion kilometres ! This reinforces my original conjecture that in the absence of a large mass close by, Einstein's thought experiment makes no sense. He is using gravity as an explanation of itself.

Kryptid: The point I was trying to make is that an acceleration of 9.8m/s2, 50 billion kilometres from earth or other gravitational influences,is in no way representative of the gravitational force on earth.

Instead as Janus points out the force that would be experienced by the spaceship would be the same force that it would experience if it were on an earth that possessed a radius of 50 billion kilometres !

This reinforces my original conjecture that in the absence of a large mass close by, Einstein's thought experiment makes no sense.

He is using gravity as an explanation of itself.

The point I was trying to make is that an acceleration of 9.8m/s2, 50 billion kilometres from earth or other gravitational influences,is in no way representative of the gravitational force on earth.

Bored Chemist: Kryptid: How would you tell the difference?

Bored Chemist: The person in the spaceship will know that he is not in a gravitational field because he is floating around. Just as the astronauts in the space station are floating around even though they are in a state of accelerated motion around the earth.

Kryptid:And yet those astronauts floating around in space are, indeed, in a gravitational field.

You will forgive me if your answer appears somewhat inane. Would you go as far as to say they (the astronauts) are in a diminished gravitational field.

The point is even though they are in an accelerated state, there is no sense of up and down, as you suggest there should be?

kryptid : It's the same kind of situation where you are sealed inside of a box and then dropped out of an airplane. Inside the box, you would be floating just like the astronauts in space.

According to Newton’s third law the astronauts should be exerting an equal and opposite reaction to that which they are experiencing.

According to the example you have given they do not experience a force because they are weightless (i.e., in free fall).

My point is that astronauts in my example (i.e., in a spaceship far from any gravitational influences), would also be weightless and in free fall and hence the force of acceleration exerted on the ship would not affect them.

Only if this "force of acceleration" you speak of is the force caused by the gravity of the planet. The acceleration caused by the rocket engines would still very much be felt…….Unless you are somehow under the bizarre assumption that G-forces due to acceleration don't exist…..

Now take that rocket and move out to 50 billion miles from the Earth. But still firing its engines at the sane thrust as before. Now this of course will be more thrust than the pull of gravity from the Earth and the rocket will accelerate away from the Earth. An occupant inside the ship however will still weigh the same on a scale in the ship and objects will still fall towards the floor of the ship just like they did when the ship was hovering just at the surface of the Earth. Relative to the rocket, objects in this accelerating rocket behave just like they would in a gravitational field.This is the gist of the equivalence principle.