- #1

John SpaceY

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- TL;DR Summary
- Link between speed and external gravity to a moving mass m (a spacecraft for example)

Hello,

I have a question linked to gravity and speed of light :

According to the Special Theory of Relativity, the speed of light cannot be exceeded because it would need an infinitive energy to accelerate the relativistic mass of a moving objet (a space craft for example) : indeed if the moving object has a mass m at rest, this mass would become M (the relativistic mass) and this mass M will tend towards infinity when the speed v of m will go towards c.

I understand this point, and so if the spacecraft of mass m has a motor, this motor will not be able to give an infinite enrgy to m and so v will be always lower than c.

But I see an exception if we consider an external gravity to m.

Suppose that the motor of the spacecraft could bring enough energy to reach a speed of 0,9c for the speed of m (not possible today but one day maybe) : if there is an external gravity to the mass m, this external gravity (a "black-hole for example with a very high mass MG) will accelerate the mass m towards him and this acceleration is not linked to the mass m of the spacecraft (and so it is not linked to its relativistic mass M).

The acceleration of the external gravity MG will be proportional to the mass MG and will be divided by the squared distance between m and the center of the gravity MG.

And so if the spacecraft of mass m (or M) will be very near of MG and if MG is very high, with only few steps of calculation the speed of the spacecraft will go from 0,9c to c (because of the high acceleration given by the external gravity MG to m and this acceleration is not linked to m and so not limited by the relativistic mass M and so no issue with a lack of energy), and the speed will exceed c very soon.

The situation is different here because the energy doesn't come from inside the spacecraft (from the motor for example) but the energy comes from the outside and the acceleration is not linked to m.

I would like to know if this calculation is OK or if there is a mistake ?

And if there is a mistake, where it is and what is the mistake ?

Thank you in advance for your answers

John

I have a question linked to gravity and speed of light :

According to the Special Theory of Relativity, the speed of light cannot be exceeded because it would need an infinitive energy to accelerate the relativistic mass of a moving objet (a space craft for example) : indeed if the moving object has a mass m at rest, this mass would become M (the relativistic mass) and this mass M will tend towards infinity when the speed v of m will go towards c.

I understand this point, and so if the spacecraft of mass m has a motor, this motor will not be able to give an infinite enrgy to m and so v will be always lower than c.

But I see an exception if we consider an external gravity to m.

Suppose that the motor of the spacecraft could bring enough energy to reach a speed of 0,9c for the speed of m (not possible today but one day maybe) : if there is an external gravity to the mass m, this external gravity (a "black-hole for example with a very high mass MG) will accelerate the mass m towards him and this acceleration is not linked to the mass m of the spacecraft (and so it is not linked to its relativistic mass M).

The acceleration of the external gravity MG will be proportional to the mass MG and will be divided by the squared distance between m and the center of the gravity MG.

And so if the spacecraft of mass m (or M) will be very near of MG and if MG is very high, with only few steps of calculation the speed of the spacecraft will go from 0,9c to c (because of the high acceleration given by the external gravity MG to m and this acceleration is not linked to m and so not limited by the relativistic mass M and so no issue with a lack of energy), and the speed will exceed c very soon.

The situation is different here because the energy doesn't come from inside the spacecraft (from the motor for example) but the energy comes from the outside and the acceleration is not linked to m.

I would like to know if this calculation is OK or if there is a mistake ?

And if there is a mistake, where it is and what is the mistake ?

Thank you in advance for your answers

John