# Fields in SR

• I
Hello! I was wondering if the electric and gravitational fields are the same for a moving and a stationary object. The electric field (assume it is created by a stationary charge) is ##E = \frac{q}{\epsilon_0 4 \pi r^2}##, for a stationary observer, but it is higher for a moving one, as the r is getting smaller, while all the other are constant. Is this correct? For gravitational field, the formula would be ##G\frac{M}{r^2}##. The same reasoning can be applied here, only that in this case the mass M seems to increase. Are my reasoning correct? And if so, why does the electric and gravitational field behave differently, beside the math involved? Thank you!

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Orodruin
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The electric field is not the same for a moving and for a stationary charge. Not only does the electric field change, it also mixes with the magnetic field under Lorentz transformations.

There is no gravitation in SR.

The electric field is not the same for a moving and for a stationary charge. Not only does the electric field change, it also mixes with the magnetic field under Lorentz transformations.

There is no gravitation in SR.
What do you mean by there is no gravitation in SR. You can still treat problems in SR when forces are involved. The nature of the force shouldn't matter, so it can be created by gravity, right?

Orodruin
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You can still treat problems in SR when forces are involved.
Gravitation is not a force in relativity. Forces in relativity need to be local as action at a distance would violate causality. You cannot go about just assuming that nothing will change with the gravitational field and it is best to keep away from all considerations of gravity in SR.'

On the other hand, classical electromagnetism (in the form of Maxwell's equations) is fully relativistically covariant. It is in fact one of the cornerstones in how relativity was conceived.

Thuring
SR considers inertial systems. No force, no acceleration. Constant straight velocity.

Orodruin
Staff Emeritus