Suppose that we could observe from outside a system expanding radially at relativistic speed (dr/dt about c, constant and/or accelerated). It can be an ideal balloon, or a spherical distribution of particles.

What would it look like? A shrinking sphere? Or a sphere expanding slower than expected? Nothing of the above?

Suppose that we could observe from outside a system expanding radially at relativistic speed ($\frac{dr}{dt}$ about $c$, constant and/or accelerated). It can be an ideal balloon, or a spherical distribution of particles.

What would it look like? A shrinking sphere? Or a sphere expanding slower than expected? Nothing of the above?

Suppose that we could observe from outside a system expanding radially at relativistic speed (dr/dt about c). It can be an ideal balloon, or a spherical distribution of particles.

What would it look like? A shrinking sphere? Or a sphere expanding slower than expected? Nothing of the above?

Suppose that we could observe from outside a system expanding radially at relativistic speed (dr/dt about c, constant and/or accelerated). It can be an ideal balloon, or a spherical distribution of particles.

What would it look like? A shrinking sphere? Or a sphere expanding slower than expected? Nothing of the above?