Spaceship arriving at a planet

  • Thread starter Thread starter norvegicusbas
  • Start date Start date
  • Tags Tags
    Planet Spaceship
norvegicusbas
Messages
3
Reaction score
0
Hello.
Me and a friend of mine were trying to get our heads around a few of the paradoxes that are found within Einstein's theory of relativity and he came up with something we could not work out ( though I am sure someone here will be able to :)

Imagine you were in a spaceship traveling at the speed of light towards a distant planet. This planet is very dark and the spaceship needs to put on its headlights to see exactly where this planet is. Soon as the headlights are switched on all those aboard the spaceship ( according to their reference frame ) see the light from the headlights shine off into the blackness of space at the speed of light and strike the planet. With the planet well lit from the spaceships headlights the ship continues to approach for an eventual landing. But what will the people on the planets surface see? Do they see the light from the headlights arriving at a point in time before the arrival of the spaceship?
 
Physics news on Phys.org
The light from the headlights of the spaceship will always arrive before the spaceship arrives. The spaceship can (at least hypothetically) approach the planet with a speed almost the speed of light but it can never reach the speed of light.
 
Passionflower said:
The light from the headlights of the spaceship will always arrive before the spaceship arrives. The spaceship can (at least hypothetically) approach the planet with a speed almost the speed of light but it can never reach the speed of light.

Thankyou Passionflower for your quick reply.
What would the outcome be though if the spaceship was made by some incredibly advanced alien race and could be constructed ( along with the passengers ) from a massless material?
 
norvegicusbas said:
Thankyou Passionflower for your quick reply.
What would the outcome be though if the spaceship was made by some incredibly advanced alien race and could be constructed ( along with the passengers ) from a massless material?
Well in that case it could never slow down and was doomed forever to travel at the speed of light. But clearly you must understand there is no such material.
 
norvegicusbas said:
Thankyou Passionflower for your quick reply.
What would the outcome be though if the spaceship was made by some incredibly advanced alien race and could be constructed ( along with the passengers ) from a massless material?
In that case the ship does not have its own inertial rest frame, so it is no longer true that the light from the headlights must move at c in the frame of the ship.
 
OK, so this has bugged me for a while about the equivalence principle and the black hole information paradox. If black holes "evaporate" via Hawking radiation, then they cannot exist forever. So, from my external perspective, watching the person fall in, they slow down, freeze, and redshift to "nothing," but never cross the event horizon. Does the equivalence principle say my perspective is valid? If it does, is it possible that that person really never crossed the event horizon? The...
In this video I can see a person walking around lines of curvature on a sphere with an arrow strapped to his waist. His task is to keep the arrow pointed in the same direction How does he do this ? Does he use a reference point like the stars? (that only move very slowly) If that is how he keeps the arrow pointing in the same direction, is that equivalent to saying that he orients the arrow wrt the 3d space that the sphere is embedded in? So ,although one refers to intrinsic curvature...
So, to calculate a proper time of a worldline in SR using an inertial frame is quite easy. But I struggled a bit using a "rotating frame metric" and now I'm not sure whether I'll do it right. Couls someone point me in the right direction? "What have you tried?" Well, trying to help truly absolute layppl with some variation of a "Circular Twin Paradox" not using an inertial frame of reference for whatevere reason. I thought it would be a bit of a challenge so I made a derivation or...
Back
Top