The Question
(Submitted May 16, 1997)
A Space traveler is under constant acceleration, ignore for a moment the
propulsion unit or fuel requirements. As the traveler approaches the
Speed Of light, "The way I understand it " the hull of the ship would be
undergoing tremendous stresses, High Energy Photons would be bombarding
the ship at an ever increasing energy level. While behind the ship, light
would be shifting into the infrared.
Light from the approaching Red Giant would be shifted into the Gamma Ray region.
Time would be coming to a standstill. The Ship would be attaining great mass.
That the Speed of Light the occupant would be seared by "All Radiation "
"All Energy " "All Mass " and be at "All Time ". Is this basically the
correct idea?
If it is, the other question is: Speed is linked to Time and Mass/Gravity,
so it leads me to think there is some sort of "agent " such as
"air
molecules in a planetary atmosphere " that is getting compressed or
otherwise affected. As though a fabric is being stretched.
I understand that we live on the edge/surface of an expanding "Soap
Bubble ", the Past being at the nonexistent center while the future being
what we are expanding into. Have I got it right so far?
The Answer
I asked my colleague Demos Kazanas to address your question. His answer
follows:
The observer which keeps constant acceleration will not feel any stresses
other than the normal when he approaches the speed of light. stresses are
caused by acceleration, not velocity and since the acceleration is constant
there will be no more stresses when the velocity is large or small.
It is true there will be a blueshift of all forward coming photons and
if one wants to compute that, yes there will be stresses from their interaction
with the space ship. Other than that, in as much as the observer does not
interact with the outside he should feel as comfortable as when he sits
in his office.
The power requirements of course become humongous because of the amount
of fuel necessary to approach the speed of light arbitrarily close. One
can compute at which point the mass of the fuel required to keep the ship
accelerating becomes so high that its self gravity would cause it to collapse
as a black hole. Of course the observer (assumed human) would have been
crushed long before due to the intense gravitational field of his own ship.
Yes, your picture of the expanding universe is (we believe) basically correct
if we assume that the universe is indeed closed. if it is open then the
soap bubble analogy does not hold and one would have to consider a different
kind of hypersurface which extends to infinity.
I hope that this does answer some of your questions.
Jim Lochner
for Ask an Astrophysicist
