Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Speedy ship flies through the sun

  1. Jun 24, 2009 #1

    Buckethead

    User Avatar
    Gold Member

    If a ship was traveling from afar toward our sun at 99.9999... C and skimmed the outer shell of the sun and continued on, would it burn up? From inside the ship, the trip through the shell might take a billionth or trillionth of a second, hardly enough time for the interior of the ship to heat up, but from an observer on earth the ship is taking perhaps a few seconds to make this passage, surely enough time to disintegrate the ship.
     
  2. jcsd
  3. Jun 24, 2009 #2

    Jonathan Scott

    User Avatar
    Gold Member

    From the point of view of the ship, the sun is approaching at near c, so its radiation is extremely blue-shifted and intense as it approaches, even though this doesn't last for long.

    (I'm assuming for purposes of this question that you're treating the space around the sun as a total vacuum, otherwise friction heating would also be a major problem).

    A hypothetical ship that could travel near c would have to be incredibly robust anyway; a collision with the tiniest dust particle would dissipate huge amounts of energy.
     
  4. Jun 24, 2009 #3

    mathman

    User Avatar
    Science Advisor
    Gold Member

    Forget the sun's temperature, hitting that much mass would destroy the ship.
     
  5. Jun 24, 2009 #4
    I think considering the gravitational pull of the great mass of the sun, ur ship (and any pilot in it) would would be elongated like spaghetti long before it reached the suns surface, assuming it was structurally super flexible, any images of the ship to an earth observer ever increasingly red-shifted
     
  6. Jun 24, 2009 #5
    You all appear to be missing the basic point of Buckethead's question, which is:

    If a ship travelling at near-c travels through a phenomenon for a period of time which, from an Earth observer's point of view, should result in the destruction of the ship, but from the ship's point of view is a negligible and harmless period of time, would the ship be destroyed or not?
     
  7. Jun 24, 2009 #6

    russ_watters

    User Avatar

    Staff: Mentor

    Don't let the short time fool you: the energy of impact is proportional to the square of the velocity, so hitting something (anything) at higher speed does more damage than hitting it at lower speed, despite (because of!) the time being shorter.
     
  8. Jun 24, 2009 #7

    Buckethead

    User Avatar
    Gold Member

    Thanks all for your replies, but as nisse mentioned, you are really evading the essence of the question. Yes, there are impact problems at high speed and so on but these are purely mechanical. What I am questioning here is the fact that from one frame of reference the super hot gasses have enought time to burn through the skin of the ship, but from another, there is simply not enough time to do so.
     
  9. Jun 24, 2009 #8
    One might naturally assume that if the ship burned up in one inertial frame, it would burn up in another. Proving the two complex processes are the same in each inerial frame is another matter.
     
  10. Jun 24, 2009 #9

    atyy

    User Avatar
    Science Advisor

    In which frame of reference?
     
  11. Jun 24, 2009 #10

    JesseM

    User Avatar
    Science Advisor

    Why do you think there is not enough time? Any time one body gets hot by being immersed in a medium, it's because of huge number of tiny collisions between the traveling body and the particles of the medium--that's the basic way heat transfer works. So, you can't get around the fact that in the ship's frame, the particles colliding with it contain vastly more energy than they do in the frame of the medium, and are therefore capable of destroying it much more quickly.
     
  12. Jun 25, 2009 #11

    Jonathan Scott

    User Avatar
    Gold Member

    If you are actually talking about contact with the gases, then the temperature of the sun is irrelevant. Temperature is a measure of average kinetic energy per molecule. The effective temperature due to the relative velocity of the gas molecules would be so high that the original temperature wouldn't make any difference.

    This also applies to the heat from the radiation. From the point of view of the ship, the sun is approaching near c and is preceded by an extremely intense "shockwave" of energetic radiation (probably gamma radiation if you're really that close to the speed of light) which could probably destroy any ordinary form of matter.
     
  13. Jun 25, 2009 #12

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    But that assumes that from the ship's point of view it is a "negligible and harmless period of time", and it's not. The gas is denser and hotter (and please, let us not quibble about that) and as such is more destructive, so the ship has the same reaction in both frames.

    As it must.
     
  14. Jun 25, 2009 #13

    russ_watters

    User Avatar

    Staff: Mentor

    At high speed, you can't separate the thermodynamics from the aerodynamics. Johnathan Scott is right: the kinetic energy of the collision (whether you model it as a bunch of tiny collisions or a dynamic compression of a gas is irrelevant) is so high that it doesn't matter how hot the gas is. This is why the SR-71 gets hot when flying at Mach 3 even when flying in a region where the air temperature is below 0.
    The speed (and therefore the energy) involved is so high that from both frames of reference, the ship disintegrates.
     
  15. Jun 25, 2009 #14

    Saw

    User Avatar
    Gold Member

    Not disagreeing with previous answers, there may be something else that you should take into account and which, if you do not, may be the reason for your concern:

    You seem to be assuming that, because two observers disagree on how much time has elapsed between two events, they may also disagree on what happens: for instance, whether the ship disintegrates or not. It is not so. An essential rule of SR (albeit sometimes not highlighted enough) is that events happen for all observers. All practical problems, as far as I know, rely on the occurrence or not of events. Ergo, all observers agree on the solution to practical problems, like whether the ship disintegrates or not.

    Your problem can be decomposed as follows: (i) how many collisions take place between the molecules of the gas and the molecules of the ship and (ii) at what velocity and hence with what kinetic energy. (i) is a number of events happening or not and (ii) also depends on other events, i.e., the previous collisions of other gas molecules among themselves. All observers should agree that those events happen.

    Let us say that for example we judge from the sun frame and from the ship frame. The ship enters the gas medium at v wrt the sun = 0.5 c. At this time the ship synchronizes its clock with the sun observer there located and the latter with a sun observer located at the centre of the sun, by sending to him a light signal and following the Einstein convention (I know, it’s quite unreal…). The ship disintegrates when the ship reaches the centre of the sun and the ship’s clock reads 2 microseconds. The centre-of-the-sun clock reads at that event 2.309 microseconds. In the sun frame, the ship, obviously, has also disintegrated: the sun observer located there has witnessed so. It simply happens that passengers in the ship frame should count on having 2 microseconds of their proper time to kiss farewell among them before disintegrating, while sun observers would calculate that they can kiss each other during 2.309 microseconds while the ship disintegrates…
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Speedy ship flies through the sun
Loading...