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Heat and objects approaching the speed of light

  1. Dec 4, 2007 #1
    Imagine a space craft on a course to the center of the sun. As the craft approaches the sun, the gravitational force of the star would speed up the object perhaps near the speed of light. As we all know, the closer an object is to the speed of light, the more time slows down for the object. My question is since the craft is going fast enough for time to slow down for it, would it take longer for the sun's heat to melt the craft?

    Bonus points for anyone who does that math and can determine that it is plausible if a man made object can make it to the center of the sun if indeed the answer to my question is yes.
  2. jcsd
  3. Dec 4, 2007 #2


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    Welcome to PF, Jism411.
    No even remotely normal star's gravity will accelerate anything to near light speed. You need a neutron star or black hole for that.
    It might be possible that some day an exotic material or force field could protect a ship flying into the sun, but I certainly wouldn't try it with anything that we currently have.
  4. Dec 4, 2007 #3

    If I follow what you are saying correctly the answer is yes, and no. While the sun's gravity will pull a ship to nowhere near the speed of light (it would need to be compressed from it's radius of about 700,000 kilometers to about 2 kilometers to become a black hole. But that aside, the sun's gravitation will accelerate you creating a tiny, but measurable time dilation effect. (theoretically any two objects moving in relation to each other experience some dilation, but most of the time the amount is trivial even at orbital speeds) So, from the observers on the ship, the heat will take slightly longer to affect the ship. From the outside observer the heat will take exactly the same length of time as normal. The point is that the ship is still at the same LOCATION in space when it's heat is at X. It is just that the time it takes the observer to get there makes it appear to be a discontinuity.
  5. Dec 4, 2007 #4


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    Actually, Wysard, you have that dilation effect backward. Everything would appear normal to the occupants of the ship; outside observers would see them slow down.
  6. Dec 5, 2007 #5
    Danger, you are correct, but that's not exactly what I was trying to point out. Grrr...these altered frames of reference can be so tricky to talk about...

    See if I have it right this way. For the people say on Earth watching the ship it takes a tiny amount longer to get to say, the surface of the sun, (where for the sake of argument I have chosen as an arbitrary reference point where the heat of the sun probably has a significant and measurable impact on the ship :surprised: ) than Newtonian physics would expect due to some tiny Lorentz contraction. For the people on the ship, from thier perspective it takes a tiny amount longer to get to the surface of the sun.

    But regardless of the frame of the observer and thier "local" time, the moment the ship "feels the heat" as it were, is the moment it hits the surface of the sun. A distinction by geometry, as opposed to a relativistic one.

    Is that more clear?
  7. Dec 5, 2007 #6


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    Sorry... no. :frown:
    I think maybe it's time for someone else with more understanding of the situation to get involved.
  8. Dec 5, 2007 #7
    Jism411: Forgot the second part of your question. We don't have anything that I am aware of that will withstand the approximate 15 million degrees C at the centre of the sun. Worse, while the surface of the sun is around the temperature of molten iron around 6,000 degrees Celsius ( which helps account for sunspot activity) the corona above the surface of the sun can get up to millions of degrees. So you need to build a ship that can not only withstand enormous heat, but also being hot, and then cold, and then hot again without shattering or losing it's properties. Then add the pressure at the core of the sun that exists to keep that hot nuclear material from plastering itself all over the nearby space and I can't concieve of an any off the shelf engineering solution.

    Danger: You're a droll little fellow... And I couldn't agree more.
  9. Dec 5, 2007 #8


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    Bob the Fascist Dictator says to his committee "We're going to kill 1 million of X and 1 Y". His committee ask "Why kill 1 Y?". You just did the same.

    Rephrase the question. A spacecraft made of cotton wool approaches the sun at near the speed of light. How long does the spacecraft take to get vapourised, compared to a spacecraft approacing at the speed of say, sound?

    Anyway, the answer is no, just the time factor won't change anything. The Sun still sees an object speeding towards it, and that object will be vapourised in whatever time the Sun needs to vapourise that object. How deep it can go depends on how fast it approaches.

    The only difference is, an observer on the spacecraft can sit back with popcorn and watch his crewmates get boiled in front of him before he becomes the next sunspot.
    Last edited: Dec 5, 2007
  10. Dec 5, 2007 #9
    Nothing like doing a faceplant into a couple of thousand miles of hot steel to get your attention. As Han Solo put it "That would make your day real quick, wouldn't it?"

    Having pointed out that at this point it is silly to try it in other than hypothetical terms, can you give the good gentleman some pointers on the relativistic aspects that danger and I could not?
  11. Dec 6, 2007 #10


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    You don't need to get relativity and time dilation involved here. Regardless of the temperature of the sun, if you are exposed to it for a brief enough period of time there will not be sufficient energy transfered to damage the ship. Simply use any ablative shielding you wish and make it thick enough to not burn all the way through during your brief journey into the sun.

    Just make sure that you don't slow down much!!!

    The real problem is if you are going so fast that the background radiation gets blue-shifted to a high temperature. You can't pass through the background radiation in a short amount of time.
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