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What are the consequences of violating (or almost) speed c

  1. Aug 9, 2012 #1
    I was thinking about what happens to something with mass as it approaches speed c and came to the following conclusion.

    It accumulates so much mass that it spontaneously collapses into a black hole.

    Is it correct?
  2. jcsd
  3. Aug 9, 2012 #2


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    Staff: Mentor

    No. In fact, nothing interesting happens. The easiest way of seeing this is to consider that as far as the object is concerned, it's not moving at all; it's sitting still while the rest of the universe is rushing past in the opposite direction.
  4. Aug 9, 2012 #3
    Thanks for your reply Nugatory, it is not what I was expecting :)

    Where am I going wrong?

    When something approaches ever closer to speed c it gains mass, if it reached c it would have infinite mass so how can something reach .99999999999999999c and not weigh so much that it wouldn't turn into a black hole.
  5. Aug 9, 2012 #4


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    Staff: Mentor

    You are going wrong when you speak of something moving at .999999999999c (or any other speed, for that matter) and not saying what that speeed is relative to.

    Are you moving at .99c right now? No, says the person standing next to you. Yes, says the creature in a distant galaxy that's moving at that speed relative to our solar system, who happens to be watching you with a telescope. They're both right.

    When we say that an object's mass increases at its speed approaches that of light, that's a sloppy shorthand for describing how the equation F=ma remains true for all observers, even though their measurements of time and distance, and hence of acceleration, are different if they have different relative speeds.
  6. Aug 9, 2012 #5
    Now your making me think sideways!

    If I restated it as 'If an object with mass was "accelerated" to .99999999999999999c'

    I think I understand what you mean mean by its speed being different to various observers but your explanation is making me think that its true energy wont be realised until it hits something.
  7. Aug 9, 2012 #6
    There's no such thing as "true energy." Energy is a reference-frame dependent quantity. Even in Newtonian physics the energy depends on reference frame. What is the kinetic energy of a baseball sitting on the ground? Zero, says you, standing next to it, observing it at rest. 1/2 mv^2, says your friend driving by in a car.

    No, you can't turn a baseball into a black hole by throwing it at nearly c. You are becoming confused by the (confusing, and basically wrong) concept of relativistic mass. It will basically never help you to think of bodies gaining mass as they accelerate towards c. They don't. The reasons bodies cannot travel at c have nothing to do with their mass. They have to do with geometry and Lorentz symmetry: i.e. the ways that different reference frames are related to each other.
  8. Aug 9, 2012 #7
    Well there goes my plan to destroy earth :D

    I searched google for "relativistic mass" that you mentioned and found this page.
    http://www.relativisticmass.com/ [Broken]

    I sort of think I'm starting to get the idea, the increase in speed relative to you means you measure its mass differently but its gravitational field remains constant?
    Last edited by a moderator: May 6, 2017
  9. Aug 9, 2012 #8


    Staff: Mentor

  10. Aug 9, 2012 #9
  11. Aug 9, 2012 #10


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    Staff: Mentor

    From the point of view of a proton in the Large Hadron Collider, you are moving at a speed infinitesimally close to c. Are you a black hole? :wink:
  12. Aug 9, 2012 #11
    Only on Mondays :smile:
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