If a mass is moving with speed of light does it converts into energy of remains as mass it self?As per relativity theory if a mass moves with speeds comparable to speed of light then the time on the mass will be moving slower when compared to the time from where it has been started from.So if you use relativity theory as the mass approaches its speed to speed of light ,then the time or watch on the mass stops or the mass gains infinite time or does it convert to energy or what else can happen?can anyone give a try for this question?

  • $\begingroup$ A massive object cannot move at the speed of light (relative to anything). $\endgroup$
    – WillO
    Commented Mar 12, 2015 at 16:25
  • $\begingroup$ It can move , but you cannot measure, because it gets shifted to other world. $\endgroup$
    – vamshi
    Commented Sep 8, 2020 at 12:51

1 Answer 1


One of the things that frequently trouble beginners to special relativity is that all velocities are relative. We can accelerate protons to $0.999999991c$ in the Large Hadron Collider, but from the proton's perspective it is at rest and it's everything outside the collider that's moving. So we can be confident that nothing happens to objects moving at near light speed velocities, because nothing has happened to us even though we are moving at light speed velocities relative to other observers.

It is certainly true that from our perspective time slows down for a fast moving object e.g. an astronaut on a fast moving rocket. However the astronaut would still observe time passing at the normal rate, and indeed they would observe our time to have slowed.

All this seems utterly bizarre, but that's only because we don't usually observe things moving that fast so we aren't used to the effects it has. As you study relativity and get used to it you'll find the effects like time dilation seem more natural (then you start studying general relativity and it all gets weird again :-).

  • $\begingroup$ Curious that this answer appeared the Low Quality review queue... $\endgroup$
    – Kyle Kanos
    Commented Jan 14, 2015 at 13:25
  • $\begingroup$ Are you sure about that: "However the astronaut would still observe time passing at the normal rate, and indeed they would observe our time to have slowed"? It seems that our time should be increased for the astronaut. That's why the astronaut returns younger. $\endgroup$
    – Dmitry
    Commented May 15, 2016 at 1:33
  • $\begingroup$ @Dmitry: if two observers are moving in a straight line at constant speed each will see the other's time passing more slowly. When you say the astronaut returns younger I assume you're talking abut the twin paradox but that involves accelerated motion. $\endgroup$ Commented May 15, 2016 at 6:05
  • $\begingroup$ Acceleration motion makes astronauts time slower for us and our time faster for the astronaut. Time won't be slower for both. There is no other way to be the astronaut younger as it's proved by math calculation. $\endgroup$
    – Dmitry
    Commented May 15, 2016 at 10:20
  • $\begingroup$ May be there is a parallel world,This question may be have a different answer in coming future. $\endgroup$
    – vamshi
    Commented Sep 8, 2020 at 12:51

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