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As you approach the speed of light it requires more and more energy to carry on accelerating up to the speed of light. More energy is equivalent to more mass. More mass is equivalent to a slower passage of time (gravitational time dilation).

Is speed related to mass?

If so much energy is required to move at the speed of light that it can't be done, then how does light do it?

And we know light does do exactly that, it travels at the speed of light, so what energy causes the light to travel at such high speed?

Quote from: MikeS on 16/05/2011 07:54:44As you approach the speed of light it requires more and more energy to carry on accelerating up to the speed of light. More energy is equivalent to more mass. More mass is equivalent to a slower passage of time (gravitational time dilation).That isn't true. The kind of mass you gain by moving fast isn't the same as gravitational mass. There are two kinds of mass used in relativity, and you're confusing relativistic mass (which goes up when you move fast) with rest mass (which doesn't).

More mass is equivalent to a slower passage of time (gravitational time dilation).

Quote from: MikeS on 16/05/2011 07:54:44More mass is equivalent to a slower passage of time (gravitational time dilation).Which type of mass are you talking about here?

Quote from: JP on 17/05/2011 07:23:23Quote from: MikeS on 16/05/2011 07:54:44More mass is equivalent to a slower passage of time (gravitational time dilation).Which type of mass are you talking about here?Relativistic mass

Quote from: MikeS on 17/05/2011 07:39:25Quote from: JP on 17/05/2011 07:23:23Quote from: MikeS on 16/05/2011 07:54:44More mass is equivalent to a slower passage of time (gravitational time dilation).Which type of mass are you talking about here?Relativistic massThat's the problem. Relativistic mass is not equivalent to gravitational time dilation. Invariant mass does.If your mass is moving and you want to compute it's effect on space-time, you need to use the stress-energy tensor, which accounts for the energy and momentum of motion. This is definitely not the relativistic mass either.

Quote from: JP on 17/05/2011 07:57:56Quote from: MikeS on 17/05/2011 07:39:25Quote from: JP on 17/05/2011 07:23:23Quote from: MikeS on 16/05/2011 07:54:44More mass is equivalent to a slower passage of time (gravitational time dilation).Which type of mass are you talking about here?Relativistic massThat's the problem. Relativistic mass is not equivalent to gravitational time dilation. Invariant mass does.If your mass is moving and you want to compute it's effect on space-time, you need to use the stress-energy tensor, which accounts for the energy and momentum of motion. This is definitely not the relativistic mass either. What does cause the passage of time to dilate when travelling at near to the speed of light?

It's a consequence of special relativity: that everyone in an inertial reference frame measures the speed of light to be constant. Also, it's important to remember that time dilation is only apparent when two observers in different reference frames compare clocks. If I'm traveling near the speed of light, I don't notice anything funny happening on board my spaceship, since it's all in the same reference frame as me so all the clocks run the same as mine.

They are part of that frame of reference and wouldn't notice anything amiss, even if the spaceship accelerated up to the speed of light, in which case they would be frozen in time. So can we actually say that mass travelling at the speed of light experiences the passage of time?

There is a direct correlation between time dilation and relativistic mass, they both have the same relativistic dilation for any unique observer.

Quote from: MikeS on 17/05/2011 11:02:20 They are part of that frame of reference and wouldn't notice anything amiss, even if the spaceship accelerated up to the speed of light, in which case they would be frozen in time. So can we actually say that mass travelling at the speed of light experiences the passage of time?Mass can't move at the speed of light, so that question can't be answered. Trying to answer it by plugging v=c into the Lorentz factor leads to nonsensical results because the entire theory was derived under the assumption that the case where v=c cannot be handled for objects with mass.

yes, but it is not so fancy if you believe in Einstein's Equivalence Principle.

Quote from: JP on 17/05/2011 11:05:58Quote from: MikeS on 17/05/2011 11:02:20 They are part of that frame of reference and wouldn't notice anything amiss, even if the spaceship accelerated up to the speed of light, in which case they would be frozen in time. So can we actually say that mass travelling at the speed of light experiences the passage of time?Mass can't move at the speed of light, so that question can't be answered. Trying to answer it by plugging v=c into the Lorentz factor leads to nonsensical results because the entire theory was derived under the assumption that the case where v=c cannot be handled for objects with mass.I was simply continuing the example you gave. The trend being nothing that travels at the speed of light experiences any passage of time.

Quote from: CPT ArkAngel on 17/05/2011 11:32:38yes, but it is not so fancy if you believe in Einstein's Equivalence Principle.At last.

And relativistic mass still isn't equivalent to inertial or gravitational mass.

JPGoing back to the space-ship. As it accelerates up to the speed of light it experiences no passage of time and its length has diminished to zero (?). It would seem that the space-ship has possibly lost two of the four dimensions of space time. If this were the case then its mass would only have to compress two spacial dimensions out of existence to become a singularity not the usual four of space time. Just a thought.

Think of two mirrors at rest relative yourself, then let a light-corn bounce between them. As it does you will find the path that light-corn to take being a straight path, back and forth, a little like a pendulum. Now let the mirrors move with you staying at earth, it won't matter if you look at them while accelerating, or after as they start to 'coast' in space. From your point of view the light-corn suddenly will move slower, due to you finding that light-corn having a longer path between the mirrors, that as it has to traverse more 'space' as the mirrors it bounce between constantly moves away from you. Also you will find the path it takes to be a diagonal one as it 'tags' after the mirrors in a zigzag motion relative you, being still.

Why does time slow down with relative speed.