# The Naked Scientists Forum

### Author Topic: what affects times more, gravity of the speed an object is moving?  (Read 233 times)

#### thedoc

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##### what affects times more, gravity of the speed an object is moving?
« on: 17/10/2016 17:53:01 »
Kamil Przybos asked the Naked Scientists:
Hello,
English is not my mother language and my question is not easy but here we go :)

If I understand Einstein's relativity it means that if you move faster time goes slower (relatively to other objects) what is more if you are closer to stronger gravitational field your time also goes slower.

If I haven't been wrong until now I have a question.

Let's imagine there is a black hole or very massive neutron star that rotates extremely fast. There is attached extremely long (let's say 1 light year long) pipe to the 'equator' of this rotating black hole.

So the end of the pipe attached to the black hole will move as fast as the black hole rotates, the other end of the pipe will move much faster.  And here comes my question. Which end decays / gets older slower? The one near the centre of the very strong gravitational field or the one moving very fast?

I know that gravitational field weakens with distance very fast but this is my question? Is the black holes's gravitational field slowing time to the same 'strength' as the object moving with the 99.999% speed of light?

I'm aware that my question might be wrong from the very beginning because of my wrong understanding of relativity though :)

Kind regards.
Best show on Earth,

Kamil from Poland
What do you think?
« Last Edit: 17/10/2016 17:53:01 by _system »

#### evan_au

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##### Re: what affects times more, gravity of the speed an object is moving?
« Reply #1 on: 17/10/2016 21:51:15 »
To a distant observer, time has effectively stopped at the event horizon of a black hole. You can't get much slower than that!

#### Janus

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##### Re: what affects times more, gravity of the speed an object is moving?
« Reply #2 on: 19/10/2016 17:42:00 »
As already pointed out, with a black hole, the maximum time dilation will always be at the event horizon.  So instead, let's consider a neutron star.

If we assume a neutron star mass of 2 solar masses with a radius of 11 km and a spin rate of 100 rotations/sec, we can create the following graph showing how fast a clock would run at different points of a pole extending from the surface as measured by a distant observer.

You will note that At the surface, clock will run at a rate of ~0.68, increases to ~0.95 at a distance of ~7 times the neutron star radius and then slows down again until somewhere between 31 and 32 times the star's radius, it runs at the same rate as the surface clock. It then continues to slow down as the radius increases.  There is a theoretical limit on the length of the pole, since its end must always be moving at less than c.

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##### Re: what affects times more, gravity of the speed an object is moving?
« Reply #2 on: 19/10/2016 17:42:00 »

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