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pinocola t1_itzub5m wrote

Reply to comment by mfb- in Would heavy unstable elements at the core of a star have a significantly extended half-life due to gravity? by SpectralMagic

Also the shell theorem shows that there is no net gravitational force at the center of a sphere. Lots of pressure down there, but the mass on all sides of the core cancels the gravity out.

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fore4runner t1_iu1rs2f wrote

Does that cancel out the time dilation as well? (It seems like it should logically, but intuitively it 'feels' like the time dilation should be at a maximum at the very centre of the body).

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pinocola t1_iu23ksq wrote

No, because light and information have to cross out of the gravity well to get to an observer, and time dilation is always measured in reference to some other point, in this case presumably outside of the core of the star.

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fore4runner t1_iu2aue3 wrote

But, if a person, in the centre of the earth shout out a laser every 1ms to a relatively stationary observer in space they would get the pulse every 1ms? But if someone on the earths surface did that, they wouldn’t, right?

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pinocola t1_iu2m0r6 wrote

The pulse from the surface would be a bit slower than once every ms due to time dilation, and the pulse from the center of the earth would be even more time dilated than that.

Time dilation comes from a speed difference or the gravity gradient you travel/observe across. The pulses of light don't observe any gravity at the core itself, but once they start traveling out from the earth, they feel the gravity from whatever portion of the earth they've traveled out from, and would appear proportionally time dilated.

If the earth were a big hollow shell like an inflated ball, two observers anywhere inside the shell would feel no gravity due to the mass of the earth, and would not observe any time dilation when observing one another (even if one was at the geometric center and another was hanging onto the inside of the shell). But an observer outside the shell would feel the entire gravity of the earth and would see both people inside the shell as time dilated by the same amount.

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Emuuuuuuu t1_iu23luc wrote

Force can be applied in many directions such that the net is zero. The force is still being applied though. Time only changes in one direction (slows down) and can't be cancelled by other directions.

It could maybe be sped back up with a very dense clump of anti-matter? Can a general relativitist chime in here?

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fore4runner t1_iu2b2mc wrote

I don’t think your right, isn’t the time dilation due to the curve of space time? So in the centre of a body of mass, space time is flat

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Fogernaut t1_iu2cz1r wrote

Isn't anti matter just opposite of matter in terms of charge? I don't think anti matter has negative mass if that's what you are thinking of.

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