Viewing a single comment thread. View all comments

mfb- t1_ity0qbe wrote

If you think of gravitational time dilation: No. It's a tiny effect for stars, just a few parts in a million. Instead of 1 second the lifetime (as seen from far away) is now 1.000005 seconds or something like that (with the exact number depending on the star) - not a big deal.

342

tobojijo t1_itynwoe wrote

Over the course of say 4 billion years that adds up to a 20,000 year difference

79

MrMurchison t1_ityp99s wrote

Sure, but that only seems like a significant difference because of human time frames. Those 20,000 years describe the difference between being at exactly half of the original mass, and functionally half of the original mass.

182

Implausibilibuddy t1_ityzueg wrote

What about gravity affecting ability for a particle to break the weak force, or is that negligible? Or pulling atoms closer together making them more likely to be hit by particle emissions from other atoms?

69

mfb- t1_itzenic wrote

Completely negligible unless you are well inside a black hole.

79

[deleted] t1_itzj21z wrote

[removed]

59

pinocola t1_itzub5m wrote

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.

27

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).

3

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.

2

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?

1

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.

2

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?

1

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

1

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.

1

alien_from_earth_14 t1_iu08lvr wrote

So any element of really high atomic number can stay stable at the singularity theoretically? Also will it be just one atom?

2

mfb- t1_iu0bfwx wrote

No, it can't be stable at the singularity, nothing (that we know) can. A nucleus will get ripped apart by tidal forces before it reaches the singularity (or whatever might be there - but for sure not atoms).

9

8spd t1_iu0pfw6 wrote

I mostly like the term "well inside a black hole", because it implies the existence of "barely inside a black hole".

2

mfb- t1_iu2wbsw wrote

The event horizon is usually seen as boundary. You can be just behind the event horizon (you can't stay there, of course).

2

Ituzzip t1_iu0dk7r wrote

Ok but what about the extreme pressure?

1

mfb- t1_iu2wlzo wrote

Also irrelevant for radioactivity. Electron degeneracy pressure can have an influence on electron capture and beta decays, neutron degeneracy pressure (neutron stars) can have an effect on the stability of nuclei.

2

vrnvorona t1_itzdqmn wrote

Isn't weak interaction only weak compared to strong interaction and is very small on atom scale?

12

nineinchgod t1_itzeuxd wrote

Yes, and at subatomic scales, gravity is by far the weakest of the fundamental forces in action.

24

ackillesBAC t1_itzf5ny wrote

Doesnt every frame always observe thier time ticking at 1s/s?

So from the point of view of a particle in a star it lives a normal time span regardless.

However an outside observer would see thier time flowing at 1.000005s/s

4

mfb- t1_itzg0jb wrote

> Doesnt every frame always observe thier time ticking at 1s/s?

Sure. That's why I discussed "(as seen from far away)" in my comment.

19

[deleted] t1_itzf544 wrote

[removed]

1

mfb- t1_itzgc2s wrote

Temperature in the Sun's core is just ~15 MK or ~1 keV, which leads to a typical gamma factor of ~1+10^(-6) for protons and ~1+5*10^(-9) for very heavy nuclei like uranium. That's a smaller effect, especially for heavy nuclei.

4

Flatworldnotearth t1_itzgu7f wrote

For extremely high temperatures in of over 2.7GK required for silicon fusion for example it could have been several orders of magnitudes greater.

1

mfb- t1_itzimnc wrote

2.7 GK / 15 MK = 200, so we get 1+10^(-6) for uranium. Still smaller than the gravitational effect, especially if we consider that we are now looking at the core of a far more massive star.

5

Flatworldnotearth t1_itzkpwd wrote

An uranium nucleus in solar core travels at around 36km/s and in a exploding star at 3GK is around 500km/s and the Lorentz factor is around 1.0000015. Reaching the effects of gravitational time dilation as you say but the heavier the star is the more gravitational time dilation it gets. Thanks for your explanation.

1

[deleted] t1_itybwxl wrote

[removed]

−3

mfb- t1_ityc918 wrote

Gravitational time dilation is based on the potential, not based on a force. The potential has its minimum (i.e. the largest time dilation) at the center.

22

DaRealKryall t1_itycuw0 wrote

Oh, I didn't know that, I stand corrected then!

Just graduated high school, but our last physics unit was special relativity; we were only taught it to be based on the velocity of an object relative to the stationary observer.

1

CrzySunshine t1_itzeop4 wrote

Gravitation is handled in General Relativity, of which Special Relativity is a much smaller (and much easier) part.

3

DaRealKryall t1_iu25haa wrote

Heh, easier by calculation, sure, but my classmates would disagree on the comprehension aspect of the questions.

1