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We can't observe any matter inside black hole, why do we still see gravitational pull from that matter?

It is obvious that you need a gravitation well to have a black hole, but it's not obvious why the gravitational pull will still be there once event horizon is formed and black hole contents (singularity?) are no longer observable.

If an event horizon of a black hole does indeed have innate gravitational pull, does the same apply to event horizon of observable universe? There's matter behind observable universe event horizon, do we get pulled towards it? If not, why not? If yes, how strong is this effect?

Qmechanic
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alamar
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  • Great question! If nothing at all can leave a black hole, how can we feel its force of gravity? Does that mean that gravity waves can travel faster than the speed of light (if they can escape and yet light can't)? (I have no idea ...) – Time4Tea Oct 29 '19 at 15:34
  • There is no "gravitational pull" in General Relativity (i.e., gravity is not a force.) Things "fall" by following the path through curved spacetime that inertia wants them to follow. The force that you feel when you stand on the Earth is not the force of the Earth pulling you down, it's the force of the solid ground pushing up against the soles of your feet, preventing you from falling (i.e., preventing you from following the path that inertia wants you to follow.) – Solomon Slow Oct 29 '19 at 16:56
  • Possible duplicate: https://physics.stackexchange.com/q/937/2451 – Qmechanic Oct 29 '19 at 19:31

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It is very important to understand the difference between static field and the EM waves of Gravitational waves.

Black holes do have static fields around them, they can have EM charge (a static EM field) and a gravitational field around them, outside the horizon.

To have the static fields around them, BHs do not need to send any information nor particles from inside the horizon. No real photon or real graviton needs to be sent from inside the horizon. So no particles need to be sent from inside the horizon.

No information needs to be sent from inside the horizon either, because the information about the static fields (EM and gravitational) is all on the horizon.

How does gravity escape a black hole?

Árpád Szendrei
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  • What about the event horizon of observable universe? Can we just say that it arises because universe is curved, thus red shift behaves like gravity? – alamar Oct 29 '19 at 18:55
  • Can we say that red shift arises from the fact that there is matter past the event horizon of observable universe? If that is not the source of red shift, what are gravitational implications of observable universe's event horizon? – alamar Oct 29 '19 at 19:04
  • @alamar gravitational redshift is because when photons travel through the expanding space (intergalactic voids), their wavelength get stretched. – Árpád Szendrei Oct 29 '19 at 19:20
  • I understand that. But what about event horizon of observable universe? Does it have gravitational properties like the event horizon of a black hole does? If not, why? – alamar Oct 29 '19 at 19:43