Jesus, I think I poked my eye.
>> The two distinct effects that Gravity Probe B was designed to see
occurred because of the Earth itself, not an extremely massive, nor
an extremely dense object.
So, its distortions of space are very subtle indeed.
One distortion is the curvature of space itself,
which should have manifested in a slight bending of the axis of the gyroscopes
in the satellite as it orbited the Earth.
The second effect was 20 times smaller still, called frame-dragging.
It's the subtle distortion of the contours of space time caused by a spinning object.
Essentially twisting the space time by a tiny amount.
Gravity Probe B detected both effects by their deviations imposed
on the gyroscopes while the telescope was locked in a very distant object,
at a fixed location in space.
The extreme distortions of space and
time expected near a black hole remain to be tested.
The distortion of space as you approach the black hole.
Produces a tunneling of what can be seen looking outwards should someone venture
close to the black hole.
At the event horizon of course, all view of the external world is lost forever.
The distortions of time are equally extreme.
In principle, if two astronauts had synchronized time keeping pieces, and
one stayed in orbit of a black hole at a safe distance,
while the other spiraled into the black hole, according to general relativity.
As seen from the astronaut at a safe distance,
the clock of the astronaut falling in would run slower and slower and
would asymptotically slow as they approach the event horizon.
In principle, at the point they reach the event horizon.
Their clock and
their image as seen from the outside would be frozen forever in time.
Is it possible to ever test this in real life?
Unfortunately black holes are rare.
The likely nearest example would be hundreds of light years away, too far for
us to venture in the near future, perhaps even in the next few centuries.
Also, falling into a solar mass black hole, or
the remnant of a massive star, would be an extremely unwise thing to do.
The differential gravity or stretching force between your head and
your feet if you fell in, on one side of your body and
the other, would be sufficient to stretch you apart and kill you.
And this is not a mild form of stretching, like pizza dough.
This is called spaghettification, where every aspect of your body from muscles,
down to nerve fibers, down to molecules,
are stretched as falling into the black hole, the gravity field increase.
So falling into a black hole is not recommended.
How big would a black hole have to be for this effect not to be disruptive?
Probably about 3,000 times the mass of the sun.
At that point, the stretching force, or the tidal force on a human-sized object
would not be so extreme as to kill that person or disrupt the object.
The second problem of an experiment of falling into the event horizon of a black
hole is that no information could be transmitted out on the conditions inside.
They will remain according to general relativities.
Forever sealed off from us.
There are many hollywood type simulations of black holes and
black holes are featured in TV shows and movies for decades.
But the real astrophysics of a black hole, general relativity can be used to predict
what it would look like in terms of space and time as you fall in.
The following animation showing how the clock is affected and how the contours of
light are affected, shows a spiraling passage in towards the event horizon.
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