What causes black holes and stars to spin?

[Leigha]

https://www.scientificamerican.com/article/what-causes-objects-such/

So, I have a few questions on this.

1. In the article, it's mentioned that the space-time distortion is exceedingly weak around Earth, as compared to black holes. What does this mean?

2. What would happen if the Earth gradually came to a halt, and stopped spinning? I know that life as we know it would be adversely affected, but would humans be able to survive it? (there is speculation from scientists, but what do you think?)

3. If one planet stopping spinning, would it affect other planets? If Earth stopped spinning, would the rest of the universe be negatively affected? I guess what I'm asking is, does Earth ''need'' the spin of other planets, and vice versa?


(Since some here don't post on SF, thought I'd share here, as well.)

[C C]

https://www.scientificamerican.com/article/what-causes-objects-such/

So, I have a few questions on this.

1. In the article, it's mentioned that the space-time distortion is exceedingly weak around Earth, as compared to black holes. What does this mean?

I haven't had a break enough to look at the article yet, but the Earth has incredibly less mass than a black hole and thus not the degree of gravitational effects. Imagine the depression that a baseball would cause in a sheet of rubber "canvas" attached to a trampoline metal framework compared to the depression a cannonball would cause. EDIT (add-on): Okay, getting a moment to glance over it, it seems to be about the aggregation of angular momentum and its effects, but why a body would be attracting so many other spinning objects to begin with still pertains to its mass (black holes have a lot more -- usually). Since the black hole has more concentrated angular momentum, it rotates faster, increasing spacetime distortion in that sense, too.

EDIT (add-on):

2. What would happen if the Earth gradually came to a halt, and stopped spinning? I know that life as we know it would be adversely affected, but would humans be able to survive it? (there is speculation from scientists, but what do you think?)

Depends upon the technology level of the humans. Surviving as if one is on the Moon or resorting to subterranean living might not even suffice if the planet atmospherically deteriorated to something like another Venus (literally hell conditions). Of course, if they were that technologically advanced, they could colonize Mars (which would be more hospitable in comparison).

[Taormina]

https://www.scientificamerican.com/article/what-causes-objects-such/

So, I have a few questions on this.

1. In the article, it's mentioned that the space-time distortion is exceedingly weak around Earth, as compared to black holes. What does this mean?

I haven't had a break enough to look at the article yet, but the Earth has incredibly less mass than a black hole and thus not the degree of gravitational effects. Imagine the depression that a baseball would cause in a sheet of rubber "canvas" attached to a trampoline metal framework compared to the depression a cannonball would cause. EDIT (add-on): Okay, getting a moment to glance over it, it seems to be about the aggregation of angular momentum and its effects, but why a body would be attracting so many other spinning objects to begin with still pertains to its mass (black holes have a lot more -- usually). Since the black hole has more concentrated angular momentum, it rotates faster, increasing spacetime distortion in that sense, too.

EDIT (add-on):

2. What would happen if the Earth gradually came to a halt, and stopped spinning? I know that life as we know it would be adversely affected, but would humans be able to survive it? (there is speculation from scientists, but what do you think?)

Depends upon the technology level of the humans. Surviving as if one is on the Moon or resorting to subterranean living might not even suffice if the planet atmospherically deteriorated to something like another Venus (literally hell conditions). Of course, if they were that technologically advanced, they could colonize Mars (which would be more hospitable in comparison).

[Syne]

Can someone do something about this spammer who can't seem to post without shilling his book?

[Leigha]

Sigh, for some reason I can't quote you CC. But, thanks for your response. That makes a lot of sense, now. So, is the mass of a black hole dependent upon how many objects its consuming? (because any object entering the event horizon is ''adding'' to its mass) Do you think it's possible for black holes to consume all of the energy and everything in the universe...eventually? Ugh, that's a scary thought!

How could we possibly fight back?  -_-

[C C]

So, is the mass of a black hole dependent upon how many objects its consuming? (because any object entering the event horizon is ''adding'' to its mass) Do you think it's possible for black holes to consume all of the energy and everything in the universe...eventually? Ugh, that's a scary thought!

How could we possibly fight back? -_-

Only a small fraction of the universe's content will be consumed by black holes eventually. Too many rival gravitational interactions at play, which in the extremely distant future will ironically work up in complexity to becoming a trend of most stars and bodies being expelled from galaxies, becoming ever more isolated. Supposedly, current black holes -- those not being fed with enough new matter during that staggering time span -- will have evaporated via Hawking radiation before then.

Sigh, for some reason I can't quote you CC.

I never thought to even ask in that Site Feedback topic, Leigha, but is the quoted reply problem specific to only certain members' posts?

[Leigha]

Black holes ''evaporating.'' Hmm. That's a curious theory. If all black holes evaporated, would that be the end of the universe?

To your question, it's hit or miss. Sometimes, I can quote with no problem, but there are times when the text box remains blank. I didn't try it just now, just assumed it wouldn't work for this thread.

[Yazata]

So, I have a few questions on this.

1. In the article, it's mentioned that the space-time distortion is exceedingly weak around Earth, as compared to black holes. What does this mean?

It's an Einsteinian way of saying that gravity is weaker. The Earth doesn't suck as much as Black Holes do. Which is one reason we like it here. We don't want to live in a place that really sucks. 

2. What would happen if the Earth gradually came to a halt, and stopped spinning?

Depends on how gradual the slow-down was. The Earth, stars and black holes spin because they have angular momentum. Not only the Earth, but everything on the Earth. If the Earth just abruptly stopped, we (and everything else including the air) would go flying off towards the east at about 1,000 mph. (The Earth might not withstand the forces and could fly apart. Not sure about that, but it wouldn't be good.)

On the other hand, if the slowdown was extremely gradual, the direct mechanical effect on us would be imperceptible. Slowdowns like that do occur in astrophysics, as orbiting bodies become tidally locked to the larger body that they are orbiting. (Takes millions of years.) That's why Mercury always shows one side to the Sun and why the Moon always shows one side to the Earth.

3. If one planet stopping spinning

That raises the question, spinning relative to what? The Moon has stopped spinning relative to the Earth, but it still spins (once per each orbit of the Earth) relative to the Sun and the "fixed" stars. (While the Earth is always one place in the Moon's sky, the Sun and the stars continue to rise and set.) These kind of ideas are the beginning of relativity theory.

And there may not be any absolute reference frame in which everything else sits like a picture in its frame. Newton thought there was. Einstein didn't. (I'm undecided, but somewhat inclined to side with Einstein. I'm just a layman though.)

would it affect other planets? If Earth stopped spinning, would the rest of the universe be negatively affected?

No.

I guess what I'm asking is, does Earth ''need'' the spin of other planets, and vice versa?

No.

Life on Earth might arguably need the Earth rotating relative to the Sun. If it didn't, one half of Earth would be in perpetual daylight and the other half in perpetual night. The Sun would always be in the same place in the daytime sky. That would dramatically change the climate and weather and all kinds of stuff like that. The day-side might become a vast desert and the night side the mother of all polar icecaps as the oceans evaporate on one side and the water vapor freezes permanently on the other. But life is adaptable and would probably survive in some form around the terminator (the dusk zone around the edges).

It's a little sobering to think that bacteria might have been the first life on Earth, and they might be the last, at the (literal) end of days. Born survivors.

[Zinjanthropos]

If a BH does not allow light to exit then is it because of gravity pulling the massless Photons in or severely tugging/flattening the space/space time surrounding the massless particles?

[Syne]

If a BH does not allow light to exit then is it because of gravity pulling the massless Photons in or severely tugging/flattening the space/space time surrounding the massless particles?

Gravity doesn't "pull" per se. The curvature of spacetime warps otherwise straight lines into curves. A planet's orbit is it moving in a straight line in a curved spacetime, and the path of light also curves near large masses. This isn't doing anything to the photons, it's just warping the spacetime they move through. And with a large enough warping of spacetime, like near a black hole, the path of light can be curved so much that it never escapes.

But then, any curving path does impart energy, which from any relative frame of reference is observed as mass. This is why photons have zero "rest mass". A photon is never at rest.