ThatCanadianGuy's Cosmos: The Gravity of the Situation

[ThatCanadianGuy]

ThatCanadianGuy here! With a post that (hopefully) will be the first in a series on astronomy, cosmology, and the history of our universe! Certainly fits the Rambling of the Wise thread, I think!

Anyways, I'd like to give readers a fun little first post, this being on the gravitational pull we all share with eachother. Ever feel that certain "special" attraction to someone? Well today I'm here to tell you that (among other bodies in space) even the MOON has a stronger attraction to you! Don't think so? Well here's the math; due to just the immense size of the moon compared to one person, even if you were hugging that "special someone" reeely tightly, the moon would still be pulling on you 300 times stronger than that person! Incidentally, the Sun has an even stronger pull! Even though it's soo much farther away, the Sun is by far the strongest and heaviest source if gravity in the Solar System, and pulls on your body 50,000 times stronger than a person!

But wait. where does the Earth come into this? Well, although the Earth is much much smaller than the Sun, you never see anyone getting "pulled" into the Sun now, do you? That's because the Earth has a much stronger pull on us since we're right on the Earth's surface, only about 6,000km from the core. That means the Earth pulls on you 80 million times stronger than a person! The lowest measure before we get to that super-squeezy hug from your "significant other" would come from Jupiter; as the largest planet in this Solar System, it's mass pulls on your body 3 times stronger than a person hugging up right next to you!

Now the you understand the "gravity" of the situation, I leave this first episode of (hmm lets think of a title real quick! :P) ThatCanadianGuy's Cosmos open to any of your questions related to gravity, from black holes to quasars, you supply the questions, I supply the answers!

If you need to find it out, I'll be sure to know it! :yeah:

[Antares]

Lol
Great post.
However I would like you to explain what you know about Black Holes :D

[MrPinnick17]

Whoah, gravity is bananas.

I'm getting pulled up and down by all of this but still I don't feel it. I've been told about a zero gravity aeroplane, I forget what it's called but it flies up and down in wavy patterns. When it flies up out of the atmosphere it loses gravity when you fly back down you gain gravity or something. It sounds really cool.

[ThatCanadianGuy]

Good God man! You're holding no stops now aren't you! Well, I know many things on the subject; in fact last year my school presentation on Black Holes garnered me an astounding mark; my teacher gave me a 105% grade! However, I don't really want to have to explain things in great detail (those posts would take too long, and would bore some people... I'll leave that for my opening posts! :D) so if you have a SPECIFIC question, I would be more than happy to answer it.

So... I'm not going to tell you everything I know. But for now I guess I'll give you a brief explanation of how they form.

1. Super-massive star collapses under it's own immense gravity; OR only it's core collapses and the star goes super nova.

2. The core shrinks, yet it's density remains the same; it's gravitational pull is magnified to the point where even photons (beams of light) cannot escape the pull of the star.

Basically, the hole isn't REALLY a "hole" its a sphere-shaped core of the star, which we cannot see because not even light can reach the escape velocity required to pass back through the black holes' event horizon (the point where once the matter goes in, it never comes out).

[Antares]

Well why do black holes appear 2 dimensional?....I think...

[ThatCanadianGuy]

Well that's just it; it's just it's appearance :D

We can't really "see" black holes, since they absorb all light we're just seeing the absence of light they create. In that vein, we can only really detect black holes by how they distort space around them (space and light seems to "bend" in a cirular pattern towards a sphere of blackness... a sphere that looks like a 2-dimensional "cicle" from the side-on that we see it). The general effect would look something like this:

http://www.sanfranciscosentinel.com/wp-content/uploads/2007/10/black-hole.jpg

So black holes really are not two dimensional; they do appear to attract materials from their most dense points (where the north and south poles of the star's core used to exist) so it can seem that things are generally pulled from one or two specific directions. In the end though, you'll get pulled in from any direction regardless.

Alot of times when math comes into play you might see mathematicians using a two-dimensional model for a black hole, simply because it's much easier to work with, and the numbers turn out right... more often. But when dealing with the reality of black holes, they do in fact exist in 4 dimensions, that is the regular 3 dimensions as well as time (a more correct word would be in "spacetime").

[ThatCanadianGuy]

Sorry for the double post :whoops:

I'd just like everyone to know that I'll be doing this sort of thing once a week; presenting my own interesting stories as well as answering your questions. If anyone would like there questions to be a part of next week's show, PM me with any and all questions you have. The questions can be about ANYTHING related to astronomy, cosmology, and the universe in general.

Stay tuned for next week's post!

[Oblivion]

How does a black hole start?

[ThatCanadianGuy]

(Read two posts above)

:D

When a star's core collapses; it shrinks in size, yet it's gravity and density stay the same; causing the gravity to be magnified to a huge amount; so far this is the only way for black holes to form. However, if you could somehow shrink the Earth to the size of a ping pong ball, yet you kept it's gravity at the same strength, the Earth would become a black hole, since the escape velocity (i.e. the speed you need to travel to escape the planet) would become faster than the speed of light.

[0=]

Its density doesn't stay the same. The density of the singularity of a black hole is, for all intents and purposes, infinite.

[ThatCanadianGuy]

Its density doesn't stay the same. The density of the singularity of a black hole is, for all intents and purposes, infinite.

^^ I know; my meaning was that the density doesn't shrink along with the size of the object (sorry for that little word slip). I was trying to show that you can't decrease the density of an object (as we know since matter can't be created or destroyed, it just becomes infinitely compacted in the singularity... and whatever it sucks in goes wherever the hell it goes xD).

[MrPinnick17]

Can you fall out of space? Or will the gravity from Space keep you floating around? But if you can't fall out of space how do things like Apollo or whatever come back to earth with no engines?

[theOperaGhost]

The earth's gravitation pull is stronger than the other ones, because it is closest. It isn't falling out of space...earth is pulling it...Earth is actually pulling on the moon, too. That's is why the moon is orbiting the earth.

[ThatCanadianGuy]

Can you fall out of space? Or will the gravity from Space keep you floating around? But if you can't fall out of space how do things like Apollo or whatever come back to earth with no engines?

Of course you can't really "fall" out of space; especially when there isn't anything to fall into :D! Unless something large enough is nearby to pull you in, you'd just float in one spot (unless you had rockets or some way to move around). However, since there is a TON of... "stuff" in the universe, there will always be at least ONE thing pulling you; either a planet, or a star, or even the rotation of this galaxy (and the super massive black hole at it's center).

The Apollo command module had small rockets for manouvering, as well as firing the ship back towards Earth; just enough force to let gravity do most of the work. The Apollo just needed that HUGE engine it sat on (the Saturn V rocket) in order to escape the Earth's gravity, which you can only do at about 7 miles per SECOND. Once in space, there isn't any air resistance, and the ship could move pretty fast with just its little atmospheric jets.

[MrPinnick17]

Nice explanation you should be a cosmonaut.

[ThatCanadianGuy]

Aw gee thanks :whoops:

My next "episode" will be up by wednesday, where I'll share with you some info into stars, energy, and marshmallows :P (you'll have to wait and see where that comes into all this :D).

Aside from my little "article" on wednesday, I'd be more than happy to answer open questions either on this thread, OR if anyone wants their question to be featured on next week's Opening Article, PM me with your question and I will be sure to include it with an answer! :yeah:

[0=]

You realize a cosmonaut is a Russian astronaut, right? Astronomy might be more appropriate.

[raiders rule]

I saw this on a show about time and it was pretty interesting, according to theorectical physics, in the very center of black holes time ceases to exists, there in no time, time is in "pause". Interseting.....also, time travel is possible......and time "rewinding" is possible, just so unlikely that it will never happen.

[ThatCanadianGuy]

I saw this on a show about time and it was pretty interesting, according to theorectical physics, in the very center of black holes time ceases to exists, there in no time, time is in "pause". Interseting.....also, time travel is possible......and time "rewinding" is possible, just so unlikely that it will never happen.

For someone falling into a black hole and crossing the horizon, this crossing is mathematically predicted to involve the transformation of your single time-like coordinate into a space-like coordinate, and your three space-like coordinates into 3 time-like coordinates. Along any of these 3 former space-like coordinates, they now all terminate on the singularity, and your experiencing them as time-like now means that you have no control over your destiny because all choices always terminate on the singularity...at least in the case of a non-rotating black hole. The coordinate which used to measure external time, now has a space-like character which affords you some wiggle room, but dynamically, in terms of these new reversed space and time coordinates, you find that no stable orbits about the singularity are possible no matter what you try to do. Without any stable orbits, and the inexorable free fall into the singularity, relativists often refer to this as the collapse of space-time geometry.

So basically... time breaks down to whatever object is falling in; anything observing the object from a safe distance can still see it falling until it is completely "swallowed".


Time travel is not possible. In any way, shape or form. "Rewinding" is even more impossible. If you want me to explain WHY, then first you're going to have to tell me why YOU think (and can prove) that it's possible. Then they'll at least get both sides of it.