big bang theory

Jello
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big bang theory

There are trillions of gaps in my knowledge on many a topic, and here is one that I need cleared up by the in-house science pros. The universe is expanding, the galaxies are traveling away from each other, and yet galaxies collide with each other. I know I've got something wrong here. Can someone please pretty please tell me what it is?

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Jello wrote:There are

Jello wrote:

There are trillions of gaps in my knowledge on many a topic, and here is one that I need cleared up by the in-house science pros. The universe is expanding, the galaxies are traveling away from each other, and yet galaxies collide with each other. I know I've got something wrong here. Can someone please pretty please tell me what it is?

The universe is expanding, but that does not mean that internal interactions between galaxies do not exist! In places where the force of gravity between galaxies overpowers the general force of expansion (since the expansion is accelerating you can imagine that it would generate a force on the galaxies), galaxies will drift together.

Imagine a huge firecracker filled with magnets. The firecracker explodes, and sends magnets flying everywhere. There is some randomization in the paths of each magnet, so some magnets are farther away from each other than others. If some of the magnets are close enough, they will stick together, and then continue on the path that the explosion set them on. This is basically the case with  the universe, except we are talking about gravity rather than magnetism, and we are talking about acellerated expansion rather than an explosion.


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Jello wrote:There are

Jello wrote:

There are trillions of gaps in my knowledge on many a topic, and here is one that I need cleared up by the in-house science pros. The universe is expanding, the galaxies are traveling away from each other, and yet galaxies collide with each other. I know I've got something wrong here. Can someone please pretty please tell me what it is?


 


I see your confusion, but it's simple.
The universe as a whole, generally, is expanding.  But what's in it is bouncing around.
Some things are moving outward faster than others, et cetera.
I lack all the nessessary jargon to explain this, perhaps.  But let me try a metaphor.
Blow up a baloon with your mouth.  Pretend air molecules are galaxies.  The universe is expanding, and yet the molecules are bumping into each other.  Now, there are many, MANY differences between the universe and this balloon idea, but I hope you get the general point I'm trying to make.  Yes, mostly the galaxies are moving outward, while that may not be the case with what's in the ballon, because the molecules in the baloon bounce off the sides of the balloon.  I know my analogy isn't perfect, but things in the universe are choas.  Instead of bouncing off the sides of the uninverse, rather the galaxies pull toward each other using their emence gravity, and others therefore move at different speeds and different directions.

Hum.  Isn't there a black hole at the center of each galaxy, like a massive one?  Funny, I had this weird idea that black holes were in fixed locations, but I know galaxies collide, so that fixed location black hole thing can't logically be true.  Huh.
I need to go freshen up on my physics and crap again.


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Ok, I'm shooting from the

Ok, I'm shooting from the hip here, so take everything I say with a grain of salt.  However, this is the way I have roughly come to understand it.

Not every galaxy is speeding away from every other galaxy.  There are clumps of galaxies and the clumps are speeding away from each other.

Our "clump" of Galaxies is called the Local Group.

Within the Local Group we have two major Galaxies and roughly 30 minor galaxies.

The two major Galaxies is ours(Milky Way) and I believe Andromeda.  Both of these galaxies will eventually crash into each other and become one super huge Galaxy.  And I guess eventually all the minor galaxies will eventually get pulled in too.  eventually everything will get all sucked down into one supermassive blackhole.

Anyways, that's a layman's way of saying it.  Cause I'm definetly a layman with this kind of thing.

http://en.wikipedia.org/wiki/Local_Group

 

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Jello
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Sweet, thanks guys, I'm

Sweet, thanks guys, I'm starting to get the gist


Grant
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expanding universe

Actually it is not expanding as if from a an explosion, it is expanding as in "just sort of getting bigger". Imagine the universe is on the surface of a balloon which is expanding. The galaxies are like magnetic dust. They wander around under their local attraction. On average they all get further apart, but some local collisions occur. The expansion thing is rather smooth and almost imperceptible on the mere galactic scale. The average distance between galaxies is about 1/10,000 of the observable universe so their interactions with each other are indeed very "local". As for the galactic central black holes, they are as moveable as anything else. They are just very heavy so nothing much else moves them, although the weight of the whole galaxy can hold them. When galaxies collide and merge they should end up with two black holes but this area of observation is quite new (it has been about 10 years since the observations of black holes in every galaxy) and so what happens to them in collision is under active discussion. You might think they would collide but actually their chances of doing so are quite small, they could tango in orbits for billions of years unless there are some effects that provide drag. And just to add to the fun, it is also becoming clear that almost all medium to large galaxies are formed by mergers of many small galaxies, several if not all of which had black hole cores of some size. Our own galaxy is now known to have swallowed quite a few neighbors. Where those cores went, no-one yet knows.

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theotherguy wrote:In places

theotherguy wrote:

In places where the force of gravity between galaxies overpowers the general force of expansion (since the expansion is accelerating you can imagine that it would generate a force on the galaxies), galaxies will drift together.
Yeah, I've heard that the expansion of universe is accelerating, but I don't know how it's possible. Isn't it a violation of a law of energy preservation? Where does this aceleration take an energy?
I guess the universe is an open system, it takes the energy from somewhere elsewhere, but do we know from where? I could imagine it's from the same place where is a vacuum energy, gravity energy, strong nuclear force, and the phenomenon of electric charge itself, but that doesn't explain much. Even more I'm curious why it's expanding, what unpleasant thing would happen in non-accelerating universe.


 

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Quote:Yeah, I've heard that

Quote:

Yeah, I've heard that the expansion of universe is accelerating, but I don't know how it's possible. Isn't it a violation of a law of energy preservation?

No, the universe is accelerating in expansion because of dark energy, which acts to counter gravity, hence the effect of mass. The divergent motion of material bodies is the result of energy that has been within the system since the Big Bang. Under a more massive system, gravity will move to counteract this and so, eventually, the system will stop expanding and start acceleration in recession. This is not what is happening because there is not enough mass.

Quote:

I guess the universe is an open system, it takes the energy from somewhere elsewhere, but do we know from where? I

This is a horrible misconception. There is nothing outside the physical universe, which we shall define as contained within the boundaries of our spatiotemporal manifold, that "feeds" it.

"Physical reality” isn’t some arbitrary demarcation. It is defined in terms of what we can systematically investigate, directly or not, by means of our senses. It is preposterous to assert that the process of systematic scientific reasoning arbitrarily excludes “non-physical explanations” because the very notion of “non-physical explanation” is contradictory.

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iluvc2h5oh
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deludedgod wrote:Quote:Yeah,

deludedgod wrote:

Quote:

Yeah, I've heard that the expansion of universe is accelerating, but I don't know how it's possible. Isn't it a violation of a law of energy preservation?

No, the universe is accelerating in expansion because of dark energy, which acts to counter gravity, hence the effect of mass. The divergent motion of material bodies is the result of energy that has been within the system since the Big Bang. Under a more massive system, gravity will move to counteract this and so, eventually, the system will stop expanding and start acceleration in recession. This is not what is happening because there is not enough mass.

Quote:

I guess the universe is an open system, it takes the energy from somewhere elsewhere, but do we know from where? I

This is a horrible misconception. There is nothing outside the physical universe, which we shall define as contained within the boundaries of our spatiotemporal manifold, that "feeds" it.

 

as per the 1st part couldnt an analogy be made that when a bullet is fired from the moment it is stationary until it reaches its top volocity it is accelerating.  Wouldnt the universe after the big bang do something like that on a larger scale?


I am average on my knowledge of "physics" physics...I only took 101 and 102 + read a brief history of time LOL.

( Oh by the way does anyone know a laymans book that explains string theory and M theory...like how they come up with formulas that predict '7'  or '11' dimentions...thanks in advance)

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