If gravitational forces attract than why is the Universe moving away from its center(recession velocities)?

Question

Is there an absolute centter where everything moves away from?

Answer 1

If the only things involved in the position of everything in space were momentum and gravity then perhaps all the planets and galaxies and superclusters could have enough momentum to fly away forever like something can have enough momentum to have an escape velocity from the earth. Also if everything didn't have enough momentum then it would eventually all fall back in together into a "big crunch".

There is another factor at play, though, in the expansion of the universe called "dark energy" which is something that causes space itself to expand! So as space itself expands everything in it is carried along outwards with the expansion. Imagine space is a table and some crumbs on it are galaxies. As the whole table expands the little crumbs will spread apart from each other.

Dark energy is very hard to study and is not well understood. The sources I cited give good overviews and should give you a better understanding.

Answer 2

Hmmm. Deep question. So far as I know the force of gravity is something that is observed, but nobody can say what the cause is. In other words, it is observed that by postulating a force of gravity, we can explain the attraction of different objects to one another and can compute orbits of the planets, satellites, etc. Gravitational force is proportional to the masses of the two objects that are attracting each other, so that an object with twice the mass will attract with twice the force. The gravitational force also falls off as the square of the distance, so that an object that is twice as far away will attract with four times less force. These are postulations that Isaac Newton made which allowed him to accurately predict the movements of the planets and other physical phenomena, but is not an explanation for the cause of gravity.

Answer 3

The Big Bang theory developed from observations of the structure of the universe and theoretical considerations. Observationally, it was determined that most spiral nebulae were receding from Earth, but those who made the observation weren't aware of the cosmological implications, nor that the supposed nebulae were actually galaxies outside our own Milky Way.

Over time, the slightly denser regions of the nearly uniformly distributed matter gravitationally attracted nearby matter and thus grew even denser, forming gas clouds, stars, galaxies, and the other astronomical structures observable today.

Your second question

Where is the center of the Universe?
Here, there, and everywhere.
by Paul Doherty, Exploratorium Teacher Institute



When astronomers look at distant galaxies to determine how fast they're moving, it looks like they're all moving away from us. Does that mean we're at the center of the universe? Well, no. It turns out that every point in the universe sees itself as the center! You can show yourself why with this activity.

Try this!
- The picture on this page has two layers-- the bottom layer represents the universe a billion years ago. The top layer represents the universe today, expanded 5% from its size a billion years ago.

- Use your mouse to drag the top (blue circle) layer randomly over the bottom one, the difference between the two is hard to see. But if you place the top layer so that one of its dots lines up with the same dot on the bottom layer, you'll notice a pattern: it looks like the dot you've chosen is the center of the expansion.

- Now choose a different dot on the top layer and line it up with its corresponding dot on the bottom layer. Once again, the universe seems to expand around that position. This will be true of any point you choose in our model universe. No matter where you are, it looks like the universe is expanding away from you!

What's going on?

The top layer (the universe today) was made by enlarging the bottom layer (the universe 1 billion years ago) by 5% percent. That means every space on the top layer is enlarged by 5 percent. The real universe is the same: in a billion years all of the spaces between galaxy clusters has expanded by about 5 percent. Viewed from any point, the universe seems to be expanding about that point.

See the picture here --> http://www.exploratorium.edu/hubble/tools/center.html

Answer 4

The Big Bang is jsut that, one BIG explosion, when something blows up their are forces pushing things away. It jsut so happens that that force pushing things away are greater then the gravitational forces pushing things apart.

There are many theroies about the ultimate fate of the universe and one is just what you are getting at. One says that the force of the Big Bang will eventually fade and the universe gets so big and then the gravitational forces will be greater and the universe will start to colapse in on itself and perhaps start the process again

Some scientists disagree with this though

It's very interesting to read

Answer 5

Gravity acts on inertial bodies, also known as mass. The so-called dark mass-energy and observable mass-energy that inhabit the universe are in-fact attracted to each other. The fatal attraction (pun intended) occurs in the black holes where mass-energy is swallowed up by the intense gravitational pulls around their horizons.

What is not affected by gravity is the universe itself. Think of the universe as a kind of transparent milk bottle filled with milk. The milk bottle is getting larger at an increasing rate, while the milk spreads out because of that increased volume of the milk bottle. So it is with our universe. It is expanding at a faster rate, and the galaxies and other mass-energies are spreading out because of that universal expansion.

Meanwhile, some of that milk is curdling, becoming lumpy, as it ages. This is the effect of gravity on the mass-energy of the universe. That is, mass-energy is constantly being drawn into each other to form curdles we call galaxies, black holes, and such. Even so, the curdles draw farther away from each other because the milk bottle universe continues to get larger.

Answer 6

While the universe is expanding the acelleration is decreasing due to gravity and eventually will stop if there is enough mass. Think of a firework display, after the inital explosion the particles are moving very fast away from the point of explosion. Eventually they move slower and slower (due to friction) and come to a stop. The universe is like the explosion but with gravity as the force not friction.

Answer 7

If you throw a ball up into the air, does it immediately fall down or does it travel a while before coming back down?

Additionally, it is postulated that there is so-called "dark energy" that is fuelling the universe's expansion

There is ostensibly a center, based on the measurements we can do to find the farthest galaxies in every direction, but there's no certainty that the expansion is anisotropic.

http://en.wikipedia.org/wiki/Universe_expansion
http://en.wikipedia.org/wiki/Hubble_constant
http://en.wikipedia.org/wiki/Dark_energy

Answer 8

The Big Bang pushed the universe out, so you must give the pendulum time to swing back.

Answer 9

Because there are other masses besides the (center) dense black hole in the universe. (i.e. Earth and Moon have attraction to each other)

Answer 10

It has to do with the big bang. Space is expanding, and shows no signs of stopping.