Is the net gravitational force of the universe zero?

Question

On a truly cosmic scale every point would be surrounded by an equal amount of mass in every direction, and so would be "pulled" equally by gravity in all directions. Would this cancel out so the net force on each point would be zero. This would seem to apply irrespective of the shape of the universe, or even if the universe was infinite.

Surely there must be something wrong with my reasoning since if it would preclude the possibility of a "Big Crunch" and I would like to know my error

Answer 1

When discussing gravity on these scales, you have to use general relativity and not Newtonian theory. In general relativity, the notion of a force of gravity is discarded, so your argument doesn't work. Instead, the degree of expansion is determined by the density of mass and energy with a 'Big Crunch' happening if the density is high enough.

Unlike what the previous answer says, there does not have to be an edge even if the universe is finite. Again, general relativity is needed to discuss this accurately, but what is found is that space and time are both curved. For a finite universe, the spatial part would be a generalization of the surface of a sphere: any direction you go, you would eventually come back to the starting place.

Answer 2

"On a truly cosmic scale every point would be surrounded by an equal amount of mass in every direction, and so would be "pulled" equally by gravity in all directions"


If the universe is infinite, then this could be true. However, if it is not infinite, then there has to be an "edge" of the universe somewhere. At this point, your assumption is no longer true and this matter should actually begin to pull back into the center of the universe. As a result, the entire universe would begin to collapse back on itself with the "Big Crunch" you mention.

The current explanation is that the universe is still expanding because the net gravitational force since the beginning of the universe has not been enough to overcome the force of the big bang.

Answer 3

Each mass in the Universe attracts every other mass so a 'point' at which the net field is zero simply doesn't exist.
But the total outwards momentum of the Universe may (or may not) be enough to cause it continue expanding until the energy density is vanishingly close to zero. This is the opposite of the 'big crunch' theory. But not enough is known about the total mass of the Universe to predict with any certainty which will happen.
Big crunch (and, possibly, another big bang and the cycle repeats), or fade away? Do we go out with a bang or a whimper?

Doug

Answer 4

the two magnetism and gravity can influence gadgets at a distance. the two get weaker because of the fact the gadgets get farther aside is distinctive. it incredibly is the reason you sense the pull of gravity from the earth, yet not from distance planets. It’s additionally why 2 magnets could pass mutually in case you place them close to one yet another, yet once you place them a ways aside not something will take place. even though, as 2 gadgets get a ways aside, the gravity between them is going down with the aid of a ingredient of 4 once you double the area, however the magnetism is going down with the aid of (a minimum of) a ingredient of 8. on the size of the image voltaic equipment, with planets a ways aside, gravity is a lot extra significant than magnetism. while held a fragment of an inch (some millimeters) removed from the refrigerator, so as that the magnet isn't touching, the magnetic stress on the magnet (from the refrigerator) is extra suitable than gravitational stress (from the Earth). as quickly as you enable the magnet pass, it continues to be pulled onto the refrigerator's metallic floor particularly than falling to the floor. Magnetism is a sturdy stress if the area between gadgets is smaller than the area between a magnet's 2 poles (North and South). In an extremely particular, loval section, magnetism is the extra suitable stress yet over a extensive section (i.e. the universe) gravity is the extra suitable stress.

Answer 5

Probably not

If so the universe would expand forever and then this universe would be the first.

That doesn't hold with conjecture.