What is the difference between a closed and an open universe and how does string theory fit into it all?

Question

I've watched a couple of programmes about this and found it fascinating but I could do with the principals re-explaining to me - I tried to explain string theory to someone the other day and singularly failed to do so!

Answer 1

In relativistic physics, there is something called the cosmological constant (CC). It is a somewhat arbitrary constant Einstein added to his equations to make the answers come out right. [See source 1.]

When Lambda (the CC) > 0, the equations give a closed, spherical universe. When Lambda ~ 0, the equations give a flat, open universe. And when Lambda < 0, they give a saddle shaped, open universe. Physicists are now leaning toward the flat universe as the shape, but there is no overwhelming consensus in this.

String theory has little or nothing to do with specifying the shape of the universe. It does, however, lend itself to explaining the origin of the universe. For example, string theory can theoretically take us back before the big bang and explain where the energy for the big bang might have come from. Colliding parallel universes is one possibility under string theory. [See source 3.]

By the way, string theory is not "pooh poohed;" however, because it is currently not testable, many, if not most, physicists regard it more as a philosophy rather than a theory. There is some hope that the Large Hadron Collider can be used to test some aspects of string theory. When that happens, string theory will evolve into a theory, if the tests are positive, or further away from being one if the tests are negative. [See source 2.]

Answer 2

The Big Bang started the huge outward expansion of matter we see nowadays. The expansion is counteracted by gravity.

A closed universe has enough matter in it, so that -eventually- gravity will win and matter will start imploding again: the Big Crunch.
In an open universe the amount of matter is not sufficient to stop the expansion. The current theory is that we are in an open universe, but barely.

Most of the mass in our Universe appears to occur in the form of dark matter. They are supposedly, made up of particles other than the already known ones. String theory predicts the existence of such extra particles.

Answer 3

Closed Universe is when there is enough matter in the universe to where gravity will eventually overcome the expansion rate and begin to collapse the universe in on itself, Big Crunch.
An Open Universe does not have enough matter to halt expansion, the universe will continue to expand becoming more and more remote.
String theory states that one dimensional, sub-plank size, vibrating strands of energy make up all matter. The vibrational patterns determine what constituent of matter is made. Strings replace the point particle. The odd thing of the theory is that it requires 10 spatial dimensions, instead of our usual 3.

Answer 4

A closed universe is one that has a specific shape and size, while an open universe has no shape or size (it is infinite in everyway.)

String theory provides a way to see what particles look like, and how they interact at that level.

Answer 5

The closed university is a programmes which oriented in full time basis at the single located building with high degree of entry qualifications.while the open university is desighnated to help the student rich the university level by simple multiple qualifications and they are not programming for the full time basis and can located in scatered area.

Answer 6

String theory has largely been pooh-poohed.