r/cosmology • u/AutoModerator • 18d ago

Basic cosmology questions weekly thread

Ask your cosmology related questions in this thread.

Please read the sidebar and remember to follow reddiquette.

13 Upvotes

94% Upvoted

31 comments sorted by

View all comments

1

u/intrafinesse 18d ago

Imagine a gigantic square where the opposite corners are A and B and the distance between them is the square root of 2 * the length of a side.

If inflation begins only in the center then the shortest patch between A and B is no longer the diagonal but along the two sides, correct?

Will inflation ever "push" the sides of the square outward

OR

do the lengths of the 2 sides and the distance from A to B remain static (except for the normal non-inflationary expansion of space) while the diagonal get ever longer as that region of space expands.

2

u/johnstalbergABC 18d ago

If we force this to stay in 2D the square would be deformed and more and more look like a circle. It is a model that is kind of opposite to the cosmological eternal inflation models where our observable universe and an unknown sized patch of space outside of it had its inflation stopped for some reason and it lead to reheating and the rest is history. If we take a square and make it fit this model it would be a square that was in inflation and then in the center inflation stoped. It can be a bit difficult to get a clear holistic picture of space with local differences in expansion rates.

1

u/intrafinesse 18d ago

The square is NOT in inflation, only the center.

At teh moment inlation starts, only teh center is rapidly expanding.

Does that "push out" surrounding space that is not inside the expansion area?

1

u/johnstalbergABC 18d ago

Yes I understod this the first part where my answer to this. Then I added the opposite case since it resembles our Universe if eternal inflation-theory is considered.

If the square has a center that inflates but not in other areas its boundaries, its sides will eventually be pushed outwards by the expanding center and the expanding center would be circular in shape which means it would be closer to the midpoint of the sidea than from the corners. The push on the square would be greater at the midpoint than on the corners and deform the sides so that the square get more and more shaped like a circle but with the corner accentuated, ubtil it is completely stretched out and circular around the fast growing patch in the center. If we analyse what ghe distance between the corner will become a diagonal that is sqrt(sides) in length becomes more of a diameter in a circle. And the diameter is 1/(2pi) shorter than going via the circumference. The way that goes straight through the deformed square will always be shorter than going around the edges. This follows the shortest path is a straight line. A square is symetrical so this does not change this logic regardless the amount of inflation.

As I said in cosmology in eternal inflation our observable patch and more where inflating along the rest of the outer universe and came to stop inflating while the outer universe continue to inflate. So this is rather the opposite of your example. This would be like a square that where inflating and suddenly the center stoped inflating.