l**n
发帖数: 67 | 1 In a universe with the same physical laws, but which is mostly water
with little bubbles in it, do the bubbles attract or repel?
Is this question meaning?(static solution)
Can we find anything analogous in our universe(negative gravitation) | q**i
发帖数: 174 | 2 I am not sure if such a universe would sustain: it would have
collapsed into a black hole long time ago under its own gravity
due to much heavier mass (water vs. vacuum/thin matter in our universe).
if for some reason, this universe keeps expanding against the gravity
(like our universe did in early stages of a big bang), the bubbles should
still attract each other (if there is small amount of mass inside
the bubbles), or remain neutral (if there is zero mass inside them).
on the flip side, this
【在 l**n 的大作中提到】
: In a universe with the same physical laws, but which is mostly water
: with little bubbles in it, do the bubbles attract or repel?
: Is this question meaning?(static solution)
: Can we find anything analogous in our universe(negative gravitation)
| f*******d
发帖数: 339 | 3
It is not meaningful, because then at large enough scale, such water would be
pulled togather by gravity to form planets or stars, which would undergo
nuclear reaction and produce other elements (water would be decomposed
to Hydrogen and Oxygen), and the intervening space is vacuum, just like ours.
(In our Universe, it is Hydrogen and Helium dominant).
【在 l**n 的大作中提到】
: In a universe with the same physical laws, but which is mostly water
: with little bubbles in it, do the bubbles attract or repel?
: Is this question meaning?(static solution)
: Can we find anything analogous in our universe(negative gravitation)
| l**n
发帖数: 67 | 4
I agree with what you said, but actually i can have several ways to rephrase
my question.
1: suppose there are two bubbles in a big tank filled with water. The big tank
is in a free fall frame(ignore any external gravitional field). Do the two
bubbles attract, repel or they don't move at all. This is just an excercise of
classical newton mechanics.
2: Take water as the vaccum which means vaccum energy is not zero. In this
highly curved space(with constant positive curvature), how do the two bub
【在 f*******d 的大作中提到】
:
: It is not meaningful, because then at large enough scale, such water would be
: pulled togather by gravity to form planets or stars, which would undergo
: nuclear reaction and produce other elements (water would be decomposed
: to Hydrogen and Oxygen), and the intervening space is vacuum, just like ours.
: (In our Universe, it is Hydrogen and Helium dominant).
|
|
