推 wwwgetcomtw:是天才物理小尖兵耶!!!! 04/04 22:39
※ 編輯: lewisweilin 來自: 99.245.10.248 (04/04 22:56)
※ 引述《Danio (丹尼歐)》之銘言：
: 在高中物理看到的問題
: 以下哪些正確?
: (A)所有的遙遠星系都以很高的速度遠離我們
: (B)恆星離地球越遠，遠離速度越快
: (C)星系離地球越遠，遠離速度越快
: (D)仙女座大星系屬於本星系團，而本星系團並不會因為宇宙膨脹而膨脹
: 答案是:ACD
: 請問B錯是不是因為恆星也可能有藍移
: 而C是因為星系對銀河系來說都很遠所以理由同A
: 但這樣D和C就有些矛盾
: 麻煩各位給我些意見
: 謝謝!
v(t) = H(t)‧d(t)
v: velocity of galaxy moving away from us due to expansion of the universe
H: the Hubble's constant
d: distance between galaxies
we see that Hubble's constant is not a constant, it changes with time (this
is due to the frame of the Cosmology Principle)
The equation tell us that the galaxy far away from us moving faster compare to
the galaxy near by
so, A is correct
B is wrong is because we are talking about galaxy not the stars or cluster
inside the galaxies(they got hold together due the gravitational force that
overcome the expansion)
Another way you can think of is that imagine you are making a toast with
some raisin on it, when you bake it, the toast expand but the raisin remain
the same size. You can think of the raisin as the galaxies and the bread is
the universe (easier to understand)
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Aside:
Cosmology Principle:
there exists a set of fundemental observers and a cosmic time such that
universe appears homogeneous and isotropic in all its properties for all
fundemental observers at a give time
fundemental observers: like human on Earth or aliens in other galaxies
universe is homogeneous and isotropic: does not change with respect to
what position you're at. The expansion of the universe appears to be the
same speed from every perspective. (Universe has NO CENTER!! or every
place is the CENTER of the universe.)
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