送交者: 大布苏 于 September 05, 2001 00:36:29:
回答: 科普(2)：宇宙中心 由 风 于 September 02, 2001 16:01:51:
隔行如隔山，我仗着胆儿整了，用词、推理都是“跟着感觉走”：-)，各位指正。
风的贴中两段文字说的实际上不一定有因果关系。我把它们分开唠唠。
1。“宇宙中心”
我找着一篇1998的文章，应该是美国的“权威”写给大众看的(见http://www.sciam.com/
specialissues/0398cosmos/0398peebles.html；GOOGLE检索词是“UNIFORMITY AND
UNIVERSE”或“UNIFORMITY UNIVERSE”)。我切一段相关的在下面，“权威”们对
“太阳系就是宇宙的中心”这种说法的答案看来是否定的。至于我的理解，我想请
风注意引文中第二段，如果所有物质(能量)都始于时空的一“点”(没有这“点”外
的“空间”的事儿！)而形成一个“无可观测边界”的“均匀分布的”系统，那么
“中心”说就说不通了。这里的“无可观测边界”还是处于假说阶段(我根据霍金的
书来猜)；但“均匀分布”从可观测的范围来看象是对的(见引的文章中数据)。
又，我比较欣赏引文第二段结里的比方。这个比喻有助于理解下面讨论2“。。。速
度”里“注2”的概念澄清。
“The existence of an expanding universe implies that the cosmos has evolved
from a dense concentration of matter into the present broadly spread distribution
of galaxies. Fred Hoyle, an English cosmologist, was the first to call this
process the big bang. Hoyle intended to disparage the theory, but the name
was so catchy it gained popularity. It is somewhat misleading, however,
to describe the expansion as some type of explosion of matter away from
some particular point in space.
That is not the picture at all: in Einstein's universe the concept of space
and the distribution of matter are intimately linked; the observed expansion
of the system of galaxies reveals the unfolding of space itself. An essential
feature of the theory is that the average density in space declines as the
universe expands; the distribution of matter forms no observable edge. In
an explosion the fastest particles move out into empty space, but in the
big bang cosmology, particles uniformly fill all space. The expansion of
the universe has had little influence on the size of galaxies or even clusters
of galaxies that are bound by gravity; space is simply opening up between
them. In this sense, the expansion is similar to a rising loaf of raisin
bread. The dough is analogous to space, and the raisins, to clusters of
galaxies. As the dough expands, the raisins move apart. Moreover, the speed
with which any two raisins move apart is directly and positively related
to the amount of dough separating them.
The evidence for the expansion of the universe has been accumulating for
some 60 years. The first important clue is the redshift. A galaxy emits
or absorbs some wavelengths of light more strongly than others. If the galaxy
is moving away from us, these emission and absorption features are shifted
to longer wavelengths--that is, they become redder as the recession velocity
increases.”
2。“在位置１＆〉２＝３〉４的运动速度。”
按HUBBLE定律星系间的相对‘漂移’速度V (RECESSIONAL VELOCITY)与其间距离 D
成正比，比例常数即为所谓HUBBLE常数H0
V = H0 X D
这样的话站在“下”上看风的说法于相对‘漂移’速度V而言应该是成立的。因为D41
〉D42 = D43 〉D44 = 0。但象开头提过的这并非“中心论”的结果，因为一个无
界均匀系统点点都是等价的(见霍兄的跟贴)。
注1：胡子老弟：我前些时跟你唠的贴里有些漏洞，即红移(正比于V)是跟距离相关
的，不是象我猜的“SEEMS IRRELEVANT”；此关系即HUBBLE定律。HUBBLE常数约在
50 到100 公里/秒XMpc (1Mpc = 1Megaparsec = 3。09X10^19公里)之间。
注2：前些跟胡子贴我按PBS网页整理出的按‘多普勒’效应理解的红移量计算公式
能把数凑上，但对红移现象严格的理解应不是那样的(详见http://www.mathsoft.com/mathcad/
library/astronomy/ 中的MATHCAD文件1“INTRODUCTION TO COSMOLOGY”，我用的
GOOGLE检索词是“HUBBLE’S CONSTANT”) ：-)。严格的说法应该是“红移产生于
宇宙膨胀”，(不是绕圈子，多GOOGLE两把你就看出区别来了：-)。但这些细节不影
响这的讨论。