3 ms·

Love, love, love this. Was surprised (which only shows my ignorance) of the sizes of some stars, compared to 1 AU. Also - how is the estimation of the size of

Love, love, love this. Was surprised (which only shows my ignorance) of the sizes of some stars, compared to 1 AU. Also - how is the estimation of the size of the universe (not the /observable/ universe) done?

diziet 17y ago
I would imagine it's done using some kind of estimate of the known current rate of expansion and assuming some kind of model for the rate of acceleration.
- Patient0 17y ago
  I thought that if the universe is "open" then it is only the visible universe that is finite, and the rest is actually infinite. i.e. there's stars "all the way" it's just that we can only see stuff 14 billion light years away. Another point: in one part it says "we are probably not at the center" - I thought the notion of a "center of the universe" was meaningless in the same sense that any point on a sphere is not "the center" (if the universe is "closed"), and you can't have a "center" of an infinite plane (if the universe is "open").
  - pfedor 17y ago
    Also he mentions preons, hypothetical particles of which quarks are made, which I believe is an idea mostly done away with.
  - wlievens 17y ago
    Stars all the way = infinite amount of stars = infinite mass = doesn't make any sense At least that's how I understand it... but IANAC
- yread 17y ago
  Yeah I was wondering about that, too. The funny thing is the universe is supposed to be 13.73 billion years old but even wikipedia states 93 billion light years as a size estimate.
char 17y ago
A reasonable way to calculate the size of the universe is to first calculate its age, and then assume expansion at the speed of light. Age can be determined by a number of factors, including calculating the age of the oldest stars we observe, using objects such as Cepheid variable stars (whose brightness is a function of time), and measuring relative velocities of distant galaxies to then figure out when they started moving (Big Bang).

diziet 17y ago

I would imagine it's done using some kind of estimate of the known current rate of expansion and assuming some kind of model for the rate of acceleration.

Patient0 17y ago
I thought that if the universe is "open" then it is only the visible universe that is finite, and the rest is actually infinite. i.e. there's stars "all the way" it's just that we can only see stuff 14 billion light years away. Another point: in one part it says "we are probably not at the center" - I thought the notion of a "center of the universe" was meaningless in the same sense that any point on a sphere is not "the center" (if the universe is "closed"), and you can't have a "center" of an infinite plane (if the universe is "open").
- pfedor 17y ago
  Also he mentions preons, hypothetical particles of which quarks are made, which I believe is an idea mostly done away with.
- wlievens 17y ago
  Stars all the way = infinite amount of stars = infinite mass = doesn't make any sense At least that's how I understand it... but IANAC
yread 17y ago
Yeah I was wondering about that, too. The funny thing is the universe is supposed to be 13.73 billion years old but even wikipedia states 93 billion light years as a size estimate.

char 17y ago

A reasonable way to calculate the size of the universe is to first calculate its age, and then assume expansion at the speed of light. Age can be determined by a number of factors, including calculating the age of the oldest stars we observe, using objects such as Cepheid variable stars (whose brightness is a function of time), and measuring relative velocities of distant galaxies to then figure out when they started moving (Big Bang).