Size and age of universe


by Rajendra_Vaidya
Tags: size, universe
marcus
marcus is offline
#19
Jun28-04, 07:08 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,793
Quote Quote by Kurdt
Hence the wishful thinking comment. I'll be sure to make my posts totally clear in the future in case anyone misinterprets. I was merely trying to establish where the value of 156 billion ly came from because I haven't read the original poster's source. I can't seem to find any reference to it.
here is a link to the original technical paper in arxiv
by Niel cornish]
and some other people
http://www.physicsforums.com/showthr...969#post244969

there you will find an arxiv link to the paper and also to a BBC popularization article IIRC, and also a link to Niel Cornish website

his 24 gigaparsec is a "radius-like" figure so you double it to 58 gigaparsec to a "diameter-like" thing and convert parsecs to lightyears and get 156 billion LY. It didnt turn into 156 billion LY until he started talking to reporters and taking interviews

it is pretty abstruse, good luck trying to understand Niel's writing.
the main thing is it is a MINIMUM size figure----the U could be flat and infinite and that is kind of the simplest picture

but if it is finite then it has to be AT LEAST what Niel says, or we would notice it curving around----he and his buddies looked for signs of it curving around in the CMB and were able to rule it out for anything smaller than what he says
Entropy
Entropy is offline
#20
Jun28-04, 07:30 PM
P: 608
We know so little about the universe I don't know how you could make a good guess. But I guess we have to start somewhere... I'd say the universe is 20+ billion years old.
chroot
chroot is offline
#21
Jun29-04, 12:40 AM
Emeritus
Sci Advisor
PF Gold
chroot's Avatar
P: 10,424
WMAP, among other experiments, has determined the universe is 13.7 billion years old. We don't have to guess.

- Warren
marcus
marcus is offline
#22
Jun29-04, 01:21 AM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,793
Quote Quote by chroot
WMAP, among other experiments, has determined the universe is 13.7 billion years old. We don't have to guess.

- Warren
Yeah Entropy, Warren is right
mainstream professional cosmologists are nearly all using the same
model of the universe
and these days they have arrived at a broad agreement on the observational data to plug into the model

the error bounds have been narrowed way down

so you take the model, which is two Friedmann equations, and you take the data (which since 1998 they are generally very confident in) and put the parameters into the model and it tells you lots of stuff: like the age is 13.7

Up until the mid 1990s the field was much more vague and there were people saying things like the universe is 20+ old, like you said just now.
But mainstream people dont say that any more because it doesnt make sense.

Of course it is your privilege to believe a very fringe thing like 20+
we can all believe what we want.
but since your taxes support the cosmology profession and they have
finally agreed on some basic things about the universe I would advise you to at least try to understand what they are saying and why they are so sure about 13.7

first understand the Friedmann equations, which are nice and simple, and then disbelieve if you are inclined towards nonconformism.
no one can blame you if you understand what you are rejecting
Rajendra_Vaidya
Rajendra_Vaidya is offline
#23
Jun29-04, 05:57 AM
P: 4
Kurdt & other friends,

The source from which I got the info is space.com

http://www.space.com/scienceastronom...ay_040524.html

As I understand our universe is like a bubble and our three dimensional space is the
surface and the thickness of the bubble.
From the illustration shown with the article, 156 BLight Yeras is the width or diameter of the universe.
Rajendra_Vaidya
Rajendra_Vaidya is offline
#24
Jun29-04, 06:06 AM
P: 4
Quote Quote by chroot
That's wrong Kurdt, and would only be true if the universe had always been the same size. Of course, it has not always been the same size. The light that was emitted very early did not have very far to travel at all, you see. The "particle horizon," which is what you're talking about, is actually 43 billion light years in radius, IIRC.

- Warren
Chroot,

You have just touched the very core of my question.

With your argument the question that arises is

If the universe was at a single point 13.7 BLY ago,
then how two points in the universe got seperated by say 43 BLYs
in 13 BLYs?
hellfire
hellfire is offline
#25
Jun29-04, 06:30 AM
Sci Advisor
P: 1,047
Quote Quote by Rajendra_Vaidya
If the universe was at a single point 13.7 BLY ago,
then how two points in the universe got seperated by say 43 BLYs
in 13 BLYs?
This is due to expansion of space.

First note that when talking about the radius of the observable universe a proper distance is meant. This is the distance between us and our particle horizon measured with a rod today (which is obviously unphysical according to special relativity).

Consider a radial photon beeing sent from our location at the time of big-bang. The location of the photon at each time is our particle horizon.

If it were no expansion of space, then the distance today between us and our particle horizon would be indeed 13.7 GLyr. But since space is expanding behind the particle horizon (between us and the photon) during this 13.7 Gyr, the proper distance between us and our particle horizon (after 13.7 Gyr) will be greater than 13.7 GLyr.

The actual distance depends on the cosmological model (in general it depends on Omega_matter, Omega_Lambda and the Hubble parameter).

Regards.
Rajendra_Vaidya
Rajendra_Vaidya is offline
#26
Jun29-04, 07:20 AM
P: 4
Quote Quote by hellfire
This is due to expansion of space.

First note that when talking about the radius of the observable universe a proper distance is meant. This is the distance between us and our particle horizon measured with a rod today (which is obviously unphysical according to special relativity).

Consider a radial photon beeing sent from our location at the time of big-bang. The location of the photon at each time is our particle horizon.

If it were no expansion of space, then the distance today between us and our particle horizon would be indeed 13.7 GLyr. But since space is expanding behind the particle horizon (between us and the photon) during this 13.7 Gyr, the proper distance between us and our particle horizon (after 13.7 Gyr) will be greater than 13.7 GLyr.

The actual distance depends on the cosmological model (in general it depends on Omega_matter, Omega_Lambda and the Hubble parameter).

Regards.
If we were tracking 'This Radial Photon' would it not appeared
to have travelled faster than light?

i.e. More than 13.7BLYs distance in 13.7BLYs.
Kurdt
Kurdt is offline
#27
Jun29-04, 07:33 AM
Emeritus
Sci Advisor
PF Gold
P: 4,975
Here, I believe it is important to note that Einstein's premise that nothing travels faster than light was not broken since the space ITSELF expanded and not matter travelling through it. We can use the inflating balloon analogy for this. Two points on the surface increase their distance from one another as the balloon expands, but neither point on the surface moves at all, it is the space expanding that moves them apart and therfore any matter embedded in spacetime does not violate this dictum.
hellfire
hellfire is offline
#28
Jun29-04, 07:56 AM
Sci Advisor
P: 1,047
Quote Quote by Rajendra_Vaidya
If we were tracking 'This Radial Photon' would it not appeared to have travelled faster than light?
Yes, the Hubble sphere (objects receding at the speed of light at a distance Rh = c/H) is located between us and our particle horizon and therefore objects located at the particle horizon recede superluminally.
shrumeo
shrumeo is offline
#29
Jun29-04, 03:01 PM
P: 250
Quote Quote by chroot
WMAP, among other experiments, has determined the universe is 13.7 billion years old. We don't have to guess.

- Warren
Then why are there stars >14 billion years old?
http://www.sciencemag.org/cgi/conten...304/5675/1226b


Register to reply

Related Discussions
age and size of the Universe Cosmology 9
Size of universe? Cosmology 9
Size of the Universe General Astronomy 7
Size of the Universe General Astronomy 10
The size of the universe General Astronomy 2