Starship Asterisk*

by **BMAONE23** » Thu Jul 30, 2009 1:41 am

an interesting site for distances to the stars and beyond
this one is good too

by **apodman** » Thu Jul 30, 2009 12:14 am

http://en.wikipedia.org/wiki/Bucephalus wrote:Bucephalus or Buchephalas (Ancient Greek: Βουκέφαλος, from βούς bous, "ox" and κεφαλή kephalē, "head" meaning "ox-head") (c. 355 BC – June, 326 BC) was Alexander the Great's horse and the most famous actual horse of antiquity.

---

Βουκέφαλος wrote:3. If the universe is 14B years old, does that mean that we'll never find anything more than 14 GIGA-LY ?
4. But, if the answer to above is yes, then something that took 14 GLY to see, would actually be at least 28 GLY by now if the object would be traveling the speed of light?

There are some posts in this topic that might help.

Also, use the search box at the top of the page to search all posts in this forum for "comoving distance" or just "comoving".

by **Βουκέφαλος** » Wed Jul 29, 2009 9:43 pm

Just got this month's Sky and Telescope talking more about this GRB. This is my first post on The Asterisk* and I had several questions:

1. What is a good red-shift to distance calculator, or is that possible, and what might be the expected degree of error.
2. Chris indicated that matter could move faster than the speed of light? Is that right, or did I misinterpret?

3. If the universe is 14B years old, does that mean that we'll never find anything more than 14 GIGA-LY ?
4. But, if the answer to above is yes, then something that took 14 GLY to see, would actually be at least 28 GLY by now if the object would be traveling the speed of light?
5. But, WOULD the object be traveling the speed of light? Or faster? Or slower?

Thanks, I'm trying to understand some of these concepts that I've read in this thread.

by **aristarchusinexile** » Wed May 27, 2009 3:27 pm

Chris Peterson wrote:
mark swain wrote:Is that you done Chris P ???? Cos i have not even started?
No, just spent most of the day working with a new horse. Too tired to give this much more thought. Maybe tomorrow.

Quit hors'n 'round, pardner, and git back to that eyepiece .. the Martian herd is a'comin.

by **Chris Peterson** » Wed May 27, 2009 3:32 am

mark swain wrote:Is that you done Chris P ???? Cos i have not even started?

No, just spent most of the day working with a new horse. Too tired to give this much more thought. Maybe tomorrow.

by **Doum** » Wed May 27, 2009 12:21 am

Doum wrote: So any observer where ever he is in the universe is at the center of the universe. So its not just the earth observer that are at the center of the univers. Yea ok. Why just consider the visible universe? I understand. I think i do. Lucky me, i am at the center of the universe.

Chris Peterson wrote:
Doum wrote:Lucky me, i am at the center of the universe.
No, I'm pretty sure I am. <g>

BMAONE23 wrote:Interesting...
The last time I looked "I" was at the center of the universe

TheUnIverse

astrolabe wrote:Hello All,

No, no, no, no, no. I am in fact the one who is at the center of the Universe and anyone who studies cosmology for their entire life would know that. Can't you see how obvious it is?

Is there a consensus here.?

by **The Code** » Tue May 26, 2009 8:27 pm

Is that you done Chris P ???? Cos i have not even started?

Mark

by **The Code** » Tue May 26, 2009 7:40 pm

Chris

Extract 1 Atom from a black hole. (singularity) Or does 1 tea spoon of neutron star weigh less than 300 billion tons? If it all come from that singularity you got to expect gravity to be stronger? and from then, get weaker and weaker?

Mark

by **Chris Peterson** » Tue May 26, 2009 7:23 pm

mark swain wrote:What i,m saying is: There should at some point in the early universe, a gravity, That strong 1 Atom would attract another Atom from 1000,s of miles away. And that gravity over billions of years is getting weaker and weaker is part of the expansion we see.

There is no indication that the gravitational constant was any different in the early Universe than it is today. So the force between two atoms at some distance then is exactly what it is today. Gravity isn't getting weaker with universal expansion.

In any case, particles at the atomic scale come together because of other forces than gravity.

by **The Code** » Tue May 26, 2009 7:19 pm

Chris wrote:
''I don't understand your suggestion that the Universe should be made of particles. The general picture of how the early Universe developed very tiny inhomogeneities which then allowed gravitational clumping is well understood. What is expanding is space time itself, not matter (dark or otherwise). Part of the "force" involved is dark energy, which has been compared with a type of anti-gravity, but isn't generally considered to be such.''

What i,m saying is: There should at some point in the early universe, a gravity, That strong 1 Atom would attract another Atom from 1000,s of miles away. And that gravity over billions of years is getting weaker and weaker is part of the expansion we see. Who was it that said ''I do not understand why gravity is so weak''

Mark

by **aristarchusinexile** » Tue May 26, 2009 7:16 pm

Chris Peterson wrote: Dark matter doesn't expand- gravitationally, it behaves just like ordinary matter, which is why we can detect it so easily.

Chris .. you're slipping badly. We observe effects a certain theory says is caused by Dark Matter. Get some extra sleep tonight.

by **aristarchusinexile** » Tue May 26, 2009 7:14 pm

Chris Peterson wrote: No, it can't be found because it doesn't physically exist in three dimensions. You would need something like a time machine to find it. Again, looking at the balloon, we, as 3D beings, can see the center of expansion. But it doesn't lie anywhere on the surface. No 2D inhabitant of that surface would ever be able to get to the center of expansion, because it lies in a direction they don't have access to.

"Now" is part of "time". The centre of the 3D universe is always in "Now" no matter how much expansion is going on. All other things being equal I see no problem, given the technology, to get to the centre of the 3D universe where our "now" will meet up and merge with the centre's "now".

by **Chris Peterson** » Tue May 26, 2009 6:53 pm

mark swain wrote:And gravity being the strong force should of made a different universe? But it did not. Is expansion happening inside matter like earth, stars, black holes dark matter etc etc?

No. Expansion happens in regions of space not bound by strong gravitational fields. That means it is happening in intergalactic space (and is limited even within galactic clusters and regions of higher mass density). Not inside atoms, not inside planets, stars, black holes, galaxies.

A dense particle, early universe with expansion from nothing everywhere should of made a universe of particles ....unless it is (''Anti gravity'') dark matter that is itself is expanding and that fuels expansion in certain regions of the universe?

I don't understand your suggestion that the Universe should be made of particles. The general picture of how the early Universe developed very tiny inhomogeneities which then allowed gravitational clumping is well understood. What is expanding is spacetime itself, not matter (dark or otherwise). Part of the "force" involved is dark energy, which has been compared with a type of anti-gravity, but isn't generally considered to be such.

Dark matter doesn't expand- gravitationally, it behaves just like ordinary matter, which is why we can detect it so easily.

by **The Code** » Tue May 26, 2009 6:31 pm

Chris P

And gravity being the strong force should of made a different universe? But it did not. Is expansion happening inside matter like earth, stars, black holes dark matter etc etc? A dense particle, early universe with expansion from nothing everywhere should of made a universe of particles ....unless it is (''Anti gravity'') dark matter that is itself is expanding and that fuels expansion in certain regions of the universe?

Mark

by **Chris Peterson** » Tue May 26, 2009 6:04 pm

Chris Peterson wrote:In the early Universe, matter was much more dense, and gravity easily led to local concentrations.

Just to avoid any confusion, especially given some of the strange ideas knocked around here about "compact matter" and the like, I don't mean that matter itself was somehow different ("denser") than it is now. It was simply that in a smaller universe, the distribution of matter was such that its density with respect to the volume of space was higher than it is today (outside of galaxies).

by **Chris Peterson** » Tue May 26, 2009 5:45 pm

mark swain wrote:What i meant was: How did expansion allow Stars to form from particles , If our universe can not crunch because of expansion. How did the stars crunch, galaxies crunch, black holes crunch????

Because gravity is much stronger than the "force" of expansion, except over cosmological distances. In the early Universe, matter was much more dense, and gravity easily led to local concentrations. Even today, clouds of gas and dust from stellar explosions comes together and condenses into vast star forming regions.

by **The Code** » Tue May 26, 2009 4:49 pm

What i meant was: How did expansion allow Stars to form from particles , If our universe can not crunch because of expansion. How did the stars crunch, galaxies crunch, black holes crunch????

Mark

by **Chris Peterson** » Tue May 26, 2009 4:46 pm

aristarchusinexile wrote:So, if the 3D universe is expanding in all directions and time equally at all times the centre will not change .. therefore it will be findable physically if the searcher has enough propulsion, protection, air, groceries and time etc.

No, it can't be found because it doesn't physically exist in three dimensions. You would need something like a time machine to find it. Again, looking at the balloon, we, as 3D beings, can see the center of expansion. But it doesn't lie anywhere on the surface. No 2D inhabitant of that surface would ever be able to get to the center of expansion, because it lies in a direction they don't have access to.

by **Chris Peterson** » Tue May 26, 2009 4:43 pm

mark swain wrote:Expansion is a power that over comes the power of gravity. This huge universe with all its mass can not crunch because Nothing is expanding into nothing every where. If this is a force to be reckoned with and is pushing everything away from each other. How can expansion be constant? If the early universe with no mass was also under the same expansion laws? How does what we see, come to be?

Expansion isn't constant, its rate is increasing. The early Universe had the same mass (energy) as the current Universe. No energy was created.

by **The Code** » Tue May 26, 2009 3:55 pm

Expansion is a power that over comes the power of gravity. This huge universe with all its mass can not crunch because Nothing is expanding into nothing every where. If this is a force to be reckoned with and is pushing everything away from each other. How can expansion be constant? If the early universe with no mass was also under the same expansion laws? How does what we see, come to be?

Mark

by **aristarchusinexile** » Tue May 26, 2009 2:46 pm

Chris Peterson wrote:
aristarchusinexile wrote: Then how can a 3D universe not have a true centre?
It can, but that center does not lie in 3D space, any more than the center of a balloon's surface lies in the 2D space of that surface. The center of the Universe is a point in spacetime. It lies in a direction (time) that we can't see. If you were a 2D creature on the surface of a balloon, you could detect that your universe was expanding, but you couldn't ever find the center of that expansion, except mathematically.

So, if the 3D universe is expanding in all directions and time equally at all times the centre will not change .. therefore it will be findable physically if the searcher has enough propulsion, protection, air, groceries and time etc.

by **Chris Peterson** » Tue May 26, 2009 2:42 pm

aristarchusinexile wrote:
Chris Peterson wrote:
aristarchusinexile wrote:Is the surface of a balloon considered 3D?
Topologically, the surface of a balloon is a 2D, non-Euclidean "plane". It can be used by analogy to help visualize the spatial part of our spacetime universe.
Then how can a 3D universe not have a true centre?

It can, but that center does not lie in 3D space, any more than the center of a balloon's surface lies in the 2D space of that surface. The center of the Universe is a point in spacetime. It lies in a direction (time) that we can't see. If you were a 2D creature on the surface of a balloon, you could detect that your universe was expanding, but you couldn't ever find the center of that expansion, except mathematically.

by **aristarchusinexile** » Tue May 26, 2009 2:32 pm

Chris Peterson wrote:
aristarchusinexile wrote:Is the surface of a balloon considered 3D?
Topologically, the surface of a balloon is a 2D, non-Euclidean "plane". It can be used by analogy to help visualize the spatial part of our spacetime universe.

Then how can a 3D universe not have a true centre?

by **Chris Peterson** » Tue May 26, 2009 2:15 pm

aristarchusinexile wrote:Is the surface of a balloon considered 3D?

Topologically, the surface of a balloon is a 2D, non-Euclidean "plane". It can be used by analogy to help visualize the spatial part of our spacetime universe.

by **aristarchusinexile** » Tue May 26, 2009 1:50 pm

Chris Peterson wrote:
Doum wrote:What i undestand from what Cris said is that the earth is obviously at the center of our visible univers. If you could move instantly a few billion years in distance then you would also be at the center of the visible univers overthere too. So, where ever you are in the univers you will always be at the center of the visible univers surounding you.
That is indisputable. However, in a more general sense, it is likely that the Earth (or any observer) is also at the center of the entire Universe (not just the visible Universe), as long as we consider its 3D structure.

Is the surface of a balloon considered 3D?

I sure wish I was with Duom, Astro and BMA as I'm certainly not at the centre of the universe or I'd be much more well balanced.

Starship Asterisk*

APOD: GRB 090423: The Farthest Explosion Yet (2009 Apr 29)

Post a reply

Expand view Topic review: APOD: GRB 090423: The Farthest Explosion Yet (2009 Apr 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)

Re: Just how small.... (GRB 090423: 2009 April 29)