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Author Topic: expanding universe  (Read 9024 times)

Offline ukmicky

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expanding universe
« on: 24/07/2005 02:37:36 »
They know the universe is expanding because most  of the galaxies are redshifting. but instead of the the fabric of space expanding causing the universe to expand.
why cant the galaxies all be moving away from each other because dark energy or dark matter is repelling them from each other. This would still cause a red shift but without the universe getting bigger.
I know there's an anwser but i dont obviously know it
« Last Edit: 24/07/2005 03:55:20 by ukmicky »


 

Offline Supercryptid

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Re: expanding universe
« Reply #1 on: 24/07/2005 05:14:40 »
The fact that some galaxies recede faster than the speed of light would be evidence enough that it is space that is expanding and not the galaxies moving themselves. Space and time are not bound by the speed of light, and are allowed to exceed it because they are neither matter nor energy. Any object resting on an area of space that is moving (or expanding) faster than light would look like it was moving faster than light itself. Relative to its own surroundings, however, that object is still moving quite subluminally.

Since no amount of energy can push an object faster than c, you can't explain superluminal galactic recession by repulsive energy alone.
 

Offline ukmicky

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Re: expanding universe
« Reply #2 on: 24/07/2005 14:08:23 »
but if galaxy A is being pushed one way at near the speed of light and galaxy B is being pushed in a different or opposite direction  it could give you a speed of separation faster than c,
and neither galaxy would be breaking any rules.
« Last Edit: 24/07/2005 14:54:55 by ukmicky »
 

Offline gsmollin

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Re: expanding universe
« Reply #3 on: 25/07/2005 19:47:39 »
quote:
Originally posted by ukmicky

but if galaxy A is being pushed one way at near the speed of light and galaxy B is being pushed in a different or opposite direction  it could give you a speed of separation faster than c,
and neither galaxy would be breaking any rules.



You don't add velocity in that manner in special relativity. If galaxy A is receding from you at .6c, and galaxy B is receding from you, in the opposite direction, at .6c, then an observer in galaxy A or B sees the other galaxy receding at .9c, NOT 1.2 c. The velocity additions assymptotically approach c, but never exceed it.
 

Offline ukmicky

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Re: expanding universe
« Reply #4 on: 27/07/2005 02:40:14 »
Thanks  I knew there had to be an awnser.
 

Offline chimera

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Re: expanding universe
« Reply #5 on: 27/07/2005 06:08:55 »
One thing to keep in mind is that it's space expanding, not so much matter (galaxies). That's why the distances between them gets bigger, while the galaxies themselves stay together. Not everything there is understood, though, since if you look closely at rotating galaxies all parts of the galaxy move at the same speed around the center, which would seem impossible if gravity alone would keep the whole shebang together. The center of the galaxy would have to rotate faster than the  edge, which is contrary to observation.

Also, NOT all galaxies have a redshift. Andromeda is blueshifted, for one, and on ramming course even (don't cancel any dates, it'll take some time yet).

Time is a great teacher, but unfortunately it kills all its pupils - Hector Louis Berlioz
 

Offline ukmicky

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Re: expanding universe
« Reply #6 on: 31/07/2005 03:56:40 »
I heard the rotation and size of a galaxy is directly proportional to the size of the blackhole in the centre.
Also i heard that as well as a andromeda there are around 100 galaxies that were blueshifting so there a lot more than just our local group of galaxies coming our way.
 
thankyou all for your replies
« Last Edit: 31/07/2005 03:57:14 by ukmicky »
 

Offline ukmicky

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Re: expanding universe
« Reply #7 on: 07/08/2005 17:49:36 »
expanding universe

gsmollin

Could it be possible that something beyond our universe is pulling on and stretching it.
Rather than the universe and the fabric of space being expanded from something within
« Last Edit: 08/08/2005 04:13:08 by ukmicky »
 

Dr. Praetoria

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Re: expanding universe
« Reply #8 on: 07/08/2005 21:41:22 »
I think I've heard that parallel universes could  have branes (like membrane constructions) that are capable of colliding into each other at certain points and, perhaps generating "big bang" phenomena there.
 

Offline David Sparkman

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Re: expanding universe
« Reply #9 on: 08/08/2005 01:48:11 »
Hmmm, if stars are moving away from us at faster than light speed, how would we ever know it? We could never see them...

What defines the edges of the universe? what is beyond where light has never gone, were gravity has not yet reached?

As time slows down in a gravity well, does time achieve an infinite progression where there is no gravity?

Rather than think these heavy thoughts my mine capitulates and remembers the ending of Men in Black, the first movie...

David
 

Offline gsmollin

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Re: expanding universe
« Reply #10 on: 09/08/2005 22:03:06 »
quote:
Originally posted by ukmicky

expanding universe

gsmollin

Could it be possible that something beyond our universe is pulling on and stretching it.
Rather than the universe and the fabric of space being expanded from something within




Something like that is one of the results of m-brane theory. It has to do with gravity, which is supposed to cross the universal boundaries. I am not in a position to answer any questions about it, though. That is is still for a specialist.

About recessional velocities: Many of the redshifts scientists measure on receding galaxies, and the cosmic microwave background radiation, are explainable by concluding that the receding galaxy has recessional velocity > c. I think any redshift greater than 3.2 is supposed to recede > c. The CMB has a redshift of ~1000. This does not square with SR. The explanation is that there are two kinds of velocity. One is in a local reference frame, where no material velocity exceeds c. Also, we still measure the speed of that redshifted CMB as c. The test is that "No thing can go past you at >c."

A recessional velocity never goes past you, and is not part of your local reference frame. It can exceed c, and this is explained as an "expanding space".
 

Offline David Sparkman

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Re: expanding universe
« Reply #11 on: 09/08/2005 22:19:47 »
Spectroscopy is one of my fields, though only from an engineering point of view. I am not sure what you mean by a red shift of 1000. The units are not familiar to me.

The quantium of energy for any element depends on the relationship between the electron and the nucelus of the atom. Temperature changes this relationship, moving at relativistic speeds does as well.

But gravitational compression in things approching neutron stars should also change the energy levels of the different shells. So I would not be so sure of the standard interpertation. There are still a lot of strange things we may not have seen or considered.

David
 

Offline Razor

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Re: expanding universe
« Reply #12 on: 09/08/2005 22:35:44 »
We dont even know how big the universe is,fair enough if it's just one big box but imagine the size of it,imagine if God was just an alien who creates universes for a living,like the ending of Men in Black for whoever have seen it.
The thing has like a big bag full of em'

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Offline simeonie

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Re: expanding universe
« Reply #13 on: 10/08/2005 11:55:41 »
Isn't the universe expanding at the speed of light? Because the light coming from light sources is going out at the speed of light and uncovering more of the universe

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Offline Razor

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Re: expanding universe
« Reply #14 on: 10/08/2005 15:23:52 »
Does'nt mean it's expanding.

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Offline gsmollin

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Re: expanding universe
« Reply #15 on: 10/08/2005 20:54:08 »
quote:
Originally posted by David Sparkman

Spectroscopy is one of my fields, though only from an engineering point of view. I am not sure what you mean by a red shift of 1000. The units are not familiar to me.

The quantium of energy for any element depends on the relationship between the electron and the nucelus of the atom. Temperature changes this relationship, moving at relativistic speeds does as well.

But gravitational compression in things approching neutron stars should also change the energy levels of the different shells. So I would not be so sure of the standard interpertation. There are still a lot of strange things we may not have seen or considered.

David



Clearly.

If you are familiar with spectroscopy, then you already know what a Dopler shift is. If a light souce is moving, its wavelength will be shortened or lengthened. Redshift is a dimensionless number that gives a ratio for the amount the wavelength has lengthened. A formula can be found here: http://www.astro.virginia.edu/~jh8h/glossary/redshift.htm

Cosmological redshift is much more difficult to understand than Dopler shift. General Relativity tells us that space is expanding between us and the rest of the universe, and is carrying away distant galaxies. A discussion of cosmological redshift can be found here: http://www.astronomycafe.net/anthol/expan.html

Google "cosmological redshift" for 201,199 more entries to read and ponder.
 

Offline simeonie

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Re: expanding universe
« Reply #16 on: 10/08/2005 21:14:33 »
Well not exactly expanding but more is becoming possible to view.

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Offline gsmollin

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Re: expanding universe
« Reply #17 on: 11/08/2005 02:20:34 »
quote:
Originally posted by simeonie

Well not exactly expanding but more is becoming possible to view.

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No, exactly expanding space. GR tells us that space can expand. Do some research on it. You don't have to believe it to make me happy, but that is exactly what it tells us.

That is different from the light-cone horizon, which just says that as time goes on, we can see further back in time because the light from distant events has had more time to reach us. So every year, we see a light year further away.

"F = ma, E = mc^2, and you can't push a string."
 

Offline ukmicky

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Re: expanding universe
« Reply #18 on: 11/08/2005 03:33:49 »
TO Gsmollin
I donít doubt your knowledge and have always treated your replies as gospel.
Itís good to have a source you can trust.[^]
But just out of interest have you ever supplied an incorrect answer on this forum.
Have you ever got anything wrong? Its human to err, have you erred yet.
Or are you inerrable.:)
« Last Edit: 13/08/2005 00:56:13 by ukmicky »
 

Offline gsmollin

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Re: expanding universe
« Reply #19 on: 11/08/2005 11:03:17 »
quote:
Originally posted by ukmicky

TO Gsmollin
I donít doubt your knowledge and have always treated your replies as gospel.
Itís good to have a source you can trust.
But just out of interest have you ever supplied an incorrect answer on this forum.
Have you ever got anything wrong? Its human to err, have you erred yet.
Or are you inerrable.




OK, it's possible I am erring for the first time, on this forum, by responding to this post. I simply try to answer questions, and occasionally post one, for the fun of it. Some people post good questions, and I enjoy finding the answers. It is rare that I fire from the hip: Most of the time I have checked references before I answer. That may be why it seems that I am "always right", but in reality, it is only good research. Anybody can do it, who has an interest. Other times, like when the question is really difficult, I will simply suggest avenues of research to the poster. Other stuff I don't get involved, like all the "God" questions. It's not science or physics, and really belongs in "just chat".

If you prefer, I won't respond to your posts. I don't want to offend you.

"F = ma, E = mc^2, and you can't push a string."
 

Offline ukmicky

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Re: expanding universe
« Reply #20 on: 12/08/2005 02:42:03 »
gsmollin
I was trying to congratulate you on all your efforts towards this forum, In my own sort of way.
You havenít offended. In fact keep up the good work. As i said its good to have a source you can trust.
The err part was just a question. Nothing meant by it. [:I]:)

« Last Edit: 13/08/2005 01:18:46 by ukmicky »
 

Offline David Sparkman

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Re: expanding universe
« Reply #21 on: 16/08/2005 03:42:22 »
Thanks for the answer on the red shift number. What I was considering was defined on one of the web sites as:

"The Gravitational Redshift is a shift in the frequency of a photon to lower energy as it climbs out of a gravitational field."

If we assume that Neutron stars come in various gravitational levels, some being not quite newtron stars, we could see red sifts all the way up to almost a singularity at which point the red shift approches infinity as the star approaches a singularity (black hole).

I don't see how the scientists can rule out this posibility, and if not, how they can prove the very large numbers they get on the expansion. The NStar mode takes no great leap of faith to believe, and is established science. The super fast expanding universe producing such red shifts is asking us to reject the simple explaination, and accept a much more complex one.

David
 

Offline vanvinhhoang

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Re: expanding universe
« Reply #22 on: 04/09/2005 11:31:45 »
In my opinion, an obvious explanation for our expanding universal no come soon. Because our space communicative technology is just at the biginning, and i have a abit ridiculous ideal is that it maybe cause of our understanding about gravity and the another forces is still not full.  I believe when we gain the theore of the unification every our current problems will solve, ofcouse consisting of this explanation
 

The Naked Scientists Forum

Re: expanding universe
« Reply #22 on: 04/09/2005 11:31:45 »

 

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