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Offline hamza

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« on: 19/12/2007 10:48:43 »
I was reading in a book about cosmology. It said that the universe was expanding and we all know that.. But the proof it gave was that scientists discovered that stars and galaxies were moving away.
            This kind of confused me. Because if we consider universe as a room and stars as people in the room. If the people(stars) are moving away from a center does not mean that the room is expanding. Its just the people that are moving towards the boundaries of the room. Help me on this one.


 

Offline rosalind dna

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« Reply #1 on: 19/12/2007 15:05:17 »
But stars are dying all the time as well including this week too. Or so I have
recently heard. So when our sun burns itself out then the earth and the rest of this galaxy will die.

http://www.rense.com/general72/size.htm
« Last Edit: 19/12/2007 15:13:29 by rosalind dna »
 

Offline lightarrow

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« Reply #2 on: 19/12/2007 15:34:26 »
I was reading in a book about cosmology. It said that the universe was expanding and we all know that.. But the proof it gave was that scientists discovered that stars and galaxies were moving away.
            This kind of confused me. Because if we consider universe as a room and stars as people in the room. If the people(stars) are moving away from a center does not mean that the room is expanding. Its just the people that are moving towards the boundaries of the room. Help me on this one.

What are the room walls in the case of the universe?
 

lyner

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« Reply #3 on: 19/12/2007 15:43:09 »
Space doesn't have to have 'edges', hamza.
'Limited yet boundless' is one expression which has been used for that idea.
 

Offline thebrain13

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« Reply #4 on: 19/12/2007 19:20:04 »
if the room was super big, and you couldnt see the walls, you could still tell that the people were moving away from you.
 

Offline Soul Surfer

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« Reply #5 on: 19/12/2007 23:51:53 »
The currently favoured cosmology is generally called "The Big Bang".  This was the derogatory name given to it by opponents of the theory back in the 1940's and 50's when there were big arguments about it. This was well before the observations that showed clearly that it was on the right track has been made.  This gives the incorrect image that the universe started like a great explosion flinging the bits apart from the centre.

What is really happening is that the space itself is expanding its as if space consisted of lots of little bits that interacted with each other and occasionally created a tiny bit more space and increased the separation between parts that were already a long way apart.  This effect is currently incredibly tiny.

The normal way of expressing this expansion of space is the hubble constant which is about 70 Km/s per Megaparsec  now that sounds quite fast until you reralise how big one megaparsec is  ie about  30,000,000,000,000,000,000 Kilometres  so it works out at about 3 x 10^-15 meteres per second per kilometere a totally umeasurably tiny amount even over long periods on galactic scales it is only detectable in quite remote galaxies.

This expansion also appears to be uniform in all locations and there is no detectable centre.
It is also predicted in the equations of relativity and not subject to the recession speed limit (the velocity of light) associated with accelerated motion.  when galaxies are so far away that they are receding at greater than the speed of light we just can't see them because the light will never reach us.  there are many reasons to believe that th whole universe is much bigger than the universe that is visible to us.

This expansion is and has almost always been incredibly finely tuned to prevent the universe collapsing back to a point or vanishing into nothing and this fine tuning is probably some very critical part of the thory of everything.

So called inflationary theories suggest that right at the beginnig this expansion was much faster and there are hints that it may again be increasing  due to "dark energy" but this reuires more explanation than neccessary at this stage in the question.
 

Offline Soul Surfer

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« Reply #6 on: 19/12/2007 23:59:33 »
rosalind dna  your statements are not clear and appear to be very mis informed and your web reference does not work.
 

Offline turnipsock

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« Reply #7 on: 20/12/2007 01:26:53 »
rosalind dna  your statements are not clear and appear to be very mis informed and your web reference does not work.
the web reference seems to work ok
 

Offline rosalind dna

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« Reply #8 on: 20/12/2007 01:43:59 »
http://www.bbc.co.uk/science/space/stars/death/index.shtml

Good that my previous link to that other website works. It should do as a friend gave it to me. Yes stars are dying in the galaxy and ever infinite universe for which no one may
ever be able to see the edge off.

If something is born so another star has to die first in my opinion that is.

Including another fact that the sun is a star which is very slowly burning itself out as
I have said before.
 

Offline Soul Surfer

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« Reply #9 on: 20/12/2007 12:29:25 »
The weblinks seem to be working for me now.

Rosalind your contributions seem to be a bit off the topic of the expanding universe but seem to be more concerned with the scale of things and the fact that we live in a universe that is evolving or changing with time and seem to have an underlying fear that life is ephemeral.

Many stars have had to die in supernova explosions to create the heavy elements that exist in our planet and are essential to allow life to evolve.

We live in an evolving universe that was very different and alien to life like ours in the past and will become so in the future.

The life and death of mankind is insignificant compared with the life and death of our solar system

The life and death of our sun is totally insignificant in the life and death of our galaxy. 

The life and death of our galaxy is totally insignificant in the life and death our universe.

The understanding and acceptance that all things must change is an important part of understanding the reality of our universe.  Peoples personal wishes and ideals are not part of this and must be set in the context of their own life and death and that of their family friends and the rest of life in this planet.
 

Offline opus

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« Reply #10 on: 20/12/2007 18:30:55 »
I have heard it said that dark matter must exist because there is a shortfall in the combined mass of everything visible in space. How is this measured?
 

Offline Soul Surfer

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« Reply #11 on: 20/12/2007 23:45:42 »
This is quite difficult to explain in a few words but I will have a go.

One of the problems is that there is and always has been several cosmological theories running at the same time and not all of them are compatable so it depends a bit on who you listen to which bits of the full story with all the options get stressed.

Space to us appears to be very flat on the largest scales (as opposed to the curved space one finds locally near to a black hole).  The currently preferred theory is that space is absolutely flat (although this has not always been the preferred theory). This sort of universe is called a closed universe but it does not continually collapse and re-expand. From the gravitational equations this requires a certain critical density of matter and energy in the universe. Matter both visible and dark would tend to reduce the expansion rate over time while dark energy would tend to speed it up.  Visible matter is clearly insufficient to close the universe.  This leaves the way open for some form of dark(or invisible) matter and energy to close the universe.  There is very strong evidence for the existence of a great deal of gravitating but invisible matter in the motions of stars in the galaxies and the motion of galaxies in their clusters.  This is almost irrefutable if you stick with the conventional theories of gravitation.  (MOND  MOdified Newtonian Dynamics is a different theory and a different story)  The latest observations suggest that the expansion could now be increasing (after slowing down for most of the time )  and this implies enough dark energy to close the universe.
 

Offline Dick1038

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« Reply #12 on: 21/12/2007 19:04:07 »
If empty space is being constantly expanding and empty space also contains energy, is more energy being added or is the energy density decreasing with time?

Also, if the expansion is increasing, would that suggest that the universe's geometry is open rather than flat?
 

Offline Soul Surfer

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« Reply #13 on: 22/12/2007 11:53:07 »
That is an interesting question and the conservation of energy suggest that it must be so if the expansion of space actually consumes energy.

Again that seems to be so because the normal idea of the flat universe was that the expansion just continues without limit and our horizon stays the same.
 

Offline opus

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« Reply #14 on: 22/12/2007 23:19:55 »
Thank you Soul Surfer, for answering my question so well. I think I understand this better now....But why, like with so many of these mind-boggling (for me) conundrums, do the answers open so many more questions?!
 

Offline Dick1038

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« Reply #15 on: 28/12/2007 18:11:41 »
Answering questions that lead to more questions is basic to science. Toward the end of the 19th century, it was thought that there was nothing left to discover!

Just wait until they figure out what dark matter is. The discovery will probably throw out a lot of our basic assertions of cosmology. It will keep future generations of Ph.D. students very busy.
« Last Edit: 28/12/2007 18:14:09 by Dick1038 »
 

Offline opus

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« Reply #16 on: 02/01/2008 19:09:46 »
yes Dick- that's why this whole science thing is so brilliant!
 

Offline lightarrow

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« Reply #17 on: 02/01/2008 19:40:28 »
yes Dick- that's why this whole science thing is so brilliant!
Also, for concepts like those ones, is pretty impossible to have a clear vision of things and to stop thinking, even after answeres.
 

Offline lightarrow

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« Reply #18 on: 02/01/2008 19:49:26 »
I have heard it said that dark matter must exist because there is a shortfall in the combined mass of everything visible in space. How is this measured?
By the observed rotation's speed of objects around the galactic centre: the speed is too high, so the more external objects should have been driven away by centrifugal force, exactly as a too fast car cannot stay in a bent and goes out of road; so there must be more mass in the galaxy, which attracts objects more, then what we are observing.
« Last Edit: 02/01/2008 19:51:06 by lightarrow »
 

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