[Fluffy]

The way I think of the universe is a BIG, but finite group of stars, planets, pulsars, etc, etc, wich is expanding.

But almost every mass in the universe throws light, and as long as I know light doesn't change into another form of energy unless it collides with a mass.

Well, then the amount of light that goes away from the universe is frightening BIG, one man could spend his life writing zeroes for counting the amount of energy lost per second, an energy that never comes back to the universe since mass can never be faster than light.

Is this what they call entropia of the universe?, I find it frightening.

[Al_U_Card]

Do not worry, my friend.

Your capacity to understand the immensity of the universe is equal to its complexity. Always remember that you are an integral part of its existence.

[Al_U_Card]

Also, the hidden dimensions that allow for the actual manifestation of the force of gravity are also responsible for the multiple frames of reference that coincide with each eventuality.

Infinity is just as big a concept as eternity so there is enough room for everything.

[jtfanclub]

Fluffy, on Dec 25 2007, 01:32 PM, said:

Well, then the amount of light that goes away from the universe is frightening BIG, one man could spend his life writing zeroes for counting the amount of energy lost per second, an energy that never comes back to the universe since mass can never be faster than light.

One theory is that the univers is a giant four dimensional sphere. So eventually, light ends up where it started, kind of like getting in an airplane and flying West until you get back to where you started.

[kenberg]

I suppose there is a choice of frightening scenarios, at least for those with the capacity to think in the sufficiently long term. I'm not completely up to date on cosmology (to put it mildly) but at one time at least there was the question of ongoing expansion forever with, I guess, everything slip-sliding away, or, on the other hand, an eventual end to the expansion followed by eventual implosion. I don't know if the issue is resolved.

"Some say the world will end in fire, others say ice... "

Myself, I am more concerned about the extra weight I have put on during the Holidays. I'm a short term worrier.

Anyway, A Merry Christmas to one and all. Put worry and strife aside. It's a beautiful universe we inhabit, if only for a while.

Ken

[blackshoe]

The Universe is a closed system, so far as I know. So the light doesn't "go away". OTOH, I'm not a cosmologist, so maybe I'm wrong.

[matmat]

time to make a fool of myself...

I think (and you may correct me if I am wrong) your question is similar in nature to what is called Olber's paradox
http://en.wikipedia.org/wiki/Olbers'_paradox.

anyhow, here are some random related things for you to chew on, and I can expand on them if you like. (no pun intended)

We do not know,in reality, how large the universe is. We only know how big the region that we can observe is.
We are actually limited in two ways as to how far we can see:
1) light has only travelled a finite distance since the universe began
2) early on the universe was a hot soup of plasma that was opaque to to light, most things that happened before this time we cannot observe (and believe me, people are trying to get around this problem)

As the universe expanded, this plasma cooled and eventually became transparent to light. This happened over a short time and all points in the universe appear to have emitted the "trapped" light simultaneously. (the gas was at a temperature of a few thousand Kelvin, so the light they will have emitted would have been similar in spectral shape to our Sun, very close to a black-body spectrum).

So what we should be seeing on Earth, when performing observations are the following things:

1) light from astronomical structures, like galaxies, stars, etc. that are associated with specific locations on the sky
2) this background radiation which should look fairly uniform no matter which way we look.

In fact we see both. but there is a caveat. When we say that the universe expands, it is not equivalent to things simply moving away from one another, i.e. it's not the same as you and a friend standing next to one another and then each taking a step away, it's as if the floor that you are standing on stretched, creating a distance between you (imagine two penmarks on a balloon that you are blowing up). In effect photons (quanta of light), which for this particular explanation are best viewed as waves, have their wavelengths stretched. If you recall your chemistry/physics, longer wavelength --> lower energy. (this effect is what's referred to cosmological redshift). So all light traveling in the universe loses energy as the universe expands.

we do, in fact, see all of the light from 1) and 2) above.
in the last 20 years there have been some beautiful observations conducted of the background mentioned above (called cosmic microwave background, CMB). You can find some pretty pictures and some better explanations than mine here:
http://en.wikipedia.org/wiki/COBE
http://en.wikipedia.org/wiki/WMAP
(edit -- somehow i didn't mention that the currently observed 'temperature' of the CMB is about 3K, or, roughly a thousand times lower than what it was when the light was originally emitted, the universe has expanded by factor of about 1000 since that time)

Just to boggle your mind a little bit:
cosmologists are generally in consensus that there was an early period of inflation where the expansion of the universe was faster than the speed of light.
http://en.wikipedia....osmic_inflation

also, measurements indicate that we live in a universe where the expansion is slightly accelerating, meaning that we should eventually start losing objects out of our observable universe, but I'll let you read about that and the competing scenarios.
http://en.wikipedia....of_the_universe

[sceptic]

the unsiverse is round, it is also very small, as outside what we know of as Space is actutaly a bigger universe in which we are but a speck of dust smaller than one of their atoms

prove me wrong, not in this life time I doubt

everytime we find something small we find it is made of smaller stuff still and everytime we find something big, the Americans have built something bigger

so in reallity the universe is just a big mixing pot of things that form into other things for lots of different reasons and on another note, no one knows if the universe is expanding, it is quite feasable that it is dying, we just do not understand the way space moves and does things, on the other hand, GOD crated everything and does not want us to know what he is up to.

It is too late to worry about making a fool of myself

[gwnn]

I thought we lived on the inside or a large sphere and the soles of any person's shoes are the proof of it (the extremes are always infinitely more worn). No surprise that the light cannot escape.

[Wackojack]

Here some more ways of comprehending the universe:

Space is in the universe rather than the universe being in space.
The big bang happened everywhere, not just one point in space.
The big bang was the explosion of space, not an explosion in space.
Space does have an end, but it does not have an edge.
There is no such thing as space or time only space-time.

A popular but limited description to try and explain the above:
The expanding universe is like a current bun swelling in the oven, with currants playing the role of galaxies and the dough representing space.

The limitation if this description is that whereas a currant bun has a centre, there is no centre of the universe. Unfortunately minced pies and Christmas pudding won't explain the universe either.

[barmar]

I've read lots of cosmology books, but something has always bugged me about the expansion of the universe: why don't the measuring sticks expand with it? E.g. to use the balloon analogy, an inhabitant of the balloon universe would presumably define an inch by placing two marks on the balloon and calling the distance between them a mile. As you blow up the balloon some more, the size of the balloon will increase, but so will the distance between the marks. We can see this growth because we live outside the balloon, in the next higher dimension. But wouldn't the balloon universe inhabitants use the marks on the balloon as their standard for measurement, and not notice the change?

[Al_U_Card]

Because reality is subjective. Your meter stick is always the meter that you know and are comfortable with. The universe that you don't know depends on someone elses subjective appreciation of it.

Quantum reality is the ultimate subjective obligation.

[jtfanclub]

barmar, on Dec 26 2007, 05:24 PM, said:

But wouldn't the balloon universe inhabitants use the marks on the balloon as their standard for measurement, and not notice the change?

When the measuring stick expands, it changes color.

We measure not the distance from Alpha Centauri to see if it's moving away from us, but see if the color of light coming from it is bluer (closer) or redder (further away).

[matmat]

jtfanclub, on Dec 26 2007, 06:37 PM, said:

barmar, on Dec 26 2007, 05:24 PM, said:

But wouldn't the balloon universe inhabitants use the marks on the balloon as their standard for measurement, and not notice the change?

When the measuring stick expands, it changes color.

We measure not the distance from Alpha Centauri to see if it's moving away from us, but see if the color of light coming from it is bluer (closer) or redder (further away).

JT's right. we are measuring how objects are moving with respect to us, rather than exactly how far away they are.

In terms of what is actually observed, we look at either absorption or emission lines from the star. i.e. features in the spectrum rather than just the color itself. This measures the velocity that the object has with respect to Earth. The process being used here is Doppler shift. Think about the pitch of the siren as a fire truck is coming toward you and moving away from you -- you should hear different frequencies in the two cases.

That said, stars are at cosmologically insignificant distances from us, in the grand scheme of things.

for the curious --measuring the distance to a cosmological object is quite difficult, in fact, there are several different ways of doing this, which give *mostly* consistent results.

[kenrexford]

This problem of the balloon expanding made me think.

Run this in reverse.

Imagine being in a room of a specific size. The room neither expands nor shrinks. However, all items in the room shrink. If all items in the room were to shrink together, including the person sitting on a chair, then that person on the chair might perceive that the walls of the room were moving away from him and the room expanding. And yet, it was him shrinking in exact proportion to everything around him.

What if the "items" in the room were shrinking to make room for more items, such that the total weight of the objects in the room was the same? Instead of one 20 lb. chair, now 20 chairs weighing 1 lb. each and 1/20 the size. The contents of the room would be getting more diverse, but the size of the room and the contents therein would be the same, in a sense. And yet, the man in the one chair would see 20 chairs and 20 men, all exactly his size. Clearly, to him, the room must be expanding to make room for all of these men and chairs.

I'm not sure, but it also seems that one would believe that shrinking chairs were moving away from the observer. I cannot exactly figure, though, why chairs might seem to be expanding out from a central point or expaning out at different rates, but this might also have an explanation.

Hummmm.

[Fluffy]

yeah, if the universe is expanding it seems like systems of systems of galaxies should be expanding as well, and systems of galaxies, and galaxies, and solar systems, and planets, and atoms.....

[helene_t]

No, if everything was expanding all our measurement sticks would expand as well so we wouldn't notice anything. In fact nothing would be expanding, since expansion is relative.

That the universe is expanding means that it expands relative to something else. Assuming the speed of light and the size of atoms don't change, the universe expands measured in lightyears or measured in atomic diameters.

[matmat]

helene_t, on Dec 27 2007, 05:19 AM, said:

No, if everything was expanding all our measurement sticks would expand as well so we wouldn't notice anything. In fact nothing would be expanding, since expansion is relative.

That the universe is expanding means that it expands relative to something else. Assuming the speed of light and the size of atoms don't change, the universe expands measured in lightyears or measured in atomic diameters.

heh
this is going to sound a little silly. Things that are bound are not moving away from one another.

galaxies, stars, earth, galaxy clusters, galaxy groups, gas clouds etc. are all held together by gravity.

in that sense my earlier statement about things drawn on a balloon that's getting blown up is wrong -- think more in terms of little droplets of water on this balloon. the distance between them increases, but the surface tension keeps the little beads the same size.

[Wackojack]

kenrexford, on Dec 26 2007, 11:08 PM, said:

This problem of the balloon expanding made me think.

Run this in reverse.

Imagine being in a room of a specific size.  The room neither expands nor shrinks.  However, all items in the room shrink.  If all items in the room were to shrink together, including the person sitting on a chair, then that person on the chair might perceive that the walls of the room were moving away from him and the room expanding.  And yet, it was him shrinking in exact proportion to everything around him.

What if the "items" in the room were shrinking to make room for more items, such that the total weight of the objects in the room was the same?  Instead of one 20 lb. chair, now 20 chairs weighing 1 lb. each and 1/20 the size.  The contents of the room would be getting more diverse, but the size of the room and the contents therein would be the same, in a sense.  And yet, the man in the one chair would see 20 chairs and 20 men, all exactly his size.  Clearly, to him, the room must be expanding to make room for all of these men and chairs.

I'm not sure, but it also seems that one would believe that shrinking chairs were moving away from the observer.  I cannot exactly figure, though, why chairs might seem to be expanding out from a central point or expaning out at different rates, but this might also have an explanation.

Hummmm.

The shrinking man clearly would feel himself shrinking as his head was rushing towards the floor. If the chairs were also shrinking, the perception of the area of the room would depend on whether or not the walls were perfectly plain. With perfectly plain walls it would appear that space was expanding (like there were no walls at all). In the universe that we inhabit how do we know that we are not all shrinking? Gravity.

[Wackojack]

helene_t, on Dec 27 2007, 05:19 AM, said:

No, if everything was expanding all our measurement sticks would expand as well so we wouldn't notice anything. In fact nothing would be expanding, since expansion is relative.

That the universe is expanding means that it expands relative to something else. Assuming the speed of light and the size of atoms don't change, the universe expands measured in lightyears or measured in atomic diameters.

The 2 statements contradict. 2nd statement assumes that space expands and we would notice if everything in it expanded also.