Question about Universe

[pimp]

Hi

I am a little confused about our Universe's size and age. If the Universe is around 13 billion years old and it is around 90 billion light years across then how can galaxy's be so far apart if the universe is so young compared to it's size???

Hope that makes sense and someone can answer it.

 

[Jadzia]

There is no intrinsic limit on its rate at which space can expand, even if that expansion increases the distance between two points greater than the speed of light, apparently.

 

[Robert Maxwell]

My memory is fuzzy, but the universe can expand faster than the speed of light because it is (theoretically) a hypersphere, right? Or that is totally unrelated. Somebody help me!

 

[Jadzia]

I don't think a hypersphere is necessary. Expansion is just different from movement, and light speed is only a factor in movement.

The point the OP is thinking about here is that if he measures the universe's radius at 90 bn lys, and age as 13 bn years, then he knows that when he looks at the 'furthest star', the light has taken 13 bn years to get to his eyes, but cannot have travelled 90bn lys unless the space it has passed through has expanded during the journey.

Because when you look at the furthest star, you've looking back in time too, to when the universe was smaller, and that star was just 13bn lys away.

So it is quite feasible that some stars are so far away, that the light they emit will never reach us, because over that distance, the universe is expanding faster than the light is encroaching upon us.

That might make us think about what the 'edge of the universe' actually is.

 

[All Seeing Eye]

During the big bang didn't the universe expand initially at faster than light speed?

 

[Timewalker]

So it is quite feasible that some stars are so far away, that the light they emit will never reach us, because over that distance, the universe is expanding faster than the light is encroaching upon us.

I find this a very sad and depressing thought.

 

[Jadzia]

That is understandable. As parts of the universe continue to separate like this, I think it is impossible for them to come back together since the force of gravity is lost too -- it's like the cosmic equivalent of schizophrenia. The cosmic linkage gradually breaks down, and the result is a gradual irreversible dissociation.

 

[Capt. Vulcan]

So eventually, assuming we have a super earth and sun that lasts indefinitely, stars should start disappearing from the sky as the light gets too far to reach us?

 

[Jadzia]

yes but it isn't like a lights out.

The light loses energy on its star trek, so we see the star red shift. It red shifts eventually to zero frequency and the star has then gone out of reach.

 

[scotthm]

Expansion is just different from movement, and light speed is only a factor in movement.

I'm afraid I'm a bit dense when it comes to this 'expansion of space' concept.

We say that 'space' is expanding and carrying the galaxies along with it, making them appear to be travelling away from one another. If we assume that space is expanding equally everywhere, that means that the space in our local area is also expanding, at the same rate.

At what point do gravity and electromagnetism overcome space's inclination to drag matter along with it? IOW, the distance between galaxies is increasing as space 'pulls' them away from one another, but stars don't seem to be expanding. Earth doesn't seem to be expanding, and we don't seem to be expanding, so the implication is that on a local level, gravity and/or electromagnetism seem to be able to overcome this tendency of matter to 'spread apart' as the space it's imbedded in expands. This leads to me next question.

It seems to me that small, compact objects would be moving through space at a rate of speed equal to the expansion of space, since they seem to hold to their nominal size as space expands around them, but that galaxies are generally stationary in space as they're dragged along with its expansion. How could the constituent parts of a galaxy be moving faster in relation to space than the galaxy itself?

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[ThunderAeroI]

Essentialy the Big Chill.

I suppose it is possible for our local group to counter the effect of the big chill, but the sky will be boring to look at with only three galxies (four if you count that dwarf one below us).

 

[Jadzia]

Well the expansion is very slight, but yes it does occur everywhere. It is also true that the space inside stars and yourself is expanding too. But these distances involved are so unimaginably tiny that gravitational and electromagnetic forces will effortlessly counteract them, and hold this "compact" matter together. Even galaxies are small on that scale. The viscous drag of the swirling galactic dusts and gases is probably a stronger quenching force than what expansion does to them.

The expansion only really has enough strength between galactic clusters, where the gravitational forces are weaker, and the expansion is stronger (greater distance).

Imagine like having a rug made of elastic. And you sit somebody on it. You stretch that rug out, but the person sitting on it doesn't expand because it's internal forces holding the person together are much stronger than the frictional forces of the rug trying to pull them apart.

However, place two people on the rug and what happens? Because the two people have no significant force holding them together, we see them separate as the rug expands between them, but each individual person holds together.

The universe is expanding like that.

 

[scotthm]

Well the expansion is very slight, but yes it does occur everywhere. It is also true that the space inside stars and yourself is expanding too. But these distances involved are so unimaginably tiny that gravitational and electromagnetic forces will effortlessly counteract them, and hold this "compact" matter together.

That's fine, as far as it goes, but how then did the 'inflationary period' of our universe's history drag so much matter along with the fabric of space when all the matter at that time was almost unimaginably dense? Shouldn't that gravitational density have been able to overcome the 'pull' of space, or was the expansion so rapid that it just overcame all other forces?

If that's the case, it's a wonder that so many electrons and protons ever got together to form atoms and visible matter at all.

---------------

 

[Jadzia]

I'm no expert in this area, so other will have to step in here and explain this theory.

But its like you're visualising an exploding mass, but then it might as well be a super massive black hole you're thinking about, and black holes don't explode in big bangs, just because they're super dense. Quite the opposite is true.

I don't think the universe had matter at that early point, and no forces existed to hold whatever it was together. Electrons and quarks were the first matter to form, and by the time of their creation, the universe was big enough to not collapse back in on itself by gravity.

I also think that expansion wasn't the only factor in the big bang - there was also a great deal of kinetic energy in the matter which condensed, which was beyond the escape velocity of the bulk of the condensing material, so the matter didn't fall back on itself as a super-massive black hole.

I'm not a proponent of the big bang theory, you know, so it's probably better for others to pick up here...


[choca-girl, checking out]

 

[TEH BABA]

Also big bang visualized as explosion is bad way they do it on science programs and scifi.

 

[Shaw]

That's fine, as far as it goes, but how then did the 'inflationary period' of our universe's history drag so much matter along with the fabric of space when all the matter at that time was almost unimaginably dense? Shouldn't that gravitational density have been able to overcome the 'pull' of space, or was the expansion so rapid that it just overcame all other forces?

If that's the case, it's a wonder that so many electrons and protons ever got together to form atoms and visible matter at all.

What gravity?

In a uniformly dense universe, gravity couldn't exist.

Those who study gravity know that the gravitational effects of a massive uniformly hollow sphere are canceled out within the hollow interior. A small, uniformly dense universe would have the same effect on every point within that universe, no matter how dense the matter energy was.

Gravity wouldn't be able to play any role until after a symmetry braking event. And it wouldn't take much... just one point a little more dense than every other point and the symmetry of the universe would shatter instantly (like the braking of a sheet of glass). Then gravity could play a part keeping denser regions from expanding as fast as less dense regions.

One of the things astronomers are looking for is where that symmetry braking event took place. It is theorized that like fractures spider-webbing out from the braking point on a window, the web like structure of galaxies (seen in mapping projects of the visible universe) might point to where the symmetry braking event of our universe took place.

 

[TEH BABA]

At the center of the universe their exist only a binary machine.

 

[Robert Maxwell]

What are its values? "Baba" and "Not Baba"?

 

[scotthm]

Gravity wouldn't be able to play any role until after a symmetry braking event. And it wouldn't take much... just one point a little more dense than every other point and the symmetry of the universe would shatter instantly (like the braking of a sheet of glass). Then gravity could play a part keeping denser regions from expanding as fast as less dense regions.

I guess this is what's confusing me.

Are you saying that space wasn't expanding uniformly, or just that matter wasn't being uniformly 'dragged' along through space because in some places it was more gravitationally bound together?

If the former, then that means that gravity affects the expansion of space. If the latter, then it seems as if some matter was more or less stationary within its local space, while other matter 'stayed put' while space expanded out away from it. If space was expanding at superluminal velocities, then these latter masses would (it seems to me) be moving through space at FTL speeds.

---------------

 

[TEH BABA]

I'm no expert in this area, so other will have to step in here and explain this theory.

But its like you're visualising an exploding mass, but then it might as well be a super massive black hole you're thinking about, and black holes don't explode in big bangs, just because they're super dense. Quite the opposite is true.

I don't think the universe had matter at that early point, and no forces existed to hold whatever it was together. Electrons and quarks were the first matter to form, and by the time of their creation, the universe was big enough to not collapse back in on itself by gravity.

I also think that expansion wasn't the only factor in the big bang - there was also a great deal of kinetic energy in the matter which condensed, which was beyond the escape velocity of the bulk of the condensing material, so the matter didn't fall back on itself as a super-massive black hole.

I'm not a proponent of the big bang theory, you know, so it's probably better for others to pick up here...


[choca-girl, checking out]

What are its values? "Baba" and "Not Baba"?

So, say we all.