The Big Bang & Distant Objects

[Peters]

A train of thought that leads to a question. I ask it only cos I'm stupid and can't get my head around the obvious answer (well to me anyway).

1. An object 10 light years away is observed as it was ten years ago.
2. The furthest observable object is some 13 billion light years away (observed through a gravitional lens of an object some 5 billion light years away).
3. The further back in time an object is then the closer it is to the point in space where the big bang occured.
4. The big bang occured at a single point in space some 14 billion years ago.
5. An object 13.5 bllion light years away is observed as it was about 500 million years after the big bang.

Question - Does it not follow that the further away an object is then the closer to the point of the bing bang it is and therefore all such distant objects must be congregated in the same area of space as observed from the earth ? The place where the big bang occured.

:confused:

[PhysBrain]

I think I understand your dilema. The main reason I haven't posted until now was that I was trying to find a reasonable explanation for what you are describing. This web page a decent description with some neat animations: http://zebu.uoregon.edu/1996/ph123/l4.html, and this one gives a few more details: http://cosmos.colorado.edu/astr1120/l12S6.htm.

The important thing to remember is that galaxies are not moving away from us in particular. No matter where you are in the universe, it appears to you that all distant objects are moving away from you and the further away they are, the faster they are moving away. From this observation, we can conclude that the universe itself is expanding, thus decreasing the net energy/mass density of the universe.

If we allow for an infinitely large universe, or at least an incredibly huge universe, then to any observer there will be some distance beyond which one cannot see because the universe beyond that distance is moving away from the observer faster than the speed of light. Photons from these distant objects cannot reach the observer since they will be red-shifted so far, that their energy cannot be detected. This distance is called the causal event horizon, or the cosmic horizon.

Now, in answer to your question, the objects that we see so very far into the past were actually quite distant from us when the universe finally cooled down sufficiently for light to propagate (before that, the universe was a big ball of plasma which continually absorbed and emitted photons at nearly every point in space - aka microwave background radiation). So, in addition to the original distance the light would have had to have traveled, we must also add 14 billion plus years of expansion which has increased the distance.

Thought Experiment: Imagine we launch a rocket from earth with a magic spool of infinitely long elevator cable. The rocket lets out the cable as it goes. Now, imagine we want to travel to the rocket in an elevator which travels at some fixed velocity up the cable. If the velocity of the elveator is less than that of the rocket, then it will never catch up. This corresponds to photons from places in the universe that we will never see. If the velocity of the elevator is greater than the rocket's, then it will eventually reach the rocket, but not before it traverses a much larger distance than that which was required when it began its journey.

So, in effect, there are two horizons beyond which we cannot see further into the past. One is the causal event horizon imposed by the speed of light and the expansion of the universe, and the other is the moment in the past when the universe first became transparent.

I'm pretty sure that, at the moment, the causal horizon is much further away than the big bang haze, but I haven't checked the numbers to be sure. If I find the values for these respective limits, or I get some free time to run the numbers, I will post them here.

[bryce]

Late answer...don't know if you're still around, but....

One way to look at, or think about it, is that the Universe isn't expanding into some pre-existing space that was already there, but space *itself* is expanding. Everywhere. Imagine our 3D space as the skin of the surface of a balloon...(forget for a second time, and 11-dimensional compactified whatevers) mark it with some dots - representing the galaxies - and blow it up...the galaxies are then rushing away from us, because the space between the galaxies is expanding.

Now suck out the air...the galaxies rush back together, and if you could suck the balloon down to nothing, all the galaxies, *and* space, would come together at a single point.

If you want to see the center of the expansion, look no farther than where you are sitting, because since space itself is expanding, *every point* is the center of the expansion.*

And, even if there were some cosmic horizion that we could peek over to see the *very* begining of time, modern "Inflationary Theory" tells us that at one point the very fabric of spacetime itself (the skin of that balloon) underwent a period where it expanded *faster* than the speed of light (space can do this, according to inflation, just not mass, energy, or information, relative to space...) so anyway, the very horizon itself flew off faster than light, and light from us may take who knows how long, if ever (esp. if the expansion is increasing or accelerating, as some think) the light will take to reach us...???

- bryce
*Yes, my model of the universe is oversimplified, and if you can't tell, pretty much a finite but unbounded hypersphere...or at least the surface of it...all nice and curved in upon itself...this is because it's an easy model for me to conceptualize, and anything else GIVES ME A FREAKIN' HEADACHE!!! My brain is too simple to understand more complicated topologies, so don't bother trying to explain any to me!!! ;)

"Your theory of a donut shaped universe intrigues me, Homer."
- Stephen Hawking, guest voicing on "The Simpsons"

[Impalaplaya]

Im so lost

[budcamp]

Bryce

Interesting!

space *itself* is expanding. Everywhere

The problem is, what is this space that is expanding, and what is it expanding into?

[K6-III]

That is a question we cannot presently answer....

[Impalaplaya]

there are lot of things we cannot explain doesnt that suck

[budcamp]

Not being able to explain things doesn't suck, that's what science is all about. Science is a search for the truth. Religion on the other hand thinks it has "the truth". So, not being able to explain things must suck for them.

When scientists are asked where the first elements of the big bang came from, we say we don't know!

When theists are asked where did God come from, they have to provide an answer, because they are preaching "the Truth".

[K6-III]

Originally posted by budcamp
Not being able to explain things doesn't suck, that's what science is all about. Science is a search for the truth. Religion on the other hand thinks it has "the truth". So, not being able to explain things must suck for them.

When scientists are asked where the first elements of the big bang came from, we say we don't know!

When theists are asked where did God come from, they have to provide an answer, because they are preaching "the Truth".

AMEN

[Impalaplaya]

Yea religion cant just say were wrong our we dont know ive asked everyone where does God come from and they said he was just there, I mean come on give me a better explanation. At least Science comes up with the most probable answer. other than it just always was

[AltToWar]

Originally posted by budcamp
Bryce

Interesting!

space *itself* is expanding. Everywhere

The problem is, what is this space that is expanding, and what is it expanding into?

Time


Just as the appearant 2Dl baloon surface is expanding and curving over a hidden 3rd dimention, our apperant 3D universe is curving over time.

the members of the balloon universe only see things moving in one direction while we blow it up. The members of the baloon univers can never go more outward or inward than the current level the ballon is inflated to.


So do we only see time moving in one direction. So are we limited to motion only within our current time.

[PhysBrain]

Space-time has an independent existence. Just because our space-time is curved, or expanding, does not necessarally mean that it is embedded inside of some higher dimensional space. I did not truly appreciate this fact until I had a course in tensor analysis. While it is true that any curved space can be represented as a sub-space inside of a flat (Euclidean) space with at least one higher dimension (ie think of a curve or surface embedded inside of a 3D Cartesian space), the presence of the higher dimensional flat space is not required. That means that I can mathematically describe all of the properties of a curved space without giving any reference to any higer dimensional embedding spaces. It is simply easier for us to visualize a curved space with respect to a flat background space. As I said, both representations are mathematically valid, however, the existence of the flat background space is not explicitly required.

So, it is not the expansion and curvature of the universe that I'm worried about. Rather, I'm concerned about the parts of the universe that are not expanding. Consider for a moment that if the universe were uniformly expanding, then everything in it would be expanding as well. The fact that we can detect that the distance between galaxies is increasing indicates to me that the atoms and molecules that compose us and our instruments are not similarly expanding.

The current cosmological theory which attempts to explain this is the dark energy hypothesis. Cosmologist seem to think that there is an as yet uknown form of energy present in intergalactic space which is driving the universal expansion. That is to say that there is some unknown process at work in intergalactic space which has the net effect of adding more space to our universe.

My own theory on this (which I am making up on the spot) is that if there is some process driving the expansion of the universe, that it is probably acting uniformly on all of space. However, this expansion does not change the conservation laws of energy and momentum. Electrons must orbit nucleii at very specific distances in the orbitals specified by quantum mechanics. The oribts of planets about stars and stars about galaxies must conserve energy and momentum according to Newton's and Einstein's theories. So, if space is expanding uniformly everywhere, then matter must continue to slip down into its self-induced gravity and potential wells. Hmmm.... if this is true, then the motion of planets and stars sliding down into the gravity wells should be detectable somehow....

Well, sorry for the rambling. I often get new ideas while I'm trying to explain things to people. If anybody is interested in further discussion of amateur comsmological musings, let me know and I'll open up another thread.

[timeshifter]

if space is always expanding, that would mean that there is no definition to the universe. if space is infinite in all directions and a group of galaxies are always moving outward from the middle, that makes a little more sense. i dont know if everyone sees it this way, but if you do, please expand on what you know of this.