Universe Expansion: Why Objects Move Away Faster The Farther We Look

[Drakkith]

Interesting question. I would guess that, as the universe continues to expand, it cools down. So, the galaxies are not moving faster, we are just moving slower. Just a guess.

When we say that the universe is 'cooling down' we mean that expansion reduces the temperature of the intergalactic medium and redshifts light traveling large distances (multi-megaparsec distance). Temperatures within galaxies and galaxy clusters is unaffected otherwise.

 

[PeterDonis]

If the past was more dense, why don't distant objects appear to be closer together than nearer objects?

I believe they do, but the relationship between redshift and brightness by itself won't tell you that. You need to look at counts of how many objects we see at different redshifts, which can be translated to a count of how many objects per unit volume there are at different redshifts. I'm pretty sure such surveys have been done and show the expected relationship (to within the accuracy of measurements, which is not very high), but unfortunately I don't have any links handy.

 

[marcus]

...
How is it that nearer more recent spacing can look the same as distant older spacing if the objects (large scale) are uniformly increasing their relative distances apart? If the past was more dense, why don't distant objects appear to be closer together than nearer objects?...

I believe they do, but the relationship between redshift and brightness by itself won't tell you that. You need to look at counts of how many objects we see at different redshifts, which can be translated to a count of how many objects per unit volume there are at different redshifts. I'm pretty sure such surveys have been done and show the expected relationship (to within the accuracy of measurements, which is not very high), but unfortunately I don't have any links handy.

Number per unit volume can be a little unintuitive because past a certain point, with increasing redshift one is looking at a smaller volumes of space (back then). And how one estimates volume at different z is model dependent.
One thing to look for that exhibits the effect Bahamagreen is talking about (that we see a compacter univerese at higher z) is the angular size minimum.
http://ned.ipac.caltech.edu/level5/March02/Sahni/Sahni4_5.html
Past a certain redshift (z=1.6) similar sized objects will look LARGER in the sky. Because they were nearer to us when their light started out.
So beyond z=1.6, the farther away it is now, the larger the angle it makes in the sky.

 

[marcus]

So when you look at a very old layer of the sky, it can have fewer galaxies, but they each cover a larger angle, and so they can be closer together in proportion to their angular size. IOW they can be fewer and yet represent a higher density of matter. It seems strange. But it is a way to see the higher density that existed in that layer of the past.
Think you wanted a visualization of the higher density...

the redshift z = 1.6 is the one corresponding to the greatest "DISTANCE THEN" when the light was emitted. It is the maximum width of the past light cone which is kind of pear shape. The maximum distance then is about 5.837 or so billion LY. Anything with higher z than 1.6 was actually NEARER than that when it emitted the light, so it is going to look larger on that account.

Here is a way to see that maximum "distance then" at z=1.6 using the Lightcone calculator (which embodies standard cosmic model with pretty much usual parameters). I ask it to plot from around year 545 million up to present (z = 0)
{\scriptsize\begin{array}{|c|c|c|c|c|c|}\hline R_{0} (Gly) & R_{\infty} (Gly) & S_{eq} & H_{0} & \Omega_\Lambda & \Omega_m\\ \hline 14.4&17.3&3400&67.9&0.693&0.307\\ \hline \end{array}} {\scriptsize\begin{array}{|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|} \hline z&T (Gy)&R (Gly)&D_{now} (Gly)&D_{then}(Gly) \\ \hline 9.0&0.545&0.82&30.68&3.07\\ \hline 8.2&0.623&0.94&29.94&3.27\\ \hline 7.4&0.712&1.07&29.17&3.48\\ \hline 6.7&0.813&1.22&28.36&3.70\\ \hline 6.0&0.928&1.39&27.51&3.92\\ \hline 5.4&1.060&1.59&26.63&4.15\\ \hline 4.9&1.210&1.81&25.70&4.37\\ \hline 4.4&1.382&2.07&24.74&4.60\\ \hline 3.9&1.577&2.35&23.73&4.82\\ \hline 3.5&1.800&2.68&22.68&5.03\\ \hline 3.1&2.054&3.05&21.59&5.24\\ \hline 2.8&2.342&3.47&20.46&5.42\\ \hline 2.5&2.670&3.94&19.27&5.58\\ \hline 2.2&3.041&4.46&18.05&5.71\\ \hline 1.9&3.462&5.05&16.77&5.80\\ \hline 1.6&3.937&5.69&15.46&5.84\\ \hline 1.4&4.471&6.39&14.11&5.82\\ \hline 1.2&5.071&7.16&12.72&5.73\\ \hline 1.0&5.740&7.97&11.30&5.56\\ \hline 0.9&6.483&8.82&9.85&5.30\\ \hline 0.7&7.303&9.70&8.39&4.93\\ \hline 0.6&8.201&10.58&6.93&4.45\\ \hline 0.4&9.177&11.45&5.48&3.85\\ \hline 0.3&10.228&12.28&4.05&3.10\\ \hline 0.2&11.350&13.06&2.65&2.22\\ \hline 0.1&12.539&13.77&1.29&1.18\\ \hline -0.0&13.787&14.40&0.00&0.00\\ \hline \end{array}}
http://www.einsteins-theory-of-relativity-4engineers.com/LightCone7/LightCone.html
One of our PF members, and his son, made the calculator.
I think it's great. It generates tables of cosmic history for you instead of just giving a one-shot number for an answer. Not hard to use, check it out.

 

[Quds Akbar]

There comes a limit where the galaxies are moving faster away from us than the speed of light because of the expanding space between us and these galaxies. This "limit" is creates a sphere called the Hubble sphere, and if our Hubble Sphere expands fast enough to catch we will be able to see the light from this galaxy , as it too will be moving away from us, but by then many years would have passed.

 

[happyman79]

How do we add vectors in space, and why does space seem to have a static equilibrium if everything in space is in motion one way or another. Eg. Earth rotates at 22,000km/h while revolves around the sun at 70,000km/h. We and our sun revolve around the galaxy at 500,000km/h while on a collision course with Andromeda at 550,000km/h while expanding in XYZ direction at 76.1km/h over mpc. And i know direction is relevant in space, but displacement has to have some role right? I know if we revolve around the sun in 365.25 days our displacement in correlation ti the sun would be zero, but to the Milky Way galaxy or to another galaxy; or to the expansion of the universe our displacement may never be returnable. Is this a cosmology question or a different type of physics?

 

[Chalnoth]

What do you mean by static equilibrium? Are you talking about the stable orbits of objects in our solar system?

Stable orbits happen for a few reasons:
1. Newtonian gravity conserves energy.
2. The Sun provides nearly all of the gravitational force in the system, for objects far away from other planets. A system with a lot of bodies of nearly-equal masses would be much more chaotic (orbits of stars through the galaxy are rather chaotic, for instance).
3. There's not much of anything for the planets to run into. Collisions would cause the orbits of the planets to decay over time.

 

[happyman79]

Well early solar system was chaotic and had lots of collisions, and we ran out of enough material to keep making plants in our solar system too right? What i mean by static equilibrium is our plant as right now is traveling through space at all those speeds through gravitation, but we do not feel any of those velocities except our Earth's rotation speed, mass, and circumference. But when you stand still on Earth you feel as if in static equilibrium ( no opposing forces, velocites, or accellerations) but are clearly being toss around space at ridiculous speeds. When an asteroid collides with Earth exerts a force on the asteroid as well, upon impact. Now whether it is the mass or speed of the Earth or asteroid making an inelastic collision is not for me to say. Theory says, that if the asteroid goes fast enough it possibly could go through the planet which isn't really an elastic or inelastic collion.

 

[happyman79]

And the Milky Way and Andromeda are a path to collide, plus a red giant named Nemesis has a binary pair with our sun, and it is questionable if they are meant to collide. Or have full orbits. But every 26 million years that other start gets perry close to our sun. ( in comparison to the universe.) one scientist said it possible could have been the reason why we got pelted by an asteroid 65 million years ago, but I'm not going to quote that directly.

 

[Chalnoth]

Well early solar system was chaotic and had lots of collisions, and we ran out of enough material to keep making plants in our solar system too right? What i mean by static equilibrium is our plant as right now is traveling through space at all those speeds through gravitation, but we do not feel any of those velocities except our Earth's rotation speed, mass, and circumference. But when you stand still on Earth you feel as if in static equilibrium ( no opposing forces, velocites, or accellerations) but are clearly being toss around space at ridiculous speeds. When an asteroid collides with Earth exerts a force on the asteroid as well, upon impact. Now whether it is the mass or speed of the Earth or asteroid making an inelastic collision is not for me to say. Theory says, that if the asteroid goes fast enough it possibly could go through the planet which isn't really an elastic or inelastic collion.

We don't feel the Earth's motion because the Earth is in free-fall. This has nothing to do with equilibrium, static or otherwise. It's just due to the fact that if you're in a container that is falling freely, you will be falling at the same rate and so will feel weightless. With the Earth, our "container" has enough gravity that we feel the Earth's gravity, but we can't feel the Earth's motion at all (well, except for its rotation, if we use very precise instruments).

 

[happyman79]

Ok so we free fall around the planet that free falls around the sun that is free falling in galaxy that is on a collision course while expanding through space. Up to the collision part we are just free falling in a continuous rotation, always ended back at start. But compared to other things in the universe we should have displacement every sec. And everything else in space is always moving to, so no point will anything reach a 0 displacement. 24 hrs of standing in the same spot you could say the displacement was 0, but the distance was a total of the circumference of the earth, but really in retrospect to the universe we have didplacement. I get throwing a ball in a car experiences the same forces as you do inside the car regardless speed of car. What i don't get and still make sense is Earth is in a car that us in car that is in a car that is on an escalator that is in an elevator. But all at the same time experiencing it all like we are in one car the while time. The two biggest things I'm not too fond off are, 1 not knowing where in the galaxy we are. 2. What direction are we going in space and what is the shape. If we observe space from every point on a sphere, and every way we could see 13.7 billion light years ( i haven't declared past yet because it cannot be defined, outside of relativity. Is it possible light has a limit or barrier or is it possible to assume the universe is sphere shape itself? And could anything we observe actually be in the future ( expanding further from the beginning of time; what ever direction that might be.)

 

[Drakkith]

The two biggest things I'm not too fond off are, 1 not knowing where in the galaxy we are.

We do know our location within our galaxy.
http://upload.wikimedia.org/wikipedia/commons/a/a7/Milky_Way_Arms_ssc2008-10.svg

2. What direction are we going in space and what is the shape.

We know which direction we are going relative to most of the other galaxies in the visible universe. I'd say that counts for our 'direction' since there is no such thing as absolute motion, only relative motion. As for the shape of the universe, that's still a work in progress.

Is it possible light has a limit or barrier or is it possible to assume the universe is sphere shape itself?

The light itself doesn't have a barrier, but there is a limit to how far we can look since the age of the universe is finite. Light beyond a certain radius simply hasn't had enough time to travel to us yet.

And could anything we observe actually be in the future ( expanding further from the beginning of time; what ever direction that might be.)

Not a chance. We can only ever observe things that are in the past.

 

[phinds]

Happyman, if you are going to continue posting on this forum, I request that you please learn the concept of paragraphs and USE that concept in your posts. Thank you.

 

[Chronos]

And the Milky Way and Andromeda are a path to collide, plus a red giant named Nemesis has a binary pair with our sun, and it is questionable if they are meant to collide. Or have full orbits. But every 26 million years that other start gets perry close to our sun. ( in comparison to the universe.) one scientist said it possible could have been the reason why we got pelted by an asteroid 65 million years ago, but I'm not going to quote that directly.

Nemesis?? Surely you jest. That dog of a hypothesis does not even qualify as an urban legend.