# The Expansion of the Universe, I finally get it!

Status
Not open for further replies.
F

#### Fallingstar1971

##### Guest
Someone here directed me to a PDF file explaining expansion. I read it over, and I think that I finally get it. I understand how those farthest galaxies can appear to be moving at near light speed or beyond. AND, I understand how they can do it without violating the light speed "speed limit"

Im going to explain what I understand. Please do NOT merge this with something in the "Unexplained" Just let me know if I am right, or I am wrong. I'm trying to "learn", and not "guess" (or at least read it over first, chime in, and when the rest of my fellow crazies start chiming in THEN flush it.)

OK here it goes. I'm stuck using two dimensions here, so please bear with me

..........

Ten points, say you are point one. Expansion begins

. . . . . . . . . .

Points have expanded EXACTLY two "spacebar" taps.

Measure the velocity of the closest point to you, say point two.(im going to toss a number in there, 1/10th of c) Now, measure the velocity of the farthest. (Again, tossing a number in there, light speed or c)

But in reality, none have gone faster than 1/10th the speed of light, its the distance that creates the illusion.

So now, if you hop along the line to any point and measure the velocity of the next adjacent point, they will be moving at 1/10th c

But looking at all the points together, that last point appears to be moving at c

This has got to be, hands down, the greatest illusion of speed that I have ever seen. Its flat out FANTASTIC. Its right up there with electricity moving at c.

So, did I get it right? If not, please direct me to where I have misunderstood. Again, I am trying to learn, so please dont flush me to the unexplained, or to free space, without letting me know where I went wrong.

(BTW to the poster that directed me to that PDF, I would have got back to you sooner, but I was horribly sick all day and am now just starting to feel better. The funny thing is, the first thing I think of is expanding dots..... . . . . . . )

Go figure

Star

R

#### ramparts

##### Guest
I'm not entirely sure if I get what you're saying, but it sounds about right. Here's the idea in a nutshell: imagine a balloon being blown up. Now put some dots - little galaxies, if you like - on said balloon. Even though none of those points actually move, they all appear to move away from each other, from the perspective of the other little dots. They appear to move because the background they're on - the balloon's surface - is expanding.

Galaxies do the same thing, with the background being space(time) itself. The speed of light in this context is meaningless - as long as the galaxies are stationary where they are, as far as the universe and the laws of physics are concerned they're not moving (or at least, not moving at c - any other velocity is relative, of course).

F

#### Fallingstar1971

##### Guest
OK yeah, that exactly right......,.instead of velocity, I should have been stating the rate of expansion. So the dots are stationary, and the Universe expanded at 1/10th the speed of light, creating the illusion that the farthest dots were receding at a speed greater than light. (from the perceptive of one of the dots of course, not an outside view, like the balloon example)

Thanks ramparts

Star

M

#### MeteorWayne

##### Guest
Note that the view is the same even if you are dot 3 or 7 or 10. All galaxies are moving away from you, and the further away they are, the faster they "appear" to be moving. Hope that helps, too

MW

F

#### Fallingstar1971

##### Guest
Yes, I only used point one as a "starting point", because it was farthest in relation to 10 as I had them displayed.

I wonder what other illusions are out there. How many other "impossible" things that are unexplained, simply because we/me lack the understanding.

One thing is for sure. The more we look, the more we learn.

Lets never stop looking

Star

O

#### oldmoal

##### Guest
You can expand on the baloon anaology by imagining a whole series of baloons, one inside the other, and all expanding at the same time. You will see that the increasing rate of exapnsion holds in 3 dimensions as well as 2. Now imagine that there is an infinite number of baloons and you have a universe. - oldmoal

M

balloons..{sigh}

S

#### SpideroftheAbyss

##### Guest
Fallingstar1971":hdclml7a said:
OK yeah, that exactly right......,.instead of velocity, I should have been stating the rate of expansion. So the dots are stationary, and the Universe expanded at 1/10th the speed of light, creating the illusion that the farthest dots were receding at a speed greater than light. (from the perceptive of one of the dots of course, not an outside view, like the balloon example)

Thanks ramparts

Star
An object in space shouldn't be visible if it is "apparently" moving away from you faster than the speed of light. Light leaving the object would essentially be left as a trail at that point, and never reach you to be visible in an expanding universe. An expanding universe works the about the same as a Hoberman sphere. http://www.hoberman.com/fold/Sphere/sphere.htm

E

#### EarthlingX

##### Guest
SpideroftheAbyss":2wkdxzmr said:
An object in space shouldn't be visible if it is "apparently" moving away from you faster than the speed of light. Light leaving the object would essentially be left as a trail at that point, and never reach you to be visible in an expanding universe. An expanding universe works the about the same as a Hoberman sphere. http://www.hoberman.com/fold/Sphere/sphere.htm
So, how much of the Universe can we really see ? How long before the farthest galaxies start disappearing behind the light speed curtain ? Could we see this effect now, in something similar to dark flow ?

Wiki : Observable universe

One option :
Both popular and professional research articles in cosmology often use the term "Universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct experimentation about any part of the Universe that is causally disconnected from us, although many credible theories require a total Universe much larger than the observable universe. No evidence exists to suggest that the boundary of the observable universe corresponds precisely to the physical boundary of the universe (if such a boundary exists); this is exceedingly unlikely in that it would imply that Earth is exactly at the center of the Universe, in violation of the Copernican principle. It is likely that the galaxies within our visible universe represent only a minuscule fraction of the galaxies in the Universe. According to the theory of cosmic inflation and its founder, Alan Guth, the lower bound for the diameter of the entire Universe could be at least in the range of 1023 to 1026 times as large as the observable universe.
second :
It is also possible that the Universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies, formed by light that has circumnavigated the Universe. It is difficult to test this hypothesis experimentally because different images of a galaxy would show different eras in its history, and consequently might appear quite different. A 2004 paper[4] claims to establish a lower bound of 24 gigaparsecs (78 billion light-years) on the diameter of the whole Universe, making it, at most, only slightly smaller than the observable universe. This value is based on matching-circle analysis of the WMAP data. However, if the recent discovery of dark flow proves to be accurate, it strongly suggests that there is matter beyond the observable universe.

I

#### ifixit

##### Guest
and when you say matter outside the visable universe i imagine the balloon not to be the edge of the universe but also being pulled apart from the density of the hydrogen shell that was ejected perhaps and contains most of the matter from the big bang.

If things scale down resonably, at least to quantum level i beleive they do. i'd have thought the possibilty that a shell of hydrogen or whatever would have blown out in the initial big bang explosion, the universe expanding but dragged out by prehaps this hydrogen matter(or what it may now be it doesnt have to glow out there i suppose.

The resent area's of accelerated galaxy cluster movement could be attributed in just the same way as WMAP shows of the microwave radiation. The minor variations in this would also apply to a dense shell of hydrogen/helium gas that was perhaps ejected.

i always wondered this and why it is they look for something invisible and non baryonic that has an interaction with gravity expanding the universe. It's so complicated.

S

#### spork

##### Guest
SpideroftheAbyss":2ms21odg said:
An object in space shouldn't be visible if it is "apparently" moving away from you faster than the speed of light. Light leaving the object would essentially be left as a trail at that point, and never reach you to be visible in an expanding universe.
I'm no rocket surgeon, but I'm not so sure I buy that. An aircraft that's flying at faster than the speed of sound can still be heard aft of the plane. It's not like it throws sound waves aft at a speed slower than it's going forward. It still disturbs the local air, and those sound waves radiate out in all directions at the speed of sound. I would think the same would be true for the object in space. Once it emits a photon, that photon will head toward me at the speed of light regardless of the speed of the object that emitted it. It will simply be red shifted due to the motion of the object - right?

S

#### SubductionZone

##### Guest
It is not that simple spork. For example take a mass that is going exactly at the speed of light, which I know is impossible, if it were to emit a photon to its rear it would be red shifted down to zero. If it were going faster than the speed of light it might not even be able to emit a regular photon. It might only be able to emit tachyons which have very strange characteristics. You cannot use Newtonian physics when you start to talk about red shifting of particles at or near the speed of light.

S

#### SpeedFreek

##### Guest
This is the expansion of the universe we are talking about, not objects moving through space.

Folks, in order to solve this conundrum we have to consider the propagation of light relative to the frame that emitted it. How is the light moving away from that distant galaxy, relative to that galaxy? It is propagating at c, relative to that galaxy. It is moving towards us at c, relative to that galaxy.

Now, due to the expansion of the universe, that galaxy has an apparent recession speed. This is not a relative velocity in the usual sense, as these recession speeds are not due to the peculiar motions of galaxies through the universe, these speeds are due to the expansion of the universe, where the metric that defines distance has been changing, over time. It is as if the spaces between highly separated galaxies are expanding - it is as if space is expanding.

At a certain distance, known as the Hubble distance, this effect causes distances to have separated such that objects would have had to move at the speed of light to have reached that distance by the time their light was emitted, if they were moving through space.

So a galaxy with an apparent recession speed of c emits a photon towards us at c. That photon propagates at c towards us, relative to that galaxy, and is immediately in a region of space that is receding from us at a little less than c. Apparent recession velocity due to the expansion of the universe is related to distance, after all. The greater the distance, the greater the recession speed. Photons emitted at the Hubble distance will propagate towards us as normal, from the point of view of the emitter. In fact, from the point of view of the emitter, they can almost reach us! So any photon emitted by an object that recedes at c will find itself in regions of space that are receding from here at less than c, and so can eventually reach us. Also, any photon just crossing into our Hubble sphere at the same time will reach us too, so we can see the light from more distant objects, objects that were apparently receding even faster than c!

They key factor that defines what we can see is the history of the rate of expansion. If the universe were still decelerating then the distance where objects apparently recede at c would be increasing and we would see more and more of the universe as time went on. But unfortunately, the expansion of the universe seems to have recently started accelerating.

In an accelerating universe there is a cosmological "event horizon" where the recession speed precludes the light from distant events from ever reaching us. Currently, this horizon is 16 billion light-years away, 2 billion light-years beyond our Hubble sphere. So, the light from events happening "now", 16 billion light-years away, in regions of the universe that have apparent recession velocities faster than light, will eventually reach us. The light from more distant events that are happening "now" will not, although we will be able to see past events that happened at greater distance, as those photons are also just crossing that cosmological event horizon right now, if you see what I mean!

W

#### wolvieb

##### Guest
I'm no science guru or whiz kid, but I'm curious, wouldn't it stand to reason that expansion would accelerate as it gets further away from the center of the universe, I mean, wouldn't there be less matter/energy/stuff to slow it down? (This assuming there is absolutely nothing to slow expansion down, making it appear as though it were speeding up. That would also make sense in the fact that if all galaxies are expanding like the dots on the balloon, the balloon itself gets thinner, causing less resistance.) Like trying to run in water, yet as you get out of the pool its a lot easier to run? I'm just curious, but it would seem to me that if there is so much dark matter and energy closer to the center of the universe, it also seems to me that closer to the center of the universe there's a larger quantity of such. In an explosion you feel the shock wave before you see the blast. That initial force would blow most of itself out before everything else that had any remote amout of density. So in a way the universe is still in essence-- blowing out. Therefore, the visable universe that we can see, must be the more dense objects from the Big Bang, and that, which we can't see, partially be the force-- still blowing out... Were there nothing to slow that force, it could continue infinitely no?

R

#### ramparts

##### Guest
The problem is that there is no center to the expansion - all of space is expanding, it's not as if the galaxies are all moving away from a central point. Think about that balloon analogy: if the universe is on the surface of that balloon, then can you point to somewhere on the surface that is the center? Of course not. All the points on the balloon aren't moving away from a central point, they're moving with the expansion of the surface itself.

That said, the balloon analogy can easily be carried too far - for example, the fact that the balloon would get thinner has no correlation to how the universe expands. Also, there doesn't need to be another spatial dimension in the universe, as there does with the balloon - that is, the surface of the balloon (which we're saying is like the universe) has no center, but if you consider the third spatial dimension, then there is a center to the balloon. That's unnecessary in the universe, it can have its own intrinsic curvature without being curved "around" something. Remember, no one is saying the universe is a balloon, just that a balloon is a good analogy in some limited cases

Status
Not open for further replies.