# Expanding universe

Discussion in 'Science and Nature' started by pintada, Jan 14, 2014.

1. I hate it when someone gets a little high and then solves one of the great problems of all time, now, i'm doing it.

Oh well.  Actually, it isn't just me and the idea has evolved over the past several days.  So:

The universe is expanding and in fact that expansion is accelerating.  The proof is that if you look out 8 billion lightyears a galaxy that you see is red-shifted more than a galaxy that is only 4 billion light years out.  A galaxy that is 13 billion light years out is moving away at prodigious speed nearing the speed of light.

But wait ...

If you look back in time 13 billion years, the galaxy you see is only a billion years from the big bang, so it stands to reason that it is hauling ass.  If you look back only 8 billion years, the galaxy is moving slower and 4 billion years ago the galaxies are moving slower.  If you look back only .5 billion years, the galaxy you see is not moving away much at all and of course the galaxies in our local group are not moving away at all.

So where is the proof that the universe is expanding?

2. #2
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lol could start with General Relativity requires it, and has yet to be falsified.

Also what do you mean by "If you look back in time 13 billion years, the galaxy you see is only a billion years from the big bang, so it stands to reason that it is hauling ass."?

More if you view a galaxay 20 billion light-years away, the light is only 5 billion years old for example, or in other words seeing the galaxy as it was 5 billion years ago.

Note to your point of the universe is expanding, veiwing something 20 billion ly away does not equate to seeing the object as it was 20 billion years ago. For example the observable universe has a radius of 46 billion ly, yet is only 13.x billion years old.

Also is your doubt coming from the idea that locally the universe is seemingly not expanding? Though across large distances it is?

I'd be so shocked if you read this paper, it is "non-technical" and there is no math, ie for the layman like me. But if interested in this stuff do yourself a favor a read it, you'll be leaps and bounds more informed then most on the topic.

What have we learned from observational cosmology ? -J.-Ch. Hamilton

3. A galaxy that is 13 billion light years away will have a larger redshift because the light has to travel through more expanding space than a galaxy that is 8 billion light years away. About an extra 5 billion light years worth of distance to cover to get to us. So a galaxy that is 13 billion light years away has 13 billion light years of expanding space to travel. A galaxy that is 8 billion light years away has 8 billion light years worth of expanding space to travel. A galaxy that is 1 billion light years away only has 1 billion light years to travel through expanding space. So the more distance covered, the greater the redshift. The further out they are doesn't mean they're moving faster, just means they are further away and the light needs to travel a greater distance through space that is expanding.

As for our galactic neighborhood, they are moving and space is expanding here too.. but that doesn't mean galaxies don't have their own momentum or movement. The Andromeda galaxy is actually moving towards us, so it's light would be blueshifted.. and the same thing would/could be happening in other local groups. You could be looking at a galactic group 13 billion light years away and the whole thing will seem to be moving away, but if you were there, the local group there would be like our local group.

4. #4
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That's wrong, distance covered has nothing to do with redshift. And you should understand what redshift is before you claim to know what it is. That goes against the grain of science.

Redshift is caused primarly by two things

1. Relative motion - that is the light from far away galaxies are red shifted because there is a comparative motion between us and it.

2. Gravity - gravity redshifts the light emitted/reflected from that body. for example light from the sun would be slightly redshifted due to the gravity of the sun.

And yes generally speaking and in this context of expanding universe and redshifted galaxies the futher out from us the greater the comparative motion, proven by the red shifted light they emite. I don't want to get into a sematics debate about "it's not really motion because it's cause by the expansion blah blah blah."

man there is a lot of hand waving in this forum lol

One cool thing to note about this expanding universe is billions of years from now, peeps won't be able to even see other galaxies as they will be receading at a speed greater then light (some are now). So much for intergalatic space travel and encounters with the third kind then ahahaha

5.
It most definitely does have to do the distance.. It's called Hubble's Law. It applies to most of the universe that is outside our local galactic group. Inside our galactic group is your #1, our relative motion or better termed, Doppler shifts.

http://www.esa.int/Our_Activities/Space_Science/What_is_red_shift

So yes, get into the semantics of it.. lol

http://en.wikipedia.org/wiki/Redshift

http://en.wikipedia.org/wiki/Hubble%27s_law
Be sure to soak in the last sentence..

I'm not saying you're wrong cause you're right, both movement and gravity can effect redshift.. but so does the distance the light has to travel in an expanding universe. That's why once you get so far out from our local galactic neighborhood, there is no blueshift. A galaxy's momentum could be carrying it in our direction, but the expansion is pushing it away from us at a faster rate.

To quote a friend:

6. #6
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Im not sure how you are interpretting that "disance" & redshift. I'll say again and difinitively that distance does not cause red shift and the only place I read that it does was from you. You said it does not mean they are moving faster.

Well, everything you quote says the opposite. My point is to clarify the redshift is cause by the comparative motion, which is greater the farther out.

Perhaps youre ignoring if expansion stopped, the light emitted today from those distant galaxies will NOT be redshifted.

Don't  be so pompous, youre still missing the point that distance merely correlates to the redshift, and that is specifically because the rate of expansion sums, so the farher away the greater the rate of expansion inturn creating a greater comparative motion which causes greater red shift. Again the distance itself has no impact, it is strictly the expansion. Just like all those sources you cited say.

Odd you'd still say it's redshifted because of the distance lol, idk maybe reading comprehension,

1. Your first site is prob very technical, in that doppler is specifically defined, where as the comparative motion from an expanding universe is quassi comparative motion. For example some galaxies are receding at a rate of greater then the speed of light, however nothing can travel greater then the speed of light...think on it reply so I can see if you get that.

2. The second calls it a "Rate", Im happy with that term. It certainly doesn't say the cause of redshift is distance.

3. The third is to explicit and calls it velocity, but does qualify it by saying interpretable velocity. (how did you not read that?)

Those three points I pulled from your sources are all saying it is redshift measured because of comparative motion between us and it. Which was my point about getting into a semantics debate about speed. Just as those sources are hesitant to call it speed, it is not speed, but quassi speed/ comparative motion. This is because there is additional space emerging in the same amount of time. No doubt that goes way over your head, just as my point did, and those sources you cited that support my point and don't even mention yours because it doesn;t even make sense physically to say distance causes redshift, distance does nothing to light. Changing geometry of spacetime does, simple as that.  pysh

So thanks for suggesting I take my own advice, but I have a pretty good understanding of redshift, not even educated good, just pretty good. You're way off on describing it...lol distance causes redshift. If you're gunna parrot what you read at least get it right.

In other words, how do you even picture redshift as happening that you believe distance causes redshift.

7.
It is your reading comprehension then.. or mine, but Ima go with yours. Notice each time I talk about this, I specify the distance the light has to travel through expanding space. I even specified that in the first thing you quoted.. Light gets "stretched out" by the expanding universe as it's traveling through the expanding universe, so naturally the more distance it needs to cover, the more it will be stretched out, the greater the redshift. We're pretty much saying the same thing, only that you're also saying distance covered has nothing to do with redshift.. when it does.. Nowhere did I say that redshift was caused only by distance, but it is an important factor in redshift.

Also, there would still be redshift if the universe stopped expanding cause galaxies can have their own momentum. Some would be moving away from us, some would be moving towards us, and some would be sitting still. The only difference would be that there would be blueshift as much as there was redshift.

8.
Yea, , I've noticed that too.

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Did you edit your posts or something? I re-read and see that nowhere did you say distance causes redshift.

In either case your posts are correctly worded. Guess it was my reading comprehension! Oppps!

10.
it says at the bottom of posts if it's been edited or not. You can see that he did not edit any of his posts.

11. #11
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Then it was my reading comprehension, must have read it how I wanted only seeing him saying that the redshift is because of distance, and interrupting it as him saying distance causes redshift.

Sorry bout that Mantikore, my mistake and poor reading comprehension

12. My thanks to PeterParker, Manticore, et. al.  I'm not saying I'm right, but I am missing something subtle.  I was not clear originally, so let me try again.

Imagine that you have access to the Hubble telescope and you are playing around with it.  You look at Andromeda and sure enough see that it is blue shifted.  (The hydrogen spectra emitted from the galaxy is more to the blue side than if you were looking at a spectrum of hydrogen produced on earth.)  Thus, we know it is moving toward us.

Now, you turn the telescope to the other galaxies in the local group.  The spectra emitted are pretty normal so you conclude that they are floating along with us - neither moving away or closer at any significant speed.

I think we are all on the same page so far.

Now point the telescope at a galaxy 1 billion light years out.  You will see that it was in fact moving away, because it is red shifted (the hydrogen lines are further down toward the red end of your spectrum).  Yes, we know that it was moving away a billion years ago, but we have no indication what it is doing now, or even if it currently exists.

Same thing for a galaxy that is was moving away at nearly the speed of light.  It was moving away 13 billion years ago - whether you say it was moving or whether you say space was expanding makes no real difference.

So my confusion arises from the fact that when one makes the measurements that show red shifting on a distant galaxy, one is also looking back in time.  In other words, I think that the speed of light in a vacuum is a constant and that this sentence fragment is patently false:  "â€¦  20 billion ly away does not equate to seeing the object as it was 20 billion years ago"

Conversely, I accept this statement from PeterParker completely:
"Redshift is caused primarly by two things
\n1. Relative motion - that is the light from far away galaxies are red shifted because there is a comparative motion between us and it.
\n2. Gravity - gravity redshifts the light emitted/reflected from that body. for example light from the sun would be slightly redshifted due to the gravity of the sun.
\nAnd yes generally speaking and in this context of expanding universe and redshifted galaxies the futher out from us the greater the comparative motion, proven by the red shifted light they emite. (sic)"
\nSo, where is the proof that the universe IS expanding NOW?
\nNote that the above is not an argument.  I am merely trying to clarify my original question.

13. #13
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Hmmm... I don't know. Im not even sure if there is "proof", or if it's just an all arrows point to that being the case, in the same sense as the big bang or that spacetime is isotropic.

This is a copy and paste from physicsforums.com that I think answers your question, because it's (hubble constant) predictions are accurate.
They also clarify the terminology of comparative motion when expanding space is between the bodies; calling it recession velocity, as opposed to relative velocity. imo though comparative motion still works, but only by avoiding using the term velocity lol

"The Hubble Constant The Hubble â€œconstantâ€ is a constant only in space, not in time,the subscript â€˜0' indicates the value of the Hubble constant today and the Hubble parameter is thought to be decreasing with time. The current accepted value is 70 kilometers/second per mega parsec, or Mpc. The latter being a unit of distance in intergalactic space described above.
Any measurement of redshift above the Hubble distance defined as H[SUB]0[/SUB] = 4300Â±400 Mpc will have a recessive velocity of greater than the speed of light. This does not violate GR because a recession velocity is not a relative velocity or an inertial velocity. It is precisely analogous to a separation speed. If, in one frame of reference, one object is moving east at .9c, and another west at .9c, they are separating by 1.8c. This is their recession velocity. Their relative velocity remains less than c. In cosmology, two things change from this simple picture: expansion can cause separation speeds much greater even than 2c; and relative velocity is not unique, but no matter what path it is compared along, it is always less than c, as expected."

Oh and it's the first line that answers the question, it's constant only in space, but varies over time, i.e. is time dependent.

14. Aha, progress.  Thanks, I appreciate your time.  This is NOT over!

If we ( my son and I ) "discover" anything definitive, I will post it.

15.
It's all good dude. Lol, I will say my patience got one hell of a workout, but we all do it from time to time.. I've always been one to believe that making a mistake is far from bad, just bad when you don't own up to a mistake.. so you got my props.

I'd say the only proof is the redshift, the cosmological redshift that is. The very reason for us seeing the redshift in distant galaxies is because of the expansion.. but I get what you're saying. If the universe just suddenly stopped expanding, the light that was redshifted would still be traveling to us, but then there would be a point where light that wasn't cosmologically redshifted begins to reach us. If the closest galaxy to us that is subject to cosmological redshift was currently 1 billion light years away from us, we wouldn't know the universe stopped expanding until 1 billion years later. It's like with the 8 minutes it takes for sunlight to get to us.. If the Sun blew up, we wouldn't know about it til 8 minutes later.

Basically the data we are getting is pointing at the universe expanding and no data coming in that it stopped expanding.. Sure, you could ponder on the idea and create theories, but until we get the data that says it stopped expanding, it'd be a 50/50 shot at best..

16. If the universe is expanding does that mean traffic is going to ease up? I certainly hope so!

17. expanding universe is a theory, actually 2
1 - ever expanding
2 - expanding and contracting
depends on what's best to you.

18. I'll be reading a while â€¦ maybe a long while.     I'm looking at the emoticons, and do stoners never feel embarassed?   LOL

I may wade through these, articles and still not get it.  Nah.   The answer is here.    its just a matter of time.

Maybe this one.