Is the red shift discrepancy the same at all distances?

ianke · Feb 4, 2007

why06 I probably didn't say it right.<img src="/images/icons/blush.gif" /> what I meant is more like tigerbiten wrote. "If the universe is expanding at a constant rate you will get a straight line. If the expansion is slowing down the line will curve oneway, speeding up will curve it the other way. " In other words, my question was more intended to ask if the red shift could have shown the difference or not between the 2 possible curves. You can't plot one single point on the time line an say which way the curve is. It can only show the overall effect in comparison with the theoretical. It takes more points observed over time to see if the expansion is linear, curved to represent a speeding up, or curved the other way to show a slowing down. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

ianke · Feb 4, 2007

John This is my dillema as well. You said,"it's like the observer deals with away but what about ago?" I'll have to admit that I am lost when what we observe is backwards to what the hypothesis is that is formed from it. It seems to me that time is the key. I'm getting more confused!<img src="/images/icons/crazy.gif" /> <div class="Discussion_UserSignature"> </div>

ianke · Feb 4, 2007

speedfreek, What do we know about the expansion issue at the present time? Also, what is the best guess in your opinion as to what is going on out there? <div class="Discussion_UserSignature"> </div>

SpeedFreek · Feb 4, 2007

To post what we know about the expansion issue at present would take a massive post, but current theory is very well summarised in this wiki article. To get a good basic understanding of physical cosmology, all those articles on the top right of that page are as good a place to start as any. The thing is, to get any deeper into these concepts requires an understanding of the field equations in general relativity, which I do not have. What is the best guess in my opinion? You might be asking the wrong man! I tend not to commit myself to anything except known facts (the earth isn't flat etc). If pushed I will rate the likelyhood if something based in its plausibility when compared to observation. My best guess is that the universe is expanding, and that expansion may well be accelerating. Space is not expanding through nothingness, so points in space do not move through nothing. The whole of space itself is expanding, and points are dragged along with it. This causes some confusion! But there is still a chance we have a lot of it wrong. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> _______________________________________________ SpeedFreek </div>

dragon04 · Feb 4, 2007

The red shift being larger than expected at the extreme distances (13.7giga light years) is used to explain the acceleration of universal expansion. If this is true, then is a proportional red shift observed for other objects closer to us. If I understand recessional velocities and the resultant observed red shift of distant objects correctly, that's precisely the dilemma that drives the debate over dark matter and dark energy. Inequal masses (galaxies or groups of them) recede from our point of view at the same rate depending on distance. They also appear to recede at potentially hyperluminal velocities. To me, this implies that a force is acting on them (and us) that ignores both Newtonian and Relativistic physics. In other words, a supercluster of 1,000 galaxies recedes at the very same rate as a single galaxy does at any given distance. At least I think that's the case. We can observe "local" gravitational effects such as our collison course with the Andromeda galaxy and the Local Group, and also observe the recession of other "local groups" with respect to our point of view. In any case, that implies to me that a more ubiquitous force that somehow ignores gravity in terms of very long distance is either "pushing" or "pulling" the Universe apart. Unfortunately, I'm not a trained Physicist. So anything I say is only the result of what has been given to me on a plate that doesn't include all those big maths that I don't understand in a significant way. <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

emperor_of_localgroup · Feb 4, 2007

I have just two points to make: 1) The redshift we see now is telling us the universe was undergoing an accelerated expansion 7+ billion years ago. Not now as many people and articles on the web are saying. The light we are detecting now started the journey that long ago. I dont think anyone can say what's happening now. 2) IMHO it is time to recheck the Redshift equation. It is way too simple , someone needs to show the breakdown conditions of the equation. <div class="Discussion_UserSignature"> Earth is Boring </div>

why06 · Feb 4, 2007

<blockquote>In reply to:<hr />Inequal masses (galaxies or groups of them) recede from our point of view at the same rate depending on distance. They also appear to recede at potentially hyperluminal velocities. To me, this implies that a force is acting on them (and us) that ignores both Newtonian and Relativistic physics. <hr /></blockquote> Good point Does this supply a reason for the expanding universe? We did not start examining the universe to the point we do now no more than 50-100 years ago (dont know exact #s) I have to agree with Ianke in saying that that amount of time is insignificant over the coarse of 13 billion years. It would be impossible t make such a judgement with so little data. <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

ianke · Feb 5, 2007

emperor_of_localgroup These are my thoughts exactly. You wrote: "1) The redshift we see now is telling us the universe was undergoing an accelerated expansion 7+ billion years ago. Not now as many people and articles on the web are saying. The light we are detecting now started the journey that long ago. I dont think anyone can say what's happening now. 2) IMHO it is time to recheck the Redshift equation. It is way too simple , someone needs to show the breakdown conditions of the equation." When I first started this thread, it was not to question expansion of the universe itself. It appears the amount of data we have confirms that. The overall redshift, cosmic microwave backround, WMBA data, etc, all seem to confirm that the expansion of the cosmos is real. What I was questioning is the accuracy of the red shift data used to explain the speeding up of that expansion. It seems to me (and I'll be the first to say that I'm no expert) that all of the data comes from a single point in time, the present. No matter how many objects they look at in the far reaches of space,and I assume it has been many, you are only looking at a single point for each individual object. You can say from those total observations that they are farther away than expected by our understanding of red shift. this allows you to extrapolate the universe has expanded faster than we first thought. However, what it does not tell you is weather that point is part of an accelerated curve, a decelerating curve, or a linear plot. To determine acceleration or not needs more points on the the graph with red shift related to time. Now, I would be willing to accept the acceleration of expansion from one point in time if nearer celestial objects could be measured to display this phenomina of dialated red shift. Nearer objects verses farther objects could, in theory, satisfy the need for time to be part of this equation. Hence my original q <div class="Discussion_UserSignature"> </div>

ianke · Feb 5, 2007

why06 your question: If the universe used to be accelerating in the past (as you said) than why would it start slow down. One would figure the speed to bigin to grow exponetially. If the universe is massive enough then it would eventually start to fall back on itself. If it is not massive enough then it will go on expandinng forever. However to accelerate the universe, you would need something pulling or pushing it apart. I think that is what the BB theory states. If you do not subscribe to the BB theory, then it takes something else all together to discribe expansion of the universe. I think (and correct me if I am wrong) that from your posts in other threads that you don't particularly agree with the Big Bang theory in its entirety. Is this correct? If so, then I am not equipped with the tools to answer your question. I have trouble enough trying to get a grasp on one theory at a time. I am just not that smart.<img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

control_group · Feb 5, 2007

<blockquote>In reply to:<hr />Firstly, remember that as distant objects look redshifted to us, we will look redshifted to them. Even with a constant rate of expansion, the further you look, the faster things move away from you. A simple example is to examine constant expansion on different length measurements. If, with a constant rate of expansion over a given time, 1 meter becomes 2 meters, then over that same time 100 km becomes 200 km, and 1 billion light years becomes 2 billion light years. <hr /></blockquote> This is where I get tripped up, but I think it might be because the cosmological term "constant rate of expansion" is not the same as the common usage. You're saying that, given a constant rate of expansion, over a period of time where displacement went from 1m to 2m, then 100ly becomes 200ly. That seems to describe exponential growth (all distances double per unit time). Whereas, in common usage, a constant rate of expansion would imply that, over a period of time where displacement went from 1m to 2m, 100ly would become 100ly+1m (constant velocity). A constant rate of expansion that results in a constant doubling rate is a very different animal. That means that the further out you go, the faster things are moving away from you. I understand that to be well-supported by observation, but it still doesn't make any intuitive sense to me. After all, in common experience, if you were to detonate something, all the pieces would fly away from each other at a constant velocity, not with an exponential rate of expansion. But then, I can't wrap my head around objects receding from each other across space while, at the same time, space itself is expanding. This is why I'm a lowly DBA, not a cosmologist, I'm afraid.

brellis · Feb 5, 2007

I, too, struggle to understand cosmotics. I have enough trouble just keeping my fingernails trimmed! <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

SpeedFreek · Feb 5, 2007

Well the reason you are tripping up is because you are probably correct in your thinking! But where we simply use the term expansion, we should really be using the term metric expansion. They way I see it, wherever you are in the universe, you seem to be at the centre of expansion, with objects receding faster the further away they are. Wherever you are. How can that possibly be true? This is from the wiki on the metric expansion of space: The metric expansion of space is a key part of science's current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions appear to grow or stretch as the universe gets older. It explains how the universe expands in the Big Bang model, a feature of our universe supported by all cosmological experiments, astrophysics calculations, and measurements to date. The expansion of space is conceptually different from other kinds of expansions and explosions that are seen in nature. Our understanding of the "fabric of the universe" (spacetime) requires that what we see normally as "space", "time", and "distance" are not absolutes, but are determined by a metric that can change. In the metric expansion of space, rather than objects in a fixed "space" moving apart into "emptiness", it is the space that contains the objects which is itself changing. It is as if without objects themselves moving, space is somehow "growing" in between them. Because it is the metric defining distance that is changing rather than objects moving in space, this expansion (and the resultant movement apart of objects) is not restricted by the speed of light upper bound that results from special relativity. <div class="Discussion_UserSignature"> _______________________________________________ SpeedFreek </div>

why06 · Feb 5, 2007

Ianke:<blockquote>In reply to:<hr /> If you do not subscribe to the BB theory, then it takes something else all together to discribe expansion of the universe. I think (and correct me if I am wrong) that from your posts in other threads that you don't particularly agree with the Big Bang theory in its entirety. Is this correct? <hr /></blockquote> You are right in saying that I don't subscribe to the BB theory. Mostly because of the confusion that we get into at the time of the BBtheory. We use the BB theory to explain how long it would have taken stars to form and so on. I do believe there is some truth to this, but the theory needs some MAJOR refining. Brellis: <blockquote>In reply to:<hr />I, too, struggle to understand cosmotics. I have enough trouble just keeping my fingernails trimmed<hr /></blockquote> first of all its "cosmetics", The idea was there, but your jokes need some refining at the punch line...... speedfreak: <blockquote>In reply to:<hr />They way I see it, wherever you are in the universe, you seem to be at the centre of expansion, with objects receding faster the further away they are. Wherever you are. How can that possibly be true? <hr /></blockquote> You said farther away... Which brings up the question:" Farther away from what?. Farther away from the time of the Big Bang you recede faster. If we are the center (theoretically) than things farther away from us seem like they are moving away faster from us. Thankyou <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

ianke · Feb 5, 2007

Control_Group Remember that what was stated by speedfreek is not exponential expansion. 1 becomes 2, 2 becomes 4, and so on is linear. Just plot this out on a graph an you will see this. Yes you are right about the confusion though. It does get difficult <img src="/images/icons/smile.gif" /> It helps me to try to keep in mind that the expansion only looks like that from your point of view. In other words, if you change your point of view 100 light years away from your original point then 1m expands to 2m, 1 light year expands to 2ltyrs. if you look back to where you were 100light years becomes 200light years respectively in the same timeframe. Try to remember that it isn't the objects doing the expansion it is the spacetime that is really doing the expanding. The points of matter just get dragged along. <div class="Discussion_UserSignature"> </div>

SpeedFreek · Feb 5, 2007

It is harder than it seems to describe these concepts, for sure! Imagine the whole of space has points, 1 unit apart. The space in between each of those points expands to double it's original size. So where all the points were 1 unit apart, now all points are 2 units apart. This is linear, or constant expansion. Now put yourself on one of those points. The first point from yours was originally 1 unit away, the second point was 2 units away and the 100th point was 100 units away. After the expansion, the first point would now be 2 units away, the second point 4 units away and the 100th point would be 200 units away! There is a whole extra unit in between each point. <div class="Discussion_UserSignature"> _______________________________________________ SpeedFreek </div>

acsindg · Feb 5, 2007

Hi Going a step further; If the outer limit redshift is the same in every direction then we are at or near the centre of the universe. As the fabric of space inside the universe is magnetized then we see the boundary as being where space stops and nothing begins. See alternative magnoflux universe Part 3 for details of the permittivity and permeability of free space for details

emperor_of_localgroup · Feb 5, 2007

Are you aware of a new finding that speed of galaxies are quantized? The speed is quantized by 72km/sec or 36Km/sec, using of course the redshift. But the thing that is still not clear to me is whether the speeds of individual stars in a galaxy are quantized or speeds of galaxies are quantized. It is similar to the quantized energy levels of an atom. If it is true, the universe is becoming an interesting place each day. @Control_Group: If they are talking about an accelerated expansion, then it must follow the good old motion formula, a=(v-v0)/t Where 't' is the time over which speeds of a galaxy is measured, v0 is the speed of the galaxy when measurements start, v is the new speed after time t. And acceleration 'a' is non-zero and positive. <div class="Discussion_UserSignature"> Earth is Boring </div>

R1 · Feb 6, 2007

well it's all helping understand this better. I can see in speedfreeks explanation that in the example of 100 million lightyears the discrepancy would be about 700,000 lightyears, or less than 1% , and if they're able to obtain more than one piece of data from the same supernova by knowing how long ago it burst that definitely helps. What I was trying to visualize was a plot of all these recession speeds strictly on a time chart by substituting all the words 'lightyears' with the words 'years ago', but I'll put that off till another time. there's no problem understanding an expansion at alarming rates, and I'm starting to get more puzzled now by the cosmic background. <div class="Discussion_UserSignature"> </div>

R1 · Feb 6, 2007

I heard of the cosmic background being described as an echo, but could it actually be nothing more than distant light that we're seeing, except we perceive it as microwave radiation because of the rapid stretching of space-time making the waves longer? in other words couldn't it be nothing more than light with a hell of a big redshift way below red and even past the infrared scale? that's what happens to light going through space-time that is being stretched (expanded) at an extremely fast speed, <div class="Discussion_UserSignature"> </div>

control_group · Feb 6, 2007

<blockquote>In reply to:<hr />Remember that what was stated by speedfreek is not exponential expansion. 1 becomes 2, 2 becomes 4, and so on is linear. Just plot this out on a graph an you will see this. Yes you are right about the confusion though. It does get difficult It helps me to try to keep in mind that the expansion only looks like that from your point of view. In other words, if you change your point of view 100 light years away from your original point then 1m expands to 2m, 1 light year expands to 2ltyrs. if you look back to where you were 100light years becomes 200light years respectively in the same timeframe. Try to remember that it isn't the objects doing the expansion it is the spacetime that is really doing the expanding. The points of matter just get dragged along. <hr /></blockquote> I guess I'm still not getting it - if I make a graph where the y value doubles for every unit increase along the x, that won't be a straight line: <pre> * * * * * * * * ** ** ** ** *** *** **** ***** </pre> That may not be the most clear thing ever, but on paper, it's obvious to me that it's not a straight line, it's an exponential curve. The other way of looking at it is to look at the numbers in the series. For y to double with each unit of x, the series has to be: x = 0, y = 1 x = 1, y = 2 x = 2, y = 4 x = 3, y = 8 x = 4, y = 16 Which, as an equation, is: y = 2^x which is an exponential function, not a linear one. Unless, of course, I'm completely misunderstanding the original statement, that over the same unit of time, 1m became 2m and 1ly became 2ly. Which is entirely possible, since I really have a hard time getting my head around items separating in space while space itself also stretches out.

ianke · Feb 6, 2007

speedfreek In yor post you said: "After the expansion, the first point would now be 2 units away, the second point 4 units away and the 100th point would be 200 units away! There is a whole extra unit in between each point. " By definition that is a 2X linear expansion. you could plot on a graph all day and it is still a straight line. It is the same if it is 3X ,1.5X, 1,000,000X they are all a straight line when it comes to expansion. To show speeding up it has to be a little more expansion for each unit of time applied to the same measured space. (1becomes 2 in time) Then the next unit of time the same distance would increase a little more (1 becomes 2.1 in the same amount of time). example only! Then you could say that acceleration has occured., and would plot out on a graph as a positive curve. <img src="/images/icons/smile.gif" /> I think this is what they say when the talk about expansion speeding up. Is this correct? <div class="Discussion_UserSignature"> </div>

control_group · Feb 6, 2007

<blockquote>In reply to:<hr /> Re: Is the red shift discrepancy the same at all distances? [re: Ianke][link to this post] Reply It is harder than it seems to describe these concepts, for sure! Imagine the whole of space has points, 1 unit apart. The space in between each of those points expands to double it's original size. So where all the points were 1 unit apart, now all points are 2 units apart. This is linear, or constant expansion. Now put yourself on one of those points. The first point from yours was originally 1 unit away, the second point was 2 units away and the 100th point was 100 units away. After the expansion, the first point would now be 2 units away, the second point 4 units away and the 100th point would be 200 units away! There is a whole extra unit in between each point.<hr /></blockquote> And that's exactly the part that I have the hardest time with. Because now we're not talking about simple motion, as would be naively expected of the Big Bang, where everything flies apart at a given velocity. We're talking about redefining the very units of linear measurement. The idea of space getting bigger (as opposed to the stuff in it getting further apart) is a troubling one for me for the reasons I mentioned in my post just above: it seems like mathematical ad-hockery to explain how two objects that began adjacent can be 2ly apart after one year without either exceeding c. I realize, of course, that it's my understanding that's flawed, not the current body of physics/cosmology, but I don't know how, exactly, my understanding is flawed.

ianke · Feb 6, 2007

x = 0, y = 1 x = 1, y = 2 x = 2, y = 4 x = 3, y = 8 x = 4, y = 16 You are exactly right. I guess what I am thinking of is different starting distances over the same 1 yearof expansion. Thanks for the correction. I will have to back up and restate my point or retract it. I'll need a little time to think this one through. <img src="/images/icons/blush.gif" /> <div class="Discussion_UserSignature"> </div>

ianke · Feb 6, 2007

Wait. In the example you were looking at I did say "in the same time frame". So the statement is still valid. In other words for however long it takes space to expand for any one unit to double, then all units double in that same time ( lm or 1ltyr they are both double) Also I don't think the rate is 2X /year. I don't have any idea what that rate is but I pretty sure it is longer than that. There is a point though, if the distance is large enough, that the expansion of space will be sufficiant that it would expand faster than light could travel from that object towards us. Weird I know! <div class="Discussion_UserSignature"> </div>

control_group · Feb 6, 2007

OK, let me try looking at this another way, to see if something falls into place in my head. I'm picturing an explosion where some number of objects start out adjacent and then are thrust apart from each other by a single impulse. I'll use meters and seconds as units, just for convenience. So let's say that the initial velocity is 1m/s. After one second, two objects (objects A and B) on opposite sides of the starting point will be 2m apart, after 2 seconds, 4m, after 3 seconds, 6m, etc. That's (obviously) a linear rate of expansion. Every second, the sphere defined by the objects increases in diameter by 2m. So, over the second second (!), the distance between opposing objects doubles. The question is, does the distance between all objects double, irrespective of their separation at the end of the first second? So let's look at an object (object C) that's traveling a path perpendicular to the line formed by the two objects we've been looking at. Simple trigonometry gives us a straight line distance between A and C will be 1.4142m. After two seconds, the radius is 2m, so the distance between A and C is 2.8284m, an exact doubling. This, then, represents the equidistant separation of a third object - C is doubling its distance from both A and B as the the distance between A and B doubles. It should be clear, though, that an object at any other angle will be closer to either A or B (and further from either B or A, respectively) at the end of the second second. So, as the distance between A and B doubles, it is not the case that the distance between any two points doubles. I think, then, that a linear rate of expansion does not result in the doubling of all distances over any given unit of time. Under this model, we should expect to see more distant objects receding faster than closer objects - which, if my understanding is correct, is exactly what we do observe; so it seems a linear model of expansion is supported. However, i

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