Is the red shift discrepancy the same at all distances?

ianke · Feb 1, 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. Example: Do we see that same increasing rate between the local group and the next closest cluster of galaxies? In other words, does that same discrepancy in the red shift show up for closer observations? <div class="Discussion_UserSignature"> </div>

R1 · Feb 1, 2007

as I understand it the more distant the object, the greater the red shift, and the closer the object, the smaller the red shift, so the farther objects must be receding faster than the closer objects. <div class="Discussion_UserSignature"> </div>

ianke · Feb 2, 2007

That is true, but I think that there is an observed redshift that says that even then expansion is speeding up. An acceleration of the expansion, if you will, that is going faster than the theory hypothesized. What I am asking is if this accelration is observed in the complete range of distances? note: I am not a real fan of dark energy, but I am talking about the part of the red shift that they use to hypothesize it's existance. <div class="Discussion_UserSignature"> </div>

brellis · Feb 2, 2007

hello Ianke I'm in way over my head here, but I wanna try to chime in with my simplistic understanding: 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. Example: Do we see that same increasing rate between the local group and the next closest cluster of galaxies? In other words, does that same discrepancy in the red shift show up for closer observations? As I understand it, the 'acceleration' is consistent in relation to the distance of the galaxies we observe. The 'discrepancy' occurs when trying to get the Hubble Constant to work with the apparent age of the universe. The Hubble Constant was at one point going to tell us if the Universe would expand forever, contract towards another BB, or stabilize for an eternal, rosy universal future. <img src="/images/icons/wink.gif" /> The numbers they're getting now are so far towards an expanding universe, I can't remember the last time I've even heard the term Hubble Constant mentioned! If you set aside the BB theory, you don't get things like galaxies older than the universe, or red-shifting too dramatically. When the redshift of a distant galaxy places it within a billion years of the BB, they've had to massage the theory to keep it in sync with the apparent age of the universe, so 'inflation' has been invented and incorporated into the theory. Speedfreek is really good at explaining this stuff. Speedy, if you or anyone else can take the time, please correct me if I misunderstand! <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

ianke · Feb 2, 2007

Hello brellis I am certainly no authority in the field of cosmology as can be seen by my perhaps feeble questions. I guess that what I am trying to do is get a handle on the whole "expansion speeding up" issue. Perhaps I have it wrong when it comes to where the theory originates from, but I am under the impression that the excessive amount of red shift at the far end of the visible universe is where the theory of acceleration of the overall expansion comes from. It would seem to me that if the universe is speeding up then the redshift would be more ascue in the nearer observations, and less so at the farther ones. I had a very usefull discussion with speedfreek on this topic before from another angle, and you are correct in the fact that he seems to have a gift for the subject. The whole issue has my head spinning though. <img src="/images/icons/crazy.gif" /> <div class="Discussion_UserSignature"> </div>

ianke · Feb 2, 2007

Hello tigerbiten This is exactly what I am thinking, but don't we need another point in time for each object we observe? Without such data, you can not draw a curve one way or the other. (I drew some plots to show this but can not figure out how to attach them yet) However, your post stated the exact thoughts that they would have shown. I guess my next question is what data has others leaning toward speeding up? Thanks for the post! You discribed my thoughts to a tee. <div class="Discussion_UserSignature"> </div>

brellis · Feb 2, 2007

I had a very usefull discussion with speedfreek on this topic before from another angle, and you are correct in the fact that he seems to have a gift for the subject. The whole issue has my head spinning though. Indeed, three cheers for speedfreek! Speedy came to my assistance in this thread where the little pea in my head started spinning a little bit too fast for my own good <img src="/images/icons/smile.gif" /> I am under the impression that the excessive amount of red shift at the far end of the visible universe is where the theory of acceleration of the overall expansion comes from. It would seem to me that if the universe is speeding up then the redshift would be more ascue in the nearer observations, and less so at the farther ones. Thanks to you and tiger for your illuminating comments. I now recall "seeing" some articles on attributing some aspects of expansion to dark energy. Notice I used "seeing" as opposed to "reading" which would indicate "comprehending", a status to which I currently aspire in the area of cosmology. <img src="/images/icons/cool.gif" /> I've decided to LOVE cosmology -- it is both humbling and liberating. It is science about something that's really there, but at a safe enough distance in spacetime for creative thinking to come into play. Cosmology forces really smart, well-informed people to speculate, which lets newbies into the game, because anyone can speculate. Who knows, one of us might accidentally lead the great thinkers to a solution to the puzzle of the universe! Anyhoo, on my next break from my "day job" I'll poke around and see if I can find those articles. cheers, brad <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

brellis · Feb 2, 2007

I'm also gonna send an S.O.S to speedfreek <img src="/images/icons/cool.gif" /> <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

SpeedFreek · Feb 2, 2007

Hehe, thanks for the vote of confidence, although I am hoping it isn't misplaced! I have no formal qualifications relevent to cosmology, but I am very interested in the subject. I tend to only post in threads where I am confident I have a relevent point to make. I will peruse this thread and see what I can come up with, but I'm not making any promises! I do make horrible mistakes in my posts sometimes, but I leave that to others to point out! <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> _______________________________________________ SpeedFreek </div>

why06 · Feb 2, 2007

Hooray for speedfreak! Tell us your knowlegde of the space and time so we may worship you.... <img src="/images/icons/wink.gif" /> laugh a little <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

brellis · Feb 2, 2007

It seems like the Universe is just too young! Here's a 2002 Study Estimating the Universe to be 13 Billion Years Old The universe is about 13 billion years old, slightly younger than previously believed, according to a study that measured the cooling of the embers in ancient dying stars. Experts said the finding gives "very comparable results" to an earlier study that used a different method to conclude that the universe burst into existence with the theoretical "Big Bang" between 13 and 14 billion years ago. Harvey B. Richer, an astronomer at the University of British Columbia, said the Hubble Space Telescope gathered images of the faintest dying stars it could find in M4, a star cluster some 7,000 light years away. Richer said the fading stars, called white dwarfs, are actually burnt out coals of stars that were once up to eight times the size of the sun. After they exhausted their fuel, the stars collapsed into Earth-sized spheres of cooling embers that eventually will turn cold and wink out of sight. Earlier studies had established the rate of cooling for these stars, said Richer. By looking at the very faintest and oldest white dwarfs possible, astronomers can use this cooling rate to estimate the age of the universe. Here's a BBC Article on Expansion where Hubble's ACS measured supernovae from two distant galaxies and established that those two galaxies were moving away from each other at an expanding rate: Astronomers Zlatan Tsvetanov of Johns Hopkins and Dan Magee of the University of California-Santa Cruz compared earlier Hubble images of the same patch of sky with those obtained by the new ACS images to find the supernovae. It was information from studies of Type 1a that a few <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

brellis · Feb 2, 2007

I just had an epiphany. Cosmology is very much like music. I am a professional musician. I started piano lessons at age 4, got 'eddicated' very well, and I've had good fortune in adulthood. I could be a total snob about music, but I realized a long time ago that music occupies both sides of the brain: my education gives me a head start calculating the physics of music, but if a completely uneducated person doesn't like a piece of music, that opinion is just as valid as mine. Cosmology is similar: because all the elements of cosmology are so far "out there", a layman like me can apply his wits to a cosmological problem with some degree of impunity. I can offer speculation on BB theory even though I don't have an educational pedigree; on the other hand I will look like a fool if I stand on a corner and shout: the sun will NOT come up tomorrow! <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

why06 · Feb 3, 2007

Great articles brellis, that really does add a great deal of backing to Dark matter and the Big Bang theory. There is certainly something out there causing the lensing, but I have a feeling that the outcome will be very different from what we think. One day someone will come up with an idea in cosmology as great and as long in the making as the periodic table was to chemistry. Good job on your "ED-DU-MA CATE-TION"-you smart folk are always getting epiphanies. <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

ianke · Feb 3, 2007

These are quite good articles on the matter at hand brellis. However, I will have to take a little time to do the family thing today, so it will be later if not tomorow before I can get back to you on them. "Later Dudes" <div class="Discussion_UserSignature"> </div>

why06 · Feb 3, 2007

Peace, <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

SpeedFreek · Feb 3, 2007

See, you don't really need my input in this thread at all! <img src="/images/icons/smile.gif" /> What I will do is post some background to the subject as I understand it. Feel free to correct any errors here! Ianke originally asked if the observed discrepancy in redshift measurements was proportional between closer and distant objects. Firstly, redshift can refer to cosmological redshift, which reflects the amount the space has expanded since the light started it's journey. In any measurement of redshift we have to determine what proportion of that redshift was caused by the expansion of space and what proportion was caused by either relativistic doppler effect or gravitational redshift. Redshift is not a measure of a single factor and it is important to remember this. <img src="/images/icons/smile.gif" /> Let's go back to the beginning of our understanding of cosmic expansion and work through it a little. Brellis mentioned the Hubble Constant. In 1929 Hubble published a claim that the radial velocities of galaxies are proportional to their distance. The redshift of a galaxy is a measure of its radial velocity, and it can be measured using a spectrograph to determine the Doppler shift. His first set of data showed that if you plot a graph for galaxies of redshift against distance, the data points on this graph all sit in an approximate straight line. This graph represents the data that was used to derive what is now known as the Hubble constant. Unfortunately his first set of data implied an age for the universe of only 2 billion years! We had already worked out that the Earth was much older than that, and so his expansion theory was regarded with sceptisism, and science started working with the steady state model instead. Later, it was realised that Hubble had made a mistake and had confused two different kinds of Cepheid variable stars used for calibrating distances, and also that what Hubble thought were <div class="Discussion_UserSignature"> _______________________________________________ SpeedFreek </div>

why06 · Feb 3, 2007

You said: "See, you don't really need my input in this thread at all! <img src="/images/icons/smile.gif" />" -That's what I thought too before I read 50+ lines of type <img src="/images/icons/crazy.gif" /> Good Response <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

ianke · Feb 4, 2007

I think your last line really puts my question in perspective. "Most of our data tells us either recent expansion or overall expansion, but our estimates of time and distance have a larger margin of error the further we look. We really need data for early expansion!" There does seem to be a question then as to what truly is going on. (Are we observing an acceleration to the expansion, or are we observing the reflection of a faster speed in the past?) Since the data we use both comes from 13.7 billion years ago, and our accuracy is not absolutely boiler plate, we can't say that it is or is not accelerating now. Does this statement sound accurate? Also, if the above statment is true, it seems to blow a fairly large hole in the dark energy theory. The overall speed of expansion could be slowing down. Hence dark energy (if it exists at all) is not pushing or pulling like so many theories seem to rely on at present. If so, all that we can do is take a WAG (Wild- Insert body part starting with A-Guess) at the reality of expansion for now.<img src="/images/icons/rolleyes.gif" /> I still do not see why so many have jumped on the accelerated expansion side of the possibility wagon. Perhaps there is a lot more to the data than I have seen. Thanks to all of you on this one!<img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

SpeedFreek · Feb 4, 2007

Well, to put it more accurately, we have lots of evidence that the universe might be expanding, and only a little (but growing) evidence that the expansion might be accelerating. My post was soley referring to redshift. The simple point is that redshift alone cannot confirm acceleration, and your post was asking if the redshift can interpreted in a different way. We need other data points combined with redshift to confirm that. Distant supernova are one set of data that seems to confirm acceleration. If the expansion was decelerating (i.e. the reflection of a faster speed in the past) then the distant supernova should look brighter than they do. If we knew how bright the other distant objects should be due to constant expandsion, we could see if they were brighter or fainter than they should be, but we only have confidence in our estimates for supernova, and those aren't too common. The problem is that the "curve" only needs to be very slight for there to be acceleration or deceleration. The data points on that curve we have for supernova show acceleration, but we need more data than that to confirm it for sure, preferably from a different source. But we do have some different sources, like the WMAP experiment. WMAP seems to confirm the acceleration too. Using accurate measurements of the temperature across the universe, WMAP claims to confirm: The universe is 13.7 billion ± 200 million years old. The universe is composed of: 4% ordinary baryonic matter 22% an unknown type of dark matter, which does not emit or absorb light. 74% a mysterious dark energy, which acts to accelerate expansion. The Hubble constant is 70 (km/s)/Mpc, +2.4/-3.2 The data are consistent with a flat geometry. CMB polarization results provide experimental confirmation of cosmic inflation favoring the simplest versions of the theory. The way science works is to make observatio <div class="Discussion_UserSignature"> _______________________________________________ SpeedFreek </div>

R1 · Feb 4, 2007

I think the new Planck satellite will give us more data about a long time ago. I usually get confused by not including the elapsed time measurement into the dimming and red-shift formula. This may or may not be what the post specifically addresses, but to me it has caused some confusion in the past. For example, consider supenova A which is relatively close to us, and supernova B which is way on out there near the outfield, A is about 5 billion light years and B is about 10 billion light years. Then I get confused when an observer says the universe expansion is accelerating , because supernova B is more dim than it should be, the observer said that because the SN B is dimmer than it should be and 10 billion lyr 'away' but my mind says because SN B is dimmer and 10 billion yr 'ago' the expansion appears Decelerating, NOT accelerating , because 5 billion years 'ago', supernovas are brighter more recently it's like the observer deals with away but what about ago? wouldn't the more time ago need to have little or no red shift at all and actually appear brighter, not dimmer than items and events taking place 5 billion years 'AFTER' that stuff way out there took place and closer to the present time? <div class="Discussion_UserSignature"> </div>

why06 · Feb 4, 2007

Speedfreak: what does WMAP stand for? Ianke: 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. <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

Swampcat · Feb 4, 2007

"what does WMAP stand for?" WMAP Google is your friend <img src="/images/icons/wink.gif" />. <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

R1 · Feb 4, 2007

is the Planck probe supposed to be any better than than the Wilkinson WMAP? I understand the Planck will map the entire sky in 9 wavelengths, and sensitivity up to a few millionths of a degree. <div class="Discussion_UserSignature"> </div>

Swampcat · Feb 4, 2007

""is the Planck probe supposed to be any better than than the Wilkinson WMAP?" According to this ESA webpage "Planck will be at least ten times more sensitive than MAP." More info at the webpage. Google is your friend <img src="/images/icons/wink.gif" />. <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

SpeedFreek · Feb 4, 2007

John, I agree that on the surface, it looks backwards! But we have to dig deeper. 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. The distant objects only look like they are travelling so fast to us. In their local space right now, space is expanding at a similar rate as it is for us right now. So, if we use this simple model where the expansion rate is the same at any given time, at any point in the universe, what we are looking for is a change in that rate over time. With the supernovae, the fact that they are dimmer than they should look simply means the universe is expanding, we have to measure supernova at different distances (points in time) to build up data on whether the expansion has been constant or not. Now let's go even deeper! <img src="/images/icons/wink.gif" /> (I lifted this text from here, but the emphasis is my own). One line of evidence for acceleration of expansion comes from the so-called Type Ia supernovae--supernovae that result from the accumulation of too much hydrogen on a white dwarf, from its companion star. As Chandrasekhar discovered analytically in the early years of the 20th century, once the mass of a white dwarf exceeds a certain limit, now called the Chandrasekhar Limit, it goes supernova. Since the limit is pretty stable (or so astronomers think), every Type Ia supernova should behave more or less the same. That's why they can be used as "standard candles" in determining the d <div class="Discussion_UserSignature"> _______________________________________________ SpeedFreek </div>

Is the red shift discrepancy the same at all distances?

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