Measuring distance using time

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askold

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I've never been able to understand this - <br /><br />Astronomers have calculated the age of the universe at about 15Billion years by measuring the redshift of light coming from the most didtance objects.<br /><br />Astronomers say that the universe is 15Billion years old because light from the most distance objects has taken 15Billion years to get here.<br /><br />How did we get 15Billion lightyears away from that object in 15Billion years. We'd have to be moving apart at the speed of light.<br /><br />How is that possible?<br /><br />Thanks
 
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alkalin

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The notion of inflation fills in the rest for you, that space itself and all matter and dimensions of any kind simply can grow in size even much faster that the speed of light, without the need for energy to make it happen, and there are math equations to express this of course. The notions are that shortly after the BB, inflation happened, and put everything where we see it. (there cannot be any proof of these notions whatsoever. They do not come from real physics) <br /><br />So we really do not need expansion to explain the red shift. (I’m being a little facetious, since there is a perfectly good explanation of red shift which current cosmology does not want to recognize)<br />
 
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askold

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Thanks, I didn't know about inflation - I looked up some info on the Web.<br /><br />So, if shortly after the BB the universe expanded an unknown amount, possibly faster than the speed of light, how can we now equate distance to time?<br /><br />That is, how can astronomers say that since that light-source out there is 15Billion light years away, we are looking at something that is 15Billion years old?<br /><br />Thanks
 
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alkalin

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I think you are asking a question that has bothered me for some time. I personally cannot accept that the two notions of expansion and inflation are compatible because inflation puts everything everywhere because that is what we see in terms of physical location, but in terms of light you still must have a slow expansion from the beginning in order to correctly describe the (Doppler based) red-shift. If inflation interrupted the expansion sequence, then we simply cannot know when the universe began, mostly because we do not know the extent, speed, time frame, and linearity of inflation.<br /><br />If inflation is presumed to have expanded everything, in my view this includes photons and the red shift itself which tells us what is going on? Imo, what a can of worms!!!!!<br />
 
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kmarinas86

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and all the worms have been eaten.'<br /><br />next theory! <img src="/images/icons/tongue.gif" />
 
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Maddad

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askold<br />"<font color="yellow"> how can astronomers say that since that light-source out there is 15Billion light years away, we are looking at something that is 15Billion years old?</font><br /><br />A light year is a measure of distance as opposed to time. It is the distance that light traveles in one year. If the object is 15 x 10<sup>9</sup> lightyears away, then by definition it must have taken that light 15 x 10<sup>9</sup> years to reach us.
 
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siarad

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That confuses me too. It simply shows the object was there 15B years ago & by some legerdemain working out it took x time to appear. Science is largely based upon linearity, with the exception of inflation which is seemingly guesswork. Real life has a lot of chaos & indeed this PC & yours relies upon chaos to work at all.
 
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askold

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maddad: you say "A light year is a measure of distance as opposed to time. It is the distance that light traveles in one year. If the object is 15 x 109 lightyears away, then by definition it must have taken that light 15 x 109 years to reach us. "<br /><br />Yes I understand that. My original question was - if something got 15B light years away from us in 15B years (it's 15B years younger than us) then it must be traveling away from us at the speed of light.<br /><br />Then a poster said that inflation tells us that soon after the BB things arranged themselves in an unknown manner all over the universe.<br /><br />So, now, if we measure how far something is from us how can we say anything about its age. We don't know what happened when everything moved around during inflation. I sounds like we have an unknown variable - so how can we solve the equation?<br /><br />That's my confusion. What data do astronomers use to calculate the age of those distant objects? You just see an anouncement like "using the Hubble space telecsope, astronomers have seen an object 14B light years away from Earth so it must be 14B years younger than our little part of the universe".
 
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siarad

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Ah I think I see your problem. Close distances are measured by parallax & then something else & then Cepheid stars. Sorry don't really know about this but Saiph, I think, did a topic on this before the big crash. So you see if you know the distance & the speed of light C, <i>said</i> to be a constant & seems true locally unless space is bent, then the age is known.<br />Age = distance/C but doesn't mean the object <i>still</i> exists but <i>when</i> it existed
 
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alkalin

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Astronomers ignore inflation in the type of question you have asked. They use the red shift value in determining distance. If something has a red shift value of , say 2, they know it has a corresponding distance based on the Doppler principle. Again, inflation is not considered in this, and the older more traditional ideas of pure expansion are used instead.<br /><br />In some respects, inflation is not a very logical idea, so maybe this is why it is ignored. Yet it is absolutely needed to put objects in the universe where we see them. If you think about it, this is what we see: “edge’ of universe 15 BLYs in one direction, as it was 15Billion years ago, “edge’ of universe 15 BLYs in opposite direction, as it was 15 Billion years ago, and our local universe that has been right here for 15 Billion years. How can you explain this without some sort of inflation notion???? Only part of this scenario might be explainable with relativity field equations that can be used to describe curvature of space/time.<br /><br />Cepheids cannot be used in great distances such as this because we cannot see individual stars in very distant galaxies. But we can measure a galaxies red shift and get relative brightness data from them to get distance.<br />
 
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alkalin

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In regards to the universe’s age, this is based on expansion ideas that came from early attempts astronomers made to understand why there was a red shift seen in very distant galaxies. When the ideas behind the Doppler rational became popular, then came also the idea that we could determine the age of the universe simply based on Doppler, since Doppler is a rate of separation that can be measured between distant galaxies. So now the universe is calculated based on these notions to be about 13.7 billion years old, because that is when everything in the universe had to be in a very small location.<br /><br />There are other constants such as distance scales that are being refined however.<br /><br />But we do not see this type of actual universe when we look at it as I’ve previously stated. We see a universe that is spherical in shape and has a diameter of 27.4 billion LYs for an age of objects of 13.7 billion years. So this is the reason cosmologists have delved in the theoretical or magical math, to try to salvage the notion of expansion due to a Doppler caused red shift.<br /><br />I’m not much of a fan of some of the notions they have come up with, especially inflation. My preference for a universe model is morphed steady state, and depends on a different cause for the red shift.<br />
 
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