A Question About Peering Into The Past

[drophammer]

I know that when we use powerful sensing equipment to "see" out to 13 billion light years, we are seeing into the past.<br /><br />Shouldn't there be a direction where there is nothing to see out at that distance?<br /><br />Thanks...<br /><br />Drophammer

 

[Maddad]

If you were at the center of the universe, wouldn't you expect to see something in every direction?

 

[mooware]

If anyone knew where the center of the universe is.. Provided of course there is a center.<br /><br />

 

[Maddad]

Before you consider whether there is one, first think about what you would see if you were there.

 

[centsworth_II]

It's hard to talk about cosmic things and not sound mystical. For example, I could say that any place you pick in the universe (any place that you are) is its center, since the rest of the universe will be expanding from that point (except for local gravitationally induced activity). But it is probably more acurate to say that the universe has no center. This implies also that it has no edge -- like the surface of a ball.<br /><br /><br /><b>A Simple Example</b><br /><br />Suppose you are looking at at galaxy X, 12 billion light years away. You see it as it was 12 billion years ago. Suppose now that a being in Galaxy X is looking at <b>your</b> galaxy AT THE SAME TIME. He is seeing <b>your</b> galaxy as it was 12 billion years ago. He also sees your galaxy rushing away at incredible speed due to the expansion of the universe. He also sees every other galaxcy in the universe moving away from Galaxy X.<br /><br />So, no matter what galaxy in the universe an observer is on, the experience will be the same. He will see all the other galaxies as they were in the past (his past) and he sees all other galaxies moving away as the universe expands. It seems to any "person" in any galaxy in the universe that they are at the "center" of the universe. <div class="Discussion_UserSignature"> </div>

 

[pizzaguy]

Good post, but I think that every girl/woman I have dated must have tried all that ......... 'cause they always seemed to think that THEY were the center of the universe. <img src="/images/icons/crazy.gif" /> <div class="Discussion_UserSignature"> <font size="1"><em>Note to Dr. Henry:  The testosterone shots are working!</em></font> </div>

 

[centsworth_II]

Suppose every girl/woman you have dated comes from Galaxy X. I wonder how they see you?<img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[drophammer]

Okay, but let's assume we are not in the center of the universe.<br /><br />We should be able to see that in some directions, we cannot "see" back as far as we can in other directions, right?<br /><br />Is that, in fact, the case?<br />Drophammer

 

[centsworth_II]

<font color="yellow">"We should be able to see that in some directions, we cannot "see" back as far as we can in other directions, right?</font><br /><br />Wrong. In my limited understanding of current theory:<br /><br />Ignoring the limitations imposed by intervening dust and gas, our instuments should be able to see equally far in any direction. Whatever direction we look in, we should see the same general distribution of galaxies and the youngest, most distant galaxies should be at generally the same distance from us -- in any direction. <br /><br />This is what is known as the isotropic nature of the universe (it looks the same in all directions). And as I mentioned previously, an observer in any galaxy in the universe should see the same thing: the same general distribution of galaxies in any direction and the same distance to the farthest galaxies in any direction. If someone were to prove that the universe is not isotropic, I think this would be very big news.<br /> <div class="Discussion_UserSignature"> </div>

 

[mental_avenger]

You may be right, but not for that reason. IF the Universe expanded from a single point, then any direciton you looked, all the other galaxies would be moving away at a velocity that was proportional to their distance.<br /><br />Now, here is the hard part. IF you could see infinitely far in all directions, THEN you would see some galaxies further away in one direction than another, IF you were not at the center. However, there is an automatic limiter built into this expanding universe.<br /><br />Essentially, the further away a galaxy is, the faster it is moving away from you. There is a distance, which appears to be about 17 billion lightyears away, where the galaxies are receeding from us so fast that they approach the speed of light, relative to us. That distance, in every direction from us, is know as the edge of the observable universe. That is because everything past that point is moving at greater than c relative to us, so that we can never see it, nor can we ever catch up to it if we traveled towards it. For all practical purposes, the edge of the observable universe is the edge of the Univrse for us. That puts us at the center of the (observable) Universe. <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[centsworth_II]

<font color="yellow">"For all practical purposes, the edge of the observable universe is the edge of the Univrse for us. That puts us at the center of the (observable) Universe."</font><br /><br />And <b>every</b> observer in the universe, no matter what galaxy they reside in, will see <b>themselves</b> as being at the center of the observable universe. And we will all be right! <br /> <div class="Discussion_UserSignature"> </div>

 

[siarad]

The Universe was recently shown to be 13.7b years old so even at the speed of light the outer edge can only be that far away. So, how can visible objects be farther away. Don't quote anything other than linear travel as that is what is used in measuring distances, Inflation is not taken into account & may never have happened putting it in the realms of philosophy not science.

 

[siarad]

I think you missed my second sentence<br />Thanks for the link, no time to view now.

 

[Maddad]

Drophammer<br />"<font color="yellow">Okay, but let's assume we are not in the center of the universe. We should be able to see that in some directions, we cannot "see" back as far as we can in other directions, right? Is that, in fact, the case? </font><br /><br />We have essentially the same view in every direction, which is the foundation for the currently accepted explanatory claim that the universe has no center. There is however one other possibility.<br /><br />Whe we look 13 billion light years away, we see objects as they were 13 billion years ago. Some quick calculation with the Hubble Mostly Constant reveals that objects at this distance should recede at the speed of light, and that is just about what we observe. 13 BLY = 4,000 megaparsecs. Multiply by 70 km/sec/megaparsec for the HMC recessional speed and those distant objects should receed at 280,000 kilometers per second, close enough to the speed of light to wonder what would happen tomorrow when these objects are just a little bit further away.<br /><br />When they are further away, they will receed from us faster than the speed of light. At that point we would never again be able to see them. Their gravity could never again attract us. We could never again get close enough to see them. They are no longer in our universe in any meaningful way.<br /><br />Since they were already running away from us at the speed of light 13 billion years ago, and they're going faster and faster all the time, how fast are they going now? It's why we think that the actual size of the universe is now about 11 times bigger, 150 billion light years across. Those objects today are leaving us at 11 times the speed of light. Tomorrow it will be 12 times.<br /><br />With the actual universe being 1,300 (11 cubed) times bigger than what we can see, we cannot see a difference in stellar distribution from one side of the universe to the other. Although it appears isotropic to us, the same in all directions, we are un

 

[alkalin]

Maddad, do your calculations include inflation?<br /><br />To allude that the universe is 13 b years old is hogwash?? Yet I do it sometimes also. There is more to this story. The past 13 billion years and more is our own local universe as well. All around us. It is not expanding, and a study recently was done which verified this??<br /><br />13.7 billion years ago we are suppose to see a point or the origin of the big bang according to expansion notions. Sounds rather contradictory to me. Everything in all directions is moving away from us out there 13.7 billion years ago???? It seems that the point of origin is much too important for some reason? It’s on all sides of us??? And don’t try using your fancy math to convince me otherwise. Just get me out of this paranoia. Hahaha.<br /><br />I don’t think even Scotty can fix it. (Sorry Scotty, it’s not your fault)<br />

 

[Maddad]

I start thinking about universal expansion after inflation, so I'm not considering it. Taking a point shortly after the big bang, say 700 million years, we see the universe as it was 13 billion years ago. All parts were rushing apart from each other, including us from other parts, the size of the universe being something less than 700 million light-years. Although we had inflation in the first part of that 700 million years, the majority of it involved expansion at less than the speed of light.<br /><br />We see those parts today as they were then. In 13 billion years wouldn't they have moved even further away since they were then moving away from us at nearly the speed of light? Since they move faster the further they get, wouldn't they today be a LOT further away because over the eons they'd wind up traveling many times the speed of light away from us? Whatever the exact number is, they're a long ways away.

 

[alkalin]

Maddad, I’m not questioning some of what might be the results of what it was back then, IF we make important assumptions. Inflation is one of them. Don’t forget what big bang theorists were saying only a few short years ago; that all we needed was a distance scale and the Doppler formula and, wallah, we have the small primordial universe to look at at the calculated age. What went wrong?<br /><br />13.7 b years is that number. But if we look out at the universe at an age of 13 b years, we see a sphere of 26 b Lys across!<br /><br />There are other items to consider, but for now a couple more: Very large galaxies are seen out there over 10 b years in the past and at that time they had stars in them that are over 10 b years old. Anyone should be able to handle this math.<br /><br />That distant galaxies are moving faster that the speed of light is a testable feature of the distant universe. If these distant galaxies do not wink out, so to speak, but continue to shift to the red, then obviously some other factor is at work here rather than that they are moving away from us.<br /><br />Just might be correlation--yes indeed. Light does change it’s wavelength in free space. How do we know? If we do it in the lab, nature should be able to handle it too.<br />

 

[chmee]

If the universe is truly isotropic lets play a mind game...<br /><br />Lets say we pick out a galaxy at the edge of the observable universe, at 13 billion light years (BLY). Now, let's assume we are magicly transported to this galaxy taking zero time (I know imposible, but this is a mind game).<br /><br />Now at that new galaxy we pick out a new galaxy at the edge of their observable universe (13 BLY) but 180 degrees (in the opposite direction) from the galaxy we started at. We then are magically transported to this 3rd galaxy.<br /><br />Are you saying that in an isotropic universe we would could repeat this excercise an infinite number of times and the observable universe would always look the same?<br /><br />Wouldn't after repeating this about 10 times (130 billion light years) we would approach the "edge" of the expanding universe and would not see galaxies anymore in one direction?

 

[Maddad]

alkalin<br />"<font color="yellow">13.7 b years is that number. But if we look out at the universe at an age of 13 b years, we see a sphere of 26 b Lys across!</font><br /><br />Those two nubers are internally consistent. When we look in any one direction 13 billion years, we are looking from the center of the universe to the observable edge. This is the radius. When we speak of the sphere of the universe being 26 billion light years across, we are talking about the diameter.<br /><br />I am unconcerned with disant galaxy apparently showing stars in it that are older than the galaxy itself. The ages are our best estimates, but they are subject to error. For instance, estimates for the distance to the Southern Pinwheel Galaxy galaxy range from 10 to 25 million light-years. If we use the 15 mly figure, and then resolve an individual star (an accomplishment that we believe we cannot do at a range of more than 10 mly), this does not mean the 15 mly figure must be wrong. It could mean that we underestimated our resolving ability. We are always refining our estimates based on new information.

 

[alkalin]

I rather think the universe is a morphed steady-state, but did have a beginning. It is a lot older than we think, so for your mind game, you might repeat your exercise perhaps a hundred times before seeing an edge.

 

[alkalin]

“I am unconcerned with disant galaxy apparently showing stars in it that are older than the galaxy itself. The ages are our best estimates, but they are subject to error. For instance, estimates for the distance to the Southern Pinwheel Galaxy galaxy range from 10 to 25 million light-years. If we use the 15 mly figure, and then resolve an individual star (an accomplishment that we believe we cannot do at a range of more than 10 mly), this does not mean the 15 mly figure must be wrong. It could mean that we underestimated our resolving ability. We are always refining our estimates based on new information.”<br /><br /><br />Distant galaxies, and the near ones too, often show very distinct color trends due to the age of the major portion of the stars in them. We are not talking about a Doppler effect here, so I’m not sure why this would not concern you.<br /><br />It sounds like you are describing the short range methods of Cepheids when you are discussing the Pinwheel. We are not talking about resolving individual stars when the distant galaxies are spectrographically measured for red shift!! You know, the ones even over 10 B Lys distant.<br /><br /><br />Just remember, inflation is not real. It is based on a math expression that cannot be tested for validity.<br />

 

[cougar10]

Isn't it true that the idea of an isotropic universe is inconsistent with the notion of three dimensional space and an expanding universe? If one posits an omniscient, hypothetical observer, won't the universe appear spherical, oblong, or flat, but not isotropic? <br /><br />Thanks, Cougar

 

[alkalin]

E45, thanks for the reminder.<br /><br />If big bang theory is what you are looking for, go for it. This site gives perhaps as good an explanation as any right now. For me there is possibly at least one serious flaw. <br /><br />DL. (Luminosity distance) For every doubling of distance, actual number of photons is 1/4th their previous number per unit area. So at 10 B Lys you get one fourth as many photons as what you get at 5 B Lys over a given telescope aperture. Consequently the dwell time is far greater to get the same photon density. One factor in luminosity reliability is you may not know what the sizes are of objects you are looking at. The smaller they are, generally the dimmer they are.<br /><br />DA. (Angular distance) A rather incorrect assumption that this is reliable, if you ask me. It just might be a false rational for the very large galaxies you see close to the ‘edge’. <br /><br />Angular measure depends on resolving with good definition. Not easy when viewing objects so far away there are no distinguishing features to resolve. Therefore actual size of distant galaxies is mostly assumption. As you spend lots of time collecting light on a very distant and dim object, you get a greater spread of light for various reasons, and these effects can falsely make the object look much larger than it really is. This might be why the graphic shows this value decreasing with distance due to an increase in red shift??? My gut tells me the further away an object is, the angle becomes smaller and the more red shifted the light from it will be, and these things should be true whether you include travel time or not for light to get here. So I do not buy the plot on this one. A little more critical thinking needs to go into that plot, for me anyway.<br /><br />DC. (Comoving distance) The value I think doesn’t agree with other peoples views very well.<br /><br />DLT. (Light travel time distance) “Boy, we are traveling fast......Slow down Scotty.....your going t

 

[tom_hobbes]

I thought I understood you until the third paragraph from the end. Oh well. <div class="Discussion_UserSignature"> <p><font size="2" color="#339966"> I wish I could remember<br /> But my selective memory<br /> Won't let me</font><font size="2" color="#99cc00"> </font><font size="3" color="#339966"><font size="2">- </font></font><font size="1" color="#339966">Mark Oliver Everett</font></p><p> </p> </div>

 

[alkalin]

Sorry bout that one. Doesn’t make much sense to me either, now that I think about it.