# Seeing Farther/Younger Universe **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [January 19, 2001, 10:07pm UTC](https://boards.straightdope.com/t/seeing-farther-younger-universe/50925 "2001-01-19T22:07:23Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![foxfyre](https://avatars.discourse-cdn.com/v4/letter/f/aeb1de/32.png) [@foxfyre](https://boards.straightdope.com/u/foxfyre)\ **Post date:** [January 19, 2001, 10:07pm UTC](https://boards.straightdope.com/t/seeing-farther-younger-universe/50925/1 "2001-01-19T22:07:23Z")
> [@](#): > > \*\*Dear Straight Dope: > > The idea that the FARTHER we are able to see into the universe, the YOUNGER the objects we see, seems paradoxical because if we could see FAR ENOUGH, we would see the beginning of the universe; and since the Big Bang holds that it all started from a single point, the objects we see would not be far away at all, but RIGHT ON TOP OF US. What gives? [--Tom.McAfee@sterinfo.com](mailto:--Tom.McAfee@sterinfo.com)\*\* > > SDSTAFF Ian replies with help from UnDeadDude: > > I can see why Cecil decided to let the Straight Dope Science Advisory Board have a crack at this one. It’s such a softball. Uhh…What is the answer to this question. -Fox ---
**Author:** ![foxfyre](https://avatars.discourse-cdn.com/v4/letter/f/aeb1de/32.png) [@foxfyre](https://boards.straightdope.com/u/foxfyre)\ **Post date:** [January 19, 2001, 10:15pm UTC](https://boards.straightdope.com/t/seeing-farther-younger-universe/50925/2 "2001-01-19T22:15:49Z")
oh and heres a link, sorry: [http://www.straightdope.com/mailbag/mbigbang.html](http://www.straightdope.com/mailbag/mbigbang.html) -Fox ---
**Author:** ![Akatsukami](https://avatars.discourse-cdn.com/v4/letter/a/ea666f/32.png) [@Akatsukami](https://boards.straightdope.com/u/Akatsukami)\ **Post date:** [January 21, 2001, 12:04am UTC](https://boards.straightdope.com/t/seeing-farther-younger-universe/50925/3 "2001-01-21T00:04:51Z")
Well, [Tom.McAfee@sterinfo.com](mailto:Tom.McAfee@sterinfo.com) has, at a minimum, worded the question badly. Now, far be it from me to suppose that I can compete with **Ian** and **Undead Dude**. However, let me indulge in a little interrogation of myself: Q: Can we really see younger objects the farther we look into space? A: Sort of. Since light has a finite speed, every object that we see has emitted (or reflected, although that’s not significant at distances of more than few billion kilometers) the light by which we see it some time ago. For the lamp on my nightstand, we’re talking a few thousand picoseconds ago. For the Sun, that’s about eight minutes ago. For the Andromeda Galaxy, that two million years ago. For some quasar, that’s a few eons (one eon = 10[sup]9[/sup] years) ago. Q: But how do we know that that quasar’s not really just outside the solar system? A: The light from that quasar is severely red-shifted. The Hubble constant (rate at which the universe is expanding) or H[sub]0[/sub], is reckoned to be about 50-100 kilometers per second per million parsecs (km/s/Mpc). That is, if something is receding (has a red-shift) at 100 km/s, it’s about 1-2 Mpc away. (Actually, 1-2 Mpc is far too little distance to determine H[sub]0[/sub] over; things have their own velocities which conceal the expansion of the universe.) (I will also note that, as I am not a cosmologist, any comment that I make is based on information about 5-10 years old. There may be a better determination of H[sub]0[/sub] that I haven’t heard of yet). Q: But how do we know that the light from the quasar is _really_ red-shifted, and isn’t just “tired”, or reddened by absorption by intergalactic matter, or something? A: We can measure the atomic absorption (Fraunhofer) lines, which occur at certain precise frequencies. So, we can measure where those lines are in the light, and see that the frequencies really _have_ shifted, not that the bluer frequencies have been preferentially absorbed. As for “tired light” theories, well, at best they’re not only unproven, but don’t give testable results any different from the ones that we have now. Q: OK, so quasars really _are_ way out there. So why can’t we see back to the Big Bang. A: When light is red-shifted, it also loses energy (in fact, the two phrases are identical; trust me on this one, at least for the length of this post). A photon from the Big Bang would have been red-shifted to infinite frequency – and zero energy. It’s gone! In fact, there are suggestions (not yet proven conclusively) that what we see isn’t “the universe”, it’s just the part of the universe that light has had the time to arrive here (this depends on whether H[sub]0[/sub] is decreasing with time; for the past several decades, it has been thought to be, but opinions have changed recently). Additionally, about 100,000 years after the Big Whatever, it is thought that the temperature of the universe (_i.e._, the energy of the photons that pervade every part of it, that we now call the “3°K background radiation”) dropped far enough due to red-shifting that electrons could attach themselves to nuclei and form atoms, a process called “recombination”. Prior to that, the electrons were constantly being blasted away by those photons – which is just another way of saying that universe was filled with an opaque electron gas. Q: OK, OK, but what _100,001_ years after the Big Whatever? Why can’t we see (at least if we have a big enough telescope) stuff that’s _here_ now, and was _there_ then. A: Because it _wasn’t_ there then. Remember, stuff isn’t moving (well, it is, but for purposes of this problem, it might as well be standing still), the universe, the very fabric of space-time (whatever _that_ means) is expanding. The stuff that’s at the edge of the universe (so to speak; I know that the universe doesn’t really _have_ an edge) now was at the edge of the Universe 10 eons ago; the edge was just a lot closer then. Q: “The Big Whatever”? What do you mean? A: Hey, isn’t this post long enough? ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [January 21, 2001, 1:55pm UTC](https://boards.straightdope.com/t/seeing-farther-younger-universe/50925/4 "2001-01-21T13:55:03Z")
I’m not sure what happened to that report, but we’re working on restoring it. ---
**Author:** ![Arnold\_Winkelried](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@Arnold\_Winkelried](https://boards.straightdope.com/u/Arnold_Winkelried)\ **Post date:** [January 21, 2001, 6:44pm UTC](https://boards.straightdope.com/t/seeing-farther-younger-universe/50925/5 "2001-01-21T18:44:24Z")
Some related staff reports: [How do they figure the distance between celestial bodies? (07-Nov-2000)](http://www.straightdope.com/mailbag/mstardistance.html) [Are the stars really all burned out, and all we see is the glow? (05-Apr-2000)](http://www.straightdope.com/mailbag/moldstars.html) ---
**Author:** ![Doug\_Yanega](https://avatars.discourse-cdn.com/v4/letter/d/b5e925/32.png) [@Doug\_Yanega](https://boards.straightdope.com/u/Doug_Yanega)\ **Post date:** [January 21, 2001, 11:24pm UTC](https://boards.straightdope.com/t/seeing-farther-younger-universe/50925/6 "2001-01-21T23:24:32Z")
There’s aone other Q:A combo not covered that probably should be: Q: Okay, so there was an opaque electron gas all over, so we can’t see the explosion. but if we COULD see back to the Big Whatever, which direction would we have to look to see it? A: (the explanation I’ve heard) No matter _which_ direction we look we see the background radiation left over, because we’re looking at three dimensions and the universe is 4-dimensional - the idea is that space-time is sort of curved in on itself so what we might personally think of in three dimensions as being a sphere defining the “edge of space” is more like a point at the “center of time”. The analogy sometimes used is that of 2-dimensional people living on the surface of an enormous expanding balloon; their “universe” only has two dimensions, neither of which holds the actual axis along which their universe is expanding. If they could fire a 2-D rocket towards the “edge” (as they perceive it) fast enough, it would complete a big loop and end up where it started. ---
**Author:** ![foxfyre](https://avatars.discourse-cdn.com/v4/letter/f/aeb1de/32.png) [@foxfyre](https://boards.straightdope.com/u/foxfyre)\ **Post date:** [January 22, 2001, 3:18pm UTC](https://boards.straightdope.com/t/seeing-farther-younger-universe/50925/7 "2001-01-22T15:18:56Z")
Cool, thanks. I always wondered about looking ‘back in time’ by looking far away, and a Discovery channel show said that if they look far enough out they find nothing other than tiny, young, blue galaxies. A couple of questions, most of the relate to that topic. First, how does the expansion relate to how far back in time you see? By this I mean lets say a galaxy is 1000 light years away (I know thats very close, but its an example) the light takes 1000 years to get hear. by the time that light gets here, the galaxy is 2000 lightyears away. Now, what would that do to the red shift, etc? Also wouldnt it seem like the galaxy is 2000 light years away but the light only took 1000 years to get there? I need to brush up on my General and Special Relativity knowlege, its been a long time since ive studyed that. Also, why are quasars not in the solar system? Is it possible they only exist back in time trillions of years? -Fox