This question was inspired vaguely and indirectly by today's APOD (3 May 2007). After searching the topic in this site and at Wikipedia, I am still puzzled.
I understand that the "observable universe" is a perfect sphere, with Earth (assuming that is where the observer is located) at its center and with a diameter of about 78-90 billion light years (Gly).
I also think I understand that the total Universe (observable plus unobservable) is almost completely unknown, but is probably much larger than the observable universe, or may be infinite, but could also (less likely) be smaller than the observable universe, if, for example, light passes through it more than once, creating multiple images of the same object separated by vast time intervals -- similar to a hall-of-mirrors illusion where the room looks larger than it actually is.
My question is: do we know where we are located within the total Universe? We know where our solar system is located within the Milky Way galaxy, in relation to the galactic plane and to the galactic center. Is there any absolute reference point, such as a center point, or an outer boundary, for the Universe? If not, then does the question "where are we in the Universe" have any meaning?
The age of the Universe is widely agreed to be about 13.7 Gy. The farthest known quasars are 12 Gly distant. Are the most distant quasars, say, those more than 10 Gly, evenly distributed in all directions around Earth, or are they clustered in one direction or scarce or absent in another direction?
The cosmic background radiation was found by WMAP to be homogenous at cosmological scales. Do we know in which direction from Earth the Big Bang occurred? Or does that question even have any meaning?
Where is Earth located within the Universe?
Under current theory, there are no absolute points of reference within the Universe; the only way we can say where Earth lies is by relating its position to the positions of the objects around it.
According to the inflationary big bang theory, the universe would have no center, nor an edge, since it didn't explode outward from a point in pre-existing space, but rather all of space itself was created and expanded. My favorite analogy likens finding the center of the universe to finding the center of the surface of an expanding balloon. There isn't one.
According to the inflationary big bang theory, the universe would have no center, nor an edge, since it didn't explode outward from a point in pre-existing space, but rather all of space itself was created and expanded. My favorite analogy likens finding the center of the universe to finding the center of the surface of an expanding balloon. There isn't one.
Don't just stand there, get that other dog!
Yes -- Earth is the center of the observable universe for an observer on Earth.rigelan wrote:Umm. The earth is the center of the universe.
http://en.wikipedia.org/wiki/Observable_universe
Forgive me if my thinking is excessively linear, but here is a cosmological problem that defies logic. Let us assume that our portion of the known universe is 13.7 billion years old, and it started out at a point and expanded to it's current shape and size over the past 13.7 billion years. Now let us assume that one of the most distant objects from earth detected by telescopes is a quasar called "quasar X" 12 billion light years away.
Can someone explain to me how two objects can get 12 billion light years apart in only 13.7 billion years? Logically, relative to the quasar, we would have to travel at 88% of the speed of light for 13.7 billion years to get here. (I am saying "we" because quasar X hasn't had 13.7 billion years to move, it only has had 1.7 billion years, as we are viewing something as it appeared 12 billion years ago).
So either we are moving at a speed of 88% the speed of light all the time, with some major time-warping to figure out, or the universe was a lot bigger than we think it was 13.7 billion years ago.
Thoughts / rebuttals please.
-goredsox
Can someone explain to me how two objects can get 12 billion light years apart in only 13.7 billion years? Logically, relative to the quasar, we would have to travel at 88% of the speed of light for 13.7 billion years to get here. (I am saying "we" because quasar X hasn't had 13.7 billion years to move, it only has had 1.7 billion years, as we are viewing something as it appeared 12 billion years ago).
So either we are moving at a speed of 88% the speed of light all the time, with some major time-warping to figure out, or the universe was a lot bigger than we think it was 13.7 billion years ago.
Thoughts / rebuttals please.
-goredsox
Well, in the inflationary model of big bang cosmology, the universe, shortly after the instant of the big bang, underwent a period of superluminal expansion (inflation).
Also note that although objects in space cannot exceed the local speed of light, the expansion of space between them can cause them to recede from each other faster than light.
http://en.wikipedia.org/wiki/Cosmic_inflation
http://en.wikipedia.org/wiki/Big_Bang
Also note that although objects in space cannot exceed the local speed of light, the expansion of space between them can cause them to recede from each other faster than light.
http://en.wikipedia.org/wiki/Cosmic_inflation
http://en.wikipedia.org/wiki/Big_Bang
Don't just stand there, get that other dog!
I do not know the answer, but I agree with Javachip. It is an important question because if 10Gly objects are uniformly distributed around us, the "diameter" of the universe would be over 20Gly. This would be a counterintuitive finding (at least for me) as the universe is only 13.7 Gy old. although I suppose I will buy the supposition that 2 objects flying at about 90% the speed of light for the entire age of the universe could get 20 Gly apart. It stretches credulity, however.
I looked at the Wiki reference links posted by Qev. It appears from Qev's comment that the universe is thought to have "inflated" faster than the speed of light. Are we to suppose that energy moved in opposite directions, as above, and then got converted into matter later?
I looked at the Wiki reference links posted by Qev. It appears from Qev's comment that the universe is thought to have "inflated" faster than the speed of light. Are we to suppose that energy moved in opposite directions, as above, and then got converted into matter later?
Aye, but those objects that are 20Gly from each other won't be able to see each other.
http://curious.astro.cornell.edu/questi ... number=387
And the limit of the speed of light isn't relative to spacetime. It is only useful when comparing how fast one one object APPEARS to a second object.
If an object flies away to the LEFT at (1/2) speed of light, and a second flies to the RIGHT at (1/2) speed of light compared to you on the earth, then do they appear to travel the speed of light away from each other? no. Its more like (3/4) speed of light.
Correct me if I'm wrong, but I don't think there is an actual limit to how fast you travel, the limit is on how fast you can appear to travel compared to a second object's point of view.
http://curious.astro.cornell.edu/questi ... number=387
And the limit of the speed of light isn't relative to spacetime. It is only useful when comparing how fast one one object APPEARS to a second object.
If an object flies away to the LEFT at (1/2) speed of light, and a second flies to the RIGHT at (1/2) speed of light compared to you on the earth, then do they appear to travel the speed of light away from each other? no. Its more like (3/4) speed of light.
Correct me if I'm wrong, but I don't think there is an actual limit to how fast you travel, the limit is on how fast you can appear to travel compared to a second object's point of view.
Hey I found a couple images on the distribution of quasars, see if these are any good.
http://www.ioffe.rssi.ru/astro/QC/notebook.htm
And I think the furthest quasars that we can see are 13.7 GLY away, hence our estimate for the age of the universe.
One note about the pictures: There seems to be a lack of quasars about the galactic equator. But I think that makes sense, because all the stars in the Milky way probably blind us to the distant quasars.
http://www.ioffe.rssi.ru/astro/QC/notebook.htm
And I think the furthest quasars that we can see are 13.7 GLY away, hence our estimate for the age of the universe.
One note about the pictures: There seems to be a lack of quasars about the galactic equator. But I think that makes sense, because all the stars in the Milky way probably blind us to the distant quasars.
where we are
http://www.anzwers.org/free/universe/index.html
http://www.anzwers.org/free/universe/index.html
Unless........Aye, but those objects that are 20Gly from each other won't be able to see each other.
Unless they are the same object! The quasar map link rigelan posted shows a lot of mirror symmetries. This suggests the possibility that if you look at two really distant objects in opposite directions, you are actually seeing the same object from different perspectives. In other words, if space is curved (like the balloon analagy Qev mentioned), the earth is not so much at the center of the universe; rather, it is at the opposite pole from some really distant quasars. Or at least, at the opposite pole from where a bunch of quasars were 10-12 billion years ago.