13.1 billion light years object observed.

[Ramon163]

Last year Astronomers observed a self-destructing star 13.1 billion light years away. Happening only 630 million years after the big bang. While it is amazing that we are able to observe objects that far away, questions arose.

Now for a moment, let's imagine our universe in it's 3 axis (y, x and z), and our planet is position x 0, y 0, z 0. And let's say the object observed at a distance of 13.1 billion light years was located on the x axis. So it would be at position x +13.1 billion light years.

Common knowledge is that the big bang occurred 13.7 billion years ago.
Now the question arises, how are we able to observe objects in the -x axis direction? Even if everything traveled at the speed of light since the big bang occurred 13.7 billion years ago (which is theoretically impossible), we would only be able to observe 630 million years of light in the -x direction (not even taking into account the time light takes for that light to reach us from that direction). I am an "Inflationist" myself, but even cosmic inflation does not account for this does it?

I am probably missing a vital aspect to this that explains everything, and I look forward to hearing it :).

 

[hadsed]

Inflation actually does account for this. Space is expanding, so fast that galaxies seem to be moving away from us faster than the speed of light. They're not actually moving really, but space itself is expanding so it looks like it. Perhaps you'd be correct in saying that galaxies are moving away from us faster than the speed of light, but the important thing is to recognize that it's because space is expanding.

The observable universe is like a 13.7 billion lightyear bubble around us. This applies in all directions, and anything beyond that would never reach us. However, think about how inflation works. If it's expanding faster than the speed of light, eventually there will be some things that used to be in our little 'bubble' (which is increasing as the age of our universe increases) but isn't anymore because the expansion is faster than light. Now think of it backwards. It seems perfectly plausible for something to have happened 630 million years after the big bang but to be 13.1 billion light years away from us because of the faster-than-light expansion of space due to inflation.

 

[marcus]

RAMON
your post has some misconceptions. try reading the Lineweaver article that corrects popular misconceptions about expansion cosmology, the link is in my sig.

the picture of an explosion from a point outwards into empty space is wrong. lineweaver will explain the right picture

According to standard cosmic model*
if star exploded at .6 billion years, and we get the light today 13.1 billion years later,
then the distance to the star WAS about 3 billion LY when it exploded
and the distance IS NOW about 30 billion LY
and the redshift of the incoming light is about 8.5

*commonly used parameters .27, .73, 71 for matter, lambda, Hubble constant

If you want to check that, go to this calculator:
http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html
and over at the left type in the usual parameters .27 for matter, .73 for lambda, and 71 for Hubble. then put in the redshift 8.5 and press "calculate".

It's usual for the distances in cosmology to increase faster than the speed of light.
I'm talking about the distance you would measure if you could stop expansion at a certain moment, so the distance wouldn't be constantly changing while you were trying to measure it. That is the distance (socalled "proper" distance) that is used to formulate Hubble law that describes the general pattern of expansion. The speed limit of special relativity does not apply.

check out the calculator. Have fun!

Light travel time is not a very useful measure of distance. Because distances have been expanding at different rates through history. Light travel time does not correspond in any simple way to distance, either back then, or right now.

Redshift is probably your one best handle on "how long ago?" and "how far away?" questions. The redshift is what you have to put into most cosmology calculators in order to get the other info. So always go for the redshift.

In your case the redshift of the light from the exploding star was about 8.5.

You can get another calculator if you google "wright calculator". the parameters .27, .73, and 71 are already put in for you in that one. So just put in 8.5 and press "general".

 

[Ramon163]

Wow, thank you so much. This was very illuminating for me :).
This certainly adds a whole other dimension to my understanding of the origin and evolution of our universe.

I could not have asked for a more to the point answer :).
You guys are my heroes

 

[Sage Lee]

Well, not me, this only further confused me. You lost me at "increasing faster than the speed of light." I thought nothing could happen faster than the speed of light. So how exactly do distances increase faster than the speed of light?

(Keep in mind I might as well be mentally retarded when it comes to these things, and as such it may be pointless to try and explain, and yet... I ask anyway.)

I mean, I'm ridiculously out of my league here, I'm not really sure what I'm doing on a physics forum. I've never taken a physics class; I skipped most of the logic 101 class I took years ago; I was always frustrated by complex math.

For instance, if you talk to me about redshift, I'm going to say, what the hell is redshift? And the uncertainty principle confounds me, it just seems so counter-intuitive that knowing more precisley momentum makes is so that position becomes less certain, but whatever, I certainly can't argue since I don't fully understand.)

Anyway, I'm just pointing out my cluelessness so you understand that any explanations given here need to be pretty simplistic - if that's even possible in this context - or I won't understand it. But I ask again, how or why is it usual in cosmology for distances to increase faster than the speed of light? Why does the speed limit not apply?

 

[Tanelorn]

Sage, You are correct that the speed of light is constant and nothing can travel faster than the speed of light. However what is changing is that the space in between us and the furthest objects we can see is expanding very rapidly producing red shift. Other objects even further away from us beyond the observable universe can be traveling away from us faster than the speed of light simply due to the expansion of space between us.

In theory objects at the limit of the observable universe are traveling away from us at the speed of light. Some Physicits think that the universe might be 10 to power 30 times the observable universe so if something like this is true this could mean objects are receding from us at 10 to power 30 times the speed of light!

 

[Sage Lee]

Yeah, but what the hell is red shift? (No, just kidding, but I did warn you...)

Still fairly confusing, but let me see if this is what we're talking about:

Nothing is actually moving faster than the speed of light, but the expansion of space gives some things the appearance of moving faster than the speed of light...?

Using the balloon analogy: if there were two ants crawling on the surface of an expanding balloon, they would get farther away from each other at a rate faster than the speed they're actually traveling would suggest, giving them the appearance of traveling faster than they actually are...?

 

[hadsed]

Yes, that's correct.

 

[Sage Lee]

Yes, that's correct.

So then, if we want to achieve faster than light travel, we need only to emulate this effect and manipulate the "space between" rather than trying to get something to actually travel that fast... psshh, how have we not done that yet? Someone should get on that.

(I know sarcasm doesn't often come across well in writing, so I'll just say... um, yeah.)

 

[Chronos]

I recommend two papers:
http://www.astronomycafe.net/cosm/expan.html
http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf
The former is by Sten Odenwald, and expressed in laymenesque terms. The latter is the paper by Lineweaver that was recommended by Marcus. It is a technical review complete with unfathomable math and mind bending diagrams. Lineweaver does, however, have a knack for putting into words the meaning of the technical parts of the discussion. See in particular section 3.3 of this paper. Bear in mind we routinely observe CMB photons emitted at redshift z~1100. You can detect these photons with an FM radio. The crackling noise you hear between stations is, in part, due to CMB photons [re: http://www.universetoday.com/25560/the-switch-to-digital-switches-off-big-bang-tv-signal/] .

 

[hadsed]

So then, if we want to achieve faster than light travel, we need only to emulate this effect and manipulate the "space between" rather than trying to get something to actually travel that fast... psshh, how have we not done that yet? Someone should get on that.

(I know sarcasm doesn't often come across well in writing, so I'll just say... um, yeah.)

Well it would only work if we were trying to get away from something faster than light. Obviously it wouldn't work if we were trying to get closer to something, which would be the only practical reason you'd want to travel faster than light.

 

[Tanelorn]

The CMBR black body radiation center frequency is 160.2 GHz. FM radio is 100MHz but I can see that there is enough in band energy to create static.

 

[Sage Lee]

I recommend two papers:
http://www.astronomycafe.net/cosm/expan.html
http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf
The former is by Sten Odenwald, and expressed in laymenesque terms. The latter is the paper by Lineweaver that was recommended by Marcus. It is a technical review complete with unfathomable math and mind bending diagrams. Lineweaver does, however, have a knack for putting into words the meaning of the technical parts of the discussion. See in particular section 3.3 of this paper. Bear in mind we routinely observe CMB photons emitted at redshift z~1100. You can detect these photons with an FM radio. The crackling noise you hear between stations is, in part, due to CMB photons [re: http://www.universetoday.com/25560/the-switch-to-digital-switches-off-big-bang-tv-signal/] .

Awesome link(s), thank you. I need to read it again though (only read the first one so far); it's still fairly hard to absorb some of the stuff for someone like me, as it's not as laymenesque as you might think, but it's still pretty comprehensible. I found it funny though that the article took up less than half the web page, leaving a large black, blank space at the bottom, and I found myself wondering if the article was left room to expand...

Well it would only work if we were trying to get away from something faster than light. Obviously it wouldn't work if we were trying to get closer to something, which would be the only practical reason you'd want to travel faster than light.

Well duh, I was talking about contracting the space between, not expanding it! (Still just joking around here; I actually realized what you said while I was writing my tongue-in-cheek comment, but I wanted to say it anyway so I replaced the word "expand" with the word "manipulate.")

My second thought after reading your comment was that it would really depend on what's chasing you...

I promise though, as soon as I find a way to contract the space between two objects, in a reversal of what's happening with the expansion of the universe, you guys'll be the first to know.

 

[Sage Lee]

Hmmm, you know I just had a(nother) random thought - and again, keep in mind I don't understand this stuff - so bear with me:

If gravitational fields are just a geometrical curvature of spacetime, then in theory, could (does) a suppermassive gravitational field curve spacetime enough to pull two objects closer together in the manner I suggested? Or at least slow down the relative expansion between those two objects?

If that didn't make sense, what I'm imagining is that balloon again, with the two ants, and a finger depressing a spot on the balloon between the two ants enough to bring them temporarily closer together (a futile struggle of course, since the balloon continues to expand, but I'm just wondering out loud here.)

 

[hadsed]

If I'm not mistaken, gravity doesn't affect inflation, so space would continue to expand unless you figured out the underlying mechanism for inflation.