How Can We Observe the Oldest and Most Distant Object in the Universe?

[showup]

Oldest and Distant object??

Last week, astronomers discovered the most oldest and distant object (cluster of stars, dust and gas) using Hubble and calculated that it is 13.2 billion light years away from earth[1]. I am not really sure how this is correct? Based on the fact that our universe is about 13.68 billion years old, if light from that newly identified distant object would have originated 13.2 billion years ago, considering the fact 13.2 billion years ago Earth and that object would have been a maximum of only 480 million light years away to each other and hence the light would have actually reached Earth in 480 million years! Right?? If so, how they are observing something that happened 480 million years after BB?

[1] http://www.cbsnews.com/network/news...les/aec546e66f53a7b44390052c1e751d6b-151.html

 

[JaredJames]

There's been some identical threads on this subject in the past regarding the expansion of space, I'll try and dig them up for you and post them here.

 

[D H]

Last week, astronomers discovered the most oldest and distant object (cluster of stars, dust and gas) using Hubble and calculated that it is 13.2 billion light years away from earth[1]. I am not really sure how this is correct? Based on the fact that our universe is about 13.68 billion years old, if light from that newly identified distant object would have originated 13.2 billion years ago, considering the fact 13.2 billion years ago Earth and that object would have been a maximum of only 480 million light years away to each other and hence the light would have actually reached Earth in 480 million years! Right?? If so, how they are observing something that happened 480 million years after BB?

The universe is expanding.

At the time the light that we see right now was emitted from that galaxy, the distance between our galaxy and that galaxy was a whole lot less than 13.2 billion light years. Due to the expansion of space, that galaxy is now about 31.7 billion light years away from us (co-moving distance).

An analogy that might help is to imagine the photons that we are now seeing coming from that distant galaxy as inch worms crawling at a constant speed (the speed of light) across a very flexible rubber band that grows ever longer as time passes. Every time the inch worm takes a step the rubber band stretches a bit. At the time the inch worm started its journey the distance to our galaxy was rather small. The inch worm can still reach us even though the distance between that distant galaxy and ours has grow by a huge amount, much more than the product of the speed of light and the age of the universe.

 

[marcus]

showup, I don't have anything to add to what Jared and DH already said, which is clear and right AFAICS, but here is some extra source material in case anyone is interested.

This is an unconfirmed redshift 10 object. It takes a while to double check and confirm.
There is another object almost as far, which has been confirmed. Redshift 8.6

These objects already have their Wikipedia pages.
Here is the one showup mentioned:
http://en.wikipedia.org/wiki/UDFj-39546284

You can see from the Wiki page that the estimated redshift is 10.3

The previous champ has (now confirmed) redshift 8.55.
http://arxiv.org/abs/1010.4312
or let's say 8.6 not to put too fine a point on it.
The article was posted back in October 2010

The previous champ has its Wiki page here:
http://en.wikipedia.org/wiki/UDFy-38135539

=====================
showup, the confusion you are talking about is primarily caused by poor journalism, where they encourage people to use light travel time as a gauge of distance.

In a world where distances are expanding, light travel time can be a misleading measure, since the distances were changing while the light was traveling.

Redshift is a measure which has a definite unambiguous meaning. It's the thing to focus on. You can convert redshift (symbol z, like z=8.6, or z=10.3) into other stuff like travel time or age of universe at time light was emitted, just by googling "wright calculator".

One of the distance measures that wright calculator gives you (when you plug in some redshift z that you are interested in) is a "now" distance or "freeze-frame" distance which is the distance to the object, or what is left of it, if you could freeze the expansion process now, and then go about the business of measuring the distance, say by the travel time of a signal.

That is less ambiguous because the distance you are trying to measure is not changing all the while you are trying to measure it.

The calculator also gives the freeze-frame distance "then"----how far the object was back when the light started on its way towards the matter that became our galaxy and us. (If you could have frozen the expansion process back then, at that moment, and measured by radar or signal timing or any such conventional way). In the calculator output it is labeled "angular size distance".

You can see the "then" distance is a lot less than the "now" distance. In the case of a redshift 8 object, it is less by a factor of 9. The distance back then, when the light started on its journey, is only 1/9 of the distance now, when the light arrives at the Hubble telescope and the picture is photographed.

 

[marcus]

@showup

DH already said it clearly and concisely, but I have some extra time right now so I will repeat the story with more detail. We are talking about an object detected recently where the recognizable rainbow lines of different atoms glow had been shifted by z=10.

That means that all the wavelengths in the light were longer by a factor of z+1 = 11.
You always add one, by convention. z=0.5 means the now wavelength is 1.5 times the original then wavelength. (z=0.5 means the wavelength is 50% longer, so the factor is 1.5, just a convention)

So they tell the journalist that, and he googles "wright calculator" (everybody uses it).
http://www.astro.ucla.edu/~wright/CosmoCalc.html
And he puts z=10 and presses the "general" button.
And he sees that the light travel time was 13.2 billion years.

You should try this. That way you share experience with the standard cosmo model with everybody else, the astronomers, the journalists, the people here.

You will see that the calculator says the light took 13.2 billion years to get here.

What's more if you had frozen the expansion process and measured the distance by timing a light signal, the initial distance back then, when the light started out, was 2.86 billion lightyears, and the distance now is 31.5 billion light years.

Do you see where the calculator gives you those distances 2.86 and 31.5?

Moreover one should be 11 times the other because during the 13.2 billion years the light was traveling distances have increased by a factor of 11. That applies to largescale distances between things not held together by gravity, and it is the basic meaning of saying redshift z=10.

If a journalist says the light travel time was 13.2 billion years, try not to think of that as a distance. Just think of it as a travel time, or the "lookback" time---we are seeing the group of stars as they were 13.2 billion years ago.

What is actually measured by the spectrometer is the redshift, and the two relevant distances are 2.86 and 31.5 are derived from that.

If the journalist actually says 13.2 billion "lightyears" just ignore the sloppiness and think of it as him just telling you the light's travel time of 13.2 billion years.

 

[Chronos]

I too prefer redshift over other 'yardsticks'. The principle utility of redshift is it gives us a comparative basis for judging distance to remote objects. Converting this to a light travel time, or distance 'now', is model dependent and based on your choice of 'standard 'candles'. The uncertainties involved are complicated. I prefer light travel time. It is more comprehensible to most people - hence the popsci approach.

 

[showup]

Thanks for explaining me several things that i wasn't aware of. I had a belief that the outer brim of the universe will be about a maximum of 13.67 light years away from the point of BB. That's why such a doubt originated in me. I never thought that it would have expanded to 31.5 light years distance. My idea was based on light's velocity. If Universe is now expanded to 31.5 light years distance from point of BB that means the cosmos are moving faster than light?!? Am i correct here? Doesn't this need infinite amount of energy expenditure? How is this possible? Also the background radiation too moving with the cosmos? Or it is lagging at 13.67 at the speed of light? I would appreciate your answers. Thank you.

 

[JaredJames]

The expansion of the universe can make it appear as though objects are moving faster than the speed of light (diverging galaxies for example). But in reality they are all moving at sub-luminal velocities.

If you imagine to objects moving away from each other at, say, 50mph and then the ground between them expanded it would appear they are moving faster than 50mph.

 

[EnumaElish]

AFAIK, "point of BB" is a meaningless concept. BB was everywhere.

 

[phinds]

Another way to think about the whole misleading notion of things moving faster than the speed of light (and I think I'm just saying the same thing as jarednjames here) is that the speed of objects relative to each other is not the same as the sum of the absolute velocities of the two unless the frame of reference remains unchanged and because of expansion we do not live in an unchanging universe in that sense.

 

[JaredJames]

unless the frame of reference remains unchanged

If we take the Earth as our zero point in a coordinate system then our reference point doesn't change.

 

[phinds]

If we take the Earth as our zero point in a coordinate system then our reference point doesn't change.

Correct. The reference POINT doesn't change, but the FRAME does, because the universe is expanding.

 

[JaredJames]

Sorry, got the terms mixed up.

Either way, I don't see why the reference frame changes.

Surely the fact we can observe galaxies moving away from us at >c tells us that our reference frame hasn't changed.

That aside, you can easily flip this and have two objects converging on Earth at 0.9c each. If we ignore spatial expansion (let's assume the scale is too small for it to matter) then our reference frame is fixed and yet you can't just add up the velocities.

Hence, I don't see how this holds up:

the speed of objects relative to each other is not the same as the sum of the absolute velocities of the two unless the frame of reference remains unchanged