Another question about the universe.

[bdewoody]

The galaxies we see through the Hubble telescope that are so many billions of light years old, where are they now? Or is that question even valid? Even stars on the other side of our galaxy we are seeing their position 100 thousand years ago so how can we determine where they are now or is that information even relevant?

 

[drwayne]

You are correct, ignoring for a moment the subtleties of the notion of "at the current time", clearly,
distant objects are not where we see them "at the current time".

Depending on how distant the objects are, we might have a decent velocity estimate on the
object, so we might be able to do a d = v * t estimate.

Wayne

 

[bdewoody]

So, do the maps we see on the science channel take this into account or do they just reflect what is seen through the telescopes?

 

[MeteorWayne]

So, do the maps we see on the science channel take this into account or do they just reflect what is seen through the telescopes?

It would depend on which show on which subject. It's TV, so I wouldn't assume anything about the accuracy of anything without verifying it. Most likely if it's a photo, it is based on the light as we see it. If it's an artist representation, who knows.

That's why we real geeks read the journals, since it is explained exactly what each image represents.

 

[SpeedFreek]

The galaxies we see through the Hubble telescope that are so many billions of light years old, where are they now?

The highest redshift galaxies seen by Hubble so far are around 12.9 billion light-years away (in terms of light travel time). Those galaxies were only around 3.5 billion light-years away (angular diameter distance) when they emitted the light we are now seeing. It is estimated that those galaxies would be around 29 billion light-years away (co-moving distance) today.

http://www.atlasoftheuniverse.com/redshift.html explains the principles mentioned above (but it uses old figures which are now considered a little high).

 

[dragon04]

156 billion light years

"All the pieces add up to 78 billion-light-years. The light has not traveled that far, but 'the starting point of a photon reaching us today after travelling for 13.7 billion years is now 78 billion light-years away,' Cornish said. That would be the radius of the universe, and twice that -- 156 billion light-years -- is the diameter. That's based on a view going 90 percent of the way back in time, so it might be slightly larger."

Good article from the SDC Archive

 

[SpeedFreek]

156 billion light years

"All the pieces add up to 78 billion-light-years. The light has not traveled that far, but 'the starting point of a photon reaching us today after travelling for 13.7 billion years is now 78 billion light-years away,' Cornish said. That would be the radius of the universe, and twice that -- 156 billion light-years -- is the diameter. That's based on a view going 90 percent of the way back in time, so it might be slightly larger."

Good article from the SDC Archive

Unfortunately, that's not such a good article, as the person that wrote that article misunderstood what Neil Cornish was trying to say. The 78 billion light-year figure is correct, but the 156 billion light-years is not.

Our observable universe is 46 billion light-years in radius, giving it a diameter of 92 billion light-years. Cornish was part of group of scientists that were examining the WMAP data of the Cosmic Background Radiation, and that data represents our observable universe. They were looking for repeated patterns in the data that would indicate that the fundamental domain of the whole universe is smaller than our observable universe - if that were the case, we might be looking at the same regions of space when we look in different directions - the regions at the edge of our observable universe would overlap on opposite sides!

What Cornish's team found is that at least 78 billion light-years of our 92 billion light-year diameter observable universe is comprised of unique space, so the lower limit on the size of the whole universe is a diameter of 78 billion years. Unfortunately, a lot of science correspondents misunderstood the true nature of the teams findings and the 156 billion light-year figure was widely (but wrongly) reported.

Notice that, in the article you linked, only the 78 billion light-year figure is an actual quote from Cornish - that 156 billion light-year figure seems to be an assumption made by the writer of the commentary. They then quote Cornish saying "It can be thought of as a spherical diameter is the usual sense," but he is referring to the 78 billion light-year figure he just gave!

The article confused a lot of people! Then the confusion was compounded even further, when they asked Cornish for clarification. Cornish's answer at the bottom of that article is simply about how the universe can expand faster than light without violating General Relativity (which is why the whole universe can be at least 78 billion light-years across after only 13.7 billion years). But again, the introduction to his clarification seems to imply he is talking about the 156 billion light-year figure, when he certainly was not!

This issue is mentioned here:

http://en.wikipedia.org/wiki/Observable ... onceptions

And the original scientific paper on which it is based:

http://arxiv.org/abs/astro-ph/0604616

Clues to the shape of our Universe can be found by searching the CMB for matching circles of temperature patterns. A full sky search of the CMB, mapped extremely accurately by NASA's WMAP satellite, returned no detection of such matching circles and placed a lower bound on the size of the Universe at 24 Gpc. This lower bound can be extended by optimally filtering the WMAP power spectrum.

24 Gigaparsecs = 78 billion light-years = the minimum size of the whole universe. The paper above talks of using other methods to check for "repeated space" (my simplistic term for it) all the way to ~28 Gpc (92 billion light-years), which is the diameter of the observable universe.

Unfortunately, during the interview, Cornish either did not explain what he meant very well or was taken out of context. When he says that "the starting point of a photon reaching us today after travelling for 13.7 billion years is now 78 billion light-years away", what he could have said was something like at least 78 billion light-years of our observable universe is comprised of unique space.

Light can only have travelled halfway across our observable universe theoretically, so the maximum distance that the starting point for a photon reaching us today could have achieved is 46 billion light-years away. If the fundamental domain of the universe is a minimum of 78 billion light-years across, that is the lower limit for the largest distance that two coordinates in space have receded from each other in the time since the universe began.

Confusing, eh?

 

[derekmcd]

I emailed SDC a couple years ago to have that article removed. No such luck. If you google "size of the universe", it is still the top of the list. Wiki has a link to that SDC article under 'misconsceptions'.