5 ms·

It sort of is nitpicking. We haven't observed objects with redshifts that indicate distances larger than 13.some Gly away. Yes, the physical objects are farth

by MAGZine 11y ago

It sort of is nitpicking. We haven't observed objects with redshifts that indicate distances larger than 13.some Gly away. Yes, the physical objects are farther, but the point is moot. Those objects aren't the same as what we see today. They're totally different. We don't know what they look like today. Even low-mass stars have lived and died. In summary, there is no way for us to see those 46.5 Gly objects other than wait 50 Gy (with our given technology)

goodside 11y ago
Yes, it's true that the most distant galaxies we've observed are only around 13 Gly away, but the fact that number is so close to (speed_of_light * age_of_universe) is just a coincidence. We could, in principle, see light emitted from points in space that are currently 46.5 Gly away, but all such light was emitted long before any galaxies had formed. The OP wasn't mentioning that we can see to a maximum distance of ~13 Gly as an unrelated fact with its own cause, it was saying it was because the Universe is ~13 Gy old and that's how far light can travel in that time, which isn't true.
- goodside 11y ago
  Correction: I'm an idiot; see xenophonf's comment.
xenophonf 11y ago
I assume you're talking about UDFy-38135539 (https://en.wikipedia.org/wiki/UDFy-38135539 https://en.wikipedia.org/wiki/UDFy-38135539), with a redshift of z=8.6. It is not 13 Gly away, even though the light detected by Hubble's infrared camera was emitted about 13 billion years ago. Due to the metric expansion of space, the distance to that object is around 32 Gly (9710 Mpc according to http://www.bo.astro.it/~cappi/CosmoWidget.html http://www.bo.astro.it/~cappi/CosmoWidget.html).
- MAGZine 11y ago
  that is one object with a suggested redshift of z=8.6. However, we do not know the distance of that object because not only was the image taken in the visible spectra (by Hubble), but the spectroscopic results re: it's distance have not been reproducible, and so the distance figure is challenged. Fortunately, we have other galaxies, such as EGSY8p7 (z=8.68) have been imaged in the infrared, and as such, their distance confirmed. However, you've just reiterated what GP has said. I maintain that nobody is denying that the object that has been observed is more distant than it was 13Gy ago, however, the light that we are currently observing emanated from an object that was only 13Gly away. As I stated in my previous comment, the galaxies that we are presently observing are much different, and much farther away today, it's just going to take a lot of time for us to see what they look like today. You're seeing a baby and claiming to have seen the senile crank that the baby potentially became over 19Gy. The baby we're currently observing may as well be dead. If the article author is stating that 13Gly is the maximum distance anything can be from us, then the author is false. However, that's not what the author is saying. The author is saying we cannot see past 13Gly because the light has not arrived, and this is patently TRUE. The author makes NO claim about the current location of the objects.
  - xenophonf 11y ago
    the light that we are currently observing emanated from an object that was only 13Gly away Using http://www.astro.ucla.edu/~wright/CosmoCalc.html http://www.astro.ucla.edu/~wright/CosmoCalc.html, the light of an object at redshift z=8.68 was emitted 13.141 Gyr ago, 0.579 Gyr after the Big Bang. The co-moving distance (to where that object was) is 30.444 Gly, but at the time the light was emitted, it was only 3.145 Gly away (=30.444 Gly/(1+8.68)). we cannot see past 13Gly because the light has not arrived, and this is patently TRUE We should be able to detect light from Population III stars, i.e., redshifts between z=20 and z=100, so about 13.540-13.704 Gyr in the past (about 0.016-0.180 Gyr since the Big Bang) and at a co-moving distance of about 35.851-42.045 Gly (or distances from us in the past of 0.416-1.707 Gly). Edited to add: For more information, refer to https://en.wikipedia.org/wiki/Scale_factor_%28cosmology%29 https://en.wikipedia.org/wiki/Scale_factor_%28cosmology%29, specifically the FLRW metric, https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtr....

by MAGZine 11y ago

goodside 11y ago

Yes, it's true that the most distant galaxies we've observed are only around 13 Gly away, but the fact that number is so close to (speed_of_light * age_of_universe) is just a coincidence. We could, in principle, see light emitted from points in space that are currently 46.5 Gly away, but all such light was emitted long before any galaxies had formed. The OP wasn't mentioning that we can see to a maximum distance of ~13 Gly as an unrelated fact with its own cause, it was saying it was because the Universe is ~13 Gy old and that's how far light can travel in that time, which isn't true.

goodside 11y ago
Correction: I'm an idiot; see xenophonf's comment.

xenophonf 11y ago

I assume you're talking about UDFy-38135539 (https://en.wikipedia.org/wiki/UDFy-38135539 https://en.wikipedia.org/wiki/UDFy-38135539), with a redshift of z=8.6. It is not 13 Gly away, even though the light detected by Hubble's infrared camera was emitted about 13 billion years ago. Due to the metric expansion of space, the distance to that object is around 32 Gly (9710 Mpc according to http://www.bo.astro.it/~cappi/CosmoWidget.html http://www.bo.astro.it/~cappi/CosmoWidget.html).

MAGZine 11y ago
that is one object with a suggested redshift of z=8.6. However, we do not know the distance of that object because not only was the image taken in the visible spectra (by Hubble), but the spectroscopic results re: it's distance have not been reproducible, and so the distance figure is challenged. Fortunately, we have other galaxies, such as EGSY8p7 (z=8.68) have been imaged in the infrared, and as such, their distance confirmed. However, you've just reiterated what GP has said. I maintain that nobody is denying that the object that has been observed is more distant than it was 13Gy ago, however, the light that we are currently observing emanated from an object that was only 13Gly away. As I stated in my previous comment, the galaxies that we are presently observing are much different, and much farther away today, it's just going to take a lot of time for us to see what they look like today. You're seeing a baby and claiming to have seen the senile crank that the baby potentially became over 19Gy. The baby we're currently observing may as well be dead. If the article author is stating that 13Gly is the maximum distance anything can be from us, then the author is false. However, that's not what the author is saying. The author is saying we cannot see past 13Gly because the light has not arrived, and this is patently TRUE. The author makes NO claim about the current location of the objects.
- xenophonf 11y ago
  the light that we are currently observing emanated from an object that was only 13Gly away Using http://www.astro.ucla.edu/~wright/CosmoCalc.html http://www.astro.ucla.edu/~wright/CosmoCalc.html, the light of an object at redshift z=8.68 was emitted 13.141 Gyr ago, 0.579 Gyr after the Big Bang. The co-moving distance (to where that object was) is 30.444 Gly, but at the time the light was emitted, it was only 3.145 Gly away (=30.444 Gly/(1+8.68)). we cannot see past 13Gly because the light has not arrived, and this is patently TRUE We should be able to detect light from Population III stars, i.e., redshifts between z=20 and z=100, so about 13.540-13.704 Gyr in the past (about 0.016-0.180 Gyr since the Big Bang) and at a co-moving distance of about 35.851-42.045 Gly (or distances from us in the past of 0.416-1.707 Gly). Edited to add: For more information, refer to https://en.wikipedia.org/wiki/Scale_factor_%28cosmology%29 https://en.wikipedia.org/wiki/Scale_factor_%28cosmology%29, specifically the FLRW metric, https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtr....