By using powerful telescopes on land and space, what's the farthest point humans have explored or viewed?
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6$\begingroup$ Does this answer your question? en.wikipedia.org/wiki/… $\endgroup$– planetmakerNov 16, 2020 at 16:52
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1$\begingroup$ The CMB is yet more far away, although it is not viewed by telescopes. $\endgroup$– peterhNov 16, 2020 at 21:53
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1$\begingroup$ Can you add some more details? $\endgroup$– fasterthanlightNov 17, 2020 at 1:30
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$\begingroup$ @fasterthanlight sometimes a new user asking their first question on a challenging topic like this simply can't add further details. Instead, a short answer can help put things into perspective. $\endgroup$– uhohNov 17, 2020 at 3:27
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1$\begingroup$ @planetmaker there is no process by which a Stack Exchange question can be closed as duplicate of a Wikipedia article. The whole idea here is to cite sources within answers. "Does this answer your question?" mimics the message that close-as-duplicate voting generates, so we should try use other words if possible, and avoid confusing rhetorical questions especially immediately under the first question asked by a new user. $\endgroup$– uhohNov 17, 2020 at 6:59
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3 Answers
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This is a really interesting question to many and it deserves an answer post even if folks close it.
In Wikipedia's List of the most distant astronomical objects we can see that the distances that the light travelled to get to us are all around 13 giga light years, and it's no coincidence that the age of the universe is also about 13 billion years.
We can't really call that the actual distance to the object because the size of the universe is changing and the size of the observable universe is changing as well.
So while we like to say we are seeing really really far away, we should really think about it as seeing really really far back in time, because on the scale of the universe the speed of light is actually incredibly slow :-)
No matter how big of a telescope we build with unbelievable light gathering power, we'll never be able to see "farther" than a certain distance. There's a currently unknowably larger universe out there whose light and gravity has not and probably never will reach us
It's almost certainly based on current understanding, but that's subject to change of course ;-)
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1$\begingroup$ In the spirit of quoting rather than linking it is maybe worth saying that the Wikipedia page you link gives a galaxy called GN-z11 as the most distant object actually imaged. It has its own wikipedia page en.wikipedia.org/wiki/GN-z11 $\endgroup$ Nov 17, 2020 at 7:40
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$\begingroup$ @SteveLinton Thanks! I'm amenable to you adding that as a new answer or just going ahead and adding it to this one. Your answers are always great so the former is better in my opinion, but I also always welcome helpful edits to my posts. $\endgroup$– uhohNov 17, 2020 at 7:49
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Supplementary to @uhoh's answer:
According to the wikipedia page he links, the most distant imaged object is a galaxy classed GN-z11.
GN-z11 is a high-redshift galaxy found in the constellation Ursa Major. The discovery was published in a paper headed by P.A. Oesch and Gabriel Brammer (Cosmic Dawn Center). GN-z11 is currently the oldest and most distant known galaxy in the observable universe. GN-z11 has a spectroscopic redshift of z = 11.09, which corresponds to a proper distance of approximately 32 billion light-years (9.8 billion parsecs). The object's name is derived from its location in the GOODS-North field of galaxies and its high cosmological redshift number (GN + z11). GN-z11 is observed as it existed 13.4 billion years ago, just 400 million years after the Big Bang; as a result, GN-z11's distance is sometimes inappropriately reported as 13.4 billion light-years, its light-travel distance measurement.
Beyond that distance (or, as it usually more helpful to think of it, further back in time) as @RobJeffries observes, we detect the cosmic microwave background and we can "explore" its exact spectrum and distribution around the sky, but we can't yet detect any specific objects beyond GN-z11.
answered Nov 17, 2020 at 9:00
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$\begingroup$ Well, there aren't any objects in the material that emitted the CMB, just atoms, and perhaps the occasional small molecule. $\endgroup$– PM 2RingNov 17, 2020 at 16:22
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Distance in astronomy is equivalent to looking back in time, because of the finite speed of light.
If it's an object you're interested in, then Which galaxy is receding from the Milky Way the fastest? What is known of the mechanism behind its recession? covers it. There are various high redshift objects around $z=11$ which are being seen a few hundred million years after the big bang and whose light took more than 13 billion years to reach us.
However, direct exploration by telescopes takes us back to the cosmic microwave background, formed 400,000 years after the big bang. The light from this has been travelling for 13.7 billion years.
If we want to see further, the CMB provides an impenetrable fog from which no more distant electromagnetic waves can emerge. However, there are opportunities to study the cosmic neutrino and gravitational backgrounds from earlier (and more distant, though not by much) epochs.
Arguably we have "explored" some of these most distant regions by using telescopes to investigate the "primordial" chemical abundances of helium, deuterium and lithium, which tell us about conditions in the first seconds to minutes after the big bang.
If one accepts this indirect exploration, then the fact we observe a matter filled universe is exploring the conditions less than $10^{-12}$s after the big bang.
