APOD: The Observable Universe (2022 Mar 16)

[JohnD]

What? That we are each at the center of a unique and different observable universe is a simple fact. There is no alternative explanation. An observable universe is defined by a sphere of a certain radius around a 3D point. There are an infinite number of such center points in the Universe. The apparent edge of the universe I see is different from the apparent edge of the one you see.

(Whether we are all at our own centers of the Universe as a whole depends upon how we define "center" and on the topology of the Universe.)

Ah! If you would care to edit your statement to read that every one has a different edge to their universe, then I will agree, but the contents will be identical, or as near identical as makes no difference. The probability that there will be a significant difference between our universes is infinitesimally small. In fact a great deal smaller than you could split a hair!
John

[Chris Peterson]

What? That we are each at the center of a unique and different observable universe is a simple fact. There is no alternative explanation. An observable universe is defined by a sphere of a certain radius around a 3D point. There are an infinite number of such center points in the Universe. The apparent edge of the universe I see is different from the apparent edge of the one you see.

(Whether we are all at our own centers of the Universe as a whole depends upon how we define "center" and on the topology of the Universe.)

Ah! If you would care to edit your statement to read that every one has a different edge to their universe, then I will agree, but the contents will be identical, or as near identical as makes no difference. The probability that there will be a significant difference between our universes is infinitesimally small. In fact a great deal smaller than you could split a hair!
John

We all have the same universe, which has no edges and has the same contents for everyone.

We all have different observable universes, with different contents. The closer together we are, the more of those contents that will be the same (probability is not involved). But never all of them. And indeed, there are observable universes with no contents at all in common.

[lefthip]

As a believer in the scientific principle, the universe can only be that which we can detect by sight or otherwise. Multiverses or the infinite universe are only conjectures, although reasonable hypotheses, and may ultimately prove to be correct. But, right now our universe is a sphere of about 13.5 billion light years diameter.
Or is it? Do we know where we sit in this sphere in relation to its centre? I would assume that it is not the centre, as that would be very statistically unlikely. So, if we can "see" 13.5 billion light years, shouldn't we be able to say with some significant degree of certainty that the universe is actually much larger. We have discovered the redshift which suggests the all galaxies are moving away from each other. Couldn't these redshifts be triangulated to point to a centre and calculate its position (in relation to everything else)?
+

[Chris Peterson]

As a believer in the scientific principle, the universe can only be that which we can detect by sight or otherwise. Multiverses or the infinite universe are only conjectures, although reasonable hypotheses, and may ultimately prove to be correct. But, right now our universe is a sphere of about 13.5 billion light years diameter.
Or is it? Do we know where we sit in this sphere in relation to its centre? I would assume that it is not the centre, as that would be very statistically unlikely. So, if we can "see" 13.5 billion light years, shouldn't we be able to say with some significant degree of certainty that the universe is actually much larger. We have discovered the redshift which suggests the all galaxies are moving away from each other. Couldn't these redshifts be triangulated to point to a centre and calculate its position (in relation to everything else)?
+

Theory and a wealth of supportive evidence argue against the Universe being a sphere. An observable universe is spherical. Not the Universe. In three dimensions, the Universe has no center and no edges, although we can reasonably argue that every 3D point within it represents a center point with respect to everything else. The only "edge" that makes any sense is the 3D surface that everything exists on, and which is expanding outward along the time axis... an axis we have no access to in either direction.

Theory can reasonably support either an open or closed universe, a finite or an infinite universe. The jury is still out in that regard. But we can very reasonably say that the edge of the observable universe lies 46 billion light years away, not 13.5 billion.

[AVAO]

Why does it seem that M66 is listed twice?

Good point. Because the artist behind the image likes it so much? M66

(Or he got distracted - darn, I forgot to buy milk, and I bet I didn't include M66 among the galaxies in my picture of the observable Universe - better fix that right away...)

Ann

I like M66 too! Unfortunately her left arm is broken. Someone should help her urgently
(The image is a superposition of different IR wavelengths)


Jac Berne (flickr)

[johnnydeep]

What does this statement mean:

Some neutrinos and gravitational waves that surround us come from even farther out, but humanity does not yet have the technology to detect them.

[Chris Peterson]

What does this statement mean:

Some neutrinos and gravitational waves that surround us come from even farther out, but humanity does not yet have the technology to detect them.

We commonly treat the edge of the observable universe as the horizon where it was opaque to electromagnetic radiation. But the actual edge is a bit beyond that, where it is receding from us at greater than c. Things like gravitational waves from beyond the opaque edge can reach us, and could theoretically give us the ability to collect information right to the true observability horizon.

[Grizzly]

I hate to be "that guy", but the spelling mistakes are over the top. One I can forgive, but I stopped counting after 5.

[Ann]

As a believer in the scientific principle, the universe can only be that which we can detect by sight or otherwise. Multiverses or the infinite universe are only conjectures, although reasonable hypotheses, and may ultimately prove to be correct. But, right now our universe is a sphere of about 13.5 billion light years diameter.
Or is it? Do we know where we sit in this sphere in relation to its centre? I would assume that it is not the centre, as that would be very statistically unlikely. So, if we can "see" 13.5 billion light years, shouldn't we be able to say with some significant degree of certainty that the universe is actually much larger. We have discovered the redshift which suggests the all galaxies are moving away from each other. Couldn't these redshifts be triangulated to point to a centre and calculate its position (in relation to everything else)?
+

Theory and a wealth of supportive evidence argue against the Universe being a sphere. An observable universe is spherical. Not the Universe. In three dimensions, the Universe has no center and no edges, although we can reasonably argue that every 3D point within it represents a center point with respect to everything else. The only "edge" that makes any sense is the 3D surface that everything exists on, and which is expanding outward along the time axis... an axis we have no access to in either direction.

Theory can reasonably support either an open or closed universe, a finite or an infinite universe. The jury is still out in that regard. But we can very reasonably say that the edge of the observable universe lies 46 billion light years away, not 13.5 billion.

Chris, haven't you said that the edge of the Universe is the Big Bang (or whatever we choose to call the very beginning of the Universe - some say that inflation came before the Big Bang)?

As for whether the Universe is open or closed, shouldn't we, at least as a starting point, use Occam's Razor and choose the simplest answer? So that, if the Universe is flat, it is most likely open (and only topology can change that)?

Of course, we are not sure if the Universe is really, truly, absolutely flat. It could be marginally, marginally spherical, and therefore finite and closed.

Ann

[JohnD]

We all have different observable universes, with different contents. The closer together we are, the more of those contents that will be the same (probability is not involved). But never all of them. And indeed, there are observable universes with no contents at all in common.

Wow! Really? You can see into universes other than our own?

"Hello, is that the Nobel Committee? I have a nomination!"

John

[Chris Peterson]

As a believer in the scientific principle, the universe can only be that which we can detect by sight or otherwise. Multiverses or the infinite universe are only conjectures, although reasonable hypotheses, and may ultimately prove to be correct. But, right now our universe is a sphere of about 13.5 billion light years diameter.
Or is it? Do we know where we sit in this sphere in relation to its centre? I would assume that it is not the centre, as that would be very statistically unlikely. So, if we can "see" 13.5 billion light years, shouldn't we be able to say with some significant degree of certainty that the universe is actually much larger. We have discovered the redshift which suggests the all galaxies are moving away from each other. Couldn't these redshifts be triangulated to point to a centre and calculate its position (in relation to everything else)?
+

Theory and a wealth of supportive evidence argue against the Universe being a sphere. An observable universe is spherical. Not the Universe. In three dimensions, the Universe has no center and no edges, although we can reasonably argue that every 3D point within it represents a center point with respect to everything else. The only "edge" that makes any sense is the 3D surface that everything exists on, and which is expanding outward along the time axis... an axis we have no access to in either direction.

Theory can reasonably support either an open or closed universe, a finite or an infinite universe. The jury is still out in that regard. But we can very reasonably say that the edge of the observable universe lies 46 billion light years away, not 13.5 billion.

Chris, haven't you said that the edge of the Universe is the Big Bang (or whatever we choose to call the very beginning of the Universe - some say that inflation came before the Big Bang)?

No. The Big Bang is the center of the Universe. We're riding outward on the edge.

As for whether the Universe is open or closed, shouldn't we, at least as a starting point, use Occam's Razor and choose the simplest answer? So that, if the Universe is flat, it is most likely open (and only topology can change that)?

Of course, we are not sure if the Universe is really, truly, absolutely flat. It could be marginally, marginally spherical, and therefore finite and closed.

Yes. I'd bet on flat. But that's not yet firmly established.

[Chris Peterson]

We all have different observable universes, with different contents. The closer together we are, the more of those contents that will be the same (probability is not involved). But never all of them. And indeed, there are observable universes with no contents at all in common.

Wow! Really? You can see into universes other than our own?

I have no idea how you're getting that from my comments. I'm discussing nothing here but our universe. No others.

[JohnD]

Eh? You are " discussing nothing here but our universe. No others."

But Chris, you said/wrote, " And indeed, there are observable universes with no contents at all in common." Where are they, how can you observe them? You cannot be referring to the Universes observed by you and by anyone else, as their contents will be the same.

But I would agree with your prior sentence, that "the closer together we are, the more of those contents that will be the same" so perhaps I fail to see what you mean by the second.
John

[Chris Peterson]

Eh? You are " discussing nothing here but our universe. No others."

But Chris, you said/wrote, " And indeed, there are observable universes with no contents at all in common." Where are they, how can you observe them? You cannot be referring to the Universes observed by you and by anyone else, as their contents will be the same.

But I would agree with your prior sentence, that "the closer together we are, the more of those contents that will be the same" so perhaps I fail to see what you mean by the second.
John

Observable universes are nothing more than the visible bubbles within the Universe that are centered on any given observer (or any given 3D point). They are not different universes.

An observer beyond our visible horizon (who would still be in the Universe) would see their own horizon making it impossible to see us. We would each have an observable universe with no contents in common. This is just basic special relativity. Two points in a spacelike region, causally disconnected.

[Tanmoy Ghorui]

Where are the black holes? Or is it any mouth of a black holes?

[johnnydeep]

What does this statement mean:

Some neutrinos and gravitational waves that surround us come from even farther out, but humanity does not yet have the technology to detect them.

We commonly treat the edge of the observable universe as the horizon where it was opaque to electromagnetic radiation. But the actual edge is a bit beyond that, where it is receding from us at greater than c. Things like gravitational waves from beyond the opaque edge can reach us, and could theoretically give us the ability to collect information right to the true observability horizon.

[ Sorry for the late reply, but I'm still working through old posts that I missed due to accidentally flagging the "concam" email alerts as SPAM. ]

Ok, so, there's the opaque edge of the universe, contrasted with the absolute observability limit which is a little farther, but not necessarily beyond the c recession velocity threshold. Neutrinos or GWs originating from within this threshold could reach us. But anything originating from beyond the c recession velocity threshold would never reach us, right?